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The international Chernobyl project technical report: Assessment of radiological consequences and evaluation of protective measures
Nucl. Med. Eiol. Vol. 21, No. I, pp. 3-7, 1994 Printed in Great Britain. All rights reserved
Copyright
0969-8051/94 $6.00 + 0.00 Q 1994 Pergamon Press Ltd
Review
The International Chernobyl Project Technical Report: Assessment of Radiological Consequences and Evaluation of Protective Measures Report by an International Advisory Committee (printed by the International Atomic Energy Agency in Vienna, 1991) Preface by the Chairman of the International Advisory Committee, Itsuzo Shigematsu, Radiation Effects Research Foundation, Hiroshima, Japan This is probably the most comprehensive international report ever compiled, in the wake of the now “worst-ever” peace-time nuclear disaster. The nuclear power plant in Chernobyl, which is located about 90 km north of Kiev, comprised four reactors, Units 1, 2, 3 and 4. At about 1.24 a.m. Moscow time on 26 April 1986 the reactor cover was blown off and the core laid wide open. By November 1986, 237 persons were being treated for acute radiation syndrome, and at the time of publication of this report a total of 28 had died. The Chernobyl disaster was of international dimensions, and scientists of the USSR sent an interim report to the International Atomic Energy Agency which was summarized in the IAEA Safety Series (IAEA, 1986). The next step to involve international cooperation is best described in the Introduction (Section 3) to the International Advisory Committee (IAC) technical report itself: “In a letter dated 6 December 1989 to the Director General of the IAEA, the Government of the USSR requested that the IAEA initiate and co-ordinate the organization and implementation of ‘an international experts’ assessment of the concept which the USSR has evolved to enable the population to live safely in areas affected by radioactive contamination following the Chernobyl accident, and an evaluation of the effectiveness of steps taken in these areas to safeguard the health of the population’.” From this it is clear that the request objectives:
had two
(1) To examine the assessment of the radiological situation in the contaminated areas
(2) To evaluate the criteria that were developed to ensure safe living conditions in the affected areas. Implicit in this was the corollary objective: to advise the Government of the USSR whether additional protective measures, especially disruptive measures such as relocation, should be implemented in order to ensure safe living conditions for the population still living in contaminated areas. The main report is the IAC technical report, comprising 640 pages. There are then three summary reports, namely the “Proceedings of an International Conference” of 63 pages; “An Overview” of 57 pages: and two “Surface Contamination Maps”, comprising two high-quality maps, prepared from data obtained by Russian scientists, one depicting, in different colors, four levels of surface ground contamination caused by cesium-137 between 1 and above 40 Ci, km*, over an area of approximately 350 x 1000 km in the Republics of Byelorussia, Russia and the Ukraine in December 1989; and the other, covering a smaller area, showing, in different colors, three levels of surface ground contamination caused by strontium90 between 1 and above 3 Ci/km’, with an inset showing levels of 239Pu and 240Pu above 0.1 Ci/km’ within an approximate 30-km-radius circle around the reactor. In addition to the Preface, Acknowledgements and an Editorial Note, the report comprises eight “parts” (A--H), two annexes and a 44-page list of “Participants in the International Chernobyl Project”. The titles of the parts, together with those of the annexes dealing primarily with the accumulated data, should give some idea of their scope. They are: Part A Part B Part C
Introduction Broadening Understanding Historical Portrayal
4
Review Part D Part E Part F Part G Part H Annex I Annex II
Environmental Contamination Radiation Exposure of the Population Health Impact Protective Measures Conclusions and Recommendations ‘37Csand “Sr Contamination Levels Questions Put to Experts Lists of Participants in the International Chernobyl Project
After the Introduction (Part A), Part B presents a useful survey of the principles of radiation dosimetry, and the effects of the interactions of radiation with people, plants (forests, croplands and meadows, lichen), animals (mammals, birds, reptiles and amphibians, invertebrates) and aquatic organisms. A useful and informative diagram (B Section 3.2.3, Fig. 3) gives “Estimated collective dose commitments (in man-sieverts per gigawatt-year) in relation to different methods of generating electricity”. Briefly the data give the following dose commitments, in man.Sv/GW.y, as functions of the methods used: coal, 4.0; nuclear, 2.5; geothermal, 2.0; peat, 2.0; oil, 0.5; and natural gas, 0.03. (Incidentally, “man/Sv” appears in error twice on this same page.) In the Synopsis (Section 3.3) to Part B it is stated that: “Under normal conditions, the contribution of nuclear power production to radiation exposure is orders of magnitude lower than the exposure to which an individual is subjected to all other sources. In terms of the collective dose commitment, under normal conditions and excluding the commitment from the very long lived radionuclides, average public exposure to the production of nuclear generated electricity is equivalent to one additional hour of average exposure to natural background radiation yearly. When these long lived radionuclides (mainly 14C)are included, the committed dose is equivalent to that due to slightly more than one and a half days of natural background radiation yearly.” Certainly the death and disease tolls of mining coal must still be much greater. With new and safer reactors on the drawing board or in operation in several countries, filthy death-dealing fossil fuels must surely soon be relegated to the trash-can of history even before their supply is exhausted within the 300 or so years remaining of “Hubbert’s pimple” (Hubbert, 1956). “Health Effects of Radiation” are covered in Part B Section 5 and deal with “Deterministic” and “Stochastic” effects from terminal and hereditary to pre-natal (Sections 5.1-5.3). It is fortunate that “The 1990 Recommendations of the International Commission on Radiation Protection” (ICRP, 1991) were circulated in time for the term “non-stochastic”
