Generalized depletion chain simplification based on significance analysis

The depletion chain defined by evaluated nuclear data library is unnecessarily complex for most applications in reactor physics. The simplification methods are confronted with two difficulties. Firstly, the number of possible simplified depletion chains is excessively large. Secondly, depletion calculation is dynamic process coupled with neutronics, which means the simplified depletion chain has to be able to catch the main features of the entire physical process. Thus, in this paper, a generalized depletion chain simplification method is proposed with limited approximations employed. It defines the significance of the entire depletion calculation as the neutron production and absorption and the number densities of the important nuclides. And then it evaluates the significance value of each reaction channel and decay nuclides by perturbed depletion calculations. Since short-lived nuclides are intended to be reduced from the depletion chain, delayed decay heat precursors are introduced in order to consider short-term decay heat.