What
We Really Know About North Korea’s Nuclear Weapons, By Siegfried S. Hecker
And What We Don’t Yet Know for Sure
In January 2004, the director of North Korea’s
Yongbyon Nuclear Scientific Research Center handed me a sealed glass jar with
plutonium metal inside in an effort to convince me that his country had a
nuclear deterrent. To make the same point last week, Pyongyang lofted a missile 2,800 miles into space and
declared it had a nuclear-tipped missile that could reach all of the United
States. Has the country’s nuclear program really come that far?
As global anxiety over North Korea grows and the
war of words between U.S. President Donald Trump and North Korean leader Kim
Jong Un escalates, it is more important than ever to be precise about what we
know, and what we don’t, about Pyongyang’s nuclear weapons program and delivery
systems. In 2004, nothing I saw on my visit persuaded me that Pyongyang could
build a bomb and deliver it. But more recent visits, along with several kinds
of open-source analysis, leave little doubt of North Korea’s impressive progress in producing bomb fuel,
building powerful nuclear devices, and test-launching a wide variety of
missiles—and its determined efforts to integrate all three into a
nuclear-tipped missile.
Extensive experience with shorter-range missiles
and 11 years of nuclear tests most likely enable North Korea to mount a nuclear
warhead on missiles that can reach all of South Korea and Japan. That
capability, along with massive artillery firepower trained on Seoul, should be
enough to deter Washington. By my assessment, however, North Korea will need at
least two more years and several more missile and nuclear tests before it can
hit the U.S. mainland.
WHAT IT TAKES
A credible nuclear deterrent requires not just
fuel for a nuclear bomb, but also the ability to weaponize (that is, design and
build the bomb) and to field delivery systems that can get the bomb to a
target. It also requires demonstrating these capabilities—and the will to use
them—to an adversary. There may be little doubt of Kim’s willingness to use a
nuclear weapon if the situation required it. Assessing his exact capabilities,
however, has been a greater challenge, even for the U.S. government.
Pyongyang has often aided such efforts by
allowing peeks at its key assets. It has built much of its nuclear and missile
complex in full view of satellites and routinely released footage of its
leaders’ inspections of weapons and facilities. It has also allowed foreign,
nongovernment specialists to visit those facilities. My assessment of North
Korean capabilities is based on my own seven visits and ongoing analysis of all
open-source information.
There are two basic types of nuclear fuel:
plutonium, which is produced in reactors, and uranium, which is enriched to
weapon grade in centrifuges. North Korea’s plutonium inventory can be estimated
with high confidence because the design details of Yongbyon’s 5-megawatt
reactor are well known, and its operation is easily monitored by commercial
satellite imagery. International teams have inspected North Korea’s reactor
complex during times of diplomacy, and I have visited the plutonium facilities
and met Yongbyon’s very capable technical staff several times. I estimate that
North Korea has 20 to 40 kilograms of plutonium, sufficient for four to eight
bombs.
Estimates of highly enriched uranium are much
less certain. Centrifuge facilities are virtually impossible to spot from afar.
Yet in November 2010, during my last visit, North Korea allowed me to view its
recently completed modern centrifuge facility. (To my knowledge, no outsider
aside from those on our small Stanford University team has seen this or any
other North Korean centrifuge facility.) Based on that visit, satellite
imagery, and probabilistic analysis of the import and production of key
materials and components, I estimate that North Korea has 250–500 kilograms of
highly enriched uranium—sufficient for roughly 12 to 24 additional nuclear
weapons. (This assumes the existence of one or more covert centrifuge
facilities, necessary for testing technology before deploying it in the
large-scale facility I saw.)
North Korea likely has the ability to produce a
small number of hydrogen bombs.
North Korea also likely has the ability to
produce a small number of hydrogen bombs. These require heavy forms of
hydrogen—deuterium and tritium—for the fusion stage of the device, which is
triggered by a plutonium or uranium fission bomb. North Korea has demonstrated
the ability to produce deuterium and tritium, as well as a lithium compound,
Lithium-6 deuteride, which can produce tritium in situ in the
fusion stage of a hydrogen bomb’s detonation.
THE MAKING OF A NORTH KOREAN BOMB
Since 2006, North Korea has conducted six
underground nuclear tests. Seismographs around the world have picked up the
tremors, allowing estimates of the likely explosive power of each bomb. Two of
the most recent tests, in 2016, have had a destructive power of 10–25 kilotons,
equivalent to the bombs that destroyed Hiroshima and Nagasaki. The sixth test,
on September 13, 2017, was 10 times stronger, with a probably explosive power
of 200–250 kilotons—suggesting the successful detonation of a two-stage
hydrogen bomb. (Pyongyang’s claims that its fourth test, in January 2016, was a
hydrogen bomb did not appear credible at the time.) A few hours earlier, the
government had released photos of Kim with a mock-up of such a device. Though
such designs are generally considered to be among any government’s most closely
guarded secrets, North Korea has publicized them more than once.
