North Koreas Nuclear Weapons: Latest Developments

North Korea’s Nuclear Weapons:
Latest Developments
Sharon Squassoni
Specialist in National Defense
Foreign Affairs, Defense, and Trade Division
On October 9, 2006, North Korea conducted a nuclear test, with a yield of under
1 kiloton (vice the anticipated 4-kiloton yield) . The United States and other countries
condemned the test and the U.N. Security Council passed Resolution 1718 on October
14, which requires North Korea to refrain from nuclear or missile tests, rejoin the
Nuclear Nonproliferation Treaty (NPT), and dismantle its WMD programs. The test is
the latest provocative act of many since 2002, when North Korea ended an eight-year
freeze on its plutonium production program, expelled international inspectors and
restarted facilities. North Korea may now have enough Pu for eight to ten weapons. On
February 13, 2007, North Korea reached an agreement with other members of the Six-
Party talks to begin the initial phase (60 days) of implementing the Joint Statement from
September 2005 on denuclearization. Key components include halting production at
Yongbyon and delivery of heavy fuel oil. Many other aspects are yet to be decided.
This report will be updated as needed.
In the early 1980s, U.S. satellites tracked a growing indigenous nuclear program in
North Korea. A small nuclear reactor at Yongbyon (5MWe), capable of producing about
6kg of plutonium per year, began operating in 1986.1 Later that year, U.S. satellites
detected high explosives testing and a new plant to separate plutonium. In addition,
construction of two larger reactors (50MWe at Yongbyon and 200MWe at Taechon) added
to evidence of a serious clandestine effort. Although North Korea had joined the Nuclear
Nonproliferation Treaty in 1985, the safeguards inspections that began only in 1992 raised
questions about how much plutonium North Korea had produced covertly. In 1994, North
Korea pledged, under the Agreed Framework with the United States, to freeze its plutonium

1 5MWe is a power rating for the reactor, indicating that it produces 5 million watts of electricity
per day (very small). Reactors are also described in terms of million watts of heat (MW thermal).

programs and eventually dismantle them in return for several kinds of assistance.2 At that
time, Western intelligence agencies estimated that North Korea had separated enough
plutonium for one or two bombs; other sources estimated four to five bombs.
Weapons Production Milestones
Acquiring fissile material — plutonium-239 or highly enriched uranium (HEU) —
is the key hurdle in nuclear weapons development.3 Producing these two materials is
technically challenging; in comparison, many experts believe weaponization to be
relatively easy.4 North Korea has industrial-scale uranium mining, and plants for milling,
refining, and converting uranium; it also has a fuel fabrication plant, a nuclear reactor, and
a reprocessing plant — in short, everything needed to produce Pu-239. In its nuclear
reactor, North Korea uses magnox fuel — natural uranium (>99%U-238) metal, wrapped
in magnesium-alloy cladding. About 8000 fuel rods constitute a fuel core for the reactor.
When irradiated in a reactor, natural uranium fuel absorbs a neutron and then decays
into plutonium (Pu-239). Fuel that remains in the reactor for a long time becomes
contaminated by the isotope Pu-240, which can “poison” the functioning of a nuclear
weapon.5 Spent or irradiated fuel, which poses radiological hazards, must cool after
removal from the reactor. The cooling phase, estimated by some at five months, is
proportional to the fuel burn-up. Reprocessing to separate plutonium from waste products
and uranium is the next step. North Korea uses a PUREX separation process, like the
United States. After shearing off the fuel cladding, the fuel is dissolved in nitric acid.
Components (plutonium, uranium, waste) of the fuel are separated into different streams
using organic solvents. In small quantities, separation can be done in hot cells, but larger
quantities require significant shielding to prevent deadly exposure to radiation.6
North Korea appears to have mastered the engineering requirements of plutonium
production. Its 5MWe nuclear reactor operated from 1986 to 1994, restarting in January
2003. North Korean officials claimed to have separated plutonium in hot cells and tested
the reprocessing plant in 1990, and to have reprocessed all 8000 fuel rods from the 5MWe
reactor between January and June 2003. The January 2004 unofficial U.S. delegation
reported that “All indications from the display in the control room are that the reactor is
operating smoothly now....However, we have no way of assessing independently how well
the reactor has operated during the past year.”7 The same delegation reported that the
reprocessing “facility appeared in good repair,” in contrast to a 1992 IAEA assessment

