Analysis of Radiation Exposure for Additional Naval Personnel at Operation Castle -- Supplemental Report

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ANALYSIS OF RADIATION EXPOSURE FOR ADDITIONAL NAVAL PERSONNEL Post Office Box 1303, 1710 Goodridge Drive, McLean, Virginia ZZIO.?, (703) 82143M

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REPORT DOCUMENTATION PAGE i 6a. NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL Approved for public, release; distribution 1s unllml ted. Defense Nuclear Agency 9 PROCUREMENT INSTRUMENT IDENTIFICATION NUMBER 10 SOURCE OF FUNOING NuMBERS ANALYSIS OF RADIATION EXPOSURE FOR ADDITIONAL NAVAL PERSONNEL AT OPERATION CASTLE-- 13a, TYPE OF REPORT 13b. TIME COVERED 14 OATE OF REPORT (t’w,IWOntf!,D~y) 5. PAGE COUNT This work was sr)onsored by the Defense Nuclear Agency under RDT&E RMSS Code O&M/PDA RMC CODE 1310 DOT 00 90019 RARP 3500 A 17 COSATI COOES 18 SUBJECT TERMS (Contfnw on reverse !f necessary and d~ntjfy by Mxk number) Radiation Exposure Assessment Nuclear Test Personnel Review (NTPR) 19. ABSTRACT (conrinuc on reverse Ifnece$rary and Idertnfy by Mock numhr) This report supplements DNA-TR-84-6, which analyzed the radiation exposure for sixteen ships and the residence islands of Enewetak and Kwajalein Atolls at Operation CASTLE in 1954. Film badge doses are reconstructed for eight additional ships (RECLAIMER, SHEA, COCOPA, MENDER, MOLALA, TAWAKONI, PC-1546, and LST-1146) that participated in the operation. Although the radiation environments were basically the same as used in the first report, the characterization of such environments is considerably more complex. not only because additional data are available for use in defining the contamination of the ships and the lagoon, but also because several ships were engaged in activities that resulted in exposures not considered or required in the initial report. In contrast to the ships previously considered, fallout from Shot BRAVO was of lesser contribution to DOFORM 1473,81aMAR 83 APR edmon may De used until exhausted. SECURITY CMSSIFICATION OF THIS PAGE

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SECURITY CLASSIFICATION OF THIS PAGE the total exposure on most ships; additional sources of exposure, such as from proximity to fallout-contaminated vessels, were significant contributors to dose. Additionally, the analysis of avail able dosimetry, which is considered necessary for establishing confidence in the dose calculations, is much more comprehensive due to the use of extensive microfilm records, not available in the previous analysis. Utilizing the reconstructed radiation environments from deck contamination, water shine, proximate ship shine, and contaminated hulls and piping, an equivalent film badge dose is calculated and compared with the analyzed dosimetry. Comparisons are made less significant by a shortage of badge readings, and by cohort badging that may have resulted in non-representative doses being assigned to unbadged personnel. Considering this, agreement is good (within a few hundred millirem) when doses were high but less when doses were low. In all cases., overall totals appear to be in Calculated mean doses range from a low of 0,30 rem for the crew of USS RECLAIMER to a high of 2.2 rem for the crew of USS COCOPA. The calculated doses should be used when badged members of cohorts, due to duties, ratings, and locations, do not appear to be representative of the cohort as a whole.

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TABLE OF CONTENTS 3.1.1 Project3.4- Sea Minefield Neutralization by Means of a 3.1.2 Project 1.4- Underwater Pressure Measurements ............. 3.1.3 Project 6.4- Proof Testing of Atomic Weapons Ship

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TABLE OF CONTENTS (Concluded) DOSE CALCULATIONS FOR USS RECLAIMER (ARS-42) ....... DOSE CALCULATIONS FOR USS COCOPA (ATF-lO1) ............ DOSE CALCULATIONS FOR USS MENDER (ARSD-2) ............ DOSE CALCULATIONS FOR USS MOLALA (ATF-106) ........... DOSE CALCULATIONS FOR USS TAWAKONI (ATF- 114) ....... 7 CONCLUSIONS AND TOTAL DOSE SUMMARY ............... .. ............ 107

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LIST OF ILLUSTRATIONS Estimated topside intensity on USS RECLAIMER (ARS-42) following Topside intensity on USS SHEA (DM-30) following Shot UNION ................ 29 Topside intensity on USS COCOPA (ATF- 101) following Shot BRAVO ......... 32 3.5 Topside intensity on USS COCOPA (ATF-101) following Shot ROMEO ......... 34 3.6 Topside intensity on USS COCOPA (ATF- 101) following Shot UNION ......... 35 3.7 Topside intensity on USS MENDER (ARSD-2) following Shot ROMEO ......... 40 3.8 . Topside intensity on USS MENDER (ARSD-2) following Shot UNION .......... 42 3.9 Estimated topside intensity on USS MOLALA (ATF- 106) following 3.10 Topside intensity on USS MOLALA (ATF-106) following Shot ROMEO ......... 49 3.11 Estimated topside intensity on USS MOLALA (ATF- 106) following 3.12 Estimated topside intensity on USS TAWAKONI (ATF-1 14) following 3.14 Estimated topside intensity on USS PC-1546 following Shot ROMEO ............ 65 3.15 Estimated topside intensity on USS LST- 1146 following Shot ROMEO ........... 68

