NUCLEAR WEAPONS TECHNOLOGY

SECTION V
NUCLEAR WEAPONS TECHNOLOGY

 

 

 

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SECTION 5—NUCLEAR WEAPONS TECHNOLOGY
Scope
5.1 Enrichment Feedstocks Production ........................................ II-5-10
5.2 Uranium Enrichment Processes .............................................. II-5-13
5.3 Nuclear Fission Reactors ........................................................ II-5-42
5.4 Plutonium Extraction (Reprocessing) .................................... II-5-48
5.5 Lithium Production ................................................................. II-5-54
5.6 Nuclear Weapons Design and Development .......................... II-5-58
5.7 Safing, Arming, Fuzing, and Firing ........................................ II-5-67
5.8 Radiological Weapons ............................................................ II-5-75
5.9 Manufacturing of Nuclear Components ................................. II-5-79
5.10 Nuclear Weapons Development Testing ................................. II-5-91
5.11 Nuclear Weapons Custody, Transport, and Control ............... II-5-109
5.12 Heavy Water Production ......................................................... II-5-112
5.13 Tritium Production ................................................................. II-5-117
BACKGROUND
General
This section examines the technologies needed to construct nuclear and radiological
weapons and to employ both kinds of weapons either for military purposes or
an act of terror. Since their introduction in 1945, nuclear explosives have been the
most feared of the weapons of mass destruction, in part because of their ability to
cause enormous instantaneous devastation and of the persistent effects of the radiation
they emit, unseen and undetectable by unaided human senses. The Manhattan Project
cost the United States $2 billion in 1945 spending power and required the combined
efforts of a continent-spanning industrial enterprise and a pool of scientists, many of
whom had already been awarded the Nobel Prize and many more who would go on to
become Nobel Laureates. This array of talent was needed in 1942 if there were to be
any hope of completing a weapon during the Second World War. Because nuclear
fission was discovered in Germany, which remained the home of many brilliant scientists,
the United States correctly perceived itself to be in a race to build an atomic
bomb.
For many decades the Manhattan Project provided the paradigm against which
any potential proliferator’s efforts would be measured. Fifty years after the Trinity
explosion, it has been recognized that the Manhattan Project is just one of a spectrum
of approaches to the acquisition of a nuclear capability. At the low end of the scale, a
nation may find a way to obtain a complete working nuclear bomb from a willing or
unwilling supplier; at the other end, it may elect to construct a complete nuclear infrastructure
including the mining of uranium, the enrichment of uranium metal in the
fissile isotope 235U, the production and extraction of plutonium, the production of tritium,
and the separation of deuterium and 6Li to build thermonuclear weapons. At an
intermediate level, the Republic of South Africa constructed six quite simple nuclear
devices for a total project cost of less than $1 billion (1980’s purchasing power) using
no more than 400 people and indigenous technology.
Highlights
• The design and production of nuclear weapons in 1997 is a far
simpler process than it was during the Manhattan Project.
• Indigenous development of nuclear weapons is possible for
countries with industrial bases no greater than that of Iraq in 1990.
Given a source of fissile material, even terrorist groups could
construct their own nuclear explosive devices.
• At least two types of nuclear weapons can be built and fielded
without any kind of yield test, and the possessors could have
reasonable confidence in the performance of those devices.
• The standing up of elite units to take custody of nuclear weapons or
to employ them would be a useful indicator that a proliferant is
approaching the completion of its first weapon.
• The acquisition of fissile material in sufficient quantity is the most
formidable obstacle to the production of nuclear weapons.

