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) we re investigated with respect to structure using scanning electron micr oscopy 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 consis ting of small-sized (1-2 mu m) spherical uranium granulates were also identified. These granulates were similar to particles identified in N orway. About 25% of the particles investigated were covered by lead, w hich is attributed to a release during the last stage of the accident. Particles from Windscale released under low-temperature conditions ha ve a flake-like layered structure, varying in size (10-250 mu m) and a ctivity levels. Thus the travelling distance for these particles may b e substantially longer than previously anticipated for spheres. The su rfaces 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 ass ociated with condensed particles or with ionic tracers. However, mobil ization of especially Sr-90 due to weathering of hot particles should be expected in the years to come.