2 See CRS Report RL33590, North Korea’s Nuclear Weapons Development and Diplomacy, by
Larry Niksch.
3 Highly enriched uranium (HEU) has 20% or more U-235 isotope; 90% U-235 is weapons-grade.
4 The physical principles of weaponization are well-known, but producing a weapon with high
reliability, effectiveness and efficiency without testing presents significant challenges.
5 Plutonium that stays in a reactor for a long time (reactor-grade, with high “burn-up”) contains
about 20% Pu-240; weapons-grade plutonium contains less than 7% Pu-240.
6 Hot cells are heavily shielded rooms with remote handling equipment for working with
irradiated materials.
7 Siegfried Hecker, Jan. 21, 2004, testimony before Senate Foreign Relations Committee.

of the reprocessing plant as “extremely primitive.” In the end, however, significant
growth in North Korea’s arsenal depends on the completion of the two larger reactors and
progress in the reported uranium enrichment program.
In January 2004, North Korean officials showed an unofficial U.S. delegation
alloyed “scrap” from a plutonium (Pu) casting operation. Alloying plutonium with other
materials is “common in plutonium metallurgy to retain the delta-phase of plutonium,
which makes it easier to cast and shape” (two steps in weapons production).8 Dr.
Siegfried Hecker, a delegation member, assessed that the stated density of the material
was consistent with plutonium alloyed with gallium or aluminum. If so, this could
indicate a certain sophistication in North Korea’s handling of Pu metal, but without
testing the material, Hecker could not confirm that the metal was plutonium or that it was
alloyed, or that it was from the most recent reprocessing campaign.
There is no reliable information on North Korean nuclear weapons design. Although
the U.S. Director of National Intelligence confirmed that a nuclear test was conducted on
October 9, 2006 in the vicinity of P’unggye, the sub-kiloton yield of the test suggests that
the weapon design or manufacturing process likely needs improvement.9 Environmental
clues suggest that the device used plutonium. By comparison, a simple plutonium
implosion device normally would produce a larger blast, perhaps 5 to 20 kilotons. The
first nuclear tests conducted by other states range from 9 kt (Pakistan) to 60kt, but tests
by the United States, China, Britain and Russia were in the 20kt-range. Implosion
devices, which use sophisticated lenses of high explosives to compress fissile material,
are generally thought to require testing, although the CIA suggested in 2003 that North
Korea could validate its weapons design using extensive high explosives testing.10 It is
possible that Pakistani scientist A.Q. Khan may have provided North Korea the same
Chinese-origin nuclear weapon design he provided to Libya. If so, this might help North
Korea develop a reliable warhead for ballistic missiles — small, light and robust enough
to tolerate the extreme conditions encountered through a ballistic trajectory. Although
former DIA Director Jacoby told the Senate Armed Services Committee in April 2005
that North Korea had the capability to arm a missile with a nuclear device, Pentagon
officials later backtracked from that assessment.
Estimating Nuclear Material Production
Most estimates of nuclear weapon stockpiles are based on estimated fissile material
production. Factors in plutonium production include the average power level of the
reactor; days of operation; how much of the fuel is reprocessed and how quickly, and how
much plutonium is lost in production processes. According to North Korea, the 5MWe
reactor performed poorly early on, unevenly irradiating the rods. There is no data on the
reactor’s current performance or the reprocessing facility’s efficiency. North Korea told
the IAEA that during the 1990 “hot test,” it lost almost 30% of the plutonium in the waste

8 Hecker, Jan. 21, 2004, testimony before SFRC.
9 Text of statement available at []
10 CIA response to questions for the record, August 18, 2003, submitted by the Senate Select
Committee on Intelligence, full text available at [


streams.11 A key consideration is whether or not the reprocessing plant can run
continuously, since frequent shutdowns can lead to plutonium losses. According to North
Korean officials in January 2004, the plant annual throughput is 110 tons of spent fuel,
about twice the fuel load of the 5MWe reactor. A final factor in assessing how many
weapons North Korea can produce is whether North Korea’s technical sophistication
enables it to use more or less material than the international standards of 8kg of Pu and

25kg for HEU per weapon. North Korea’s abilities here are unknown.

