HOT PARTICLES IN ACCIDENTAL RELEASES FROM CHERNOBYL AND WINDSCALE NUCLEAR INSTALLATIONS

Fuel particles released during the accident at the Chernobyl reactor (1986) and during the operation at the Windscale (UK) pile (1952-57) were investigated with respect to structure using scanning electron microscopy and composition using X-ray microanalysis and gamma-, beta- and alpha-spectrometry. Particles from Chernobyl released at a relatively high temperature-have in general a compact crystalline-like structure with a relatively uniform surface layer of uranium. Aggregates consisting of small-sized (1-2 mu m) spherical uranium granulates were also identified. These granulates were similar to particles identified in Norway. About 25% of the particles investigated were covered by lead, which is attributed to a release during the last stage of the accident. Particles from Windscale released under low-temperature conditions have a flake-like layered structure, varying in size (10-250 mu m) and activity levels. Thus the travelling distance for these particles may be substantially longer than previously anticipated for spheres. The surfaces of these particles were also composed of uranium. The mobility of radionuclides associated with fuel particles of different structure is believed at least initially to be low when compared with those associated with condensed particles or with ionic tracers. However, mobilization of especially Sr-90 due to weathering of hot particles should be expected in the years to come.