 

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Although talented people are essential to the success of any nuclear weapons program,
the fundamental physics, chemistry, and engineering involved are widely understood;
no basic research is required to construct a nuclear weapon. Therefore, a nuclear
weapons project begun in 1996 does not require the brilliant scientists who were needed
for the Manhattan Project.1
Acquisition of a militarily significant nuclear capability involves, however, more
than simply the purchase or construction of a single nuclear device or weapon. It
requires attention to issues of safety and handling of the weapons, reliability and predictability
of entire systems, efficient use of scarce and valuable special nuclear material
(SNM) (plutonium and enriched uranium), chains of custody and procedures for
authorizing the use of the weapons, and the careful training of the military personnel
who will deliver weapons to their targets.
In contrast, a nuclear device used for terrorism need not be constructed to survive
a complex stockpile-to-target sequence, need not have a predictable and reliable yield,
and need not be efficient in its use of nuclear material. Although major acts of terrorism
are often rehearsed and the terrorists trained for the operation, the level of training
probably is not remotely comparable to that necessary in a military establishment entrusted
with the nuclear mission.
Testing of Nuclear Weapons
The first nuclear weapon used in combat used an untested gun-assembled design,
but a very simple and inefficient one. The first implosion device was tested on July 16,
1945, near Alamogordo, New Mexico, and an identical “physics package” (the portion
of the weapon including fissile and fusion fuels plus high explosives) was swiftly
incorporated into the bomb dropped on Nagasaki.
Nuclear weaponry has advanced considerably since 1945, as can be seen at an
unclassified level by comparing the size and weight of “Fat Man” with the far smaller,
lighter, and more powerful weapons carried by modern ballistic missiles.
Most nations of the world, including those of proliferation interest, have subscribed
to the 1963 Limited Test Ban Treaty, which requires that nuclear explosions
only take place underground. Underground testing can be detected by seismic means
and by observing radioactive effluent in the atmosphere. It is probably easier to detect
and identify a small nuclear test in the atmosphere than it is to detect and identify a
similarly sized underground test. In either case, highly specialized instrumentation is
required if a nuclear test explosion is to yield useful data to the nation carrying out the
1 When the Manhattan Project began far less than a microgram of plutonium had been made
throughout the world, and plutonium chemistry could only be guessed at; the numbers of
neutrons released on average in 235U and 239Pu fissions were unknown; the fission cross
sections (probabilities that an interaction would occur) were equally unknown, as was the
neutron absorption cross section of carbon.
experiment. A Comprehensive Test Ban Treaty was opened for signature and signed at
the United Nations on 24 September 1996 by the five declared nuclear weapon states,
Israel, and several other states. By the end of February 1998, more than 140 states had
signed the accord. The Treaty bans all further tests which produce nuclear yield. In all
probability, most of the nations of greatest proliferation concern will be persuaded to
accede to the accord, although the present government of India has refused to sign.
Rate of Change of Nuclear Weapons Technology
American nuclear technology evolved rapidly between 1944 and 1950, moving
from the primitive Fat Man and Little Boy to more sophisticated, lighter, more powerful,
and more efficient designs. Much design effort shifted from fission to thermonuclear
weapons after President Truman decided that the United States should proceed
to develop a hydrogen bomb, a task which occupied the Los Alamos Laboratory from
1950 through 1952.2 From 1952 until the early years of the ICBM era [roughly to the
development of the first multiple independently targeted reentry vehicles (MIRVs) in
the late 1960’s], new concepts in both fission primary and fusion secondary design
were developed rapidly. However, after the introduction of the principal families of
weapons in the modern stockpile (approximately the mid 1970’s), the rate of design
innovations and truly new concepts slowed as nuclear weapon technology became a
mature science. It is believed that other nations’ experiences have been roughly similar,
although the United States probably has the greatest breadth of experience with
innovative designs simply because of the more than 1,100 nuclear detonations it has
conducted. The number of useful variations on the themes of primary and secondary
design is finite, and designers’ final choices are frequently constrained by considerations
of weapon size, weight, safety, and the availability of special materials.
U.S. nuclear weapons technology is mature and might not have shown many more
qualitative advances over the long haul, even absent a test ban. The same is roughly
true for Russia, the UK, and possibly for France.
The design of the nuclear device for a specific nuclear weapon is constrained by
several factors. The most important of these are the weight the delivery vehicle can
carry plus the size of the space available in which to carry the weapon (e.g., the diameter
and length of a nosecone or the length and width of a bomb bay). The required
yield of the device is established by the target vulnerability. The possible yield is set
by the state of nuclear weapon technology and by the availability of special materials.
Finally, the choices of specific design details of the device are determined by the taste
of its designers, who will be influenced by their experience and the traditions of their
organization.
2 The ÒMikeÓ test of Operation Ivy, 1 November, 1952, was the first explosion of a true
two-stage thermonuclear device. The ÒGeorgeÓ shot of Operation Greenhouse (May 9,
1951) confirmed for the first time that a fission device could produce the conditions
needed to ignite a thermonuclear reaction.

