Estimation of neutron fluence distribution within German PWR components for decommissioning studies

By the mid of April 2023, all German nuclear power plants (NPPs) will have been shut down. The final shutdown is followed by a post-operational phase in which measures can be carried out to prepare for the NPPs dismantling and decommissioning. One of the tasks in preparation for the dismantling is to acquire knowledge of the activation distribution within the reactor components. The activation levels depend on the neutron fluence rate within the reactor. Therefore, to achieve this task, a 3D detailed Monte Carlo model of a German PWR has been developed to calculate the neutron fluence rate distribution over the reactor geometry. The prediction credibility of the developed model was validated via metal foil-activation measurements carried out in two active PWRs. The results showed that the model is reliable and suitable for evaluating the neutron radiation field for the following activation calculations. This paper presents the Monte Carlo model and describes the calculations and measurement procedures.