On Weapons Plutonium in the Arctic Environment (Thule, Greenland)

University dissertation from Risø National Laboratory, Information Service Department, P.O. Box 49, DK-4000 Roskilde, Denmark

Abstract: This thesis concerns a nuclear accident that occurred in the Thule (Pituffik) area, NW Greenland in 1968, called the Thule accident. Results are based on different analytical techniques, i.e. gamma spectrometry, alpha spectrometry, ICP-MS, SEM with EDX and different sediment models, i.e. (CRS, CIC). The scope of the thesis is the study of hot particles. Studies on these have shown several interesting features, e.g. that they carry most of the activity dispersed from the accident, moreover, they have been very useful in the determination of the source term for the Thule accident debris. Paper I, is an overview of the results from the Thule-97 expedition. This paper concerns the marine environment, i.e. water, sediment and benthic animals in the Bylot Sound. The main conclusions are; that plutonium is not transported from the contaminated sediments into the surface water in this shelf sea, the debris has been efficiently buried in the sediment to great depth as a result of biological activity and transfer of plutonium to benthic biota is low. Paper II, concludes that the resuspension of accident debris on land has been limited and indications were, that americium has a faster transport mechanism from the catchment area to lakes than plutonium and radio lead. Paper III, is a method description of inventory calculation techniques in sediment with heterogeneous activity concentration, i.e. hot particles are present in the samples. It is concluded that earlier inventory estimates have been under estimated and that the new inventory is about 3.8 kg (10 TBq) of 239,240Pu. Paper IV, describes hot particle separation/identification techniques using real-time digital image systems. These techniques are much faster than conventionally used autoradiography and give the results in real time. Paper V, is a study of single isolated hot particles. The most interesting result is that the fission material in the weapons involved in the accident mostly consisted of 235U (about 4times more in mass than 239Pu). This paper concludes that there are at least two different source terms for the Thule accident debris. Another interesting feature is that it seems like uranium is leaching from the particles faster than plutonium and americium.

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