The D-D Neutron Generator as an Alternative to Isotopic Neutron Sources in International Safeguards*

The 235U mass assay of bulk uranium items such as oxide canisters, fuel pellets, and fuel assemblies is not achievable by traditional gamma-ray assay techniques due to the limited penetration of the item by the characteristic 235U gamma rays. Instead, fast neutron interrogation methods such as active neutron coincidence counting must be used. For international safeguards applications, the most commonly used active neutron systems, the Active Well Coincidence Counter (AWCC), Uranium Neutron Collar (UNCL) and 252Cf Shuffler, rely on fast neutron interrogation using an isotopic neutron source [i.e., 252Cf or Am(Li)] to achieve better measurement accuracies than are possible using gamma-ray techniques for high-mass, high-density items. However, the Am(Li) sources required for the AWCC and UNCL systems are no longer manufactured, and newly produced systems rely on limited supplies of sources salvaged from disused instruments. The shuffler systems rely on the use of high-output 252Cf sources, which while still available have become extremely costly for use in routine operations and require replacement every five to seven years. Lack of a suitable alternative neutron interrogation source would leave a potentially significant gap in the safeguarding of uranium processing facilities. In this work, we make use of Oak Ridge National Laboratory’s Large Volume Active Well Coincidence Counter (LV-AWCC) and a commercially available D-D neutron generator to examine the potential of the D-D neutron generator as an alternative to the isotopic sources. We present the expected performance of the LV-AWCC with D-D generator for the assay of 235U based on the results of Monte Carlo N-Particle simulations.