OECD/NEA INTERNATIONAL BENCHMARK ON POWER DISTRIBUTION WITHIN MOX FUELED ASSEMBLIES

摘要

The second phase of an OECD/NEA international benchmark exercise for prediction of powerrndistribution within MOX fueled assemblies has been undertaken. Ten institutions world-wide contributedrnto this exercise, and more than 15 calculation schemes were examined including the majority of thernmethods used for reactor design: collision probability, SN transport (finite differences and nodal),rndiffusion (finite differences and nodal), Monte Carlo, power reconstruction methods, etc. In thisrnbenchmark exercise, not only numerical schemes in production code systems, but also the globalrnperformance including cross-section data reduction methods were investigated.rnThe benchmark geometry consists of one central MOX assembly surrounded by eight UO2 assemblies.rnThe MOX assembly contains fuel pins in three different plutonium enrichments (4.3%, 7.0% and 8.7%).rnFor each of the fuel cells, k￥, critical buckling, migration area, and absorption/fission reaction rates perrnisotope in one group and three groups involving the 5 keV and 4 eV boundaries were investigated.rnFor core calculations, keff and pin-by-pin group integrated fission rates on 1/8 of the geometry, includingrn235U fission rate in the central cell of each assembly, were reported.rnThe standard deviations in k￥ are about ±500 pcm for the MOX cells and ±600 pcm for the UO2 cell.rnThese deviations are due to the differences in the nuclear data libraries and the different self-shieldingrnmethods used. Concerning core calculations, the average keff is 1.0708 with a spread of ±860 pcm.rnThe spread is directly related to the nuclear data libraries and to the calculation methods used. As for thernpin-by-pin power distribution, a global overestimation of MOX pin power up to 1.3% is observed. At therninterface between the MOX pins and the first UO2 row, the power difference is about 1.5% (+1.3% in thernMOX 4.3 row, and -0.2% in the UO_2 row).