SEDIMENT MIXING AND BURIAL OF THE PU-239,PU-240 PULSE FROM THE 1968 THULE, GREENLAND NUCLEAR-WEAPONS ACCIDENT

A suite of sediment cores was collected in 1984 in Bylot Sound, Greenl and, at the site where a US B-52 bomber crashed on the ice in 1968 res ulting in the rupture of four nuclear weapons and the release of 1 TBq of plutonium to the underlying seawater/sediment environment. Measure ments of Pu-239,Pu-240 indicated that weapons-plutonium has been prefe rentially deposited in the fine-grained bottom sediments covering the basins in the vicinity of the crash site. Only minimal dispersal of Pu -239,Pu-240 to distances greater than 1 km from the crash site can be inferred from comparisons of the 1984 sediment core studies with those undertaken in 1974 and 1979. Pb-210 distributions measured in the sed iment cores have been simulated using a bio-diffusion model which indi cates that burial of Pu-139,Pu-240 has occurred by the processes of bi oturbation and sediment accumulation (at rates of 0.09-0.40 g cm(-2) y ear). Bioturbation has both enhanced the rate of burial of Pu-239,Pu-2 40 in the sediments and also maintained an elevated Pu-239,Pu-240 conc entration in the mixing zone at the sediment-water interface. Burial o f of Pu-239,Pu-240 is adequately characterized by the model using a 19 68, pulsed input function, indicating that resuspension and transport of weapons-Pu-239,Pu-240 following the accident have nor been major fa ctors in the dispersal of this contaminant. These results represent a potential case study for. the dispersal of plutonium from radioactive dumpsites located in similar, shallow arctic marine environments on th e Russian continental shelf.