Symposium on Advanced Sensors and Modeling Techniques for Nuclear Reactor Safety

Progress in Micro-Layered Fast Neutron Detectors

The study of accident tolerant fuels is ongoing at the Transient Reactor Test Facility (TREAT) at Idaho National Laboratory. The TREAT Facility provides quick, high-energy neutron pulses that simulate various accident conditions. These neutron pulses are presently detected using an array of fast-neutron detectors called Hornyak buttons. Hornyak buttons suffer from poor detection efficiency and significant Ĉerenkov radiation contamination in the signal. A new enabling technology, the micro-layered fast-neutron detector (MLFD), is presented to monitor neutron flux changes during mild-to-severe reactor accidents. The MLFD was designed to overcome the shortcomings of the Hornyak buttons and to improve detection efficiency. The MLFD is a novel proton-recoil scintillation detector constituting microscale alternating layers of hydrogenous medium and ZnS:Ag. The device employs peripheral photon detection for maximizing light collection while minimizing both gamma-ray and Ĉerenkov radiation background. The layered design offers several advantages, e.g., it overcomes the light-opacity limitation of polycrystalline ZnS, recoil protons have a high probability of reacting with the scintillation grains in their forward-directional path, the design and photomultiplier orientation eliminates the need for extraneous light guides, and the orientation largely minimizes Ĉerenkov generation and collection. The most striking ability of the MLFD is that its efficiency can be scaled higher by simply adding layers and increasing the length, up to 20 cm. Presently, a 40-mm MLFD has an intrinsic detection efficiency of 9.2% for a bare ²⁵²Cf source.