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LIST OF TABLES Calculated film badge dose, USSSHEA(DM-30) .................................... 74 Evaluation of cohort badging of a given unit for a given badging period ........... 92 Applicability of a cohort badge reading to an individual in the cohort .............. 93 Additional topside exposure on support ships resulting from decontamination

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Operation CASTLE was a series of atmospheric nuclear tests conducted by the Atomic Energy Commission (AEC) at the Pacific Proving Grounds (PPG) during the Spring of 1954. Radiological safety procedures generally included the issuance of film badges to about 10 percent of the personnel throughout the operation and to individuals during periods of potentially significant radiation exposure. Cohort badging, defined as group dose determination from one badge wearer, was the primary means of determining individual exposures. Recorded dosimeuy is available for most personnel assigned to the ships. However, it is noted that available dosimetry forms are incomplete as to dates and times of recorded exposures. Moreover, recorded dosimetry from cohort badging has been shown to be not always representative of the entire cohort due to dissimilar activities within the group. Hence, reconstmcted doses, including uncertainty analyses, are necessary for high-confidence assessments of the doses received by these personnel. Reference 1 reports the results of dose reconstntctions for personnel on sixteen of the ships participating at Operation CASTLE, as well as for island-based personnel on Enewetak and Kwajalein Atolls; this companion report documents the analysis for eight additional ships of interest. The methodology of Reference 1 is employed herein. Appropriate material from the reference is repeated for reader convenience. For brevity, detailed derivations, discussions, and listings are cited but not repeated. As in the case of the sixteen ships evaluated in Reference 1, this report describes the operations, the radiological situation, and the time-space relationships of each of the eight ships with respect to the radiological environment. The results are portrayed as equivalent film badge doses for the crews of each of the ships. There were six shots in the Operation CASTLE test series: BRAVO, ROMEO, KOON, UNION, YANKEE, and NECTAR. The fmt five were detonated on Bikini Atoll; Shot NECTAR was detonated on Enewetak. Figure 1.1 depicts the locations of Bikini and Enewetak with respect to the other atolls comprising the northern Marshall Islands. Figures 1.2 and 1.3 show the main features of Bikini and Enewetak, respectively, and the locations of the CASTLE detonations; the pertinent details of each test are summarized in table 1.1 (Reference 2).

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Table 1.1. Operation CASTLE shot data. Shot Name YJ&i Location BRAVO 1 Mar 54 (0645) 15 Mt Bikini (Sand pit off Nam Island) ROMEO 27 Mar 54 (0630) llMt Bikini (Barge, BRAVO crater) KOON 7 Apr 54 (0620) 110 Kt Bikini (Eneman Island) UNION 26 Apr 54 (0605) 6.9 Mt Bikini (Barge off Iroij Island) YANKEE 5 May 54 (0610) 13.5 Mt Bikini (Barge, UNION crater) NECTAR 14 May 54 (0620) 1.69 Mt Enewetak (Barge, MIKE crater). The nuclear tests were conducted by a joint military organization designated as Joint Task Force Seven (JTF-7). Although military in form, it was comprised of military, civil semice, and contractor personnel. JTF-7 was organized into five main task groups, with Task Group 7.3 being the naval contingent. Most of the approximately 6,000 personnel assigned to TG 7.3 were aboard the various task group ships; however, approximately 650 were stationed on Enewetak and Kwajalein Atolls. Table 1.2 lists the TG 7.3 ships and the task units to which they were assigned, for which dose -reconstructions are specifically addressed in this report. Also tabulated are the approximate number of personnel assi=syed to each ship. In Reference 1, procedures developed in previous dose reconstruction efforts were adapted to the shipboard radiological environments of Operation CASTLE, The basic procedures used in Reference 1 have been utilized in this companion report. Each step is pursued to a level of detail governed by the availability of data. Sufficient data were recorded at the time and enough have survived to understand the ship and land operations and to characterize the radiation environment. Individual ship deck logs (Reference 3) serve as an authoritative source of ship position and activity. Radiation intensity data and crew activity scenarios are applied to reconstruct the timedependent radiation environment for a typical crewman on each of the eight ships of interest.

