Evaluation of External Radiation Dosimetry Records at the Savannah River Site, 1951–1989
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Journal of Exposure Science and Environmental Epidemiology (2007) 17, 13–24 r 2007 Nature Publishing Group All rights reserved 1559-0631/07/$30.00 www.nature.com/jes Evaluation of external radiation dosimetry records at the Savannah River Site, 1951–1989 DAVID B. RICHARDSONa, STEVE WINGa, ROBERT D. DANIELSb aDepartment of Epidemiology, School of Public Health, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA bHealth-related Energy Research Branch, National Institute for Occupational Safety and Health, Cincinnati, OH 45226, USA The Savannah River Site (SRS) is one of the largest facilities in the nation’s nuclear weapons complex. To date, little information has been published regarding radiation risk estimates derived from epidemiological studies of SRS workers. As part of an ongoing epidemiological cohort study of SRS workers, we have assessed the suitability of the Site’s personnel radiation dosimetry information for use in epidemiological analyses. This paper provides information on historical dosimetry methods, recording practices, and the completeness of computerized dosimetry information for workers employed at SRS during the period 1951–1989, when the site was operated by the du Pont Company. The study includes 18,883 workers hired at SRS between 1951 and 1987 who were employed for at least 90 days. Documents relating to external radiation dosimetry methods were reviewed, recorded doses were examined to evaluate recording practices, and the completeness ofmonitoring was assessed by comparing employment history and computerized dosimetry records, and by implementing a ‘‘nearby’’ procedure for estimating values for missing annual dosimetry records. Dosimeter technology evolved over this period from two-element film dosimeters to multielement thermoluminescent dosimeters. Dosimetry measurements were recorded consistently in 0.05 millisievert (mSv) increments. Prior to 1973, recording thresholds of0.10–0.15 mSv were used while from 1973 to 1989 a recording threshold of 0.05 mSv was used. We abstracted nearly 3 person-Sv ofdosimetry information that was available in hardcopy but not in computerized format. The collective dose from the computerized and abstracted records totaled 512.1 person-Sv. A ‘‘nearby’’ method was used to estimate dose values for 13,812 employment-years for which dosimetry information was not available. The average estimated value was 0.6 mSv and the assigned collective dose derived via the ‘‘nearby’’ procedure was 8.7 person-Sv. The consistency ofdosimetry practices at SRS and the completeness ofhistorical dosimetry records a re supportive oftheir use in epidemiologic research. Journal of Exposure Science and Environmental Epidemiology (2007) 17, 13–24. doi:10.1038/sj.jes.7500515; published online 28 June 2006 Keywords: Savannah River Site, radiation, dosimetry. Introduction plutonium was shipped from the plant. The Site’s tritium facilities were completed in October 1955. Production The Savannah River Site (SRS) is a 310-square mile facility activities at the Site have involved the operation offive large located near Aiken, SC and Augusta, GA. In 1950, the E.I. reactors, two chemical separation areas, a heavy water du Pont Nemours and Company contracted with the Atomic extraction plant, nuclear fuel and target fabrication plants, as Energy Commission to design, construct, and operate a well as test reactors, power plants, and laboratories. E.I. du facility to produce materials, primarily tritium and pluto- Pont Nemours and Company managed and operated the site nium, for the government’s nuclear weapons program. through March 31, 1989. More recent activities at the site Construction oftemporary facilitieswas completed in May include recycling and reloading tritium in the nation’s nuclear 1951; these served as the headquarters for the Construction weapons, as well as nuclear waste management and Division. By August 1952, a heavy water plant at SRS had environmental restoration. become operational, and in December 1953 the Site’s first Previous epidemiological studies ofSRS workers have production reactor went critical. In 1954, the first separations reported evidence ofan excess number ofleukemia deaths facility became operational and three additional production among hourly-paid male employees compared to the reactors were brought on line. By December, 1954 the first expected number based upon US mortality rates and evidence ofa positive relationship between cumulative external radiation dose and leukemia mortality (Cragle 1. Address all correspondence to: Dr. David B. Richardson, Department et al., 1988, 1998; Wartenberg et al., 2001). We are currently ofEpidemiology, School ofPublic Health, University ofNorth