Radiological evaluation of the transuranic remaining contamination in Palomares (Spain): A historical review

Journal of Environmental Radioactivity 203 (2019) 55–70

Contents lists available at ScienceDirect

Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad

Radiological evaluation of the transuranic remaining contamination in Palomares (Spain): A historical review

T

C. Sanchoa,∗, R. García-Tenoriob a b

Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain Centro Nacional de Aceleradores, CNA, (Universidad de Sevilla-Junta de Andalucía-CSIC), Sevilla, Spain

ARTICLE INFO

ABSTRACT

Keywords: Palomares accident Source characterization Monitoring Hot-`particles Bioavailabilty

This paper shows the studies carried out in Palomares (Almería, Spain) following the ground dispersion of nuclear material as a result of the air crash accident that took place in 1966, in which four nuclear bombs were involved. As a consequence of the Palomares accident, plutonium (Pu) and uranium (U) were dispersed over an area of approximately 2.3 km2 due to the chemical explosion of two of them. The most relevant activities carried out by CIEMAT, along with other national and international institutions in the Palomares scenario are detailed. These activities, performed for over 50 years, focus mainly in the characterization of the contamination source, in the continuous environmental and personal radiological monitoring programs, in the construction of a detailed superficial and 3-D mapping distribution of the remaining contamination and in the evaluation of the bioavailability of the transuranics still remaining in the area.

1. Introduction This article gives a detailed overview of the most relevant investigations done by national and international institutions, especially those made by the Centro de Investigaciones Energéticas Medioambientales y Tecnológicas (CIEMAT), as a consequence of the accident that took place in Palomares in 1966. Palomares is a Spanish village, within the municipality of Cuevas del Almanzora, located in the province of Almería in the southeast of Spain. On January 17, 1966, at 10.30 a.m., a B-52 bomber and a USAF KC135 tanker of the United States of America Air Force (USAF) collided during a refueling operation at 9,144 m over Palomares. Following the collision, the B-52 bomber broke into pieces at high altitude; and KC135 remained fairly intact while it plummeted to the ground, exploding just before crash landing (487.7 m) and again on ground contact (Place et al., 1975). Large amounts of debris were scattered on the ground, some of them near homes located in Palomares (Fig. 1). In the accident, the four Mk 28 FI thermonuclear weapons (#) carried by the B-52 were dispersed over a wide area between Cuevas del Almanzora and Vera, and in the Mediterranean sea between Puerto Rey and Villaricos (Wilson, 1966). The Mk28 FI type hydrogen bombs were numbered following the order as they were found and were damaged to various degrees (Moore, 1966). The first of the four nuclear weapons was found intact, with its primary parachute deployed, in a terraced,

∗

Corresponding author. E-mail address: [email protected] (C. Sancho).

https://doi.org/10.1016/j.jenvrad.2019.02.015 Received 26 January 2019; Accepted 23 February 2019 0265-931X/ © 2019 Elsevier Ltd. All rights reserved.

cultivated area about 1 mile southeast of the village of Palomares (Place et al., 1975; US Air Force, 1966), next to the dry bed of the Almanzora river. A radiation survey showed that no radioactivity had escaped from the weapon. Weapons # 2 and # 3 suffered a conventional detonation presumably upon impact on the ground as a result of the malfunction of their parachutes, causing extensive plutonium (Pu) contamination in the surrounding areas. Weapon # 2 landed approximately 1.7 km west of the village (designated as impact point # 2), causing a crater of about 6.1 m in diameter and 1.8 m in depth; weapon # 3 landed at the eastern edge of Palomares (designated impact point # 3). On April 7th, weapon # 4 was recovered intact from the Mediterranean sea, about 8 km offshore Palomares. As a consequence of the accident, plutonium (Pu) and uranium (U) were dispersed over an area of approximately 2.3 km2. The 239+240Pu activities disseminated in the accident were estimated in the range 3.5 1012–32 1012 Bq (Pu mass in the range 1.5–13.5 kg) although these estimates were highly speculative and should not be used with high degree of confidence (Iranzo et al., 1998). A fraction of this Pu was removed from the contaminated area in the remediation program applied just after the accident as will be detailed later on. It is documented that in addition to weapon-grade Pu, the bombs also contained 235U and 3H (US Air Force, 1966). But, considering the specific activity of 235U (5 orders of magnitude lower than plutonium) and consequently its low activity concentration in the contaminated

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

Fig. 1. Thermonuclear weapons and aircraft debris disseminated at Palomares site. The letters B and K show the places where debris of damaged aircrafts B-52 and KC-135 were found after the impact. W indicates the impact points of the four weapons involved (W-1, W-2, W-3 and W-4). Red, orange, earth and blue colors shaded on the figure demarcate the most contaminated area, called in 1966 “Zero line”. The vertical thick black lines limit Zones 2, 3 and 5 respectively, as they were named. On the lower right side the position where the bomb 4 was found is shown. Red triangle indicates the point where bombs fell from the plane. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

soils, as well as the short half-life of 3H and the time span from the accident, it can be stated that both radionuclides are non-relevant from the radiological point of view. A radiation survey started two days after the accident in order to know the extent and the levels of ground contamination. Visible fragments from both bombs and aircrafts were recovered; superficial αcontamination levels were measured on soil, vegetation and houses, and external contamination of Palomares residents was monitored. The US Air Forces (USAF) identified the area most affected by radioactive contamination, establishing the so-called “Zero Line” (Fig. 1) that comprised about 226 ha, from Puerto Blanco (Zone 2, the area where weapon # 2 was found) to the slopes of Sierra Almagrera. This “Zero Line” included Zones 2 and 3, and the connecting area between them, called Zone 5. Another contaminated area (not included in the Figure and called zone 6) that comprised about 192 ha, was located about 1.2 km from the eastern boundary of Zone 3, north of Villaricos, a village which is separated from Palomares by the Almanzora river (US Air Force, 1966). Two weeks after the accident, soil remediation actions and crop removal were initiated. The most contaminated areas inside the “Zero Line” were remediated either by soil removal or by plowing. In fact, the top 10 cm of soil were removed from impact points # 2 (1.6 ha) and # 3 (0.6 ha), namely 827 m3 of soil with a Pu original contamination above 1200 kBq m−2 (Fig. 2), while when contamination levels were between 1200 and 120 kBq m−2, the soil was plowed to a depth between 25 and 30 cm and to a variable depth up to 25 cm when it was contaminated with levels between 120 and 12 kBq m−2 in order to dilute the radioactive elements. One hundred twenty ha inside the “Zero Line” showed contamination levels lower than 12 kBq m−2, being some of them sprinkled with water or light diesel oil just after the accident. Simultaneously, contaminated vegetation was removed from 242 ha. When Pu levels were higher than 7 kBq m−2, this vegetation was loaded into barrels together with the removed contaminated soil and temporarily stored in Zone 2. The vegetation with levels lower than 7 kBq m−2 was also removed and incinerated on the dry bed of the Almanzora river near its mouth, taking advantage of the night land-tosea breezes. High pressure water and detergents were used to wash bushes, trees and houses. Several layers of paint were applied to the outside of the houses in order to fix the contamination and to prevent resuspension in the air, avoiding entering into the houses through windows or openings in the walls. The interposition of layers of dense material (in this case, calcium oxides) would absorb the weakly penetrating alpha radiation (Ramos, 1968).

Finally, 1400 t of soil and vegetation (4810 barrels) were shipped to the USA: 4808 barrels were deposited at Savannah River Facility in Aiken, South Carolina, on the April 8, 1966, and the other two were destined to Los Alamos for research purposes (Place et al., 1975). The area affected by the accident is characterized by a subtropical Mediterranean climate with arid or semi-arid features and with temperatures that oscillate throughout the year between 12 and 27 °C approximately. The average annual rainfall is about 200 mm, irregularly distributed, causing sporadic floods (AEMET, the Spanish Agency of Meteorology). The terrain consists of vast plains that extend to the sea, especially in the Almanzora river mouth, while its western part composes relieves of approximately 70 m high. In general, the ground is hard, rocky and dry, coexisting porphyry and volcanic lamproitic rocks. Soils are taxonomically included in the order of entisols (Espinosa, 2003). Particle size distribution consists mainly of 55% of silt (grain size 5–63 μm), 36% of sand particle exceeding 63 μm, and 8.7% of clay particle (grain size less 5 μm), with presence of oxidizing agents (ratio Fe2+/Fe3+ = 0.18) (Espinosa, 2003; Iranzo et al., 1991). A detailed hydrogeological study of the affected areas close to impact points # 2 and # 3 was done in 2008 (ENUSA Industrias Avanzadas S.A., 2008), indicating that ground water levels are located between 10.23 m and 18.53 m in Zone 2 and 27.75 m in Zone 3. The hydro-chemical analyses carried out in the underground water samples collected from these areas, showed a high solids content and a predominance of: Cl−, SO42−, Na+ and Mg2+, characteristic of salty water. Despite the adverse environmental conditions of the area, there has been a noticeable development of the agriculture in Palomares, even in the affected areas, for most of the last 50 years with an exponential increase in the number of greenhouses with intensive production of vegetables. Since the accident, personnel surveillance programs (medical and radiological) of the inhabitants of Palomares are conducted in order to determine external and internal contamination (Iranzo et al., 1987a,b). Environmental radiological surveillance was initiated also in the same year of the accident and it has been running up to date (Aragón et al., 2017). In addition, a detailed radiological three-dimensional study (3D) of the affected areas was carried out from 2007 to 2009 in order to know the magnitude of the extent of the remaining contamination (Sáez et al., 2009; Sáez, 2008; Sancho and Gutiérrez, 2007). The study was done according to the Plan for Energy and Environmental Research in the Field of Radiological Surveillance (PIEM-VR), approved by the Spanish Government on December 17, 2004, being CIEMAT assigned to develop 56

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

Fig. 2. Environmental sampling stations. The upper part of the figure depicts the original sampling areas designed in 1966: Four air sampling stations (2-1, 2-2, P and 3-2) and six plots within the contaminated area (2-1, 2-2, 5-1, 5-2, 3-1 and 3-2) where environmental soil and vegetation sampling were carried out. The 5-3B plot corresponds to the area selected as background land outside the “Zero Line“. Original contamination ground levels are indicated with different colors as was explained in Fig. 1. At the bottom the sampling stations included in the current surveillance program are displayed: On the left all sampling stations are shown surrounded by a blue circle except station number 33, selected as a background sampling plot. On the right, the location of the stations and “Zero Line“ are shown. The thick blue line marked in the coastal zone delimits the area where the fish are captured as part of the marine ecosystem surveillance. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

it.

year the Spanish Nuclear Safety Council (CSN) fixed the radiological criteria for the use control of contaminated lands as follows:

Previously to the construction of the 3D maps, it was not until 2004 when the effective control of the affected lands located in Zones 2 and Zone 3 was initiated by expropriating the most contaminated areas (Fig. 3). Based on the national regulation that established in 2001 an effective dose limit of 1 mSv y−1 for the population members, the same

a) Total restriction of use, for those lands in which activities would give rise to a dose rate of 5 mSv y−1 (the concentration derived for 239+240 Pu is 25 Bq g−1). 57

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

Fig. 3. Fenced areas with access restrictions. The areas with radiological data above the restriction criteria set by CSN in 2001 are indicated with colors: Green indicates no restricted areas; yellow indicates partially restricted areas and red total restricted areas. Blue and brown lines show the limits that fall within the scope of PIEM-VR: Controlled areas in 2005 (Zones 2 and 3) and in 2007 (Zone 2, 2-bis, 3 and 6). Coordinates UTM are presented in the axes X and Y of the figure. Meteorological stations installed in 1985 (Tower 1), 1992 (Tower 2) and 2008 (Tower 3) are also shown. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

b) Partial restriction for lands in which activities would give rise a dose rate of 1 mSv y−1 (the concentration derived for 239+240Pu is 5 Bq g−1) (CSN, 2013).

