Verification of Hellos and Helios/Afen Against PWR Critical Experiments Loaded with High Plutonium Content MOX Fuels

We have verified a neutron and gamma transport code, HELIOS1.4, and HELIOS/AFEN core nuclear analysis procedure against two mock-ups (ALL-MOX and GD-MOX) of PWR critical experiments loaded with high plutonium content MOX fuels. HELIOS slightly overestimates the criticality but within an acceptable error bound, and calculates pin power distribution with an RMS error less than 1.1% for both ALL-MOX and GD-MOX mock-up cores. The HELIOS/AFEN core nuclear analysis procedure, based on the single assembly calculation for nodal group constants generation, has been also verified against the same two mock-ups. It was found that the energy group dependent power form function should be applied in pin power reconstruction for MOX fuel assembly. The AFEN reconstructed pin powers in MOX and UO2 fuel assemblies are in good agreement with the experiments; the RMS error is about 1.7% for the MOX assembly of both mock-ups, which is comparable to 1.9% for UO2 fuel assembly. This result assures the quality of HELIOS/AFEN procedure in accurately calculating the pin power distribution in PWR core intermixed with high plutonium content MOX and UO2 fuel assemblies. (C) 1999 Elsevier Science Ltd. Ail rights reserved.