South Korea and weapons of mass destruction

South Korea has the raw materials and equipment to produce a nuclear weapon but has not. In August 2004, South Korea revealed the extent of its highly secretive and sensitive nuclear research programs to the IAEA, including some experiments which were conducted without the obligatory reporting to the International Atomic Energy Agency (IAEA) called for by South Korea's safeguards agreement. The failure to report was reported by the IAEA Secretariat to the IAEA Board of Governors; however, the IAEA Board of Governors decided to not make a formal finding of noncompliance. If the South created nuclear weapons it could change the balance of power on the Korean peninsula. However, South Korea has continued on a stated policy of non-proliferation of nuclear weapons and has adopted a policy to maintain a nuclear-free Korean Peninsula.

By contrast, North Korea has and is developing additional nuclear weapons.

Early nuclear ambitions
When the United States notified the South Korean administration of its plan to withdraw USFK in July 1970, South Korea first considered the possibility of an independent nuclear program. Under the direction of South Korea's Weapons Exploitation Committee, the country attempted to obtain plutonium reprocessing facilities following the pullout of the 26,000 American soldiers of the 7th Infantry Division in 1971. After South Vietnam had fallen in April 1975, then South Korean president Park Chung-hee first mentioned about its nuclear weapons aspiration during the press conference on 12 June 1975. However, under pressure from the United States, France eventually decided not to deliver a reprocessing facility to South Korea in 1975. South Korea's nuclear weapons research program effectively ended on April 23, 1975, with its ratification of the Nuclear Non-Proliferation Treaty.

Post-NPT programs
The South Korean government insists that its nuclear program is for peaceful purposes only.

Previously unreported experiments
In 1982, scientists at the Korean Atomic Energy Research Institute performed an experiment in which they extracted several milligrams of plutonium. Although plutonium has uses other than the manufacture of weapons, the United States later insisted that South Korea not attempt to reprocess plutonium in any way. In exchange, the US agreed to transfer reactor technology and give financial assistance to South Korea's nuclear energy program. It was revealed in 2004 that some South Korean scientists continued some studies; for example, in 1983 and 1984 Korea Atomic Energy Research Institute was conducting chemical experiments related to the handling of spent fuel that crossed the reprocessing boundary.

Later, in an experiment at the same facility in 2000, scientists enriched 200 milligrams of uranium to near-weapons grade (up to 77 percent) using laser enrichment. The South Korean government claimed that this research was conducted without its knowledge. While uranium enriched to 77 percent is usually not considered weapons-grade, it could theoretically be used to construct a nuclear weapon. HEU with a purity of 20% or more is usable in a weapon, but this route is less desirable because far more material is required to obtain critical mass; thus, the Koreans would have needed to produce much more material to construct a nuclear weapon. This event and the earlier extraction of plutonium went unreported to the IAEA until late 2004.

IAEA response
Following Seoul's disclosure of the above incidents, the IAEA launched a full investigation into South Korea's nuclear activities. In a report issued on November 11, 2004, the IAEA described the South Korean government's failure to report its nuclear activities a matter of "serious concern", but accepted that these experiments never produced more than very small amounts of weaponizeable fissile material. The Board of Governors decided to not make a formal finding of noncompliance, and the matter was not referred to the Security Council.

Pierre Goldschmidt, former head of the department of safeguards at the IAEA, has called on the Board of Governors to adopt generic resolutions which would apply to all states in such circumstances and has argued "political considerations played a dominant role in the board’s decision" to not make a formal finding of non-compliance.

American nuclear weapons in South Korea
The US first deployed nuclear weapons to South Korea in 1958, and numbers peaked in the late 1960s at close to 950, including a mix of tactical and strategic weapons.

Following its accession to the Nuclear Non-Proliferation Treaty in 1985, the government of North Korea had cited the presence of US tactical nuclear weapons in South Korea as a reason to avoid completing a safeguards agreement with the International Atomic Energy Agency. In 1991, President George H W Bush announced the withdrawal of all naval and land-based tactical nuclear weapons deployed abroad, including approximately 100 such weapons based in South Korea. In December 1991, the governments of North and South Korea signed a Joint Declaration on the Denuclearization of the Korean Peninsula, and in January 1992, the North concluded a comprehensive safeguards agreement with the IAEA.

In 2013, South Korean Prime Minister Chung Hong-won rejected calls to again station American tactical nuclear weapons in South Korea.

In 2017, during a period of unusually high tension, the South Korean defence minister suggested it was worth reviewing the redeployment of U.S. nuclear weapons to the Korean peninsula.

Public opinion
In the late 1990s, a notable minority of South Koreans supported the country's effort to reprocess materials, although only a small number called for the government to obtain nuclear weapons.

With the escalation of the 2017 North Korea crisis, amid worries that the United States might hesitate to defend South Korea from a North Korean attack for fear of inviting a missile attack against the United States, public opinion turned strongly in favour of a South Korean nuclear arsenal, with polls showing that 60% of South Koreans supported building nuclear weapons.

Nuclear-capable state
Although currently South Korea is under the US nuclear umbrella of protection, it could very well break away and try to develop its own nuclear weapons if necessary. Like Japan, South Korea has the raw materials, technology, and resources to create nuclear weapons. Previous incidents show the Republic of Korea (ROK) to be able to possess nuclear weapons in anywhere from one to three years if necessary. The ROK has been shown before to create enriched uranium up to 77%, which although not particularly powerful, shows that South Korea has the potential to make nuclear weapons with more highly enriched uranium. South Korea does not have any ICBMs but possesses a wide range of SRBM and MRBMs through the Hyunmoo series of ballistic/cruise missiles currently fielded to the ROK Army. The Hyunmoo series of ballistic missiles works similarly to the American Tomahawk Missile, which can be armed with the W80 and W84 nuclear warheads. Theoretically, if needed, the 500 kg conventional warhead could be replaced by a small nuclear warhead. The Hyunmoo missiles can already cover the entire range of North Korea and would drastically change the North's disposition if the South had nuclear armed MRBMs. Even though the ROK could procure nukes, currently like Japan it sees no reason to do so with the protection of the American nuclear arsenal. However, if a conflict erupts with the North, South Korea could quickly evolve into a nuclear-armed state and pose even with the North with the support of the US. According to Suh Kune-yull, a professor of nuclear engineering at Seoul National University, “If we decide to stand on our own feet and put our resources together, we can build nuclear weapons in six months”.