compiled. 2. Spatial and grain-size distribution of the remaining contamination in the soils

The derived 239+240Pu concentrations mentioned above correspond respectively to approximately 5 and 1 Bq g−1 of 241Am. The 3D study showed the existence of contamination on a total of 30 ha that are currently under the Spanish Administration control: 10 ha were located in the vicinity of impact points # 2 and # 3, and in a plot located to the north of the Zone 2 called Zone 2-bis (Fig. 3). The other 20 ha were located in Zone 6, part of them included in the original “Zero Line”. The 3D study also confirmed the existence of the contamination mostly as a heterogeneous distribution of radioactive particles with sizes varying from submicron to fragment size above 1 mm, some of them with high activity, the so-called “hot particles”. The contamination in particle form demanded of a very careful and detailed screening in the construction of the 3D contamination maps, and the performance of particular studies for source contamination characterization. The details of the spatial distribution of the remaining contamination in the affected terrestrial area (the 3D study) will be shown in Section 2 of this paper, followed by a review of the studies performed in relation with the characterization of the contamination source (Section 3) and a compilation of the main outputs from the environmental surveillance programs applied in the area (section 4). Finally, in section 5, radioecological studies performed evaluating the environmental behavior of the contamination and the magnitude of the possible transfers from the contaminated land to plants, crops and wildlife will be

On December 2003, CIEMAT sent to the nuclear Spanish regulator (CSN) the proposal called “Research Plan to be developed by CIEMAT in Palomares (PIEM-VR) lands requiring special environmental radiological monitoring”, in order to gain knowledge about the radiological situation in the zone and to be able to select environmental recovery strategies for the affected areas. This Plan proposed the implementation of a research program to be carried out by CIEMAT, as well as to implement the restriction of land use based on the radiological criteria established by the CSN in 2001 (CSN, 2013). Following this plan, and with the information available at this moment, initially total or partial restrictions were established for those lands in which to perform activities gave rise to a dose rate of 5 mSv y−1 due to a 239+240Pu derived concentration of 25 Bq g−1 or 1 mSv y−1 due to derived concentration of 5 Bq g−1 (Fig. 3). Land use restrictions included affected areas of Zones 2 and 3 (5.5 ha in the vicinity of the impact point # 2, approximately 0.4 ha near the impact point # 3), and another 1 ha near the zone of impact point # 2 but outside of the “Zero Line”. In addition, radiological and medical control of people and environmental surveillance, followed without interruptions since 1966, continue. In 2007, the 3D radiological characterization of contaminated areas was initiated, ending in 2009. Superficial (also called extensive) and intensive studies were carried out (Sáez et al., 2009). In addition to the 58

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

georeferenced records of 241Am activity concentration in the top 15 cm of soil were obtained. This time, plots of lands of 1 × 1 m were measured in Zones 2, 2-bis and 3, while forced by the terrain orography as close as possible measurements were done in Zone 6. A static measurement system for radiation (so called ESTARAD) based on FIDLER detectors was used (Sáez, 2008). DINARAD and STARAD systems were designed to perform radiological measurements outdoors using up to four detectors simultaneously; the measurements were collected automatically with sub-metric precision of the geographical position. Each system was controlled by software designed ad hoc to perform either dynamic or static measurements. With the ESTARAD system MDA values of the order of 0.01 Bq g−1 were reached, one order of magnitude lower than that obtained with the DINARAD system. In addition, inspections of the Zones 2 and 3 were carried out by means of in-ground radar data acquisition system, that allowed to locate two trenches, called A and B, within Zone 2 (Fig. 4). These trenches were possibly excavated to dispose contaminated material during the remedial tasks carried out in 1966: 400 m2 with an approximate depth of 2.5 m and a volume of 1,000 m3 for trench A, and 1,000 m2 with an approximate depth of 5 m (built in the shape of a ramp) and a volume of 3,000 m3 for trench B. The content of the trenches remains unknown. Zones 2 and 3 were also inspected for metallic debris related to the plane crash, detecting metallic objects in ten points of Zone 3 which correlates with high values in the measurements made with the FIDLER detectors. Once the extensive and intensive studies were concluded, the presence of contamination in 10 ha of the expropriated lands in Zones 2 and 3, 10 ha additional of adjoining plots of lands and 20 ha in Zone 6 with an approximately extent of 1 km in length and 200 m width located in Sierra Almagrera was confirmed. In April 29, 2008, the CSN ratified the need to apply the restriction criteria for land use in all contaminated zones, including Zone 6 (CSN, 2008), thus confirming the scope of the PIEM-VR. In March 2009, CIEMAT published the final report of the 3D radiation map of Palomares (Sáez et al., 2009). The updated radiological characterization identified the affected lands where contamination levels were above the partial or total restriction criteria established by the CSN (Fig. 3). The study confirmed that the source term with radiological involvement due to the accident was comprised of 238Pu, 239Pu, 240 Pu and 241Pu and 241Am. Determination of the 239+240Pu/241Am ratio using LEPS detectors was developed: 879 samples collected from Zones 2, 2-bis, 3 and 6 were analyzed. The 239+240Pu/241Am ratios obtained ranged between 3.0 and 4.0, although most of them were lightly below 4 (Sáez et al., 2009). In order to validate this method, results were compared with those obtained from the analyses of analogous samples collected from Palomares, which were distributed to four national laboratories: Applied Nuclear Physics Laboratory -University of Seville, Laboratory Measurement of Low Activity -University of the Basque Country, Laboratory of Environmental Radiological

3D study, granulometric distribution of contamination in soils from Zones 2, 2-bis, 3 and 6 was performed to have a precise knowledge of the radiological situation at Palomares site. 2.1. Superficial radiological characterization The development of the 3D radiological map included the superficial radiological characterization of the 15 first cm of the soil over an extension of 660 ha (extensive study) (Sáez, 2008; Sancho and Gutiérrez, 2007), that included the 226 ha initially considered within the Zero Line. The geographic information system (GIS) software ArcGIS 9.2 (Environmental Systems Research Institute, U.S.A) was used for the spatial data processing and its analysis. A model of the surface contamination distribution was obtained. For the extensive study, plots of land of 25 × 25 m were characterized (Sancho and Gutiérrez, 2007), showing that the highest contaminated areas by 241Am were within the boundaries of the already controlled 10 ha located in Zones 2 and 3, that had been expropriated in 2005. Nevertheless, there were other plots with 241Am concentration higher than 0.8 Bq g−1: a) b) c) d)

1 ha located to the north of Zone 2. 0.5 ha located to the north east of Zone 2 (called 2-bis). 0.3 ha located on the eastern edge of Zone 3. 20 ha on the south west hill of Sierra Almagrera, located in Zone 6 (Fig. 3).

On September 28, 2007, the scope of the PIEM-VR was extended to a total of 30 ha (CSN, 2008). The extensive characterization on contamination distribution was completed at the end of 2007; about 63,000 data of georeferenced radiological measurements were registered using a dynamic measurement system for radiation (so called DINARAD), based on Field Instrument for Detection of Low Energy Radiation (FIDLER). In addition, drill cores were obtained at different depths: 0–5, 5–10 and 10–15 cm, collecting a total of 1848 undisturbed soil samples from Zones 2, 3 and 6 (Sáez, 2008). These samples were measured by using two FIDLER detectors facing each side of the disk that contained the soil samples. In order to verify the results obtained with FIDLER detectors, 642 samples (35% of the total collected soil samples) were measured with LEPS detectors. The extensive study showed the extension of the contamination in each zone, with a total of 197,235 m2 with 239+240Pu concentrations higher than 5 Bq g−1 and 23,283 m2 with concentrations higher than 25 Bq g−1 (Table 1). 2.2. Intensive radiological characterization A total of 40 ha located in Zones 2, 2-bis, 3 and 6 previously characterized superficially, were subjected to intensive characterization. More than 500 lineal km were checked and more than 262,000 Table 1 Soil volumes of Palomares with 2009).

239+240

Pu activity concentrations higher than 5 Bq g−1 (partial restriction use) and 25 Bq g−1 (total restriction use) (Sáez et al.,

239+240

>5

Pu activity concentrations, Bq g−1 > 25

Zone 2 0–15 cm deep Affected area (m2) 0–15 cm deep Affected volume (m3) 0,1–5 m deep Affected volume (m3) Total affected volume (m3)

>5

> 25

Zone 2-bis

>5

> 25

Zone 3

>5

> 25

Zone 6

>5

> 25

TOTAL

59000 8850 12670

15774 2366 556

32200 4830 271

5607 841 0

6035 905 2245

712 107 108

100000 20000 0

1190 238 0

197235 34585 15186

23283 3552 664

21520∗

2922**

5101

841

3150

215

20000

238

49771

4216

*It includes the affected volume within the trenches: A (2270 m3) and B (669 m3). **It includes the affected volume within the trenches: A (310 m3) and B (79 m3). 59

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

Fig. 4. Zones 2 (including trenches A and B), 2-bis and 3 are shown. Bore holes drilled in areas of interest are represented by cylinders. 241Am activity concentration ranges in soil are indicated with different colors, from light blue (0.01 Bq g−1) to red (10 Bq g−1). Red and green numbers shown in the figures of Zone 2 and 3 represent UTM coordinates. Red numbers shown in the figure of trench A represent depth (m). Figure has been taken from the technical report “Three dimensional radiological map of Palomares. Final Report”. Adapted from Sáez et al. (2009). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

Analysis,Technological Institute La Marañosa- Spanish Ministry of Defence and Laboratory of Medium and Low Activity Waste - CIEMAT. The samples were analyzed by α-spectrometry, β-spectrometry and Ɣspectrometry using LEPS detectors and by Inductively Coupled Plasma Mass Spectrometry (ICPMS) (Sáez et al., 2009). 239+240Pu/241Am ratio

was proved to be consistent in the affected areas, about 4, thus justifying the choice of 241Am to assess the Palomares radiological contamination. The 60 keV Ɣ-rays emitted by decay of 241Am detected using LEPS detectors was used as surrogate for the measurement of Pu and Am contamination. 60

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

Table 2 Weight percentage, activity percentage and activity concentration of the dry sieved samples collected in 12 specific areas located within Zone 2, 2-bis, 3 and 6. Sourcea

Percentage Weight

Activity

Activity Concentration [241Am]

Percentage

Bq g−1

Weight

Uncertainty 2σ

Fraction < 250 μm Z2 Hill Z2 Runoff Z2 Impact Z2 North Drill core slope Pit B Drill core Pit A Drill core Pit B Z2-bis Z3 Drill core Z3 Z6 East Z6 West

43.53 80.45 86.60 87.13 70.83 57.07 77.38 40.19 42.67 22.82 29.01 29.05

98.48 95.78 97.11 99.16 99.55 69.75 95.40 98.02 86.84 93.05 97.92 98.17

36.95 75.53 80.25 80.49 64.04 50.62 68.87 29.28 35.47 17.79 24.18 25.51

90.33 95.14 94.44 95.73 89.49 63.35 93.79 92.86 70.29 87.12 93.55 91.57

Activity

Bq g−1

Uncertainty 2σ

1.09 0.77 5.03 1.43 2.85 187,81 4,89 0,23 1,60 0,82 0,11 0,57

0.03 0.05 0.15 0.05 0.11 1.56 0.15 0.01 0.06 0.03 0.01 0.01

4.43 0.69 5.71 2.66 34.64 197.26 4.53 0.50 3.10 1.34 0.26 1.68

0.13 0.05 0.14 0.08 0.53 1.47 0.13 0.02 0.07 0.04 0.02 0.04

Fraction > 250 μm 60.51 3.42 20.18 12.28 163.76 321.94 24.51 10.43 13.27 33.11 9.19 46.06

