Preliminary External - Dose Estimates for Future Bikini Atoll Inhabitants

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The field portion of the June 1975 radiological survey of Bikini and Bneu Islands of Bikini Atoll was accomplished by a very intense’and thorough effort by 21 people representing six different organizations. The number of samples collected and the amount of information obtained during the ten-day survey is a direct result of the cooperation and diligent effort of the following individuals: Environmental Protection Agency, Las Vegas, Nevada Lawrence Livermore Laboratory Lawrence Livermore Laboratory Lawrence Livermore Laboratory Trust Territory of the Pacific Islands Lawrence Livermore Laboratory Lawrence Livermore Laboratory Nevada Operations Office (ERDA) Trust Territory of the Pacific Islands, Division of Operational Safety .(ERDA) Lawrence Livermore Laboratory University of Washington Lawrence Livermore Laboratory -Environmental Protection Agency, Las Vegas, Nevada Lawrence Livermore Laboratory Nevada Operations Office (ERDA) Lawrence Livermore Laboratory .The survey crew extends its thanks to Dr. Guy Haywood for medical support during the survey operation and to the Nevada Operations.Office and Pacific Area Support Office< for’ support services which resulted in a smooth and efficient survey. Support from the ‘i Kwajalein’Missile Range and. the site contra-ctor, Global .Associates, as well as from the The outstanding cooperation .of personnel from the Trust Territory of the Pacific Islands. and. from the Office of the District Administrator of the Marshall .Is-lands, ,as well as that of the Bikini people-, played an important part ‘in the successful completion

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FOR FUTURE BIKINI ATOLL INHABITANTS ’ With the objective of evaluating the.potential radiation doses that may be received by the returning Bikinians, a survey was conducted during June 1975 of the residual radioactivity in the terrestrial environment on Bikini and Eneu Islands of Bikini,Atoll. The survey included measuring environmental gamma-ray exposure rates for use in evaluating the external gammadoses, and collecting numerous soil, lens water, and vegetation samples for use in assessing the.internal doses via pertinent food chains. This report describes the gamma-ray exposure rate measurements and their use in conjunction with population statistics and expected life styles for evaluating the potential external gamma-ray doses associated with various options for housing locations on Bikini and Eneu Islands. (The evaluation of the internal dose’ contribution via food chains will be published in subThe results of the survey reveal’ that the external exposLre rates on Bikini Island are highly variable. Values near the shores are generally of the order of lo-20 uR/hr, while those within the interior average.about 40 uR/hr with a range of- roughly 30-100 uR/hr. Eneu Island, however, is characterized by more or less uniformly distributed gammaradiation levels of less than 10 uR/hr over the’entire island. For the external dose determination a set of most likely living patterns was chosen. These were based.upon the various options for housing locations along the’lagoon road and within the interior ,.portions of Bikini Island as well as, aloilg the lagoon side of EneuIsland. As expected, living on .Eneu fsland.results. in the lowest doses:: O.l? rem during the fir.st year and 2.7 rem during 30 years 6 The highest values, 0.28 rem during the first . year’and 5.7 rem over 30 years, may potentialiy be received by inhabitants living within the interior of Bikini -Island.. Other options under consideration produce intermediate. A radiological, survey of Bikini and En& Islands of the Bikini Atoll was conducted during June- 1975 to assess the potential radiation &es that maj! be received by. the the Pacific. It is sit.uated in the northern part of Micronesia. in the- Central Pacific Ocean about 3600 km southwest of ~Iionolulu’. The atoll consists of a n&be* of small . islands on an elliptical cora-1 reef surrounding a 1;agoon with major and minor axes having dimensions of 35 and 27 km; respectively. The islands are shown in Fig. 1. : The total

