HEW Archive North Korea

North Korea's Nuclear Weapons Program

Last changed 25 October 2006


North Korea, or the Democratic People's Republic of Korea (DPRK), acquired its first significant nuclear facilities from the Soviet Union in 1965, a small, 2-MW (thermal output), light-water-moderated, research reactor that burned highly enriched uranium. This research reactor, the IRT-2000, was subsequently upgraded to 4 MW and then 8 MW. The reactor was placed under IAEA safeguards in 1977.

A small radiochemical laboratory in located in Pyongyang, built with Soviet aid in the 1970s. Small quantities of plutonium were separated there in 1975 from Soviet-supplied irradiated fuel. Later gram quantities of plutonium produced in the IRT-2000 were also separated.

These facilities are located in the main nuclear complex at Yongbyon, 100 kilometers north of Pyongyang, on the Kuryong River.

In the late 1970s and early 1980s North Korea began working to reduce its reliance on outside assistance for its nuclear program. It began mining or producing uranium and reactor-grade graphite, and in 1980 began construction of a small graphite-moderated, natural uranium power reactor began at Yongbyon.

Intelligence revealed the project in 1984, prior to its first operation in 1986. This reactor is based on 1950s MAGNOX power reactor technology (graphite moderator, aluminum-magnesium clad natural uranium fuel, carbon dioxide gas cooling) which is very good for producing weapon grade plutonium as a byproduct. After startup problems, it was operating at 20 MWth (thermal output) by 1990, its output is also described as being 5 MWe (electrical output).

A larger 50 MW MAGNOX-type reactor began under construction at Yongbyon with a completion date in 1995, but construction was suspended in 1994. A 200 MW of the same design under construction at Taechon, 100 kilometers north of Pyongyang was likewise suspended in 1994.

A large secret plutonium separation facility was built at Yongbyon early in the 1980s capable of handling several hundreds of tons of fuel a year, enough to handle fuel from all of the reactors. The existence of this plant was discovered through intelligence in 1989.

Under pressure from the Soviet Union, North Korea joined the Non-Proliferation Treaty (NPT) on 12 December 1985, and declared to the International Atomic Energy Agency (IAEA) the existence of the Yongbyon facility. Not long after joining the NPT issues with North Korea's compliance began to be encountered. North Korea did not accept the comprehensive IAEA safeguards agreement covering all its nuclear activities required by the NPT for seven years. A large secret plutonium separation facility was built at Yongbyon early in the 1980s capable of handling several hundreds of tons of fuel a year, enough to handle fuel from all of the reactors. This facility was not declared to the IAEA, its existence of this plant was discovered through intelligence in 1989.

Following the declaration by U.S. President George H. W. Bush and President Roh Tae Woo of South Korea (the Republic of Korea or ROK) in December 1991 that there were no U.S. tactical nuclear weapons in Korea international efforts to denuclearize the Korean peninsula gathered momentum. These efforts produced the Joint Declaration on North-South Denuclearization in early 1992 that not only called for a nuclear-weapon-free peninsula but also prohibited both the DPRK and ROK from possessing facilities for enriching uranium or for separating plutonium from spent reactor fuel. It also provided for reciprocal inspections between the two countries, though they could not agree on the sites that would be inspected.

Later in 1992, however, North Korea accepted the NPT-required safeguards agreement for inspection of all its nuclear installations by the IAEA. On 4 May 1992 North Korea made its initial declaration of its holdings of nuclear materials as required. During an inspection by the IAEA soon after to verify this declaration, North Korea revealed that it had separated 100 g of plutonium in March 1990. The plutonium samples examined by the IAEA had a composition of 97.56% Pu-239, and 2.44% Pu-240 ([May 2001]).

Subsequent analysis of environmental samples and U.S. satellite images allowed the IAEA to determine that more plutonium had been separated than the North Korean had admitted. This led to a crisis in which demands for more inspections resulted in an announcement by North Korea that it would withdraw from the NPT. Intensive multi-party negotiation by the U.S., China, South Korea and Japan led North Korea on the last day of the 90-day notice period for withdrawal from the NPT, 11 June 1993, to announce that it would remain a party to that treaty, at least for the time being. In a joint statement with the U.S., the DPRK said it had "decided unilaterally to suspend as long as necessary the effectuation of its withdrawal from" the NPT.

A series of negotiation efforts ensued over the next 16 months. In exchange for shutting down its 20 MW reactor, and other reactor construction projects, North Korea demanded that much larger light water power reactors (LWRs) be provided. While the discussions continued, North Korea unloaded the irradiated fuel (some 8,000 rods) from its reactor while preventing the IAEA from observing and taking measurements. This destroyed the ability of the IAEA to confirm North Korea's statements about the reactor's operating history, and raised fears that it extraction of the plutonium was imminent. North Korea also mobilized its military and moved onto a war footing.

