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South Korea's Nuclear Capabilities, Missiles, and the Next War

Zachary Keck, NPEC Wohlstetter Public Affairs Fellow, has published two articles about nuclear weapons in South Korea. The first argues that redeploying U.S. tactical nuclear weapons in South Korea would have no military utility while also undermining alliance relations. The second one, co-authored with NPEC Research Coordinator, Leon Whyte, highlights how South Korea could use its reactor-grade plutonium to build a nuclear weapons arsenal.

The first article is "4 Reasons America Shouldn't Send Nuclear Weapons to South Korea or Japan." The second article is "Can South Korea Build a Nuclear Bomb in 6 Months?" Both are posted in their entirety below. 

Sep 25, 2017

4 Reasons America Shouldn't Send Nuclear Weapons to South Korea or Japan

September 15, 2017

By Zachary Keck

As I have been writing about in recent weeks, the United States and its Asia-Pacific allies have been scrambling to respond to the rapid advances in North Korea’s nuclear program. One idea that has been floated is to redeploy tactical nuclear weapons in South Korea and perhaps even Japan.

To be sure, there have long been lawmakers in South Korea who have been advocating this idea. And, although South Korea’s government continues to oppose such a measure, the idea is been discussed at the highest levels. For instance, South Korean Defense Minister Song Young-moo said that he mentioned to his American counterpart, James Mattis, “that some South Korean lawmakers and media are strongly pushing for [U.S.] tactical nuclear weapons” to be returned to South Korea.

Then, NBC News reported that the Trump administration is “not ruling out” redeploying the tactical nuclear weapons to South Korea. A few days later, Sen. John McCain also argued that the United States should “seriously consider” putting nuclear weapons back in South Korea, and a senior delegation of South Korean lawmakers was in Washington this week to ask for them. Not to be outdone, former Japanese Defense Minister Shigeru Ishiba called for his country to start discussing hosting U.S. nuclear weapons, despite Tokyo’s long-standing pledge that it will not possess, manufacture or host nuclear weapons on Japanese territory. This is particularly notable given that Ishiba has been bandied about as a possible successor to Japan’s current prime minister, Shinzo Abe.

I have argued repeatedly that the United States should use the North Korean threat to strengthen its military posture in the Asia-Pacific region. Nonetheless, deploying nuclear weapons in South Korea or Japan is a terrible idea and not for the usual reasons given (Kim Jong-un is not going to surrender his nuclear weapons because America decided not to redeploy tactical nuclear weapons to the Korean Peninsula). Instead, there are at least four major reasons why America should not send nuclear weapons to Asia.

An Idea Past Its Expiration Date

The United States began forward deploying tactical nuclear weapons in Asia and Europe in the 1950 for one simple reason: it had no other choice. The initial Cold War nuclear-capable bombers like the B-29 and the B-50 did not have the range to conduct a round-trip flight from the United States to the Soviet Union (or North Korea). The United States also lacked a missile with sufficient range at this time as well—the first intercontinental ballistic missile wasn’t declared operational until 1959.

Still, the initial ICBMs and the long-range bomber, the B-52, were not able to meet America’s military needs at the time. During the Cold War, the United States intended to use tactical nuclear weapons to defeat conventional attacks by the Soviet Union in Europe and North Korea on the Korean Peninsula. The bombers flying from the United States took far too long to get to the fight. While U.S.-based ICBMs could reach the peninsula quickly, they were widely inaccurate and therefore ill-suited to be used against tactical targets. Especially starting in the 1980s and improving since, America’s long-range nuclear-capable missiles, both the land-based and sea-based ones, are extremely accurate, so they perform the same missions envisioned for tactical nuclear weapons.

