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Assessing cost and effectiveness of radiation decontamination in Fukushima Prefecture, Japan
Journal of Environmental Radioactivity xxx (2015) 1e9
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Journal of Environmental Radioactivity journal homepage: www.elsevier.com/locate/jenvrad
Assessing cost and effectiveness of radiation decontamination in Fukushima Prefecture, Japan Tetsuo Yasutaka*, Wataru Naito National Institute of Advanced Industrial Science and Technology, Ibaraki, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 January 2015 Received in revised form 4 May 2015 Accepted 11 May 2015 Available online xxx
Despite the enormous cost of radiation decontamination in Fukushima Prefecture, it is not clear what levels of reduction in external radiation exposure are possible in the Special Decontamination Area, the Intensive Contamination Survey Areas and the whole of Fukushima. The objective of this study was to evaluate the cost and effectiveness of radiation decontamination in Fukushima Prefecture in its entirety. Using a geographic information system, we calculated the costs of removal, storage containers, transport, and temporary and interim storage facilities as well as the reduction in air dose rate for a cumulative external exposure for 9000 1 km 1 km mesh units incorporating 51 municipalities. The decontamination cost for the basic scenario, for which forested areas within 20 m of habitation areas were decontaminated, was JPY2.53e5.12 trillion; the resulting reduction in annual external dose was about 2500 person-Sv. The transport, storage, and administrative costs of decontamination waste and removed soil reached JPY1.55e2.12 trillion under this scenario. Although implementing decontamination of all forested areas provides some major reductions in the external radiation dose for the average inhabitant, decontamination costs could potentially exceed JPY16 trillion. These results indicate that technologies for reducing the volume of decontamination waste and removed soil should be considered to reduce storage costs and that further discussions about forest decontamination policies are needed. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Decontamination Cost and effectiveness Radiation contamination Fukushima
1. Introduction The accident at the Tokyo Electric Power Company Fukushima Daiichi nuclear power plant (F1NPP) released radionuclides into the atmosphere, which were then transported by the wind before being deposited on land and sea surfaces via precipitation. Approximately 22% of these radionuclides were deposited on land (Morino et al., 2011), and to this day, a large quantity of radionuclides remains in soil in agricultural and urban areas, on asphalt and concrete surfaces, on the leaves and bark of trees, and in the litter layer (organic layer) of the soil in forests (Ministry of Education, Culture, Sports, Science and Technology, Japan, 2011). Airborne monitoring surveys of large areas have revealed a zone of highdensity surface deposition of cesium-134 and cesium-137 extending to the northwest from F1NPP (Ministry of Education Culture Sports Science and Technology in Japan, 2011).
* Corresponding author. National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan. Tel.: þ81 29 849 1545; fax: þ81 29 861 8795. E-mail address: [email protected] (T. Yasutaka).
On January 2012, the Japanese government enacted the Act on Special Measures Concerning the Handling of Environment Pollution by Radioactive Materials Discharged by the Nuclear Power Station Accident Associated with the Tohoku DistricteOff the Pacific Ocean Earthquake That Occurred on March 11, 2011 (also called the Act on Special Measures Concerning the Handling of Pollution by Radioactive Materials). The objective of the Act was to promptly reduce the impact of radioactive substances from the accident on human health and to living environment, effective 1 January 2012, on the environment. Under this legislation, decontamination guidelines were released in December 2011 by the Japanese Ministry of the Environment (2011) that detailed methods for surveying and measuring the degree of environmental contamination in highly contaminated areas as well as measures for decontamination and guidelines for collection, transport, and storage of removed soil. In January 2012, the Ministry announced a decontamination roadmap to be implemented under the direct supervision of the Japanese government (Policy for Decontamination in the Special Decontamination Area). Progress has been made in establishing frameworks and guidelines for full-scale decontamination; actual decontamination work has already started. However, pilot surface decontamination studies have found that it
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will take time for some areas to return to their pre-accident state even after decontamination work has been completed on account of differences in decontamination efficiency due to the type of land use and the air dose of a particular area (Fukushima Prefecture, 2012b; Japan Atomic Energy Agency, 2012)). Decontamination is currently underway in Fukushima Prefecture; as of October 2014, the implementation fraction of decontamination activity was around 30e80% against total decontamination planning area (Japanese Ministry of the Environment, 2014), although progress varies depending on land use and the city, town, or village. Decontamination of affected areas is extremely important so that residents may return to their normal day-to-day lives. When considering a post-decontamination return, both the prevalent air dose rate and the cumulative dose are one of the main factors for evacuees to decide whether to return home or not.is the one of the important factors. In this sense, it is important that the prevalent air dose rate and cumulative doses be evaluated under multiple decontamination scenarios, that the decontamination effectiveness be quantified, and that the decontamination and associated costs be estimated and analyzed. Progress is being made in building up data for air dose mapping and in evaluating decontamination methods and their efficiencies; however, there are few examples of research that integrates these findings at a regional level and quantitatively assesses both the associated costs and the effectiveness of exposure reduction by decontamination. One relevant example is the work of Yasutaka et al. (2013a), who used a geographic information system (GIS) to evaluate the efficacies of air dose and cumulative external radiation dose reduction through decontamination of 11 municipalities located in the Special Decontamination Area (SDZ) from which residents were or are currently evacuated. The SDZ includes areas located within a 20-km radius of the F1NPP or where the cumulative dose 1 year after the accident was expected to exceed 20 mSv/year. Yasutaka et al. (2013a) found that although there were quantifiable reductions in air dose within the SDZ, there were limits to the effectiveness of decontamination and areas still remained that were affected by radiation. Furthermore, (Yasutaka et al., 2013b) evaluated decontamination costs and external radiation dose reduction effects under multiple decontamination scenarios for the SDZ; in the basic scenario, decontamination costs were estimated to be JPY1.3e2.7 trillion. They found that the overall decontamination cost was
primarily influenced by whether or not the decontamination method for agricultural land generated waste. These previously published investigations quantitatively evaluated the cost and efficacy of decontamination within the SDZ. However, yet to be made is a quantitative assessment that also encompasses Intensive Contamination Survey Areas (ICAs) in Fukushima Prefecture with radionuclide concentrations lower than those in the SDZ. These ICAs include 40 unevacuated municipalities where decontamination efforts are being carried out by local governments. The overall area of the ICAs is eight times that of the total SDZ area, and decontamination methods and geographical scope philosophies vary, as do the quantities of waste generated. For these reasons, ICAs need to be evaluated alongside the SDZ to conduct an overall assessment of decontamination cost and efficiency. Furthermore, decontamination of forested areas in Fukushima Prefecture is being carried out in accordance with guidelines that currently stipulate only areas that lie within 20 m of areas of habitation (ca. 70% of the prefecture is covered in forest). However, according to one estimate, this approach will result in only around 5% of the overall forested area in the SDZ being decontaminated (Yasutaka et al., 2013b). With calls for further decontamination of forests coming from various quarters, it is important to estimate the cost and efficacy of a wider area of forest decontamination. The objective of this study was to evaluate the cost and effectiveness of various decontamination scenarios over the entirety Fukushima Prefecture. We applied the evaluation methods described by Yasutaka et al. (2013a) to ICAs as well; with the current decontamination policy for Fukushima Prefecture as the basic case, we evaluated decontamination costs and efficiencies for multiple scenarios including forest decontamination.
2. Materials and methods 2.1. Target areas The target areas were the 11 municipalities in the SDZ from which residents were evacuated after the nuclear accident and the 40 municipalities in the unevacuated ICAs (Fig. 1). The target areas occupy an area of 7836 km2 with a non-evacuated population of ca. 1,698,000 (2010 census).
Fig. 1. Target area of research.
Please cite this article in press as: Yasutaka, T., Naito, W., Assessing cost and effectiveness of radiation decontamination in Fukushima Prefecture, Japan, Journal of Environmental Radioactivity (2015), http://dx.doi.org/10.1016/j.jenvrad.2015.05.012
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2.2. Air dose rate, land use, and population density spatial data We integrated and analyzed air dose rate, land use, and population density spatial data in 9000 1 km 1 km mesh units using GIS (ArcGIS Version 1.0). The air dose rate distribution at an elevation of 1 m above ground level (obtained from the Fourth Airborne Monitoring Survey undertaken by the Ministry of Education, Culture, Sports, Science and Technology, Japan (2011)) was used for the air dose rate data. For each mesh unit (100 m 100 m), the estimated air dose rate at the center was used as a representative value; then, to calculate the air dose rate for each 1 km 1 km mesh unit, we used the arithmetic means of the air dose rates of all 100 m 100 m meshes. These values included background radiation (average: 0.04e0.05 mSv/h (National Institute of Advanced Industrial Science and Technology, 2011)). For this analysis, we used 0.045 mSv/h as the background value. Land use subdivided mesh data from the National Land Numerical Information database (JFY 2009) was used for land use data (Japanese Ministry of Land Infrastructure Taransport and Tourism, 2012). The mesh size was 100 m 100 m; the original twelve classifications of land use were reclassified into six: paddy fields, other agricultural land, forest, land for buildings, roads, and other uses. Furthermore, 'to estimate residential area for 1 km 1 km meshes in the ICAs where buildings accounted for less than 50% of the area, the number of residential households was multiplied by the average area lot size for a single house in Fukushima Prefecture (400 m2/household; 2008 Housing and Land Survey); this estimate was compared with the area occupied by buildings, with the larger value being adopted. If the area occupied by buildings increased by above correlation coefficient, the areas for agriculture and forest were reduced. Road density/road length mesh data from the National Land Numerical Information database (Japanese Ministry of Land Infrastructure Taransport and Tourism, 2012) were used for road length. Grid square statistics from the 2010 population census was used for population distribution. When a boundary between the SDZ and ICAs existed within a 1 km 1 km mesh, the mesh was partitioned along the border of the municipalities (cities, towns, or villages) lying within the mesh. Here, the area ratio for each 1 km 1 km mesh was used when proportionally distributing land use areas, population, and road lengths. 2.3. Decontamination methods, efficiency, and cost The decontamination process comprises decontamination itself; temporary storage of decontamination waste and removed soil in containers; transport of waste; volume reduction of waste; and temporary, interim, and final storage of waste. Decontamination efficiency, the quantity of waste generated, and cost depend on land use, air dose rate, and the decontamination method adopted. Our
3
research was based on the decontamination methods currently employed in Fukushima Prefecture (Table 1). Decontamination efficiency varies depending on the decontamination method and the air dose rate prior to decontamination (Japan Atomic Energy Agency, 2012). The decontamination efficiency for each decontamination method was set as indicated in Table 1 based on the findings of Yasutaka et al. (2013a, 2013b), who compiled air dose and land use data according to demonstration tests by the Japan Atomic Energy Agency. Decontamination efficiencies for decontamination methods for ICAs (F2, R2, RB3) that were not evaluated in the abovementioned papers were assumed to be at 50% of the efficiencies of the most efficient decontamination methods (F1, R1, RB2) reported for municipal decontamination in Fukushima City and Koriyama City. Unit costs (per flexible container) were estimated for decontamination and removal of the generated waste (Table 2) and for storage containers, temporary storage sites, transport costs, and reduction of the volume of combustible material (Table 3). These estimated unit costs were based on decontamination pilot studies and demonstration test data from the Japan Atomic Energy Agency (2012) and Fukushima Prefecture (2012a,b), interviews with members of officials from Fukushima Prefecture, other information in the public domain, and information on similar technologies. Two sets of unit costs for decontamination were calculated: the basic unit cost and the maximum unit cost (the highest unit cost identified from interviews and other information). Next, the authors focus on the generated waste management including temporary storage facilities, volume reduction and interim storage facilities. Waste management procedure in this research was based on the flow chart and the basic policy of Ministry of Environment (Japanese Ministry of Environment, 2013). The combustible waste generated through decontamination was stored at temporary storage facilities. The volume of this waste was reduced by incineration, and the incineration ash was transferred to interim storage facilities. Japanese government made a plan that these incineration ashes with highly radioactive cesium concentration and leachable characteristics would be stored in concreteshielded structures facilities (Japanese Ministry of Environment, 2013). We assumed the unit cost of this type of storage site as JPY100,000 per flexible container after volume reduction.by referring to the unit cost information of strictly controlled type landfill site in Japan. After being transferred to interim storage facilities, incombustibles (soil) were planned to be stored at soil storage facilities in the interim storage facilities (Japanese Ministry of Environment, 2013). Because of the building constitution of soil storage facilities was similar to that of the controlled landfills wastes sites, the cost of soil storage facilities in the interim storage facilities was assumed to be JPY30,000 per flexible container.
