An analysis of the experiments with erbium for the RBMK design - 250

The paper presents two series of the experiments in the critical facility performed to examine a standard RBMK fuel load and a load with erbium poison. The rods filled with erbium oxide powder and installed in a fuel assembly were used for the modeling of an erbium fuel. The experiments were performed under room temperature. The goal of the experiments was to determine the influence of erbium on the void reactivity effect and to give the data for neutron codes validation. The disagreement between the results of the experiments and calculations was obtained for some experiments. To explain this disagreement the direct modeling of the experiment in space and time was performed by STEPAN code. Besides the pulsed neutron source method was used for a number dehydrated assemblies to make measurements more accurate. The MCNP4A code was chosen for final calculated analyses of the experiments. Qualitative confirmation of calculated predictions was obtained, however discrepancy in estimations of reactivity effects was not always within interval of errors. (author)