Optimal configurations for passive monitoring in low gamma and neutron environments

Special nuclear material (SNM) storage vaults presently require periodic inventories as part of their safeguards and security plan. Associated with these inventories are a significant number of person hours with corresponding high cost. In addition, the entry necessary for these verification inventories subjects personnel to elevated radiation exposures. The requirement for human intervention in the vault is also a weak link in the total security effort. Thus, there is a significant need to provide a cost-effective, automated system for SNM vault monitoring to decrease or eliminate the need for human intervention into SNM storage vaults. Targeting these needs in 9 the safeguards and security community, a prototype system for remotely monitoring SNM sources based on fiber-optic and scintillator technology (FAST) was developed and demonstrated at Oak Ridge. A variety of FAST detectors have been designed and tested for gamma and thermal neutron detection for monitoring enriched uranium and plutonium (with moderation). The gamma-sensitive detector system was successfully demonstrated as a remote monitor of five depleted uranium sources in a Modular Storage Vault at a distance of five meters. The thermal neutron-sensitive detector system was tested using a 56.91 meV beam line at the Oak Ridge High Flux Isotope Reactor (HIFR)