Radiation doses in countries of the northern hemisphere from the chernobyl nuclear reactor accident

Environment International, Vol. 14, pp. 75-82, 1988

0160-4120/88 $3.00 + .00 Copyright © 1988 Pergamon Press plc

Printed in the USA. All rights reserved.

RADIATION DOSES IN COUNTRIES OF THE NORTHERN HEMISPHERE FROM THE CHERNOBYL NUCLEAR REACTOR ACCIDENT

B. G. Bennett Monitoring and Assessment Research Centre, 459A Fulham Road, London SW10 OQX, United Kingdom

A. Bouville National Cancer Institute, Environmental Measurements Laboratory, 376 Hudson Street, New York, New York 10014, USA

(Received 4 December 1987; Accepted 10 May 1988) Radionuclides released from the Chernobyl accident have been dispersed throughout the Northern Hemisphere. Values are collected here of the estimates so far provided of the resultant radiation exposures in countries. The collective effective dose equivalent commitment is of the order of 800,000 man Sv. Average individual dose commitments outside the USSR range up to 4 mSv, which is approximately twice the normal annual dose from natural background radiation. The estimated average doses in countries decrease in a regular fashion with distances from the accident site.

Radionuclide Release

tenth day resulted in increased release rates of up to 300 PBq/d. This was caused by contained heat within the reactor from the many tons of boron carbide, dolomite, clay, and lead which had been used to smother the fire (International Atomic Energy Agency, 1986). The total estimated release, decay corrected to May 6 was 1900 PBq. Variable fractions of core materials were released in the accident. It could be assumed that essentially 100% of noble gases present, such as 8~Kr and '33Xe, was released. The volatile elements iodine, tellurium, and caesium were preferentially released: 10% to 20% of the core inventory. Other radionuclides, including barium and strontium and more refractory elements cerium, ruthenium, zirconium, molybdenum, and transuranium elements, were released in 2% to 5% fractions of the core inventories. Estimated release amounts are listed in Table 1, which were based on air and deposition measurements made within the USSR. Evidence from far-field measurements (e.g., Anspaugh et al., 1987) indicates that the total caesium releases may have been underestimated by a factor of 2. The radionuclide composition varied slightly over the ten day release period as different mechanisms were acting. Activity ratios of radionuclides measured in air and deposition at various times and at different

The accident at the Chernobyl nuclear power reactor occurred in the early hours of April 26, 1986. Control of the reactor was lost during a low power operation test. Some safety systems had been switched off and almost all of the control rods had been withdrawn from the core. Instabilities in the reactor led to a very rapid power excursion which could not be controlled or prevented by manual intervention. A steam explosion ruptured the reactor vessel, and a second explosion two or three seconds later ejected hot pieces of the reactor from the building. The graphite core ignited and burned for several days. Damage to the reactor from the initial explosions and the subsequent fire led to substantial release of radioactive materials to the atmosphere. The Soviet authorities have given information on the time pattern of release and have estimated the total activities and composition of the ejected material (International Atomic Energy Agency, 1986). The most substantial release occurred in conjunction with the initial explosions on April 26 when some 750-800 PBq total activity was dispersed (1 PBq - 10 '2 Bq). As the fire was gradually brought under control, the release rate was reduced to less than 100 PBq/d by the sixth day. A subsequent heating period until the 75

76

B . G . Bennett and A. Bouville

Table 1. Activity amounts of radionuclides released (International Atomic Energy Agency, 1986). Short-lived radionuclides~

Long-lived radionuclides

Half-life b (d)

Amount (PBq)

Haft-life (y)

Amount (PBq)

