WPFC/AFCS Expert Group Benchmark on Dose Rate Calculations

This report describes ENEA’s contribution to the WPCF/AFCS Expert Group benchmark on dose rate calculations. The results refer to the two parts in which the Benchmark is divided: 1. verification of the self-protection properties for spent PWR UOX and MOX fuel assemblies and code-to-code comparison of nuclide inventories and gamma dose rates; 2. validation of the gamma dose rates calculation strategy with the gamma dose rate measurements performed on a W15x15 UOX fuel assembly in 1981. In the verification part, five different calculation strategies were simultaneously used to compare the performance of the codes. Overall, a good agreement between the five strategies in terms of nuclide inventories, gamma sources and gamma dose rates is observed. In the validation part, the calculations were performed with Origen-S in the depletion and decay phases and MCNPX in the photon transport phase. The gamma dose rate values for the ANSI/ANS-6.1.1-1977 conversion factor are around 20% higher than those for the ANSI/ANS-6.1.1-1991 conversion factor. Compared to the measured values, the calculated ones differ at most -44% with the ANSI/ANS-6.1.1-1977 factor and -55% with the ANSI/ANS-6.1.1-1991 factor.