to be replaced by “deterministic”! But is this even wholly satisfactory when one has widely ranging thresholds depending on whether the dose is acute or prolonged, and a need to use the concept of a “mean lethal dose”? Or are not “deterministic” and “stochastic” just highfalutin and confusing ways of saying, respectively and clearly, that exposure of human tissue to ionizing radiation may cause “cell death” or “cell mutation”? Part B, Section 6, “Environmental Effects of Radiation on Species Other than Man” is a short but interesting description of the responses to radiation of the flora and fauna of the world and the denizens of its waters. Part C, “Historical Portrayal” describes, most vividly the ghastly chaos immediately following the accident, the courageous countermeasures, the evacuation of people and livestock, limiting damage, the behavior of the radioactive plumes, health and ecological effects, medical follow-up measures by doctors, health physicists and medical workers and students, and so on. But this historical portrayal does not seem to trace backwards from 1.24 a.m. on 26 April 1986, to describe the positive void coefficient of the reactor, or the details of the experiment being carried out. Sections 4 and 5 of Part C deal, respectively, with “Socioeconomic Effects and The Sociopolitical Setting”. An introductory paragraph points out amongst other things that hundreds of thousands of inhabitants have had their lives disrupted by the accident. “Close to 115,000 people have been evacuated and there is the possibility that an additional 200,000 or more will be relocated in the future, depending on decisions to be taken on intervention criteria.” And in the next paragraph “Some 650,000 persons were involved in the clean-up of the plant site and the 30 km zone” around the plant. “Over 275,000 are now living in ‘strict control zones’, areas where rigorous radiation surveys continue to be conducted.” Such were the societal and accompanying economic problems facing the authorities in 1991. Contamination” deals Part D, “Environmental with the independent corroboration by the IAC Project “of official and unofficial contamination data for radionuclides in the soil, water and air in the regions . . . that [had] been affected by the Chernobyl accident. In particular, the information presented on the contamination maps [was to] be corroborated.” In view of the enormity of the task, the members of the international group concentrated “on the corroboration of the measurements” made by several scientific institutions and regulatory agencies of the USSR “of the following major radionuclides in the environment: ‘34Cs, ‘37Cs, 90Sr and 239Pu as well as ‘hot’ particles.” In some 80 further pages of Part D there is a plethora of USSR and IAEA data with respect to environmental measurements and intercomparative quality-control exercises between the USSR and IAEA laboratories.
5
Review
Finally in Sections 4.2 and 4.3 the results from the intercomparison exercises and the independent environmental surveys are summarized. The intercomparison exercises gave spotty results, some reliable, some high and some low, but the report itself must be consulted for a reliable assessment. As examples the Soviet results for 13’Cs concentration in soil are reliable; but analyses of 239Puand 90Sr in soil “have a general tendency toward partly significant overestimation of the actual value” (possibly “recommended value” is meant here). And “In the case of vegetation, the actual 13’Csconcentration may be higher than the official analytical result, whereas 90Srresults are more likely to be representative of the actual value” and so on. Then in Section 4.3 “The results obtained by all methods corroborated to varying degrees the general validity of the categories for 13’Cssurface deposition used in official Soviet fallout maps”. It seems that there were no wild discrepancies, but the interested expert must form an opinion by a personal perusal of the report. One slight irritation in Part D is the misuse throughout of the term “nuclide”. A “nuclide” is defined internationally as any species of atom, stable or radioactive; but the latter is also definitively termed a radionuclide, which is a special unstable class of nuclide. Thus to say, as in Part D, Section 3.9 that “nuclide levels outdoors were found to be low” could mean that the concentrations of oxygen and nitrogen were getting low. If one gets tired of using such a long word as radionuclide one can vary it by stating that “activity levels outdoors were low”. Usually the context clarifies the error, but the IAEA knows better! But it is not always so obvious, as in the first paragraphs of Sections 3.7 and 3.8. Part E begins, in Sections 2 and 3 respectively, with a “Description of the Soviet Methodology for Dose Assessment” and a “Review of the Soviet Dose Methodology”. In the latter section Table 4 gives values of the dose to the thyroid from a single acute inhalation of 13’1calculated by the USSR model and by two ICRP models, for 1,6 and 30 days after intake and for different age groups. The results tabulated show a very satisfactory correlation. Measurements to obtain estimates of dosage to the inhabitants due to external irradiation and ingestion of radionuclides were then made in seven selected settlements in the contaminated areas outside the 30-km-radius exclusion zone around the damaged reactor. Between 5 July and 7 September 1990 over 9000 whole-body measurements were made using a mobile counting van provided by the Service Centrale de Protection contre les Rayonnements Ionisants (SCPRI), France. One down-to-earth comment in Part F, Section 4.2.2 “Years of life lost” strikes one’s eye, and gives one pause for thought: “However, those persons who develop radiation induced cancer would eventually have died of some other cause had they not been irradiated.”
