Year
2014
Abstract
Neutron coincidence and neutron multiplicity counting have long been essential tools in international safeguards and M aterial C ontrol and A ccountability programs. However, the ongoing reduced availability and high cost of 3 He gas , which has been t raditionally used in these measurement systems , threaten to further limit the use of these techniques for these applications . In this paper we examine the use of a D irect M ultiplication M easurement (DMM) approach to extend the dynamic range of traditional neutron coincidence counting systems, potentially allowing comparatively low - performance systems, such as the widely used High Level Neutron Coincidence Counter (HLNCC - II) , to provide a comparable level of measurement precision for the impure mixed oxide ( MOX) materials expected from higher - efficiency multiplicity counting systems . Our general goal in developing the DMM technique was to enable the three - parameter multiplicity analysis to be performed using relatively modest performance neutron coincidence c ounting systems that require far less 3 He in comparison to the high - performance multiplicity counters typically used in this application . Because the technique requires less gas , these vital safeguards and accounting missions can be achieved within reduced gas allocations. The DMM technique provides a measurement of the item multiplication based on the induced fission rates from an external neutron interrogation source. We have performed an initial study of the performance of the technique using two standar d assay systems : the Oak Ridge 252 Cf shuffler and the Oak Ridge Large Volume Active Well Coincidence Counter (LAWCC) . In this paper the results of Monte Carlo simulations for both MOX and uranium materials are presented along with some preliminary measurem ent results for reference containers of uranium oxide.