Table 1 Decontamination methods and their efficiencies (Fukushima Prefecture, 2012a,b; Japanese Ministry of the Environment, 2011).
Agricultural
Forest Road Residential and building
A1 A2 A3 A4 F1 F2 R1 R2 RB1 RB2 RB3
Weeding/Stripping 5 cm topsoil/Covering Soil Weeding/Stripping 5 cm topsoil Interchanging topsoil with subsoil with zeolite and potassium Plowing with zeolite and potassium Removal of fallen leaves and humus surface Removal of fallen leaves Shot blasting and side ditch sweeping Road and side ditch sweeping. Whole decontamination Whole decontamination Local decontamination (only high air dose area)
&1mSv/h
1e3 mSv/h
3e10 mSv/h
>10mSv/h
0.34 0.34 0.34 0.21 0.19 0.10 0.15 0.08 0.29 0.29 0.15
0.49 0.49 0.49 0.31 0.27 0.14 0.30 0.15 0.35 0.35 0.18
0.47 0.47 0.47 0.29 0.39 0.20 0.41 0.20 0.49 0.49 0.25
0.80 0.80 0.80 0.50 0.59 0.30 0.66 0.33 0.70 0.70 0.35
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Table 2 Unit costs for decontamination and generated waste. Land-use
Agricultural
Forest Road Residential and building
Decontamination method
A1 A2 A3 A4 F1 F2 R1 R2 RB1 RB2 RB3
Weeding/Stripping 5 cm topsoil/Covering Soil Weeding/Stripping 5 cm topsoil Interchanging topsoil with subsoil with zeolite and potassium Plowing with zeolite and potassium Removal of fallen leaves and humus surface Removal of fallen leaves Shot blasting and side ditch sweeping Road and side ditch sweeping. Whole decontamination Whole decontamination Local decontamination (only high air dose area)
Unit cost (10 thousand JPY/hectare)
Number of flexible containers (units/hectare)
Target area
Removal
Flex. Containers
Temporary storage
Incombustible
Combustible
SDZ
ICA
950 625 (100)-310
652 652 0
1630 1630 0
715 715 0
100 100 0
B B B
B
(20)-33 745 60e280 480 240/km 1750e3500 1750e3500 125e250
0 424 208 24 70 120 120 9
0 1060 520 60 176 300 300 22
0 270 0 30 88 140 100 7
0 260 260 0 0 0 50 4
B B
The interim storage facilities are to be built in the areas neighboring the F1NPP. Therefore, waste transport costs were estimated based on transport by a 10-tonne truck from the center of each 1 km 1 km mesh to the F1NPP. An additional 22% was added to these estimates to cover general expenses such as radiation monitoring costs. This ratio was estimated by comparing “the actual ordered cost” with “our estimation cost” of decontamination activity and building temporally storage site at 6 municipalities in SDZ. In addition, in Difficult-to-Return Zones, the working efficiency of decontamination activity was supposed to decrease and the cost of management and countermeasure of external exposure for decontamination workers to increase because of high air dose rates in these areas. For this reason,
B B
B B B B B
we added an additional 70% to costs (decontamination costs, temporary storage site costs, transport costs) for these zones. 2.4. Decontamination scenarios Table 4 describes the various decontamination scenarios. Separate decontamination scenarios were set for the SDZ and ICAs, and decontamination methods and decontamination areas were varied, for a total of four scenarios. Decontamination areas for ICAs were set on the basis of annual exposures that were based on air doses as of November 2011 from the Fourth Airborne Monitoring Survey undertaken by the Ministry of Education, Culture, Sports, Science and Technology, Japan (2011).
Table 3 Unit costs for management and storage. Item
Unit cost
Source, notes
Storage container
JPY8000
Transport 1 Decontamination site/Temporary storage site
JPY3100/container
Temporary storage site
JPY20,000/container
Transport 2 Temporary storage site / Interim storage facility
JPY 3800e16,000/ container
Interim storage facility
Combustibles volume reduction
JPY2000/container
Combustibles incineration residue storage
JPY100,000/container
Incombustibles storage
JPY30,000/container
Use of weather-resistant flexible container conforming to Ministry of the Environment decontamination guidelines. Based on information from company websites and interviews, unit cost was estimated at JPY5000e8000. Unit cost was set at the upper level. Calculated assuming transport by 4-tonne truck over one-way distance of 5 km and referring to provisional estimation standards for decontamination work in SDZs from the Ministry of the Environment. Estimate based on interviews and provisional estimation standards for decontamination work in SDZs from the Ministry of the Environment. Transport distance was calculated as distance from each municipality's public office to the vicinity of F1NPP. Calculated based on transport using a 10-tonne truck, and with reference to provisional estimation standards for decontamination work in SDZs from the Ministry of the Environment. Assuming volume reduction carried out within interim storage facility. Assuming volume reduction by incineration of combustibles (fallen leaves, etc.), combustibles volume reduction cost: Estimated based on incineration cost of JPY13,450e18,790/tonne (from Ministry of the Environment 6th Feedback Session on 3R and Handling of Kitchen Refuse: Document 1. Cost Comparison of Methane Fermentation Facility and Incineration Facility) and specific gravity of combustibles in a flexible container (prior to incineration) of o.1 (JAEA Decontamination Report p. 224), giving a range of JPY1345e1879/m3. JPY2000/container was adopted based on the maximum value. Further, volume reduction ratio was set at 95%. Assuming high concentration, leachable material storage unit cost (JPY/m3) of JPY100,000/container (0.9 m3): Unit cost assumes strictly controlled landfill site but no such data could be obtained. For this reason, a unit cost that was around three times the cost of the low-leachables unit storage cost was adopted based on interviews with relevant parties. The receiving unit cost at controlled landfill sites for low concentration, non-leachable material storage was adopted. Using the surplus soil unit processing cost of the Shiga Clean Center, a controlled landfill site of JPY17,850/tonne and a specific gravity of 1.8 translated to a cost of JPY 28,917/container (0.9 m3). Thus, JPY30,000/container was adopted. Source: Shiga Clean Center website www.kouka.ne.jp/~skj-ccs/clean/riyo.html#hyou02
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Table 4 Decontamination scenarios. Land-use
Agricultural
Scenario Scenario 1
(Basic Scenario)
Area
A1
SDZ
△ >5000 Bq/kg
Forest A2
A3 △ <5000 Bq/kg
Scenario 3
Scenario 4
(Basic Scenario 2)
(Minimum Scenario)
(Maximum Scenario)
SDZ ICA
Road F2
-
B
B
B
B △ >1 mSv
B △ >1 mSv
B △ >1 mSv
RB3
△ >5 mSv
△ 1e5 mSv
△ >1 mSv B △ >5 mSv
△ 1e5 mSv
B △ >1 mSv
>1 mSv
RB2
B
B
-
RB1
△ >1 mSv
>1 mSv
△ >1 mSv
Residential and building R2
B
-
B
R1
>1 mSv
△ >1 mSv
SDZ ICA SDZ ICA
F1
△ >1 mSv
ICA Scenario 2
A4
B △ >1 mSv
△ >1 mSv
B: Whole area. -: We set that forest adjacent to 100-m mesh units used as paddy fields, other agricultural land, or buildings were decontaminated, whereas other areas of forest were not to be decontaminated. Moreover, of the mesh units that contained forest to be decontam-inated, we assumed that only 20% of the forests in these mesh units would be decontaminated, as specified in the guidelines of the Ministry of the Environment. △: We set the decontamination area with annual external exposure or concentration.