From Section 4 of Part E to the end of Part G, some 284 pages, the IAC report is rich with data on radioactive contamination of the local environment and many tables and figures dealing with observed and expected health effects. However, for all but the most dedicated addicts to deadly detail, 19 pages of the Overview comprising Chapters 3, 4 and 5 (with the same titles as Parts E, F and G), provide an outline of the relevant data, and of the International Advisory Committee’s conclusions and recommendations. It is also easier to obtain a much more integrated grasp of the data from the Overview presentation which is in the form of vertical “bar graphs” in different colors, with each vertical bar representing a percentage or a quantity, such as dose with different colors representing different ranges of dose, and the abscissa representing, perhaps, different settlements (e.g. small towns). If, however, the abscissa represents a continuously changing function the “vertical bar” graph becomes a histogram. But, in Parts E, F and G of the main report, the data are almost entirely presented in tables, and it often requires the addition of all, or parts of columns of figures to obtain the overall picture given by the “bar graphs” at a glance. The introduction to Chapter 2 of the Overview states, very succinctly, the raison d’etre of the Chernobyl project: “The Chernobyl accident involved the largest short term release from a single source of radioactive materials to the atmosphere ever recorded. Of the materials released from the reactor core, four elements have dominated the short term and long term radiological situation in the affected areas of the USSR: iodine (primarily 13’1),cesium (‘34Cs, 13’Cs),strontium (primarily 90Sr) and plutonium (239Pu, 240Pu). In addition, highly radioactive fuel fragments (hot particles) were released.” Chapter 3 states the problem: “Information on radiation risk is not well understood by the public. . In the first few weeks after the accident, the significant radiation exposure to the population was due to the 13’1radionuclide. This could have been inhaled from the plume, though that represented only a minor pathway for population exposure. More important were the drinking of milk from cows, grazing on contaminated pastures and the consumption of contaminated leafy vegetables. Increasingly, as time passed, the largest proportion of the exposure arose from the ‘j’Cs radionuclide as a result of both exposure to external irradiation from surface contamination and internal exposure resulting from the consumption of contaminated food.”
6
Review
Thereafter follows a series of “bar graphs” showing “official” (USSR) estimates of dose compared with those of the Chernobyl project in the seven “selected settlements”; official estimates of absorbed dose to the thyroids of women and children due to 13’1in the seven settlements; project measurements of external dose to the population in the settlements by means of 8000 personal film-badge dosimeters made available (to be worn by day and placed by the bed at night) and measured, after two-month exposures, by the French SCPRI; and so on. In the last film-badgedosimeter survey it is stated that 90% of the results were below the detection limit of 0.2 mSv for a two-month exposure. But it seems that in the case of the Novozybkov settlement an error may have been made in translating the data for the 0.2-l mSv range from Table 3-l of Annex 3 to Part E, to the “bar graph” in the Overview. The number of persons in this range of external dose was 564 out of 1882 which is about 30% compared with about 12% in the “bar graph’. But in that low-dose range any such error would be of no importance with regard to policy. The rest of the 55-page Overview is well worth the reading. But here one can only summarize some of the “General Conclusions” and “Detailed Conclusions” reached by the International Advisory Committee: (1) Ranges in the estimate of 70-year (19862056) external and internal dose to residents in selected settlements due to cesium and strontium: IAC external 60-l 30 mSv, internal 20-30 mSv, total 80-60 mSv; USSR external 80-160 mSv, internal 60-230 mSv, total 150-400 mSv. Overall agreement to within a factor of between 2 and 3. (2) The USSR procedures for dose assessment reported to the project use deterministic models that are designed not to underestimate doses. Probabilistic dose-assessment methods should be developed so that more realistic estimates of dose are eventually available and uncertainties in the calculation are fully assessed. (3) The intervention levels of dose for evacuation established by the authorities were consistent with international guidance at the time of the accident. . . . The general policy for administration of stable iodine established by the authorities was in compliance with the international guidance at the time of the accident. The numerical values of the intervention levels, however, were not in full agreement with those recommended internationally. (4) It appears that due account has not been taken by the authorities of the many negative *The reviewer is very grateful to Dr Helen ApSimon details she provided in this paragraph.
