Speaker
Description
The accurate assessment of fissile mass within radioactive waste drums is crucial for effective radioactive waste management, nuclear safety, and criticality prevention. Passive and active neutron measurements are indispensable tools for quantifying residual actinides of interest, such as plutonium and uranium, in both waste management and spent fuel reprocessing contexts. For several years, the Nuclear Measurement Laboratory (NML) at CEA Cadarache (France) has conducted preliminary studies, feasibility demonstrations, measurement station designs, and performance evaluations using the Monte Carlo code MCNP. Recently, the NML successfully employed the PHITS Monte Carlo code to simulate large-gap solid detectors for neutron spectroscopy and neutron activation analysis of rare metals. To assess PHITS' performance for neutron measurements, this study presents a comparative analysis with MCNP, the established reference code.
The specific case study involves a modular neutron measurement station designed within the European MICADO project. This station aims to characterize the mass of plutonium and uranium in 40- to 400-liter drums using coincidence and Die-Away Differential Technique (DDT) measurements with 84 Helium-3 proportional counters. This work compares MCNP and PHITS for relevant physical quantities associated with passive (detection efficiency, real coincidences counting and calculation of calibration coefficient CC40 for Pu-240 equivalent mass) and active (fission rate, active calibration coefficient for Pu-239) neutron measurements. Additionally, the computational efficiency of both codes is also evaluated.
The results demonstrate excellent agreement between MCNP and PHITS, with the majority of deviations not exceeding 10%. This high level of concordance instills confidence in the broader application of PHITS for neutron measurement simulations. While PHITS exhibited longer computation times in certain cases, the PHITS development team through a dedicated patch has addressed this issue.
