The use of nuclear weapons in Ukraine remains very unlikely, although not inconceivable. Surveyed experts assess that the risk of tactical nuclear weapons use could increase, depending on Russia's interpretation of Ukraine's efforts to regain de facto control of Crimea or the Donbas.
Any nuclear use would lower the threshold of nuclear weapons use for all nuclear-armed States, including the Democratic People's Republic of Korea (DPRK), thus increasing the risk of nuclear escalation on the Korean Peninsula.
Experts envision any nuclear use in Ukraine resulting in wide-ranging, long-term global consequences, including hollowing of the nonproliferation regime, shifting and hardening of alliances, and a loss of faith in negative security assurances and extended deterrence.
The prevention of increasing the risk of nuclear weapon use on the Korean Peninsula requires actions to prevent the use of nuclear weapons anywhere in the world
The use of a nuclear weapon anywhere in the world would have far-reaching consequences, with effects extending well beyond the immediate area of impact. ONN has previously noted that any further escalation in Ukraine could potentially expand into an increase in military activity or force re-alignment in the Northeast Asia region. Even the Republic of Korea (ROK) leadership has contemplated the implications, as evidenced by President Yoon's recent statements. 
To more fully understand how nuclear use in Ukraine could affect security on the Korean Peninsula and more broadly in Northeast Asia, ONN sought the views of the ONN Engagement Network, including Ambassador CHUN Yungwoo and Dr. SUZUKI Tatsujiro, as well as experts in nuclear policy and diplomacy, including Dr. James ACTON, Mr. Glyn FORD, Mr. Pavel PODVIG and Dr. Polina SINOVETS. These experts kindly contributed their insights on how they see the risks of the use of nuclear weapons in Ukraine and the potential global impacts of such use, noting what they assess as the general perception from Seoul, Tokyo, Washington, London, Moscow and Kyiv.
Overall, these experts agree that while the risk of nuclear escalation in Ukraine remains low, it cannot be excluded entirely. In particular, there is consensus that the risk of strategic nuclear weapons use remains minimal. While some experts do not see any plausible battlefield use for low-yield nuclear weapons in Ukraine, others assess that the use of non-strategic or tactical nuclear weapons has become more likely and dependent on the conditions of the conflict. In particular, existential threats to the Russian State could increase the likelihood of Russian use of tactical nuclear weapons; experts observe that efforts to retake de facto control of Crimea, and perhaps also some areas of the Donbas, could be perceived as a threat to the Kremlin's notion of Russian territorial integrity.
Nuclear weapon use in Ukraine is also deterred by international norms and global interdependencies, as any State that would use nuclear weapons would be met by strong international condemnation. Experts note that in addition to Western and other global opposition to any nuclear use, China and India would also strongly oppose the use of nuclear weapons, as would the Russian military leadership. As noted by Ambassador Chun, "[u]sing even a tactical nuclear weapon would be far more costly for Russia than losing the war". However, there is some concern that Russia's rational self-interest could be deprioritised in favour of the personal whims of Russian political leadership. Although the deliberate use of any type of nuclear weapon may remain low, Dr. Suzuki notes that accidental, inadvertent, or otherwise "unintended use of nuclear weapons is possible under the severe pressure and tense security environment". Such risks would be further heightened should nuclear weapons readiness levels be increased.
Should the worst-case scenario of nuclear use in Ukraine be realised, experts see indications that there would be near-universal condemnation internationally. The strongest immediate response would be expected from NATO, the West and allies such as Japan and the ROK, to include profound and comprehensive sanctions that could have far-reaching impacts on the global economy. Some experts would expect strong reactions from civil society, especially in Japan, where contradictory calls for both disarmament and nuclear sharing could be strengthened.
While the experts foresee no immediate military and security changes, nuclear use would lower the threshold of nuclear weapons use for all nuclear-armed States, including the DPRK. Regarding longer-term impacts of any nuclear use in Ukraine, experts envision wide-ranging global negative consequences, including hollowing the nuclear nonproliferation regime, loss of faith in negative security assurances and extended deterrence, destruction of the international sanctions regime, shifting and hardening of alliances, dramatic increases in hostilities and defence spending, potential strengthening of nationalism and right-wing populism, and economic and political relations return to Cold War. Depending on how the situation unfolds, experts could anticipate intensifying calls in Japan and the ROK for nuclear sharing or hedging and overhauling defence policies and alliances. Nuclear use could even strengthen the position of those who would seek to develop domestic nuclear weapons, including in Northeast Asia.
The DPRK in particular would not be expected to either endorse or denounce any use of nuclear weapons, as it would neither want to legitimise nuclear first use (cautious that a first use could be directed against it) nor weaken its alliance with Russia. However, by standing on Russia's side from the beginning of the invasion of Ukraine, the DPRK made a drastic turn from its traditional position of opposing the invasion of a smaller country. As such, some experts expect the DPRK to continue to back Moscow regardless, even possibly offering support to any justifications given for a nuclear attack. In contrast, others note that the DPRK may follow China's reaction. Finally, should there be a diversion of US and allied forces away from Northeast Asia as a result of the nuclear use, the DPRK may move to take advantage of the power vacuum.
Experts expect long-term impacts on the DPRK to vary, depending on the outcome of the nuclear weapon use and the international reactions. If the nuclear use does not achieve its objectives, the DPRK could reconsider its nuclear strategy. That said, as previously mentioned, any lowering of the overall threshold of nuclear use would also likely be reflected in the DPRK's strategy. The hardening of global alliances resulting from nuclear use would further decrease the potential for any diplomatic means to reduce nuclear risks on the Korean Peninsula.
Overall, the impacts in Northeast Asia of any nuclear weapon use in Ukraine, while ranging in intensity based on the scenario, would be overwhelmingly negative for security and general regional prosperity. Increased hostilities, the hardening of alliances, destruction of the Nuclear Nonproliferation Treaty regime, nuclear proliferation and lowering nuclear use thresholds are possible. The prevention of increasing the risk of nuclear weapon use on the Korean Peninsula would thus require actions to prevent the use of nuclear weapons anywhere in the world.
 The AP Interview: Korean leader cites North's serious threat, Associated Press, 11 January 2023, available at: https://apnews.com/article/politics-south-korea-north-japan-united-states-government-06eda2aee0a8b33c30419251e06cd69f