L/ILW Waste Characterisation by the ENEA Multi-Technique Gamma System SRWGA

The SEA Radioactive Waste Gamma Analyser (SRWGA), is the gamma assay system of the ENEA Laboratory for L/ILW Waste Characterisation, which started operating in 1996 as a simple gamma scanner and has been under a continuous improvement process to became a multi-techniques system. The SRWGA is designed for the assay of radioactive waste drums containing gamma emitting nuclides. The system operates with an XtRa (extended range) Ge coaxial detector. This is liquid nitrogen colled, and shielded by means of a lead cylinder with two collimation windows; one mixed transmission source is provided. The system allows the application of four different measuring techniques, each one with its peculiar field of application, depending on waste characteristics or measuring time: Open Geometry, Segmented Gamma Scanning (with multi-energy transmission correction), Angular Scanning and, recently, Low Resolution Emission and Transmission Tomography, as the SRWGA is now endowed with new mechanical motions systems for tomographic capabilities. Tomographic reconstructions are obtained by means of a backprojection filtered by convolution methods (for transmission tomography) and Best Likelihood Maximisation (for emission tomography). The information obtained with transmission and emission tomography allows the localisation of matrix dishomogeneities and hot spots, carrying out a strong reduction of total activity uncertainties. This work presents the experimental results obtained using certified γ sources located in known matrices.