Then, in a June 1994 visit to North Korea sanctioned by U.S. President Clinton, former President Jimmy Carter met with it's leader Kim Il Sung and reported afterwards that the crisis was over. The DPRK had agreed not to reprocess the spent fuel, accepted IAEA inspection of its reactors and other facilities declared by it to the IAEA, and to freeze its existing nuclear program. In return, North Korea expected assistance in securing LWRs and an end to U.S. efforts to impose sanctions if IAEA inspectors were denied access to other locations. South Korea then announced that it was prepared to provide technology and major financing for two LWRs.

When U.S. and DPRK negotiators met again, they produced the Agreed Framework of October 1994 that gave more detail to the basic agreement announced in the August 1993 joint statement and in President Carter's press conference. The Agreed Framework was signed by the two nations on 21 October 1994.

Under the Agreed Framework North Korea refrained from reprocessing the unloaded reactor fuel or operating the reactor further for nine more years.

A clear sign that the role of diplomacy in managing the behavior of North Korea toward its nuclear program was drawing to an end came during President George W. Bush's State of the Union speech on 29 January 2002 when he characterized North Korea as belonging to "an axis of evil," a choice of words that signaled the administration's lack of faith or interest in diplomatic engagement.

The current crisis, that has continued with the recent nuclear test by North Korea, erupted in early October 2002, when North Korean officials did not deny charges made by James A. Kelly, the U.S. Assistant Secretary of State for East Asian and Pacific Affairs, that Pyongyang had a secret uranium enrichment program in violation of its commitments. According to a June 2002 CIA report, described by Seymour Hersh in the 27 January 2003 New Yorker, in 1997 Pakistan gave North Korea high-speed centrifuges and data on building and testing an enriched uranium nuclear weapon, in return North Korea gave Pakistan missile technology and parts. The North Korea violation was made public by the U.S. on 16 October 2002.

A rancorous public dispute over the violations continued for the enxt several weeks. On 13 November President Bush, in a meeting with senior advisers Wednesday, decided that the United States would suspend further shipments of fuel oil that had been supplied under the Agreed Framework in December unless North Korea took the necessary steps to come back into compliance.

The North Korean response to fuel shipment suspension came on 12 December when it announced that it would restart the Yongbyon reactor. North Korean tehn removed the IAEA safeguard seals at the nuclear research center in Yongbyon, shut down the monitoring cameras, and ordered the IAEA inspectors out of the country. On 10 January 2003 Pyongyang announced its withdrawal from the NPT, becoming the only country ever to do so. North Korea restarted its 20 MW reactor and reprocessing plant at Yongbyon, and by June 2003 scientists had extracted plutonium from the 8,000 spent fuel rods kept at the site, according to North Korean officials. Western analysts estimate that this reprocessing would have resulted in 25-30 kilograms of plutonium.

Although North Korea was detected to be in violation of the NPT and the Agreed Framework in secretly obtaining and pursuing uranium enrichment technology, there is no evidence that any enrichment facility has been built or is operating, or that North Korea possesses any enriched uranium.

North Korea has had a long history of reneging on its commitments and cheating. This a reality that the U.S. has had to confront repeatedly and presents the challenge of addressing it in such fashion that the outcome furthers long term U.S. interests. Despite the caustic effect of deception by North Korea during the period from December 1985 to 1992, when it secretly separated plutonium sufficient to build one to two bombs, diplomacy and the Agreed Framework successfully froze in place North Korea's weapon production program for 11 years, from 1992 to 2003, during which time no plutonium was bred in reactors, nor was any separated for use in weapons. If North Korea's weapons program had gone forward unabated the small 20 MW reactor alone would have produced material for another 11 bombs; the larger reactors could have produced material for as many as a hundred more.

The confrontational approach taken by the George W. Bush administration in addressing this crisis led to North Korea's decision to reactivate its long suspended nuclear weapons production program. All of the fissile material known to be in North Korean hands was produced either during the administration of George H. W. Bush, or during the current George W. Bush administration.

The Test

On the morning of 9 October 2006 North Korea informed the Chinese government that they should expect a four kiloton nuclear test. Twenty minutes later, at 01:35:28 UTC, a seismic event occurred at 41.294 degrees N latitude, 129.094 degrees E longitude, with a magnitude of 4.2, according to the U.S. Geological Survey. The test was followed by a public declaration of success by the North Korean government.

Although the initial USGS data provided a position uncertainty of 7 kilometers, it placed the site approximately 42 kilometers northwest of Kilchu, in Hwaseong-gun, North Hamgyeong Province. This coincides with a site of suspicious tunneling and construction activities that were first reported in 2005, on the east slope of remote 7231 feet high Mant'ap-san Mountain. Subsequent reports during the past month indicate that the North Koreans had excavated a 700 m-long horizontal tunnel under Mant'ap-san. An unpaved road extends 19 km from the test site to the nearest town of Punggye-ri along the Namdae River.

