When accounting for nuclear material, neutron well counters are a common and reliable instrument to measure plutonium mass. In addition to mass quantification, determining the isotopic composition is useful to provide more information about a nuclear sample and further verify the nuclear material accounting process. For facilities that utilize neutron well counters in a fixed inline configuration, such as glovebox line processes, it is likely that design restraints will make it difficult to include high-resolution gamma detectors, such as a germanium detector, near a neutron well counter. This requires nuclear samples to be measured separately for gamma spectroscopy. The transportation of nuclear material also introduces a dynamic background that can result in invalid background subtraction and potentially provide incorrect information about the nuclear sample. This research integrates gamma detectors in a neutron well counter for performing identification and quantification measurements simultaneously to reduce the measurement time and improve the efficiency of the nuclear material accounting process. A traditional neutron well counter was modeled with the addition of cadmium zinc telluride (CZT) gamma detectors to replace 3He neutron detectors. CZT detectors were chosen due to their smaller size and adequate resolution for isotopic composition. Simulations were run using the Monte Carlo N-Particle Transport (MCNP) code for its interface to design and optimize radiation detectors and the environment around them. A plutonium source was modeled inside the well cavity of the well counter to emulate a detector measurement and tallies were used in MCNP to track the information about the sample. Additional studies were performed to verify neutron coincidence parameters and analyze the background sensitivity of the CZTs. The methodology behind these simulations provides insight on the effectiveness of introducing gamma detectors in a neutron well counter for nuclear material accounting.
Year
2024
Abstract