The Fission Products (FP) group constant treatment for long-life Pb-Bi-cooled fast power reactors

Abstract

In this study we focus on the Fission Products (FP) group constant treatment by considering around 50 of the most important nuclides. We then calculate the fission product effective yield for each of the modified chains and also generate one group constant using the System for Reactor Analysis Code (SRAC) and other methods (Origen, etc.). We use two approaches for investigating the important FP nuclides: the equilibrium model and the numerical solution for the time-dependent model. Based on the results we obtained three global patterns of the time-dependent atomic density change during burn-up for the considered nuclides. The first pattern is about nuclides that soon reach the asymptotic value, which can be grouped together by weight that may depend on parameters such as flux and power density. The second pattern includes nuclides that change during burn-up, with a nonlinear pattern, which can be combined into one group or more by nonlinear weight (quadratic, cubic, etc.). The third pattern is about nuclides that change in an almost linear way during burn-up, which can be grouped into two or more group constants by flux level, power level and time.