ear Weapons: Latest Developments
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).

2
See CRS Report RL33590, North Koreas Nuclear Weapons Program, by Larry Niksch.
Congressional Research Service The Library of Congress
CRS Report for Congress
Received through the CRS Web
Order Code RS21391
Updated October 18, 2006
North Koreas Nuclear Weapons:
Latest Developments
Sharon Squassoni
Specialist in National Defense
Foreign Affairs, Defense, and Trade Division
Summary
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,
having continued its production throughout the fits and starts of the Six-Party Talks.
This report will be updated as needed.
Background
In the early1980s, 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 programs and eventually dismantle them in return for several kinds
of assistance.
2
At that time, Western intelligence agencies estimated that North Korea had CRS-2
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 holds 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.
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
of the reprocessing plant as extremely primitive. In the end, however, significant
growth in North Koreas arsenal depends on the completion of the two larger reactors and
progress in the reported uranium enrichment program. CRS-3
8
Hecker, Jan. 21, 2004, testimony before SFRC.
9
Text of statement available at http://www.dni.gov/announcements/20061016_release.pdf
10
CIA response to questions for the record, August 18, 2003, submitted by the Senate Select
C o m m i t t e e o n I n t e l l i g e n c e , f u l l t e x t a v a i l a b l e a t
http://www.fas.org/irp/congress/2003_hr/021103qfr-cia.pdf.
11
David Albright and Kevin ONeill, editors, Solving the North Korean Nuclear Puzzle, ISIS
Report, ISIS Press, 2000, p. 88.
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 Koreas 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 in the vicinity of Punggye, 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
reactors current performance or the reprocessing facilitys efficiency. North Korea told
the IAEA that during the 1990 hot test, it lost almost 30% of the plutonium in the waste
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 CRS-4
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,
2005.
14
N. Korea Building Bombs, Its Envoy Says, Los Angeles Times, June 9,