for the
aspects of relocation in formulating the relocation policy. There are indications from studies in other areas that the mass relocation of people leads to a reduction in average life expectancy (through increased stress and changes in lifestyle) and a reduced quality of life in a new habitat. . . . In applying a lifetime dose criterion for relocation, it is inappropriate to take account of past doses. Intervention may reduce the risk of adverse health effects in proportion to the dose averted but it can have no influence on doses already received before the intervention. This vivid description and analysis of the tragedy of Chernobyl will, as did the follow-up of those of Hiroshima and Nagasaki, provide extremely valuable data for the practitioners of nuclear medicine and for health physicists, but the appetites of their run-ofthe-mill scientific colleagues, and, presumably, many of the readers of this journal, may well be satisfied by the extremely well-written and well-produced Overview. No reference appears to have been made in this report to the assessment of radionuclide fall-out obtained by computer modeling based on meteorological conditions and the composition and temporal variation of the release. However, extensive calculations were undertaken in the USSR by the late Vladimir Borzilov and colleagues (Sedunov et al. 1989a, b) which provided a very good overall picture of the pattern of atmospheric transport and consequent contamination, both within the local 30-km zone and out to larger distances across the Soviet Union. Even with limited information outside the Soviet Union it was possible to deduce a lot about the accident in the immediate aftermath from modeling applications, including estimates of the quantities of different radionuclides emitted in different phases of the lo-day release period, and the spread of contamination from dry and wet deposition across Europe (e.g. ApSimon et al. 1989). Since the Chernobyl accident more sophisticated models have been developed for use in any future nuclear emergencies, linked to weather forecasting capabilities.* However, the scope of the Chernobyl project was limited to the Soviet Union itself, and the report only makes passing reference to the increase of radiation dose outside the USSR in Part B, Section 3.2.4, Figs 6 and 7 based on a report by UNSCEAR (1988). In the worst area, Southeast Europe, the 30-year dose equivalent commitment due to Chernobyl was only 1.2 mSv compared with a 30-year effective dose equivalent from natural sources of 70 mSv. Views expressed in this review are not necessarily those of the National Institute of Standards and Technology, NIST. W. B. MANN NIST
Review
References ApSimon H. M., Wilson J. J. N. and Simms K. L. (1989) Analysis of the dispersal and deposition of radionuclides from Chernobyl across Europe. Proc. R. Sot. Lond., A 425, 365. Hubbert M. K. (1956) Nuclear Energy and the Fossil Fuels, Publication No. 95. Shell Development Company, Exploration and Production Research Division, Houston, Tex. IAEA (1986) Summar?, Report on the Post-accident Review Meeting on the Chernobyl Accident, IAEA Safety Series No. 75INSAG-1. Review Meeting on the Chernobyl Accident, International Atomic Energy Agency, Vienna. ICRP (1991) The 1990 Recommendations of the International Commission on Radiological Protection, ICRP Report No. 60. Pergamon Press, Oxford. Sedunov Yu. S., Borzilov V. A., Klepikova N. V., Troyanova N. I. and Chernokozhin E. V. (1989b) A set
I
of models for radionuclide transport and its application for estimating source parameters and describing contamination after the Chernobyl accident, Proceedings of the First international Workshop on Past Severe Accidents and their Consequences, p. 125, USSR Academy of Sciences. Sedunov Yu. S., Borzilov V. A., Klepikova N. V., Troyanova N. I. and Chernokozhin E. V. (1989a) Physico-mathematical modelling of regional transport in the atmosphere of radioactive substances following the Chernobyl accident. In International Meeting qf the European Association ,for the Science of Air Pollution, “Evaluation of Atmospheric Dispersion Models Applied to the Release from Chernobyl”, J. ijsterreiche Beitrage xr Meteorologie and Geophysik, Nov. 14-19, 1, Vienna. UNSCEAR (1988) Sources, effects and risks of ionizing radiation. Report to the General Assembly by the United Nations Scientific Committee on the Effects of Ionizing Radiation (UNSCEAR), E.8 1X.7. United Nations. New York.