0.81 0.06 0.27 0.17 1.15 2.14 0.48 0.19 0.14 0.42 0.10 0.69

56.60 19.79 13.69 13.14 29.36 43.11 22.86 59.94 57.47 77.25 71.15 71.08

Fraction < 125 μm Z2 Hill Z2 Runoff Z2 Impact Z2 North Drill core slope Pit B Drill core Pit A Drill core Pit B Z2-bis Z3 Drill core Z3 Z6 East Z6 West

Activity Concentration [241Am]

2.31 5.30 3.82 1.74 0.72 30.74 5.62 3.27 14.11 7.82 2.94 2.95

Fraction > 125 μm 65.39 3.62 21.18 12.83 162.83 329.64 27.08 13.55 12.92 39.78 10.54 48.93

0.94 0.07 0.29 0.18 1.24 2.36 0.54 0.27 0.14 0.54 0.12 0.78

63.18 24.69 19.99 19.75 36.15 49.56 31.34 70.85 64.65 82.28 75.98 74.62

10.46 5.94 6.34 4.87 10.75 37.11 7.14 8.22 30.75 13.61 7.29 9.21

a Z2 Hill, hill located north to the point of impact of bomb 2 within Zone 2; Z2 Runoff, runoff located south to the point of impact of the Bomb 2 in Zone 2; Z2 Impact, point of impact of Bomb 2; Z2 North, located north close to the point of impact of Bomb 2 in Zone 2; Drill core slope Pit B, drill core obtained in a slope of the pit B to the west of the impact of bomb 2; Drill core Pit A and Drill core Pit B, drill cores obtained in pit A and pit B respectively both located in Zone 2; Z2-bis, located in Zone 2-bis to the north of Zone 2; Z3, located close to point of impact of bomb 3 in Zone 3; Drill core Z3, obtained under a house located in Zone 3 close to the point of impact of bomb 3; Z6 East and Z6 West are located to the east and the west of Zone 6, respectively.

areas were 0.25 μSv h−1 to 1 m and 0.33 μSv h−1 in contact with the ground. In January 2009, CIEMAT requested the IAEA to perform an International Peer Review on the application of International Safety Standards for the Radiation Protection of the Public in the Environment of Palomares (Spain), including the methods used and the results obtained in the characterization of the contamination in soil. The experts team of the IAEA (IAEA, 2009), considered that dynamic and static measurements carried out in Palomares were appropriate to characterize the contamination distribution; and the validation of the 239+240 Pu/241Am ratio determined by CIEMAT and the other Spanish laboratories involved in the inter-comparison exercise was accepted to identify the source term of the contamination. The IAEA experts stated that produced information was very rigorous, being the 3D characterization a very useful input into the preparation of remediation strategy plan.

In order to estimate the depth of the contamination, a total of 321 bore holes were drilled in Zones 2, 2-bis, 3 and 6 at depths between 0.5 and 6 m; a first screening was done analyzing 7500 data with FIDLER detectors. Subsequently, 734 samples were prepared and measured with both types of detectors, FIDLER and LEPS. The data were processed with the Environmental Visualization System C-Tech 9.3 software (Scientific Software Group, U.S.A), and tridimensional volumetric models of the contamination present in each Zone were obtained (Fig. 4). The 3D study showed diversity of profiles in Zones 2 and 3 that according to the authors of the study were caused by agricultural activities and land movements. Contamination in the subsoil of the Zones 2, 2-bis and 3 was observed beyond 4, 1 and 4 m depth, respectively. In general, it was not observed contamination in the subsoil in those points of the Zones 2, 2-bis and 3 where there was not surface contamination. Zone 6 and the hills located in Zone 2 had strictly superficial contamination, not being observed contamination beyond 20 cm of depth. According to the authors, due to the orography of the Sierra Almagrera, Zone 6 had remained undisturbed since 1966, thus considering that the contaminated area was limited to the one identified in the superficial characterization. Both trenches A y B, located in the Zone 2, showed complex profiles with contamination at depth greater than 4 m, possibly due to the remedial actions carried out in 1966. As a conclusion, a total volume of soil of 49,771 and 4,216 m3 that exceed 5 Bq g−1 and 25 Bq g−1 of 239+240Pu respectively was estimated (Table 1). Most part of the contamination was localised in Zone 2 (43%) followed by Zone 6 (41%). The 3D study allowed estimating the current 239+240Pu inventory in Zones 2, 2-bis, 3 and 6: 317, 31, 34 and 103 g respectively. The external irradiation risk was insignificant even in those areas with high transuranic concentrations; the maximum dose rates reported in the affected

2.3. Granulometric distribution of contamination in soil Once the 3D radiological map was completed, the following step to cover the final objective of recovery of the areas contaminated by the Palomares accident was centered in to study the possible treatments to be applied to the contaminated soil in order to concentrate the activity and reduce as much as possible the volume of waste generated. This reduction of the contaminated soil was planned to be carried out using industrial processes common in mining and treatment of aggregates, introducing the necessary modifications for the safe handling of materials with radioactive contamination in the processes as well as in the equipment and facilities. Previous studies evaluated different methods to reduce the volume 61

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

of Pu in contaminated soils based on physicochemical properties of this transuranic element such as paramagnetic separation, density or flotation process and scrubbing and wet sieving (Papelis et al., 1996; Torrao et al., 2003). According to the results obtained, the most reliable method for contaminated soil volume reduction was to separate the soil by particle size, reaching volume (mass) reductions of the order of 70% (Papelis et al., 1996). As a complement to the 3D characterization, a granulometric study of Palomares affected soil was carried out by CIEMAT to investigate Pu activity distribution in soil depending on grain size, and to evaluate the possible reduction of the volume of contaminated soil attending to its granulometric characteristics. Several fractions covering the range between 10 μm and 2 mm were obtained by dry sieving (Sáez and Aragón, 2010), and fractions between 5 μm and 100 μm by wet sieving (Lanzas et al., 2014).

them from the soil (Sáez and Aragón, 2010). 2.3.2. Wet sieving Wet sieving was performed with samples collected from Zones 2, 2bis, 3 and 6. Several tests were carried out with different objectives: a) To verify that under normal conditions of treatment there was no presence of activity in the washing water or flocculated sludge containing solids with size lower than 5 μm: Contamination was found incidentally (one sample out of 30) and with very low activity values (0.30 Bq g−1 of 241Am). b) To check the effect of changes in the pH of the washing water. Seven aliquots of one soil sample collected within Zone 2-bis containing 1% of solids were prepared at different pH (from 3.40 to 9.60) and the changes in the pH neither produced an appreciable increase in the concentration of isotope activity measured in the washing water nor in the weight ratio of solids separated therefrom. c) To verify the presence of aggregates and to remove the contamination, the fractions > 2 mm that had been previously separated by dry sieving from 10 soil samples collected within Zones 2, 2-bis, 3 and 6, were subjected to wet treatment by adding water to obtain a mixture containing 10% of solids. It was possible to filter out at 100 μm an average of 8.5% of the total weight of the sample, which contained 39.3% on average of the activity measured on the initial sample (fraction > 2 mm). According to the results obtained, the areas with the highest amount of solid aggregates were Zone 2 Runoff, Zone 2 North, Zone 2-bis and Zone 6 East (Lanzas et al., 2014). d) In addition to the tests mentioned before, two groups of aliquots containing 1% and 10% of solids were prepared from 7 soil samples with aerodynamic size < 2 mm. Subsequently, fractions of 100, 50, 25, 10 and 5 μm were obtained by wet sieving. Variations in the percentage solids indicated, in some cases, that a higher concentration of solids in the mixture provided an increase of 241Am activity in the smaller fractions; in sample 149 (Fig. 6) a 10% solids mixture was used and 80% of the activity was separated for grain sizes between 50 and 10 μm, but in other cases a different situation was observed; in sample 356 (Fig. 6), the fraction with grain size between 25 and 10 μm contained about 50% of the sample activity independently of the solids concentration.

2.3.1. Dry sieving Dry sieving was performed on 70 soil samples collected from 12 specific plots located within Zones 2, 2-bis, 3 and 6 (Sáez and Aragón, 2010): Seven of them were located in Zone 2, one in Zone 2-bis, two in Zone 3 and two in Zone 6 (Table 2). A total of 48 samples were collected from the first top 15 cm of soil and 22 were extracted from drill probes between 20 and 420 cm depth. The weight and activity percentages as well as total activity concentration of each fraction were calculated for each group of samples collected at specific points. A high activity concentration in the fractions lower than 250 and 125 μm was observed, both showing similar values (Table 2, Fig. 5), what confirmed that most of the activity was present in soil grains with a size lower than 125 μm. The separation at 125 μm (fraction > 125 μm) gave 241Am activity concentration values below 1 Bq g−1 on the samples collected within Zone 2 Runoff, Zone 2-bis and Zone 6 East plots. The same thing happened with Drill core Zone 3 and Zone 6 West plots when the samples were separated at 250 μm (fraction > 250 μm). But values between 1 and 5 Bq g−1 resulted in the fraction > 250 μm from the samples collected within Zone 2 Hill, Zone 2 Impact, Zone 2 North, Pit B and Zone 3 plots, while the separation of the samples collected within Pit A did not improve the initial situation. In conclusion, the dry sieving allows a possible quantitative reduction of about 70% for Zone 2 Hill, 2-bis, 3 and 6 plots (they constitute 6.0%, 10.2%, 6.3% and 40.2% of the total volume of soil affected) while it was suggested by the scientists in charge of the study to carry out the wet sieving of the lands of Zone 2 in order to separate the aggregate material. Therefore wet treatment for the other lands located in Zone 2 (37.2% of the total volume of soil affected) was considered in order to know if it is possible to break up the aggregates present in the soil samples, and thus release the contaminated particles and remove

3. Characterization of the contamination source Knowledge about the structural and physical characteristics of the Pu source-term in the area is essential to assess the short-term and the long-term consequences of the contamination, since it can have a great Fig. 5. Weight and activity percentage of granulometric fractions obtained by dry sieving of samples collected at twelve specific areas located within Zones 2, 2-bis, 3 and 6. The weight percentages of the samples are shown by vertical bars and the activity percentages by a continuous line. Granulometric fractions lower than 250 or 125 μm are indicated on dark blue color and clear blue color respectively. Red line corresponds to 50% of the weight percentage and activity percentage of the granulometric fractions studied. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

62

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

Fig. 6. Granulometric curve and activity distribution of two sample treated by wet sieving. The original samples called 149 and 356 were collected in Zone 2 Hill and Zone 2 North respectively. Washing mixtures labeled as 149-AL-1 and 149-AL-3 contained 10% (orange) and 1% (green) of solids respectively. Mixtures labeled as 356-AL-1 and 356-AL-3 contained 10% (blue) and 1% (red) of solids respectively. Dotted lines represent activity distribution and continuous lines represent weight percentage of the samples. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

influence on the mobility and biological uptake of the transuranic elements in the affected ecosystem with subsequent implications for dose and environmental impact assessments (Salbu et al., 1998). In Palomares, most of the Pu content is in particulate form, as it has been reflected historically in the studies carried out involving soil samples collected from various zones within the mentioned ecosystem. These studies revealed the existence of a very heterogeneous distribution of the Pu contamination (it is well known that a heterogeneous distribution of the contamination is the main signal of the existence of radioactive particles in an ecosystem). In Palomares the soil can act as a sink for deposited particles and particulate soil may also act as a potential diffuse source in the future. Thus, knowledge with respect to particle characteristics and processes influencing particle weathering and remobilisation of associated radionuclides is needed to assess long-term impact from radioactive particle contamination. The ecosystem transfers of particle associated radionuclides will be delayed until particle weathering and remobilisation of associated radionuclides occur (Salbu et al., 2018). The particles size in Palomares vary from submicron to fragment size above 1 mm, some of them with high activity, the so-called “hot particles” (Aragón, 2003; Aragón et al., 2008; Espinosa, 2003; García López et al., 2007; Gonzalo de Diego, 2010; Lind et al., 2007). Morphology of particles is granulated and/or massive (Lind, 2006), some of them have well-defined fracture lines (Aragón, 2003; Aragón et al., 2008) like the one showed in Fig. 7 (Aragón et al., 2015a). The particles are a mixture of enriched U and weapon-grade Pu material (the weapon nuclear fuel mass was mostly 20% enriched U with an average mass ratio Pu/U of 0.8). SEM-EDX mapping and SRbased micro-XRF mapping indicated that U and Pu were no homogeneously distributed in the particles with Pu/U mass ratios ranging between 0.5 and 1.5. ESEM- EDX high resolution revealed that U and Pu are co-localised on all the particle investigated surfaces, but surface inclusions enriched in U and depleted in Pu were observed (Lind et al., 2007).

