Nuclear data analyses for improving the safety of advanced lead-cooled reactors

Abstract

A target accuracy assessment of the effective neutron multiplication factor, keff, for MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) lead-bismuth cooled fast reactor has been performed with JEFF-3.3 and ENDF/B-VIII.0 state-of-the-art nuclear data libraries and the SUMMON system. Uncertainties in keff due to uncertainties in nuclear data have been assessed against the target accuracies provided by SG-26 of the WPEC of OECD/NEA in 2008 for LFR. Results show that keff target accuracy is still exceeded by more than a factor of two using the latest nuclear data evaluations released in 2018. Consequently, nuclear data assimilation has been carried out using criticality experiments from the International Criticality Safety Benchmark Evaluation Project that are representative of MYRRHA. The results from this work show that the level of accuracy needed in nuclear data cannot be obtained using only differential experiments, but the combination of experimental covariance data and integral experiments together with Generalised Least Squares technique can provide adjusted nuclear data capable of predicting reactor properties with lower uncertainty and consistent with differential data.

Impact of nuclear data evaluations on data assimilation for an LFR

“…239 Pu (n,γ) 0 .185 Total uncertainty in k e f f 0.756 CIEMAT to perform complete automated sensitivity and uncertainty analyses of the most relevant criticality safety parameters of detailed complex reactor designs from the neutronic point of view, i.e., k e f f , β e f f , Λ e f f and reactivity coefficients, using state-of-the-art nuclear data libraries and covariances. The data assimilation (DA) has been done with DAWN [14], a data adjustment code developed by CIEMAT that uses Bayesian inference and a deterministic approach (the generalized least squares methodology) and integral experiments from the International Criticality Safety Benchmark Evaluation Project (ICSBEP) similar to the system, to adjust nuclear data and constrain uncertainties. Finally, a model of ALFRED at nominal conditions at Beginning of Cycle has been used in the calculations.…”