Militarily Useless

Relatedly, basing tactical nuclear weapons in Japan or South Korea would have absolutely no military utility. This is especially true in the case of Japan. Since America’s missiles are regulated by the Intermediate Range Treaty (INF), it can’t produce non-ICBM ground-based missiles with a range of over 500 km. This is not far enough to reach North Korea from Japan. A ballistic missile with a less than 500 km could reach North Korea from the Republic of Korea. However, to hit the northern part of the Democratic People’s Republic of Korea these missiles would have to be based in northern part of South Korea, which would make it especially vulnerable (more on this below).

More to the point, as alluded to above, the incredible accuracy of precision-guided missiles using nuclear weapons militarily unnecessary under most circumstances. If you can hit a target straight on the mark, you don’t need a high yield bomb to destroy it. But, the United States does have increasingly higher-yield conventional bombs just in case (albeit ones delivered by air).

But most importantly, the United States and South Korea do not need to use tactical nuclear weapons to defeat a North Korean invasion. The alliance’s conventional capabilities are more than adequate for this task. The only real mission nuclear weapons serve on the Korean Peninsula is deterring North Korea from using its own nuclear weapons, and retaliating if it does attack America or its allies with the bomb. American ICBMs, bombers and ballistic missile submarines would be the preferred systems for carrying out this retaliation. As Secretary of Defense Mattis put it this week, “We have a nuclear deterrent and its location is immaterial.”

Unnecessary Headaches and Juicy Targets

If redeploying tactical nuclear targets were simply militarily irrelevant, perhaps some might be in favor of this policy for political reasons. In reality, however, they would be a net negative both for military and political reasons.

They would detract from their military strength by forcing the United States and its allies to divert attention and resources from their conventional forces. First, each warhead sent to South Korea would require special U.S. personnel to handle them. The sites themselves would first require up front costs to construct or redesign them to handle nuclear weapons. Once in place, they would also require significant personnel to protect them from outsider or insider threats.

Depending on the type of tactical nuclear weapons sent, it would also possibly divert South Korean and Japanese attention and resources. For instance, in Europe some U.S. tactical bombs are maintained by the United States while allies manage the aircraft that would be used to deliver them. This requires that the European allies refit some of their aircraft to be used for nuclear weapons rather than for conventional use. It also necessitates some of their military personnel be trained in these missions. Replicating this system in South Korea or Japan would be extremely counterproductive at a time when attention should be focused on improving conventional capabilities.

Besides diverting attention and resources from where they belong, deploying tactical nuclear weapons would simply create juicy targets for North Korea (and perhaps China) to target in the event on conflict. As one Japanese official recently warned: “If it's understood that there are nuclear weapons here, Japan could end up becoming more of a target.” This is especially true now that North Korea is developing far more accurate conventional missiles. Once again, protecting the sites would force the United States to deploy sufficient missile defense systems, and even then some missiles could get through. There are already plenty of targets the United States and its allies must protect against Pyongyang’s missiles. There is no reason to create new ones that have no military utility.

Alliance Troubles

The most commonly cited argument for deploying tactical nuclear weapons is to strengthen America’s alliances with South Korea and Japan. In reality, tactical nuclear weapons often create intense and unnecessary tensions with allies.

To begin with, as noted above, South Korea’s government has repeatedly insisted it does not want America to bring tactical nuclear weapons back. More importantly, however, history has shown that forward deployed nuclear weapons create a bunch of thorny questions for the alliance.

For instance, in the very first years of the Cold War the British agreed (without much thought) to allow America to base its nuclear bombers on English territory. It was only a few years later, as B-29 bombers began arriving, that British officials began to seriously think through the potential complications of this basing arrangement. Specifically, they began to worry that the United States might believe it could use its bombers to conduct nuclear attacks on the Soviet Union without London’s approval. They were correct.

The United States and Great Britain entered into intense ongoing negotiations where the latter insisted it be involved in any decisions to use nuclear weapons that were stationed on its territory. Washington would only agree to vague assurances of consultations while refusing to give Britain veto power over any decision to use nuclear weapons. The issue also went beyond senior leadership and became an issue of public opinion. In the end, the United States basically won the issue while providing the British with face saving language for public consumption.

