Phenomenological Model for Estimating the Activity of Fission Products in Nuclear Fuel and Accidental Reactor Emissions

A phenomenological model is proposed for estimating the production of fission products with half-life ∼1 day and longer in the core of a thermal reactor. The model takes account of the fissioning of 235U, 239Pu, and 241Pu by thermal neutrons and 238U by fission-spectrum neutrons. The fission rate of individual nuclides can contain exponential time dependences and power-law dependences of the form t, t2, and t3. The model makes it possible to obtain in an analytic form the dependence of the specific mass and specific activity on the operating time of the reactor for most fission products which are of practical interest in radioecology. The calculations were performed for a RBMK-1000 reactor operating in a constant-power regime. In all cases, the analytic calculations agree with the numerical calculations.