Research reactors around the world serve a vital role in a variety of uses, from education and training in nuclear technology to producing radioisotopes for medical and industrial use. According to recent Center for Nuclear Security Science and Policy Initiatives (NSSPI) graduate Dongyoul Lee, the propagation of research reactors was fueled after President Dwight D. Eisenhower’s “Atoms for Peace” program and the formation of the International Atomic Energy Agency (IAEA) in 1957 “began an active program of providing training, as well as nuclear safeguards to worldwide users of nuclear technology, including the Democratic People’s Republic of Korea (DPRK).” Many of these research reactors that have been operating since the 1950s and 1960s are fueled by highly enriched uranium (HEU).
Over the past 40 years, however, the U.S. has led an effort to convert the world’s research reactors to low-enriched uranium, which is less likely to be misused as a weapon. “The conversion of fuel in nuclear research reactors from HEU to LEU,” said Lee, “is a global trend for meeting the objectives of nuclear non-proliferation.”
Lee worked with NSSPI Director Dr. Sunil Chirayath on a project to assess the feasibility of converting the 8-megawatt IRT-type research reactor in North Korea, the IRT-DPRK, from HEU to LEU. The IRT-DPRK is currently fueled with uranium enriched with 80 wt% uranium-235. As the DPRK is not under IAEA safeguards since its withdrawal from the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) in 2003, there is an increased risk of HEU being diverted to non-peaceful uses.
Lee believes that the conversion of the IRT-DPRK from HEU fuel could be a softer target for the denuclearization of the DPRK, since it “will not affect the DPRK’s security concerns but at the same time will reduce further proliferation. In comparison to other agenda items of the denuclearization of DPRK such as shutting down of the 5 MWe nuclear reactor and the irradiated fuel reprocessing plant that separates plutonium, the management of the IRT-DPRK may be less sensitive.”
His discussions with DPRK expert Dr. Siegfried Hecker, a NSSPI Distinguished Faculty Fellow, also led him to understand that the conversion could be viewed favorably, or at least not without strict objection, since DPRK officials expressed difficulties with obtaining the HEU fuel required to run the research reactor.
To study the feasibility of converting the IRT-DPRK, Lee developed a Monte Carlo radiation transport model of its reactor core and performed neutronics simulations. He compared the reactor performance by examining the parameters such as neutron flux, effective neutron multiplication factor, neutron reactivity, temperature reactivity coefficients, fuel lifetime, etc., with the current 80 wt% 235U enriched HEU fuel type (UAl: uranium aluminum alloy) and the potential 19.9 wt% 235U tubular LEU fuel (UAl) and 19.75wt% 235U HANARO LEU fuel (𝑈3𝑆𝑖: uranium silicide).
One potential proliferation risk of the conversion, the production of plutonium, was assessed and compared by performing fuel burnup simulations for these three types of fuel. The neutronics simulation of fuel burnup in the reactor, as well as the buildup of fission products and other actinides, including plutonium, were carried out using the Monte Carlo radiation transport code, MCNP6.2. The MCNP6.2 code was selected because it is suitable for modeling the complex geometry of the reactor fuel and uses very accurate energy-dependent neutron interaction point cross-sections.
Dongyoul stated that “two potential LEU fuels showed suitable performance with sufficient excess reactivity and the thermal neutron flux to replace the HEU fuel from a neutronics perspective.”
Lee hopes that the results of his study can form the basis for further discussions on the nuclear weapons denuclearization of DPRK and can contribute to the global nuclear non-proliferation regime.
Lee says that his experience in NSSPI was enriched by the opportunity to interact with Dr. Hecker, who is an expert on the North Korean nuclear program and has “visited DPRK several times in the past, toured their nuclear facilities, and discussed with officials in charge.”
In August 2023, Lee earned his M.S. degree in nuclear engineering with a specialization in nuclear nonproliferation from Texas A&M University. Prior to joining NSSPI, Lee received his B.A. in Military History and Bachelor of Military Arts and Science degrees from the Korean Military Academy. He has since returned to the Republic of Korea to resume his duties as a Major in the South Korean army.