 

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A Caution on the Use of “Authoritative Control Documents and Tables”
Authoritative lists of export-controlled and militarily critical equipment and materials
used in the construction and testing of nuclear weapons necessarily have flaws:
• They consistently lag the technology actually available on the world market.
Some items at the threshold of the Nuclear Suppliers Group (NSG) Dual-Use
List restrictions may not be available as newly manufactured equipment. on
the other hand, it would be improper to place the thresholds higher, since
equipment much less sophisticated than can be bought today was used with
great success in both the United States and the Former Soviet Union.
• Second, these limits do not always define the limits at which the technologies
have utility to proliferators.
OVERVIEW
This section will discuss the fundamentals of nuclear weapons design, engineering,
and production including the production of special nuclear materials (uranium
enriched to greater than 20 percent in the isotope 235U, 233U, and for plutonium). It will
also look at the other technologies including production of uranium and plutonium
metal; manufacturing; nuclear testing; lithium production; safing, arming, fuzing, and
firing (SAFF); radiological weapons; the custody, transport, and control of nuclear
weapons; heavy water production; and tritium production.
It is possible to capture schematically the progress in nuclear weapons technology
and the technologies which support nuclear weapons in the following graph (Figure
5.0-1). The X axis is time, beginning in 1942 when the Manhattan Project was fully
activated. The top two lines show the development of electronics and the introduction
of devices which affected the design of the non-nuclear components of the weapons.
The second pair of lines shows the progress made in preparing special nuclear materials,
with the processes above the dashed line referring to methods of enriching uranium
and those below the dashed line referring to plutonium production and the materials
for fusion weapons.
The oddly shaped heavy curve shows the rate at which U.S. nuclear weapons
scientists made new discoveries and progress. The distance between the two curves
represents the rate of progress, while the area between the curves from 1942 to any
arbitrary date gives an estimate of the total knowledge acquired. The rate of progress
drops almost to zero on 30 October 1958, when the Eisenhower-Khrushchev Moratorium
on nuclear testing went into effect.
Superimposed on the heavy curve are events of historic importance: the first
testing and use of nuclear weapons, the first Soviet test along with the dates when
other nations joined the nuclear club, the evolution of hydrogen weapons and boosting,
the introduction of powerful computers, computerized numerically controlled
(CNC) tools, the year when the IBM PC made its appearance on desktops, tailored
effects weapons such as the x-ray laser, and the end of nuclear testing. Specific U.S.
achievements are also noted in the area bounded by the heavy curves. A similar chart
could be made for the progress of every other nuclear weapon state, acknowledged or
unacknowledged, if the information were available.
This chart illustrates several trends which are important to an understanding of the
process by which a proliferator might gain a nuclear capability. At the same time, it
indicates the few choke points where the control of technologies might be helpful. The
top line shows advances over time in electronic components. The second and third
lines show advances over time in the production of SNM. All five acknowledged
nuclear weapons states (NWSs) are shown to have tested their first devices before
computer numerically controlled machine tools and four- or five-axis machine tools
were generally available.
Modern computers incorporating large amounts of solid-state fast memory did
not make their appearance until the early 1970’s, and even fast transistorized (not
integrated circuit chips) computers were not generally available until the early 1960’s.
By the time such computers became available to the American design laboratories,
most of the fundamental families of modern nuclear weapons had already been conceived,
designed, and tested. Computation brought a new ability to design for nuclear
weapon safety and a new capability to execute complex designs which might reduce
the amount of fissile materials and other scarce fuels used in the weapons.
Finally, an inspection of the chart indicates very rapid qualitative progress in the
early years of the U.S. nuclear effort, with new design types and wholly new weapon
families emerging in rapid succession. In part, this occurred because the creative scientists
were given permission to try almost any idea which sounded good, and in part
it is because of the rapid interplay between conceptual advances and all-up nuclear
tests. During the 1958–61 moratorium on testing the rate at which new ideas were
introduced slowed, although a great deal of progress towards ensuring weapon safety
was made. By the early 1970’s the era of new concepts in nuclear weapon design had
virtually come to an end, although qualitative improvements in yield, weight, and the
efficient use of special materials were made.
Similar statements, differing in detail but not in outline, could probably be made
for each of the five NWSs and any threshold states with active weapons projects.
However, it is unlikely that the evolution of nuclear designs, means of assembly, and
initiation followed the same course in any two countries.
More detailed descriptions of the various components of a nuclear weapons program
will be found in the numbered sections below.
Production of Fuel for Nuclear Weapons
Ordinary uranium contains only 0.72 percent 235U, the highly fissionable isotope,
the rest of the material being largely the much less fissionable isotope 238U (which
cannot sustain a chain reaction). The fissile material must be separated from the rest of
the uranium by a process known as enrichment. Several enrichment techniques have

