Analysis of Radiation Exposure Service Personnel on Rongerik Atoll Operation Castle, Shot Bravo

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ANALYSIS OF RADIATION EXPOSURE SERVICE PERSONNEL ON RONGERIK ATOLL OPERATION CASTLE, SHOT BRAVO Past Office Box 130.3, 1710 Goodridge Drive, McLean, Virginia 27102, (703B2143(XI

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REPORT DOCUMENTATION PAGE 4 PERFORMING ORGANIZATION REPORT NuMBER(S) 5. MONITORING ORGANIZATION REPORT NUMBER(S) 6a. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF Monitoring ORGANIZATION International Corporation Defense Nuclear Agency 3a. NAME OF FUNDING i SPONSORING 8b OFFICE SYMBOL 9 PROCUREMENT INSTRUMENT IDENTIFICATION NUMSER PROGRAM PROJECT TASK WORK UNIT Washington, DC 20305 ELEMENT NO. NO NO. ACCESSION NO. ANALYSIS OF RADIATION EXPOSURE, SERVICE PERSONNEL ON RONGERIK ATOLL, 3a TYPE OF REPORT 13b. TIME COVERED 14. DATE OF REPORT (Year, Month, Day) 1S. PAGE COUNT This work sponsored by the Defense Nuclear Agency under RDT&E RMSS Code 17 COSATI CODES 18. SUBJECT TERMS (Continue on necessary lnd identify by block number) FIELD GROUP I SUB-GROUP Operation CASTLE, Sho Rongerik Atoll Radiation Exposure, Assess . 19 ABSTRACT (Continue on reverse If necessary and identify by block number) External and internal doses are reconstructed for the 28 American servicemen statio~,e Atoll, Marshall Islands, who were exposed to fallout on 1-2 March 1954 from Shot Brav of Operation CASTLE. External doses are determined from limited radiation survey and film bad’~”information. Internal dose commitments are derived from urinalysis data. The magnitude of the calculated activity intake suggests the principal pathways. Reconstructed film badge doses are approximately 40 rem, with adjustments from individual activity scenarios, as available. Internal dose commitments to the thyroid and large intestine (nearly all firstyear dose) provide the only significant increments to the external dose. Total doses are approximately 230 rem to the thyroid, 115 rem to the lower large intestine, 85 rem to the upper large intestine, and about 40 to 50 rem to all other organs. 20. DISTRIBUTION / AVAILABILITY OF ABSTRACT 21 ASSTRACT SECURITY C SSIFICATION )D FORM1473,84 MAR 83 APR edition maybe used unt!l exhausted. All other ldit!ons l re obscdets. SECURITY CLASSIFICATION OF THIS PAGE

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LIST OF TABLES INTRODUCTION AND SUMMARY BACKGROUND AND AVAILABLE DATA 2.2 AVAILABLE DATA AND ASSUMPTIONS TECHNICAL APPROACH -- EXTERNAL DOSE 3.2 AVAILABLE FILM BADGE DATA 3.3 COMPARISON OF ESTIMATED FILM BADGE DOSES WITH FILM BADGE DATA TECHNICAL APPROACH -- INTERNAL DOSE 4.3 PATHWAYS AND DOSE CONVERSION FACTORS RESULTS AND COMPARATIVE ANALYSIS 5.2 COMPARISON WITH PREVIOUS DOSE DETERMINATIONS “6 LIST OF REFERENCES Appendix SAMPLE CASE INTERVIEW

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LIST OF TABLES Preliminary dose estimates for personnel on Film badge dosimetry results, Rongerik Atoll, 1-2 March 1954 Comparison o dosimetry results with doses calculated. tm ,+’~? ! Reconstructed gamma radiation doses for military personnel stationed on Rongerik Atoll, 1 and 2 March 1954 Fifty-year internal dose commitments for military personnel stationed on Rongerik Atoll, 1 and 2 March 1954 Calculated film badge dose for one airman (CN 406)

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.< INTRODUCTION AND SUMMARY During t$e period 1-2 March 1954, twenty-eight Army and Air Force personnel stationed at ~ongerik Atoll in the Marshall Islands were exposed to radioactive fallout from Shot Bravo/of Operation CASTLE. The purpose of this report is to determine the whole body gamma radiation dose received by these personnel prior to their evacuation from the atoll, plus their organ dose commitments from internal emitters. on Rongerik, modeled deposition, measurbd decay rates, and a later reading on Rongerik. Personnel activity scenarios are considered in conjunction with radiation shielding factors to arrive at film badge doses on an individual basis. Although film ~ badge readings are available, they relate inadequately to personnel dose. Readingsthat reflect well-specified exposures indicate good agreement with corresponding inhalation and ingestion of .-’Bravo fallout radionuclides are calculated. Intake of iodine-1 31 is determined frorn-tiie body metabolism of iodine that led to a measured activity of 1-131 in a pooled urine sample taken 17 days after ‘,Bravo. The radionuclide inventory for the time of intake is normalized to the level of 1-131 activity, thereby indicating the full intake of radioactivity. ~lib se conversion factors for each radionuclid~ are developed for calculation of internal dose commitments to c organ. The cal 76 rem. Other or an doses do not add significantly to the externafia-rnrn-a dose: ~.

