Performance of a DrumScan^® HRGS Solo Scanner for the Assay of Legacy Waste at the Belgoprocess Site

On the sites of Belgoprocess several thousands of drums containing conditioned legacy waste are stored. A significant number of these waste packages are 220 litre drums containing radioactive waste embedded into inactive bitumen. Most of the radioactive waste in these drums was generated during the development and production of MOX-fuels and the operation of the Eurochemic reprocessing plant. The current state of a number of these packages is no longer acceptable for long term storage. In order to make the waste packages acceptable for interim storage a repackaging process was developed. The process involves the repackaging of the waste items into 400 or 700 litre waste drums and a non-destructive gamma-ray assay (NDA) measurement performed on the new package. The aim of the NDA measurement is to detect significant quantities of fissile material in order to demonstrate compliance with the operational limits of the storage building. Since the waste items are destined for geological disposal, there is no specific need for a detection limit in the order of milligrams of plutonium as required for surface disposal. To meet this NDA requirement Babcock International Group supplied, calibrated and commissioned an open geometry system from its HRGS product range. The DrumScan® HRGS Solo assay system was delivered to the Belgoprocess site in 2009 after completing a series of factory acceptance tests performed in the UK. In May 2009 after successful completion of the site acceptance tests performed in Belgium, the system has been undergoing extensive testing and validation by Belgoprocess in order to demonstrate acceptance and compliance to the Belgian Radioactive Waste Agency, NIRAS/ONDRAF. After a careful evaluation of the qualification file, NIRAS/ONDRAF approved the system for operational measurements at the end of 2010. This paper provides a detailed description of the NDA requirement, calibration methodology, system validation tests and overall measurement performance of the system.