How Significant is the Dismantlement of Yongbyon?

South Korean officials inspect the Yongbyon nuclear complex in January 2009. (Photo: AFP-JIJI-Japan Times.)

In Hanoi, President Trump rejected a proposal by Kim Jong Un to dismantle nuclear facilities at the Yongbyon Nuclear Scientific Research Center in exchange for lifting most of the economic sanctions imposed by the United Nations Security Council since March 2016.[1] For his part, Chairman Kim rejected Trump’s ambitious proposal to dismantle all of North Korea’s nuclear weapons and missile programs in exchange for lifting all US sanctions. In the aftermath of Hanoi, US Special Representative for North Korea Stephen Biegun and his North Korean counterpart Ambassador Kim Hyok Chol may resume negotiations to find a compromise between “too little and too big.” Such negotiations are likely to include further proposals to constrain or cease North Korean production of fissile material (plutonium and enriched uranium) in exchange for reciprocal actions by the US, including an “end-of-war declaration” ending the Korean War, establishment of liaison offices, and partial sanctions relief.

This article assesses the significance of dismantling nuclear facilities at Yongbyon for constraining North Korea’s nuclear weapons capabilities. Reportedly, North Korea has not yet specified exactly which facilities in Yongbyon would be dismantled. It may seek to spare some facilities to employ scientists and continue civilian operations, such as radioisotope production. For the sake of simplicity, in this article, I assume that a dismantlement deal will include all the major nuclear facilities at Yongbyon, including the 5 MWe gas-graphite reactor and related reprocessing facility, the IRT-2000 Soviet-supplied research reactor and related hot cells, the 25 MWe experimental light water reactor (under construction), the gas centrifuge uranium enrichment facility and (suspected) Lithium-6 enrichment facility, as well as related fuel cycle facilities for conversion and fuel fabrication.[2] In addition, any spent fuel that has not been reprocessed would be removed.

Plutonium, Tritium and Uranium

There are three central uncertainties in evaluating the significance of dismantling Yongbyon.

The first uncertainty concerns plutonium. Dismantling the 5 MWe reactor and reprocessing facility at Yongbyon and disposing of any spent fuel would eliminate North Korea’s only known source for producing additional plutonium. However, the impact of capping plutonium supplies on the number and type of nuclear weapons in North Korea’s arsenal is difficult to determine. If plutonium is an essential requirement for North Korea’s thermonuclear weapons (presumably the device tested in September 2017), then the limit on plutonium supplies would limit the number of such weapons in North Korea’s arsenal to the quantity of plutonium on hand divided by the amount of plutonium used per weapon. For example, if the total amount of available plutonium is 20 to 40 kilograms and 4 to 6 kilograms of plutonium are required for each weapon, then the total arsenal would be in the range of 3 to 10 thermonuclear weapons. Of course, this is a rough estimate because the total quantity of plutonium available and the amount used in each weapon is not publicly known.

If, however, North Korea manufactures thermonuclear weapons without using plutonium, then the limit on plutonium supplies would not prevent North Korea from building additional thermonuclear weapons as long as additional supplies of weapons-grade uranium are available. For advanced nuclear weapons states, plutonium is the material of choice for thermonuclear weapons to reduce size and weight, but thermonuclear weapons can also be made entirely with weapons-grade uranium. It is necessary to know the details of North Korea’s thermonuclear weapons design to determine the significance of ceasing plutonium production in North Korea.

The second uncertainty involves tritium. Tritium gas is widely used in modern nuclear weapons to increase yield for a given quantity of fissile material (plutonium or weapons-grade uranium) in fission weapons. This technique is also used to reduce the overall weight and size of nuclear warheads. Because tritium has a short half-life of 12.3 years, a source of fresh supply is necessary to maintain the gas charge in a “boosted” fission device.[3] Tritium is commonly produced by irradiating Lithium-6 targets in a nuclear reactor and then separating the tritium in a radiochemical laboratory. However, tritium can also be produced in a linear accelerator or even purchased in small quantities on the open market because tritium is used for a variety of non-nuclear civilian uses.

With respect to North Korea, dismantling the 5 MWe reactor and the IRT-2000 and associated radiochemical facilities would certainly eliminate the most obvious sources for tritium production. However, it would not necessarily prevent North Korea from acquiring or producing additional tritium, for example, from a linear accelerator (if one exists in North Korea). In any event, the importance of tritium to North Korea’s nuclear weapons program depends on whether North Korea uses tritium gas in its more advanced fission and fusion weapons. Tritium gas is not essential for thermonuclear weapons or even boosting.[4]

The final uncertainty—and the most important—concerns enriched uranium. Dismantlement of the enrichment facility at Yongbyon would not prevent North Korea from continuing to produce weapons-grade uranium at undeclared enrichment facilities outside Yongbyon; without knowing the output capacity of its enrichment facility relative to the capacity of undeclared enrichment facilities, it is not possible to calculate the significance of ending enrichment at the site. For example, if its enrichment facility represents a small fraction of North Korea’s overall enrichment capability, then shutting it down would not substantially reduce North Korea’s ability to produce additional nuclear weapons. Even if the enrichment plant there represents a more significant portion of North Korea’s overall enrichment capacity, dismantling the plant would have little long-term effect if North Korea is free to increase its capacity at undeclared enrichment facilities.

