US–South Korea Nuclear‑Powered Submarine Deal

US–South Korea Nuclear‑Powered Submarine Deal

Why in News?

The United States and South Korea have announced a landmark deal that opens a new chapter in defense and technology cooperation. As part of this partnership, South Korea will build advanced nuclear submarines with U.S. support.

Highlights of the US–South Korea Recent Deal

• The United States has formally announced a landmark deal with South Korea.
• As part of the deal, South Korea will invest US$ 350 billion into the United States. Out of this, US$ 150 billion is earmarked specifically for the shipbuilding sector. The remaining US$ 200 billion will go into other strategic industries, such as AI, semiconductors, and nuclear energy.
• To help maintain stability in South Korea’s currency, the investment comes with a cap: no more than US$ 20 billion per year.
• In return, the U.S. is reducing its tariffs on certain South Korean goods: the rate will be brought down to 15%, from a previous 25% to deepen economic ties and improve trade flow.
• The two countries will collaborate closely on fuel supply for submarine reactors. South Korea has also secured U.S. backing for greater authority over uranium enrichment and spent‑fuel reprocessing to support peaceful nuclear uses.
• A shipbuilding working group will be formed between the U.S. and South Korea to coordinate efforts. This partnership will cover both commercial ships and combat‑ready military vessels.  
• According to Seoul’s defense ministry, the first nuclear‑powered submarine could be launched by the mid to late 2030s, if fuel and construction go as planned. 

Status of Nuclear‑Powered Capabilities in South Korea

• South Korea’s navy operates about 21 conventional submarines. Every one of these submarines runs on diesel‑electric propulsion, not nuclear power. 
• Some of the newer submarines use Air‑Independent Propulsion (AIP) systems. The AIP capability helps these subs stay submerged for longer than traditional diesel boats. South Korea does not yet have any nuclear-powered submarines in its fleet.
• In previous decades, South Korea did explore a nuclear weapons program. It later abandoned that program under heavy pressure from the United States.
• South Korea also signed the Non‑Proliferation Treaty (NPT) in 1975, committing not to pursue nuclear arms.  Public and political debate about nuclear armament has grown recently. South Korea has maintained its non‑nuclear‑weapon‑state status. 
• South Korea runs a strong civilian nuclear power program. The country currently has 26 operational nuclear reactors. These reactors generate approximately 30% of the nation’s electricity. The total capacity of its reactors is about 26 GWe (gigawatt-electric).
• South Korea has expressed interest in reprocessing spent nuclear fuel for industrial and energy reasons. South Korea says its goal is not weapons but industrial‑scale fuel production. 
• It is also a member of key international export control groups like the Nuclear Suppliers Group (NSG). This commitment has long guided South Korea’s nuclear policy and limited its weapons options.

North Korea Building a Nuclear‑Powered Submarine

• North Korea has publicly revealed that it is constructing a nuclear‑powered submarine, and South Korean intelligence believe that Russia has provided key technical assistance. 
• The submarine shown in state media appears to be around 6,000 to 7,000 tonnes, and experts estimate that it can carry about 10 missiles, possibly nuclear‑capable ones.
• According to South Korean intelligence, Russia may have supplied North Korea with a small nuclear reactor module, something Pyongyang reportedly could not build well on its own. In return, North Korea has deployed more than 10,000 troops to support Russia in the war in Ukraine.
• In March 2025, North Korea released photos of a nuclear-powered submarine under construction, showing Kim Jong Un visiting the shipyard.
• Experts warn that developing a nuclear‑powered submarine in future would give North Korea a stealthy undersea launch platform, making it harder to detect missile launches. If completed and successfully tested, this submarine could dramatically raise security concerns in South Korea, the United States, and other regional powers. 

Strategic Significance of the US–South Korea Nuclear‑Powered Submarine Deal

• Strengthening Deterrence Against North Korea: This deal significantly boosts South Korea’s ability to deter North Korean threats. Nuclear‑powered submarines can stay submerged much longer than diesel‑electric ones. They can thus track North Korea’s submarine‑launched ballistic missiles more effectively. This persistent undersea presence strengthens Seoul’s defensive posture. 
• Deepening U.S.–ROK Security Alliance: By sharing sensitive nuclear‑propulsion technology, the United States is reaffirming its long-term commitment to South Korea. The 2025 fact sheet explicitly supports Seoul’s submarine ambitions as part of a broader security pact. South Korea has pledged to raise its defense spending to 3.5% of its GDP.
• Balancing Power in the Indo‑Pacific: The submarines could play a role in the broader Indo-Pacific strategy. U.S. naval leadership has stated that using Korean nuclear submarines to counter China is a “natural expectation.” This implicitly ties South Korea more deeply into U.S. efforts to contain or balance China’s growing maritime power. 
• Enhancing South Korea’s Strategic Autonomy: For decades, South Korea has lacked the ability to enrich uranium or reprocess spent fuel under its 123 nuclear cooperation pact with the U.S. The agreement now gives Seoul backing to expand its authority over uranium enrichment and nuclear fuel reprocessing. 
• Industrial and Technological Leap: The submarine deal also underpins a major defense-industrial collaboration. South Korea already has strong shipbuilding capacity and nuclear infrastructure. Building nuclear submarines will push its technological capabilities higher. This strengthens its naval engineering base and helps develop high-performance nuclear propulsion systems. 

What is a Nuclear‑Powered Submarine?

• About: A nuclear‑powered submarine is a submerged vessel that uses a nuclear reactor to generate power instead of conventional diesel engines or batteries. The nuclear reactor produces heat from fission of enriched uranium, and this heat drives a steam turbine that propels the submarine. The submarine can remain submerged for very long periods.

• Features: 

• • • Unlimited Underwater Endurance: The nuclear reactor allows the submarine to stay deep underwater almost indefinitely. Only the supply of food and other consumables limits how long the vessel can remain submerged. 
    • High Speed and Sustained Power: A nuclear‑powered sub can move at high speed for extended durations. It does not need to slow down to conserve battery, unlike diesel-electric subs. 
    • Very Long Range: These submarines have a nearly unlimited operational radius because they do not need to refuel for years. Their mission endurance depends on crew endurance, not fuel.
    • Powerful Propulsion System: The reactor’s heat is used in a pressurized-water reactor design in many submarines. The reactor heats water, which then turns turbines, driving the propeller with great force.
    • Stealth and Strategic Value: They can stay submerged for very long durations and move at high speed, nuclear subs make excellent platforms for strategic missions, including patrol, deterrence, intelligence gathering, and missile launch.
  • Worldwide: In total, six countries currently operate nuclear‑powered submarines. 66 (United States), 31 (Russia), 12 (China), 10 (United Kingdom), 9 (France) and 2 (India).

• Operational Importance: Nuclear‑powered submarines form a key part of nuclear deterrence, especially the ones that carry ballistic missiles (SSBNs). They provide second‑strike capability for countries that arm them with nuclear missiles, because they can hide underwater for long periods.