Scenario 1 is the basic scenario that complies with the policy of the Japanese Ministry of Environment. In this scenario, about 5 cm of topsoil was stripped from the 50% of agricultural land in the SDZ exhibiting a high air dose rate area, and 5 cm of clean covering soil was added (A1). For the remaining 50% of agricultural land with low air dose rates, topsoil was assumed to be interchanged with subsoil (A3). Plowing with zeolite and potassium (A4) was adopted for agricultural land in ICAs where the annual additional effective dose exceeded 1 mSv. Decontamination of forested areas in the SDZ and the ICAs, which account for approximately 70% of prefectural land use, was carried out in accordance with the policy of the Ministry of the Environment (forested areas within 20 m of areas of habitation): decontamination of 20% of the area of each 100 m 100 m of forest adjoining paddy fields and other agricultural land and buildings. Furthermore, in ICAs, forested areas with an annual additional effective dose exceeding 1 mSv were decontaminated. In the SDZ, forest decontamination entailed removal of fallen leaves and humus surface (F1), whereas in ICAs, it involved removal of fallen leaves only (F2). Shot blasting and side ditch sweeping (R1) were carried out for all roads in the SDZ, whereas only road and side ditch sweeping (R2) was undertaken in ICAs where the annual additional effective dose exceeded 1 mSv. Whole decontamination (RB1) was undertaken for all residential and other built-up areas in the SDZ, whereas whole decontamination (RB2) was carried out for those areas in ICAs where the annual additional effective dose exceeded 5 mSv. For ICAs where the annual additional effective dose was 1e5 mSv, local decontamination (only high air dose areas) (RB3) was carried out. In Scenario 2, all of agricultural land in the SDZ, about 5 cm of topsoil was stripped and 5 cm of clean covering soil was added (A1). In addition, whole decontamination (RB2) was carried out for builtup areas in ICAs where the annual additional effective dose exceeded 1 mSv. In Scenario 3 (minimum case), topsoil was interchanged with subsoil with zeolite and potassium for all agricultural land in the SDZ (A3). In Scenario 4 (maximum case), 5 cm of topsoil was stripped from all agricultural land in the SDZ, and 5 cm of covering soil was added (A1), whereas topsoil was interchanged with subsoil with zeolite and potassium for all agricultural land in ICAs (A3). In addition, this scenario assumed that not only the forest adjacent to 100-m mesh units used as paddy fields, other agricultural lands, or buildings but also other forest areas were decontaminated in the
SDZ. For the ICA, decontamination was carried out areas where the annual additional effective dose exceeded 1 mSv (RB2). 2.5. Post-decontamination air dose calculation We calculated 100 m 100 m air dose rates after decontamination by multiplying the 100 m 100 m air dose rates (excluding background) prior to decontamination by the residual factor calculated from the percentage of decrease (100 e the rate of decrease) for each land use. Then, the 100 m 100 m post-decontamination air dose rates for land uses (land for buildings, rice paddies, other agricultural land, roads, forested areas within 20 m of a habitation area) that were decontaminated were averaged over each 1 km 1 km mesh, and this value was adopted as the post-decontamination air dose rate for each 1 km 1 km mesh (calculations were carried out assuming that the entire area of each 100 m 100 m unit of forested area within 20 m of a habitation area was decontaminated). Furthermore, the post-decontamination air dose rate was taken to be equivalent to the pre-decontamination air dose rate for areas in which no land use types were subject to decontamination within a 1 km 1 km mesh. The post-decontamination air dose was calculated for 1 April 2016, assuming that decontamination would be completed by 31 March 2016. 2.6. Calculation of additional external radiation dose Individual external radiation doses (mSv/day) are not the same as the outdoor air dose (mSv/day) because the majority of radioactive fallout is present outdoors; indoors, the distances from sources of radiation are greater and walls having a shielding effect (IAEA, 2000). According to IAEA-TECDOC-1162, the external conversion coefficient for a two-story wood-frame house is 0.4 (shielding ratio: 0.6); for a concrete block or brick house, the coefficient is 0.2 (shielding ratio: 0.8). In Japan, the Ministry of the Environment currently evaluates the daily individual external effective dose from the air dose rate assuming 8 h spent outdoors and 16 h spent indoors and an indoor air dose rate that is 40% of the outdoor air dose rate (Japanese Ministry of the Environment, 2011). Based on these assumptions, the external radiation dose is taken as 0.6 of the air dose. Meanwhile, several researches have recently attempted to estimate external conversion coefficients according to individual external radiation dose and air dose data for children and adults. Date City (2012a,b), Nihonmatsu City (2012a,b), and Naito et al.
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(2014) were confirmed that average individual radiation doses of around 0.1e0.4 of the external air dose rates using dosimeters. However the number of persons being measured was limited, these estimated external conversion coefficients should be validated by the further research. For this reason, in this study, we used the value of 0.6 as an external exposure conversion coefficient for the air dose adopted by the Ministry of the Environment. Next we calculated annual cumulative external doses under the following assumptions: the 134Cs/137C concentration ratio on 25 March 2011 was 1:1 the air dose on 5 November 2011 was attributable only to radioactive Cs the reduction in concentration of radioactive Cs was due only to decay (weathering was not considered) the annual dose was calculated assuming return on 1 April 2016 (ca. 5 years after the accident) For these calculations, we used the half-lives of radioactive Cs (134Cs: 2.06 years; 137Cs: 30 years) and the contribution ratio of each nuclide to the air dose (conversion of ambient dose rate from deposition [(mSv/h)/(kBq/m2)]) (from IAEA conversion coefficient table CF3a; (IAEA, 2000). 2.7. Index of effectiveness of decontamination As an index of effectiveness of decontamination (ED) for each 1 km 1 km mesh, we calculated the amount of total reduction of annual external dose for each 1 km 1 km mesh (person-Sv) by multiplying the amount of reduction of annual external dose by the population for each 1 km 1 km mesh. 3. Results 3.1. Estimates of decontamination costs Overall decontamination costs for the scenarios that comply with the policy of the Japanese government (Scenarios 1 and 2) are JPY2.03e5.12 trillion (total cost), JPY1.33e2.02 trillion (cost for the
SDZ), and JPY0.70e3.10 trillion (cost for the ICAs) (Table 5). Although the areas where decontamination has been implemented in the ICAs total around 3e11 times the area of the SDZ, the decontamination costs for the SDZ and ICAs are in the same range. The SDZ decontamination cost for Scenario 2 is 1.7 times that of the previous study result (JPY1.2 trillion; Yasutaka et al., 2013b) because the new estimate includes waste transport costs, administrative costs (22%), and areas of high radiation (Difficult-to-Return Zones). Close to 70% of the ICA decontamination cost consists of removal costs; for the SDZ, removal costs account for around 25% of the decontamination cost, with costs associated with temporary storage sites, transport, and interim storage facilities accounting for most of the decontamination cost. The reason for this difference between the SDZ and ICAs is that 5 cm of topsoil stripping was assumed when calculating the cost for agricultural land in the SDZ; in the ICAs, topsoil was assumed to be interchanged with subsoil, and, therefore, little removed soil is generated. Decontamination and construction of temporary storage sites are currently underway in Fukushima Prefecture (Japanese Ministry of the Environment, 2014), but the technology for reducing the volume of decontamination waste and removed soil has not yet been selected and applied, and no interim storage sites have been built. The cost for Scenario 3 (minimum case) is JPY1.14 trillion, which is JPY0.89 trillion lower than the cost for Scenario 1. Scenario 1 for the SDZ entailed removal of 5 cm of topsoil from 50% of agricultural lands, whereas in Scenario 3, interchanging topsoil with subsoil was adopted as the decontamination method for agricultural lands. As shown by Yasutaka et al. (2013b), the quantity of waste generated in decontaminating agricultural land varies considerably depending on the decontamination method used; consequently, differences in the quantity of generated waste resulted in large differences between agricultural land decontamination methods in the costs associated with storage containers, temporary storage sites, and interim storage facilities. In Scenario 4 (maximum case), all forested areas with over 1 mSv/year were assumed to be decontaminated: the total cost for this decontamination was estimated to be JPY16.17 trillion. Furthermore, in this calculation, the decontamination unit cost for
Table 5 Estimated costs and cost breakdown (trillion yen) for decontaminating Fukushima Prefecture.
Target area Decontamination area Scenario 1
Scenario 2
Scenario 3
Scenario 4
Total Decontamination Flex. Containers Temporary storage Transport$Interim storage Total Decontamination Flex. Containers Temporary storage Transport$Interim storage Total Decontamination Flex. Containers Temporary storage Transport$Interim storage Total Decontamination Flex. Containers Temporary storage Transport$Interim storage
Special decontamination zone revised Yasutaka et al. (2013b)
Intensive contamination survey area
Total
1,117 km2 295 km2 1.33 0.29 0.11 0.31 0.43 2.02 0.53 0.18 0.55 0.76 0.44 0.25 0.03 0.08 0.09 5.72 1.22 0.60 1.80 2.11
7836 km2 922〜3330 km2 0.7 0.41 0.04 0.1 0.14 3.1 2.15 0.14 0.34 0.47 0.7 0.41 0.04 0.1 0.14 10.45 3.52 1.15 2.88 2.90
8953 km2 1317〜3625 km2 2.03 0.70 0.15 0.41 0.57 5.12 2.68 0.32 0.89 1.23 1.14 0.66 0.07 0.18 0.23 16.17 4.74 1.75 4.68 5.01
26% 9% 28% 37% 26% 9% 27% 38% 55% 6% 18% 20% 21% 10% 32% 36%
59% 6% 14% 20% 69% 5% 11% 15% 59% 6% 14% 20% 34% 11% 28% 28%
38% 8% 22% 31% 52% 6% 17% 24% 58% 6% 16% 20% 29% 11% 29% 31%
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7
Fig. 2. Comparison of the annual external exposure distribution on 1 April 2016 for each 1 km 1 km mesh without decontamination and with decontamination Scenarios 1 and 4.
forested areas was assumed to be equal to that for forested areas within 20 m of habitation areas; however, the decontamination unit cost increases with increasing distance from habitation areas, which suggests that the decontamination unit cost would be higher than that listed for Scenario 4. In areas such as Fukushima Prefecture, where forest accounts for over 70% of the overall area, the policy adopted for forest decontamination strongly influences the total decontamination cost. 3.2. Comparison of decontamination effects Although there was an effect on habitation area air dose depending on whether or not decontamination was implemented, there were no marked differences among the decontamination scenarios adopted in this study (Fig. 2). ED values for Scenario 1
a
covered a wide range in the 1 km 1 km meshes, from 106 to 100 person-Sv, and increased as population increased (Fig. 3a). In contrast, ED values for Scenario 1 were poorly correlated with air dose rate (Fig. 3b). The reduction in annual individual additional effective dose for all decontamination scenarios was 1666 person-Sv, for the SDZ and 876e1245 person-Sv, for the ICAs (Table 6). Although the reduction rate for the SDZ was somewhat larger than the reduction rates for the ICAs, the magnitudes of the rates were similar, unlike the large differences between the decontamination efficiencies (Table 1). The large extent of reduction for the ICAs is mainly associated with population density. The population of the SDZ before the accident is about 90,000, whereas the population of an ICA in an area exposed to over 1 mSv/year is 1,530,000. This result suggests that ED values vary depending on not only the decontamination efficiency but also
b
Fig. 3. Relationship between ED for each 1 km 1 km mesh and (a) population and (b) air dose rate.
