The MOX Powder Calculation Challenge OECD Benchmark Proposal and CRISTAL-RIB Results
Résumé
In 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 had
highlighted the poor database of representative experiments of low-moderated MOX powders, this blind
benchmark 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 powder
moisture 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 benchmarks
experiments, 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 using
EOLE 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.
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