Californium-252 Production Validation Studies at the High Flux Isotope Reactor with Campaign 78 Data

Validation of ²⁵²Cf production via computational simulation of actinide oxide ceramic-metallic, or cermet, pellet irradiations in the High Flux Isotope Reactor (HFIR) is an important ongoing activity to support the conversion of HFIR from highly enriched uranium (HEU) to low-enriched uranium (LEU) fuel. Accurate predictions of ²⁵²Cf production must be demonstrated with the current HEU core to provide sufficient confidence that an LEU core can carry out this vital mission. This paper presents results from a series of studies based on current HFIR analysis tools and data from a recent Cf-252 irradiation campaign. The HFIRCON and Shift transport and depletion codes with ENDF/B-VII.0 and ENDF/B-VII.1 cross sections were used to model and simulate HFIR Cycles 479-482. The HFIRCON simulation with ENDF/B-VII.0 cross sections calculated a ²⁵²Cf mass of 90.4 mg, about 1 standard deviation lower than the measurement of 93.2 ± 2.7 mg. The results of the HFIRCON simulation with ENDF/B-VII.1 cross sections and both Shift simulations using both libraries were within 3 standard deviations of the measurement. Relative to the measured result, both tools estimated higher ²⁵²Cf masses with ENDF/B-VII.1 cross sections and lower masses with ENDF/B-VII.0. In addition to isotopic evolution evaluations, temporal fission densities and heat deposition rates were analyzed because they are important parameters for nuclear safety. The peak pellet heat deposition rate and cumulative fission density were about 2.4 kW/cm³ and 4.0 × 10²⁰ fissions/cm³, respectively. Future work includes validation of other irradiation campaigns, evaluation of nuclear data deficiencies, and a thorough comparison of production metrics with the HEU core and a proposed LEU core.