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BACKGROUND AND AVAILABLE DATA The total yield of the thermonuclear explosion was approximately 15-megatons TNT equivalent. The nuclear device was mounted on a barge in shallow water, about seven feet above the surface of a coral reef. The radioactive fallout from Shot Bravo contaminated an area extending from about 20 statute miles upwind to over 330 miles downwind and varying in width to over 60 miles. Included within the area of major contamination were Bikini Atoll and three downwind atolls: Ailinginae Atoll, Rongelap Atoll, and Rongerik Atoll (References 1, 2). Among these atolls, Marshallese were present on Ailinginae and Rongelap, and American servicemen only on Rongerik. ~ Twenty-eight servicemen (25 Air Force personnel and 3 Army personnel) operated a weather station on Rongerik Atoll, about 150 miles east of Bikini. At approximately 1407 hours (almost 7!4 hours after the Bravo detonation) the deposition of fallout cm Rongerik was detected by a low-level gamma radiation monitoring instrument and subsequently observed visually. At 1500 hours, a message was sent to Joint Task Force (JTF) Headquarters on Enewetak Atoll (Reference 3) notifying them of the fallout on Rongerik. Approximately one-half hour later, a reply came back from Enewetak instructing the military personnel on Rongerik to put on long-sleeved shirts, trousers, hats, and GI shoes, and to remain inside as much as possible, consistent with their normal work routine. At about 2330 hours, another message was received directing all personneI to cease operations and move inside permanent buildings. At 1245 hours on 2 March 1954, eight men, the first eight on the alphabetical detachment roster, were evacuated from Rongerik to Kwajalein Atoll by airplane; the remaining twenty men were evacuated by airplane at approximately 1800 hours

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Upon arrival at Kwajalein Atoll, the personnel evacuated from Rongerik were monitored for personal contamination and decontaminated. The decontamination program, consisting of repeated showers and radiation monitoring, continued from 2 March through 6 March. While at Kwajalein, the film badges that had originally been issued to the Rongerik detachment were collected and processed. In addition, urine samples, both pooled and individual, were collected and sent to laboratories in the United States for analysis. Late in April, the servicemen from Rongerik were transferred from Kwajalein to Tripler Army Hospital (Honolulu, Hawaii) for further observation and subsequent return to duty (References 3, 4). 2.2 AVAILABLE DATA AND ASSUMPTIONS Just prior to the first evacuation on 2 March, a gamma intensity reading was obtained with an uncalibrated AN/PDR-39 radiation survey meter. Because the operating condition of the instrument was not known at the time of its use, this! reading (2000 mR/hr @ H+28.5 hours-- Reference 5) is used only to indicate the general magnitude of the fallout intensity at the time of the first evacuation. The first radiological survey with calibrated instruments on the atoll was conducted on 10 . March 1954, nine days after the shot. At this time the rad-safe survey team encountered average radiation intensity readings of 280 mR/hr on the island where the military personnel had been stationed. The ordy other radiation intensity data available from Rongerik were obtained on 1 March when a low-level gamma background monitoring instrument at the weather station began to register at 1407 hours and then went off scale (100 mR/hr) at 1437,4‘~1 ,~ ~!~’- of gamma intensity with time. Unfortunately, the utilized were from Bikini Atoll and may not be were made to determine the ~J.= --- only data complete enough to be completely representative of the fallout decay on Rongerik Atoll. Radiation intensity readings obtained from the Bikini lagoon (How Island) indicated decay rates that varied considerably from the traditional t- 1.2 rule . Average values for the ~exponent, obtained with several gamma ionization time-intensity meters on Bikini (Reference 6), are as follows:

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in comparison to t , of this significant neutron-activation products of the U-238 in a thermonuclear device. i3ecaus~l fallout decay rate data on Rongerik Atoll are not available, dose calculations for ~ilitary personnel on Rongerik are made using the measured decay rates on Bikini and the measured radiation intensity on Rongerik Atoll (280 mR/hr at D+9 days). In addition, the radiation environment during fallout deposition must be more explicitly defined. From the gamma background_monitoring instrument on Rongerik, the time of arrival of measurable fallout fro Brav ga~.&n determined to ~ be 1407 hours, or 7.4 hours after the shot. The radiation lme-intensit y recordings on - Bikini indicated that, once fallout began, a period of 1-2 hours elapsed while fallout was occurring before the radiation levels reached a maximum and began to decay, even though fallout was still continuing (Reference 7). Other data were obtained aboard three Task Force 7.3 ships that were positioned at various distances downwind,.. . from the ,,~ra~>GZ. On one of these ships-- the GYPSY--fallout commenced approximately 7 hours after detonation, about the time of arrival on Rongerik. The GYPSY data indicated that at least 4 hours of significant fallout occurred. The exact duration cannot be determined because ship washdown procedures were initiated while the intensity was still increasing. The data indicate, however, that at locations downwind from Bikini, the time to maximum intensity was somewhat longer than it was on Bikini. Based on these data, a five-hour period of significant fallout deposition is used to characterize the radiation environment on Rongerik. It is assumed that 90 percent of the fallout, by mass, was deposited during this interval.