The Korea Institute of Geoscience & Mineral Resources (KIGAM), South Korea's state-run geoscience institute, adjusted its estimate of the epicenter on 13 October to 41.26 degrees N latitude and 129.17 degrees E longitude.

Two measurements of the seismic magnitude of the test have been published: magnitude 4.2 by the USGS, and between 3.58 and 3.7 by the KIGAM. An uncertainty in seismic magnitude of 0.5 translates into an uncertainty in yield of about a factor of three. Compounding this uncertainty is that relationship between seismic magnitude and yield which depends upon the hardness of the rock in which the explosive is buried.

The explosive yield has been estimated by Terry Wallace, a seismologist at Los Alamos National Laboratory, to be between 0.5 and 2 kilotons, with 90 percent confidence that the yield is less than 1 kiloton. Lynn R. Sykes of Columbia University estimates a yield of 0.4 kilotons, with 68 percent confidence that the yield is between 0.2 and 0.7 kilotons and a 95 percent probability that the yield is less than 1 kiloton. Other published median yield estimates have been 500 and 550 tons ([Garwin and von Hippel 2006]).

The test was conducted deep underground in a horizontal tunnel which prevented the immediate or large scale release of radioactivity. Nonetheless a high percentage of underground nuclear tests leak detectable levels of radioactivity, most reliably radioactive isotopes of the inert gases krypton and xenon, which can leak through natural or blast induced fissures in the surrounding rock driven by the high pressures resulting from the explosion. Leaks can be become detectable at the surface on a time scale ranging from tens of minutes to days ([Adushkin and Leith 2001]).

Atmospheric sampling missions flown by the Air Force's specialized WC-135 Constant Phoenix, the last Cold War era "sniffer" plane still in service, were begun by the United States shortly after the test. On 13 October it was reported that traces of radioactivity had been detected and on 16 October National Intelligence Director John Negroponte's office released a statement confirming that samples collected on 11 October showed that the test was indeed a nuclear blast, laying to rest some initial speculation that the low yield explosion might in fact be simply a very large conventional explosive blast.

Subsequent analysis of samples has shown that the fissile material used in the test was plutonium. Since different fissile materials produce different proportions of various radionuclides, measuring these ratios (such as the ratios of Xe-133, Xe-133m and Xe-135) can unambiguously determine the fissile material used. Leaks of additional isotopes which can occur would make the determination even easier.

IsotopeHalf-lifePu-239 fission yieldU-235 fission yield
Xe-1335.25 days6.98% 6.70%
Xe-133m2.19 days0.232%0.189%
Xe-1359.14 hours7.60%6.54%
From Radiochemistry in Nuclear Power Reactors, Chien C. Lin, Committee on Nuclear and Radiochemistry, National Research Council, 1996, p. 204.

Garwin and von Hippel report that if radioxenon leaked into the atmosphere at a rate of only 0.1 percent a day, a concentration of 10,000 atoms per cubic meter of air would be detectable downwind three days after the test, one hundred times the detectability threshold. If the isotope ratio of about 8000 radioxenon atoms could be measured, then the identity of the fissile parent could be established as being plutonium with 95 percent certaintly ([Garwin and von Hippel 2006]).

The North Koreans have high grade plutonium (content of neutron emitting Pu-240 measured at 2.44% by the IAEA in the July 1992, compared to 6% for U.S. weapons plutonium), so problems with predetonation are almost certainly not the cause.([May 2001])

The low yield, almost certainly less than a quarter of its reported planned yield, indicates a partial failure of the device. The most likely cause is poor implosion performance (that is, poor compression), though late initiation is also a possibility.

Regarding the possibility of poor compression, it should be observed that they are likely trying to develop a relatively sophisticated light system suitable for missiles, in the range of 500-1000 kg, not the 3500 kg design of the WWII Fat Man, which proved very reliable. Failure might be due to problems perfecting the design, or simply some test-related technical fault in an otherwise sound design.

The relatively low yield announced prior to the test was possibly to conserve plutonium of which North Korea has a fairly limited supply.

Seismic Location Maps and Seismic Recording

U.S. Geological Survey Map

The section of the map where the test was detected is bracketed in green. Click here to see a close-up of the test location.

[Adushkin and Leith 2001] Vitaly V. Adushkin, William Leith. The Containment of Soviet Underground Nuclear Explosions, U.S. Department of the Interior Geological Survey, Open File Report 01-312, September 2001, p. 37-38 and 41.

[May 2001] Michael May ed. Verifying the Agreed Framework, Center for Global Security Research, Lawrence Livermore National Laboratory, Center for International Security and Cooperation, Stanford University, UCRL-ID-142036, CGSR-2001-001, April 2001.

[Garwin and von Hippel 2006] Richard L. Garwin and Frank N. von Hippel. A Technical Analysis of North Korea's Oct. 9 Nuclear Test, Arms Control Today, November 2006.

HEW Archive North Korea