TECHNIQUES AND METHODS IN NUCM MATERIALS TRACEABILITY

HEU AND PLUTONIUM OF UNKNOWN ORIGIN HEU SAMPLE Isotopic signatures and correlation methods were applied to determine the origins of HEU and plutonium samples reported as illicit trafficking in nuclear materials. In the HEU case, the isotopic concentrations reported in weight percent (w/o) were 1.078, 87.768, 0.210, and 10.944 for U-234, U-235, U-236, and U-238, respectively. The isotopic signature of U-236 at the product level of about 0.210 percent indicates that in the enrichment process the initial feed U-236 concentration could have ranged in the 0.004 to 0.007 percent leveI, and the depleted uranium stream could have U-235 tails ranging between 0.2 and 0.3 percent. The U-236 feed concentration level is indicative of uranium-reprocessing streams from very low-burnup fuels. The reported U- 234 and U-236 isotopics indicates that the HEU sample is the product of a gas diffusion isotopic separation process of a uranium product stream from reprocessed low-burnup fuels. PLUTONIUM SAMPLE The measured concentration of the Pu-242 isotope at the level of 0.688 weight (w/o) percent in the plutonium vector, 0.17, 87.56, 10.78, 0.809, 0.688 percent of Pu-238, Pu-239, Pu-240, Pu- 241, and Pu-242, respectively, as reported in the plutonium sample, is indicative of natural uranium fuel irradiated in the extreme outer regions of the rector core. In the outer regions of the core, the spectrum is softer, the Pu-239 generation is much reduced, and the transmutations of the higher plutonium isotopes are increased. The reported Pu-!U 1 concentration at the 1 percent level compared to the normally anticipated level of about 2 percent, which is consistent with the low burnup of natural uranium, indicates that the sample is representative of irradiated natural uranium fuel reprocessed some 15 years ago. However, in the outer-region of the core, the Pu/U ratio is extremely low (low flux level) and for Pu-239 at about 87 percent, the burnup is also very low. The amount of plutonium produced in this region could therefore be insignificant.