Published online by Cambridge University Press: 03 September 2012
On April 25, 1986, the nuclear reactor Unit 4 (RBMK) at Chernobyl, Ukraine,exploded. Besides molecular species, the fallout contained particles ofrelatively high specific activity (hot particles) with a wide range ofchemical compositions. The composition of a hot particle bears informationabout its genesis. Particle sizes ranged from a few to 100s of micrometers.Data on a hot particle, found in Berlin, Germany, is presented and discussedin context with earlier measurements on other particles to understand theirgenesis. The chemical composition was determined by electron probe microanalysis. Our particles are either reactor fuel (one) or fission productalloys (nine). The alloys were formed during normal reactor operation.Strongly varying concentrations of Fe and Ni suggest that at least some ofour particles reacted with molten structural material of the reactor. Theparticles were mobilized by fuel oxidation or fuel dust generation duringthe accident. The fission product composition can only be explained if weassume that the alloys remained in the solid state in the course of theaccident. Some particles may have been ejected during the explosion, otherslater while the reactor was burning. Activities (103Ru and 106Ru, originally up to 160,000 Bq) of our ten year oldparticles were re-measured but were no longer detectable. No long-livedγ-emitters were found. The 99Tc activity was calculated and foundto only lBq. The γ -spectrum of the fuel particle still shows137Cs (1 Bq) and 60Co (<1 Bq).