5.245 8.04 12.74 63.98 39.28 2.75 32.50 284.3 50.5 3.26 2.355 162.8

1700 260 160 140 120 110 100 90 80 48 4 0.8

1.01 30.0 10.72 2.062 29.12 14.4 6537 24065 87.74

58 38 33 19 8 5.1 0.06 0.03 0.03

ln~Xe 1~11 14°Ba 9~Zr l°aRu 99Mo 141Ce ~44Ce "gSr 13=Te 239Np 24zCm

l°rRu 137Cs 85Kr 134Cs 9°Sr z41Pu z4°pu 23apu 238pu

aDecay corrected to 6 May 1986. bReference: 1CRP Publication 38 (International Commission on Radiological Protection, 1983).

locations varied accordingly. There were also variations with distance. Larger particles of core material were deposited in the more immediate vicinity of the reactor. Deposition of strontium and zirconium was significant only within the Soviet Union. The volatile elements were subjected to longer range transport. Dispersion and Deposition At the time of the accident, surface winds at the Chernobyl site were very weak and variable. However, at 1500 m winds were 8-10 m/s from the southeast. It is evident from first detection of activity in Sweden at a distance of 1200 km within 36 hours after the onset of releases, that the explosions and convective heat from the reactor carried debris at least to this altitude. Aircraft measurements in Poland found significant activity at 6-9 km in the troposphere in the initial days after the accident and lesser amounts at 15 km in the lower stratosphere (Jaworowski and Kownacka, 1988). Variable wind speeds and directions at different altitudes and changes over the ten day release period led to a complex dispersion pattern. The initial spread of radioactive material was carried northwestward over Sweden and southern Finland. Some of this plume at lower altitude and subsequent releases moved southwestward over Poland, Czechoslovakia, western Hungary, Austria, southern Federal Republic of Germany, eastern Switzerland and northern Italy. Releases on April 29-30 spread southward across Bulgaria, Romania, Yugoslavia, Greece, and western Turkey. Other emissions were carried eastward across the USSR. General tropospheric dispersion spread measurable activity throughout the northern hemisphere. As interhemispheric mixing is inefficient, there

was insignificant transfer to the Southern Hemisphere. Deposition of radioactive materials occurred mainly in association with rainfall, which occurred very sporadically throughout Europe in the first week of May 1986. Highest activity deposition outside the USSR was recorded in north-central Sweden, where local levels of 137Cs reached 200 kBq/m 2 (Swedish National Institute of Radiation Protection, 1986). Deposition of 137Cs of 40-45 kBq/m 2 was measured in the southern region of Tessin in Switzerland and in southeast Bavaria in the Federal Republic of Germany (Hauptabteilung for die Sicherheit der Kunlagen, 1986; Gesellschaft for Strahlen- und Umweltforschung, 1986). Deposition of at least 1 kBq/m 2 occurred in southern Scandinavia, eastern and southern Europe, western Europe into eastern France and in an area of the northwestern United Kingdom. Within many European countries the deposition pattern was very uneven. This resulted in contamination of agricultural areas and exposure fields for populations which were regionally quite variable. Transfer to Foods

Deposition of iodine and caesium on grass consumed by dairy cows and on surfaces of leafy vegetables can lead to relatively rapid transfer to humans. Because of the short half-life of 1311 (8.04 days), milk and leafy vegetables are the only foods of importance. The longer half-lives of 134Cs (2.06 years) and ~37Cs (30.0 years) allow transfer via meat, grain products, other vegetables and fruit as well. In northern Europe, cows were not yet on pasture in early May and holding them indoors for a further two to three weeks limited the maximum levels of 1311 in milk. High measured concentrations were around 200 Bq/1 in Sweden (Swedish National Institute of Radiation Protection, 1986), 700 Bq/1 in the German Democratic Republic (Loessner and Roehnsch, 1986) and 1000 to 2000 Bq/1 in Hungary (Hungarian Atomic Energy Commission, 1986) and Switzerland (Hauptabteilung for die Sicherheit der Kunlagen, 1986). More widely collected and distributed dairy milk had much lower values in all areas. Milk of sheep and goats was noted in several areas to contain much higher concentrations of 1~1Iand 137Cs than cows' milk from the same areas due to differences in feeding habits and metabolism of the animals. For example, 1311levels in milk in Greece in early May were reported to be 9000 Bq/l (goat milk), 2500 Bq/l (sheep milk) and 200 Bq/1 (cow milk) (Greek Atomic Energy Commission, 1986). Meat of grazing animals can acquire significant levels of ~37Cs. This is particularly so for reindeer feeding on lichens which tenaciously retain surface deposited material. Large numbers of reindeer in Sweden acquired 1:~7Cs levels of more than 10,000 Bq/kg (Swedish National Institute of Radiation Protection,