Based on micro-XANES studies it was also concluded that the particle matrices are U and Pu mixtures, most probably in the form of oxides/hydroxides. The oxidation state of U seems to be predominantly + IV (UO2) with a minor and variable contribution of higher oxidation states (U3O8) while Pu seems to be present as Pu (III)/ Pu(IV), Pu(IV)/Pu(V) or a mixture of all three oxidation states. Neither metallic U or Pu nor uranyl or Pu (VI) could be observed (Lind et al., 2007). In the most contaminated areas, a high proportion of the particles are adhered/coated with inert soil material, forming solid aggregates with several decens of micrometer size. This fact was evidenced in the granulometric studies shown previously, and it is extremely important from a radiological risk assessment point of view, because aggregates with these sizes could not be suspended, and consequently inhaled by the public and wildlife. On the other hand, the isotope ratios of the deposited radionuclides after the accident have also been extensively studied and defined, because for example the activity ratios of 238Pu and 240Pu versus 239Pu are a specific signature of the fuel used in the Palomares weapons that permits to distinguish from other scenarios, including the global fallout. In this frame, 238Pu/239+240Pu ratios have been studied in both, the terrestrial (Aragón et al., 2008; Chamizo et al., 2006; Espinosa, 2003; Gascó et al., 1997; Lind, 2006; Rubio et al., 2000; Rubio and Martín, 2001) and the marine environments of Palomares (Gascó et al., 1995, 1997; Mitchell et al., 1997; Romero, 1991); the 238Pu/239+240Pu activity ratio mean values estimated from soil samples collected close to the impact point # 2 (0.027 ± 0.002, backdated to 1966) (σ = 1) (Gascó et al., 1997) and from marine sediments collected approximately 5 km off-shore Palomares in 1991 (0.0275 ± 0.0012) (σ = 1) (Mitchell et al., 1997) verified the presence of weapon grade Pu. The 240Pu/239Pu atom ratio has been also determined in heavily contaminated soils, and individual isolated particles by applying mass spectrometric techniques (ICP-MS and AMS) (Chamizo et al., 2006; Lind et al., 2007; Pöllänen et al., 2006) and even high-resolution ƔFig. 7. Scanning Electron Microscope image of the particle isolated from an air filter. Images were obtained with a Hitachi SU6600 analytical SEM (accelerating voltage 25.0 kV, secondary electron image resolution 14.6 mm). Two magnifications are shown: 2000.00× on the left and 15000.0× on the right. Figure taken from the report CRP-IAEA “Environmental Behavior and Potential biological Impact of Radioactive Particles”. Annual Progress Report 2014.

63

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

Fig. 8. Number of environmental samples recorded in CIEMAT database. Data correspond to the surveillances carried out from 1966 to 2016. Different type of samples are shown with the followings colors: Blue indicates water samples, red shows animal products (milk and honey), lilac correspond to air filters, yellow to soil and sediments samples, orange to samples from wild and farm animals and green to vegetable samples (both indicator plants and crops). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

spectrometry (Jimenez-Ramos et al., 2010), being the values obtained, in the range 0.056–0.066, a fingerprint of weapon-grade Pu. Other isotope ratios have been analyzed. High 235U/238U isotope ratios, evidencing the presence of enriched U has also been confirmed in particles collected from the contaminated Palomares area (JiménezRamos et al., 2007) and a characteristic 241Am/239Pu activity ratio of 0.31 ± 0.02 could be associated to the contamination in Palomares in 2009 (241Am formed as daughter of the 241Pu present in the disseminated nuclear fuel). The study of time evolution of this last isotopic ratio has even allowed to date the separation of Pu from the reactor between 1956 and 1960, and to conclude that he activity ratio 241 Am/239Pu of 0.31 ± 0.02 will be constant for the period 2006–2066. This allow to determine Pu activity through direct measurement of 59.5 keV photons from 241Am. Finally, in addition to the isotopic ratios determined in the 3D study: 239+240Pu/241Am = 4 and 238Pu/241Am = 0.1, other isotope ratios such as: 238Pu/239+240Pu = 0.02; 241Pu/241Am = 3 and 240 Pu/239Pu = 0.0659 were provided by the laboratories involved in the map construction.

called 2-0 was established near the impact point # 2. At national level, in 1986 the Spanish Nuclear security Council (CSN), accepted the first so-called Radiological Surveillance Plan (PVR) proposed by the JEN (Iranzo, 1987), that continued until 2011 when a more extensive and accurate monitoring program -Environmental Radiological Surveillance Program (PVRA)- was proposed by CIEMAT and accepted by CSN in 2012 (Aragón et al., 2012a). This 2011 program included monitoring of marine and terrestrial ecosystems, including the surveillance of the terrestrial ecosystem covering an extensive area beyond the “Zero Line“, with a radius of 2600 m and an area of 21.23 km2 (Fig. 2). The Program was reviewed in 2015 covering the same area, but adding two new sampling stations to the 31 already existing (stations 32 and 33 respectively) (Antón and Aragón, 2015). The obtained results are included in a local database for environmental samples, called RERA database, and annually reported to the CSN. These samples are as follows: Air filters, water (seawater, drinking water, irrigation water and fresh water), dry deposit, total deposit (dry deposit and rain water), indicator animals (gastropods of the genera Helix, Otala and Theba), foods (animals, animal products and crops), indicator plants (among others Thymus vulgaris, Stipa tenacissima, Foeniculum vulgare, and Launaea arborescens, Beta vulgaris cicla), soil, river sediments and beach sand. A total number of 13,192 samples have been analyzed between 1966 and 2016 (Fig. 8): 3,787 (28.7%) air samples (include air filter and total deposit), 84 (0.6%) water samples, 116 (0.9%) animal samples of which 44 came from farms and 72 were wild, 92 (0.7%) animal products of which 88 were milk samples and 4 honey samples, 5,787 (43.9%) vegetables samples of which 4,949 were crops and 838 wild vegetation samples, and a total of 3,326 (25.2%) samples that included soil and sediments. Soil samples are distributed as follows: 1,588 superficial soil samples (maximum depth 15 cm), 1,602 soil samples (≤50 cm depth) and 61 probes (> 50 cm depth). A total of 75 sediments samples were analyzed (Lanzas, 2017).

4. Historical evolution of the environmental radiological surveillance carried out in Palomares since 1966 One month after the accident, human and environmental samples were collected and submitted to the United States Air Force Radiological Health Laboratory (USAF RHL), for analysis (US Air Force, 1966). In addition, shortly after the accident, in 1966, the so-called INDALO project was implemented by the DOE and the Spanish Nuclear Energy (JEN), currently CIEMAT. This agreement included medical tests and radiological monitoring of the inhabitants of Palomares and the environment, and with some renovations and small modifications have been under application until performing under the framework of the PIEM-VR, the radiological superficial study of the affected areas as well as the 3D study on the distribution of the contamination shown in Section 2. Five months after the accident the radiological surveillance of contaminated areas was initiated (Fowler et al., 1968). Six sampling plots (50 × 50 m2) were established to collect and analyze soil and vegetation samples and an additional plot called 5-3B was selected about 0.5 km north, outside the “Zero Line” as a background sampling point (Fig. 2). In addition, four air sampling stations were set up: Two were located in the area around impact point # 2 (stations 2-1 and 2-2 respectively), one in the village of Palomares (station P) and another in the area around impact point # 3 (station 3-2) (Fig. 2). Later a plot

4.1. Radiological studies of the terrestrial ecosystem Palomares is an area where intensive farming is performed as the driving force of the economy of its inhabitants. In addition, in this Spanish region grazing animal adapted to the harsh climate conditions, such as goats, provide an additional income for farmers. Due to the possible incorporation of Pu and Am into the food chain and contribution to the effective dose of the locals, plant and animal samples collected from the affected areas or close to them have been analyzed since the accident and included in the surveillance programs. 64

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

4.1.1. Wild vegetation and crop samples The program to evaluate the contamination of the vegetation started the same year of the accident (Fowler et al., 1968). In the decade of 70′s and 80′s main crops in Palomares were tomatoes, barley and alfalfa. With the time, a greater number of vegetables species were cultivated and included in the surveillance programs (tomatoes, potatoes, melons, watermelons, barley, corn, olives, oranges, lemons). Both, the edible and non-edible parts of the plants were analyzed. The analyses performed on crop samples collected in Zones 2 y 3 in 80′s showed contamination in different parts (plants, skin and fruits); 239+240Pu concentration detected in the tomato samples collected in 1986 ranged between 4.4 Bq kg−1 ± 13% and 0.075 Bq kg−1 ± 18.9% (plant samples), 0.03 Bq kg−1 ± 16% and 0.43 Bq kg−1 ± 13% (referred to kg of skin samples), and 0.11 Bq kg−1 ± 16% (only contamination in one fruit sample was observed). Regarding 241Am, contamination was measured only in plant samples, with values ranging between 0.5 Bq kg−1 ± 17% and 2,67 Bq kg−1 ± 5% (Iranzo, 1987). Higher contamination values were observed in a sample of barley spicules collected in Zone 2 in 1987 (9,702 ± 1,451 Bq kg−1) (Iranzo et al., 1987a) or in non-edible parts of other unwashed vegetables, such as the one observed in one sample of melon collected in the Zone 2 in 1988 (1,622 ± 243 Bq kg−1 of 239+240Pu); Although a low resuspension factor in Palomares was described (García-Olivares and Iranzo, 1997; Iranzo et al., 1994), resuspension of plutonium particles in soil was demonstrated in the past by the observation of the low number of washed fruits samples contaminated with 239+240Pu, compared to the contamination observed over unwashed fruit samples or other parts of the plant (Iranzo et al., 1988a, 1989a). Nevertheless, according to the data included in the RERA database, the great majority of wild vegetation samples analyzed showed very low activity concentration values of 239+240Pu, although in some exceptional cases more than 10 Bq g−1 were measured in samples collected prior 2007 within Zones 2 and 3 (Lanzas et al., 2015; Lanzas, 2017). In order to know the radiological potential risk of the consumption of crops cultivated in Zone 2, committed effective dose to 50 years was estimated (Iranzo et al., 1988b). To complete this estimation, it was assumed that the diet of people from Palomares would only include products collected from contaminated areas at that time. The calculated committed effective dose derived from the consumption of tomato, watermelon, wheat and cauliflower cultivated in the Zone 2, in 1988, was 22.2 μSv y−1. A lower value was obtained, 6.6 μSv y−1, for a period of five years (2005–2009) taking into account a greater variety of vegetable species, as well as snails and milk collected outside the contaminated fenced areas (Espinosa et al., 2010). Additionally in water samples collected in the terrestrial area (drinking water, irrigation water and fresh water), no contamination has been observed so far (Lanzas, 2017) having consequently null dosimetric implications.

