Year
2011
Abstract
This work is a part of a larger effort sponsored by the Next Generation Safeguards Initiative (NGSI) to develop an integrated instrument, comprised of individual nondestructive assay (NDA) techniques with complementary features, that is fully capable of determining Pu mass in spent fuel assemblies. While the first phase of the NGSI research effort focused on simulating the expected performance of individual NDA techniques, this paper will present preliminary work on the second research phase of the NGSI effort which involves integrating two instruments together. The two NDA techniques being integrated are differential die-away (DDA) and delayed neutrons (DN). The DDA technique measures the prompt neutron signal induced following active interrogation by thermal neutrons. As such the DDA signal is a stronger indicator of presence of the fissile isotopes 239Pu and 241Pu in spent fuel relative to 235U on a per gram basis given the relatively elevated cross sections and the number of neutrons emitted per fission (nubar) of the Pu isotopes. In contrast, the DN technique measures the delayed neutron signal emitted by fission fragments after induced fission. The DN signal is a stronger indicator of presence of the 235U relative to 239Pu since ~2.1 times as many DN’s are emitted following 235U fission.