Radiation doses in the Northern Hemisphere 1986). High levels of '37Cs in sheep (> 1000 Bq/kg) have persisted for over a year since the accident in the higher deposition areas of northwest England and southwest Scotland. High levels of 'arCs have been noted in certain other foods, such as mushrooms, wild berries, lake fish, nuts and tea leaves. These foods could, in some cases, be important contributors to individual doses, however, they are normally not widely consumed in sufficient quantities from single local sources to affect population doses.

General Aspects of Dose Assessment Much experience has been gained over the years in assessing radiation doses to populations from radioactive materials dispersed in the environment, particularly that from atmospheric testing of nuclear weapons carried out until 1980. Summaries of measurement and modelling of environmental behavior have been included in reports of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) (United Nations, 1982). In many respects, this assessment methodology can be carried forward to dose evaluations from the Chernobyl accident release. A report on this is in preparation by UNSCEAR for publication in 1988. There are important differences, however, from the weapons fallout pattern which resulted from large number of tests at various locations with considerable stratospheric injection which spread debris more widely and uniformly through hemispheric regions. The release from Chernobyl was from a single location and of relatively brief duration. The dispersion and deposition were dependent on tropospheric winds and rains which occurred during a few days following the accident. Seasonal features were of importance for the Chernobyl release. Agricultural conditions, for example, varied from north to south in Europe with pasturing and growing seasons either not yet or already underway. Many countries took specific countermeasures to prevent transfer and absorption of radionuclides by man, including administering iodide tablets, keeping cows off pasture, restricting import and sale of contaminated foods. The pathways of importance for radionuclides released in the Chernobyl accident are external irradiation from deposited materials and ingestion of radionuclides incorporated into foods. These are both of long-term significance due to the large presence of '3rCs in the accidental release. Additional pathways which could be considered include irradiation from radioactivity in air (cloud gamma) and inhalation of airborne material. These are both of short-term and minor significance. Radionuclides of importance in the dose assessment include '3tI, 'a4Cs, and "~TCs. These are the only sub-

77 stantial contributors to the ingestion pathway. In addition to the caesium isotopes, external exposure from deposited material occurred mostly for relatively short periods, from '°ZRu, '°rRu, '3Z]Te/'32I, '4°Ba/140La, 99M0 and 136Cs. The isotopes of importance in cloud gamma exposure were '32Te, mI, '4°La, '°3Ru and mCs. For inhalation, radionuclides contributing to dose included '°~Ru, '3ZI'e, 12~Te, in addition to '3'I, '34Cs, and 137Cs. Dose assessments thus far completed (e.g., Webb and Morrey, 1987), indicate that doses from ingestion of radionuclides in foods were of most importance during the first year following the accident. In subsequent years, continued irradiation from deposited radionuclides will make important contributions to the doses received, and dose commitments will be nearly equally due to the ingestion and external gamma pathways. Exposures due to inhalation and cloud gamma are estimated to make contributions of the order of 1% to dose commitments.

