Calculation methods for safety assessments of research reactors

The BER II (Berliner Experimental Reactor) is an open pool type reactor located in Berlin (Germany), primarily used for neutron scattering experiments. It has been in operation since 1973. After each core refuelling, the German safety authority imposes to perform a large amount of low power measurements in order to demonstrate that the new core fulfils the limits allowed by the SAR (Safety Analysis Report). Absorbers reactivity worth and fluxes measurements are systematically carried out to check the compliance of the new core. In order to reproduce these measurements, AREVA TA and BER II have decided to perform a set of neutronic calculations with COCONEUT (COre COnception NEUtronic Tool). This scheme is based on both multigroup transport (2D) theory and diffusion theory (3D) using APOLLO2 and CRONOS2 deterministic codes. It allows one to evaluate the main performances and safety parameters for any types of MTR-type fuel core with a minimal amount of time and effort. The aims of this study are to evaluate the compliance of COCONEUT calculations to safety assessments. Results of the calculations are benchmarked with experimental data from Kern #117 core's BOC (Begin Of Cycle). This paper presents the first comparisons between the experimental data from BER II and the results of COCONEUT calculations on the reactivity worth of the absorbers. (author)