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land area is about 6 km2, and the land height generally level. The islands vary in size from small sandbars of a few hundred square area to islands having areas of about 2 km’. The islands of most importance immediate habitation are Bikini and Eneu Islands. A total of 23 nuclear tests took place during the testing period. Most of the tests were conducted on barges anchored in the lagoon or on the reef. All islands were subjected to varying degrees of close-in fallout. Generally, the prevailing winds transported the radioactive debris clouds toward the southwest. One exception, however, occurred during the Bravo event when unexpected changes in the wind directions caused the cloud to travel toward the east over Bikini Island. Most of the radioactive contamination on Bikini Island is due to this event. This recent survey was designed to evaluate the potential external gammadoses associated with proposed housing locations on Bikini and Eneu Islands, and to evaluate the potential doses received through the major terrestrial food crops on the atoll. The survey teams therefore directed their efforts in three major areas: (1) Gamma-ray exposure rate measurements and surface soil collections will provide a means for evaluating . the external gammadoses associated with proposed housing locations. Gammaspectral analyses,of the soil samples will provide information on the fractional contributions of different radionuclides to the external dose. This will enable us to evaluate long-term whole-body doses from this exposure pathway. (2) Collection of lens water samples.will suppiy information on the radionuclide activity levels in the groundwater and on the cycling of radionuclides in the atoll ecosystem. In addition, salinity measurements and lens capacity measurements were made at each well to determine the quality and quantity soil collections will provide information concerning the radionuclide concentrations in critical food products to evaluate the dose contribution via .food chains. It will also provide information on .the correlation between soil type, .soil radiondclide concentrations, ‘. necessary in order to develop predictive models. This is the first in a series.of reports which will be based upon the June 1975 survey data; it is directed only at preliminary estimates of the external gamma-ray doses.. The report describes our techniques for measur.ing geographical variability.of the gammaray exposure rates on Bikini and Eneu Is-lands and how we used the resulting data in conjunction with population stati.stics and=expected living patterns ,to estimate the extema.1 gammadoses.. Estimates. of the integral first-year and $O+ear doses associated. with various options for housing locations on Bikini and Eneu Islands’ are. presented, and compared with appropriat-e guide values. The reader shduld.notg that these estimates are still preliminary in nature and may undergo changes when all of the resdts of -the survey become .avai-lable. Further information concerning radiation doses that may potentially be received via groundwater and vazious’ food chains will be published upon tffe compl-etion 0; the analyses of the many soil, vegetation; and water samples that were collected during

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Techniques Used to Measure Gamma-Ray Exposure Rates Since the external dose is expected to be almost entirely due to gamma-emitting radionuclides, with only minor contributions from alpha and beta emitters, it was essential to obtain the best possible description of the geographical variability of the gamma-ray exposure rates on Bikini and Eneu Islands. Several techniques were used to measure these exposure rates, since each technique has its own set of limitations (i.e., nonlinear energy response, portability of equipment, and extent of geographical coverage). These techniques included making measurements with the use of portable, hand-held NaI scintillation detectors, a commercially available pressurized ion chamber, and two types crystal with ratemeter readout. The instruments were calibrated with a 137Cs point source on the primary calibration range of the National Environmental Research Center, Las Vegas, Nevada. Since the response of this instrument is energy-dependent, it overresponds when the gammaflux is due to scattering from a buried area source rather than from a point source as used in the calibration. Therefore it was necessary to normalize these measurements to those obtained by the pressurized ion chamber. This instrument utilizes a stainless steel sphere filled with high-pressure ultrapure argon.. The current produced meter with digital readout. The instrument exhibits an essentially flat energy response over all gamma-ray energies of interest to this survey. It was calibrated by the manu- ’ facturer and verified by several ERDAlaboratories. Measurements of the exposure rates at 1 m above. the ground were made with the NaI scintillators at about 2500 locations on a.30-m rectangular grid over the entire surf&e of Bikini Island and at about 200 locations on a 120-m grid on Eneu Island. Comparison y . measurements between the pressurized ion chamber and the NaI. scintillators were aade at. * . roughly 200 locations selected -from within the interior portions of the islands, the. village areas , and along the beaches, In addition, the gamma.exposure rates are currentiy being.measured by means of LiF and CaF2:dy TLD chips that.were placed at some 80 locations on the two islands. The LiF chip’displays an essentially flat energy -response and excellent thermal stability. Our extensive experience with this chip in a variety of environmental radiation measure-. ment programs at Livermdre as well as the Enewetak s-urvey indicate6 that the resdlts obtairied by this detector may also serve as an excellent reference to which measurements. obtained by other techniques can be compared. The CaF2 TLDs have an enhanced energy response at low energies and may be used to detect possib1e low-energy radiation fields. An attempt is also being made to assess the contribution of the beta’radiation to the total exposure rate by placing absorbers of various thicknesses over arrays of.TLDs at

