Decommissioning of the BR3 biological shield: How a proper data analysis facilitates the D&D process

BR3, a former pilot reactor for Belgian commercial power plants, is currently being decommissioned. Because most technical equipment and installations are already dismantled, the focus of decommissioning is now on the building structure itself. More precisely, on the activated concrete biological shield surrounding the former reactor core. Before defining a dismantling strategy, it is essential to characterize the structure and compare results with the requirements for the various disposal options in the country of the licensee. The initial characterization of the BR3 biological shield was selected as use case within the EU horizon 2020 project INSIDER (INSIDER, 2017). Within this project we applied a data analysis and sampling design strategy (INSIDER D. a., 2019), resulting in a 3D model for the activity distribution throughout the entire concrete structure. In a next stage, the model was compared with conditional and unconditional release limits leading to clear targets on which parts and sections need to be removed to specific disposal sites. These targets served as input for the physical dismantling strategy itself, to decide which techniques are suitable for the job. As part of this project, test sections are defined, mainly for two purposes. On one hand to test and select on possible dismantling techniques, like hydraulic hammering and diamond wire cutting. On the other hand, to be used as verification of the modelled activity distribution which is initially based on a limited sampling size. This paper describes the implementation of the data analysis and sampling design strategy as developed in the INSIDER project. Additionally, actual results of dismantling of the test sections demonstrate the soundness of the approach. Throughout the project, the availability of the model and visual representations turned out to be crucial. Not only as a reference and communication aid for dismantling experts and regulatory bodies, but also to optimize the dismantling strategy development.