Free Release Waste Characterisation During the Decommissioning of Windscale Pile 2 Chimney

The decommissioning of Windscale Pile 2 Chimney resulted in the removal of one of most historically significant and prominent features of the Sellafield site. The project was the first large scale concrete “free release” operation to be undertaken on the Sellafield nuclear site, producing 4500 tons of concrete of which 3000 tons was demonstrated to be “free release”. The paper describes the radiometric techniques employed in the characterization and segregation of the concrete into Low Level Waste (LLW), Very Low Level Waste (VLLW) and Free Release categories. It examines the robust solutions that were developed to meet the technical and regulatory challenges of the project, which included the definition of free release, the selection of averaging volumes, the testing and validation of the monitoring systems employed for bulk quantities of concrete and the identification and removal of small numbers of fuel particles from the free release waste stream. As a result of interest shown by other BNFL and UKAEA decommissioning projects at Sellafield, the paper finishes by discussing ways in which the system may be developed to assay other waste streams.