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The chips were annealed on the atoll immediately prior to being placed on the islands for the roughly three-month exposure period which ends during September 1975. At that,time, the chips will be retrieved for readout at LLL. Calibration and signal fading studies are being carried out by exposing separate sets of chips to a 137cs point source before and after the exposure period. The results of the TLD measurements will appear in a later report on this survey. The geographical variability of the gammaexposure rates for Bikini and Eneu Islands are shown in Figs. 2 and 3. These data, expressed in units of microroentgens per hour (uR/hr), have been normalized to the output from the pressurized ion chamber. Note that the levels for Bikini Island are considerably higher than those for Eneu Island. Also note the complex patterns displayed on Bikini Island. This complexity may possibly be due to the inhomogeneity in the original fallout pattern produced by the Bravo event as well as the extensive earth-moving activities performed over the entire island as part of the agricultural rehabilitation program. The exposure rates near the shores are typically of the order of lo-20 uR/hr, while the elevated interior values vary over a wide range of roughly 30-100 uR/hr. The,interior portions of the island may be visualized as having a general background of about 30-40 uR/hr with numerous irregularly shaped areas exhibiting elevated levels superimposed in a random fashion over this general background. Eneu Island, on the other hand, is characterized by low (less than 10 uR/hr) and more or less uniformly distributed gamma’radiation levels over the entire island. These exposure rates are expected to be,accurate to within, approximately lo%, although final confirmation of this must wait until the results of the TLD program become available. No corrections . have been made for the natural background contribution. Based upon our ‘experience at Enewetak Atoll’ and the data of Bennett and Beck2 collected during .the 1967 Bikini survey, we expect the primary contribution to the gamma exposure rates to be due to 137Cs and 6oCo activities in the. soil. Trace quantities of other ‘gammaemitters such as 12’Sb, “‘Eu, and 241Am are expected to contribute at most a few percent to the total exposure rates. -The gammaspectral analyses of the several hundred soil samples’collected on both islands will reveal the current mix of these In addition to the gamma-ray exposure rates, one needs to consider the expected living patterns of the future inhabitants in order to evaluate the external dose problem. Of course, many uncertainties are inherent in the prediction of future living patterns: However, the fcllowing cases ; shown in Table 1, have been proposed as a reasonable selection of possible conditions that would cover the range of doses that could be received by any sizable segment of the population. 3 This will allow any other reasonable

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Table 1. Assumed living patterns. 1 No use of Bikini Island for the present as a housing or food production area. Use of Eneu Island for housing and food production. Unrestricted use of fish throughout the atoll. 2 Limited use of Bikini Island with residence in houses already constructed. No additional house construction on Bikini Island for the present. Use of coconuts grown on Bikini Island. Other food crops grown on Eneu Island only. Unrestricted use of fish from all parts of the atoll. Use of Bikini Island lens water for agriculture only. 3 Limited use of Bikini Island with the following remedial actions taken: (a)-placing 5 cm of clean coral gravel around the existing houses out to a distance of 10 m, and (b) removal of the top 20 cm of soil and replacement with clean soil out to a distance of 10 m around the houses. All foods grown on’Bikini Island are acceptable except pandanus and breadfruit. Unrestricted use of fish throughout the atoll. Use of Bikini Island lens water for agriculture only. 4 Limited use of Bikini Island with Phase II houses constructed only along the lagoon road within area 2 of Fig. 4. Remedial actions 3a and 3b are taken. Use of coconuts grown on Bikini Island. .No use of pandanus and breadfruit from Bikini Island. Unrestricted use of fish throughout the 5 Phase II housing construction ‘according to .the, Preliminary Bikini. Atoll Master Plan, but no use of pandanus and breadfruit from Bikini Island. Unrestricted use of fish throughout the atoll. Lens water for agriculture and washing only. 6 Phase II housing constructed according to the.Preliminary Bikini Atoll Master Plan. All foods grown on Bikini Island are acceptable. Unrestricted’ use of fish throughout the atoll. Lens water.used for agriculture and . ‘pattern to be inferred by proper utilizetion of the results obtained for these cases. Note that the cases also include assumptions on the food production and consumption plans of the returning population. This. information is on,ly required for the internal -dose assessment via the specific -food chains, and hence is ,not-pertinent to the external dose The cases, are based upon the assumpt%on that the people will reside -on &he; purposes of this report, the cases are primarily directed. toward assessing the external dose associated with various opti:ons .for housing locations :on the two isiands. The first .remaining cases assume’residence on Bikini Island at different vil,lage sites with various remedial actions baing taken to reduce the’exposure rate-s. Thus, cases 2-4 assume the residences are situated along the-.,lagoon road on Bikini Island, areas ,l and 2 in Fig. 4, ‘while cases 5 and 6 assume the people will live within the interior portions of the.isiand,

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Table 2. Population breakdown by age and geographical living patterns. Infants and Children and small children adolescents Men Women Fraction of population (%) 16 41 22 21 Fraction of time spent …