Calibration of the K-Area 252Cf Shuffler to Measure Uranium in EU-Pu Oxide

To extend their ability to perform accountability and verification measurements of 235U in a U-Pu oxide matrix, the K-Area Material Storage facility commissioned the development and construction of a Passive/Active 252Cf Shuffler. A series of 252Cf, PuO2, and U-Pu oxide standards, in addition to a single U3O8 standard, were measured to characterize and calibrate the shuffler. Accompanying these measurements were simulations using MCNP5/MCNPX, aimed at isolating the neutron count- rate contributions for each of the nuclides present. Two calibration methods for determining the 235U content in mixed U-Pu oxide were then developed, yielding comparable results. The first determines the 235U mass by estimating the 239Pu/235U ratio-dependent contributions from the primary delayed neutron contributors. The second defines an average linear response based on the 235U and 239Pu mass contents. In each case, it was observed that self-shielding due to 235U mass has a large influence on the observed rates, requiring bounds on the applicable limits of each calibration method.