Carolina conducting an updated study ofSRS workers utilizing at Chapel Hill, Chapel Hill, NC 27599, USA. Tel: þ 1 919 966 2675. historical records ofannual whole body radiation dose Fax: þ 1 919 966 2089. E-mail: [email protected] Received 4 April 2006; accepted 5 June 2006; published online 28 June estimates. These dosimetry records originally were collected 2006 and maintained for radiation protection and compliance Richardson et al. Savannah River Site dosimetry data purposes rather than for research purposes. Decisions occupational exposure ofpersonnel to radiation was under regarding monitoring policies or recording practices that the supervision ofradiation protection staff.In some cases, were appropriate in the context ofmonitoring for compliance a health physics area corresponded to a specific location may differ from those that would ideally be used if (such as a specific nuclear reactor), while in other cases it monitoring were conducted for research purposes. Therefore, corresponded to a defined area encompassing a number of as part ofour study, we have assessed the suitability ofusing work locations dedicated to a specific process (e.g., separa- SRS historical records ofannual whole body radiation dose tions). We abstracted information used to classify workers estimates for epidemiologic purposes. according to the health physics area in which they worked in The objectives ofthis paper are the following: to provide a each calendar year from quarterly dosimetry logbooks summary ofhistorical external radiation dosimetry methods (1958–1989). Ifa worker was missing information on health employed at SRS during the period when the Site was physics area for a given employment-year, but had a known operated by E.I. du Pont Nemours and Company; to health physics area for an adjacent time period during which evaluate the recording practices used by the SRS personnel they were employed in the same job, then, for the purposes of dosimetry program during these years; to utilize employment exposure imputations, we assigned that health physics area to history information in conjunction with computerized the employment-year. dosimetry records in order to assess the potential for exposure measurement error due to incomplete radiation Computerized Radiation Dosimetry Records dosimetry information; and, to apply a previously developed In 1979 a computerized personnel dosimetry system, referred method for estimating radiation doses in unmonitored to as the Health Protection Annual Radiation Exposure employment periods in order to assess the impact ofusing History (HPAREH) system, was implemented at SRS. For imputed values on worker dose estimates. all Site employees who were actively employed in 1979, a history file ofannual radiation exposure information was Materials and methods entered into the HPAREH system from hardcopy personnel folders and logbooks (1951–1964), magnetic tapes of The analyses in this report focus on a cohort of 18,883 logbooks (1965–1972), and HP Master File magnetic tapes Savannah River Site workers who were hired by the du Pont (1973–1979). Since 1979 dosimetry information has been Company prior to 1987 and who worked at least 90 days. routinely entered into the HPAREH system. Recorded Workers without complete information on name, SSN, date values include estimates ofshallow dose (i.e., skin dose), ofbirth, and date offirst hire were excluded. This cohort of notably from beta particles, that was evaluated via the workers expands upon the cohort examined by Cragle et al. personnel dosimetry system by including an uncovered, or (1988, 1998) by including white males hired between 1975 open-window, reading; deep (penetrating) dose, such as and 1986 and by including white females and non-white doses from medium- to high-energy photons, that was males and females. evaluated by including shielded-window readings; neutron A file containing work history information was constructed dose that was measured by a separate neutron dosimetry by manually entering du Pont payroll records that describe system; and tritium dose measured via bioassay methods. dates ofemployment and job title changes into a computer Workers who terminated employment at SRS prior to file. Job titles were standardized and grouped. Using this 1979 are not included in the HPAREH system. However, information a file was created that describes the number of an electronic file ofannual radiation dose estimates forthe days that a worker was employed during each calendar year period 1951–1979 was constructed for the purposes of (1951–1989), and the longest held occupation during each epidemiological research conducted by the DuPont Corpora- calendar year. Our analyses ofthe completeness ofcompu- tion (Appendix, available with the electronic version ofthis terized whole body dose estimates refer to ‘‘employment-