resulting in an estimated annual dose per individual due to ingestion of meat lower than 1 μSv. Lung samples (complete organ), showed values between 0.01 ± 0.00 Bq kg−1 and 0.13 ± 0.01 Bq kg−1. Bone analyses indicated values between 0.02 ± 0.01 Bq kg−1 and 0.07 ± 0.03 Bq kg−1 (Espinosa et al., 2008). Only two wild rabbits hunted in the vicinity of Zones 2 and 6 in 2012 were analyzed. Following α and Ɣ-spectrometry analyses, 239+240 Pu and 241Am were not detected. Minimum Detectable Activity (MDA) values for 239+240Pu obtained in these samples were respectively 27.20 10−3 and 22.54 10−3 Bq kg−1 fresh weight, and 0.29 Bq kg−1 and 0.26 Bq kg−1 for 241Am (Aragón et al., 2013). 4.1.3. Milk and honey samples In addition to the animal samples, products derived from animal such as honey and milk have also been analyzed. The first honey sample analyzed was collected more than 30 years after the accident from an apiculture holding located to the east of the Zone 2 and shows 239+240 Pu activity levels by α-spectrometry ≤ 25.66 10−3 Bq kg−1 (Espinosa et al., 2000), but after that, honey samples were included as a part of systematic sampling in the PVRA approved by CSN in 2012, although they are a type of samples whose collection depends on flowering, so it has not been possible to collect them every year. When possible, samples are collected from apiculture holding situated close to the Zone 6 (Antón and Aragón, 2015; Aragón et al., 2012b). MDA values were obtained for 241Am in the samples collected in 2014 and 2015 (0.208 and 0.256 Bq kg−1, respectively). Due to the lack of rain in 2016 no honey sample was available. Goat and cow milk samples were collected for the first time in 1987 and 1998 respectively (Iranzo et al.,1987a, 1988a). The calculated committed effective dose (50 y) due to 239+240Pu ingestion present in this kind of samples between 2005 and 2009 showed no risk due to consumption of these animal products (7.5 10−4 μSv y−1 and 6.02 10−1 μSv y−1 for goat and cow milk respectively) (Espinosa et al., 2010). 4.1.4. Snails We can conclude indicating that no radiological risk has been observed so far due to consumption of meet or food derived from animals and cultivated plants out of the affected areas. Nevertheless, special attention should be paid to the consumption of wild terrestrial snails. Palomares is an area where snails have been traditionally consumed. According to current data from the Ministry of Agriculture, Fishing, Food and Environment, Spain accounts for a snail consumption of 400 g y−1 person−1. The transfer of transuranic elements from soil to gastropods collected from the areas affected by the Palomares accident has been proved (Aragón et al., 2006), highlighting in principle the need to analyzing this type of samples as bio indicators of transuranic contamination present in Palomares, and even more, to raise awareness in the population of the potential risk of their consumption if collected from the contaminated areas. However, on the frame of a recent EUfunded project (COMET, 2017), this problem has been put in context: 239+240 Pu activity concentrations have been found in the soft-tissues of all the analyzed snails collected in the contaminated Zone 2, although the levels found were quite moderate and variable in the range 2–150 mBq per individual. A very conservative assessment assuming an annual consumption of 1 kg of fresh snails per year, and an average activity concentration of 241Am of 20 Bq kg−1, yields an average effective dose rate due to ingestion of the transuranics of < 30 μSv y−1, i.e. less than the one due the ingestion of 210Po (50 μSv y−1), natural radionuclide also present in the soft-tissues analyzed with an average activity concentration of 40 Bq kg−1 (Diaz-Francés, personnel communication).

4.1.2. Wild and farm animals Monitoring programs have also included the occasional analysis of wild rabbits and farm animals such as chickens, goats and sheep that grazed on fields next to Zone 2. In 1987 ten chickens were analyzed to determine the 239+240Pu activity concentration in muscle, bone and feathers. They had been fed with local products and reared in a poultry yard located next to Zone 2 throughout 1987. Alpha spectrometry revealed the presence of 239+240Pu only in the feather samples, with concentrations ranging from 0.17 Bq kg−1 to 0.94 Bq kg−1 (Iranzo et al., 1988a, 1989a). This external contamination was due to direct exposure to the contamination since chicken moved freely both in the poultry yard and on the surrounded contaminated areas, where the average values of 239+240Pu activity concentration in soil was 2 103 Bq kg−1. In relation to the radiological monitoring of cattle, diverse tissues (muscle, liver, lung and bone) from goats and sheep were analyzed in 2008. The liver and muscle samples showed values between 0.11 ± 0.01 Bq kg−1 and 0.001 ± 0.00 Bq kg−1 respectively,

4.2. Air monitoring Since the accident, one of the main concerns related to Palomares 65

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

dwellers has been the risk of inhalation of the transuranics still present in the affected areas. Airborne contamination surveillance in the area of Palomares was initiated about three months after the remedial actions carried out in 1966 (Iranzo et al., 1998). Samples of radioactive aerosols were collected using high-volume samplers, placed at four locations to control Pu airborne activity concentration: Two samplers were located in the area around impact point # 2 (stations 2-1 and 2-2), one in the village of Palomares (station P) and another in the area around impact point # 3 (station 3-2). Air sampling was done throughout the period 1966–1980, except at the station 3-2 which stopped running in October 1966. The ones placed at stations, 2-2 and P, were replaced by new ones in 1981 and later in 1983 (Iranzo et al., 1998). Nowadays there are three air sampling stations: E21, E22 and E23 sited close to Zones 2, 2-bis and at Palomares town; they replace former 2-1, 2-2 and P stations (Fig. 2). Out of a total of 3,841 air samples analyzed between 1966 and 2017, 20.3% were collected from stations E21 and former 21, 40.8% from E22 and 2-2, 36.2% from E23 and station P, and 2.7% from station 3-2. 239+240 Pu was determined in 3,152 samples, and 241Am in 640 samples. The 239+240Pu determinations showed than 25% of the analyzed samples had values lower than 1.5 10−6 Bq m−3, 73% between 1.5 10−6 and 150 10−6 Bq m−3 and 2% greater than 150 10−6 Bq m−3. 241 Am determinations cover the 23%, 76% and 1% for the mentioned ranges (Lanzas, 2017). The highest frequency of air filters with activity concentration values higher than 150 10−6 Bq m−3 were collected from the station E21. The committed effective doses to adults living in Palomares from intake of 239Pu for a 30 y period (1966–1996) were estimated in previous studies, assuming a chronical inhalation: 37 μSv y−1 for urban workers and 210 μSv y−1 for agricultural workers (Espinosa et al., 1998; Iranzo et al., 1998); the calculated values were lower than the limit established for the public members, 1 mSv y−1 (RD 786/2001, de 6 de julio, 2001). According to the estimations made from the updated measurement results of the air filters collected from 1966 to 2014, the committed effective doses values due to inhalation of the isotopes mentioned above vary from a minimum of 0.34 μSv y−1, registered in 2004 and 2005, to a maximum of 67.56 μSv y−1 in 1986, which represent 0.03% and 6.76% respectively, of the annual dose limit for the public members (Lanzas et al., 2015).

the sediments near the Almanzora river mouth (Gascó et al., 1991, 1995; Iranzo et al., 1989b). These studies together with others carried out with sediment samples collected from the continental shelf, slope (200–600 m) and abyssal plain (> 600 m) in the neighboring coasts of Palomares, confirmed the input of transuranics from the river to the sea as consequence of the flood that took place in 1973 (Gascó et al., 1991; Gascó, 1990; Romero, 1991). However, the presence of high transuranic concentrations in areas away from the coast, at 20 km, also confirmed the transport route by the wind (Romero et al., 1991; Romero, 1991). High sediment distribution coefficients (Kd) (104–105 l kg−1), in the continental shelf of Palomares indicate a marked tendency of the transuranic elements to be deposited onto the sediments rather than to remain in solution (Gascó et al., 1994a). The Pu distribution observed in marine sediments collected from the continental shelf of Palomares in 1991 showed to be in general inhomogeneous in the first cm. In fact, a sediment core 20 cm long collected in the Aguas river submarine canyon, sliced in 1.5 cm layers and analyzed by both α-spectrometry and Accelerator Mass Spectrometry (AMS), showed the presence of hot particles on the basis of the heterogeneities observed in three of the 17 slices analyzed (at 2 and 5–6 cm depth) (Chamizo et al., 2010). In relation to the studies carried out with the marine biota off the coast of Palomares, the presence of transuranics in seaweed was observed. In the summer of 1988 and 1989, two seaweed sampling campaigns were carried out along the Andalusian coasts (Manjón et al., 1995). The MDA value for 239+240Pu and 241Am was estimated to be around 0.005–0.010 Bq kg−1 dry weight. The concentration values in the seaweed samples collected in Palomares in the campaign of 1988 were 1.08 ± 0.60 Bq kg−1 (239+240Pu) and 0.17 ± 0.02 Bq kg−1 (241Am) dry weight, and 2.02 ± 0.02 Bq kg−1 and 0.42 ± 0.05 Bq kg−1 dry weight respectively for those collected in 1989. These values were 10–20 times higher than in the rest of the seaweed samples collected along the Andalusian coasts but far from Palomares. The average values of the activity ratios, 238Pu/239+240Pu = 0.024 ± 0.007 and 241 Am/239+240Pu = 0.18 ± 0.04, were lower than those found at the rest of sampling stations in the Andalusian coast (0.47 ± 0.013 for 241 Am/239+240Pu, attributed to fallout), indicating, that the average value of 238Pu/239+240Pu ratio observed at Palomares sampling station was due to mixed sources, fallout and weapon grade Pu. In the upper levels of the marine trophic chain of the Vera Gulf, transuranic activity concentrations similar to those found in other areas of the Mediterranean were found (Gascó et al., 1994b). The authors appointed that the radiological contamination observed came from fallout, and consequently, there was no significant radiological risk for the population that could consume products of marine origin in that area. RERA database contains also information of the marine water samples collected since 2011 in the Quitapellejos beach (30N 606711 4121023), next to the current sampling station E30 (30N 606738.401 4121054.601) (Fig. 2) (Antón and Aragón, 2015). Only MDA values have been obtained. These MDA for 239+240Pu, obtained by α-spectrometry ranged between 0.37 10−3 and 0.13 Bq l−1 (Aragón et al., 2012b, 2013) and between 9.00 10−2 Bq l−1 and 7.03 101 Bq m−3 for 241 Am by Ɣ-spectrometry (Aragón et al., 2015b, 2016, 2017).

