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Undeclared uranium hitches a ride on cobalt exports from Congo, study says
Philippe (left) and Manzuk quantified the amount of uranium that has been exported from the DRC in cobalt shipments or left behind in the environment. (Photo: Joel Hallberg/UW–Madison)
Researchers at the University of Wisconsin–Madison and Princeton University have published a study in Nature Communications that calls attention to a blind spot in nuclear nonproliferation: The Democratic Republic of the Congo (DRC) has exported thousands of metric tons of uranium, and there is no accounting for where it has gone.
In partnership with Lighthouse Reports and the Financial Times, UW–Madison nuclear engineering professor and nuclear security expert Sébastien Philippe and Ryan Manzuk, a geologist and research fellow in Philippe’s group and at Princeton, conducted the study using countrywide mineralization and geochemical data.
Z. D. Whetstone, K. J. Kearfott
Nuclear Technology | Volume 176 | Number 3 | December 2011 | Pages 395-413
Technical Paper | Radiation Transport and Protection | doi.org/10.13182/NT10-118
Articles are hosted by Taylor and Francis Online.
This research was conducted to determine the optimal way to shield a compact, isotropic neutron source into a beam for active interrogation neutron systems. To define the restricted emission angle and to protect nearby personnel when stand-off distances are limited, shielding materials were added around the source. Because of limited space in many locations where active neutron interrogation is employed, a compact yet effective design was desired. Using the Monte Carlo N-Particle Transport Code, several shielding geometries were modeled. Materials investigated were polyethylene, polyethylene enriched with 10B, water, bismuth, steel, nickel, INCONEL® alloy 600, tungsten, lead, and depleted uranium. Various simulations were run testing the individual materials and combinations of them. It was found that at a stand-off distance of 1.5 m from the source, the most effective shielding configuration is a combination of several layers of polyethylene and steel. Without any shielding, the dose is 3.71 × 10-15 Sv/source particle. With a shielding consisting of multiple layers of steel totaling 30 cm thickness interspersed with several layers of polyethylene totaling 20 cm thickness, the dose drops to 3.68 × 10-17 Sv/emitted neutron at radians opposite the shield opening. The layered shielding approach is more effective at reducing dose equivalent and neutron fluence than shields made out of single continuous layers of the same material and thicknesses. Adding boron to the polyethylene and substituting tungsten for steel would make the shielding more effective but would add mass and cost.