Safeguards monitoring is conducted by the International Atomic Energy Agency (IAEA) in nuclear facilities as part of the Nuclear Non-proliferation Treaty (NPT). This monitoring is meant to ensure the peaceful use of nuclear energy and to assure the community that countries are not misusing nuclear technologies or materials to produce nuclear weapons. Melek Derman, a graduate student working with former Director of the Texas A&M Center for Nuclear Security Science and Policy Initiatives (NSSPI), Dr. Sunil Chirayath, is investigating nuclear safeguards approaches for the Molten Salt Reactor (MSR), an advanced reactor technology being developed as a promising option for future nuclear energy production. According to Derman, “Recent nuclear safeguards regulations are designed for traditional, solid-fueled light water reactors. In this study, a safeguards monitoring approach was developed for a theoretical MSR designed at Texas A&M University. It aims to contribute new safeguards strategies to be developed to facilitate the integration of MSRs into the sector to address their unique safeguards challenges.”
One of these challenges is related to the way traditional fuel assemblies are accounted for in a traditional light water reactor (LWR). Because of the nature of these LWR fuel assemblies, they can be tracked as items using their serial numbers for nuclear safeguards monitoring resulting in the material unaccounted for, or MUF, to be zero. With MSRs, however, fuel is used in bulk and molten form, circulating outside the reactor core in pipes. Bulk material accountancy is very difficult due to the inherent uncertainty linked to the measurement system used.
“Since current safeguards monitoring regulations are designed based on traditional large LWRs and are inapplicable to MSR safeguards applications,” explained Derman, “There is a need for further studies to meet the IAEA’s objectives. Therefore, these safeguards approach development studies are critically important for non-proliferation authorities to ensure that nuclear material is used only for declared peaceful purposes.”
Derman modeled an MSR using the Monte Carlo radiation transport code, MCNP. She then analyzed some of the well-studied fission products generated in the fuel salt to determine if any could be used as an indirect signature for nuclear materials, especially plutonium monitoring and its mass estimation. Her results identified the correlations of plutonium mass with cesium-137 activity and the cesium-134 to cesium-137 activity ratio as methods that could be utilized to quantify plutonium mass at all fuel burnup levels, from low to ultra-high by using a high-purity (HPGe) detector. She also found that the activity ratio of europium-154 to cesium-137 could be applicable even for very high fuel burnup levels to estimate plutonium mass. However, it does not provide accurate results at ultra-high fuel burnup levels above 100 GWd/MTU due to its saturation.
Derman says that her proposed safeguards monitoring approach “provides a process monitoring method for estimating the plutonium mass in the circulating fuel salt in MSR at different fuel burnup levels so that any diversion of Pu for non-peaceful purposes can be prevented through early detection and deterrence.”
Participation in NSSPI activities has been very important to Derman’s graduate school journey. “Firstly,” she said, “The academic support and collaboration within the NSSPI have been invaluable. We have shared insights on research projects, participated in our research presentations, and provided feedback on each other’s work, which has significantly enhanced my learning experience. Networking with peers with similar interests has opened up numerous doors for me. These connections have not only enriched my academic pursuits but also laid the groundwork for future professional collaborations.”
She also credits NSSPI for the many opportunities for professional development she has had during her time as a Master’s student, from meeting and interacting with renowned experts to attending short courses like the recent SEE-LANL Non-destructive Assay Training course at Los Alamos National Laboratory and the upcoming Safeguards Laboratory short course at Oak Ridge National Laboratory.
“Using all the radiation detection equipment I was theoretically and computationally interested in during my research was a unique experience for me,” she explained in discussing her experience at SEE-LANL. “I learned about advanced technology equipment developed to meet IAEA needs and discussed them with expert engineers.”
Derman will be graduating from Texas A&M in May with a Master of Science degree in nuclear engineering. Prior to joining NSSPI, she earned a B.S. degree in Physics from Akdeniz University in Turkiye and a B.A. in Business Administration from Anadolu University. After graduation, she plans to continue her studies and pursue a Ph.D.