What Does North Korea Have Now?
Secretary of State Powell stated in December 2002 that “We now believe they [North
Koreans] have a couple of nuclear weapons and have had them for years.”12 On February
10, 2005, North Korea announced that it had manufactured “nukes” for self-defense and
that it would bolster its nuclear weapons arsenal.13 In June 2005, Vice Foreign Minister
Kim Gye Gwan told ABC News that “We have enough nuclear bombs to defend against
a U.S. attack. As for specifically how many we have, that is a secret.” Kim also said
North Korea was building more bombs and when asked about delivery systems, said “our
scientists have the knowledge, comparable to other scientists around the world.”14 Some
Members of Congress interpreted then-CIA Director Porter Goss’ statements in March
2005 on a “range” of nuclear weapon estimates to confirm that North Korea’s arsenal has
multiplied.15 In December 2005, the North Korean foreign ministry stated that it would
“increase [its] self-reliant national defense capacity, including nuclear deterrent.”16 In
October 2006, North Korea’s Foreign Ministry said that “nuclear weapons will serve as
[a] reliable war deterrent.”
Has North Korea Reprocessed the Existing Spent Fuel?. On July 13,

2003, North Korean officials told U.S. officials in New York that they had completed17

reprocessing the 8000 fuel rods on June 30. On January 8, 2004, North Korean officials
told an unofficial U.S. delegation that the reprocessing campaign began in mid-January
2003 and ended at the end of June 2003. In all, they reportedly reprocessed 50 tons of
spent fuel in less than six months, which tracks with earlier estimates that North Korea
could reprocess about 11 tons/month, roughly enough plutonium for one bomb per month.
An unofficial U.S. delegation in January 2004 concluded that the spent fuel pond no
longer held the 8,000 fuel rods and surmised that they could have been moved to another
storage location, but not without significant health and safety risks. The delegation was

11 David Albright and Kevin O’Neill, editors, Solving the North Korean Nuclear Puzzle, ISIS
Report, ISIS Press, 2000, p. 88.
12 Transcript of Dec. 29, 2002, Meet the Press.
13 “North Korea Says It Has Nuclear Weapons and Rejects Talks,” New York Times, Feb. 10,


14 “N. Korea Building Bombs, Its Envoy Says,” Los Angeles Times, June 9, 2005.
15 Carl Levin and Hillary Clinton, “North Korea’s Rising Urgency,” Washington Post, July 5,


16 “N. Korea: Nuclear Program to Expand,” Philadelphia Inquirer, Dec. 20, 2005.
17 “North Korea Says It Has Made Fuel For Atom Bombs,” New York Times, July 15, 2003.

not allowed to visit the Dry Storage Building, where the fuel rods likely would have been
stored before reprocessing. The delegation also did not visit waste facilities.
Reprocessing the 8,000 fuel rods from the 5MWe reactor would yield between 25 and
30kg of plutonium, perhaps for four to six weapons, but the exact amount of plutonium
that might have been reprocessed is unknown. In 2004, North Korean officials stated that
the reprocessing campaign was conducted continuously (four 6-hour shifts). U.S. efforts
to detect Krypton-85 (a by-product of reprocessing) reportedly suggested that some
reprocessing had taken place, but were largely inconclusive.
Adding to the Arsenal
Make New Plutonium in 5MWe Reactor. On February 6, 2003, North Korean
officials announced that the 5MWe reactor was operating, and commercial satellite
photography confirmed activity in March. In January 2004, North Korean officials told
U.S. visitors that the reactor was now operating smoothly at 100% of its rated power. The
U.S. visitors noted that the display in the reactor control room and steam plumes from the
cooling towers confirmed operation, but that there was no way of knowing how it had
operated over the last year. In April 2005, the reactor was shut down, and on May 11,

