Non-destructive assay of drum package radioactive wastes utilizing tomographic gamma scanning

摘要

A methodology for nondestructive assay (NDA) of drum packaged radioactive waste materials is investigated using Emission Computed Tomography procedures. The current predominant NDA technique is the use of the Segmented Gamma Scanner. Tomographic Gamma Scanning improves upon this method by providing a low resolution three-dimensional image of the source distribution, yielding both spatial and activity information. Reconstruction of the source distribution is accomplished by utilization of algebraic techniques with a nine by six voxel model with detector information gathered over scanning intervals of ninety degrees. Construction of a linear system to describe the scenario was accomplished using a point-source response function methodology, where a 54 x 120 matrix contained the projected detector responses for each source-detector geometry. Entries in this matrix were calculated using the point-kernal shielding code QAD-CGGP. Validation was performed using the MCNP photon transport code. Solutions to the linear system were determined using the Non-Negative Least Squares (NNLS) algorithm and the LSMOD algorithm. A series of four scans were performed, each reconstructing the source distribution of a mock-up waste package containing a single 73 mCi Cs-137 point source. For each scan, the source was located in a different location. Results of the reconstruction routines accurately predict the location and activity of the source.