Copyright
0969-8051/94 $6.00 + 0.00 Q 1994 Pergamon Press Ltd
Review
The International Chernobyl Project Technical Report: Assessment of Radiological Consequences and Evaluation of Protective Measures Report by an International Advisory Committee (printed by the International Atomic Energy Agency in Vienna, 1991) Preface by the Chairman of the International Advisory Committee, Itsuzo Shigematsu, Radiation Effects Research Foundation, Hiroshima, Japan This is probably the most comprehensive international report ever compiled, in the wake of the now “worst-ever” peace-time nuclear disaster. The nuclear power plant in Chernobyl, which is located about 90 km north of Kiev, comprised four reactors, Units 1, 2, 3 and 4. At about 1.24 a.m. Moscow time on 26 April 1986 the reactor cover was blown off and the core laid wide open. By November 1986, 237 persons were being treated for acute radiation syndrome, and at the time of publication of this report a total of 28 had died. The Chernobyl disaster was of international dimensions, and scientists of the USSR sent an interim report to the International Atomic Energy Agency which was summarized in the IAEA Safety Series (IAEA, 1986). The next step to involve international cooperation is best described in the Introduction (Section 3) to the International Advisory Committee (IAC) technical report itself: “In a letter dated 6 December 1989 to the Director General of the IAEA, the Government of the USSR requested that the IAEA initiate and co-ordinate the organization and implementation of ‘an international experts’ assessment of the concept which the USSR has evolved to enable the population to live safely in areas affected by radioactive contamination following the Chernobyl accident, and an evaluation of the effectiveness of steps taken in these areas to safeguard the health of the population’.” From this it is clear that the request objectives:
had two
(1) To examine the assessment of the radiological situation in the contaminated areas
(2) To evaluate the criteria that were developed to ensure safe living conditions in the affected areas. Implicit in this was the corollary objective: to advise the Government of the USSR whether additional protective measures, especially disruptive measures such as relocation, should be implemented in order to ensure safe living conditions for the population still living in contaminated areas. The main report is the IAC technical report, comprising 640 pages. There are then three summary reports, namely the “Proceedings of an International Conference” of 63 pages; “An Overview” of 57 pages: and two “Surface Contamination Maps”, comprising two high-quality maps, prepared from data obtained by Russian scientists, one depicting, in different colors, four levels of surface ground contamination caused by cesium-137 between 1 and above 40 Ci, km*, over an area of approximately 350 x 1000 km in the Republics of Byelorussia, Russia and the Ukraine in December 1989; and the other, covering a smaller area, showing, in different colors, three levels of surface ground contamination caused by strontium90 between 1 and above 3 Ci/km’, with an inset showing levels of 239Pu and 240Pu above 0.1 Ci/km’ within an approximate 30-km-radius circle around the reactor. In addition to the Preface, Acknowledgements and an Editorial Note, the report comprises eight “parts” (A--H), two annexes and a 44-page list of “Participants in the International Chernobyl Project”. The titles of the parts, together with those of the annexes dealing primarily with the accumulated data, should give some idea of their scope. They are: Part A Part B Part C
Introduction Broadening Understanding Historical Portrayal
4
Review Part D Part E Part F Part G Part H Annex I Annex II
Environmental Contamination Radiation Exposure of the Population Health Impact Protective Measures Conclusions and Recommendations ‘37Csand “Sr Contamination Levels Questions Put to Experts Lists of Participants in the International Chernobyl Project
After the Introduction (Part A), Part B presents a useful survey of the principles of radiation dosimetry, and the effects of the interactions of radiation with people, plants (forests, croplands and meadows, lichen), animals (mammals, birds, reptiles and amphibians, invertebrates) and aquatic organisms. A useful and informative diagram (B Section 3.2.3, Fig. 3) gives “Estimated collective dose commitments (in man-sieverts per gigawatt-year) in relation to different methods of generating electricity”. Briefly the data give the following dose commitments, in man.Sv/GW.y, as functions of the methods used: coal, 4.0; nuclear, 2.5; geothermal, 2.0; peat, 2.0; oil, 0.5; and natural gas, 0.03. (Incidentally, “man/Sv” appears in error twice on this same page.) In the Synopsis (Section 3.3) to Part B it is stated that: “Under normal conditions, the contribution of nuclear power production to radiation exposure is orders of magnitude lower than the exposure to which an individual is subjected to all other sources. In terms of the collective dose commitment, under normal conditions and excluding the commitment from the very long lived radionuclides, average public exposure to the production of nuclear generated electricity is equivalent to one additional hour of average exposure to natural background radiation yearly. When these long lived radionuclides (mainly 14C)are included, the committed dose is equivalent to that due to slightly more than one and a half days of natural background radiation yearly.” Certainly the death and disease tolls of mining coal must still be much greater. With new and safer reactors on the drawing board or in operation in several countries, filthy death-dealing fossil fuels must surely soon be relegated to the trash-can of history even before their supply is exhausted within the 300 or so years remaining of “Hubbert’s pimple” (Hubbert, 1956). “Health Effects of Radiation” are covered in Part B Section 5 and deal with “Deterministic” and “Stochastic” effects from terminal and hereditary to pre-natal (Sections 5.1-5.3). It is fortunate that “The 1990 Recommendations of the International Commission on Radiation Protection” (ICRP, 1991) were circulated in time for the term “non-stochastic”