 

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been used. The earliest successful methods were electromagnetic isotope separation
(EMIS), in which large magnets are used to separate ions of the two isotopes,3 and
gaseous diffusion, in which the gas uranium hexafluoride (UF6) is passed through a
porous barrier material; the lighter molecules containing 235U penetrate the barrier
slightly more rapidly, and with enough stages significant separation can be accomplished.
Both gaseous diffusion and EMIS require enormous amounts of electricity.
More efficient methods have been developed.
The third method in widespread use is the gas centrifuge [Urenco (Netherlands,
Germany, UK), Russia, Japan] in which UF6 gas is whirled inside complex rotor assemblies
and centrifugal force pushes molecules containing the heavier isotope to the
outside. Again, many stages are needed to produce the highly enriched uranium needed
for a weapon, but centrifuge enrichment requires much less electricity than either of
the older technologies.
Atomic and molecular laser isotope separation (LIS) techniques use lasers to selectively
excite atoms or molecules containing one isotope of uranium so that they can
be preferentially extracted. Although LIS appears promising, the technology has proven
to be extremely difficult to master and may be beyond the reach of even technically
advanced states.
The South African nuclear program used an aerodynamic separation technique in
an indigenously designed and built device called a vortex tube. In the vortex a mixture
of UF6 gas and hydrogen is injected tangentially into a tube, which tapers to a small
exit aperture at one or both ends; centrifugal force provides the separation. The Becker
Nozzle Process, also an aerodynamic separation technique, was developed in Germany.
The Becker process is not in common use; the vortex tube was used in South
Africa for producing reactor fuel with a 235U content of around 3–5 percent in addition
to making 80–93 percent 235U for the weapons program. Aerodynamic enrichment
processes require large amounts of electricity and are not generally considered economically
competitive; even the South African enrichment plant has apparently been
closed.
Uranium enriched to 20 percent or more 235U is called highly enriched (HEU).
Uranium enriched above the natural 235U abundance but to less than 20 percent is called
low-enriched (LEU).
Plutonium is produced in nuclear reactors by bombarding “fertile” 238U with
neutrons from the chain reaction. Since each fission produces only slightly more than
two neutrons, on average, the neutron “economy” must be managed carefully, which
requires good instrumentation and an understanding of reactor physics, to have enough
neutrons to irradiate useful quantities of 238U.4 A typical production reactor produces
about 0.8 atoms of plutonium for each nucleus of 235U which fissions. A good rule of
thumb is that 1 gram of plutonium is produced for each megawatt (thermal)-day of
reactor operation. Light-water power reactors make fewer plutonium nuclei per uranium
fission than graphite-moderated production reactors.
The plutonium must be extracted chemically in a reprocessing plant. Reprocessing
is a complicated process involving the handling of highly radioactive materials and
must be done by robots or by humans using remote manipulating equipment. At some
stages of the process simple glove boxes with lead glass windows suffice. Reprocessing
is intrinsically dangerous because of the use of hot acids in which plutonium and
intensely radioactive short-lived fission products are dissolved. Some observers have,
however, suggested that the safety measures could be relaxed to the extent that the
proliferator deems his technicians to be “expendable.” Disposal of the high-level waste
from reprocessing is difficult. Any reprocessing facility requires large quantities of
concrete for shielding and will vent radioactive gases (131I, for example) to the atmosphere.
Tritium for thermonuclear weapons is usually produced in a nuclear reactor similar
or identical to that used to make plutonium. Neutrons from the reactor are used to
irradiate lithium metal, and the nuclear reaction produces a triton.
Lithium-6, an isotope of lithium, is used in some thermonuclear weapons. When
struck by a neutron, 6Li (actually the compound 7Li nucleus formed in the collision)
frequently disintegrates into tritium and 4He. Thus, the tritium needed for the secondary
of a fusion weapon can be formed in place within the nuclear device and need not
be transported from the factory to the target as heavy hydrogen.
The lighter isotope, 6Li, is separated from the principal isotope, 7Li, in a process
which exploits the fact that the lighter isotope more readily forms an amalgam with
mercury than does the heavier one. This process is called “COLEX” (Column Exchange).
Lithium hydroxide is dissolved in water, and the aqueous solution is brought
into contact with the mercury. Lithium-6 ions in the solution tend to migrate into the
mercury, while 7Li in the amalgam tends to migrate back into the aqueous hydroxide
solution. The reaction is generally carried out in large columnar processors. While
other processes for separating the lithium isotopes have been tried, the United States
found COLEX to be the most successful. It is believed that the Soviet Union chose the
same process.
3 The first large-scale uranium enrichment facility, the Y-12 plant at Oak Ridge, Tennessee,
used EMIS in devices called Òcalutrons.Ó The process was abandoned in the United States
because of its high consumption of electricity, but was adopted by the Iraqis because of its
relative simplicity and their ability to procure the magnet material without encountering
technology transfer obstacles.
4 Note, however, that during the Manhattan Project the United States was able to scale an
operating 250 watt reactor to a 250 megawatt production reactor. Although the
instrumentation of the day was far less sophisticated than that in use today, the scientists
working the problem were exceptional.

