Atmospheric Nuclear Tests

The SCOPE—RADTEST Program^** consists of an international collaborative study involving Russia, the U.S.A., the U.K., China, and Kazakhstan. It focuses on the releases of radioactivity that resulted from nuclear test explosions that have taken place at various test sites around the world for peaceful and military purposes.

The recently established SCOPE-RADTEST programme is examining releases of radioactivity due to nuclear detonations which have occurred at various test sites around the world, for peaceful and military purposes, taking into consideration both ecological and human effects. A summary of the proceedings of the NATO/SCOPE-RADTEST ARW held in January 1994 in Vienna is provided.

209 nuclear tests were conducted in the atmosphere, on the ground and under water (Table 1) at two USSR test sites — Semipalatinsk and Northern (Novaya Zemlya). The total energy yield of the tested nuclear devices was ~246 Mt of TNT equivalent, however, after the redistribution their share corresponded to 2.7% and 97.3%, respectively (Table 2).

The potential for the contamination of ground water beneath the Nevada Test Site (NTS) by nuclear testing has long been recognized. The United States has conducted underground nuclear weapons testing at NTS since 1957, and a considerable amount of radioactive material has been deposited in the subsurface by this work. As a part of the U.S. Department of Energy Nevada Operations Office’s Underground Test Area Operable Unit (UGTA OP), the Lawrence Livermore National Laboratory (LLNL) has compiled an inventory of radionuclides produced by underground LLNL weapons tests from 1957 through 1992.

As far back as the first years of intensive nuclear testing, many countries, first of all USSR and USA, established their national systems for monitoring radioactive contamination of the environment. In the time of peace they were focused on the identification of the fact of a nuclear test conduct and on estimation of relevant contamination levels. Those systems in the USSR, USA, and in their defence allies were of global nature.

The problem of radioactive contamination of the natural environment has recently taken on new urgency, particularly since the Chemobyl accident. Existing radioactively contaminated areas are being thoroughly studied; new areas contaminated by well known and insufficiently studied sources are being discovered. Problems of sea and ocean contamination are considered separately, in particular radwaste contamination. This paper deals with the most important issue, i.e., reconstructing the nature and quantitative indices of terrain radioactive contamination which occurred months or years ago.

The nuclear test site located to the west and west-south of the city of Semipalatinsk was one of the largest test sites in the former USSR. It so happened that the first atomic and the first thermonuclear devices manufactured in the USSR were detonated there. A large part of the atmospheric nuclear tests (including the surface and contact ones) and later the underground explosions, both in adits and wells, were conducted there. The first test under the Soviet program of developing and using nuclear devices for peaceful purposes was conducted there as well. All atmospheric tests were performed at that test site, including 99 air and 25 surface explosions [Dubasov et al., 1993b]. There are two types of surface explosions: contact explosion — when the device is placed at the ground level, and the other one — when the devices are secured on the towers of different height. Of course, there was the reason for radioactive contamination of the closest zone and sometimes at the boundary of the test site (Fig.1) [Dubasov et al., 1993b]. According to Deriglazov at al., 1993 and Dubasov at al., 1993a only 11 explosions out of 25 surface tests formed the radioactive fallout patterns beyond the Semipalatinsk Test Site (STS).

This study attempts to simulate nuclear cloud movement and radioactive fallout produced by nuclear explosion tests in the atmosphere.

The dynamic cloud rise method is used in this model for which nuclear debris deposition before cloud stabilization is considered. The cloud height is a function of nuclear weapon yield and the time after explosion. As nuclear debris particles are rising with the cloud, they also fall because of gravity. The nuclear cloud is considered as a cylinder that may be divided vertically into discs. The particle size is also divided into classes. The discs move and drop individually with the cloud and wind. The radioactivity per unit area at any point of ground surface is the sum of each disc activity resulting from landing around a given point.

