North Korea’s nuclear tests have grown steadily more
destructive, and the country continues to pursue its longtime goal of
putting a nuclear warhead on an intercontinental missile capable of reaching targets around the globe.
The United States recently ordered an aircraft carrier and other warships toward the Korean Peninsula in a show of force intended to discourage the North from testing a nuclear weapon.
While examining satellite imagery, experts have
observed a wide range of activity at Mount Mantap, a mile-high peak
where North Korea conducts its nuclear tests. Beneath the mountain, a
system of tunnels has been excavated for the past five detonations of
the North’s nuclear bombs.
North Korea often marks significant dates
with shows of military force, and analysts say it might detonate a
nuclear weapon to celebrate the birthday this Saturday of the nation’s
founder, Kim Il-sung, the grandfather of the current leader, Kim
Jong-un.
Since late 2013, piles of rocky debris from the
excavation of the site’s North tunnel system have grown quite large —
now big enough to cover a football field, and quite high. It’s the largest pile ever observed there. Work on the excavation has recently slowed, quite likely signaling readiness for the next detonation.
Jan. 5, 2017 Jan. 22, 2017
Source: DigitalGlobe Imagery
So too, observers of the test site have recently noted
a lot of water being pumped out of the North tunnel system – presumably
to prevent washouts and keep it dry for test instrumentation.
Groundwater is often a problem in tunneling as it can slow progress,
weaken structures and cause shorts in electrical gear.
Scientists at the Los Alamos weapons lab who have studied images of the large debris pile recently concluded
that Mount Mantap could withstand a nuclear explosion of up to 282
kilotons – roughly 20 times stronger than the Hiroshima blast.
Previously, the largest detonations were in the Hiroshima range.
No one outside of North Korea knows for sure what
could take place or how big the blast might be. It’s a guessing game —
though a sophisticated one for Washington’s intelligence agencies, and
less so for civilians armed only with unclassified information. Either
way, it’s a detective story full of clues, questions and a protagonist
with a clear motive.
Experts in satellite imagery, military analysts around
the world, and geologists and physicists track progress at the remote
site mainly through the observation of tunneling, building construction,
truck movements and, though harder to see, personnel moves.
Mount Mantap is the world’s only active nuclear test site. Most other nuclear states long ago gave up such explosions in a coordinated effort to end arms races and their dangerous and costly spirals of military action and reaction.
In North Korea, the test devices are buried deep
inside tunnels bored through solid rock far below Mount Mantap’s peaks,
creating field labs for nuclear experiments. The nearest major city,
Chongjin, is situated about 50 miles to the northeast.
The tunnels for the North’s tests are excavated just
over halfway up Mount Mantap, which rises to a height of 7,234 feet. The
bomb is placed at the end of the tunnel, which gets partly backfilled
to prevent radioactive leakage, and then detonated in the test.
To pinpoint the geographic site of the nuclear blasts,
experts rely on the kind of seismologic data used to track earthquakes.
Similarly, each of the North’s detonations has generated shock waves
that register around the globe.
Experts say
the North’s tunnel system will quite likely play a significant role in
future testing because it is the busiest area at the Punggye-ri nuclear
test site, has a conspicuous perimeter fence and has the largest amount
of protective rock directly overhead.
Several independent teams,
including ones from China, South Korea, Norway and the United States,
have gathered seismic readings from the North’s bomb tests. In addition,
a world body known as the the Comprehensive Test Ban Treaty
Organization, based in Vienna, Austria, operates a sprawling network of global sensors.
Last year, a team of South Korean scientists
confirmed a test’s exact location within Mount Mantap by studying data
from a radar satellite that detected subtle elevation changes on the
mountain’s surface.
The North has shown technical
savvy in pacing its nuclear tests to increase the amount of time for
bomb makers to conduct detailed analyses of the blasts and learn from
mistakes.
“They’ve done five tests in 10 years,” said Siegfried
S. Hecker, a Stanford professor who once directed the Los Alamos weapons
laboratory in New Mexico, the birthplace of the atomic bomb. “You can
learn a lot in that time.”
In contrast, he added, India and Pakistan conducted a rush of nuclear detonations in May 1998 in what experts called a blitz of saber rattling. “They couldn’t have learned much,” Dr. Hecker said.
North Korea’s past tests are thought to have centered on mastering a simple type of atomic bomb, known as an implosion device.
Some of the tests may have featured “boosted” atomic
bombs, however — meaning that an injection of tritium, a radioactive
form of hydrogen, could have increased their destructive power. All such
fuels, known as thermonuclear, need the high heats from an exploding
atom bomb for ignition.
“It’s possible that North Korea has already boosted,”
said Gregory S. Jones, a scientist at the Rand Corporation who analyzes
nuclear issues. Like other experts, he pointed to the nation’s two
nuclear detonations last year as possible tests of small boosted arms.
As signs of the North’s interest in boosting, experts
cite modifications to a reactor that could make tritium, as well as
construction of a plant that could gather up the radioactive gas.
Boosted arms can raise the destructive power of atomic blasts or greatly
reduce their need for atomic fuel. That savings can significantly
lighten and shrink the resulting arms, making them easier to hurl over
long distances. Boosting is considered a main step to scaling down
warheads so they can fit atop intercontinental missiles.
Nine countries possess nuclear arms, most having advanced over time from making simple atom bombs to advanced hydrogen bombs. Nuclear experts say North Korea’s program is at an intermediate phase of development — somewhere between stages one and three. The
secret to achieving more destructive power is to raise the amount of
thermonuclear fuel that an exploding atom bomb can ignite.
STAGE 1
Imposion Atom Bomb
uses conventional explosives to compress and ignite atomic fuel
Imposion Atom Bomb
uses conventional explosives to compress and ignite atomic fuel
Destructive power
Experts say the likelihood of North Korea making
strides in its nuclear program has risen with the recent evidence that
the nation tried to sell excess lithium-6, which is the main ingredient for making thermonuclear fuels, including tritium.
So too, satellite images of the mountainous test site
reveal the digging of the deep tunnel system, which could allow the
detonation of a larger device.
On March 28, a satellite image showed people gathered
in front of an administrative building at the test site. The last time
such a large group was observed was on Jan. 4, 2013, a little more than a
month before North Korea’s third nuclear detonation.
Experts see the recent gathering as yet another
sign that the North may be getting closer to detonating a device in its
increasingly long series of nuclear tests.
“The fact these formations can be seen suggests that
Pyongyang is sending a political message that the sixth nuclear test
will be conducted soon,” wrote Joseph S. Bermudez Jr., and Jack Liu,
experts at 38 North, an analysis group that closely tracks North Korea.
“Alternatively, it may be engaged in a well-planned game of
brinkmanship.”
