Reactivity effect of various radioisotopes in pressure tube type heavy water reactor using the computer code IGDC

Abstract

Core reactivity depends on balance between production and loss mechanisms of different radio-isotopes in the reactor. During reactor operation, depending on the burn-up, several nuclides are present and they contribute to the reactivity in different ways. Also, the concentration of these nuclides i.e. fission products and actinides change with irradiation in a nuclear reactor. The computer code IGDC (Isotopic Generation and Depletion Code) is capable of simulating many nuclides simultaneously and study the relative behavior of the different isotopes present at any instant of time. In this research paper, an attempt has been made to quantify the change in reactivity due to various important fission products and actinides during irradiation as well as during shutdown state and restart of the reactor. The infinite homogenous model has been adopted for estimating the reactivity equivalence at any instant in time. The research work also led to a new factor RELIFIX (RELative Importance Factor of fIssion product w.r.t. Xe-135) where the absorption characteristic of each individual isotope is parameterized with respect to that of xenon-135. In this paper, we also discuss the importance of RELIFIX parameter in the operation of PT-HWR (pressure tube type heavy water reactor) similar to PHWR (pressurized heavy water reactor).