Development of an Alternative to the Helium-3 Based Active Well Coincidence Counter with Boron Coated Straws

Abstract

An active well coincidence counter (AWCC) is used for Nondestructive Assay (NDA) of special nuclear material. This counter was developed for the International Atomic Energy Agency (IAEA) to perform in field inspections. Whether the sample that is analyzed spontaneously fissions or requires a neutron source to induce fission, multiple neutrons are emitted simultaneously in the event of fission. If the sample being quantified spontaneously fissions, then the AWCC can be used in passive mode. When the sample requires neutron induced fission, a small neutron source can be placed in equidistant compartments and the AWCC will be used in active neutron coincidence mode. Coincident neutron characteristics vary depending on the isotope, which allows for the sample to be identified and quantified. Since the inception of the AWCC, the detector has utilized ^3He. The shortage of ^3He gas in the world has created a necessity for an alternative neutron detection medium. A promising neutron detection option is boron-coated straws (BCS). The efficacy of BCS as a neutron detector has been proven in radiation portal monitors, vehicle mounted modular detectors, and handheld detectors, but has yet to be assessed in an AWCC with its original footprint. Analysis of the original AWCC with^ 3He and alternatives with ^10B-lined tubes and BCS was done in MCNPX. The comparison of the original technology to the proposed alternative was done in an effort to find a viable option for replacing ^3He as the detection medium.