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4. Discussion
We have shown that the total estimated decontamination cost can exceed JPY16 trillion if all forested areas with over 1 mSv/year are assumed to be decontaminated. Furthermore, implementing decontamination of all forested areas provides no major reduction in the external radiation dose for the average inhabitant. However, many people who live or have lived in these regions have traditionally obtained drinking water from streams and runoff and utilized the harvest from the forest and satoyama (boundary forest areas used by local inhabitants), including mushrooms, edible wild plants, and firewoods. Additionally, about 1800 workers are employed by the forest industry. For these people, the forest, the satoyama, and its harvest are inseparable from their lives. Recent research has shown that the annual runoff rate of radiocesium in the forest is very low, only 0.1e0.3% per year of total deposition (National Institute for Environmental Studies, 2012); thus, if decontamination is not carried out in forested areas, a major portion of radiocesium deposited in the forest will remain for many years. Decontamination of forested areas more than 20 m from areas of habitation resulted in only a minor reduction in the external radiation dose for the average person. However, the external radiation dose may be significant for forestry and satoyama workers. Therefore, the external radiation dose for workers in forested areas is best evaluated on a site-by-site basis rather than over a wide area. Deciding on a strategy that takes into account the forest industry and forest utilization is important in guiding forest decontamination policy. A comprehensive debate on approaches to forest decontamination that addresses both forest utilization and the costs and effects of decontamination is required.
4.1. Need for volume reduction technology
4.3. Key parameter of decontamination effectiveness
Currently, decontamination is underway in Fukushima Prefecture based on a basic case approach; as of October 2014, around 60e80% of ICA decontamination had been completed (Japanese Ministry of the Environment, 2014). In contrast, construction of temporary storage sites and interim storage facilities, which account for an estimated 50% of the overall cost of decontamination, has been delayed; transport, storage, and administrative costs will be required (JPY1.55e2.12 trillion for Basic Scenarios 1 and 2). Furthermore, securing routes for transporting the more than 20 million tonnes of decontamination waste and removed soil that will be generated is a major challenge. To reduce the amount of decontamination waste t and removed soil hat must be stored and transported, technologies for volume reduction of ash from incineration of combustibles and of incombustibles such as washed soils must be developed and applied. The Japanese government is currently mainly considering volume reduction by incineration of combustibles. However, for further cost reduction, application of a volume reduction technology for incombustibles should be discussed. A comprehensive analysis of contaminated waste and soil management methods is required to address these challenges; this analysis should include technical assessment and discussion of the necessity for volume reduction of incombustibles, combustibles, and ash from incineration of combustibles; in addition, assessing the management and storage of low-concentration radioactive cesium-containing soil and methods for using controlled landfill sites should lead to a significant reduction in the amount of material requiring transport.
Our results indicate that ED values for the 1 km 1 km meshes vary widely, ranging from 106 to 100 person-Sv,. ED values are affected mainly by population density, but air dose rate before decontamination and decontamination efficiency also affect ED values. The decontamination efficiency for the 1 km 1 km meshes ranged from 0.08 to 0.80 (Table 1), the air dose rate ranged from 0.23 to 8 mSv/h, but the population density ranged from 1 to 10,000 persons/km2. The differences in the ranges of the parameters are the reason that the ED value was mainly affected by population density. If we evaluate the effectiveness of decontamination by the sum of the reduction rates of the external exposure per person for each 1 km 1 km mesh, the population density is a more important parameter than the air dose rate for the Fukushima accident. Although the decontamination effectiveness such as ED value is an important parameter and can be used as a surrogate for understanding the distribution of societal risk in the affected areas, this concept should be used with care. For example, this ED index might evaluate that priority of decontamination of area with an individual high dose and a small number of people is not high, compared with the area with individual low dose and large number of people. For an illustrative purpose, we have applied to the ED concept to the case of decontamination in Fukushima Prefecture and ED value is one of index for decision making of decontamination. Reducing high dose individuals is another significant purpose for decontamination in the affected areas in Fukushima. It is important to establish the decontamination strategies for reducing societal risk and high dose individuals in a mutually complementary manner.
Table 6 Reductions in annual additional radiation doses for each decontamination scenario (person-Sv).
SC1 SC2 SC3 SC4
(Basic Scenario) (Basic Scenario 2) (Minimum Scenario) (Maximum Scenario)
SDZ
ICA
Total
1666 1666 1666 1666
876 1031 876 1245
2542 2697 2542 2911
An external exposure conversion coefficient is 0.6.
the population density. If the objective of decontamination is to maximize sustainability of population living in the affected areas after decontamination, to a certain degree, then special consideration should be given to the decontamination in high population areas. Understandably, ED value is one of index for decision making of decontamination. From the view of reducing individual high doses, another index should be used for the decontamination in areas with the highest dose rates. The difference between the scenarios in the ICAs is attributable to whether whole decontamination (Scenarios 1 and 3) or local decontamination (Scenarios 2 and 4) was carried out. Although there is no major difference in the efficiencies for whole decontamination (35%) and local decontamination (18%), a large population (approximately 1,030,000) resides in areas exposed to 1e5 mSv/year; for this reason, the reduction in annual individual additional effective dose was large for the whole-decontamination scenarios.
4.2. Forest decontamination policy 5. Conclusions Debate on the rate of progress of decontamination is expected to gain momentum, as will discussion related to decontamination in the future of forests in uninhabited areas.
(1) The decontamination costs for the basic scenarios (Scenarios 1 and 2) were JPY2.53e5.12 trillion. Although the
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decontamination area of the ICAs is around 3e11 times the area of the SDZ, the total decontamination costs are of the same order. (2) Removal costs account for a high proportion of the decontamination cost for the ICAs. Costs related to temporary storage sites and interim storage facilities for the SDZ are estimated to account for 41e62% (JPY1.55e2.12 trillion) of the total decontamination cost. (3) The cost for decontaminating all forested areas could potentially exceed JPY16 trillion but would provide no major reduction in the external radiation dose for the average inhabitant. If the Japanese government reconsiders the current policy of the Ministry of the Environment (forested areas within 20 m of areas of habitation), then policy and procedures for forest decontamination should be carefully reassessed. (4) For the Fukushima accident, if we evaluate the effectiveness of decontamination by the sum of the reduction rate of external exposure per person for each 1 km 1 km mesh, population density is a more important parameter than air dose rate. Acknowledgments The authors would like to thank Mr. Motoki Uesaka and Mr. Eiichi Yasoda for their assistance with the analyses. The authors would also like to thank Dr. Junko Nakanishi, Dr. Isao Kawaguchi, Dr. Michio Murakami, Dr. Kyoko Ono, Dr. Shizuka Hashimoto, Ms. Yumi Iwasaki, Dr. Kikuo Yoshida, and Dr. Atsuo Kishimoto for providing valuable comments. This work was supported by JSPS KAKENHI Grant Number 26241023, 25289207 and AIST Environment and Energy Unit. References Date City, 2012a. Date City Bulletin. Disaster Preparation Issue, No. 45 Jan. 26. http:// www.city.date.fukushima.jp/kouhou/pdf-rinzi/rinzi45.pdf. Date City, 2012b. Date City Environmental Radiation Measurement Results. http:// www.city.date.fukushima.jp/groups/hosyasen/1keka.pdf.
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Fukushima Prefecture, 2012a. Decontamination Countermeasure Operation Implementation Guideline. http://wwwcms.pref.fukushima.jp/download/1/jyosen_ 0119youryou.pdf. Fukushima Prefecture, 2012b. Fukushima Prefecture Surface Decontamination Model Project. http://wwwcms.pref.fukushima.jp/download/1/summary20120330. pdf. IAEA, 2000. Generic Procedures for Assessment and Response during Radiological Emergency. Japan Atomic Energy Agency, 2012. Implementation Report on Decontamination Relating to the Fukushima Daiichi Nuclear Powerstation. http://www.jaea.go.jp/ fukushima/kankyoanzen/d-model_report.html. Japanese Ministry of Environment, 2013. Basic Policy on Interim Storage and Other Facilities Required for the Handling of the Environmental Pollution from Radioactive Materials Associated with the Accident at Tokyo Electric Power Co.’s Fukushima Daiichi Nuclear Power Stations (2015, 4.23). http://josen.env. go.jp/en/roadmap/pdf/chart1_5.pdf. Japanese Ministry of Land Infrastructure Taransport and Tourism, 2012. National Land Numerical Information Download Service. http://nlftp.mlit.go.jp/ksj-e/ index.html. Japanese Ministry of the Environment, 2011. Decontamination Guidelines Ver. 1, Dec. 2011. Japanese Ministry of the Environment, 2014. Progress on Off-site Cleanup Efforts in Japan(December, 2014) (2014, 12.31). http://josen.env.go.jp/en/. Ministry of Education Culture Sports Science and Technology in Japan, 2011. Results of the Fourth Airborne Monitoring Survey by MEXT(December 16, 2011). http:// radioactivity.mext.go.jp/ja/contents/5000/4901/24/1910_1216.pdf. Morino, Y., Ohara, T., Nishizawa, M., 2011. Atmospheric behavior, deposition, and budget of radioactive materials from the Fukushima Daiichi nuclear power plant in March 2011. Geophys. Res. Lett. 38. Naito, W., Uesaka, M., Yamada, C., Ishii, H., 2014. Evaluation of dose from external irradiation for individuals living in areas affected by the Fukushima Daiichi nuclear plant accident. Radiat. Prot. Dosim. 163, 353e361. National Institute for Environmental Studies, 2012. NIES Annual Report, pp. 94e95. National Institute of Advanced Industrial Science and Technology, 2011. Geochimical Map of the Sea and Land of Japan. Nihonmatsu City, 2012a. City Measurement Result Independent Municipal Measurement Results (Up until April 30, 2012). http://www.city.nihonmatsu.lg.jp/ site/higashinihondaishinsai-kanren/20120724-1.html. Nihonmatsu City, 2012b. Residents Radiation Exposure Dose Survey Result Announcement Meeting Materials. http://www.city.nihonmatsu.lg.jp/uploaded/ attachment/10014.pdf. Yasutaka, T., Iwasaki, Y., Hashimoto, S., Naito, W., Ono, K., Kishimoto, A., Yoshida, K., Murakami, M., Kawaguchi, I., Oka, T., Nakanishi, J., 2013a. A GIS-based evaluation of the effect of decontamination on effective doses due to long-term external exposures in Fukushima. Chemosphere 93, 1222e1229. Yasutaka, T., Naito, W., Nakanishi, J., 2013b. Cost and effectiveness of decontamination strategies in radiation contaminated areas in Fukushima in regard to external radiation dose. PLoS One 8, 11.
