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On 6 January 2016, the Democratic People’s Republic of Korea (DPRK) announced that it had successfully detonated a ‘hydrogen’ or thermonuclear device. Previously, the DPRK has carried out nuclear tests on 12 February 2013, 25 May 2009 and 9 October 2006. Furthermore, the DPRK is reportedly also continuing with the development and testing of both land and submarine launched ballistic missiles. Thus, the DPRK is pursuing a full-fledged nuclear weapon programme that comprises a complete nuclear fuel cycle—uranium enrichment and plutonium separation—nuclear testing and associated nuclear-weapon delivery systems.
As on previous occasions, commentary by Western officials and non-government experts is raising doubts about the capabilities of the DPRK to manufacture and test nuclear explosive devices—this time, thermonuclear devices. On each of the previous three occasions of announced tests by the DPRK, subsequent information and data concluded that nuclear detonations had in fact been carried out.
According to the International Monitoring System of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) in Vienna, an ‘unusual seismic event’ was detected in the DPRK on 6 January at 01:30:00 (UTC) in the vicinity of the Punggye-ri test site. The seismic signature of a nuclear detonation is clearly distinguishable from that of an earthquake as shown below.
Furthermore, nuclear tests can vent various noble gases  (such as Xenon-133) and other fission products into the atmosphere, which can be picked up by the radionuclide monitoring stations of the CTBTO  and by planes equipped with radionuclide detection sensors. For example, the USA has deployed a WC-135 ‘sniffer’ plane ‘Constant Phoenix’  for this purpose. In 2006, the CTBTO picked up Xenon-133 released by the DPRK test, but not in 2009, and in 2013 detected Xenon-133 and Xenon-131m. It is likely the DPRK has improved its containment measures to prevent such releases into the atmosphere. The image below released by the Korean Central News Agency (KCNA) in 2013 shows the containment measures deployed by the DPRK for its nuclear tests to prevent or minimize venting of noble gases and other fission products. As yet there are no reports of detection of venting from the 6 January test.
The nuclear weapons or ‘atomic bombs’ used by the USA against Japan in World War II were ‘fission’ devices based on U-235 (highly enriched uranium) and Pu-239 (weapon-usable plutonium). These bombs split or fissioned the nuclear material to release energy through a self-sustaining chain reaction. Reportedly, the ‘Fat Man’ nuclear bomb detonated over Nagasaki in 1945 used about 6.2 kilograms of plutonium and produced an explosive yield of about 20 kilotons (equivalent to 20,000 tons of TNT high-explosive). Some scientists note that modern nuclear weapons can be made with 4 kilograms or less of plutonium. To produce greater intensity of fission, deuterium and tritium (D-T) gas can be introduced into the core of a fission device resulting in fusion that releases high-energy neutrons, which leads to more complete fissioning. This is called ‘boosting’, that is increasing the explosive yield. ‘Fusion’ or thermonuclear or ‘hydrogen’ bombs can be much more powerful though smaller in physical dimensions than fission weapons, but are more complex weapon designs utilising the fusion of heavy isotopes of hydrogen: deuterium and tritium.
It remains to be seen if it can be concluded that the DPRK has indeed tested a thermonuclear device, as even if Xenon-133 and other particulates are detected all that can be proven is that a nuclear test has been carried out. Sceptics argue that the seismic signature of the 6 January event in the DPRK, measuring about 4.85 on the Richter scale, suggests that the yield of the detonation was too small to be from a thermonuclear device.
DPRK Nuclear Weapon Programme
As usual, many Western sources are voicing scepticism about the DPRK’s nuclear weapon capabilities as in 2006, 2009 and 2013, when they grudgingly acknowledged later that the DPRK indeed had carried out nuclear tests. It would be a mistake to underestimate the capabilities of the DPRK’s nuclear weapon programme. These sources were in a similar self-induced state of denial about Iran’s uranium enrichment capability and eventually had to acknowledge the reality that Iran had installed some 19,000 centrifuges and produced more than 16,000 kilograms of low enriched uranium and to negotiate an agreement on a Joint Comprehensive Plan of Action (JCPOA) with Iran that was concluded in July 2015. In the final analysis, what is more important is that the DPRK has carried out yet another nuclear test and is sending a political signal regarding the continuing development of its nuclear weapon programme despite opposition and condemnation from several sources. Development by the DPRK of a thermonuclear device is only a matter of time.
It is likely that in developing its nuclear weapon programme, the DPRK is not only bolstering its defence capabilities against a militarily resurgent Japan and against the economically more powerful Republic of Korea, but also may be signalling and accumulating bargaining chips for future negotiations within the Six Party Talks or some other framework for engagement such as a JCPOA. This would not be unprecedented as the DPRK previously has traded away certain nuclear assets, as in the 1994 ‘Agreed Framework’ and the ‘Initial Actions’ on the freeze on its nuclear programme and the disabling of certain nuclear facilities as agreed in 2007, but then walked away from these agreements citing undue pressure and ‘hostile actions’ by the USA and its allies.
The Way Forward
The adoption of additional resolutions by the UN Security Council condemning the DPRK and imposing even more sanctions serve little purpose other than to unnecessarily punish the hapless civilian population of the DPRK and to demonstrate yet again the impotence and ineffectiveness of current policies of isolating and sanctioning the DPRK. Unfortunately, some of the policies not only of the DPRK, but also of the USA as well as of South Korea and Japan—two countries that have previously hosted US nuclear weapons on their respective territories and are covered by US nuclear defence arrangements—have contributed to the stalemate in the so-called Six Party Talks (DPRK, Republic of Korea, China, Japan, Russia and the USA) that were suspended in 2009.
Just as engagement by the EU/E3+3  with Iran (2013-2015) and by the UK and USA with Libya (2003) regarding their nuclear programmes resulted in favourable non-proliferation outcomes, it is essential to resume engagement with the DPRK on some sort of JCPOA. Unconditional resumption of the moribund Six Party Talks would be a good start, albeit with a clear focus on nuclear issues, with the objective of bringing the DPRK back into the fold of the nuclear Non-Proliferation Treaty (NPT) and its associated IAEA safeguards, while addressing the DPRK’s and other parties’ security concerns. The only feasible option is a diplomatic outcome that takes into account the legitimate security interests of all relevant negotiating parties. Furthermore, moving towards establishing a nuclear-weapon-free zone in Northeast Asia, covering the Korean Peninsula and Japan, would be a complementary confidence- and security-building measure.
 An underground nuclear explosion can eject radioactive material–solid and gaseous–into the environment. These substances provide the ultimate evidence of a nuclear detonation. Their detection depends on many factors, in particular on the geological setting in which the detonation took place. A well-contained underground nuclear explosion will not release solid radioactive residues into the atmosphere. But there is another way to detect such explosions–by finding their gaseous releases, radioactive noble gases, in particular Xenon. Noble gas atoms are very small and pass easily through rock and sediment. Once in the atmosphere, the gas is dispersed by the winds and can be picked up by radionuclide detectors, thus providing the 'smoking gun' evidence of a nuclear explosion.
 The CTBTO, based in Vienna, is the international organization responsible for ensuring that no nuclear explosion goes undetected. It uses four complementary verification technologies: seismic, hydroacoustic, infrasound and radionuclide monitoring.
 The 'WC-135 Constant Phoenix' is a military derivative of the Boeing-707 passenger airliner used by the USA to verify compliance of the 1963 Partial Nuclear-Test-Ban Treaty by collecting noble gases such as Xenon-133, fission products and particulates released by nuclear tests.
 European Union, France, Germany and the UK; plus China, Russian Federation and the USA.