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on Bikini Atoll Deposition of Rongerik Time After Burst (hr) Figure 1. Fallout intensit versus time after burst (Shot Bravo) {normalized to in ensity reading on Rongerik. >..,$.

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~G~In order to calculate the radiation doses to personnel on Rongerlk fro Bravo fallout, the free-field radiation environment must be specified mathematically. Further, the calculated doses are dependent on any protection or shielding that was provided by buildings in which they stayed until they were evacuated. (1) Free-Field Radiation on Rongerik Based on the available data, the free-field radiation environment on Rongerik is estimated as follows: @yf:’’:~o (For times greater than 48 hours after burst, the radiation decay ollowed a t -1.5 decay rate. From the radiation intensity of !28 R/hr measured on Rongerik on 10 March (about 216 hours after burst), the intensity at 48 hours after burst (148) is: ‘1-.815Similarly, from I 8 and the radiation decay according to t 48 hours after detonation, the intensity after cessation of fallout through the time of During fallout deposition, this decay applies to landed fallout particles (the change in decay exponent at 10 hours is too early in the deposition to noticeably affect the calculations). Thus, it is necessary to determine the fraction of time-normalized activity (or mass, for constant specific activity) deposited with time. This deposition is assumed to occur as a Gaussian (normal) distribution in time, reflecting a similar

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spatial (horizontal) distribution in the nuclear cloud. A correction is applied for lateral diffusion of the cloud. For an increase in cloud area in direct proportion to time, the concentration of fallout particles is inversely proportional to time. The rate of deposition with time (T) is of the form: Parameters a and b are chosen to match the meter reading Q~ 100 mR/hr at 7.9 hours and for the central 90 percent of the deposition to occur in 5 ho’uis;~”he normalization to total deposition is provided by c. Fallout accumulated through time t is represented by the time integral of the above expression. The choice of the lower limit of integration is not crucial; the observed time of fallout onset is satisfactory. The complete expression for intensity with time is then:a Figure 2 depicts this relationship, which serves as the basis for the dose calculations. The peak intensity of 7 R/hr occurs at the end of the estimated interval of significant fallout (9 to 14 hours). (2) Personnel Activities on Rongerik Atoll, 1-2 March 1954 After being evacuated to Kwajalein, each person who was on Rongerik was interviewed to determine his specific activities during the period 1 March until evacuation on 2 March. Other pertinent data concerning their exposure conditions ‘*”were also. . obtained such as clothing worn, food and drink consumed, and their recollection of what the fallout resembled. A synopsis of alI of these interviews (Reference 3) is used in reconstructing the radiation exposure estimates in this memorandum. Seventeen of the interviews were in sufficient detail that the individuals’ activities during the exposure period could be fairly well established on an hour-to-hour basis. For intervals without specified activities, reasonable assumptions are made that high-side the calculated radiation doses. The Appendix contains an example of the information available and the procedure employed in order to reconstruct the dose for one individual.

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(3) Protection Factors on Rongerik Atoll During the initial radiological survey of Rongerik on 10 March 1954 (Reference 8), specific locations were surveyed with an AN/PDR-39 survey meters. In addition to the average reading of 280 mR/hr found at various locations on the island, the survey team also took intensity readings both inside and outside of the various structures utilized by the military personnel during their exposure period. The ratio of the intensity outside to the radiation intensity inside is defined as the protection factor and gives a measure of the radiation protection or shielding provided by the structure. From the 10 March survey data, each type of structure and its measured protection factor are as follows: (4) Film Badge Doses With the free-field radiation intensity (It) as defined previously, film badge doses for the military personnel on Rongerik can be calculated for each time interval (t, to t2) to which a protection factor (PFi) applies, as follows: where ‘fb = Dose as would be recorded by a film badge worn on the chest (0.7) = Factor to convert integrated free-field radiation intensity to

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The maximum possible dose to a film badge worn continuously through the time of final evacuation is obtained by using PF= 1 throughout, i.e., no radiation protection available on the island. The upper limit of integration in this case would be 35 1/4 hours after burst, which corresponds to final evacuation at 1800 hours, 2 March. A dose of 87 rem results. If a film badge was not worn, but instead left out in the open, the (0.7) factor would not enter into the calculations. As an example, one film badge was left hanging from a tent post (PF assumed to be 1) until H+28.75 hours (1 130 hours, 2 March) at which time it was placed in the mess hall (PF=2) until the second group evacuated. The calculated dose is 112 rem. All of the film badge dose calculations are dependent on the accuracy of integrated intensities derived from Figure 2. Uncertainty, especially concerning the duration of fallout deposition, is evidenced in a comparison with limited film badge dosirnetry data (Section 3.3). Thus, film badge dose calculations in this section, represent initial estimates. For the seventeen individuals who provided sufficient information in their postevacuation interviews to reconstruct their activities, the preliminary, film badge …