4.3. Radiological studies of the marine ecosystem There has been a big concern about the possible presence of contamination and its impact on the marine ecosystem next to the Palomares coast as consequence of the accident. The first samplings of marine sediments began in the Vera Gulf close to Palomares in 1985 to determine the inventory of Pu and Am in marine sediments, to investigate the land-sea transport of transuranics to the continental shelf and to evaluate their possible incorporation to man through the marine trophic chain (Gascó et al., 1991, 1994a; Romero, 1991). Since then, sediments have been studied over time (Antón et al., 1995; Antón et al., 1994; Antón, 1998; Gascó et al., 2002; Gascó et al., 1995; Gascó et al., 1994b; Gascó and Antón, 1997; Gascó et al., 1991; Gascó, 1990; Iranzo et al., 1989b; Mitchell et al., 1997; Romero et al., 1991; Romero et al., 1992). Based on the results obtained from several studies, two transuranic transfer routes to the continental shelf (< 200 m) were proposed: Via aerial delivery at the time of the accident and via dragging of the remaining contamination through the Almanzora river, during flooding events. Rainfall is scarce at Palomares, but this area has reached the maximum rainfall index per day in Spain; severe floods have been documented, among others in 1970, 1973 and 1977 (Capel, 1987). As a result of these floods, big amounts of ground soil reached the adjacent sea. According to the results obtained from the analyses of marine sediment samples, several authors found enhanced levels of Pu and Am at the continental shelf, with higher levels of transuranic concentrations in

5. Bioavailability of transuranic elements released in the Palomares accident As it has been previously indicated, radioactive particles released from a source and deposited in the environment represent point sources of short- and long-term radioecological significance. Direct effects relate to internal doses following inhalation of respiratory particles, as well as skin doses received from surface contamination. Long-term effects relate to ecosystem transfer of radionuclides remobilised from radioactive particles over time, due to weathering, being this potential transfer very much dependent of particle characteristics such as 66

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

elemental composition, morphology, structural changes and chemical composition (Salbu et al., 2004). Palomares radioactive particles seem to be quite refractory to environmental conditions since they persist in soil quite inaltered after several decades. This fact is supported for the characterization analysis performed in some particles indicating that the U and Pu in the particles are mostly present in the form of oxides (PuO2 and UO2) that are quite insoluble forms. In soil areas contaminated in 1966 and that has remained unaltered until now, the vertical migration of the contamination is negligible, being found 40 y after the accident all the Pu in the upper cm. In addition, and supporting the previous comment, low soilplant 239+240Pu concentration ratios, between 0.09 10−3 and 8.9 10−3 were observed in tomato, barley and alfalfa samples collected in Zones 2, 5 and 3, in 1988; (Iranzo et al., 1988a, 1998). In order to gain a more detailed information about the environmental behavior of the particle Pu remaining in Palomares, since the accident different tests analyzing the degree of solubilization of Pu in contact either with abiotic or biotic agents have been performed. These studies showed that the degree of solubility of Palomares particles seems to be in general quite low and dependent on several factors such as pH, temperature, presence of oxidants and/or reducing agents and the surface area of the particles (Baeza et al., 2005; Espinosa, 2003; Iranzo et al., 1991; Jiménez-Ramos et al., 2008). A first study was conducted in the 80`s submitting soil aliquots to a sequential leaching method. The results indicate that the most mobile fraction of 239+240Pu which is made up of the soluble, exchangeable and inorganically absorbed fractions, constitutes only 0.2% of the 239+240 Pu extracted. Associated with organic matter were 6% of the total 239+240Pu, and the remaining 93% were associated with sesquioxides or are in the two residual fractions (sexquioxide-bound Pu amount to 34% and the residual part to 59%). Solubility studies performed using simply water as extractant reinforce the conclusion obtained in the previous experiment about the low percentage of the Pu dissolved, although significant increase in the aqueous solubility of Pu oxide present in soils was observed with time. The average value of the Pu solubility in water determined in five samples was 0.0082% (σ = 0.006) in 1986, while determinations carried out in samples taken in 1999 and 2000 indicated an increase of the Pu solubility of two orders of magnitude (Espinosa et al., 2005), most likely due to the oxidation of Pu on the surface particles and the increase of the specific surface of the Pu oxide particles due to the fragmentation of the nuclear material. The results obtained by Lind et al. (2007) indicating the existence of a small fraction of the U and Pu in oxidation states that may differ from +4, and the existence of Pu/U heterogeneities on particle surfaces support the fact that the particles represent a higher remobilisation potential than previously anticipated/ observed. Several facts can have influence in the observed increment of Pu solubility in water over time. The alteration of the topography of the land in Area 2 in the 80′s as the land owners redistributed soil taken from hillsides to increase the amount of land available for cultivation and the massive construction of greenhouses that retain moisture and allow crop production all the year round are factors that have the potential of a change in the Pu soil chemistry with increasing time. In an independent study performed in order to make an empirical assessment of the Palomares Pu availability by plant uptake, leaching experiments using 1 M Cl2Mg at pH = 7 as the most suitable extractant were performed (Jiménez-Ramos et al., 2008), being applied to soils with different degree of contamination. The obtained results indicated that the bioavailable fraction was relatively variable but low and ranges from 0.4 to 6%, with the great majority of values being lower than 1%. Another study performed more than 30 years after the accident (Espinosa et al., 2005) shows that the possible presence of organic fertilizers in soils such as cow urine mixed with solid excrements could increase Pu solubility, as demonstrated in soil samples collected from Zones 2 and 3 treated with cow urine; a Pu (239+240Pu and 238Pu)

solubility value up to 18% was observed. The authors indicated that the solubilization was probably due to the oxidation of the actinides by the presence of HNO3 due to decomposition of the urea. The percentage of plutonium dissolved with the cow urine is similar to the one obtained with sodium pyrophosphate acting as extracting solution and should be considered as a clear warning of what might happen if organic fertilizers are used in the contaminated area. Another type of leaching studies was performed by using 0.16 M HCl as extracting reagent. In this case the objective was to simulate with this extractant human gastrointestinal tract fluids in order to know the possible solubilization of Pu if some uncontrolled digestion of contaminated soil is produced. The results obtained in these experiments show the low availability of Pu through this extractant (10%) in soil samples collected in Palomares (Lind et al., 2005b; Jiménez-Ramos et al., 2008) in part due to the buffering effects of the Palomares soils (the acidity of the 0.16 M HCl extractant is considerably neutralized in its reaction with the soils). Lung solubility experiments were also performed by submitting total soil and < 5 μm fractions (respirable fractions) to a synthetic physiological solution mimicking the lung fluid. After 3 months of interaction, it was observed that the amount leached of total soil did not exceed 0.5% of the total Pu contained in the sample. With the < 5 μm fraction, during the first weeks of this experiment similar percentages of 239+240 Pu and 241Am were dissolved, but the percentage of 238Pu were several times higher. The total amount of 239+240Pu and 241Am extracted during the first 140 days were less than 0.58% and 0.32% respectively of the total 239+240Pu and 241Am contained in the respirable fraction of soil. For 238Pu the values were about 2% (Espinosa et al., 2005). All the tests performed confirm the low uptake of Pu by plants (Burley, 1997), and the low Pu solubility with its persistence in soil after several decades, despite having been in contact with biological fertilizers, microorganisms or even animals such as gasteropods that could have had a long-term action over Pu present in soil. Nevertheless, in spite of the mentioned facts, it is evident that only fragmented and no directly comparable efforts have been done in the past in relation with the leaching studies being applied. In most cases “local” laboratory protocols have been used that are difficult to replicate, or in some cases avoid the possibility of result intercomparisons. In order to avoid and overcome similar problems, and with the end to generate values directly comparable and reproducible between laboratories, special efforts have been devoted recently to define joint, scientifically agreed protocols for abiotic and biotic transformation studies between the participants of the EU-funded COMET (COordination and ImpleMentation of a pan-European projecT for radioecology) and the participants of the IAEA CRP “Coordination Research Project on Environmental Behaviour and Potential Biological Impact of radioactive Particles”. One of the main outputs of this joint international collaboration has been these protocols (COMET, 2017). With basis in the leaching protocols defined by consensus, isolated Palomares particles have been exposed to: a) Abiotic reagents such as rain water, sea water, irrigation water and synthetic solutions mimicking body fluid such as simulated stomach fluid. b) Biological systems such as rumen liquids from grazing animals. In addition, and in parallel to the transformation experiments applied on single Radioactive Particles (RP), similar experiments (with also a well-defined and specific protocol) has been applied on aliquots from bulk samples from which the particles were isolated. In both cases (particles and soils) the leaching evolution has been studied over time, because the solubilization is clearly time-dependent, and the obtained desorption curves have been submitted to parametrization. The set of results obtained in these last experiments are under evaluation, although in general it can be indicated that they confirm the 67

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio

low solubilization rate of Pu from Palomares contaminated soils under the action of the different agents tested (rain water, irrigation water, 0.16 M HCl, cow rumen). However, it has been also observed that the weathering varies widely under the action of the same extractant in different soil aliquots due to the heterogeneous nature of the soil contamination. In the case of isolated Palomares particles it has been also confirmed the very low weathering rates under the action of aqueous solutions (irrigation water, rain water).

4.

6. Final remarks

5.

The Palomares accident is not the only one that happened in similar circumstances; A similar accident in Thule (Greenland, 21 of January 1968) released also to the environment U and Pu containing particles remarkably similar to the Palomares particles with respect to elemental distribution, morphology and oxidation states (Lind et al., 2005a, 2007). In spite of the fact that the particle analyses provided information about the similarity of the source, the scenarios in which the accidents took place are completely different. In the Thule accident the particles were dispersed in a marine environment after a B-52 bomber impacted on the surface of the sea ice of Bylot Sound breaking up 2500 m2 of the 60 cm thick ice, contaminating also to a lesser extent a terrestrial ecosystem which stays frozen for the most part of the year, while in Palomares accident mostly a terrestrial semi-desertic ecosystem was affected. Leaching experiments (0.16 M HCl) performed on the frame of the previously mentioned EU-COMET and IAEA CRP Hotparticle projects, indicates that the Thule sediment particles appears to be more leachable than those in Palomares soils (COMET, 2017) reflecting that the weathering processes and their evolution over time are also scenario related (not only source-related). We will finish indicating that the information gained until now about the distribution, extension and behavior of the transuranic contamination in the Palomares area, and the experience of the team involved in the construction of the 3D maps and the granulometric speciation of the contamination is an excellent basis to perform in the near future some steps for the cleaning of the area, by removing in the restricted zones most of the transuranic activity. In fact, different restorations test and pilot studies have been performed which are out of the scope of this paper.

6.

7.

8.

of Pu in soil after several decades, despite having been in contact with biological fertilizers, microorganisms or even animals such as gastropods that could have had a long-term action over Pu present in soil. 239+240Pu seems to be highly insoluble in water, not easily available, thus hindering their transfer through the food chain. Particular attention should be paid to the possible contamination of people due to the risk of inhalation of radiological particles within the urban area of Palomares since the resuspension phenomenon has been documented. From 2007 to 2009 a detailed 3D map of the remaining transuranic contamination in the terrestrial area affected by the accident was constructed. The quality of this study was validated by IAEA which perform an International Peer Review on the application of international safety standards for the radiation protection of the members of public in the environment of Palomares, including the methods used and the results obtained in the characterization of the contamination in soil. In addition, in April 2010, a team of experts from the Directorate General for Energy, European Commission, visited the affected areas, confirming the correct surveillance programs carried out in Palomares (Gitzinger and Henrich, 2010). The 3D study along with previous ones carried out in the Palomares area, has allowed knowing which transuranic elements are present in the affected area: 238Pu, 239Pu, 240Pu, 241Pu, 241Am and 235U, distributed on the soil surface and in depth. Moreover, the 3D characterization resulted also in updating the estimation of the inventory of: 239+240Pu: 317 g, 31 g, 34 g and 103 g within Zones 2, 2bis, 3 and 6. The contamination present in some areas of the terrestrial ecosystem has made necessary the adoption of measures for the control of use and access to them, and for surveillance of the surrounding territory. Now we know where the contamination is, but there is still a huge challenge to accomplish: the rehabilitation of the contaminated land at Palomares site. With regard to the marine ecosystem, the surveillance carried out in Palomares indicate that although some traces and signals of Pu coming from the accident can be found, there is no radiological risk for the population derived from consumption of the marine products coming from that coastal area.

