Radiological Performance of an Automated HPGe Assay System for Bulk Containers of Decommissioning Waste Intended for Free Release

The decommissioning of a nuclear power plant is an immense engineering effort requiring an array of specialist tools and techniques. The decommissioning activities generate large quantities of lowactivity waste. For economic disposal, it is desirable to certify the waste as suitable for free release. Every container must be assayed to a sufficient degree of accuracy and sensitivity so that it may be certified as “free release”. The more reliable the analysis, the lower the total cost of decommissioning because of the high cost of radioactive waste disposal. Since the waste quantities are large, a suitable measurement system must be highly automated, reliable, and sensitive enough to reliably demonstrate that the free release criteria have been met. The automated system is required to measure a variety of sample sizes and forms: bags, boxes, and B25 containers, with densities approximately in the range 100 kg/m to 2000 kg/m. This paper gives the radiological performance (detection limits) of a commercial system designed for this application, installed at the SOGIN decommissioning sites at Caorso, Trino and Latina, Italy. The assay systems were developed by El.Se. Srl (ITALY) in collaboration with ORTEC. Each system uses four ORTEC Interchangeable Detector Module (IDM) mechanically cooled HPGe spectrometers. The IDMs simplify the mechanical design and improve the serviceability. Analysis of spectra is performed using the ORTEC ISOPlus waste assay software under control of a user interface developed using National Instruments LabView. A new “average MDA” algorithm has been developed and implemented. The system will be fully described and performance data will be presented.