to be replaced by “deterministic”! But is this even wholly satisfactory when one has widely ranging thresholds depending on whether the dose is acute or prolonged, and a need to use the concept of a “mean lethal dose”? Or are not “deterministic” and “stochastic” just highfalutin and confusing ways of saying, respectively and clearly, that exposure of human tissue to ionizing radiation may cause “cell death” or “cell mutation”? Part B, Section 6, “Environmental Effects of Radiation on Species Other than Man” is a short but interesting description of the responses to radiation of the flora and fauna of the world and the denizens of its waters. Part C, “Historical Portrayal” describes, most vividly the ghastly chaos immediately following the accident, the courageous countermeasures, the evacuation of people and livestock, limiting damage, the behavior of the radioactive plumes, health and ecological effects, medical follow-up measures by doctors, health physicists and medical workers and students, and so on. But this historical portrayal does not seem to trace backwards from 1.24 a.m. on 26 April 1986, to describe the positive void coefficient of the reactor, or the details of the experiment being carried out. Sections 4 and 5 of Part C deal, respectively, with “Socioeconomic Effects and The Sociopolitical Setting”. An introductory paragraph points out amongst other things that hundreds of thousands of inhabitants have had their lives disrupted by the accident. “Close to 115,000 people have been evacuated and there is the possibility that an additional 200,000 or more will be relocated in the future, depending on decisions to be taken on intervention criteria.” And in the next paragraph “Some 650,000 persons were involved in the clean-up of the plant site and the 30 km zone” around the plant. “Over 275,000 are now living in ‘strict control zones’, areas where rigorous radiation surveys continue to be conducted.” Such were the societal and accompanying economic problems facing the authorities in 1991. Contamination” deals Part D, “Environmental with the independent corroboration by the IAC Project “of official and unofficial contamination data for radionuclides in the soil, water and air in the regions . . . that [had] been affected by the Chernobyl accident. In particular, the information presented on the contamination maps [was to] be corroborated.” In view of the enormity of the task, the members of the international group concentrated “on the corroboration of the measurements” made by several scientific institutions and regulatory agencies of the USSR “of the following major radionuclides in the environment: ‘34Cs, ‘37Cs, 90Sr and 239Pu as well as ‘hot’ particles.” In some 80 further pages of Part D there is a plethora of USSR and IAEA data with respect to environmental measurements and intercomparative quality-control exercises between the USSR and IAEA laboratories.
5
Review
Finally in Sections 4.2 and 4.3 the results from the intercomparison exercises and the independent environmental surveys are summarized. The intercomparison exercises gave spotty results, some reliable, some high and some low, but the report itself must be consulted for a reliable assessment. As examples the Soviet results for 13’Cs concentration in soil are reliable; but analyses of 239Puand 90Sr in soil “have a general tendency toward partly significant overestimation of the actual value” (possibly “recommended value” is meant here). And “In the case of vegetation, the actual 13’Csconcentration may be higher than the official analytical result, whereas 90Srresults are more likely to be representative of the actual value” and so on. Then in Section 4.3 “The results obtained by all methods corroborated to varying degrees the general validity of the categories for 13’Cssurface deposition used in official Soviet fallout maps”. It seems that there were no wild discrepancies, but the interested expert must form an opinion by a personal perusal of the report. One slight irritation in Part D is the misuse throughout of the term “nuclide”. A “nuclide” is defined internationally as any species of atom, stable or radioactive; but the latter is also definitively termed a radionuclide, which is a special unstable class of nuclide. Thus to say, as in Part D, Section 3.9 that “nuclide levels outdoors were found to be low” could mean that the concentrations of oxygen and nitrogen were getting low. If one gets tired of using such a long word as radionuclide one can vary it by stating that “activity levels outdoors were low”. Usually the context clarifies the error, but the IAEA knows better! But it is not always so obvious, as in the first paragraphs of Sections 3.7 and 3.8. Part E begins, in Sections 2 and 3 respectively, with a “Description of the Soviet Methodology for Dose Assessment” and a “Review of the Soviet Dose Methodology”. In the latter section Table 4 gives values of the dose to the thyroid from a single acute inhalation of 13’1calculated by the USSR model and by two ICRP models, for 1,6 and 30 days after intake and for different age groups. The results tabulated show a very satisfactory correlation. Measurements to obtain estimates of dosage to the inhabitants due to external irradiation and ingestion of radionuclides were then made in seven selected settlements in the contaminated areas outside the 30-km-radius exclusion zone around the damaged reactor. Between 5 July and 7 September 1990 over 9000 whole-body measurements were made using a mobile counting van provided by the Service Centrale de Protection contre les Rayonnements Ionisants (SCPRI), France. One down-to-earth comment in Part F, Section 4.2.2 “Years of life lost” strikes one’s eye, and gives one pause for thought: “However, those persons who develop radiation induced cancer would eventually have died of some other cause had they not been irradiated.”
