Qualification of Apollo2.8/jeff-3.1.1 code package for the calculations of PWR plutonium recycling using the epicure experiments - 336

The recent release of the JEFF-3.1.1/CEA2005v4 nuclear data library and the latest improvements of the APOLLO2.8 code (281-group SHEM energy mesh, mixture self-shielding treatment and performing 2D solver using the method of characteristics) have allowed the development of new powerful LWR calculation schemes: reference SHEM-MOC and optimized REL2005 for industrial applications. For three years, CEA has been carrying out an intensive qualification program of this new APOLLO2.8 neutronics package. This paper is devoted to the experimental validation of the pin-by-pin power distribution in the specific case of the plutonium recycling in French 900 MWe PWRs. UH1.4 (UO2 17x17 mock-up) and UMZONE (mixed MOX-UO2 loading mock-up) experiments from the EPICURE program performed in the EOLE facility at Cadarache Centre have been analysed. Calculation results show good agreements with the experiments: - Reactivity is slightly over-predicted for the two configurations : +480 pcm ± 600 pcm (2σ) with SHEM-MOC and +510 pcm ± 600 pcm (2σ) with REL2005 - The average power ratio P MOX/PUO2 is also slightly over-predicted but remains within 2σ experimental uncertainty margins: +1.2% ± 2.4% (2σ) with SHEM-MOC and +1.8% ± 2.4% (2σ) with REL2005. - one pin excepted in each type of assembly, the results obtained on pin-by-pin fission rates for UO2 and MOX assemblies are also very satisfactory, in particular near the interface: ±1.4% ± 1.6% (2σ) with SHEM-MOC and ±1.5% ± 1.6% (2σ) with REL2005. These results demonstrate the ability of both APOLLO2.8 schemes and JEFF-3.1.1 library to predict major neutronics parameters of MOX-UO2 fuelled cores, with the same precision as the UO2 cores. (authors)