Improved holdup blender assay system (IBAS) slope validation measurements to improve nuclear material accountancy of high alpha holdup

LaFleur, A. M.*; Nakamura, Hironobu ; Menlove, H. O.*; Mukai, Yasunobu ; Swinhoe, M. T.*; Marlow, J. B.*; Kurita, Tsutomu 

The IBAS (Improved Holdup Blender Assay System) system for safeguards and nuclear material accountancy (NMA) of holdup measurements is used at PCDF. The purpose of this detector is to measure the doubles rate from each glovebox in order to determine the mass of Pu holdup. In order to establish calibration curves for the IBAS detector and improve the holdup measurement methodology, JAEA conducted the IBAS calibration exercise with LANL support using MOX standards in 2010. In 2011, a cleanout exercise was performed and the results showed that the holdup removed from the glovebox had a significantly higher alpha term (alpha = 15.8 - 31.5) than the MOX standards (alpha = 0.67) used to establish the 2010 calibration curves. To further investigate these findings, JAEA conducted slope validation measurements in 2013 to confirm the validity of IBAS calibration slopes for the case of high alpha holdup. This paper describes the IBAS slope validation tests, analysis of the experimental results, and the evaluation of the need for a correction factor for the high alpha holdup. Quantifying the alpha term of the holdup in each glove box and understanding how this value changes over time is important to improving the overall NMA at PCDF. The results from this work will provide invaluable experimental data that directly supports safeguards and NMA measurements of plutonium holdup in gloveboxes.