LFR mock-up reactivity effects

This work was carried out in the framework of the EU FP7 project “Fast Reactor Experiments for hYbrid Applications” (FREYA). In the Work Package 4 Task 4.1 (WP4 T4.1) a critical mock-up representative of the Lead Fast Reactor (LFR) concept was defined and assembled in the VENUS-F zero-power reactor at SCK•CEN research centre (Mol, B). Afterwards, standard core characterisation measurements were performed in T4.2 and reported in Deliverable D4.2. The LFR design chosen as reference is the 300 MWth ALFRED core, developed during the EU FP7 LEADER project. This technical report (Deliverable D4.3) summarises the T4.3 activities, that are:  the experimental measurements carried out to evaluate the void reactivity effects;  the Calculated-to-Experimental (C/E) comparisons between neutronic codes and standard core characterisation measurements (D4.2), as well as the C/E for the void effect analyses. The neutronic tools adopted for this study are the deterministic code ERANOS and the Monte Carlo codes MCNP and SERPENT, coupled with different neutron data libraries (e.g., JEFF and ENDF/B). Generally, a good C/E agreement was found for both standard and void effect measurements. But, for what concerns the core criticality, a C/E of about 1.01 was obtained with deterministic and stochastic codes in the “worst” library cases. Therefore, a dedicated study was performed to identify the possible causes of such discrepancy (between code - library and experiment, among the different libraries), by investigating the major contributors to the uncertainty on criticality in terms of reactivity effects.