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Before Chairman Kim and President Trump met in Singapore last June, two nuclear policy veterans surveyed the “long and complicated process” ahead . Reflecting on their experience with post-Soviet republics in the 1990s, former U.S. Senators Sam Nunn and Richard Lugar wrote that securing a peaceful Korean Peninsula “will require unconventional thinking and steps that are much broader than denuclearization.”
For at least 40 years, physicists have explored the unconventional idea of using neutrino detectors to monitor nuclear reactors . Neutrino emissions from a reactor core can indicate an anomalous reactor startup or, in some cases. diversion of plutonium from the core. Compared to other fission signatures, neutrino signals are virtually impossible to mask, alter, or mimic. In the last year, physicists have demonstrated detectors that can observe these signals without needing an underground site. Meanwhile, neutrino physics has become a frontier in basic science, particularly among North Korea’s neighbors, South Korea and China.
Motivated by the renewed international dialogue with North Korea, we joined physics colleagues from South Korea, China, Japan, Russia, Europe, and the United States to outline how neutrinos could play a small role in diplomacy on the Korean Peninsula . Beyond verifying the shutdown of plutonium producing reactors, neutrino-based projects could support broader steps to reintegrate North Korea into the international community.
Meter-scale neutrino detectors could verify shutdown of reactors at Yongbyon
A key part of North Korea’s nuclear weapons program is the Yongbyon Nuclear Research Center. Yongbyon hosts the 5 MWe gas-graphite reactor that produced plutonium for the North Korea’s weapons program, a newer Experimental Light Water Reactor, older reactor projects, fuel processing facilities, and a uranium enrichment facility [4, 5, 6]. Since the Singapore summit, North and South Korea  and the United States  have suggested the dismantlement of Yongbyon as a possible step in reducing tensions.
If leaders agree to eliminate one or more reactors at Yongbyon, the U.S. and others may seek assurance that the reactors remain shut down during the long cool-down period preceding dismantlement. Traditional monitoring tools include onsite inspections and satellite observation of the site. Neutrino detectors could complement these approaches, perhaps as an early step toward more comprehensive action at Yongbyon. Unlike full reactor inspections, installing neutrino detectors would not require access to the most sensitive parts of the site. Compared to satellite imaging, neutrino detectors offer more persistent and precise reactor observations and an opportunity for cooperative engagement on the ground.
The technology to perform neutrino-based reactor monitoring is well demonstrated. Physicists have observed reactor on-off transitions in neutrino detectors since the 1980s [9, 10]. As of 2018, many groups worldwide are observing reactor neutrinos in meter-scale systems [11-17]. These detectors are largely motivated by searches for new physics in the neutrino sector, but they also demonstrate practical features for reactor monitoring. Instead of using an underground site to control backgrounds, several detectors now use design features and analysis techniques to allow on-surface operation. Some groups have built detectors inside shipping containers or trailers, indicating feasibility for rapid field deployment. Reactor neutrino detectors now operate for months or years with little onsite maintenance, continuously sending data offsite for analysis.
At Yongbyon, we and our colleagues estimate that a meter-scale scintillator detector could provide timely notice of unauthorized reactor startups following a shutdown agreement . A capable detector could fit inside a standard shipping container. As a basis for sensitivity estimates, we use the efficiency and backgrounds measured in the 4-ton PROSPECT detector, currently observing neutrinos from a reactor at Oak Ridge National Laboratory . If placed 20 meters from the 5 MWe reactor core, a similar detector could identify a reactor startup at 95% confidence level within 2 days. At the larger Experimental Light Water Reactor, a detector could identify a startup within 2 hours and potentially monitor the fuel evolution (see  for more details). Neutrinos could be observed from a standoff distance longer than 20 meters, but the required detector size scales with the square of the distance. The PROSPECT detector was constructed in less than a year for about $5 million.
Neutrino physics is an opportunity to engage North Korean scientists and engineers
Deploying neutrino detectors at Yongbyon would require coordination between technical teams from North Korea and other nations. However, it would not require exchange of classified or militarily sensitive information. Details on the design and use of reactor neutrino detectors are available in the open scientific literature. Neutrino detectors are therefore a low-stakes opportunity for scientists and engineers from North Korea and other nations to work together. As in former Soviet republics, such cooperative work could help to rebuild trust and redirect scientists and engineers from the weapons program to non-military applications.
Cooperative deployment of neutrino detectors at Yongbyon could open the door to wider scientific engagement in and beyond the region. The physics communities in South Korea, China, Japan, Russia, Europe, and the United States could support the effort from multiple angles. For example, scientists from North Korea could receive initial training in neutrino physics in China. Detectors at Yongbyon could be paired with detectors at power reactors in South Korea, furthering North-South unity. Major new neutrino experiments in East Asia, such as Hyper-Kamiokande in Japan  (and possibly South Korea ) and JUNO in China , are natural opportunities to strengthen peaceful regional ties. With time, other countries could consider student and scientist exchanges with North Korea in the area of particle physics.
Neutrino detectors can be a small step, among wider efforts
Of course, neutrino physics can be only a small part of reducing nuclear risks on the Korean Peninsula. The enrichment and reprocessing facilities at Yongbyon are not amenable to neutrino-based monitoring. In North Korea, a full program of Cooperative Threat Reduction—the term Nunn and Lugar coined for multilateral efforts in the former Soviet Union—would include many other components. Still, it bears some reflection that neutrino physics as an experimental science began with former weapons scientists at a plutonium production reactor . On another continent, the 1954 founding of CERN was one of the first diplomatic agreements between Germany, France, and their neighbors following World War II.
Seven months after the Singapore summit, Nunn and Lugar’s prediction of a “long and complicated process” for the nuclear talks seems correct. It may be much longer before joint objectives become clear, including the future of the reactors at Yongbyon. Nonetheless, policymakers could consider preparing neutrino-based tools, among others, in case further steps become possible. The final engineering work for a field-ready neutrino system could begin immediately. We encourage policymakers to consider this unconventional idea within the broader pursuit of a stable, secure Korean Peninsula.
Rachel Carr is a Stanton Nuclear Security Fellow in the Department of Nuclear Science and Engineering at MIT. Patrick Huber is Professor of Physics and Director of the Center for Neutrino Physics at Virginia Tech.
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These contributions have not been peer-refereed. They represent solely the view(s) of the author(s) and not necessarily the view of APS.