Principal Features of Chernobyl Hot Particles: Phase, Chemical and Radionuclide Compositions

Abstract

The accident at the Chernobyl Nuclear Power Plant (ChNPP) 4^th Unit on 26 April 1986 was accompanied by the destruction of a reactor core and the release of solid and gaseous radioactive products. As a result of the accident, a part solid radioactive materials of the 4^th Unit was dispersed by the explosion. The hot particles released settled on the surface of soil hundreds kilometers from ChNPP in the Sweden [1], Germany [2,7], Poland [2,3,7], Belorussia [4] and in particular, Ukraine [5,6,8]. The size of hot particles vary from one to hundreds microns. The bulk radioactivity of a single particle based on the initial activity calculated for 26^th April 1986 might differ by hundreds of kBq. While particle size tends to decrease with increasing distance from the 4^th Unit, some relatively large particles of 100–300 micron in size were collected 12 km West of ChNPP. Phase, chemical and radionuclide compositions of hot particles are essentially heterogeneous [1–8]. We have suggested dividing all hot particles into two main groups: 1) fuel particles — with relatively homogeneous matrix consisted of uranium oxides, UO_2+x; 2) fuel-constructional particles — with a complex chemical matrix and/or multi-phase composition that is a result of high-temperature interaction between nuclear fuel, (UO_2+x), and cladding materials such as zircaloy and stainless steel composed of Fe-Gr-Ni. The temperature could have exceed 2600°C. In some places of Western Plume in Chernobyl region these particles achieve up to 40 % of all hot particles [8]. Radionuclide composition of hot particles depends on the chemical and phase composition of their matrices [1,2,7,8].