Simulated Imaging Results from Active Interrogation of Highly Enriched Uranium

Year
2016
Author(s)
Michael C. Hamel - Department of Nuclear Engineering & Radiological Sciences
S. D. Clarke - University of Michigan
S. A. Pozzi - Department of Nuclear Engineering & Radiological Sciences, University of Michigan
John K. Polack - Department of Nuclear Engineering & Radiological Sciences, University of Michigan
T.L. Beames-Canivet - Department of Nuclear Engineering and Radiological Sciences University of Michigan
L.O. Supic - Department of Nuclear Engineering and Radiological Science, University of Michigan
Abstract
The Dual-Particle Imager (DPI) is a system designed to detect, identify, and localize the neutron and gamma-ray signatures emitted from special nuclear material (SNM). The DPI is a neutron and Compton scatter camera which uses liquid organic and NaI(Tl) scintillators in a a two-plane geometry. Passive detection of neutrons and gamma rays enables the imaging of weapons-grade plutonium; however, the neutron emission rate from spontaneous fission in highly enriched uranium (HEU) is too small to reliably detect with passive measurements. Imaging materials such as HEU requires active interrogation. The DPI will be part of an active interrogation measurement campaign at the Nevada National Security Site Device Assembly Facility in July, 2016 where a 13.7-kg sphere of HEU will be activated with D-T, D-D, and AmLi neutron sources. The HEU will be measured bare, and shielded with polyethylene, iron, and tungsten. These experiments will test the ability of the DPI to accurately characterize shielded SNM. This paper will describe the Monte Carlo simulations run in support of the experiments using MCNPX-PoliMi. Simulated results will include the density of fissions in the Rocky Flats shells and the expected neutron and gamma-ray count rates in the system, which will be used to determine the amount of shielding required to prevent the data acquisition system from saturating. Images and energy spectra of the simulated experiments will also be reconstructed to help determine appropriate measurement times for each configuration.