During the first week of June, two seemingly unrelated events took place in Seoul. On June 3, U.S. and South Korean officials encounter to discuss the implementation of the South Korean civilian reprocessing and enrichment program. The same evening, conservative Seoul Mayor Oh Se-hoon was re-elected. As fortuitous as they may be, these events should serve as a reminder that South Korea’s nuclear and political futures are closely intertwined.
South Korea’s nuclear future
In September 2025, the United States broke with long-term policy practice and expressed support for South Korea’s ambitions to acquire uranium enrichment and reprocessing, intended to secure Seoul’s supply of nuclear fuel, and improve its management of spent fuel.
The announcement came as a big surprise. Since the United States discovered South Korea’s secret nuclear weapons program in the 1970s, it has prevented Seoul from acquiring these technologies because they could also be used in the production of nuclear weapons. In April 2025, just months before this surprising announcement, the US Department of Energy designated South Korea as “sensitive country,“A designation usually reserved for nuclear proliferators like Syria, Iran and North Korea. Apparently, the designation was the result of a South Korean national’s involvement in industrial espionage against American companies. But members of the Democratic Progressive Party (DP), then in political opposition, were quick to attribute it In recent years, mostly conservative politicians have called for Seoul to acquire nuclear weapons.
What has changed? In the months that followed, South Korea held early elections to replace deposed President Yoon Suk-yeol, who had been the first South Korean president to publicly address the nuclear issue (statements to which he later returned). Progressive Lee Jae-myung won the June 2025 election, and senior members of his cabinet quickly set about denying that South Korea would ever pursue its nuclear ambitions under his leadership. In an essay for the Seoul-based think tank Asia-Pacific Leadership Network, Foreign Minister Cho Hyun called non-proliferation is “a strategic imperative” for South Korea.
Lee himself argued in public: most recently June 8that South Korea would not be able to withstand the international sanctions imposed on it if it went nuclear at some point in the future.
At the political level, the Lee administration has therefore made considerable efforts to refute and tone down any talk of nuclearization. The president also enjoys historically high – albeit declining – popularity ratings, and his party just won 12 of 16 mayoral and gubernatorial seats in recent local elections. Nuclear issues are certainly far too specialized to decide South Korea’s election results, but Lee appears to have a broad mandate to shape South Korea’s nuclear policy going forward.
But political winds can change quickly in South Korea. And Lee may be sowing nuclear seeds on a political terrain that could yet evolve rapidly under his feet.
South Korea Political future
Such a shift may already be apparent in a crucial constituency that the PD failed to win in recent local elections: the capital itself. Conservative Seoul Mayor Oh Se-hoon beat Lee’s hand-picked candidate to win his third consecutive term (and fifth overall).
Oh is a seasoned politician, who has skillfully navigated the Korean political landscape and staged comebacks. He wisely distanced himself from former President Yoon and the infighting that followed his impeachment. Although he is considered a promising presidential candidate, Oh refrained from throwing his hat into the conservative race ahead of the 2025 snap election, recognizing that it was poised to deliver an inevitable victory to progressives. Instead, he stuck to his seat as mayor.
This strategy seems to have paid off. While he was widely expected to lose his mayoral race, Oh made a comeback late on election night, bucking the national trend that routed conservative candidates in most other districts.
Oh’s victory should give pause to anyone who expects progressive electoral successes to continue to pile up in the years to come. Recent history confirms this prediction: the 2020 National Assembly elections were another landslide victory for the DP, and no one at the time would have predicted that a conservative candidate would win the presidency just two years later.
But Oh isn’t just a future presidential hopeful. His record is also mixed when it comes to his views on South Korea’s nuclear future. In 2019, he called for a “further discussion» on South Korea’s nuclear armament, and in 2023 explicitly called on South Korea to build nuclear weapons.
In 2024, he moderated his position somewhat, calling on South Korea to increase its nuclear latency. This position – towards which the nuclear debate gravitated during the final year of Yoon’s presidency – would lead South Korea to expand enrichment and reprocessing to the point where it could quickly produce a nuclear weapon if deemed necessary. However, as Toby Dalton and Adam Mount underlinesthis position is in practice indistinguishable from that according to which South Korea must develop enrichment and reprocessing for civilian purposes.
And therein lies the problem: nuclear technologies developed today for peaceful purposes could be used in the future for non-peaceful purposes. The deciding factor is not the technologies themselves, but the policymakers who instill intent into them.
How to ensure South Korea’s non-proliferation status
South Korea’s nuclear and political future is far from set in stone. But it is almost certain that, over the next decade, South Korea will acquire enrichment and reprocessing capabilities. And at some point, before or after that, a government more willing to explore the path to a weapon will inevitably return to power. Before that happens, today’s political leaders must make every effort to commit tomorrow’s governments to non-proliferation.
The simplest solution would be for South Korea to abandon its enrichment and reprocessing activities. It could find alternatives to Russian and Chinese uranium, as well as other solutions for storing spent fuel that do not require reprocessing.
But this is unlikely to happen. South Korea has sought these capabilities for years and is unlikely to give them up now. If the United States reneges on its promise, it could cause a crisis of confidence in alliance relations and further worsen the situation, thereby strengthening the position of those who advocate for an independent nuclear capability.
However, the very existence of enrichment and reprocessing capabilities constitutes – by definition – a nuclear latency problem. South Korea should therefore seek to provide as many assurances as possible that it will not, at some point in the future, use these capabilities to build a bomb. These safeguards can never be perfect, but enough of them can add up to make proliferation prohibitively expensive. Dalton and Mount call this “active non-proliferation.”
These measures could take several forms. These should not just be political declarations, but also technical and legal measures that cannot be quickly reversed, or commercial and diplomatic arrangements that would create dependencies too costly to reverse. The Lee administration’s decision to use US-sourced low-enriched uranium in future South Korean nuclear submarines (another surprise announcement) is an example of such an arrangement.
South Korea’s export of nuclear reactors is another form of implicit insurance: each additional reactor South Korea exports and each nuclear energy memorandum of understanding it signs with another country further increases the cost of nuclear power.
But South Korea could and should do more. It must think carefully about where to locate its enrichment facilities, to what level to enrich the uranium, and with whom to do it. It must recognize that there is a compromise between proliferation guarantees and “nuclear sovereignty”. For example, Seoul should avoid any arrangement that would allow it to independently enrich uranium to a high level at facilities located on Korean territory, but instead seek to paths that increase transparency and international control, such as black boxing technology abroad. At the same time, South Korean lawmakers should seek to encode enshrine the peaceful use of nuclear energy in law and explicitly prohibit proliferative activities.
There is a nascent but insufficient debate in South Korea about how to credibly assure the international community that a future government will not one day use its future enrichment and reprocessing capabilities to build nuclear weapons. The Lee administration’s public declarations renouncing nuclear weapons are welcome, but would be even more so if coupled with comprehensive efforts, by the president and his party, that could demonstrate to the international community that South Korea’s nonproliferation status will be maintained indefinitely.