Dose Estimates Detailed assessments of the radiological impact of the accident are being conducted in many of the countries in which significant deposition of radioactive materials occurred following the accident. However, very few of those assessments which consider only the doses received by the population living in those particular countries have so far been published. In order to obtain a general picture of the radiological consequences of the accident, it is more useful at this time to resort to the rough assessments of the dose estimates for the populations of many countries that have been carried out independently by two international organizations, namely the Commission of the European Communities (CEC) and the Nuclear Energy Agency of the Organization for Economic Cooperation and Development (NEA/OECD), and by the United States Department of Energy (DOE). The methods used by the three organizations to derive their dose estimates are as follows: The Commission of European Communities (CEC) (Morrey et al., 1987) based its estimate on environmental measurements (exposure rates, air concentrations, deposition, levels in food) made during the first month after the accident and on calculations made using mathematical models of radionuclide transfer through the environment and to man; in this way, uniformity was ensured as to the type of dose to calculate and on the assumptions used to derive the doses from the environmental measurements; The U.S. Department of Energy (DOE) (Anspaugh et al., 1987, U.S. Dept. of Energy, 1987), like CEC, used early monitoring data and mathematical models of transfer to man. DOE relied to a greater extent on mathematical models as it essentially restricted the monitoring data it considered to early exposure rates

78

or deposition per unit area of ~a~Ior ~aTCs,associated to estimated times of initial arrival of the radioactive cloud in the countries considered and to a representative radionuclide breakdown; here again, the doses in the countries considered are all calculated in the same way; The Nuclear Energy Agency (NEA) (Nuclear Energy Agency of the OECD, 1987) used a different approach as it requested its member countries to provide their own estimates. The advantage of this approach is that the assessment was made by people with a thorough knowledge of the representativity and validity of their monitoring data as well as of environmental characteristics, agricultural practices and dietary habits that could have an influence on the dose estimates for the populations of their countries; on the other hand, there was no uniformity in the assumptions used to derive the dose estimates. Some of the results obtained by the three organizations are shown in Tables 2 to 4 which present, respectively: the collective effective dose equivalent commitments (estimated by CEC and DOE). the collective effective dose equivalents committed from the exposures or intakes during the first year following the accident (estimated by CEC, DOE and NEA), the collective thyroid doses committed from exposures or intakes during the first year after the accident (estimated by CEC, DOE and NEA). The countries for which data are available are listed according to their geographical locations: Europe, Asia, and North America. In order to estimate totals of collective doses to the populations of the three continents, a single value was assigned to each country, which, in the first instance, is the country reported result, if available; otherwise the average of the other available estimates is used. In addition, in order to obtain a more complete picture of the overall situation, information on collective dose estimates for the populations of the USSR (Ilyin and Pavlovskij, 1987) was incorporated in Tables 2 to 4. The countries listed in Tables 2 to 4 represent 98% of the total population in Europe, 60% of the total population in Asia, and 50% of the total population of North America. The collective dose estimates obtained for the three continents show clearly that the bulk of the total collective dose is expected to be received by the populations living in Europe. This conclusion remains valid if the rest of the world (i.e., in the continents of Africa, Australia, and South America), is taken into account, as very little deposition occurred on those continents. The only way in which people living in the Southern Hemisphere could have incurred significant doses is from ingestion of certain foodstuffs imported