The particle size and activity distribution is supposed to be log-normal. In the early stage of the burst, the width of the clouds depends upon the weapon yield. After about one hour of burst, it is controlled by large-scale atmospheric turbulence. The horizontal relative diffusion parameter is from Gifford’s (1982) results of Lagrangian-dynamical theory. The radioactivity decay follows the law of t ^−1.25

The calculated results are compared with the DELFIC model for 4 cases. The model demonstrates an increased precision of 50% and is simpler and clearer.

A general view of internal radiation dose caused by local fallout from nuclear explosions is provided. Four aspects involved in the estimation of this dose are discussed including physical and chemical properties of local fallout, metabolic parameters of fission products in the human body, anatomical and physiological parameters for reference Chinese adults, and the methods of rapid estimation of intake of early fallout and internal radiation dose caused by it.

Following the nuclear explosions, people located in downwind areas of resultant radioactive fallout can be exposed to both external and internal doses from the radiation primarily generated by the fission part of the weapon. During the occurrence of fallout, the external dose is caused by radioactive particles passing overhead and deposited on the ground surface, while internal dose is caused by inhalation and ingestion of radioactivity (Glasstone and Dolan, 1977; SIPRI, 1981; Harwell et al., 1984; Conlin and Walker, 1987).

Since the 1950s, extensive studies have been made on the magnitude of external dose to humans from fallout following nuclear explosions, but the literature on internal dose estimation from local fallout in a nuclear war situation is far less abundant than that for external dose. Whicher and Kircher (1987) referred to studies indicating that “…doses to most organs from external radiation from fallout on the ground tend to be of the same order to roughly ten fold higher than internal dose via ingestion”. Rotblat’s estimation was that internal dose is roughly 20% of the external dose from local fallout (Peterson and Shapiro, 1992) with confirmation provided by the result from other studies (Levanon and Pernick, 1988; Ng et al., 1990).

The internal dose from fallout following nuclear explosions are also relevant to Chinese health physicists. This paper is intended as a preliminary discussion in this field based upon Chinese data.

The Off-Site Radiation Exposure Review Project (ORERP) was established by the U.S. Department of Energy to (1) collect, preserve, and disseminate historical data related to radioactive fallout and health effects from nuclear testing, and (2) reconstruct, insofar as possible, the exposures to the off-site public from nuclear testing at the Nevada Test Site and doses to individuals resulting from these exposures. The goals, methods, and example results of the ORERP are presented.

The historical data on the cumulative individual external y exposures are tabulated for communities around the Nevada Test Site for the time periods of 1961 to the signing of the Limited Test Ban Treaty on 5 August 1963, and from then until 1975. The collective exposures during the two time periods are calculated to be 610 and 320 person-R^† respectively. The total collective external γ exposure from 1951 through 1975 for these communities is calculated to be 86,000 person-R. The area considered includes the counties of Clark, Lincoln, Nye, and White Pine in Nevada and the counties of Iron and Washington in Utah; inclusion of Salt Lake City would have substantially increased the calculated collective exposure because of the large population. The methods of calculation are reviewed. Also, the historical data on the assessment of dose via ingestion are reviewed with emphasis on the dose to the thyroid of infants living in St. George, Utah, at the time of fallout from event HARRY on 19 May 1953.

During periods of weapons testing at the Nevada Test Site (NTS) between 1951 and 1958, the Environmental Measurements Laboratory (EML) monitored daily fallout at about 100 sites in the U.S. using gummed-film collectors. These gummed-film data represent the only comprehensive set of actual measurements of fallout during this period for areas outside the immediate vicinity of the NTS. The measured β activities originally reported by EML have been reviewed and reevaluated. This reevaluation corrected a number of errors in the original data set and allowed fairly accurate estimates to be made of specific radionuclide depositions from individual NTS shots. Estimates of the geographical and temporal variations in cumulative ¹³⁷Cs and ¹³¹I depositions from all NTS shots through 1957 are presented, as well as estimates of the relative impact of particular shots and test series. The revised gummed-film estimates of total NTS fallout depositions are compared with estimates based on contemporary and historical soil sample analyses. These reevaluated gummed-film fallout deposition estimates are being extensively utilized in a number of ongoing programs to reconstruct the radiation exposure of the U.S. population from Nevada weapons testing.

