Reclassification of Legacy Wastes to Minimise Disposal Costs and Phantom Inventory –
The UDASS Experience at LLWR

The management of nuclear waste has evolved and improved over the decades but remains dependent on accurate characterisation. With the refinement of non-destructive radiometric assay techniques which focus on minimising the measurement uncertainty and hence the reported radioactive inventory, it is possible to revisit the classification of legacy wastes leading to considerable savings in storage and disposal costs. The UK Low Level Waste Repository (LLWR) had 1808 drums of legacy waste from the Magazines that had been classified as ILW PCM (Intermediate Level Waste – Plutonium Contaminated Material) based on historical measurements. A small sample had been re-measured and found to be low level waste, so a campaign was initiated to re-assay all the drums to correctly consign them to the lowest radiological category. The ANTECH UDASS (Universal Drum Assay and Segregation Service), developed from extensive experience in manufacturing waste assay instruments and conducting services, was selected. The UDASS incorporates numerous refinements and updates to existing measurement technologies to optimise measurement efficiency and minimise measurement error. Examples include the variable aperture collimator permitting optimal measurement of a wide range of drum activities and a specialised high efficiency high purity Germanium (HPGe) detector to enhance measurement performance. The UDASS incorporates several operation modes which, after a pre-scan of the waste drum, delivers important information. One can select tailored settings to optimize measurement results as a function of the drum matrix contents heterogeneity. The measurement results are scrutinised by experienced radiometric physicists to ensure that the results are valid prior to their issue and use. The ANTECH UDASS measurement process has been subject to rigorous testing, validation and approval by LLWR and Sellafield technical authorities and accredited to ISO 17025 by the UK Accreditation Service (UKAS). The measurement campaign has resulted in 90% of the drums being reclassified from ILW to Low Level Waste (LLW) and 80% of the resulting LLW were reclassified to categories below LLW permitting landfill disposal. Savings of over £9MGBP and a significantly reduction of the LLWR site radiometric inventory were achieved.