Abstract and subjects
To provide an accurate accounting of plutonium present in the reprocessing facility wastes, we must be concerned with the possible presence of 244Cm in the same wastes. Curium-244 has a very high specific activity; the equivalent 240Pueff mass of 1 gram of 244Cm is 1.06 x 105 grams. Clearly, a significant bias in the Pu assay of a sample can occur if a measurement does not account for the presence of 244Cm in a sample. In this paper we present a method for the identification of curium contamination in low-activity wastes and a means of obtaining an independent passive neutron assay of 240Pu and 244Cm for certain cases. Neutron multiplicity counting provides three distinct observable parameters (singles, doubles, and triples) and permits the determination of the three unknowns (a, masses,, masscm) in a waste matrix. Other parameters of interest in multiplicity counting can be considered as known values; the leakage multiplication (ML) of waste drums is unity owing to the small quantity of material present in the matrix; the system efficiency (E) is treated as a known quantity and confirmed by the add-a-source correction as required. In the case of wastes free of 244Cm contamination, the analysis allows the operator to ensure that there is no Cm present in the wastes and that any observed neutron sources are attributable to Pu. If there is some minor Cm contamination in the wastes, the curium and Pu masses can be independently measured and reported. In the case of some first separation cycle wastes, the Cm content may overwhelm the neutron counting to such an extent that the Cm and Pu neutrons cannot be distinguished. If this is the case, historical Cm/Pu ratios may be used to infer the Pu content as is done in high-activity waste streams. In this report, we examine the level of curium contamination that can be tolerated and produce independent Pu and Cm assays from multiplicity counting.