REVIEW OF NON DESTRUCTIVE ASSAY TECHNIQUES UTILISED FOR DECOMMISSIONING OF PLUTONIUM FACILITIES AT AWE

摘要

Over the past fifteen years AWE has decommissioned and size reduced a large number of glove boxes that contained a wide spectrum of equipment that ranged from highly radiation attenuating structures, such as furnaces and lathes, to other less radiation attenuating apparatus, such as small discrete tools or simple work benches. In order to generate meaningful glove box residual fissile material inventory data, which can constructively inform the selection of measures needed to underwrite the criticality safety of size reduction and consignment to waste activities, several different types of Non Destructive Assay (NDA) measurement techniques are available at AWE. These are deployed for the estimate of the residual fissile material inventory prior to decommissioning activities and for the final NDA of waste containers, post decommissioning. The techniques range from the Decommissioning In-Situ Plutonium Inventory Monitor (DISPIM), through other Neutron Coincidence Counting (NCC) techniques (Neutron Panel monitoring) and gamma measurements to consideration of Thermo Luminescent Detector (TLD) data. This paper will present a comparison of the fissile material identified in the waste generated post decommissioning operations to the NDA estimate of the residual fissile material inventory for the glove boxes, as well as provide a direct comparison between the different NDA techniques available at AWE. The findings to date indicate that the glove box residual fissile material inventory used for criticality safety purposes bounds the decommissioning process, subject to the suitable deployment of the NDA technique and the inclusion of appropriate uncertainties.