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Assessing cost and effectiveness of radiation decontamination in Fukushima Prefecture, Japan Tetsuo Yasutaka*, Wataru Naito National Institute of Advanced Industrial Science and Technology, Ibaraki, Japan
a r t i c l e i n f o
a b s t r a c t
Article history: Received 6 January 2015 Received in revised form 4 May 2015 Accepted 11 May 2015 Available online xxx
Despite the enormous cost of radiation decontamination in Fukushima Prefecture, it is not clear what levels of reduction in external radiation exposure are possible in the Special Decontamination Area, the Intensive Contamination Survey Areas and the whole of Fukushima. The objective of this study was to evaluate the cost and effectiveness of radiation decontamination in Fukushima Prefecture in its entirety. Using a geographic information system, we calculated the costs of removal, storage containers, transport, and temporary and interim storage facilities as well as the reduction in air dose rate for a cumulative external exposure for 9000 1 km 1 km mesh units incorporating 51 municipalities. The decontamination cost for the basic scenario, for which forested areas within 20 m of habitation areas were decontaminated, was JPY2.53e5.12 trillion; the resulting reduction in annual external dose was about 2500 person-Sv. The transport, storage, and administrative costs of decontamination waste and removed soil reached JPY1.55e2.12 trillion under this scenario. Although implementing decontamination of all forested areas provides some major reductions in the external radiation dose for the average inhabitant, decontamination costs could potentially exceed JPY16 trillion. These results indicate that technologies for reducing the volume of decontamination waste and removed soil should be considered to reduce storage costs and that further discussions about forest decontamination policies are needed. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Decontamination Cost and effectiveness Radiation contamination Fukushima
1. Introduction The accident at the Tokyo Electric Power Company Fukushima Daiichi nuclear power plant (F1NPP) released radionuclides into the atmosphere, which were then transported by the wind before being deposited on land and sea surfaces via precipitation. Approximately 22% of these radionuclides were deposited on land (Morino et al., 2011), and to this day, a large quantity of radionuclides remains in soil in agricultural and urban areas, on asphalt and concrete surfaces, on the leaves and bark of trees, and in the litter layer (organic layer) of the soil in forests (Ministry of Education, Culture, Sports, Science and Technology, Japan, 2011). Airborne monitoring surveys of large areas have revealed a zone of highdensity surface deposition of cesium-134 and cesium-137 extending to the northwest from F1NPP (Ministry of Education Culture Sports Science and Technology in Japan, 2011).
* Corresponding author. National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan. Tel.: þ81 29 849 1545; fax: þ81 29 861 8795. E-mail address: [email protected] (T. Yasutaka).
On January 2012, the Japanese government enacted the Act on Special Measures Concerning the Handling of Environment Pollution by Radioactive Materials Discharged by the Nuclear Power Station Accident Associated with the Tohoku DistricteOff the Pacific Ocean Earthquake That Occurred on March 11, 2011 (also called the Act on Special Measures Concerning the Handling of Pollution by Radioactive Materials). The objective of the Act was to promptly reduce the impact of radioactive substances from the accident on human health and to living environment, effective 1 January 2012, on the environment. Under this legislation, decontamination guidelines were released in December 2011 by the Japanese Ministry of the Environment (2011) that detailed methods for surveying and measuring the degree of environmental contamination in highly contaminated areas as well as measures for decontamination and guidelines for collection, transport, and storage of removed soil. In January 2012, the Ministry announced a decontamination roadmap to be implemented under the direct supervision of the Japanese government (Policy for Decontamination in the Special Decontamination Area). Progress has been made in establishing frameworks and guidelines for full-scale decontamination; actual decontamination work has already started. However, pilot surface decontamination studies have found that it
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will take time for some areas to return to their pre-accident state even after decontamination work has been completed on account of differences in decontamination efficiency due to the type of land use and the air dose of a particular area (Fukushima Prefecture, 2012b; Japan Atomic Energy Agency, 2012)). Decontamination is currently underway in Fukushima Prefecture; as of October 2014, the implementation fraction of decontamination activity was around 30e80% against total decontamination planning area (Japanese Ministry of the Environment, 2014), although progress varies depending on land use and the city, town, or village. Decontamination of affected areas is extremely important so that residents may return to their normal day-to-day lives. When considering a post-decontamination return, both the prevalent air dose rate and the cumulative dose are one of the main factors for evacuees to decide whether to return home or not.is the one of the important factors. In this sense, it is important that the prevalent air dose rate and cumulative doses be evaluated under multiple decontamination scenarios, that the decontamination effectiveness be quantified, and that the decontamination and associated costs be estimated and analyzed. Progress is being made in building up data for air dose mapping and in evaluating decontamination methods and their efficiencies; however, there are few examples of research that integrates these findings at a regional level and quantitatively assesses both the associated costs and the effectiveness of exposure reduction by decontamination. One relevant example is the work of Yasutaka et al. (2013a), who used a geographic information system (GIS) to evaluate the efficacies of air dose and cumulative external radiation dose reduction through decontamination of 11 municipalities located in the Special Decontamination Area (SDZ) from which residents were or are currently evacuated. The SDZ includes areas located within a 20-km radius of the F1NPP or where the cumulative dose 1 year after the accident was expected to exceed 20 mSv/year. Yasutaka et al. (2013a) found that although there were quantifiable reductions in air dose within the SDZ, there were limits to the effectiveness of decontamination and areas still remained that were affected by radiation. Furthermore, (Yasutaka et al., 2013b) evaluated decontamination costs and external radiation dose reduction effects under multiple decontamination scenarios for the SDZ; in the basic scenario, decontamination costs were estimated to be JPY1.3e2.7 trillion. They found that the overall decontamination cost was
primarily influenced by whether or not the decontamination method for agricultural land generated waste. These previously published investigations quantitatively evaluated the cost and efficacy of decontamination within the SDZ. However, yet to be made is a quantitative assessment that also encompasses Intensive Contamination Survey Areas (ICAs) in Fukushima Prefecture with radionuclide concentrations lower than those in the SDZ. These ICAs include 40 unevacuated municipalities where decontamination efforts are being carried out by local governments. The overall area of the ICAs is eight times that of the total SDZ area, and decontamination methods and geographical scope philosophies vary, as do the quantities of waste generated. For these reasons, ICAs need to be evaluated alongside the SDZ to conduct an overall assessment of decontamination cost and efficiency. Furthermore, decontamination of forested areas in Fukushima Prefecture is being carried out in accordance with guidelines that currently stipulate only areas that lie within 20 m of areas of habitation (ca. 70% of the prefecture is covered in forest). However, according to one estimate, this approach will result in only around 5% of the overall forested area in the SDZ being decontaminated (Yasutaka et al., 2013b). With calls for further decontamination of forests coming from various quarters, it is important to estimate the cost and efficacy of a wider area of forest decontamination. The objective of this study was to evaluate the cost and effectiveness of various decontamination scenarios over the entirety Fukushima Prefecture. We applied the evaluation methods described by Yasutaka et al. (2013a) to ICAs as well; with the current decontamination policy for Fukushima Prefecture as the basic case, we evaluated decontamination costs and efficiencies for multiple scenarios including forest decontamination.
2. Materials and methods 2.1. Target areas The target areas were the 11 municipalities in the SDZ from which residents were evacuated after the nuclear accident and the 40 municipalities in the unevacuated ICAs (Fig. 1). The target areas occupy an area of 7836 km2 with a non-evacuated population of ca. 1,698,000 (2010 census).
Fig. 1. Target area of research.
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2.2. Air dose rate, land use, and population density spatial data We integrated and analyzed air dose rate, land use, and population density spatial data in 9000 1 km 1 km mesh units using GIS (ArcGIS Version 1.0). The air dose rate distribution at an elevation of 1 m above ground level (obtained from the Fourth Airborne Monitoring Survey undertaken by the Ministry of Education, Culture, Sports, Science and Technology, Japan (2011)) was used for the air dose rate data. For each mesh unit (100 m 100 m), the estimated air dose rate at the center was used as a representative value; then, to calculate the air dose rate for each 1 km 1 km mesh unit, we used the arithmetic means of the air dose rates of all 100 m 100 m meshes. These values included background radiation (average: 0.04e0.05 mSv/h (National Institute of Advanced Industrial Science and Technology, 2011)). For this analysis, we used 0.045 mSv/h as the background value. Land use subdivided mesh data from the National Land Numerical Information database (JFY 2009) was used for land use data (Japanese Ministry of Land Infrastructure Taransport and Tourism, 2012). The mesh size was 100 m 100 m; the original twelve classifications of land use were reclassified into six: paddy fields, other agricultural land, forest, land for buildings, roads, and other uses. Furthermore, 'to estimate residential area for 1 km 1 km meshes in the ICAs where buildings accounted for less than 50% of the area, the number of residential households was multiplied by the average area lot size for a single house in Fukushima Prefecture (400 m2/household; 2008 Housing and Land Survey); this estimate was compared with the area occupied by buildings, with the larger value being adopted. If the area occupied by buildings increased by above correlation coefficient, the areas for agriculture and forest were reduced. Road density/road length mesh data from the National Land Numerical Information database (Japanese Ministry of Land Infrastructure Taransport and Tourism, 2012) were used for road length. Grid square statistics from the 2010 population census was used for population distribution. When a boundary between the SDZ and ICAs existed within a 1 km 1 km mesh, the mesh was partitioned along the border of the municipalities (cities, towns, or villages) lying within the mesh. Here, the area ratio for each 1 km 1 km mesh was used when proportionally distributing land use areas, population, and road lengths. 2.3. Decontamination methods, efficiency, and cost The decontamination process comprises decontamination itself; temporary storage of decontamination waste and removed soil in containers; transport of waste; volume reduction of waste; and temporary, interim, and final storage of waste. Decontamination efficiency, the quantity of waste generated, and cost depend on land use, air dose rate, and the decontamination method adopted. Our
3
research was based on the decontamination methods currently employed in Fukushima Prefecture (Table 1). Decontamination efficiency varies depending on the decontamination method and the air dose rate prior to decontamination (Japan Atomic Energy Agency, 2012). The decontamination efficiency for each decontamination method was set as indicated in Table 1 based on the findings of Yasutaka et al. (2013a, 2013b), who compiled air dose and land use data according to demonstration tests by the Japan Atomic Energy Agency. Decontamination efficiencies for decontamination methods for ICAs (F2, R2, RB3) that were not evaluated in the abovementioned papers were assumed to be at 50% of the efficiencies of the most efficient decontamination methods (F1, R1, RB2) reported for municipal decontamination in Fukushima City and Koriyama City. Unit costs (per flexible container) were estimated for decontamination and removal of the generated waste (Table 2) and for storage containers, temporary storage sites, transport costs, and reduction of the volume of combustible material (Table 3). These estimated unit costs were based on decontamination pilot studies and demonstration test data from the Japan Atomic Energy Agency (2012) and Fukushima Prefecture (2012a,b), interviews with members of officials from Fukushima Prefecture, other information in the public domain, and information on similar technologies. Two sets of unit costs for decontamination were calculated: the basic unit cost and the maximum unit cost (the highest unit cost identified from interviews and other information). Next, the authors focus on the generated waste management including temporary storage facilities, volume reduction and interim storage facilities. Waste management procedure in this research was based on the flow chart and the basic policy of Ministry of Environment (Japanese Ministry of Environment, 2013). The combustible waste generated through decontamination was stored at temporary storage facilities. The volume of this waste was reduced by incineration, and the incineration ash was transferred to interim storage facilities. Japanese government made a plan that these incineration ashes with highly radioactive cesium concentration and leachable characteristics would be stored in concreteshielded structures facilities (Japanese Ministry of Environment, 2013). We assumed the unit cost of this type of storage site as JPY100,000 per flexible container after volume reduction.by referring to the unit cost information of strictly controlled type landfill site in Japan. After being transferred to interim storage facilities, incombustibles (soil) were planned to be stored at soil storage facilities in the interim storage facilities (Japanese Ministry of Environment, 2013). Because of the building constitution of soil storage facilities was similar to that of the controlled landfills wastes sites, the cost of soil storage facilities in the interim storage facilities was assumed to be JPY30,000 per flexible container.
