Active neutron coincidence counting to determine fissile mass of uranium oxide containing ²³³U and ²³⁵U

Journal Article · Fri Jan 17 00:00:00 EST 2025 · Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment

DOI:https://doi.org/10.1016/j.nima.2025.170231· OSTI ID:2506856

Lockhart, Madeline ^[1]; Reed, Richard L. ^[2]; Evans, Louise G. ^[2]; Henzl, Vlad ^[3]; Mattingly, John ^[4]

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1. North Carolina State University, Raleigh, NC (United States); Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
2. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
3. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
4. North Carolina State University, Raleigh, NC (United States)

Active neutron coincidence measurements of uranium oxide (UO₃) were conducted with an active well coincidence counter (AWCC) at Oak Ridge National Laboratory (ORNL). We performed systematic measurements with the AWCC in fast and thermal mode of well-documented uranium oxide items containing ²³³U, ²³⁵U, and mixtures of the two isotopes up to 144 g of total fissile mass. The objective was to document active neutron coincidence measurements of items containing ²³³U and to assess the feasibility of ²³³U characterization and discrimination from ²³⁵U using existing neutron-based safeguards instrumentation and measurement methods. The colocation of ²³³U with other isotopes of uranium, including ²³⁵U, presents a challenge because existing nondestructive assay (NDA) methods are not tailored to these isotopic mixtures. Therefore, neutron signatures of ²³³U-bearing materials were performed and documented to inform the safeguards community when addressing future nuclear nonproliferation needs related to ²³³U for material control and accountability and potential thorium-based advanced reactors, which breed ²³³U. The neutron coincidence measurements described contribute to the foundation for future development of material characterization methods and provide experimental data points for validation of simulations. We measured active calibration curves, which relate the fissile mass to the coincident count rate, for 2–80 g of ²³³U, 2–64 g²³⁵U, and 4–144 g of a mixture of ²³³U and ²³⁵U. In thermal mode, the total fissile mass could be determined, but isotope discrimination is not possible. An unknown mixed item was measured in thermal mode and the total fissile mass was calculated within 1σ of the declared mass. In fast mode, we observe a difference between the ²³³U and ²³⁵U curves, but a low coincidence count rate and high uncertainty prevent statistically meaningful determination of fissile mass, especially for ²³⁵U.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 2506856
• Alternate ID(s): OSTI ID: 2507000
• Report Number(s): LA-UR--24-26797
• Journal Information: Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment, Journal Name: Nuclear Instruments and Methods in Physics Research. Section A, Accelerators, Spectrometers, Detectors and Associated Equipment Vol. 1072; ISSN 0168-9002
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
AWCC
Active coincidence calibration curve
Active neutron interrogation
Fast mode active well coincidence counter
Fissile mass
Neutron coincidence counting
Thermal mode
Uranium oxide
Uranium-233
Uranium-235
nondestructive assay