From Section 4 of Part E to the end of Part G, some 284 pages, the IAC report is rich with data on radioactive contamination of the local environment and many tables and figures dealing with observed and expected health effects. However, for all but the most dedicated addicts to deadly detail, 19 pages of the Overview comprising Chapters 3, 4 and 5 (with the same titles as Parts E, F and G), provide an outline of the relevant data, and of the International Advisory Committee’s conclusions and recommendations. It is also easier to obtain a much more integrated grasp of the data from the Overview presentation which is in the form of vertical “bar graphs” in different colors, with each vertical bar representing a percentage or a quantity, such as dose with different colors representing different ranges of dose, and the abscissa representing, perhaps, different settlements (e.g. small towns). If, however, the abscissa represents a continuously changing function the “vertical bar” graph becomes a histogram. But, in Parts E, F and G of the main report, the data are almost entirely presented in tables, and it often requires the addition of all, or parts of columns of figures to obtain the overall picture given by the “bar graphs” at a glance. The introduction to Chapter 2 of the Overview states, very succinctly, the raison d’etre of the Chernobyl project: “The Chernobyl accident involved the largest short term release from a single source of radioactive materials to the atmosphere ever recorded. Of the materials released from the reactor core, four elements have dominated the short term and long term radiological situation in the affected areas of the USSR: iodine (primarily 13’1),cesium (‘34Cs, 13’Cs),strontium (primarily 90Sr) and plutonium (239Pu, 240Pu). In addition, highly radioactive fuel fragments (hot particles) were released.” Chapter 3 states the problem: “Information on radiation risk is not well understood by the public. . In the first few weeks after the accident, the significant radiation exposure to the population was due to the 13’1radionuclide. This could have been inhaled from the plume, though that represented only a minor pathway for population exposure. More important were the drinking of milk from cows, grazing on contaminated pastures and the consumption of contaminated leafy vegetables. Increasingly, as time passed, the largest proportion of the exposure arose from the ‘j’Cs radionuclide as a result of both exposure to external irradiation from surface contamination and internal exposure resulting from the consumption of contaminated food.”
6
Review
Thereafter follows a series of “bar graphs” showing “official” (USSR) estimates of dose compared with those of the Chernobyl project in the seven “selected settlements”; official estimates of absorbed dose to the thyroids of women and children due to 13’1in the seven settlements; project measurements of external dose to the population in the settlements by means of 8000 personal film-badge dosimeters made available (to be worn by day and placed by the bed at night) and measured, after two-month exposures, by the French SCPRI; and so on. In the last film-badgedosimeter survey it is stated that 90% of the results were below the detection limit of 0.2 mSv for a two-month exposure. But it seems that in the case of the Novozybkov settlement an error may have been made in translating the data for the 0.2-l mSv range from Table 3-l of Annex 3 to Part E, to the “bar graph” in the Overview. The number of persons in this range of external dose was 564 out of 1882 which is about 30% compared with about 12% in the “bar graph’. But in that low-dose range any such error would be of no importance with regard to policy. The rest of the 55-page Overview is well worth the reading. But here one can only summarize some of the “General Conclusions” and “Detailed Conclusions” reached by the International Advisory Committee: (1) Ranges in the estimate of 70-year (19862056) external and internal dose to residents in selected settlements due to cesium and strontium: IAC external 60-l 30 mSv, internal 20-30 mSv, total 80-60 mSv; USSR external 80-160 mSv, internal 60-230 mSv, total 150-400 mSv. Overall agreement to within a factor of between 2 and 3. (2) The USSR procedures for dose assessment reported to the project use deterministic models that are designed not to underestimate doses. Probabilistic dose-assessment methods should be developed so that more realistic estimates of dose are eventually available and uncertainties in the calculation are fully assessed. (3) The intervention levels of dose for evacuation established by the authorities were consistent with international guidance at the time of the accident. . . . The general policy for administration of stable iodine established by the authorities was in compliance with the international guidance at the time of the accident. The numerical values of the intervention levels, however, were not in full agreement with those recommended internationally. (4) It appears that due account has not been taken by the authorities of the many negative *The reviewer is very grateful to Dr Helen ApSimon details she provided in this paragraph.
