Studies of Plutonium Aerosol Resuspension at the Time of the Maralinga Cleanup

Abstract

At the former nuclear test site at Maralinga, South Australia, soil cleanup began in October 1996 with the objective to remove the potential for residual plutonium (Pu) exposures to the public. In this case the cleanup was to restore access to the closed test site. The proposed long-term land use was primarily to be a hunting area for Pitjantjatjara (Aboriginal) people, but also presumably to be available to the public who might have an interest in the history of the site. The long-term management objective for the site was to allow casual use, but to prohibit habitation. The goal of this study is to provide an evaluation of the Maralinga soil cleanup in terms of potential long-term public inhalation exposures to particulate Pu, and in terms of a contribution to planning and conducting any such soil Pu-cleanup. Such cleanups might be carried out for example, on the Nevada Test Site in the United States. For Pu that has been deposited on the soil by atmospheric sources of finely divided particles, the dominant exposure pathway to humans is by inhalation. Other exposure pathways are less important because the Pu particles become oxidized into a nearly insoluble form, do not easily entermore » into the food chain, nor are they significantly transferred through the intestine to the bloodstream should Pu become ingested. The purpose of this report is to provide results of the Pu resuspension measurements made before, during, and after the Pu cleanup at Maralinga, to compare these against similar measurements made elsewhere, and to interpret the results as they relate to potential long-term public exposures. (Exposures to Pu in dust plumes produced by mechanical disturbance during cleanup are considered short-term, unlikely to be significant for purposes of this report, and are not included). A considerable amount of research had been conducted at Maralinga by the Australian Radiation Laboratory, now the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA), prior to the cleanup (Johnston et al, 1992, Williams 1993, Johnston et al 1993, Burns et al 1994, Burns et al 1995). ARPANSA staff made major contributions to delineate the areas with Pu in the soil, to determine the degree of secondary soil contamination by fission products from nuclear testing, to measure Pu resuspension by wind erosion of the undisturbed soil, and to prepare assessments of the human health risk from residual soil Pu. In addition, ARPANSA supported the Maralinga cleanup to assure compliance with criteria set by an independent technical advisory committee. During the cleanup ARPANSA monitored the residual Pu in the soil and certified that the cleanup was complete according to the criteria. It was not the reduction in potential inhalation exposure that usually was the main driver of the cleanup, but the requirement to also remove individual hot particles and fragments. It is the residual microscopic particles of Pu in the soil, however, that have the potential for long-term human exposure. The resuspension of respirable-size Pu particles has been studied with specialized equipment at the Nevada Test Site (Gilbert et al 1988a, Gilbert et al 1988b, Shinn et al 1989, and Shinn 1992), and at Bikini and Enewetak in the Marshall Islands (Shinn et al 1997). These efforts were in large part contributed by the Health and Ecological Assessment Division, University of California, Lawrence Livermore National Laboratory (LLNL). The study reported here is a collaboration between ARPANSA and LLNL, and was jointly supported by the United States Department of Energy, and the Commonwealth of Australia Department of Primary Industry and Energy.« less