High resolution gamma spectrometry systems for assay of low level radioactive waste

This paper describes the Nuclear Electric Low Level Waste (LLW) Assay System, designed to produce the radioactivity inventory information required to demonstrate compliance with requirements contained in Certificates of Authorization for disposal of radioactive waste in the UK. The nucleonic and drum handling systems are discussed, together with the software, with particular reference to the choice of waste matrix self-shielding correction methodology. The system validation technique is described, showing that the system generates adequate, reproducible data. The part played by LLW fingerprinting in assaying non-gamma emitting isotopes is also discussed together with developments to enable measurement at de minimis levels. LLW Assay Systems are currently being installed at most Nuclear Electric sites