In sum, determining the significance of dismantling nuclear facilities at Yongbyon requires detailed knowledge about the design and construction of North Korea’s more advanced nuclear weapons, as well as accurate information about the country’s entire enrichment complex, both within and outside Yongbyon. This information is not publicly available. In a worst-case scenario, dismantlement of Yongbyon might have no effect on the North’s ability to produce additional thermonuclear weapons; alternatively, dismantling the complex might prevent or limit further production of thermonuclear weapons. In any event, North Korea could continue to produce weapons-grade uranium for additional fission weapons at undeclared enrichment facilities outside of the Yongbyon complex. At best, dismantlement of the Yongbyon enrichment plant could reduce the rate of production of fission weapons, but would not stop it.[5]

Policy Implications

In my experience, North Koreans often begin negotiations by asking a very high price for a very small give on their part. If that initial offer is rejected, the North Koreans are not shy about coming back to the bargaining table to discuss proposals to give more and get less in return. Thus, the failure at Hanoi may turn out to be a prelude to a more realistic North Korean negotiating posture. On the American side, the proposal to eliminate all of North Korea’s nuclear and missile programs in a single grand bargain is obviously not achievable. Having experienced failure first hand, President Trump may be amenable to a more modest incremental process of denuclearization that would stretch out over many years.

If so, US-DPRK negotiations are likely to focus on proposals to curtail or cease fissile material production in North Korea to “cap” or “freeze” its nuclear weapons arsenal, as a first step towards reduction and eventual elimination. The benefits of a US deal with the North to dismantle Yongbyon should not be dismissed, but they should also not be oversold. If the US decides to buy it, the administration shouldn’t pay too much for the prize. Washington needs to preserve as much bargaining leverage as possible to achieve a real freeze on fissile material production, which would require North Korea to allow international inspections to verify that secret facilities outside Yongbyon are shut down and dismantled.

Equally important, the US should not allow North Korea to drag out the dismantlement of Yongbyon for years. Technically, the key facilities at Yongbyon can be “dismantled” (or rendered virtually unrepairable) within months, using various inelegant shortcuts that would probably not be approved by the Environmental Protection Agency. During this period of dismantlement, US and DPRK negotiators should try to hammer out the difficult and intrusive measures necessary to verify a comprehensive freeze on fissile material production, including a North Korean declaration of its secret fissile material production facilities. In other words, a deal to dismantle Yongbyon could begin a process that would eventually lead to the more technically significant step of shutting down and dismantling all of North Korea’s fissile material production facilities.

Ideally, an agreement to dismantle Yongbyon would be part of a bigger package that includes the next step of implementing a comprehensive freeze and effective verification system within a specific time frame. The package would also have to specify the additional measures that the US will take once a comprehensive freeze has been implemented, such as further sanctions relief and steps towards normalizing political and economic relations with the US. Finally, a bigger diplomatic package needs to include North Korean agreement that a freeze on fissile material production is a first step towards reduction and elimination of its entire nuclear and missile program and forces. Correspondingly, the US should not accept North Korea as a nuclear weapons state but should continue to work towards achieving peace and security on a nuclear-free Korean Peninsula.

Obviously, the complete and verifiable denuclearization of North Korea won’t happen any time soon. The country has had a nuclear weapons program for over 30 years and probably nuclear weapons for over a decade; Pyongyang has spent billions of dollars to develop these capabilities while exacting tremendous sacrifices from the North Korean people. It won’t give them up quickly or easily—and certainly not until it stops seeing the US as a threat to its survival. The strategy, therefore, should be to impose as many limits as possible on North Korea’s nuclear and missile capabilities and establish a long-term political process that might eventually create the conditions for disarmament by fundamentally transforming the US-DPRK relationship. In the meantime, the US and its allies will need to maintain a strong mutual defense of South Korea to deter North Korean use of both conventional and nuclear weapons and to prevent South Korea and Japan from deciding to build their own nuclear weapons.

  1. [1]

    For the best post-mortem, see David Sanger and Edward Wong, “Trump-Kim Talks Undone by Big Egos and Bad Bets” New York Times, March 13, 2019,

  2. [2]

    For the best public report on Yongbyon nuclear facilities, see Chaim Braun, Siegfried Hecker, Chris Lawrence, and Panos Papadiamantis, “North Korean Nuclear Facilities After the Agreed Framework,” Center for International Security and Cooperation, Stanford University, May 27, 2016,

  3. [3]

    For a primer on boosting, see Henry D. Sokolski, “Nuclear Energy Basics, Part 1: Fission, Fusion, and the Bomb,” Nonproliferation Education Policy Center, September 1, 2018.

  4. [4]

    Ibid. See for discussion of “solid boosting” using enriched Lithium-6.

  5. [5]

    While not as powerful as the thermonuclear device North Korea tested in September 2017 (estimated yield in the range of 70-280 kilotons), the last two fission devices North Korea tested in January and September 2016 had yields in the range of 7 to 16.5 kilotons and 15 to 25 kilotons respectively, based on interpretation of seismic readings. (See summary in This is approximately the same range as the two American atomic bombs that devastated the cities of Hiroshima and Nagasaki in World War II. In other words, even without thermonuclear weapons, North Korea can achieve a healthy nuclear deterrent.

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