The Effect of Sample Packaging on Multiplicity Assays of Impure Plutonium Materials

Several initiatives involve the intermediate-to long-term storage of plutonium in various forms in shielded containers. These containers vary from the ALR-8 pit storage container, or a modification of it, to department of transportation (DOT) certified 6M and 9975 containers, to the Russian AT-400R. The ALR8s are used at Pantex, the 6M and 9975 containers are being considered for intermediate storage of materials in K-Area at Westinghouse Savannah River Site, and the AT-400R will be the container used at the Mayak Fissile Material Storage Facility. These containers include in their configurations various amounts of hydrogenous materials that thermalize and capture some of the neutrons emitted by the plutonium. In this paper, we describe Monte Carlo calculations of the behaviors of these containers and their impact on neutron multiplicity assays of plutonium materials. We also explore the implications of facilities that receive and perform material control and accountability measurements on materials stored in these container types.