Table 1 Decontamination methods and their efficiencies (Fukushima Prefecture, 2012a,b; Japanese Ministry of the Environment, 2011).
Agricultural
Forest Road Residential and building
A1 A2 A3 A4 F1 F2 R1 R2 RB1 RB2 RB3
Weeding/Stripping 5 cm topsoil/Covering Soil Weeding/Stripping 5 cm topsoil Interchanging topsoil with subsoil with zeolite and potassium Plowing with zeolite and potassium Removal of fallen leaves and humus surface Removal of fallen leaves Shot blasting and side ditch sweeping Road and side ditch sweeping. Whole decontamination Whole decontamination Local decontamination (only high air dose area)
&1mSv/h
1e3 mSv/h
3e10 mSv/h
>10mSv/h
0.34 0.34 0.34 0.21 0.19 0.10 0.15 0.08 0.29 0.29 0.15
0.49 0.49 0.49 0.31 0.27 0.14 0.30 0.15 0.35 0.35 0.18
0.47 0.47 0.47 0.29 0.39 0.20 0.41 0.20 0.49 0.49 0.25
0.80 0.80 0.80 0.50 0.59 0.30 0.66 0.33 0.70 0.70 0.35
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Table 2 Unit costs for decontamination and generated waste. Land-use
Agricultural
Forest Road Residential and building
Decontamination method
A1 A2 A3 A4 F1 F2 R1 R2 RB1 RB2 RB3
Weeding/Stripping 5 cm topsoil/Covering Soil Weeding/Stripping 5 cm topsoil Interchanging topsoil with subsoil with zeolite and potassium Plowing with zeolite and potassium Removal of fallen leaves and humus surface Removal of fallen leaves Shot blasting and side ditch sweeping Road and side ditch sweeping. Whole decontamination Whole decontamination Local decontamination (only high air dose area)
Unit cost (10 thousand JPY/hectare)
Number of flexible containers (units/hectare)
Target area
Removal
Flex. Containers
Temporary storage
Incombustible
Combustible
SDZ
ICA
950 625 (100)-310
652 652 0
1630 1630 0
715 715 0
100 100 0
B B B
B
(20)-33 745 60e280 480 240/km 1750e3500 1750e3500 125e250
0 424 208 24 70 120 120 9
0 1060 520 60 176 300 300 22
0 270 0 30 88 140 100 7
0 260 260 0 0 0 50 4
B B
The interim storage facilities are to be built in the areas neighboring the F1NPP. Therefore, waste transport costs were estimated based on transport by a 10-tonne truck from the center of each 1 km 1 km mesh to the F1NPP. An additional 22% was added to these estimates to cover general expenses such as radiation monitoring costs. This ratio was estimated by comparing “the actual ordered cost” with “our estimation cost” of decontamination activity and building temporally storage site at 6 municipalities in SDZ. In addition, in Difficult-to-Return Zones, the working efficiency of decontamination activity was supposed to decrease and the cost of management and countermeasure of external exposure for decontamination workers to increase because of high air dose rates in these areas. For this reason,
B B
B B B B B
we added an additional 70% to costs (decontamination costs, temporary storage site costs, transport costs) for these zones. 2.4. Decontamination scenarios Table 4 describes the various decontamination scenarios. Separate decontamination scenarios were set for the SDZ and ICAs, and decontamination methods and decontamination areas were varied, for a total of four scenarios. Decontamination areas for ICAs were set on the basis of annual exposures that were based on air doses as of November 2011 from the Fourth Airborne Monitoring Survey undertaken by the Ministry of Education, Culture, Sports, Science and Technology, Japan (2011).
Table 3 Unit costs for management and storage. Item
Unit cost
Source, notes
Storage container
JPY8000
Transport 1 Decontamination site/Temporary storage site
JPY3100/container
Temporary storage site
JPY20,000/container
Transport 2 Temporary storage site / Interim storage facility
JPY 3800e16,000/ container
Interim storage facility
Combustibles volume reduction
JPY2000/container
Combustibles incineration residue storage
JPY100,000/container
Incombustibles storage
JPY30,000/container
Use of weather-resistant flexible container conforming to Ministry of the Environment decontamination guidelines. Based on information from company websites and interviews, unit cost was estimated at JPY5000e8000. Unit cost was set at the upper level. Calculated assuming transport by 4-tonne truck over one-way distance of 5 km and referring to provisional estimation standards for decontamination work in SDZs from the Ministry of the Environment. Estimate based on interviews and provisional estimation standards for decontamination work in SDZs from the Ministry of the Environment. Transport distance was calculated as distance from each municipality's public office to the vicinity of F1NPP. Calculated based on transport using a 10-tonne truck, and with reference to provisional estimation standards for decontamination work in SDZs from the Ministry of the Environment. Assuming volume reduction carried out within interim storage facility. Assuming volume reduction by incineration of combustibles (fallen leaves, etc.), combustibles volume reduction cost: Estimated based on incineration cost of JPY13,450e18,790/tonne (from Ministry of the Environment 6th Feedback Session on 3R and Handling of Kitchen Refuse: Document 1. Cost Comparison of Methane Fermentation Facility and Incineration Facility) and specific gravity of combustibles in a flexible container (prior to incineration) of o.1 (JAEA Decontamination Report p. 224), giving a range of JPY1345e1879/m3. JPY2000/container was adopted based on the maximum value. Further, volume reduction ratio was set at 95%. Assuming high concentration, leachable material storage unit cost (JPY/m3) of JPY100,000/container (0.9 m3): Unit cost assumes strictly controlled landfill site but no such data could be obtained. For this reason, a unit cost that was around three times the cost of the low-leachables unit storage cost was adopted based on interviews with relevant parties. The receiving unit cost at controlled landfill sites for low concentration, non-leachable material storage was adopted. Using the surplus soil unit processing cost of the Shiga Clean Center, a controlled landfill site of JPY17,850/tonne and a specific gravity of 1.8 translated to a cost of JPY 28,917/container (0.9 m3). Thus, JPY30,000/container was adopted. Source: Shiga Clean Center website www.kouka.ne.jp/~skj-ccs/clean/riyo.html#hyou02
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5
Table 4 Decontamination scenarios. Land-use
Agricultural
Scenario Scenario 1
(Basic Scenario)
Area
A1
SDZ
△ >5000 Bq/kg
Forest A2
A3 △ <5000 Bq/kg
Scenario 3
Scenario 4
(Basic Scenario 2)
(Minimum Scenario)
(Maximum Scenario)
SDZ ICA
Road F2
-
B
B
B
B △ >1 mSv
B △ >1 mSv
B △ >1 mSv
RB3
△ >5 mSv
△ 1e5 mSv
△ >1 mSv B △ >5 mSv
△ 1e5 mSv
B △ >1 mSv
>1 mSv
RB2
B
B
-
RB1
△ >1 mSv
>1 mSv
△ >1 mSv
Residential and building R2
B
-
B
R1
>1 mSv
△ >1 mSv
SDZ ICA SDZ ICA
F1
△ >1 mSv
ICA Scenario 2
A4
B △ >1 mSv
△ >1 mSv
B: Whole area. -: We set that forest adjacent to 100-m mesh units used as paddy fields, other agricultural land, or buildings were decontaminated, whereas other areas of forest were not to be decontaminated. Moreover, of the mesh units that contained forest to be decontam-inated, we assumed that only 20% of the forests in these mesh units would be decontaminated, as specified in the guidelines of the Ministry of the Environment. △: We set the decontamination area with annual external exposure or concentration.
