THERMAL NEUTRON IMAGING OF SPENT FUEL STORAGE CASK FOR SAFEGUARDS VERIFICATIONS AND OTHER POTENTIAL APPLICATIONS TO NONPROLIFERATION AND COUNTERTERRORISM

A nondestructive technique is described that can be applied to materials in sealed containers and that will provide confidence that the safeguarded materials in the container have not been partially removed since the previous inspection. Energetic neutrons emitted by spontaneous fission or by (alpha,n) reactions in stored materials are likely to be partially thermalized by hydrogenous materials in containers and to carry some information about the source strength and spatial distribution. This study addresses the question whether the thermalized fraction of the emitted neutrons can provide a signature that can be recorded by coded aperture imaging and used as a measure of integrity of the sequestered materials. In addition, for international safeguards applications, the neutrons emitted by spent fuel, should be detectable at significant stand-off distances.