Actinide-only burnup credit for pressurized water reactor spent nuclear fuel - II: Validation

The calculation of isotopic concentrations in spent nuclear fuel (SNF) asse mblies and the subcritical multiplication factor of SNF packages are two of the essential requirements of the actinide-only burnup credit methodology. To justify the accuracy of the computed values, the cone systems used to p erform the calculations must be validated Here, the techniques used for act inide-only burnup credit isotopic and criticality validation are presented and demonstrated. Fifty-four chemical assays are included in the isotopic validation benchmar k set. To perform the validation, the samples are analyzed to obtain isotop ic concentrations for each of the isotopes included in the methodology (U-2 34, U-235, U-236, U-238, Pu-238, Pu-239, Pu-240, Pu-241, Pu-242, and Am-241 ). Correction factors are computed based on the measured and calculated val ues, which are then used to conservatively bins computed isotopic concentra tions. For the criticality validation, 57 critical experiments are included in the benchmark set. The set is composed of 21 UO2 and 36 mixed-oxide experiment s, which are analyzed to determine the bias and corresponding uncertainty, ultimately resulting in an upper safety limit. This limit represents the ma ximum computed k(eff) value that would be considered subcritical.