Please note that this report was initially published in November 2022 (NEA/NSC/R(2022)3) under erroneous benchmark number IIB; in this updated version (NEA/NSC/R(2022)3/CORR) this has been corrected into IIID.
The Working Party on Nuclear Criticality Safety (WPNCS), under the Nuclear Science Committee (NSC) of the Nuclear Energy Agency (NEA), has organised several international benchmarks to assess variations in predicted kinf and nuclide concentrations in burnup calculations by different code systems. The Phase IIIC burnup credit (BUC) benchmark results for 9×9 “STEP-3” boiling water reactor (BWR) fuel assembly design, organised by the NEA Expert Group on Burnup Credit (EGBUC), showed that modelling options, i.e. spatial resolution of gadolinium pins and depletion step size, can cause significant variations in predicted kinf and assembly average nuclide concentrations. A Phase IIID BUC benchmark was subsequently organised by the NEA Expert Group on Used Nuclear Fuel criticality (EGUNF) 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 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. This report presents the results of the Phase IIID benchmark approved at the meeting of the WPNCS in July 2018. Results of 37 depletion calculations from 14 organisations in 13 countries are compared and analysed in detail.