Calibration of the Lawrence Livermore National Laboratory Passive-Active Neutron Drum ShuMer for Measurement of Highly Enriched Uranium in Mixed Oxide

As a follow-on to the Lawrence Livermore National Laboratory (LLNL) effort to calibrate the LLNL passiveactive neutrond rum (PAN) shuffler for measurement of highly enriched uranium (HEU) oxiad me, ethod has been developedt o extend the use of the PAN shuffletor the measuremento f HEU in mixed uranium-plutonium (U-Pu) oxide. This method uses the current LLNL HEU oxide calibration algorithms, appropriately corrected for the mixed U-Pu oxidea ssay time, and recently developed PuOc, alibration algorithms to yield the masso f 235Up resent via differences between the expected count rafoter the PuO, and the measured count rateo f the mixed U-Pu oxide. Thls paper describes the LLNL effort to use PAN shuffler measurements of units of certified reference material (CRM) 149 [Uranium (93% Enriched) Oxide - U30s Standard for Neutron Counting Measurements] and CRM 146 [Uranium Isotopic Standard for Gamma Spectrometry Measurements] and a selected set of LLNL Pu0,-bearing containers in consort with Monte Carlo simulations of the PAN shuffler responset o each to (1) establish and validatea correction to the HEU calibration algorithm for the mixed U-Pu oxide assay time, (2) develop a PuO, calibration algorithm that includes the effect of PuO, density( 2.4 g/cm3 to 4.8g /cm’) and container size( 8.57 cm to 9.88c m inside diameter and 9.60 cm to 13.29 cm inside height) on the PAN shuffler responsaen,d (3) develop and validate the methodf or establishing them ass of 235Up resent in an unknown of mixed U-Pu oxide