President Lee Jae-myung on the 29th publicly asked U.S. President Donald Trump to make a decision so that Korea can be supplied with fuel for nuclear-powered submarines. Attention is on whether this will serve as a signal flare for revising the nuclear cooperation agreement.
The Korean government's move to formalize securing nuclear fuel for nuclear-powered submarines is intended to compensate for the long-endurance limits of existing diesel-electric propulsion and to track and monitor the submarine forces of neighboring countries such as North Korea and China more deeply. Nuclear-powered submarines, driven by reactors, can operate for decades without refueling, a strength in sustaining long-term operations. Lee's comment that this could "ease the burden on U.S. forces" was also based on this operational capability.
The problem is fuel procurement. A reactor produces electricity from the energy released when neutrons collide with uranium and cause fission. A reactor can induce fission only in uranium-235, the uranium isotope with an atomic mass of 235. Because uranium-235 accounts for only 0.7% of natural uranium, enrichment is essential.
Under the Korea-U.S. nuclear cooperation agreement revised in June 2015, Korea may reprocess spent nuclear fuel and enrich uranium to below 20% only for research purposes. Currently, fuel for domestic commercial nuclear power plants has an enrichment level of usually 3–5% (low-enriched uranium, or LEU), optimized for power generation.
Submarines typically use highly enriched uranium (HEU), which is handled sensitively internationally because of its potential for exclusive use in nuclear weapons.
Moon Joo-hyun, a professor in the Department of Energy Engineering at Dankook University, said, "Fuel for nuclear-powered submarines may require more than 20% depending on the design," adding, "When the fuel is installed on a submarine for long periods, a relatively high enrichment level is needed."
Korea faces restrictions on uranium enrichment to high levels and reprocessing under the nuclear cooperation framework with the United States, making fuel acquisition virtually impossible without U.S. consent or easing of rules. This is why there is a view that a revision of the agreement or an exception is needed to push ahead with a nuclear-submarine program.
A bigger sticking point is that differences in enrichment levels are directly tied to military sensitivity. Raising uranium from 3% to 90% (weapons-grade) requires massive equipment and energy, but the additional effort needed to raise material already enriched to around 20% up to 90% is far less. In other words, if 20%-level material exists, the technical threshold for conversion to weapons-grade is lowered. This is why the international community strictly controls highly enriched material.
It is also practically difficult to use 3–5% fuel for commercial nuclear power directly in nuclear-powered submarines. Power plant fuel is not designed for submarine operating environments and long submerged endurance, creating significant safety, performance, and handling constraints, and it is not easy internationally to secure such fuel from a third country. Ultimately, the crux of pursuing nuclear-powered submarines is not simply a matter of technology development but overcoming diplomatic and political barriers of nonproliferation norms and allied consent.
This request is assessed as a strategic attempt to clarify that Korea's intent is "nuclear propulsion," not nuclear armament, and to seek a recalibration of role-sharing between the two countries. If bilateral consultations move into full swing, a complex diplomatic contest entangling defense, nuclear energy, and nonproliferation appears inevitable.
Wi Sung-lac, director of the Office of National Security, said regarding the request, "The Korea-U.S. nuclear cooperation agreement has already reached an understanding on a certain direction through prior consultations," adding, "Today's agenda was intended to share at the leaders' level that working-level consultations are needed to concretely advance that direction, and the U.S. side agreed." He added, "We will continue follow-up consultations between the two countries for concrete progress going forward."