Design Goals and Study for the Conversion of an Existing Cf-252 Shuffler to a Pulsed D-D Neutron Generator Based System

The classic Cf-252 shuffler is a passive/active NDA system utilized to quantify the fissile content of bulk SNM bearing debris within drummed and canned waste materials for disposition and MC&A inventory. The basic premise of the Cf-252 shuffler instrument is to measure the beta delayed neutron (DN) equilibrium yield over a period of several minutes using a rapid transport activation technique where the Cf-252 source is shuffled in and out of the assay chamber. We have been commissioned to replace the Cf-252 shuffler source with a pulsed D-D Neutron Generator (NG) within an existing, operating, Cf-252 shuffler. In this paper, we discuss the design goals which consider many aspects of limited space within the existing shuffler instrument but yet attain, or exceed, the physical performance of the original shuffler instrument. The design goals led to a comprehensive study involving MCNP models and comparisons between the modeled pulsed NG to the modeled and measured Cf-252 shuffler results. The study includes the placement of the NG and the necessity of modifying the HDPE for wiring harness access and turbo pump placement. The physics portion of the study included the comparison of using a D-D over the D-T as the NG, the pulsing frequency with respect to the dynamic die-away of the interrogating neutrons and the fission neutrons with an acceptable late gate for the DN much like the DDA system. An extensive design effort with respect to a customized, novel, high yield, constantly replenished, D-D NG involving shrinking the physical size but yet attaining 10E+9 nps when not pulsed. Once the proper approvals are in place, the Cf-252 source will be removed from the existing system, the shuffler instrument will be modified to accept the D-D NG and the system will then be subjected to a calibration and commissioning plan.