New modelling of LWR assemblies using the APOLLO2 code package

The recent package APOLLO2.8-MOC/CEA2005-SHEM developed by CEA is undergoing a large validation program. First works of development and validation of a new optimized calculation scheme called REL2005 - based on the Method of Characteristics - are presented in this paper. The comparison of APOLLO2.8/REL2005 results to reference Monte Carlo TRIPOLI4 ones on specific PWR benchmarks emphasizes the ability of the deterministic tool to calculate UOX assemblies poisoned by gadolinium within 200 pcm accuracy on multiplication factor. Validation against the CAMELEON mock-up experiment confirms this good performance: pin-by-pin power is always predicted within 2% accuracy. Comparisons against reference deterministic depletion calculations show also good agreements: Keff and pin-by-pin power are respectively predicted within 150 pcm and 1% accuracy up to 60 MWd/kg. (authors)