 

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Figure 5.0-1. Nuclear History

 

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RATIONALE
An ordinary “atomic” bomb of the kinds used in World War II uses the process of
nuclear fission to release the binding energy in certain nuclei. The energy release is
rapid and, because of the large amounts of energy locked in nuclei, violent. The principal
materials used for fission weapons are 235U and 239Pu, which are termed fissile
because they can be split into two roughly equal-mass fragments when struck by a
neutron of even low energies. When a large enough mass of either material is assembled,
a self-sustaining chain reaction results after the first fission is produced. Such a
mass is termed critical. If any more material is added to a critical mass a condition of
supercriticality results. The chain reaction in a supercritical mass increases rapidly in
intensity until the heat generated by the nuclear reactions causes the mass to expand so
greatly that the assembly is no longer critical.
Fission weapons require a system to assemble a supercritical mass from a subcritical
mass in a very short time. Two classic assembly systems have been used, gun
and implosion. In the simpler gun-type device, two subcritical masses are brought
together by using a mechanism similar to an artillery gun to shoot one mass (the projectile)
at the other mass (the target). The Hiroshima weapon was gun-assembled and
used 235U as a fuel. Gun-assembled weapons using highly enriched uranium are considered
the easiest of all nuclear devices to construct and the most foolproof. Manhattan
Project scientists were so confident in the performance of the “Little Boy” uranium
bomb that the device was not even tested before it was dropped on Hiroshima.
Because of the short time interval between spontaneous neutron emissions (and,
therefore, the large number of background neutrons) found in plutonium because of
the decay by spontaneous fission of the isotope 240Pu, Manhattan Project scientists
devised the implosion method of assembly in which high explosives are arranged to
form an imploding shock wave which compresses the fissile material to supercriticality.5
Implosion systems can be built using either 239Pu or 235U, but the gun assembly only
works for uranium. Implosion weapons are more difficult to build than gun weapons,
but they are also more efficient, requiring less SNM and producing larger yields.
The six bombs built by the Republic of South Africa were gun-assembled and
used uranium enriched to between 80 percent and 93 percent in the isotope 235U; Iraq
attempted to build an implosion bomb, also using 235U. In contrast, North Korea chose
to use 239Pu produced in a nuclear reactor.
A more powerful but more complex weapon uses the fusion of heavy isotopes of
hydrogen, deuterium, and tritium to release large numbers of neutrons when the fusile
(sometimes termed “fusionable”) material is compressed by the energy released by a
fission device called a primary. The fusion part of the weapon is called a secondary.
In the words of Sidney D. Drell, the physics packages of “nuclear weapons are
sophisticated, but not complicated.” The remainder of the weapon may be quite complicated
indeed.
Storage and Use Control Issues Regarding Nuclear Weapons
The United States has developed a complex and sophisticated system to ensure
that nuclear weapons are used only on the orders of the President or his delegated
representative. Some elements of the custodial system are the “two-man rule,” which
requires that no person be left alone with a weapon; permissive action links (PALs),
coded locks which prevent detonation of the weapon unless the correct combination is
entered; and careful psychological testing of personnel charged with the custody or
eventual use of nuclear weapons. In addition, U.S. nuclear weapons must be certified
as “one point safe,” which means that there is less than a one-in-a-million chance of a
nuclear yield greater than the equivalent of four pounds of TNT resulting from an
accident in which the high explosive in the device is detonated at the point most likely
to cause a nuclear yield.
It is believed to be unlikely that a new proliferator would insist upon one point
safety as an inherent part of pit design; the United States did not until the late 1950’s,
relying instead upon other means to prevent detonation (e.g., a component of Little
Boy was not inserted until after the Enola Gay had departed Tinian for Hiroshima). It
is also unlikely that a new actor in the nuclear world would insist upon fitting PALs to
every (or to any) nuclear weapon; the United States did not equip its submarine-launched
strategic ballistic missiles with PALs until, at the earliest, 1996, and the very first U.S.
PALs were not introduced until the mid-1950’s, when American weapons were stationed
at foreign bases where the possibility of theft or misuse was thought to be real.
Nonetheless, any possessor of nuclear weapons will take care that they are not
used by unauthorized personnel and can be employed on the orders of duly constituted
authority. Even—or, perhaps, especially—a dictator such as Saddam Hussein will
insist upon a fairly sophisticated nuclear chain of command, if only to ensure that his
weapons cannot be used by a revolutionary movement. It is also quite likely that even
the newest proliferator would handle his weapons with care and seek to build some
kind of safety devices and a reliable SAFF system into the units.
Developing Technologies
On the basis of experience, one might expect to observe significant nuclear planning
activity and the evolution of situation-specific nuclear doctrine on the part of a
new proliferator who would have to allocate carefully the “family jewels.” The development
of a nuclear strategy might be visible in the professional military literature of
the proliferator.
5 The critical mass of compressed fissile material decreases as the inverse square of the density
achieved.

 

