Hybrid Monte Carlo/deterministic activation calculation to support the decommissioning of PWRs: Validation against data from the thermal shield of the Enrico Fermi NPP

The progressive aging of nuclear power plants (NPPs) in the world is a relevant issue for the nuclear industry. The radiological characterization of the reactor is usually performed using a combination of sampling campaigns and computer simulations, and the latter are particularly useful if measurements are limited. This paper describes the development of a four-step, hybrid Monte Carlo/deterministic calculation scheme to evaluate the residual activation of a pressurized water reactor, focusing the analysis on the Enrico Fermi power plant in Italy. The scheme performance is evaluated using the ratio between the calculated specific activities and the measured ones (C/M ratio) for each point and isotope considered. The overall performance is satisfactory, as the scheme provides conservative results with a good accuracy, without excessive overestimations. The present computational scheme can be adapted to study the lifetime of a NPP, thus providing a useful support tool for the dismantling process in NPPs