Scenario 1 is the basic scenario that complies with the policy of the Japanese Ministry of Environment. In this scenario, about 5 cm of topsoil was stripped from the 50% of agricultural land in the SDZ exhibiting a high air dose rate area, and 5 cm of clean covering soil was added (A1). For the remaining 50% of agricultural land with low air dose rates, topsoil was assumed to be interchanged with subsoil (A3). Plowing with zeolite and potassium (A4) was adopted for agricultural land in ICAs where the annual additional effective dose exceeded 1 mSv. Decontamination of forested areas in the SDZ and the ICAs, which account for approximately 70% of prefectural land use, was carried out in accordance with the policy of the Ministry of the Environment (forested areas within 20 m of areas of habitation): decontamination of 20% of the area of each 100 m 100 m of forest adjoining paddy fields and other agricultural land and buildings. Furthermore, in ICAs, forested areas with an annual additional effective dose exceeding 1 mSv were decontaminated. In the SDZ, forest decontamination entailed removal of fallen leaves and humus surface (F1), whereas in ICAs, it involved removal of fallen leaves only (F2). Shot blasting and side ditch sweeping (R1) were carried out for all roads in the SDZ, whereas only road and side ditch sweeping (R2) was undertaken in ICAs where the annual additional effective dose exceeded 1 mSv. Whole decontamination (RB1) was undertaken for all residential and other built-up areas in the SDZ, whereas whole decontamination (RB2) was carried out for those areas in ICAs where the annual additional effective dose exceeded 5 mSv. For ICAs where the annual additional effective dose was 1e5 mSv, local decontamination (only high air dose areas) (RB3) was carried out. In Scenario 2, all of agricultural land in the SDZ, about 5 cm of topsoil was stripped and 5 cm of clean covering soil was added (A1). In addition, whole decontamination (RB2) was carried out for builtup areas in ICAs where the annual additional effective dose exceeded 1 mSv. In Scenario 3 (minimum case), topsoil was interchanged with subsoil with zeolite and potassium for all agricultural land in the SDZ (A3). In Scenario 4 (maximum case), 5 cm of topsoil was stripped from all agricultural land in the SDZ, and 5 cm of covering soil was added (A1), whereas topsoil was interchanged with subsoil with zeolite and potassium for all agricultural land in ICAs (A3). In addition, this scenario assumed that not only the forest adjacent to 100-m mesh units used as paddy fields, other agricultural lands, or buildings but also other forest areas were decontaminated in the
SDZ. For the ICA, decontamination was carried out areas where the annual additional effective dose exceeded 1 mSv (RB2). 2.5. Post-decontamination air dose calculation We calculated 100 m 100 m air dose rates after decontamination by multiplying the 100 m 100 m air dose rates (excluding background) prior to decontamination by the residual factor calculated from the percentage of decrease (100 e the rate of decrease) for each land use. Then, the 100 m 100 m post-decontamination air dose rates for land uses (land for buildings, rice paddies, other agricultural land, roads, forested areas within 20 m of a habitation area) that were decontaminated were averaged over each 1 km 1 km mesh, and this value was adopted as the post-decontamination air dose rate for each 1 km 1 km mesh (calculations were carried out assuming that the entire area of each 100 m 100 m unit of forested area within 20 m of a habitation area was decontaminated). Furthermore, the post-decontamination air dose rate was taken to be equivalent to the pre-decontamination air dose rate for areas in which no land use types were subject to decontamination within a 1 km 1 km mesh. The post-decontamination air dose was calculated for 1 April 2016, assuming that decontamination would be completed by 31 March 2016. 2.6. Calculation of additional external radiation dose Individual external radiation doses (mSv/day) are not the same as the outdoor air dose (mSv/day) because the majority of radioactive fallout is present outdoors; indoors, the distances from sources of radiation are greater and walls having a shielding effect (IAEA, 2000). According to IAEA-TECDOC-1162, the external conversion coefficient for a two-story wood-frame house is 0.4 (shielding ratio: 0.6); for a concrete block or brick house, the coefficient is 0.2 (shielding ratio: 0.8). In Japan, the Ministry of the Environment currently evaluates the daily individual external effective dose from the air dose rate assuming 8 h spent outdoors and 16 h spent indoors and an indoor air dose rate that is 40% of the outdoor air dose rate (Japanese Ministry of the Environment, 2011). Based on these assumptions, the external radiation dose is taken as 0.6 of the air dose. Meanwhile, several researches have recently attempted to estimate external conversion coefficients according to individual external radiation dose and air dose data for children and adults. Date City (2012a,b), Nihonmatsu City (2012a,b), and Naito et al.
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T. Yasutaka, W. Naito / Journal of Environmental Radioactivity xxx (2015) 1e9
(2014) were confirmed that average individual radiation doses of around 0.1e0.4 of the external air dose rates using dosimeters. However the number of persons being measured was limited, these estimated external conversion coefficients should be validated by the further research. For this reason, in this study, we used the value of 0.6 as an external exposure conversion coefficient for the air dose adopted by the Ministry of the Environment. Next we calculated annual cumulative external doses under the following assumptions: the 134Cs/137C concentration ratio on 25 March 2011 was 1:1 the air dose on 5 November 2011 was attributable only to radioactive Cs the reduction in concentration of radioactive Cs was due only to decay (weathering was not considered) the annual dose was calculated assuming return on 1 April 2016 (ca. 5 years after the accident) For these calculations, we used the half-lives of radioactive Cs (134Cs: 2.06 years; 137Cs: 30 years) and the contribution ratio of each nuclide to the air dose (conversion of ambient dose rate from deposition [(mSv/h)/(kBq/m2)]) (from IAEA conversion coefficient table CF3a; (IAEA, 2000). 2.7. Index of effectiveness of decontamination As an index of effectiveness of decontamination (ED) for each 1 km 1 km mesh, we calculated the amount of total reduction of annual external dose for each 1 km 1 km mesh (person-Sv) by multiplying the amount of reduction of annual external dose by the population for each 1 km 1 km mesh. 3. Results 3.1. Estimates of decontamination costs Overall decontamination costs for the scenarios that comply with the policy of the Japanese government (Scenarios 1 and 2) are JPY2.03e5.12 trillion (total cost), JPY1.33e2.02 trillion (cost for the
SDZ), and JPY0.70e3.10 trillion (cost for the ICAs) (Table 5). Although the areas where decontamination has been implemented in the ICAs total around 3e11 times the area of the SDZ, the decontamination costs for the SDZ and ICAs are in the same range. The SDZ decontamination cost for Scenario 2 is 1.7 times that of the previous study result (JPY1.2 trillion; Yasutaka et al., 2013b) because the new estimate includes waste transport costs, administrative costs (22%), and areas of high radiation (Difficult-to-Return Zones). Close to 70% of the ICA decontamination cost consists of removal costs; for the SDZ, removal costs account for around 25% of the decontamination cost, with costs associated with temporary storage sites, transport, and interim storage facilities accounting for most of the decontamination cost. The reason for this difference between the SDZ and ICAs is that 5 cm of topsoil stripping was assumed when calculating the cost for agricultural land in the SDZ; in the ICAs, topsoil was assumed to be interchanged with subsoil, and, therefore, little removed soil is generated. Decontamination and construction of temporary storage sites are currently underway in Fukushima Prefecture (Japanese Ministry of the Environment, 2014), but the technology for reducing the volume of decontamination waste and removed soil has not yet been selected and applied, and no interim storage sites have been built. The cost for Scenario 3 (minimum case) is JPY1.14 trillion, which is JPY0.89 trillion lower than the cost for Scenario 1. Scenario 1 for the SDZ entailed removal of 5 cm of topsoil from 50% of agricultural lands, whereas in Scenario 3, interchanging topsoil with subsoil was adopted as the decontamination method for agricultural lands. As shown by Yasutaka et al. (2013b), the quantity of waste generated in decontaminating agricultural land varies considerably depending on the decontamination method used; consequently, differences in the quantity of generated waste resulted in large differences between agricultural land decontamination methods in the costs associated with storage containers, temporary storage sites, and interim storage facilities. In Scenario 4 (maximum case), all forested areas with over 1 mSv/year were assumed to be decontaminated: the total cost for this decontamination was estimated to be JPY16.17 trillion. Furthermore, in this calculation, the decontamination unit cost for
Table 5 Estimated costs and cost breakdown (trillion yen) for decontaminating Fukushima Prefecture.
Target area Decontamination area Scenario 1
Scenario 2
Scenario 3
Scenario 4
Total Decontamination Flex. Containers Temporary storage Transport$Interim storage Total Decontamination Flex. Containers Temporary storage Transport$Interim storage Total Decontamination Flex. Containers Temporary storage Transport$Interim storage Total Decontamination Flex. Containers Temporary storage Transport$Interim storage
Special decontamination zone revised Yasutaka et al. (2013b)
Intensive contamination survey area
Total
1,117 km2 295 km2 1.33 0.29 0.11 0.31 0.43 2.02 0.53 0.18 0.55 0.76 0.44 0.25 0.03 0.08 0.09 5.72 1.22 0.60 1.80 2.11
7836 km2 922〜3330 km2 0.7 0.41 0.04 0.1 0.14 3.1 2.15 0.14 0.34 0.47 0.7 0.41 0.04 0.1 0.14 10.45 3.52 1.15 2.88 2.90
8953 km2 1317〜3625 km2 2.03 0.70 0.15 0.41 0.57 5.12 2.68 0.32 0.89 1.23 1.14 0.66 0.07 0.18 0.23 16.17 4.74 1.75 4.68 5.01
26% 9% 28% 37% 26% 9% 27% 38% 55% 6% 18% 20% 21% 10% 32% 36%
59% 6% 14% 20% 69% 5% 11% 15% 59% 6% 14% 20% 34% 11% 28% 28%
38% 8% 22% 31% 52% 6% 17% 24% 58% 6% 16% 20% 29% 11% 29% 31%
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7
Fig. 2. Comparison of the annual external exposure distribution on 1 April 2016 for each 1 km 1 km mesh without decontamination and with decontamination Scenarios 1 and 4.
forested areas was assumed to be equal to that for forested areas within 20 m of habitation areas; however, the decontamination unit cost increases with increasing distance from habitation areas, which suggests that the decontamination unit cost would be higher than that listed for Scenario 4. In areas such as Fukushima Prefecture, where forest accounts for over 70% of the overall area, the policy adopted for forest decontamination strongly influences the total decontamination cost. 3.2. Comparison of decontamination effects Although there was an effect on habitation area air dose depending on whether or not decontamination was implemented, there were no marked differences among the decontamination scenarios adopted in this study (Fig. 2). ED values for Scenario 1
a
covered a wide range in the 1 km 1 km meshes, from 106 to 100 person-Sv, and increased as population increased (Fig. 3a). In contrast, ED values for Scenario 1 were poorly correlated with air dose rate (Fig. 3b). The reduction in annual individual additional effective dose for all decontamination scenarios was 1666 person-Sv, for the SDZ and 876e1245 person-Sv, for the ICAs (Table 6). Although the reduction rate for the SDZ was somewhat larger than the reduction rates for the ICAs, the magnitudes of the rates were similar, unlike the large differences between the decontamination efficiencies (Table 1). The large extent of reduction for the ICAs is mainly associated with population density. The population of the SDZ before the accident is about 90,000, whereas the population of an ICA in an area exposed to over 1 mSv/year is 1,530,000. This result suggests that ED values vary depending on not only the decontamination efficiency but also
b
Fig. 3. Relationship between ED for each 1 km 1 km mesh and (a) population and (b) air dose rate.
