Research on depletion chain simplification method based on pseudo-decay nuclides

The applicability of the depletion database determines the accuracy of burnup and power calculations during core simulation. The information of depletion chains in evaluated nuclear databases is unnecessarily complex for most applications in reactor physics, leading to large, rigid, and inefficient burnup matrix. This paper introduces a method for simplifying the depletion chains, which considering the impact of various nuclides and their corresponding transmutation pathways on the calculation accuracy of reactivity rates and nuclide densities. The impact of each reaction channel and decay nuclides is evaluated by depletion calculations of typical problems. Since fission products are intended to be reduced from depletion chains, pseudo-decay nuclides are introduced to substitute the role of fission products to maintain the accuracy of decay heat calculations. The verification results show that the number of nuclides tracked to be reduced from 1500 to 200 or fewer nuclides. No significant deviations are introduced in the calculation of effective multiplication factors and nuclide number densities by the simplified depletion chains. And the pseudo-decay nuclides significantly maintain the accuracy of decay heat calculations, with the deviation of decay heat contribution to total power being less than 0.5 %.