Year
2011
Abstract
Existing neutron based systems used for the detection of Special Nuclear Material (SNM) in Safeguards application are typically based on 3He proportional counters requiring relatively large volumes of the gas (up to several thousand liters per system). Because of the severe 3He shortage, a replacement technology for neutron detection is required in the near future. There are competing demands for 3He gas from other industries, as well as medical, security and research fields. It is estimated that the total 3He annual demand is now approximately 65,000 liters compared to total worldwide annual supply of 15,000 liters. As a result of this shortage there is a major drive for alternative detection technologies to be developed for wide scale deployment as a long term replacement for 3He. There are three basic requirements for neutron detectors for safeguards applications involving detection and measurement of SNM: 1) high absolute detection efficiency, 2) low intrinsic gamma ray sensitivity of the detector and 3) maintaining neutron detection efficiency when simultaneously exposed to high gamma ray exposure rate. In addition, safeguards sensors may need to meet specific requirements of the application area including 1) security and integrity of data collection; 2) backward compatibility with existing systems and data collection methods; 3) long term electronic stability in harsh environments; 4) low or zero maintenance; 5) operability in unattended mode; 6) easy for field inspectors to operate with minimal training/specialization; and 7) applicability in a wide range of applications to allow agencies to standardize their designs. Several alternative detectors are currently available as near term replacement for 3He that could potentially meet the above requirements. These include Boron trifluoride (BF3) filled proportional counters, 10B lined proportional counters, 10B doped plastic scintillators, 6Li loaded optical fiber scintillators and 6LiF/ZnS(Ag) screens with a bulk, wavelength-shifting light-guide. The capabilities of these alternatives is reviewed with respect to the long term requirements for safeguards systems such as drum and crate assay system, slab counters, Pu/MOX canister verification and well counters. Performance is compared to the 3He baseline technology with any potential technical capability improvements that each alternative could offer also being considered.