Acknowledgements

7. Conclusions

We acknowledge the collaboration and funding of all national and international institutions, in particular, CIEMAT, CSN and DOE, which made the execution of the activities carried out in Palomares possible. This work was supported by CIEMAT (Spanish the Ministry of Science, Innovation and Universities under the General Secretariat for Scientific Policy Coordination).

In the following lines, some key points related with the transuranic contamination due to the Palomares accident are summarized: 1. After an initial cleaning of the most contaminated terrestrial area, and just few weeks after the accident, personal and environmental radiological surveillances programs started. These programs have been continuously running without interruption until now, being increased and refined with the experience gained in its application. Simultaneously, a good number of studies have been done, particularly from the 80′s, in order to gain information about the behavior of the Pu contamination. 2. In particular, due to the possible incorporation of Pu and Am into the food chain and contribution to the effective dose of the locals, crop and animal samples collected from the affected areas or close to them have been analyzed since the accident. No radiological risk has been observed so far due to consumption of meat or food derived from animals and cultivated plants out of the affected areas. However, special attention should be paid to the consumption of wild terrestrial snails. 3. To estimate the dose that the Palomares inhabitants might receive, it should be considered that the distribution of transuranics present in the affected soils appears mainly as particles isolated or associated to small size soil grains (micro-particles), and as well as solid aggregates. The studies carried out in Palomares show the persistence

Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.jenvrad.2019.02.015. References Antón, M.P., Aragón, A., 2015. Programa de vigilancia radiológica ambiental de Palomares. CIEMAT Report DT-RERA-27. Madrid, Spain. Antón, M.P., Gascó, C., Pozuelo, M., 1995. Chemical partitioning of plutonium and americium in sediments from the Palomares marine ecosystem. Rapp. Comm. Int. Mer. Med. 34, 223. Antón, M.P., Gascó, C., Sánchez-Cabeza, J.A., Pujol, L.I., 1994. Geochemical association of plutonium in marine sediments from Palomares. Radiochim. Acta 66/67, 443–446. https://doi.org/10.1524/ract.1994.6667.s1.443. Antón, M.P., 1998. Dinámica sedimentaria de radionucleidos de vida larga en el litoral Mediterráneo Occidental. Ph. D. Thesis. Universidad Complutense de Madrid, Spain. Aragón, A., Aceña, B., Burgos, D., Correa, E., Antón, M.P., Sellek, R.E., Lanzas, R., Sancho, C., 2015a. CRP-IAEA “Environmental Behavior and Potential Biological Impact of Radioactive Particles”. Annual Progress Report 2014. CIEMAT Contribution. CIEMAT Report DT-RERA-32. Madrid, Spain.

68

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio Aragón, A., Antón, M.P., Castaño, S., 2017. Vigilancia radiológica en la zona de Palomares. Informe anual al Consejo de Seguridad Nuclear (2016). CIEMAT Report DT-RERA-62. Madrid, Spain. Aragón, A., Antón, M.P., Castaño, S., 2016. Vigilancia radiológica en la zona de Palomares. Informe anual al Consejo de Seguridad Nuclear (2015). CIEMAT Report DT-RERA-56. Madrid, Spain. Aragón, A., Antón, M.P., Castaño, S., 2015b. Vigilancia radiológica en la zona de Palomares. Informe anual al Consejo de Seguridad Nuclear (2014). CIEMAT Report DT-RERA-48. Madrid, Spain. Aragón, A., Antón, M.P., Castaño, S., 2013. Vigilancia radiológica en la zona de Palomares. Informe anual al Consejo de Seguridad Nuclear (2012). CIEMAT Report DT-RERA-17. Madrid, Spain. Aragón, A., Antón, M.P., Correa, E., 2012a. Programa de vigilancia radiológica ambiental en Palomares. CIEMAT Report DT-RERA-08. Madrid, Spain. Aragón, A., Antón, M.P., Salas, C., Castaño, S., 2012b. Vgilancia radiológica en la zona de Palomares. Informe anual al Consejo de Seguridad Nuclear (primer y segundo semestre del año 2011). CIEMAT Report DT-RERA-09. Madrid, Spain. Aragón, A., Espinosa, A., Antón, M.P., 2006. Study on the contamination by transuranides of pulmonata gastropoda collected in Palomares (Spain). Czech. J. Phys. 56, D129–D132. https://doi.org/10.1007/s10582-006-0497-4. Aragón, A., 2003. Radioecología de transuránidos: Caracterización y comportamiento de partículas de combustible nuclear en suelos afectados por el accidente de Palomares. Ph.D. Thesis. Universidad Autónoma de Madrid, Madrid, Spain. Aragón, A., Espinosa, A., de la Cruz, B., Fernández, J.A., 2008. Characterization of radioactive particles from the Palomares accident. J. Environ. Radioact. 99, 1061–1067. https://doi.org/10.1016/j.jenvrad.2007.12.014. Baeza, A., Guillén, J., Espinosa, A., Aragón, A., Gutiérrez, J., 2005. A study of the bioavailability of 90Sr, 137Cs, and 239+240Pu in soils at two locations of Spain affected by different radionuclide contamination events. Radioproteccion 40, S61–S65. https:// doi.org/10.1051/radiopro:2005s1-010. Burley, G., 1997. Transuranium Elements, Volume I, Elements of Radiation Protection. U.S.A Environmental Protection Agency Report EPA 520/1-90-015. Las Vegas, U.S.A. Capel, J., 1987. Inundaciones y avenidas de los ríos del sureste español. Papeles Geogr. 13, 75–86. Chamizo, E., García-León, M., Synal, H.A., Suter, M., Wacker, L., 2006. Determination of the 240Pu/239Pu atomic ratio in soils from Palomares (Spain) by low-energy accelerator mass spectrometry. Nucl. Instrum. Methods B 249, 768–771. https://doi.org/ 10.1016/j.nimb.2006.03.136. Chamizo, E., Jiménez-Ramos, M.C., Enamorado, S.M., García-León, M., García-Tenorio, R., Mas, J.L., Masqué, P., Merino, J., Sanchez-Cabeza, J.A., 2010. Characterisation of the plutonium isotopic composition of a sediment core from Palomares, Spain, by low-energy AMS and alpha-spectrometry. Nucl. Instrum. Methods B 268, 1273–1276. https://doi.org/10.1016/j.nimb.2009.10.151. COMET, 2017. Final Report on the European Commission Funded COMET-RATE Project (Contract Number; FISSION-2012.3.4.1604494) Deliverable 3.7. ENUSA Industrias Avanzadas S.A., 2008. Proyecto de caracterización tridimensional de los terrenos expropiados de Palomares. Estudio geológico e hidrogeológico. Technical Report INF-MA-000315. Madrid, Spain. Espinosa, A., Aragón, A., de la Cruz, B., Gutiérrez, J., 2005. Influence of cow urine in the bioavailability of plutonium oxide particles in Palomares soils. Radioprot. Suppl. 1 40, S73–S77. https://doi.org/10.1051/radiopro:2005s1-012. Espinosa, E., Aragón, A., Antón, M.P., Castaño, S., Salas, C., 2010. Vigilancia radiológica en la zona de Palomares. Informe al Consejo de Seguridad Nuclear. Primer semestre del año 2010. CIEMAT Report CIEMAT/SG/INDALO-VRA/SRA/S41-060910. Madrid, Spain. Espinosa, E., Aragón, A., Castaño, S., Salas, C., Antón, M.P., 2008. Vigilancia radiológica en la zona de Palomares. Informe al Consejo de Seguridad Nuclear. Primer semestre del año 2008. CIEMAT Report CIEMAT/DMA/INDALO/M0200/02/08. Madrid, Spain. Espinosa, E., Aragón, A., Martínez, J., Gutierrez, J., Castaño, S., 2000. Vigilancia radiológica en la zona de Palomares. Informe al Consejo de Seguridad Nuclear. Primer semestre del año 2000. CIEMAT Report CIEMAT/DIAE/PPRI/51100/3/2000. Madrid, Spain. Espinosa, A., 2003. Comportamiento ambiental de las partículas de combustible nuclear (fundamentalmente Pu) tras un accidente nuclear en un ecosistema de tipo mediterráneo. Ph. D. Thesis. Universidad de Extremadura, Cáceres, Spain. Espinosa, A., Aragón, A., Stradling, N., Hodgson, A., Birchall, A., 1998. Assessment of dose to adult members of the public in Palomares from inhalation of plutonium and americium. Radiat. Protect. Dosim. 79, 161–164. https://doi.org/10.1093/ oxfordjournals.rpd.a032382. Fowler, E.B., Buchholz, J.R., Christenson, C.W., Adams, W.H., Rodríguez, E.R., Celma, M., Iranzo, E., Ramis, C.A., 1968. Soil and Plants as Indicators of the Effectiveness of a Gross Decontamination Procedure. U.S.A Atomic Energy Commission Report LA-DC9544. Los Alamos, NM, U.S.A. García-Olivares, A., Iranzo, C.E., 1997. Resuspension and transport of plutonium in the Palomares area. J. Environ. Radioact. 37, 101–114. https://doi.org/10.1016/S0265931X(96)00076-8. García López, J., Jiménez-Ramos, M.C., García-León, M., García-Tenorio, R., 2007. Characterisation of hot particles remaining in soils from Palomares (Spain) using a nuclear microprobe. Nucl. Instrum. Methods B 260, 343–348. https://doi.org/10. 1016/j.nimb.2007.02.044. Gascó, C., Antón, M.P., Espinosa, I.A., Aragón, A., Álvarez, A., Navarro, N., GarcíaToraño, R., 1997. Procedures to define Pu isotopic ratios characterizing a contaminated area in Palomares (Spain). J. Radioanal. Nucl. Chem. 222, 81–86. https:// doi.org/10.1007/BF02034251. Gascó, C., Antón, M.P., Pozuelo, M., Meral, J., González, A., Papucci, C., Delfanti, R.,