A methodology is being developed to estimate the exposure of Americans to ¹³¹I originating from atmospheric nuclear weapons tests carried out at the Nevada Test Site (NTS) during the 1950s and early 1960s. Since very few direct environmental measurements of ¹³¹I were made at that time, the assessment must rely on estimates of ¹³¹I deposition based on meteorological modeling and on measurements of total ß activity from the radioactive fallout deposited on gummed-film collectors that were located across the country. The most important source of human exposure from fallout ¹³¹I was due to the ingestion of cows’ milk The overall methodology used to assess the ¹³¹I concentration in milk and the ¹³¹I intake by people on a county basis for the most significant atmospheric tests is presented and discussed. Certain aspects of the methodology are discussed in a more detailed manner in companion papers also presented in this issue. This work is carried out within the framework of a task group established by the National Cancer Institute.

Individuals living near the Nevada Test Site were exposed to both ß and γ radiations from fission products and activation products resulting from the atmospheric testing of nuclear devices. These exposures, and the resultant doses, were functions of the amount of material deposited, the time of arrival of the debris, and the amount of shielding afforded by structures. Results are presented for each of nine generic life-styles. These are representative of the living patterns of people residing in the area. For each event at each location for which data exist, a representative of each life-style was closely followed for 30 d. The results of these detailed calculations were then extrapolated to the present, employing a stochastic model. Results displayed are the geometric means and standard deviations derived from 25 independent determinations of the various quantities shown. For each determination, required parameters were randomly selected from appropriate distributions. Calculations yielded estimates for: 1) whole-body and skin dose due to γ rays from material on the ground; 2) skin dose due to ß particles from material deposited directly on the skin; and 3) skin dose due to ß particles from material deposited on the ground. Organ dose estimates were established from the whole-body dose using appropriate conversion factors. For the homemaker life-style, the uterus dose was also calculated as a function of time for 9 mo. This assisted in estimating fetal dose as a function of gestation.

The report presents the results of an assessment of potential doses to future inhabitants of the Maralinga and Emu areas of Southern Australia, where nuclear weapons tests in the 1950s and 1960s have resulted in widespread residual radioactive contamination.

Annual effective doses of several millisieverts would be expected to result from continual occupancy within contours enclosing areas of several hundred square kilometres. Larger predicted annual effective doses — of the order of 0.5 Sv — would be expected to occur from 100% occupancy in the small regions immediately surrounding the test sites, but continual occupancy of such areas is highly unlikely because of their small size. The most significant dose pathways are the inhalation of resuspended activity and ingestion of soil by infants. An analysis of the effects of uncertainties in the dose calculation has indicated the uncertainty distribution on predicted doses from the inhalation pathway.

The urgency of the problem of assessing the environmental impact of nuclear tests conducted in the southern and northern latitudes of our planet is obvious, and the RADTEST project offers a perspective for solving it by consolidating the efforts of international experts who have information about the specificity of nuclear tests conducted at concrete test sites and who are developing a methodology for studying and analyzing their aftereffects. Our intention of participating in this project is stimulated by the opportunity to use the results which are successively generated within the scope of the Targeted Comprehensive Program of Investigations (TCPI) of Seismic, Radiological and Sanitary-Ecological Situations in the Regions of the Semipalatinsk and Northern Tests Sites (“Region” Program). The leading TCPI implementor, the Radium Institute named after V. G. Khlopin, and about 20 different research establishments are facilitating its execution. The Reference Data Publication [Mikhailov et al., 1992] furnishes an excellent example of the cooperation of scientific teams within the Region-2 TCPI framework, aimed at providing a scientific support to current radiological studies related to the operations of the Northern Test Site (NTS); it also presents a scheme of a systematic approach to comprehensive studies of test-site environmental impacts (fig. 1) which takes into consideration the factors of medical geography and elements of various international programs under the auspices of SCOPE, WHO/FAO, and the UN.