B . G . Bennett and A. Bouville

from European countries, but this was limited through regulations and controls in exporting and importing countries. Results of Table 2 indicate that the collective effective dose equivalent commitment to the world population resulting from the release of radioactive materials during the Chernobyl accident is of the order of one million man-Sievert. Tables 2 to 4 present also per caput doses, obtained by dividing the collective doses by the populations. It is to be stressed that the per caput doses are only arithmetic averages and that a very large variability is attached to the distribution of the individual doses around the arithmetic average, resulting mainly from the heterogeneity of the deposition and also from differences in living and dietary habits as well as in agedependent characteristics. The per caput doses, nevertheless, are a good index of the radiation impact of the accident in each country. Data presented in Tables 2 to 4 for European countries indicate a large range of per caput doses, the highest doses being obtained for Eastern European countries and decreasing with increasing distance from the reactor site. A log-log representation of the variation of the per caput doses, as given in Table 2, as a function of the distance between the reactor site and the nearest boundary is shown in Fig. 1. All of the countries for which data are available have been plotted with the only exception of the USSR, for obvious reasons, and of Iceland, India, Portugal, and Spain which reported very low contamination levels, implying that the radioactive cloud did not go over those countries to a significant extent. Figure 1 shows that the per caput doses estimated for the remaining 31 countries are fairly consistent. The per caput effective dose equivalent commitment obtained for the population of Europe is about 1200 /zSv (Table 2). One-third of the total dose is expected to be due to the first year of exposure or intake (Table 3), the remaining two-thirds being delivered at a much lower and relatively constant rate during the next few decades. These figures may be compared to the per caput annual effective dose equivalent of 2000/xSv due to natural sources of radiation or to the effective dose equivalent commitment of 4500/zSv, applicable to the population of the north temperate zone, resulting from past atmospheric nuclear weapons tests (United Nations, 1982). The more detailed assessments in preparation in many countries and by UNSCEAR will provide better estimates, as they are based on longer series of measurements in the environment and in man. In particular, the measurements of the ~34Csand 137Csbody burdens, which are being carried out on a significant scale, offer a direct way to calculate the dose due to the ingestion of those radionuclides, thus reducing substantially an important source of uncertainty.

Radiation doses in the Northern Hemisphere

79

Table 2. Collective effective dose equivalent commitments (man Sv) for the populations of various countries resulting from the accidental release of Chernobyl. Collective dose commitment (man Sv) Population (millions) Europe Albania Austria Belgium Bulgaria Czechoslovakia Denmark Finland France German D.R. Germany, F,R. Greece Hungary Iceland Ireland Italy Luxembourg Malta Netherlands Norway Poland Portugal Romania Spain Sweden Switzerland United Kingdom USSR (European) Byelorussia Yugoslavia

3.0 7.5 9.9 9.1 15.6 5.1 4.9 54.6 16.8 60.9 9.9 10.7 0.2 3.6 57.3 0.4 0.4 14.5 4.1 37.2 10.2 23.0 38.5 8.4 6.4 56.1 201.4 10.1 23.2

Sum or Average

692.9

Asia China India Israel Japan Kuwait Turkey USSR (Asian)

1059.5 758.9 4.3 120.7 1.8 49.3 77.4

Sum or Average

2071.9

America Canada United States

25.4 238.0

Sum or Average

263.4

CEC

940

1100 5600 30000 8500

950 27000 42 1200

2 57

3000

DOE

Average

Per Caput Dose Commitment (/xSv)

6000 14000 900 40000 10000 800 4000 12000 13000 60000 4000 13000 0 1800 60000 80 400 4000 1700 150000 0 90000 0 9000 4000 15000

6000 14000 920 40000 10000 950 4000 8800 13000 45000 6200 13000 0 1400 43000 60 400 2600 1700 150000 1 90000 30 9000 4000 9000 320000* 110000" 40000

2000 1900 90 4400 640 190 820 160 770 740 830 1200 0 390 750 150 1000 180 410 4000 0.1 3900 0.8 1100 620 160 1600 11000 1700

830000

1200

80000

9000 0 150 1200 12 17000

100 1100

9000 0 150 1200 12 17000 7000*

8 0 35 10 7 340 90

34000

20

100 1100

4 5

1200

5.

*Figure reported by the country or derived from reported data.

