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

Madeline Lockhart; Richard L. Reed; Louise G. Evans; Vlad Henzl; John Mattingly

doi:10.1016/j.nima.2025.170231

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

Madeline Lockhart, Richard L. Reed, Louise G. Evans, Vlad Henzl, John Mattingly

Research output: Contribution to journal › Article › peer-review

Abstract

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.

Original language	English
Article number	170231
Journal	Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Volume	1072
DOIs	https://doi.org/10.1016/j.nima.2025.170231
State	Published - Mar 2025

Funding

This work was supported by the U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA) Office of Defense Nuclear Nonproliferation Research and Development (DNN R&D) Safeguards program. This research was performed under appointment to the Nuclear Nonproliferation International Safeguards Fellowship Program sponsored by the National Nuclear Security Administration's Office of International Nuclear Safeguards. This work was completed on behalf of DNN R&D by a multi-laboratory team including researchers from Los Alamos National Laboratory (LANL), Oak Ridge National Laboratory (ORNL), Sandia National Laboratories (SNL), and Y-12 National Security Complex with contributions from students at the University of Tennessee, North Carolina State University, and the University of Michigan. The authors would like to acknowledge and thank research collaborators including Dr. Holly Trellue and Dr. Daniel Jackson of LANL; Dr. Heather Reedy, Dr. Oskar Searfus, Dr. Peter Marleau, Dr. Eva Uribe of SNL; and Dr. Matt Cook and Mr. Alex Roberts of Y-12 National Security Complex. The authors would also like to acknowledge and thank Greg Nutter, Dr. Robert D. McElroy, Jr. Dr. Karen Koop Hogue, Dr. Susan Smith, Ms. Rachel Hunneke, Mr. Scotty Mathews, and Mr. Dave Aguero of ORNL for assisting with the coordination, facilitation, and supervision of numerous experimental measurement campaigns, as well as for productive discussions on this topic. This work was supported by the U.S. Department of Energy (DOE) National Nuclear Security Administration (NNSA) Office of Defense Nuclear Nonproliferation Research and Development (DNN R&D) Safeguards program. This research was performed under appointment to the Nuclear Nonproliferation International Safeguards Fellowship Program sponsored by the National Nuclear Security Administration\u2019s Office of International Nuclear Safeguards.

Keywords

AWCC
Active coincidence calibration curve
Active neutron interrogation
Fast mode
Fissile mass
Neutron coincidence counting
Thermal mode
Uranium oxide
Uranium-233
Uranium-235

Access to Document

10.1016/j.nima.2025.170231

Cite this

Lockhart, M., Reed, R. L., Evans, L. G., Henzl, V., & Mattingly, J. (2025). Active neutron coincidence counting to determine fissile mass of uranium oxide containing ²³³U and ²³⁵U. Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1072, Article 170231. https://doi.org/10.1016/j.nima.2025.170231

@article{c7644a229d754801a9fc1e4bf3ccb6cb,

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

abstract = "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.",

keywords = "AWCC, Active coincidence calibration curve, Active neutron interrogation, Fast mode, Fissile mass, Neutron coincidence counting, Thermal mode, Uranium oxide, Uranium-233, Uranium-235",

author = "Madeline Lockhart and Reed, {Richard L.} and Evans, {Louise G.} and Vlad Henzl and John Mattingly",

note = "Publisher Copyright: {\textcopyright} 2025",

year = "2025",

month = mar,

doi = "10.1016/j.nima.2025.170231",

language = "English",

volume = "1072",

journal = "Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment",

issn = "0168-9002",

publisher = "Elsevier",

}

Active neutron coincidence counting to determine fissile mass of uranium oxide containing ²³³U and ²³⁵U. / Lockhart, Madeline; Reed, Richard L.; Evans, Louise G. et al.
In: Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 1072, 170231, 03.2025.

Research output: Contribution to journal › Article › peer-review

TY - JOUR

T1 - Active neutron coincidence counting to determine fissile mass of uranium oxide containing 233U and 235U

AU - Lockhart, Madeline

AU - Reed, Richard L.

AU - Evans, Louise G.

AU - Henzl, Vlad

AU - Mattingly, John

PY - 2025/3

Y1 - 2025/3

N2 - 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.

AB - 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.

KW - AWCC

KW - Active coincidence calibration curve

KW - Active neutron interrogation

KW - Fast mode

KW - Fissile mass

KW - Neutron coincidence counting

KW - Thermal mode

KW - Uranium oxide

KW - Uranium-233

KW - Uranium-235

UR - http://www.scopus.com/inward/record.url?scp=85215869527&partnerID=8YFLogxK

U2 - 10.1016/j.nima.2025.170231

DO - 10.1016/j.nima.2025.170231

M3 - Article

AN - SCOPUS:85215869527

SN - 0168-9002

VL - 1072

JO - Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

JF - Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment

M1 - 170231

ER -