for the
aspects of relocation in formulating the relocation policy. There are indications from studies in other areas that the mass relocation of people leads to a reduction in average life expectancy (through increased stress and changes in lifestyle) and a reduced quality of life in a new habitat. . . . In applying a lifetime dose criterion for relocation, it is inappropriate to take account of past doses. Intervention may reduce the risk of adverse health effects in proportion to the dose averted but it can have no influence on doses already received before the intervention. This vivid description and analysis of the tragedy of Chernobyl will, as did the follow-up of those of Hiroshima and Nagasaki, provide extremely valuable data for the practitioners of nuclear medicine and for health physicists, but the appetites of their run-ofthe-mill scientific colleagues, and, presumably, many of the readers of this journal, may well be satisfied by the extremely well-written and well-produced Overview. No reference appears to have been made in this report to the assessment of radionuclide fall-out obtained by computer modeling based on meteorological conditions and the composition and temporal variation of the release. However, extensive calculations were undertaken in the USSR by the late Vladimir Borzilov and colleagues (Sedunov et al. 1989a, b) which provided a very good overall picture of the pattern of atmospheric transport and consequent contamination, both within the local 30-km zone and out to larger distances across the Soviet Union. Even with limited information outside the Soviet Union it was possible to deduce a lot about the accident in the immediate aftermath from modeling applications, including estimates of the quantities of different radionuclides emitted in different phases of the lo-day release period, and the spread of contamination from dry and wet deposition across Europe (e.g. ApSimon et al. 1989). Since the Chernobyl accident more sophisticated models have been developed for use in any future nuclear emergencies, linked to weather forecasting capabilities.* However, the scope of the Chernobyl project was limited to the Soviet Union itself, and the report only makes passing reference to the increase of radiation dose outside the USSR in Part B, Section 3.2.4, Figs 6 and 7 based on a report by UNSCEAR (1988). In the worst area, Southeast Europe, the 30-year dose equivalent commitment due to Chernobyl was only 1.2 mSv compared with a 30-year effective dose equivalent from natural sources of 70 mSv. Views expressed in this review are not necessarily those of the National Institute of Standards and Technology, NIST. W. B. MANN NIST
Review
References ApSimon H. M., Wilson J. J. N. and Simms K. L. (1989) Analysis of the dispersal and deposition of radionuclides from Chernobyl across Europe. Proc. R. Sot. Lond., A 425, 365. Hubbert M. K. (1956) Nuclear Energy and the Fossil Fuels, Publication No. 95. Shell Development Company, Exploration and Production Research Division, Houston, Tex. IAEA (1986) Summar?, Report on the Post-accident Review Meeting on the Chernobyl Accident, IAEA Safety Series No. 75INSAG-1. Review Meeting on the Chernobyl Accident, International Atomic Energy Agency, Vienna. ICRP (1991) The 1990 Recommendations of the International Commission on Radiological Protection, ICRP Report No. 60. Pergamon Press, Oxford. Sedunov Yu. S., Borzilov V. A., Klepikova N. V., Troyanova N. I. and Chernokozhin E. V. (1989b) A set
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of models for radionuclide transport and its application for estimating source parameters and describing contamination after the Chernobyl accident, Proceedings of the First international Workshop on Past Severe Accidents and their Consequences, p. 125, USSR Academy of Sciences. Sedunov Yu. S., Borzilov V. A., Klepikova N. V., Troyanova N. I. and Chernokozhin E. V. (1989a) Physico-mathematical modelling of regional transport in the atmosphere of radioactive substances following the Chernobyl accident. In International Meeting qf the European Association ,for the Science of Air Pollution, “Evaluation of Atmospheric Dispersion Models Applied to the Release from Chernobyl”, J. ijsterreiche Beitrage xr Meteorologie and Geophysik, Nov. 14-19, 1, Vienna. UNSCEAR (1988) Sources, effects and risks of ionizing radiation. Report to the General Assembly by the United Nations Scientific Committee on the Effects of Ionizing Radiation (UNSCEAR), E.8 1X.7. United Nations. New York.