It was capable of producing about 6 kilograms (Kg) of plutonium per year and began operating in 1986. North Korea openly acknowledged a uranium enrichment program in 2009, but has said its purpose is the production of fuel for nuclear power. In November 2010, North Korea showed visiting American experts early construction of a 100 MWT light-water reactor and a newly built gas centrifuge uranium enrichment plant, both at the Yongbyon site. The North Koreans claimed the enrichment plant was operational, but this has not been independently confirmed. U.S. officials have said that it is likely other, clandestine enrichment facilities exist. Its cooling tower was destroyed in June 2008, and it has not been restarted. Reprocessing at that time is estimated to have produced 7-8 kg of separated plutonium or approximately enough for one nuclear warhead. Although North Korea's weapons program has been plutonium-based from the start, in the past decade, intelligence had emerged pointing to it pursuing a second route to a nuclear bomb using highly enriched uranium. However, North Korea's offers may have some intrinsic value on technical grounds: removal of the fresh fuel could reduce the amount of ready material to produce plutonium if the 5 MWe reactor was restarted (it would take only six months to do so); the presence of international inspectors at the newly built uranium enrichment site, depending on the degree of access given, could shed light on the extent and type of technical capability of the North Korean enrichment program. The North Korean official news agency announced a "successful" underground nuclear detonation, and seismic monitoring systems measured a resulting earthquake that was 5.1M in magnitude. The U.S. Director of National Intelligence issued a statement: 
The U.S. Intelligence Community assesses that North Korea probably conducted an underground nuclear explosion in the vicinity of P'unggye on February 12, 2013. The explosion yield was approximately several kilotons. The South Korean Ministry of Defense estimated that the test yield was between 6 and 7 kilotons. North Korea claimed that the February 12, 2013, nuclear test was to develop a "smaller and light" warhead. At a minimum, the test would likely contribute to North Korea's ability to develop a warhead that could be mounted on a long-range missile. Observers are also waiting for evidence from test emissions that might show whether the North Koreans tested a uranium or plutonium device. This information could help determine the type and sophistication of the North Korean nuclear warhead design about which little is known. These tests strengthen our assessment that North Korea has produced nuclear weapons." It is widely believed that the warhead design was an implosion device. In May 2012, North Korea changed its constitution to say that it was a "nuclear-armed state." This is the most detailed statement on North Korean nuclear use policies to date. This would be enough for at least one nuclear weapon. North Korea has said it would not include warhead information at this stage. According to press reports, at a bilateral meeting in Singapore in April 2008, the United States and North Korea agreed to a formulation in which North Korea would include its plutonium production activities in a formal declaration, and the enrichment and proliferation issues would be dealt with separately in a secret side agreement in which North Korea would "acknowledge" the U.S. concerns over North Korean proliferation to Syria without confirming or denying them. Some prominent analysts of North Korea's nuclear and missile programs emphasize that halting progress on North Korea's ability to develop a warhead on a long-range missile should be the United States' top priority, and further missile and nuclear testing would be necessary for North Korea to accomplish this.
This report summarizes what is known from open sources about the North Korean nuclear weapons program—including weapons-usable fissile material and warhead estimates—and assesses current developments in achieving denuclearization. Little detailed open-source information is available about the DPRK's nuclear weapons production capabilities, warhead sophistication, the scope and success of its uranium enrichment program, or extent of its proliferation activities. In total, it is estimated that North Korea has between 30 and 50 kilograms of separated plutonium, enough for at least half a dozen nuclear weapons. North Korea's plutonium production reactor at Yongbyon has been shuttered since its cooling tower was destroyed under international agreement in June 2008. However, on April 1, 2013, North Korea said it would resume operation of its plutonium production reactor. Experts estimate it will take approximately six months to restart. This would provide North Korea with approximately one bomb's worth of plutonium per year.
While North Korea's weapons program has been plutonium-based from the start, in the past decade, intelligence emerged pointing to a second route to a bomb using highly enriched uranium. North Korea openly acknowledged a uranium enrichment program in 2009, but has said its purpose is the production of fuel for nuclear power. In November 2010, North Korea showed visiting American experts early construction of a 100 MWT light-water reactor and a newly built gas centrifuge uranium enrichment plant, both at the Yongbyon site. The North Koreans claimed the enrichment plant was operational, but this has not been independently confirmed. U.S. officials have said that it is likely other, clandestine enrichment facilities exist. Enrichment (as well as reprocessing) technology can be used to produce material for nuclear weapons or fuel for power reactors. An enrichment capability could potentially provide North Korea with a faster way of making nuclear material for weapons and therefore is of great concern to policymakers.
North Korea has made multiple policy statements in the past year asserting its nuclear weapons status: in May 2012, North Korea changed its constitution to say that it was a "nuclear-armed state." In January 2013, North Korea said that no dialogue on denuclearization "would be possible" and it would only disarm when all the other nuclear weapon states also disarm. In March 2013, North Korea stated its goal of expanding its nuclear weapons program.
Many experts believe that the prime objective of North Korea's nuclear program is to develop a nuclear warhead that could be mounted on North Korea's intermediate-range and long-range missiles. This was confirmed by North Korean official statements in late March 2013. Miniaturization of a nuclear warhead would likely require additional nuclear and missile tests. In January 2013, a North Korean statement said that it would respond with a nuclear test "of higher level." On February 12, 2013, the North Korean official news agency announced a "successful" underground nuclear detonation, and seismic monitoring systems measured a resulting earthquake that was 5.1 in magnitude. This is magnitude is slightly higher than past tests, but yield estimates are still uncertain. The South Korean Ministry of Defense estimated that the test yield was between 6 and 7 kilotons, while the U.S. Director of National Intelligence so far has said "approximately several kilotons." North Korea claimed that the February 12, 2013, nuclear test was to develop a "smaller and light" warhead. At a minimum, the test would likely contribute to North Korea's ability to develop a warhead that could be mounted on a long-range missile. To date, no open source data on test emissions is available that might show whether the North Koreans tested a uranium or plutonium device. This information could help determine the type and sophistication of the North Korean nuclear warhead design, about which little is known.