North Korea's nuclear tests
- 6 January 2016
- From the section Asia
North Korea's nuclear programme has been a source of great concern for the international community for more than 20 years.
Nuclear ambitions
The state is now believed to have conducted four underground nuclear tests.
The latest test, announced on 6 January 2016, was described by North Korean media as a miniaturised hydrogen bomb test. There has been no independent confirmation of this, but it is the first claim of a hydrogen bomb, known to be immensely powerful.
The previous test was conducted in February 2013 and came with the state's first claim to have miniaturised a device, although an atomic device in that instance.
What this means is that it claims to have made a nuclear device small enough to fit on a missile. At the time, experts said it was impossible to confirm the claim.
Nevertheless, its nuclear ambitions have stepped up in the past year. Earlier this year, North Korea said its plutonium and highly enriched uranium facilities at nuclear plant Yongbyon had restarted.
The test site
All of the tests appear to have originated at a test site called Punggye-ri, also known as P'unggye-yok, in a remote area in the east of the country, near the town of Kilju.
Multiple rounds of international negotiations amid a strict sanctions regime - a process, which has been described as a game of cat and mouse - appear to have done little to curb North Korea's nuclear ambitions.
North Korea's previous tests followed rocket launches. The North put its first satellite into space with a long-range rocket in late 2012, in what the UN said was a banned test of ballistic missile technology, imposing sanctions.
The US is concerned that such long-range rockets could threaten its mainland with atomic bombs.
The key nuclear tests and developments
9 October 2006
Years of posturing and wrangles over the delivery of American aid culminated in October 2006 with an announcement by Pyongyang that it had carried out an underground nuclear explosion.
North Korea's first nuclear test exploded a device based on plutonium, rather than enriched uranium.
The test was conducted at P'unggye-ri, and US intelligence officials later announced that analysis of radioactive debris in air samples collected a few days later confirmed the blast had taken place.
But they estimated that it had not been a powerful one, measuring less than one kiloton, raising questions about the sophistication and effectiveness of the weapon.
This is less than a tenth of the size of the bomb dropped on Hiroshima in 1945.
In response to the test the UN approved military and economic sanctions against North Korea.
After years of on-off talks, in February 2007 Pyongyang agreed to shut down its main nuclear reactor at Yongbyon in return for aid and diplomatic concessions.
But negotiations stalled as North Korea accused its negotiating partners - the US, South Korea, Japan, China and Russia - of failing to meet agreed obligations.
25 May 2009
Barely a month after North Korea walked out of international talks on its nuclear programme, it carried out its second underground nuclear test, which was said to be more powerful than the first.
Russia's defence ministry estimated a blast of up to 20 kilotons, a similar size to the US bombs that completely destroyed Hiroshima and Nagasaki in 1945.
The US Geological Survey said a 4.7-magnitude quake was detected, 10km (six miles) underground, an indication of a nuclear explosion.
It followed hard on the heels of the test of a long-range missile that threatened Asia and could have reached the US.
The UN issued a resolution condemning the nuclear test and tightened sanctions. After the US imposed tough sanctions in August 2009, Kim Jong-il said he was willing to resume nuclear talks.
North Korea's rocket launches
- May 2015: North Korea announces it has successfully tested a submarine-launched missile for the first time, but scepticism is then poured on the claim
- Dec 2012: North Korea launches three-stage rocket, says it successfully put a satellite into orbit; US defence officials confirm object in orbit
- Apr 2012: Three-stage rocket explodes just after take-off, falls into sea
- Apr 2009: Three-stage rocket launched; North Korea says it was a success, US says it failed and fell into the sea
- Jul 2006: North Korea test-fires a long-range Taepodong-2 missile; US said it failed shortly after take-off
North Korea's missile programme
November 2010: Tour of Yongbyon
In November 2010 a US atomic scientist was given a tour of North Korea's uranium enrichment plant at Yongbyon about 100km (60 miles) north of the capital.
Siegfried Hecker was shown an experimental light-water nuclear reactor that was still under construction, and more significantly a new facility that contained "more than 1,000 centrifuges" that the North Koreans said was processing low-enriched uranium to fuel the new reactor.
He said the facility seemed designed primarily for civilian nuclear power but could easily be converted to further process uranium to weapons grade.
He described the plant as modern and clean - unlike all the other Yongbyon facilities he had seen - and said he was "stunned" at its sophistication.
12 February 2013
In the early hours of 12 February 2013, unusual seismic activity was detected around the Punggye-ri underground nuclear test site.
"It was confirmed that the nuclear test that was carried out at a high level in a safe and perfect manner using a miniaturised and lighter nuclear device with greater explosive force than previously," KCNA said.
The reference to "miniaturised" stoked fears that Pyongyang was that much closer to producing a device small enough to fit on a long-range missile.
But many experts remain sceptical. Rather, speculation was rife that the test involved a uranium device which could have significant implications for North Korea's nuclear capabilities.
However, a well-contained underground test could provide little evidence. Little was detected shortly after the test, although the Comprehensive Nuclear Test-ban Treaty Organization, compiled a paper about radiation detected 55 days later.
6 January 2016
The first indication was a geological report of a quake registering about 5.1 reported in North Korea, close to the nuclear test site.
Then KCNA announced that a successful test of a hydrogen bomb had taken place. It comes within a month of a claim by Kim Jong-un that they had an H-bomb.
Little data has been collected so far from this test, but the experts are sceptical about this claim.