This autumn it will be 45 years since the early August morning in 1949 when the first Soviet nuclear device was exploded at the Semipalatinsk Test Site (STS). At a solemn banquet on that occasion, the head of the Governmental Commission at STS, Lavrenti Beriya, asked Igor Kurchatov, “What name did we give to our device?” Quickly Kurchatov answered, “RDS-1.” “What does that mean?” asked Beriya again. “Russia! Doing! Itself!” replied Kurchatov, and all those present began to applaud, as they were certain that the “Master” (Joseph Stalin) had okayed the name. This was the birth of a new nuclear power and marked the first day of a large-scale military confrontation between the USA and the Soviet Union. In 1952 the U.K. started nuclear testing, followed in 1960 by France and in 1964 by China. The total number of atmospheric nuclear tests between 1945 and 1980 was 423 [UNSCEAR, 1982]. The recent UNSCEAR report [UNSCEAR, 1993] cites a new figure: 520 atmospheric nuclear explosions (including 8 underwater). However, the total yield remained at the level of 545 Mt: 217 Mt from fission and 328 Mt from fusion (Table 1 [UNSCEAR, 1982]). A major part of fission and fusion energy was released before August, 1963, when the Partial Test Ban Treaty was concluded. After that date only 10.8% of fission and 2.7% of fusion energy were released to the atmosphere by France and China. All the nuclear powers switched to underground nuclear-explosion programs. The estimated number of this type of nuclear tests conducted in the period from 1957 to 1992 is 1,352 explosions with a total yield of 90 Mt [UNSCEAR, 1993]. As a rule, a well-contained underground nuclear explosion results in a minimal release of radionuclides into the atmosphere. However, other radioactive materials were released to the atmosphere as a consequence of uncontained underground nuclear explosions (for example, excavation underground tests under the Plowshare Program in the U.S. and similar programs in the USSR or an abnormal radiological situation after an underground explosion) and led to local or regional environmental contamination.

Nuclear tests have resulted in a comprehensive global environmental contamination with radioactive substances, primarily with such biologically significant ones as ⁹⁰Sr and ¹³⁷Cs. By the time of systematic nuclear testing, the world science has already accumulated a certain experience in investigating the consequences of radiation impact on human beings (occupational exposure, medical exposure, Hiroshima and Nagasaki, etc). However, a new source of radiation effects, i.e. environmental contamination and, hence, food contamination, resulted in a systematic internal and external irradiation at low dose rates of practically the entire population of the Earth that required comprehensive, broad-scale investigations of potential hazards of global fallouts.

In made-sources, excluding medical exposure, the fallout from atmospheric nuclear weapon tests and some serious nuclear accidents are still worthy of attention because of the detrimental effects of radioactive contamination to humankind.

In order to study the long-term effects of participating in the United Kingdom’s atmospheric nuclear weapon tests and experimental programmes which took place in Australia and the Pacific Ocean between 1952 and 1967, a total of 21,358 men who took part in the tests have been identified from archives of the Ministry of Defence and followed up to 1 January 1991. The mortality and incidence of cancer in these men were compared with those in 22,333 controls selected from the same archives. In the period of more than 10 years after initial test participation, mortality was found to be low compared with that expected from national rates both for all neoplasms and for all other causes of death (SMRs of 0.84 and 0.82, respectively), and rates in test participants and controls were very similar (RR = 0.97, 90% CI 0.91, 1.04 for incidence of all neoplasms and RR = 1.02, 90% CI 0.96, 1.08 for mortality from all causes of death other than neoplasms). Rates were also examined for leukaemia and 26 other kinds of cancer, and for 15 other causes of death. It is concluded that participation in the nuclear weapon programme testing programmes has not had a detectable effect on the participants’ expectation of life or on their risk of developing cancer or other fatal diseases. The suggestion from a previous study that participants may have experienced small hazards of leukaemia and multiple myeloma is not supported by the additional data, and the excesses observed previously now appear likely to have been a chance finding, although the possibility that test participation may have caused a small risk of leukaemia in the early years of the tests cannot be completely ruled out.