Depletion chain simplification using pseudo-nuclides

This paper introduces a method for simplifying the depletion chains and reducing the number of nuclides tracked in a given nuclear system while adding pseudo-nuclides in order to preserve decay heat. Pseudo-nuclides are demonstrated to preserve the decay heat effects of fission product irradiation with fewer nuclides tracked overall than decay heat precursors. The functionality is implemented and tested in the reactor physics application Griffin. Extensive testing is performed using the comprehensive ENDF-B/VIII.0 decay data and microscopic cross-section libraries from ORIGEN and MC2-3. The impact on the number of nuclides that must be tracked based on effects such as changing cross-section data, changing energy group structure, changing neutron flux spectrum, and tracking decay energy release is explored in this work. Overall, the addition of pseudo-nuclides allows the number of nuclides tracked to be reduced from 1,700 to 400 or fewer nuclides, based on the criteria used in this work.