Four Democratic U.S. senators have sent a letter to President Donald Trump expressing concerns about nuclear proliferation and urging him not to allow uranium enrichment or spent nuclear fuel reprocessing in South Korea.
This move comes as President Trump threatens to raise tariffs on South Korea, claiming that agreements outlined in the U.S.-South Korea joint fact sheet are not being properly implemented. The letter also reveals growing public dissent within the U.S. regarding security agreements with South Korea.
On February 6, Senators Edward Markey (D-MA), Chris Van Hollen (D-MD), Jeffrey A. Merkley (D-OR), and Ron Wyden (D-OR) sent and publicly released this letter to President Trump.
The senators highlighted Trump’s support for procedures leading to civilian uranium enrichment and spent nuclear fuel reprocessing in South Korea, as stated in a White House fact sheet from November 13 last year. They argued that this stance contradicts long-standing bipartisan U.S. policy aimed at preventing the spread of enrichment and reprocessing technologies to curb the production of weapons-grade fissile materials.
The letter noted that the fact sheet requires all enrichment and reprocessing to align with the existing 123 Agreement between the two countries. This bilateral agreement, named after Section 123 of the U.S. Atomic Energy Act, mandates that Seoul obtain U.S. consent before enriching or reprocessing nuclear materials or technologies transferred under the agreement.
The Democratic senators pointed out that South Korea initially agreed to forgo enrichment and reprocessing when it first signed a nuclear agreement with Washington in 1972. However, during the 2015 agreement renewal, South Korea pushed to revisit this issue. While the 2015 agreement did not grant consent for enrichment and reprocessing, it established a high-level bilateral committee to explore these options.
The senators emphasized South Korea’s historical interest in nuclear weapons since the 1970s, including the United Nations (UN) investigated illegal activities. They noted that in 2016, the then-President suggested South Korea should develop nuclear weapons. Furthermore, they highlighted the Biden administration’s 2024 designation of South Korea as a sensitive country, a term used for nations posing proliferation risks.
The letter specifically mentioned that while current South Korean President Lee Jae Myung is not advocating for nuclear weapons development, there remains an active debate within South Korea about the security value of nuclear arms. Polls indicate up to 70% of South Koreans support independent nuclear armament, partly due to doubts about U.S. commitment to South Korea’s defense.
The senators stressed that South Korea possesses ballistic missiles capable of delivering nuclear warheads and has a sophisticated nuclear industry that could be utilized for nuclear armament if decided.
They warned that allowing South Korea to develop latent nuclear capabilities would lead to highly unstable outcomes on the Korean Peninsula. North Korea has already reacted by accusing the U.S. of giving South Korea a green light to become a quasi-nuclear state.
The senators argued that granting South Korea potential nuclear capabilities would undermine U.S. non-proliferation efforts. They cited ongoing negotiations for a 123 Agreement with Saudi Arabia, which has expressed nuclear ambitions and is pursuing uranium enrichment.
Referencing a letter sent to the State Department on November 17, 2025, they urged the administration to apply the strongest gold standard safeguards prohibiting enrichment and reprocessing in all nuclear cooperation processes. They warned that weaker non-proliferation measures with South Korea could complicate negotiations with Saudi Arabia and weaken the global non-proliferation regime, escalating Middle East tensions.
The senators also noted Trump’s support for South Korea’s nuclear-powered attack submarine plans, pointing out the lack of details on construction location and fuel sources. They emphasized that the current nuclear agreement prohibits South Korea from using any U.S.-origin nuclear material for military purposes, including submarine propulsion.
The letter concluded by requesting written responses to five key questions by February 13, covering potential amendments to the 123 Agreement, plans to inform Congress, details on nuclear technology transfers, considerations for enrichment and reprocessing facilities in South Korea, and specifics on the nuclear submarine program.