Validation of Neutron Flux and Activation in the Nagra AMAC model of the Mühleberg Power Plant

Abstract

The decommissioning of the Mühleberg Nuclear Power Plant (KKM) is supported by Nagra (National Cooperative for the Disposal of Radioactive Waste) through computational analysis of neutron activation in the reactor components and structures using the Nagra Advanced Methodology for Activation Characterization (AMAC). To validate these calculations, measurements of neutron flux and neutron-induced activity were carried out in the form of two foil activation campaigns (72 samples) and three concrete sampling campaigns (118 samples). Generally, the ratio of calculated to measured activities is in the order of 2 in the proximity of the reactor pressure vessel and 3 in the upper sections of the drywell. As expected, the flux in the lower (spherical) part of the drywell is significantly overestimated due to the simplified modelling of this space. The overestimation, which ratios of up to 10, can be corrected by scaling the calculated radionuclide activity distributions in the vicinity of the validation locations.