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Use Control and Weapons Delivery
Because of the high cost and high value of a new entrant’s first few nuclear weapons,
it is likely that the proliferant state would take great care to ensure that the crews
selected to deliver the special ordnance would be highly proficient in the use of their
weapon systems. This requires extensive training in the specialized procedures required
to place nuclear weapons reliably on target.
Nuclear weapons training may be both distinctive and visible, particularly when it
involves those parts of the stockpile-to-target sequence which are explicitly nuclear.
Some observers believe, however, that such training will be difficult to observe and
identify.
Expected Rates of Progress for New Proliferants
New proliferants with First-World technological bases can probably construct their
first nuclear weapons 3 to 5 years after making a political decision to do so, even
including constructing an infrastructure to make special nuclear materials, assuming
that finances and resources are available.6 The first intellectual steps towards reducing
the size and mass of fission weapons should not take more than another 1 to 2 years to
master. Boosting and multistage weapons may require anywhere from 3 to 10 more
years to develop in the absence of yield testing, and some nations may still fail to
succeed. China, however, progressed from a very simple fission design to a two-stage
weapon by its fifth full-scale test—but one of the intervening tests was an end-to-end
firing of a ballistic missile with a live nuclear warhead in its nosecone.
Radiological Weapons
Radioactive isotopes suitable for use as weapons include 137Cs, 60Co, 131I, and other
short-lived, relatively easy-to-produce fission products. The most readily available
source for the materials of radiological weapons is spent fuel from nuclear reactors;
indeed, the spent fuel rods themselves are sufficiently “hot” that they can be used
essentially directly, although chopping or pulverization would be useful. Medical isotopes
are another readily available source of radioactive material in quantities suitable
for spreading terror.
Proliferation Implication Assessment
Many of the items on which the greatest control efforts have focused, at least in
the public’s perception—computers, switch tubes, capacitors—are either not controllable
or, at a controllable level, are far more capable than what is required to design
and build a weapon.
FOREIGN TECHNOLOGY ASSESSMENT (See Figure 5.0-2)
Five nations, the United States, Russia, the United Kingdom, France, and China
are nuclear weapon states according to the definition in the Non-Proliferation Treaty
(countries that tested a nuclear explosive device before 1 January 1967). All five
possess all technologies needed to build modern compact nuclear weapons and all
have produced both high-enriched uranium and weapons-grade plutonium.
India detonated a nuclear device using plutonium implosion in 1974. India has
held no announced tests since then, although they have on occasion taken steps which
