Year
1979
Abstract
A nondestructive neutron interrogation svstem, being developed to assay the 235u content in bulk waste solids and high enriched spent fuel assemblies, is described. The instrument will be used for both nuclear materials accountability and criticality control by the facility operator. A range of fissile contents varies from 0 to 400 g in the waste and from about 8 to 12 kg in the spent fuel elements. Measurements must be obtained in the presence of large neutron (1.2 x 10' n/s) and gamma (50 000 R/h) backgrounds. The system employs fast-neutron interrogation of the sample using a 5 mg \"^Cf source combined with delayed neutron counting after the source is moved to storage. Preliminary monte carlo calculations indicate measurement precisions of better than + 5% (2cr) are obtainable for waste loadings in excess of 200 g 235U.