Abstract
Proposed thorium-based nuclear fuel cycles are likely to require quantification and verification of 233U within nuclear material. Because of their similar fission cross sections, active neutron nondestructive assay (NDA) systems may respond similarly to 233U and 235U. Traditional safeguards equipment has been optimized for 235U and 238U quantification associated with conventional uranium/plutonium fuel cycles and may not be directly applicable to 233U quantification when mixed with other actinides. This work used models of the large volume active well coincidence counter (LV-AWCC) at Oak Ridge National Laboratory to evaluate the performance of this neutron NDA system to differentiate fissile uranium isotopes. The models were developed to simulate NDA system performance in response to a number of triangular radiation signature training device sources within the central cavity or well. This work predicted that the LV-AWCC can effectively differentiate 233U from 235U in certain modes of operation. In active mode, the LV-AWCC with the cadmium liner results in different doubles count rates between the fissile isotopes for a given fissile uranium mass. Without the cadmium liner, the uranium isotopes provide a statistically indistinguishable doubles count rate response for the fissile masses considered in this work (up to approximately 150 g). The cadmium liner serves to harden the neutron interrogation spectrum, which better exploits the notable difference in the 233U and 235U fission cross sections at approximately 1 eV. In passive mode, the two fissile isotopes exhibit different doubles and singles count rates regardless of liner presence because the passive source strength of 233U is approximately 2 orders of magnitude stronger than that of 235U due to the shorter half-life and correspondingly higher (α, n) yield. We conclude that using neutron interrogation in the LV-AWCC, two measurements are needed to quantify 233U content in mixed uranium items. The first measurement is used to determine the total fissile uranium mass using a mode that cannot distinguish fissile isotopes (i.e., where a similar response is observed for both fissile uranium isotopes such as active doubles without cadmium or using a thermal neutron interrogation source). The second measurement is used to determine the 233U content by using a differentiating technique (e.g., passive doubles, passive doubles to singles ratio, active doubles with cadmium).
| Original language | English |
|---|---|
| Article number | 170176 |
| Journal | Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment |
| Volume | 1072 |
| DOIs | |
| State | Published - Mar 2025 |
Funding
The authors would like to acknowledge support from the Office of Defense Nuclear Nonproliferation Research and Development (DNN R&D) Safeguards program within the US Department of Energy’s National Nuclear Security Administration. The authors would like to acknowledge and thank Dr. Julie Gostic, DNN R&D Safeguards program manager for her support and guidance. This work was completed as a portion of project work completed on behalf of DNN R&D by a multilaboratory team including researchers from ORNL, Los Alamos National Laboratory, Sandia National Laboratories, and Y-12 National Security Complex. Also collaborating on the project were students from University of Tennessee, Knoxville; North Carolina State University; and the University of Michigan. The authors would like to acknowledge support from the Office of Defense Nuclear Nonproliferation Research and Development (DNN R&D) Safeguards program within the US Department of Energy's National Nuclear Security Administration. The authors would like to acknowledge and thank Dr. Julie Gostic, DNN R&D Safeguards program manager for her support and guidance. This work was completed as a portion of project work completed on behalf of DNN R&D by a multilaboratory team including researchers from ORNL, Los Alamos National Laboratory, Sandia National Laboratories, and Y-12 National Security Complex. Also collaborating on the project were students from University of Tennessee, Knoxville; North Carolina State University; and the University of Michigan. We would like to acknowledge and thank the following national laboratory collaborators: Dr. Vlad Henzl, Dr. Holly Trellue, and Dr. Daniel Jackson of Los Alamos National Laboratory; Dr. Heather Reedy and Dr. Oskar Searfus of Sandia National Laboratories; and Matt Cook and Alex Roberts of Y-12 National Security Complex for their productive discussions on this subject and research, as well as participation in the associated measurement campaign. We would also like to thank Greg Nutter, Karen Hogue, Susan Smith, Rachel Hunneke, Scotty Mathews, and Dave Aguero of ORNL for their help facilitating the measurement campaign. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).
Keywords
- Active well coincidence counter
- Coincidence Counting
- Nondestructive assay
- Radiation signature training device
- Uranium-233