Burnup Credit Criticality Benchmark Phase IIB: Burnup Calculations of Gadolinium-Bearing Fuel Rods in Boiling Water Reactor Assemblies for Storage and Transportation

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The NEA Expert Group on Used Nuclear Fuel criticality (EGUNF) organised a Phase IIB benchmark to re-examine code and nuclear data performance for BWR lattice calculations and focus on the depletion modelling of gadolinium fuel in the burnup region near peak reactivity. Modelling of the gadolinium pins was specified in the benchmark to limit some of the modelling variations observed in the EGBUC Phase IIIC benchmark and to better isolate differences caused by code methods and nuclear data relevant to gadolinium depletion in the burnup range important to gadolinium depletion. The benchmark problem proposed here is based on the 9×9 STEP-3 assembly geometry of the Phase IIIC benchmark. The gadolinium model and depletion step sizes to be applied by all codes are specified in the benchmark, leaving the primary variables as code transport method and nuclear data library.

This report presents the results of the Phase IIB benchmark approved at the meeting of the Working Party on Nuclear Criticality Safety (WPNCS) in July 2018. Results of 37 depletion calculations from 14 organisations in 13 countries are compared and analysed in detail.