Assay of contained waste using active and passive computed tomography

The US Department of Energy (DOE) has more than 600,000 transuranic waste drums temporarily stored at nearly 40 sites within the US. Contents of these drums must be characterized before they are transported for permanent disposal. Opening drums for examination is expensive mainly because of the safety precautions that must be taken. Current nonintrusive methods of characterizing waste in sealed drums are often inaccurate where assay errors are related to nonuniform measurement responses associated with unknown radioactive-source and waste-matrix-material distributions. These errors can be reduced by the application of imaging techniques that better measure the spatial locations of sources and matrix attenuation. Lawrence Livermore National Laboratory (LLNL) has developed an emerging gamma-ray nondestructive analysis (NDA) technology, called active and passive computed tomography (A and PCT), that identifies and accurately quantifies all detectable radioisotopes in closed containers of waste. The performance of the A and PCT technology has been determined by several open and blind tests. Several 15-replicate studies were completed for three of the four required activity ranges. The three ranges were measured by acquiring A and PCT data for three separate placements of radioactive standards within an empty-matrix drum. The standards had a total mass of 0.93, 9.3, and 33.48 g of 239Pu positioned within the drum and required 4, 0.75, and 0.5 h total assay time per replicate, respectively. The performance results are summarized in Table 1. Additional research is being performed to maintain requirements while decreasing assay time