This record of tests conclusively demonstrates
that North Korea can build nuclear devices with the power of the fission bombs
that destroyed Hiroshima and Nagasaki, as well as bombs with the destructive
power of modern hydrogen bombs. Given that record, and estimates of nuclear
materials inventories, I estimate that the upper range of nuclear materials
inventories is sufficient for roughly 25 to 30 nuclear weapons, with an annual
production rate of 6 to 7. (David Albright of the Institute for Science and
International Security has come up with a similar estimate: 15 to 34 weapons
and annual production rates of 3 to 5.) This assessment is lower than a leaked
U.S. intelligence community estimate of 60 weapons.
THE
MISSILE IS THE MESSAGE
It is another question whether those weapons are
small enough to fit on short- and long-range missiles. (Official photos of
nuclear devices are strategically positioned in front of diagrams of re-entry
vehicles, but there is no way of being sure that the photographed devices are
really identical to those tested, whatever the claims from Pyongyang.) For many
years, North Korea’s missile program appeared to lag far behind its nuclear
advances. Although the acquisition and development of short-range missiles
dates back to the mid-1980s, work on longer-range systems has started to speed
up only recently. In the past two years, North Korea has test-fired more than
40 missiles, most of which were of intermediate or long range.
Today, missile tests are the most visible part
of North Korea’s nuclear weapons quest. Successful launches are easily picked
up by international monitors and featured in official North Korean photos and
videos, many showing Kim Jong Un present and in charge. In July 2017, North
Korea passed an important milestone with the test of two Hwasong-14
missiles—intercontinental ballistic missiles, or ICBMs, that have a range
greater than 3,400 miles. Last week, it tested an even more powerful missile, a
Hwasong-15, with an estimated range of 8,000 miles, capable of reaching the
entire continental United States. Such tests have been accompanied by
diversification of North Korea’s missiles, allowing it to progress toward a
stated goal of launching at any time and from any place, including submarines.
Such impressive progress at producing fuel,
building devices, and launching a wide variety of missiles begs the question of
whether North Korea can put it all together in a single package that can deter
Washington. At the time of my 2004 visit, the leadership in Pyongyang may have
believed that a handful of primitive bombs was deterrent enough. By 2009, it
felt the need to conduct a second nuclear test to prove it had a working bomb.
More recently, it has focused on missile delivery of growing reach. And this
year, as leadership in Washington changed, it focused on a more ambitious goal:
demonstrating the ability to reach the entire United States with an ICBM,
possibly one tipped with a hydrogen bomb.
There is little doubt that North Korea could
mount a nuclear warhead on a missile that could reach South Korea or Japan.
There is little doubt that North Korea could
mount a nuclear warhead on a missile that could reach South Korea or Japan. But
ICBMs require smaller and lighter warheads that are nonetheless robust enough
to survive the entire flight trajectory, including re-entering the atmosphere.
And acquiring that capability will, by my estimate, take at least two more
years of tests.
READY TO TALK?
How has North Korea, one of the most isolated
countries in the world, been able to make such progress? It got some outside
assistance. Beginning in the 1960s, the Soviet Union helped Pyongyang pursue
peaceful applications of nuclear technologies and educated its technicians and
scientists. After 1991, collaboration with Russian and possibly Ukrainian
missile factories continued for some time, and North Korea has also taken
advantage of a leaky international export control system to acquire key
materials for the production of fissile materials, particularly for gas centrifuges
to enrich uranium. But for the most part, Pyongyang has built its nuclear
facilities and bombs on its own. Its program is now mostly self-sufficient.
After the most recent missile test, North Korea
declared that it had achieved its “goal of the completion of the rocket
weaponry system development” needed to deter U.S. aggression. Domestically,
this was an important milestone, because the regime had stated in 2013 that it
would develop a nuclear deterrent so it could turn its focus to economic development.
With this achievement, will Kim be ready to engage in diplomacy with
Washington? Although he needs more time in order to be able to credibly
threaten the entire continental United States, the fact that Kim can already
inflict enormous damage on American allies and bases in Asia may give him
sufficient assurance to start a dialogue, in an effort to reduce current
tensions and head off misunderstandings that could lead to war.
Washington should be ready to reciprocate—or if
necessary, to initiate the discussion. Talking would not represent a reward or
concession, or a signal of U.S. acceptance of a nuclear-armed North Korea. It
would instead be a first step toward reducing the risks of a nuclear
catastrophe and developing a better understanding of the other side.
Ultimately, that understanding may even help inform a negotiating strategy to
halt, roll back, and eventually eliminate North Korea’s nuclear program.
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