There's A Lot In The Way Of South Korea Acquiring Nuclear Subs

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The Republic of Korea Navy (ROKN) has a long-term expansion plan to expand its conventional submarine force. Since 2017 the ROKN has looked at arming new attack submarines with Tomahawk-like cruise missiles and considered building prospective KSS-3 attack submarines with nuclear power plants.

South Korea may be driven to acquire nuclear submarines by the vessels' perceived military prestige. They may also view nuclear-powered submarines as a potential counterbalance to North Korea's nuclear weapons. However, compared with conventional AIP submarines, the main advantage of nuclear-powered attack submarines is speed. Conventional AIP attack submarines can carry the same weapons systems as the far more expensive nuclear-powered submarines.

Joining the United States, United Kingdom, France, Russia, India, and potentially Brazil (with its indigenous program) and Australia (via the joint AUKUS program) would put South Korea in a prestigious group. Yet at the same time, it might increase the desires of North Korea, Pakistan, Japan and even Iran to expedite their expressed interests in nuclear-powered submarines.

Although South Korea's interest in nuclear submarines is quite high, non-nuclear submarine options might work best for Seoul. In addition, despite little current interest, South Korea might be better served by an AUKUS-like agreement with the United States or perhaps a leasing arrangement like that used by India to acquire nuclear submarine technology. India leased two nuclear-powered submarines, the first from the Soviet Union and the second from the Russian Federation.

South Korea has the technology to build naval propulsion reactors. Technical guidance from the United States, such as reactor core designs, would be helpful but not necessary. South Korea might look to follow the French and Chinese examples, which use low enriched uranium (LEU) as reactor fuel. These fuels may be a better option for South Korea instead of following the US/UK model of using weapons-grade highly enriched uranium (HEU) fuel or the Russian and Indian use of HEU in the range of 40% to 60% enrichment fuel.

South Korea should carefully consider the impact that nuclear-powered submarine construction could have on escalating an arms race with North Korea. North Korea will certainly view any such efforts as a provocation by South Korea as well as the US and may respond in ways that upset the regional balance of power. China could have serious concerns and react negatively to the South Korean plan, and Japan might also worry about elevating conflict possibilities in the region.

The impact on global norms and the NPT

As a non-nuclear weapons state under the NPT, South Korea is allowed to use what in International Atomic Energy Agency (IAEA) parlance is“special fissile material for military purposes” that are not related to nuclear weapons. It is also allowed under the NPT to enrich uranium.

However, materials within South Korea must still be under safeguards and the IAEA has yet to develop a safeguards methodology to deal with material in non-nuclear weapons states, such as Brazil, that are put into military use. An additional question is whether US support of such states' nuclear-powered submarines will be viewed as undercutting and weakening the NPT. China, Russia, and their partners will argue that it does.

US support of nuclear-powered submarines, either in Australia or South Korea, may weaken US safeguards and nonproliferation efforts. For the United States, doing so will need to be a risk-benefit calculation. The addition of nuclear-powered submarines in Australia and South Korea may provide some counterbalance to China's growing People's Liberation Army Navy. But it is unclear if these benefits will outweigh the risks of undercutting nonproliferation efforts and weakening the NPT.