The MOX Powder Calculation Challenge OECD Benchmark Proposal and CRISTAL-RIB Results

International audienceIn the framework of the WPNCS Expert Group on Uncertainty Analysis for Criticality Safety Assessment,we propose a blind numerical benchmark. Since the WPNCS Expert Group on Experimental Needs hadhighlighted the poor database of representative experiments of low-moderated MOX powders, this blindbenchmark is focused on MOX wet powders Three PuO$_2$ contents are proposed : 100%, 30% and 12.5%.Two Pu isotopic vectors are considered : a conservative one (0%, 71%, 17%, 11%, 1% for $^{238}$Pu up to$^{242}$Pu) and a realistic one obtained from reprocessed LWR 30 GWd/T fuels. For these 6 cases the powdermoisture rate is 3%. The MOX fissile medium is a sphere surrounded by 20 cm water reflector.The required results are the calculated K$_{eff}$ and the associated prior uncertainty. Using benchmarksexperiments, contributors should provide the projected-K$_{eff}$ and the corresponding posterior uncertainty.CRISTAL-V2 results based on JEFF3.1.1 nuclear data are presented. As an example, in the 30% PuO$_2$challenging case, the calculation uncertainty is decreased from 1160 pcm (1$\sigma$) down to 450 pcm usingEOLE and MASURCA critical Pu experiments. This uncertainty depends slightly on ‘conservative’ or‘realistic’ Pu because the representativity factor does not vary significantly with the Pu vector