80

B . G . Bennett and A. Bouville

Table 3. Collective effective dose equivalents to the populations of various countries resulting from the first year of exposure or intake. Collective Effective Dose in First Year (man Sv)

Country Europe Albania Austria Belgium Bulgaria Czechoslovakia Denmark Finland France German D.R. Germany, F.R. Greece Hungary Iceland Ireland Italy Luxembourg Malta Netherlands Norway Poland Portugal Romania Spain Sweden Switzerland United Kingdom USSR (European) Byelorussia Yugoslavia

Population (millions)

3.0 7.5 9.9 9.1 15.6 5.1 4.9 54.6 16.8 60.9 9.9 10.7 0.2 3.6 57.3 0.4 0.4 14.5 4.1 37.2 10.2 23.0 38.5 8.4 6.4 56.1 201.4 10.1 23.2

Sum or Average

692.9

Asia China India Israel Japan Kuwait Turkey USSR (Asian)

1059.5 758.9 4.3 120.7 1.8 49.3 77.4

Sum or Average

2071.9

America Canada United States

25.4 238.0

Sum or Average

263.4

CEC

NEA

480

4900 400

650 3000

140 2500 1300

14000 5200

18000 3600

660 17000 22

Small 370 28000 45

720

1.4

950 700 58

45

2100

1700 1400 2100

DOE

Average*

2000 4000 240 10000 3000 240 1200 3600 3700 18000 1200 3700 0 540 18000 24 120 1200 500 44000 0 25000 0 2500 1200 4200

2000 4900 400 10000 3000 140 2500 1300 3700 18000 3600 3700 0 370 28000 45 120 950 700 44000 58 25000 20 1700 1400 2100 98000* 28000* 24000

24000

280000

780 830

63

2400 0 40 360 4 4800

30 300

*Country estimated value used, if available (from N E A or USSR).

Per Caput Effective Dose (/.tSv)

700 650 40 1000 200 30 500 20 200 300 360 350 0 100 490 110 300 70 170 1000 6 1000 0.5 200 220 40 500 2800 1000 400

2400 0 40 780 4 830 900*

2 0 10 6 2 20 25

5000

2

63 300

2 1

360

1

Radiation doses in the Northern Hemisphere

81

Table 4. Collective thyroid doses to the populations of various countries resulting from the first year of exposure or intake. Collective Thyroid Dose in First Year (man Gy)

Country

Population (millions)

Europe Albania Austria Belgium Bulgaria Czechoslovakia Denmark Finland France German D.R. Germany, F.R. Greece Hungary Iceland Ireland Italy Lu xembourg Malta Netherlands Norway Poland Portugal Romania Spain Sweden Switzerland United Kingdom USSR (European) Byelorussia Yugoslavia

3.0 7.5 9.9 9.1 15.6 5.1 4.9 54.6 16.8 60.9 9.9 10.7 0.2 3.6 57.3 0.4 0.4 14.5 4.1 37.2 10.2 23.0 38.5 8.4 6.4 56.1 201.4 10.1 23.2

Sum or Average

692.9

Asia China India Israel Japan Kuwait Turkey USSR (Asian)

1059.5 758.9 4.3 120.7 ! .8 49.3 77.4

Sum or Average

2071.9

America Canada United States

25.4 238.0

Sum or Average

263.4

CEC

2700

2300 16000 36000 8300

1900 57000 130 4900

6.8 330

11000

NEA

DOE

9300 31000 1000 62000 20000 330 1000 4500 9000 7400 20000 30000 91000 100000 27000 8000 20000 Small 0 1800 3000 1 2 0 0 0 0 90000 160 100 600 5800 5000 1900 4000 300000 150 0 200000 0 3500 20000 8500 9000 11000 20000 17000 3100

100000

Average*

Per Caput Thyroid Dose (~Gy)

9300 17000 3100 62000 20000 330 4500 7400 30000 91000 27000 20000 0 1800 120000 160 600 5800 1900 300000 150 200000 110 3500 8500 11000 500000* 110000" 100000

3100 2300 310 6800 1300 60 920 140 1800 1500 2700 1900 0 500 2100 400 1500 400 460 8100 10 8700 3 420 1300 200 2500 10000 4300

1500000

8200 5300

95 3000

10000 0 200 2000 20 30000

100 1000

*Country estimated value used, if available (from NEA or USSR).

