Development of a new multiplying assembly for research, validation, evaluation, and learning

A new multiplying test assembly is under development at Idaho National Laboratory to support research, validation, evaluation, and learning. The item is comprised of three stacked, highly-enriched uranium (HEU) cylinders, each 11.4 cm in diameter and having a combined height of up to 11.7 cm. The combined mass of all three cylinders is 20.3 kg of HEU. Calculations for the bare configuration of the assembly indicate a multiplication level of >3.5 (keff = 0.72). Reflected configurations of the assembly, using either polyethylene or tungsten, are possible and have the capability of raising the assembly's multiplication level to greater than 10. This paper will describe the MCNP calculations performed to assess the assembly's multiplication level under different conditions and describe the resources available at INL to support the use of these materials. We will also describe some preliminary calculations and test activities using the assembly to study neutron multiplicity.