Still, this issue persisted for years and began to impact other aspects of the alliance. It came to the fore again in the 1950s when the two sides began to negotiate the stationing of American intermediate range ballistic missiles (IRBMs) in England. The following decade it appeared in another form. As one scholar has written:

For three years from 1962, MoD repeatedly tried to get assurances from the Americans who controlled NATO Defenses in Europe that they would not order British commanders to use nuclear weapons without consulting the government. But the requests were either ignored or rebuffed at high political level.

The debate over basing rights was reopened (at least in public forums) after the United States conducted bombing raids in Libya in the 1980s.

Nor was this unique to Britain. Many other countries, including France, were indignant that the United States would use nuclear weapons without their agreement. In fact, Charles de Gaulle demanded the right to veto any American or British decision to use nuclear weapons anywhere in the world. Not only would the United States not even consider this possibility, the Supreme Allied Commander in Europe, American Gen. Lauris Norstad, refused to even tell de Gaulle whether America had nuclear warheads on French soil. The French president was incredulous.

A scenario of actually using nuclear weapons is probably remote. Nonetheless, deploying tactical nuclear weapons will necessitate negotiations over who has launch control. South Korea President Moon Jae-in has already taken to publicly insisting that the United States must receive South Korean approval before launching a conventional attack. Adding nuclear weapons to the mix would only make the debate more contentious, weakening alliance cohesion at a time when unity is needed. 

Bottom line: redeploying tactical nuclear weapons is worse than unnecessary. It would actively hurt America’s military posture and alliances in the region.



Can South Korea Build a Nuclear Bomb in 6 Months?

September 22, 2017

By Zachary Keck and Leon Whyte

As tensions with North Korea are heating up, a prominent South Korean nuclear physicist said his country can build a nuclear weapon in just six months.

In a newly released Korean-language article in Chosun Monthly, Kune Y. Suh, an MIT-trained nuclear engineer at Seoul National University, argues that South Korea needs to build its own nuclear arsenal to deal with the threat posed by Pyongyang. When asked if Seoul is capable of producing such a weapon, Suh argued that the country could use its huge stockpile of plutonium to build an operational nuclear weapon in six months.

Suh didn’t go into detail about how Seoul could accomplish this feat, which is notable because its plutonium stockpile largely consists of what many dismiss as “unusable” reactor-grade plutonium. But clues to how South Korea could overcome this challenge were offered at an event our employer, the Nonproliferation Policy Education Center, hosted on Capitol Hill on September 14 for a visiting delegation of Japanese Diet members. That event, which focused on the plutonium stockpiles in northeast Asia, featured an eye-opening presentation by Bruce Goodwin, a Senior Fellow at the Center for Global Security Research at the Lawrence Livermore National Laboratory. At the event, Goodwin, one of America’s top nuclear weapons designers and plutonium experts, thoroughly debunked the myth that countries cannot use so-called reactor-grade plutonium to build nuclear weapons.

Reactor-grade plutonium refers to plutonium that has a larger percentage of the isotope Pu-240 compared with weapons-grade plutonium, which has a higher mix of the isotope, Pu-239. Many have contended that the high level of Pu-240 makes reactor-grade plutonium unsuitable for nuclear weapons because it would require too large of a critical mass, is too radioactive to handle, and is prone to a condition called “pre-initiation,” which is when the nuclear chain reaction begins too soon producing a minimal explosive yield. As the World Nuclear Association has put it, “any significant proportions of Pu-240 in it would make it hazardous to the bomb makers, as well as probably unreliable and unpredictable” for use in nuclear weapons.

