Deterministic and Stochastic Approach for a Void Reactivity Effect Evaluation: application to a Generation IV Lead Fast Reactor (LFR)

This paper concerns two independent neutronic analyses performed by means of both a deterministic and a stochastic code, with the aim of evaluating the impact of different approaches and numerical methods on the calculation of critical reactor parameters. With regards to neutronics, the optimization of core design is strongly related to the accurate determination of important quantities as power distributions, absorbers worth and reactivity coefficients. An aspect of great relevance in Lead Fast Reactors (LFR) is the actual void reactivity evaluation: the purpose of this work is therefore to outline the physical problem and to compare the results concerning void effect contributors through a ‘cross-checked’ analysis. The field of investigation assumed for the code comparison corresponds to the reference configuration of the 600 MWe European Lead-cooled SYstem (ELSY-600), one of the Lead-cooled Fast Reactors within Generation IV Nuclear Energy systems program, under investigation in the EU 6th FP. Analyses are carried out on a 1500 MWth core with typical European mixed oxide fuel (MOX) in a three enrichment zones configuration made of wrapperless subassemblies and pins in square-lattice arrangement. The deterministic code ERANOS-2.1 and the Monte Carlo MCNP-4a have been employed in conjunction with the updated nuclear data library JEFF 3.1. ERANOS-2.1 has been utilized to assess the void reactivity variation and its splitting into the most relevant nuclides. Results have been compared with Monte Carlo outcomes of an analogous analysis performed by means of MCNP-4a, in order to get a rough idea of the spread of values for the considered parameters.