2200

10000 0 200 8200 20 5300 1900"

10 0 50 70 10 110 25

26000

12

95 3000

4 13

3100

12

82

B . G . Bennett and A. Bouville

Polan~

D

Bulgaria

R°maniaHun~ ~ Aus~ia •Yugoslavia un r weden Hatta ¥

lO3 0 Greece

Finland German Oe~. Repub]i

Italy Ot'~F"Roen ]Pdl~d ui~! IIQ d,p,~o" of G. . . .

Czechoslovakia

Switzerland

•

oN°~ Y •

Ireland

Turkey

;ze~~~~til~erl ands Albania

France~

kuxembourg ~.

United Kingdom

,02 Belgium •

•

> Israel

g

10'

• K •t

•

Japan

China • UnitedStates

10~

I

IoS

,o' DISTANCE (kin)

Fig. 1. Average radiation dose to individuals in countries in relation to distance from the Chernobyl site.

References

Anspaugh, L. R., Goldman, M., and Catlin, R. J. (1987) Atmospheric releases from severe nuclear accidents: Environmental transport and pathways to man: Modelling o f radiation doses to man from Chernobyl releases. Document presented at the International Conference on Nuclear Power Performance and Safety, IAEA, Vienna, 28 September to 2 October. Gesellschaft for Strahlen- und Umweltforschung (1986) Umweltradioaktivit/it und Strahlenexposition in Sfidbayern durch den Tschernobyl Unfall. GSF 16/86. Greek Atomic Energy Commission (1986) The consequences of the Chernobyl nuclear accident in Greece. DEMO 86/4. Hungarian Atomic Energy Commission (1986) Radiation consequences in Hungary of the Chernobyl Accident. Budapest, July. Hauptabteilung ftir die Sicherheit der Kernanlagen, Switzerland (1986) Der Unfall C h e r n o b y l - ein Ueberblick fiber Ursachen und Auswirkungen. HSK-AN-1816. Ilyin, L. A. and Pavlovskij, A. O. (1987)Radiologieal consequences o f the Chernobyl aecident and measures taken to mitigate their impact. Document presented at the International Conference on Nuclear Power Performance and Safety, IAEA, Vienna, 28 September to 2 October. International Atomic Energy Agency (1986) Summary Report on the Post-Accident Review Meeting on the Chernobyl Accident. Safety Series No. 75-INSAG-1. IAEA, Vienna. International Commission on Radiological Protection (1983) Radionuclide transformations. Energy and intensity of emissions. ICRP Publication 38. Pergamen Press, Oxford.

Jaworowski, Z. and Kownacka, L. (1988) Tropospheric and stratospheric distributions of radioactive iodine and caesium after the Chernobyl accident. J. Environ. Radioactivity 6, 145-150. Loessner, V. and Roehnsch, W. (1986) Monitoring after Chernobyl, the First 150 Days. Staatliches Amt ffir Atomsicherheit und Strahlenschutz (SAAS), Berlin. Morrey, M., Brown, J., Williams, J. A. (1987) A preliminary assessment of the radiological impact of the Chernobyl reactor accident on the population of the European Communities. CEC Document (to be published as an EUR document). Nuclear Energy Agency of the OECD (1987) The radiological impact of the Chernobyl accident in OECD countries. NEA/OECD. Swedish National Institute of Radiation Protection (1986) Chernobyl - - its impact on Sweden. SSI-86-12. U.S. Department of Energy (1987) Health and environmental consequences of the Chernobyl nuclear power plant accident. DOE/ER-0332. United Nations (1982) Ionizing Radiation: Sources and Biological Effects. United Nations Scientific Committee on the Effects of Atomic Radiation 1982 Report to the General Assembly, with annexes. United Nations Sales Publication. Sales No. E.82.IX.8. United Nations, New York. Webb, G. A. M. and Morrey, M. E. (1987) The Environmental Consequences o f Chernobyl in Western Europe. Document presented at the International Conference on Nuclear Power Performance and Safety, IAEA, Vienna, 28 September to 2 October.