The United States has reportedly told South Korea that North Korea could detonate a third atomic device as soon as this week, Kyodo News reported on Monday (see GSN, May 1).
Citing an unidentified Washington-based diplomatic insider, the South Korean JoongAng Ilbo newspaper report did not say how the U.S. government had arrived at that conclusion. Both the South Korean and U.S. governments assess that highly enriched uranium would be used in the expected nuclear test, the newspaper said (Kyodo News, April 30).
International observers believe Pyongyang is likely to want to wipe away the embarrassment of last month's failed long-range rocket launch with another nuclear test that would show its advancement in uranium enrichment technology. Recent satellite images of the isolated nation's Punggye-ri atomic test site indicate excavation of a new tunnel where a nuclear device would likely be placed ahead of a detonation.
"The North has apparently finished technical preparations for a third nuclear test. What is left now is a political decision," Agence France-Presse quoted a South Korean atomic specialist as saying on Wednesday.
The spy agencies of South Korea and the United States are keeping a close watch over Punggye-ri, according to the unidentified source (Agence France-Presse/Yahoo!News, May 2).
Seoul on Tuesday said it was keeping close tabs on North Korea but did not believe another test would occur in the immediate future, the Yonhap News Agency reported.
"We are not aware at this point of any signs of an imminent nuclear test by North Korea," South Korean Foreign Ministry spokeswoman Han Hye-jin said. "But we are closely watching the situation with serious concerns over this and preparing to cope with any possibilities under close cooperation with relevant nations," she added.
Han also said South Korea's senior representative to talks focused on North Korean denuclearization is scheduled to visit China on Wednesday. South Korean envoy Lim Sung-nam is to hold talks with his Chinese equivalent, Wu Dawei, and other officials over the course of two days.
"During the visit, Lim and Chinese officials plan to assess the situation after North Korea's long-range missile launch and discuss future actions," the spokeswoman said.
The six-party talks, which involve China, Japan, Russia, the United States and both Koreas, were last held in December 2008 (Yonhap News Agency I, May 1).
South Korea and Japan on Wednesday both cautioned the North against new aggressive actions, Reuters reported.
"Japan strongly urges (North Korea) not to conduct any further provocation including nuclear tests or further (missile) launches," Kazuyuki Hamada, Japanese parliamentary vice minister for foreign affairs, said during a meeting in Vienna, Austria, on preparing for the 2015 Nuclear Nonproliferation Treaty review conference.
Pyongyang "should realize that further provocations will only exacerbate its isolation," concurred Seoul's envoy to the event, Kim Bong-hyun, a deputy minister at the South Korean Foreign Ministry (Fredrik Dahl, Reuters, May 2).
Radio Free Asia on Tuesday said an international network of sensors managed by the Preparatory Commission for the Comprehensive Test Ban Treaty Organization is focused on detecting any signs of an atomic blast from North Korea, the Korea Times reported (Kang Hyun-kyung, Korea Times, May 1).
Thousands of seismic specialists would have the technical capacity to identify waves of energy traveling through the Earth and send notification right after the detonation occurred, Agence France-Presse reported.
"Just within a very few minutes it would be really obvious that they would have done this. The only delay would be the delay in which seismic waves travel around the world to various stations," Columbia University seismology expert Paul Richards said.
The seismic wave monitoring posts closest to North Korea are in Japan and South Korea.
The seismic energy produced by an earthquake is easy to distinguish from the energy that follows an underground atomic blast, meaning there is no worry regarding scientists being unable to differentiate between the two, according to Richards.
An expert panel of the U.S. National Research Council assessed in a March report that "technical capabilities for seismic monitoring have improved substantially in the past decade, allowing much more sensitive detection, identification, and location of nuclear events" (see GSN, March 30).
Seismic detection capabilities have also grown more sensitive over the years; monitoring stations can now detect a detonation with a yield as low as 0.02 kilotons.
Pyongyang's first atomic detonation in 2006 is calculated to have produced an explosive power of 1 kiloton and a follow-up test in 2009 resulted in a slightly larger yield, AFP reported.
In addition to seismic monitoring, the international community can determine the point and place at which an atomic blast occurred by measuring nuclear fallout in the atmosphere, AFP reported. The NRC panel noted in the report that the international community's "radionuclide network has gone from being essentially nonexistent to a nearly fully functional and robust network with new technology that has surpassed most expectations."
Atomic test detection capabilities for the test ban are supplemented by those operated by some countries' intelligence agencies and armed forces.
"Lots of people will know very quickly," Natural Resources Defense Council nuclear program head Christopher Paine said (Kerry Sheridan, Agence France-Presse/Google News, May 1).
The unidentified South Korean atomic specialist said the North is assessed to have enriched enough uranium to fuel as many as six warheads, Yonhap reported.
Uranium requires an enrichment level of roughly 90 percent to be considered warhead-grade. While Pyongyang unveiled an enrichment program to the world in late 2010, international monitors have never been able to verify the size of the North's uranium stockpile or its enrichment level.
Nuclear weapons expert Siegfried Hecker in November 2010 was given a rare tour of the North's enrichment facility at the Yongbyon nuclear complex; he was told 2,000 centrifuges had been installed.
"If the North Korean claim is true, it could allow the North to make some 40 kilograms of highly enriched uranium per year, enough for one or two atomic weapons," the nuclear specialist said.
Figuring the North began enriching uranium in 2009, the nation should now have enough warhead-grade uranium for three to six weapons, he said.
"North Korea has some 3,000 nuclear-related experts" and a projected 26 million tons of raw uranium on its territory, according to the specialist.
Pyongyang is not known to have developed the capacity to produce warheads small enough to mount on missiles, though some experts believe the North is getting closer to that goal.
Hecker said in December a third atomic detonation should equip North Korea with the data it needs to build miniaturized warheads (Yonhap News Agency II, May 2).
The United States has reportedly told South Korea that North Korea could detonate a third atomic device as soon as this week, Kyodo News reported on Monday.