Goodwin’s presentation exploded each myth, which persist even though the United States tested a reactor-grade-plutonium nuclear device in 1962. First, he noted that the critical mass for reactor-grade plutonium in nuclear weapons is only two kilograms larger than weapons-grade plutonium, and much less than using highly enriched uranium. The reason why many believe a much larger critical mass is needed with reactor-grade plutonium is because Pu-240 is not very fissionable with the slow neutrons present in nuclear reactors. On the other hand, Goodwin explained, “Pu-240 is a good fissile material with fast neutrons and fast neutrons drive nuclear explosives.” The irony here, Goodwin pointed out, is that reactor-grade plutonium works better for nuclear weapons than in reactors.

The radioactivity differences between reactor and weapons-grade plutonium are also negligible. To be sure, reactor-grade plutonium is over three times as radioactive as its weapons grade counterpart, but the differences would have to be “several factors of ten” to seriously inhibit handling of the material. In fact, Goodwin’s presentation noted, “In newly built facilities, handling reactor grade is essentially the same as handling weapons grade Pu.”

The problem of pre-initiation, while real, is also overblown. As Goodwin points out, the Department of Energy released a report in 1997 that stated that “even if pre-initiation occurs at the worst possible moment (when the material first becomes compressed enough to sustain a chain reaction) the explosive yield of even a relatively simple first-generation nuclear device would be of the order of one or a few kilotons.” This is the absolute minimum yield, and in all likelihood, it would be much higher even for a first-generation device. Nonetheless, “a one-kiloton bomb would still have a radius of destruction roughly one-third that of the Hiroshima weapon, making it a potentially fearsome explosive.”

Furthermore, that same Department of Energy report noted that advanced weapon states, like Russia and the United States, “could produce weapons from reactor-grade plutonium having reliable explosive yields, weight, and other characteristics generally comparable to those of weapons made from weapons-grade plutonium.” Goodwin assured the audience that “having done this myself I can tell you that this is quite true.” He also stated: “I suspect that the industrialized states of Asia would be similarly capable to the United States and Russia in making such weapons.” It is also worth noting that South Korea has one thousand bombs’ worth of tritium. This can be used to boost fission weapons and totally eliminate the risk of pre-initiation.

Suh is therefore correct that South Korea’s reactor-grade plutonium can be used to build a nuclear arsenal. Still, its plutonium stockpile is of the unseparated variety and, unlike Japan, Seoul doesn’t have a commercial-sized reprocessing plant. Wouldn’t this prevent South Korea from building nuclear weapons in the six-month timetable that Suh outlines?

Not necessarily. South Korea and other countries could possibly build a small reprocessing plant in that time, according to a 1977 Oak Ridge National Laboratory memo written by Floyd L. Culler. In the memo, Culler outlines how a country could secretly build a chemical reprocessing plant with a capacity to process 150 tons of irradiated fuel per year. Assuming the plant was designed to process one PWR assembly per day (recovering about five kilograms of plutonium per day), Culler estimated it would take four to six months to build such a facility, with the first ten kilograms of plutonium becoming available about one week after operations began. Such a plant could be built covertly in a relatively small area in a warehouse or some other unsafeguarded area, such as the Korea Atomic Energy Research Institute’s Underground Research Tunnel, which is currently used for research on the geologic disposal of spent fuel and high-level radioactive waste. To be sure, it might take South Korea longer than six months, especially to field an operational nuclear weapon. Still, it’s undeniable that Seoul would be able to make a nuclear weapon without much difficulty.

While President Moon Jae-in has vowed not to build a nuclear weapon, a majority of South Koreans want the bomb, as do many members of the opposition party. If Seoul chooses to go this route, or continues to hint at it, Japan and China will likely ramp up their nuclear weapons options as well.


The Nonproliferation Policy Education Center (NPEC), is a 501 (c)3 nonpartisan, nonprofit, educational organization
founded in 1994 to promote a better understanding of strategic weapons proliferation issues. NPEC educates policymakers, journalists,
and university professors about proliferation threats and possible new policies and measures to meet them.
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