Update on Calibration of the Lawrence Livermore National Laboratory Passive-Active Neutron Drum Shuffler for Measurement of Highly Enriched Uranium Oxide

In October of 1999, Lawrence Livermore National Laboratory (LLNL) began an effort to calibrate the LLNL passive-active neutron (PAN) drum shuffler for measurement of highly enriched uranium (HEU) oxideA. single unit of certified reference materia(Cl RM) 149 [Uranium (93% Enriched) Oxide - U30s Standard for Neutron Counting Measurements] was usetdo (1) develop a mass calibration curve for HEU oxide in the nominal range of 393 g to 3 144 g 235Ua, nd (2) performa detailed axial and radial mappingo f the detector response overa wide region of the PAN shuffler counting chamber. Results from thesffeo rts were reported at the Institute of Nuclear Materials Management 4 lStA nnual Meeting in July2 000. This paper describes subsequent efforts by LLNL to use a unit of CRM 146 [Uranium IsotopicS tandard for Gamma Spectrometry Measurements] in consort with Monte Carlo simulations of the PAN shuffler response to CRM 149 and CRM 146 units anda selected set of containers withC RM 149-equivalent U30st o (1) extendt he low range of the reported mass calibration curve to 10 g 235U, (2) evaluate the effect U of3 0, density (2.4 g/cm3t o 4.8 g/cm3) and container size (5.24 cm to 12.17 cm inside diameter and 6.35 cm to 17.72 cm inside height) on the PAN shuffler response, and (3) develop mass calibration curves for U,O, enriched to 20.1w t% 235U and5 2.5 wt% 235u