A TIME-DEPENDENT EMISSION OF SOME RADIONUCLIDES FROM OVERHEATED NUCLEAR-FUEL

The physico-chemical characteristics of particles emitted by an overhe ated nuclear fuel may be significantly modified when they are put in c ontact with an oxidizing atmosphere at temperatures of the order of 70 0-900 degrees C. This so-called ''maturation'' stage induces reactions between radioelements and the UOx matrix of the aerosol particles. Th ese reactions, in turn, deeply influence the solubility of radioelemen ts in the environment. This paper presents experiments aimed at descri bing the behavior of characteristic radioactive elements present in nu clear fuel (Cs, Sr, Tb), which are emitted as a consequence of an acci dental thermal excursion. As the sequence of radionuclide emission fro m the nuclear fuel depends on the volatility of their chemical forms, it has to be expected that the maturation stage itself is a time-depen dent process in the sequence of emission events.