2002. Distribution profiles of Pu, Am and Cs in margin sediments from the western Mediterranean (Spanish coast). J. Environ. Radioact. 59, 75–89. https://doi.org/10. 1016/S0265-931X(01)00037-6. Gascó, C., Antón, M.P., Rivas, P., 1995. Man-made radioactivity in the Almazora Gulf and beach of Palomares, Spain. Radiat. Protect. Dosim. 58, 301–306. https://doi.org/10. 1093/oxfordjournals.rpd.a082629. Gascó, C., Antón, M.P., Romero, L., 1994a. Radioecología de transuránidos en el Mediterráneo Español. Radioproteccion 1, 21–29. Gascó, C., Antón, M.P., Romero, L., 1994b. Global inventory of radionuclides along the Mediterranean continental shelf of Spain. In: Cigna, A., Delfanti, R., Serro, R. (Eds.), The Radiological Exposure of the Population of the European Community to Radioactivity in the Mediterranean Sea. European Coomision, Rome, Italy, pp. 469–483. Gascó, C., Antón, M.P., 1997. Influence of the submarine orography on the distribution of long-lived radionuclides in the Palomares marine ecosystem. J. Environ. Radioact. 34, 111–125. https://doi.org/10.1016/0265-931X(96)00045-8. Gascó, C., Iranzo, E., Romero, L., 1991. Transuranics transfer in a Spanish marine ecosystem. J. Radioanal. Nucl. Chem. 156, 151–163. https://doi.org/10.1007/ BF02037430. Gascó, C., 1990. Estudio de la distribución de plutonio en el ecosistema marino de Palomares después de una descarga accidental de un aerosol de transuránidos. Ph. D. Thesis. Universidad Complutense de Madrid, Madrid, Spain. Gitzinger, C., Henrich, E., 2010. Plutonium Contaminated Sites in the Palomares Region. Spain. European Commission Report ES-10/01. Luxembourg, Luxembourg. Gonzalo de Diego, V., 2010. Caracterización mediante microscopía electrónica de barrido de una muestra radiactiva procedente de Palomares. CIEMAT Report DT/ME-13/II10. Madrid, Spain. International Atomic Energy Agency, 2009. International Peer Review on the Application of the International Safety Standars for the Radiation Protection of the Public in the Environment of Palomares (Spain). IAEA Final report, Vienna, Austria. Iranzo, E., Richmond, C.R., Sollet, E., Voelz, G.L., 1998. Scientific Review of Palomares Plutonium Surveillance Program 1966-1998. DOE, CIEMAT Report. Madrid, Spain. Iranzo, E., Álvarez, A., Bellido, A., Castaño, S., Espinosa, M.A., Gascó, C., Iranzo, C.E., Mingarro, E., Rivas, P., Romero, L., 1989a. Vigilancia radiológica en la zona de Palomares. Informe segundo semestre del año 1988. CIEMAT Report CIEMAT/ PRYMA/GIT/M5A01/1/89. Madrid, Spain. Iranzo, E., Álvarez, A., Bellido, A., Castaño, S., Espinosa, M.A., Iranzo, C.E., 1988a. Vigilancia radiológica en la zona de Palomares. Informe primer semestre del año 1988. CIEMAT Report M5A01/PI003/bis/88. Madrid, Spain. Iranzo, E., Castaño, S., Iranzo, C.E., Espinosa, M.A., Bellido, A., 1987a. Vigilancia radiológica en la zona de Palomares. Primer semestre de 1987. CIEMAT Report M2A/PI004/-/87. Madrid, Spain. Iranzo, E., Espinosa, A., Iranzo, C.E., 1988b. Dose estimation by bioassay for population involved in an accident with plutonium release. In: II Conference on Radiation Protection and Dosimetry. Personal Communication, Orlando, USA. Iranzo, E., Gascó, C., Romero, L., Martínez, A., Mingarro, E., Rivas, P., 1989b. Temporal Distribution of Pu and Am in Marine Environmental of Southern Coast of Spain. CIEMAT Report 641. Madrid, Spain. Iranzo, E., Rivas, P., Mingarro, E., Marín, C., Espinosa, M.A., Iranzo, C.E., 1991. Distribution and migration of plutonium in soils of an accidentally contaminated environment. Radiochim. Acta 52/53, 249–256. https://doi.org/10.1524/ract.1991. 5253.1.249. Iranzo, E., 1987. Informe sobre los resultados del plan de vigilancia radiológica asociado a la contaminación residual en la zona de Palomares durante el año 1986. CIEMAT Report CNS/SGEPR/PRO-000/47/1-87. Madrid, Spain. Iranzo, E., Espinosa, A., Martinez, J., 1994. Resuspension in the Palomares area of Spain: a summary of experimental studies. J. Aerosol Sci. 25, 833–841. https://doi.org/10. 1016/0021-8502(94)90050-7. Iranzo, E., Salvador, S., Iranzo, C.E., 1987b. Air concentrations of 239Pu and 240Pu and potential radiation doses to persons living near Pu-contaminated areas in Palomares, Spain. Health Phys. 52, 453–461. https://doi.org/10.1097/00004032-19870400000006. Jiménez-Ramos, M.C., Barros, H., García-Tenorio, R., García-León, M., Vioque, I., Manjón, G., 2007. On the presence of enriched amounts of 235U in hot particles from the terrestrial area affected by the Palomares accident (Spain). Environ. Pollut. 145, 391–394. https://doi.org/10.1016/j.envpol.2006.08.002. Jiménez-Ramos, M.C., Vioque, I., García-Tenorio, R., García León, M., 2008. Levels, distribution and bioavailability of transuranic elements released in the Palomares accident (Spain). Appl. Radiat. Isot. 66, 1679–1682. https://doi.org/10.1016/j. apradiso.2007.12.015. Jimenez-Ramos, M.C., Hurtado, S., Chamizo, E., Garcia-Tenorio, R., León Vintró, L., Mitchell, P.I., 2010. 239Pu, 240Pu and 241Am in hot-particles by low level gammaspectrometry. Environ. Sci. Technol. 44, 4247–4252. Lanzas, R., Burgos, D., Correa, E., 2014. Distribución granulométrica del suelo. CIEMAT Report DT-RERA-31. Madrid, Spain. Lanzas, R., Sellek, R.E., Correa, E., 2015. Vigilancia radiológica ambiental de Palomares. Medidas de vegetación silvestre. CIEMAT Resport DT-RERA-45. Madrid, Spain. Lanzas, R., 2017. Revisión de resultados de vigilancia radiológica de Palomares: Registros informatizados (1966-2015). CIEMAT Report DT-RERA-61. Madrid, Spain. Lind, O.C., Salbu, B., Janssens, K., Proost, K., Dahlgaard, H., 2005a. Characterization of uranium and plutonium containing particles originating from the nuclear weapons accident in Thule, Greenland, 1968. J. Environ. Radioact. 81, 21–32. https://doi.org/ 10.1016/j.jenvrad.2004.10.013. Lind, O.C., Skipperud, L., Salbu, B., 2005b. Linking radioactive particle characteristics to weathering and dissolution kinetics. In: Strand, P., Børretzen, P., Jølle, T. (Eds.), International Conference on Radioactivity in the Environment. Nice, France, pp.

69

Journal of Environmental Radioactivity 203 (2019) 55–70

C. Sancho and R. García-Tenorio 274–277. Lind, O.C., 2006. Characterization of Radioactive Particles in the Environment Using Advanced Techniques. Ph.D. Thesis. Norwegian University of Life Science, Norway. Lind, O.C., Salbu, B., Janssens, K., Proost, K., García-León, M., García-Tenorio, R., 2007. Characterization of U/Pu particles originating from the nuclear weapon accidents at Palomares, Spain, 1966 and Thule, Greenland, 1968. Sci. Total Environ. 376, 294–305. https://doi.org/10.1016/j.scitotenv.2006.11.050. Manjón, G., García-León, M., Ballestra, S., López, J.J., 1995. The presence of man-made radionuclides in the marine environment in the south of Spain. J. Environ. Radioact. 28, 171–189. https://doi.org/10.1016/0265-931X(94)00049-3. Mitchell, P.I., Vintró, L., Dahlgaard, H., Gascó, C., 1997. Perturbation in the 240Pu/239Pu global fallout ratio in local sediments following the nuclear accidents at Thule (Greenland) and Palomares Spain. Sci. Total Environ. 202, 147–153. https://doi.org/ 10.1016/S0048-9697(97)00111-3. Moore, S.A., 1966. B-52/KC-135 Collision Near Palomares, Spain (U). Sandia Laboratory Report SC-DR-66-397. Alburquerque, New Mexico, U.S.A. Nuclear Safety Council, 2013. 1966/2013 Palomares. En el camino de la normalización radiológica. CSN, Madrid, Spain. Nuclear Safety Council, 2008. Caracterización radiológica superficial detallada en Palomares. CSN Report CSN-C-SRA-08-63. Madrid, Spain. Papelis, C., Jacobson, R., Miller, F.L., Shaulis, L. k., 1996. Evaluation of Technologies for Volume Reduction of Plutonium-Contaminated Soils from the Nevada Test Site. DOE Report DOE/NV/10845-57. Nevada, U.S.A. Place, W.M., Cobb, F.C., Defferding, C.G., 1975. Palomares Summary Report. Defence Nuclear Agency Report 844. New Mexico, U.S.A. Pöllänen, R., Ketterer, M.E., Lehto, S., Hokkanen, M., Ikäheimonen, T.K., Siiskonen, T., Moring, M., Martín, A., 2006. Multi-technique characterization of a nuclear bomb particle from the Palomares accident. J. Environ. Radioact. 90, 15–28. https://doi. org/10.1016/j.jenvrad.2006.06.007. Ramos, E., 1968. Palomares two years after. [WWW Document]. https://www.osti.gov/ scitech/servlets/purl/4805285, Accessed date: 7 June 2017. Romero, L., Lobo, A., Holm, E., Sánchez, J.A., 1991. Transuranics contribution of Palomares coast: tracing history and routes to the marine environmental. In: Kersaw, P.J., Woodhead, D.S. (Eds.), Radionuclides in the Study of Marine Process. Springer Netherlands, New York, United States, pp. 245–254. Romero, L., Lobo, A., Holm, E., 1992. New aspects on the transuranics transfer in the Palomares marine environment. J. Radianal. Nucl. Chem. 161, 489–994. https://doi. org/10.1007/BF02040496.

Romero, L., 1991. Estudio del transporte tierra-mar de elementos transuránidos. Aplicación al accidente de Palomares (Almería) de 1966. PhD. Thesis. Universidad Complutense de Madrid, Spain. Rubio, P., Martín, A., 2001. Plutonium contamination from accidental release or simply fallout: study of soils at Palomares (Spain). J. Environ. Radioact. 55, 157–165. https://doi.org/10.1016/S0265-931X(00)00189-2. Rubio, M.P., Martín, A., Crespo, M.T., Gascón, J.L., 2000. Analysis of plutonium in soil samples. Appl. Radiat. Isot. 53, 259–264. https://doi.org/10.1016/S0969-8043(00) 00141-X. Sáez, J.C., Correa, E., Burgos, D., Lanzas, R., 2009. Three-dimensional Radiological Map of Palomares Final Report. CIEMAT Report SG/PIEM-VR-01/09. Madrid, Spain. Sáez, J.C., 2008. Mapa radiológico tridimensional de Palamares. Informe al Consejo de Seguridad Nuclear. Segundo semestre 2007. Caracterización radiológica superficial intensiva. CIEMAT Report DG/PRP-01/08. Madrid, Spain. Sáez, J.C., Aragón, A., 2010. Actividad de transuránicos en las fracciones granulométricas de los suelos de Palomares. CIEMAT Report SG/PIEM-VR-02/10. Madrid, Spain. Salbu, B., Krekling, T., Oughton, D.H., 1998. Characterisation of radioactive particles in the environment. Analyst 123, 843–850. https://doi.org/10.1039/A800314I. Salbu, B., Lind, O.C., Skipperud, L., 2004. Radionuclide speciation and its relevance in environmental impact assessments. J. Environ. Radioact. 74, 233–242. Salbu, B., Kaspharov, V., Lind, O.C., García-Tenorio, R., Johanssen, M.P., Child, D., Roos, P., Sancho, C., 2018. Challenges associated with the behaviour of radioactive particles in the environment. J. Environ. Radioact. 186, 101–115 2018. Sancho, S., Gutiérrez, J., 2007. Propuesta de ocupación temporal de terrenos en la zona de Palomares. CIEMAT Report DG/PR-04/07. Madrid, Spain. Spain, 2001. Real Decreto 786/2001, de 6 de julio, por el que se aprueba el Reglamento sobre protección sanitaria contra radiaciones ionizantes. pp. 27284–27393 Boletín Oficial de Estado, 26 de julio de 2001, núm. 178. Torrao, G., Carlino, R., Hoeffner, S., Navratil, J., 2003. Characterization of plutonium contaminated soils from the Nevada test site in support of evaluation of remediation technologies. In: Walsh, D. (Ed.), 9th ASME International Conference on Radioactive Waste Management and Environmental Remediation. The American Society of Medical Engineers, Oxford, UK, pp. 1907–1912. U.S.A Air Force, 1966. Broken Arrow. Palomares, Spain. U.S.A Goverment Report 133 (declassificated). U.S.A. Wilson, D.E., 1966. Analysis of Ballistics of Four MK 28 FI Weapons Released as a Result of the Collision of a B-52 and KC-135 Near Vera, Spain, on 17 January 1966. 16th US Air Force Report 135. New York, U.S.A.

70