2005, North Korean officials stated they harvested fuel rods for weapons.18 According19

to commercial satellite images, the reactor resumed operations in August 2005.
A common estimate is that the reactor generates 6 kg of Pu per year, roughly one
bomb per year, but the reactor would likely be operated for several years before fuel is
withdrawn. One estimate is that the reactor held between 10 and 15 kg Pu in April 2005,
and that North Korea could have reprocessed all the fuel by mid-2006.20 From August
2005 to 2006, the reactor could have produced another 6 kg of Pu; in total, there could be
enough separated plutonium for another three weapons.
Complete Other Reactors. The reactors at Yongbyon (50MWe) and Taechon
(200MWe) are likely several years from completion. U.S. visitors in January 2004 saw
heavy corrosion and cracks in concrete building structures at Yongbyon, reporting that the21
reactor building “looks in a terrible state of repair.” The CIA estimates that the two
reactors could generate about 275kg of plutonium per year.22 In August 2005, another
unofficial U.S. delegation to Pyongyang was told by North Korean officials that they
planned to finish building the 50MWe reactor within two years. Commercial satellite23
images in 2005 and 2006 showed little progress.
Produce Highly Enriched Uranium for Weapons. A 2002 unclassified CIA
working paper on North Korea’s nuclear weapons and uranium enrichment estimated that

18 “North Koreans Claim to Extract Fuel for Nuclear Weapons,” New York Times, May 12, 2005.
19 David Albright and Paul Brannan, “The North Korean Plutonium Stock Mid-2006,” Institute
for Science and International Security, June 26, 2006, p. 3.
20 Ibid.
21 Hecker Jan. 21, 2004 testimony before SRFC.
22 CIA unclassified point paper distributed to Congressional staff on Nov. 19, 2002.
23 Albright and Brannan, “The North Korean Plutonium Stock Mid-2006,” p. 4.

North Korea “is constructing a plant that could produce enough weapons-grade uranium
for two or more nuclear weapons per year when fully operational — which could be as
soon as mid-decade.”24 Such a plant would need to produce more than 50kg of HEU per
year, requiring cascades of thousands of centrifuges. The paper noted that in 2001, North
Korea “began seeking centrifuge-related materials in large quantities.” Pakistani
President Musharraf revealed in his September 2006 memoir, In the Line of Fire, that
“Doctor A.Q. Khan transferred nearly two dozen P-1 and P-2 centrifuges to North Korea.
He also provided North Korea with a flow meter, some special oils for centrifuges, and
coaching on centrifuge technology, including visits to top-secret centrifuge plants.”25
However, the United States has not been able get direct confirmation from Khan.
Questions have been raised about whether U.S. estimates were accurate. In a hearing
before the Senate Armed Services Committee on February 27, 2007, Joseph DeTrani, the
mission manager for North Korea from the Office of the Director of National Intelligence,
was asked by Senator Reed whether he had “any further indication of whether that
program has progressed in the last six years, one; or two, the evidence — the credibility
of the evidence that we had initially, suggesting they had a program rather than
aspirations?” DeTrani responded that “the assessment was with high confidence that,
indeed, they were making acquisitions necessary for, if you will, a production-scale
program. And we still have confidence that the program is in existence — at the
mid-confidence level.”
How to Verify North Korean Claims?
Information about North Korea’s nuclear weapons production has depended on
remote monitoring and defector information, with mixed results. Satellite images
correctly indicated the start-up of the 5MWe reactor, but gave no details about its
operations. Satellites also detected trucks at Yongbyon in late January 2003, but could
not confirm the movement of spent fuel to the reprocessing plant;26 imagery reportedly
detected activity at the reprocessing plant in April 2003, but could not confirm large-scale
reprocessing;27 and, satellite imagery could not peer into an empty spent fuel pond, which
was shown to U.S. visitors in January 2004. Even U.S. scientists visiting Pyongyang in
January 2004 could not confirm North Korean claims of having reprocessed the spent fuel
or that the material shown was in fact plutonium. Verifying those claims would require
greater access to the material and North Korean cooperation. This is particularly true in
the case of uranium enrichment; U.S. intelligence officials have said they do not know
where the uranium program is and more recently, have shown less confidence about what
the scope of the program might be. Although seismographs registered the October 9th
detonation, and environmental sampling confirmed radioactivity, there is still no
information on what North Korea intended to accomplish with the test, from technical,
security, political, and diplomatic perspectives. More data is necessary to project what
this “new” capability might mean for North Korea, the region, and the United States.

24 CIA unclassified point paper.
25 Pervez Musharraf, In the Line of Fire: A Memoir, (New York: Free Press, September 2006),
p. 296.
26 “Reactor Restarted, North Korea Says,” Washington Post, Feb. 6, 2003.
27 “US Suspects North Korea Moved Ahead on Weapons,” New York Times, May 6, 2003.