Calibration of the Lawrence Livermore National LaboratoryPassive-Active Neutron Drum Shuffler for Measurement of Highly Enriched Uranium inOxides within DOE-STD-3013-2000 Containers

摘要

Lawrence Livermore National Laboratory (LLNL) uses the LLNL passive-active neutron drum (PAN)rnshuffler (Canberra Model JCC-92) for accountability measurement of highly enriched uranium (HEU) oxidernand HEU in mixed uranium-plutonium (U-Pu) oxide. In June 2002, at the 43rd Annual Meeting of the Institute rdrnof Nuclear Material Management, LLNL reported on an extensive effort to calibrate this shuffler, based onrnstandards measurements and extensive simulations, for HEU oxides and mixed U-Pu oxides in thin-walledrnprimary and secondary containers. In August 2002, LLNL began to also use DOE-STD-3013-2000rncontainers for HEU oxide and mixed U-Pu oxide. These DOE-STD-3013-2000 containers are comprised of arnstainless steel convenience can enclosed in welded stainless steel primary and secondary containers. Comparedrnto the double thin-walled containers, the DOE-STD-3013-2000 containers have substantially thicker walls,rnand the density of materials in these containers was found to extend over a greater range (1.35 g/cm to 3rn4.62 g/cm ) than foreseen for the double thin-walled containers. Further, the DOE-STD-3013-2000 Standard 3rnallows for oxides containing at least 30 wt% Pu plus U whereas the calibration algorithms for thin-walledrncontainers were derived for virtually pure HEU or mixed U-Pu oxides. An initial series of Monte Carlornsimulations of the PAN shuffler response to given quantities of HEU oxide and mixed U-Pu oxide in DOE- DOESTD-rn3013-2000 containers was generated and compared with the response predicted by the calibrationrnSTD-algorithms for thin-walled containers. Results showed a decrease on the order of 10% in the count rate, andrnhence a decrease in the calculated U mass for measured unknowns, with some varying trends versus U mass.rnTherefore a decision was made to develop a calibration algorithm for the PAN shuffler unique to the DOE- DOESTD-rn3013-2000 container. This paper describes that effort and selected unknown item measurement results.