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T. Yasutaka, W. Naito / Journal of Environmental Radioactivity xxx (2015) 1e9
4. Discussion
We have shown that the total estimated decontamination cost can exceed JPY16 trillion if all forested areas with over 1 mSv/year are assumed to be decontaminated. Furthermore, implementing decontamination of all forested areas provides no major reduction in the external radiation dose for the average inhabitant. However, many people who live or have lived in these regions have traditionally obtained drinking water from streams and runoff and utilized the harvest from the forest and satoyama (boundary forest areas used by local inhabitants), including mushrooms, edible wild plants, and firewoods. Additionally, about 1800 workers are employed by the forest industry. For these people, the forest, the satoyama, and its harvest are inseparable from their lives. Recent research has shown that the annual runoff rate of radiocesium in the forest is very low, only 0.1e0.3% per year of total deposition (National Institute for Environmental Studies, 2012); thus, if decontamination is not carried out in forested areas, a major portion of radiocesium deposited in the forest will remain for many years. Decontamination of forested areas more than 20 m from areas of habitation resulted in only a minor reduction in the external radiation dose for the average person. However, the external radiation dose may be significant for forestry and satoyama workers. Therefore, the external radiation dose for workers in forested areas is best evaluated on a site-by-site basis rather than over a wide area. Deciding on a strategy that takes into account the forest industry and forest utilization is important in guiding forest decontamination policy. A comprehensive debate on approaches to forest decontamination that addresses both forest utilization and the costs and effects of decontamination is required.
4.1. Need for volume reduction technology
4.3. Key parameter of decontamination effectiveness
Currently, decontamination is underway in Fukushima Prefecture based on a basic case approach; as of October 2014, around 60e80% of ICA decontamination had been completed (Japanese Ministry of the Environment, 2014). In contrast, construction of temporary storage sites and interim storage facilities, which account for an estimated 50% of the overall cost of decontamination, has been delayed; transport, storage, and administrative costs will be required (JPY1.55e2.12 trillion for Basic Scenarios 1 and 2). Furthermore, securing routes for transporting the more than 20 million tonnes of decontamination waste and removed soil that will be generated is a major challenge. To reduce the amount of decontamination waste t and removed soil hat must be stored and transported, technologies for volume reduction of ash from incineration of combustibles and of incombustibles such as washed soils must be developed and applied. The Japanese government is currently mainly considering volume reduction by incineration of combustibles. However, for further cost reduction, application of a volume reduction technology for incombustibles should be discussed. A comprehensive analysis of contaminated waste and soil management methods is required to address these challenges; this analysis should include technical assessment and discussion of the necessity for volume reduction of incombustibles, combustibles, and ash from incineration of combustibles; in addition, assessing the management and storage of low-concentration radioactive cesium-containing soil and methods for using controlled landfill sites should lead to a significant reduction in the amount of material requiring transport.
Our results indicate that ED values for the 1 km 1 km meshes vary widely, ranging from 106 to 100 person-Sv,. ED values are affected mainly by population density, but air dose rate before decontamination and decontamination efficiency also affect ED values. The decontamination efficiency for the 1 km 1 km meshes ranged from 0.08 to 0.80 (Table 1), the air dose rate ranged from 0.23 to 8 mSv/h, but the population density ranged from 1 to 10,000 persons/km2. The differences in the ranges of the parameters are the reason that the ED value was mainly affected by population density. If we evaluate the effectiveness of decontamination by the sum of the reduction rates of the external exposure per person for each 1 km 1 km mesh, the population density is a more important parameter than the air dose rate for the Fukushima accident. Although the decontamination effectiveness such as ED value is an important parameter and can be used as a surrogate for understanding the distribution of societal risk in the affected areas, this concept should be used with care. For example, this ED index might evaluate that priority of decontamination of area with an individual high dose and a small number of people is not high, compared with the area with individual low dose and large number of people. For an illustrative purpose, we have applied to the ED concept to the case of decontamination in Fukushima Prefecture and ED value is one of index for decision making of decontamination. Reducing high dose individuals is another significant purpose for decontamination in the affected areas in Fukushima. It is important to establish the decontamination strategies for reducing societal risk and high dose individuals in a mutually complementary manner.
Table 6 Reductions in annual additional radiation doses for each decontamination scenario (person-Sv).
SC1 SC2 SC3 SC4
(Basic Scenario) (Basic Scenario 2) (Minimum Scenario) (Maximum Scenario)
SDZ
ICA
Total
1666 1666 1666 1666
876 1031 876 1245
2542 2697 2542 2911
An external exposure conversion coefficient is 0.6.
the population density. If the objective of decontamination is to maximize sustainability of population living in the affected areas after decontamination, to a certain degree, then special consideration should be given to the decontamination in high population areas. Understandably, ED value is one of index for decision making of decontamination. From the view of reducing individual high doses, another index should be used for the decontamination in areas with the highest dose rates. The difference between the scenarios in the ICAs is attributable to whether whole decontamination (Scenarios 1 and 3) or local decontamination (Scenarios 2 and 4) was carried out. Although there is no major difference in the efficiencies for whole decontamination (35%) and local decontamination (18%), a large population (approximately 1,030,000) resides in areas exposed to 1e5 mSv/year; for this reason, the reduction in annual individual additional effective dose was large for the whole-decontamination scenarios.
4.2. Forest decontamination policy 5. Conclusions Debate on the rate of progress of decontamination is expected to gain momentum, as will discussion related to decontamination in the future of forests in uninhabited areas.
(1) The decontamination costs for the basic scenarios (Scenarios 1 and 2) were JPY2.53e5.12 trillion. Although the
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decontamination area of the ICAs is around 3e11 times the area of the SDZ, the total decontamination costs are of the same order. (2) Removal costs account for a high proportion of the decontamination cost for the ICAs. Costs related to temporary storage sites and interim storage facilities for the SDZ are estimated to account for 41e62% (JPY1.55e2.12 trillion) of the total decontamination cost. (3) The cost for decontaminating all forested areas could potentially exceed JPY16 trillion but would provide no major reduction in the external radiation dose for the average inhabitant. If the Japanese government reconsiders the current policy of the Ministry of the Environment (forested areas within 20 m of areas of habitation), then policy and procedures for forest decontamination should be carefully reassessed. (4) For the Fukushima accident, if we evaluate the effectiveness of decontamination by the sum of the reduction rate of external exposure per person for each 1 km 1 km mesh, population density is a more important parameter than air dose rate. Acknowledgments The authors would like to thank Mr. Motoki Uesaka and Mr. Eiichi Yasoda for their assistance with the analyses. The authors would also like to thank Dr. Junko Nakanishi, Dr. Isao Kawaguchi, Dr. Michio Murakami, Dr. Kyoko Ono, Dr. Shizuka Hashimoto, Ms. Yumi Iwasaki, Dr. Kikuo Yoshida, and Dr. Atsuo Kishimoto for providing valuable comments. This work was supported by JSPS KAKENHI Grant Number 26241023, 25289207 and AIST Environment and Energy Unit. References Date City, 2012a. Date City Bulletin. Disaster Preparation Issue, No. 45 Jan. 26. http:// www.city.date.fukushima.jp/kouhou/pdf-rinzi/rinzi45.pdf. Date City, 2012b. Date City Environmental Radiation Measurement Results. http:// www.city.date.fukushima.jp/groups/hosyasen/1keka.pdf.
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Fukushima Prefecture, 2012a. Decontamination Countermeasure Operation Implementation Guideline. http://wwwcms.pref.fukushima.jp/download/1/jyosen_ 0119youryou.pdf. Fukushima Prefecture, 2012b. Fukushima Prefecture Surface Decontamination Model Project. http://wwwcms.pref.fukushima.jp/download/1/summary20120330. pdf. IAEA, 2000. Generic Procedures for Assessment and Response during Radiological Emergency. Japan Atomic Energy Agency, 2012. Implementation Report on Decontamination Relating to the Fukushima Daiichi Nuclear Powerstation. http://www.jaea.go.jp/ fukushima/kankyoanzen/d-model_report.html. Japanese Ministry of Environment, 2013. Basic Policy on Interim Storage and Other Facilities Required for the Handling of the Environmental Pollution from Radioactive Materials Associated with the Accident at Tokyo Electric Power Co.’s Fukushima Daiichi Nuclear Power Stations (2015, 4.23). http://josen.env. go.jp/en/roadmap/pdf/chart1_5.pdf. Japanese Ministry of Land Infrastructure Taransport and Tourism, 2012. National Land Numerical Information Download Service. http://nlftp.mlit.go.jp/ksj-e/ index.html. Japanese Ministry of the Environment, 2011. Decontamination Guidelines Ver. 1, Dec. 2011. Japanese Ministry of the Environment, 2014. Progress on Off-site Cleanup Efforts in Japan(December, 2014) (2014, 12.31). http://josen.env.go.jp/en/. Ministry of Education Culture Sports Science and Technology in Japan, 2011. Results of the Fourth Airborne Monitoring Survey by MEXT(December 16, 2011). http:// radioactivity.mext.go.jp/ja/contents/5000/4901/24/1910_1216.pdf. Morino, Y., Ohara, T., Nishizawa, M., 2011. Atmospheric behavior, deposition, and budget of radioactive materials from the Fukushima Daiichi nuclear power plant in March 2011. Geophys. Res. Lett. 38. Naito, W., Uesaka, M., Yamada, C., Ishii, H., 2014. Evaluation of dose from external irradiation for individuals living in areas affected by the Fukushima Daiichi nuclear plant accident. Radiat. Prot. Dosim. 163, 353e361. National Institute for Environmental Studies, 2012. NIES Annual Report, pp. 94e95. National Institute of Advanced Industrial Science and Technology, 2011. Geochimical Map of the Sea and Land of Japan. Nihonmatsu City, 2012a. City Measurement Result Independent Municipal Measurement Results (Up until April 30, 2012). http://www.city.nihonmatsu.lg.jp/ site/higashinihondaishinsai-kanren/20120724-1.html. Nihonmatsu City, 2012b. Residents Radiation Exposure Dose Survey Result Announcement Meeting Materials. http://www.city.nihonmatsu.lg.jp/uploaded/ attachment/10014.pdf. Yasutaka, T., Iwasaki, Y., Hashimoto, S., Naito, W., Ono, K., Kishimoto, A., Yoshida, K., Murakami, M., Kawaguchi, I., Oka, T., Nakanishi, J., 2013a. A GIS-based evaluation of the effect of decontamination on effective doses due to long-term external exposures in Fukushima. Chemosphere 93, 1222e1229. Yasutaka, T., Naito, W., Nakanishi, J., 2013b. Cost and effectiveness of decontamination strategies in radiation contaminated areas in Fukushima in regard to external radiation dose. PLoS One 8, 11.
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