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Table 1.2. Operation CASTLE ships addressed in this report. Task Unit 7.3.1 Surface Security Unit Task Unit 7.3.5 Utility Unit Task Element 7.3.7.2 Mine Project Element Task Unit 7.3.9 Transport Unit Characterization of the radiation environment starts with the determination of on-deck (topside) and surrounding water intensities from radiological survey data. The periodic shipboard surveys, in conjunction with fallout time-of-arrival data and nearby island sutweys, serve to define the radiological intensity as a function of time. At times following the last reported shipboard survey, a power law function determined from Bikini Atoll radiological data is utilized. Despite differences in decay rate between ship and shore because of early-time washdown, decontamination, and weathering, late-time decay, mostly from insoluble particles adhering to shipdeck or soil, is taken to be the same. As ships operated in the contaminated waters of Bikini Lagoon, their hulls and saltwater piping systems accumulated radioactive materials, thus increasing the radiation exposure to crew members while below. The radiation environment due to ship contamination is derived from a previously-developed ship contamination model (Reference 4). When ships were in contaminated waters, the “shine” of radiation therefrom exposed topside personnel. Likewise, shine from contaminated vessels that were approached led to increased topside radiation levels. Both of these types of transient exposure are quantified to augment the mean topside intensities. Specific data and detailed methodology for the development of the time-dependent radiation environments are presented in section 2 of this report. Section 3 defines the radiation

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environments, as dependent on the movements and operations of each ship, and determines the daily exposure potential. Shipboard radiation surveys indicated a considerable variation in topside intensities because of ship geometry, redisrnbution of fallout during washdown and decont~mination, and non-uniform adherence of fallout particles to ship materials. If only an average sumey reading was reported, this value is used. In those cases where readings were taken at many predetermined positions on the ship’s exposed surfaces, they represent the topside radiation field. The ship’s crew is presumed to have been located at random positions when on deck; thus, mean survey readings, appropriately decayed, are used to determine the mean intensities encountered by the crew when topside. Average topside intensities ~e also used where water shine or ship shine is involved. The limited data from Operation CASTLE that relate shine levels to radiation source strength are supplemented by radiation transport calculations that accommodate specific ship The analysis of radiation exposure to the crew also requires estimation of radiation intensities below deck and the apportionment in time of crew activities below and topside. In addition to ship contamination, the fallout on deck has been noted as a conrnbutor to beIow-deck intensities. A ship-shielding factor is defined as the ratio of the intensity below to the mean intensity topside from fallout. This factor, previously determined for each type of ship of interest in Reference 1, is roughly 0.1 and is nearly constant over the usual crew locations within a ship. Thus, the time spent topside usually dominates the fallout dose. In some cases, specific durations of topside exposure are given in ship logs for shot day (ruely thereafter) when the radiological situation altered the normal pattern of duties. Otherwise, the fraction of time spent topside is assumed to be 0.4. This follows from reasonable topside intervals such as 0800-1200, 1330The calculated dose to the crew is obtained from time integration of intensity for all intenmls below and on deck; a conversion factor is used to account for body shielding by the badge wearer (Reference 5). Day-by-day and cumulative film badge doses to the average crewman of each ship are calculated and presented in section 4. Calculations ~e continued to the end of the operation and into the post-operational period until the dose accrual falls below 1 mrem per day. An uncertainty analysis of the dose calculations is provided in section 5. In section 6, the available dosimetry records are analyzed and compared with the calculated doses. Conclusions and a total dose summary are presented in section 7.

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Since an understanding of the radiation environments encountered by the ships participating at Operation CASTLE is essential for the dose reconstructions that are presented in section 4, the discussion thereof in Reference 1 is repeated and augmented. With the exception of the operational activities of PC-1546, LST-1 146, and MOLALA, activities conducted in conjunction with project support requirements by the remainder of the ships discussed herein, occurred primarily within the confines of Bikini Lagoon. Figure 2.1 depicts the areas within the lagoon where the ships were required to spend most of their time during the operation. Areas Nan (off Eneu Island) and Tare (north of Eneman Island) were the primary anchorages for all of the task force ships throughout the operation. Areas Charlie, Dog, Fox, George, and How in the northern lagoon, were visited during technical project support activities. All of the ships addressed in this report encountered fallout after one or more of the six CASTLE detonations. In most instances, particularly where significant fallout was encountered, shipboard radiological data are available to define the topside radiation environment. In some instances, however, shipboard environments must be inferred from radiological data obtained on nearby islands, such as the residence islands of Enewetak Atoll. For each ship, an average intensity curve is presented showing the free-field radiation intensity as a function of time after each shot that resulted in significant fallout. The intensity curves are then time-integrated to yield a daily free-field integrated intensity on each ship through 31 May 1954, when the roll-up phase was Extensive radiation intensity readings obtained on Bikini Island (Bikini Atoll) following Shot BRAVO indicated decay rates that varied considerably from the traditional t-l.2 rule (Reference 6). Average values for the decay exponent, obtained l?om several gamma ionization time-intensity meter measurements on Bikini, are as follows:

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A varying decay of this type is consistent with the presence of Np-239 (tlfl = 56 hr) and U-237 (t ID = 160 hr), which are both generated in significant quantities from neutron capture in uranium. After several half-lives, when the presence of these two radioisotopes no longer dominate the decay rate, it approaches the traditional t-1”2value. In the absence of radiological survey data, the time-dependent decay rate is used in reconstructing the radiation environments on the ships covered in this report. GeneraIly, radiological data on the residence islands of Enewetak and Bikini support at- Is decay rate between 48 and 480 hours after detonation; shipboard data indicate …