would imply that a test is imminent. India does not enrich uranium. It has heavy-water
moderated reactors, not all under international safeguards.
Pakistan has an operating uranium enrichment plant. Senior Pakistani officials
have alluded to possession of a small nuclear stockpile.
South Africa constructed six simple gun-assembled uranium bombs but dismantled
them and signed the Non-Proliferation Treaty as a non-weapons state. The HEU for
these bombs was obtained from an aerodynamic isotope separation technique developed
indigenously. South Africa has shut down its aerodynamic enrichment facilities,
but is developing a molecular LIS (MLIS) process for producing LEU for commercial
nuclear power reactors.
Israel is believed by some to possess nuclear weapons. It operates one
unsafeguarded nuclear reactor at Dimona and presumably is capable of reprocessing
spent fuel to extract plutonium. It is a technically advanced state and probably has all
of the electronics needed to build and test nuclear weapons. Its elite air force may be
nuclear trained.
Iraq had a flourishing nuclear weapons and civilian nuclear program until the
1991 Gulf War. It was able to enrich uranium using EMIS and was pursuing centrifuge
enrichment as well. It anticipated constructing implosion weapons using HEU as the
fuel.
Iran has many components of a nuclear weapons program in place and has been
attempting to purchase turnkey nuclear reactors on the world market.
North Korea built and operated CO2-cooled, graphite-moderated reactors and
had built and operated a reprocessing facility before agreeing to allow the United States
and South Korea to replace its gas-graphite “power” reactor with a light-water moderated
unit less suited to the production of weapons-grade plutonium. The amount of
plutonium it currently has in hand outside of that contained in its spent fuel storage
facility is not well known by outsiders.
Sweden came very close to building nuclear weapons in the late 1960’s and early
1970’s. Many experts judge its weapon designs as sophisticated and efficient; the
6 Nations such as Germany and Japan, which have advanced civilian nuclear power programs
and stocks of plutonium (either separated or still contained in spent fuel) may be able to
produce their first weapons in even less time. Countries which have a nuclear infrastructure
and which have expended considerable effort in learning how to build nuclear weapons
while still not crossing the nuclear threshold (e.g., Sweden) also are in a favorable position
to go nuclear in short order.

 

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country has the industrial base to “go nuclear” in a short period and has adequate
amounts of plutonium contained in stored spent reactor fuel.
Switzerland had a nuclear weapons program until the early 1970’s. Both Sweden
and Switzerland are highly industrialized Western nations with broad access to a full
spectrum of modern technology, whether developed indigenously or imported. Both
operate nuclear reactors.
Germany has developed an indigenous uranium enrichment process (not believed
to be currently in use) and has adequate stocks of spent fuel from which to prepare
nuclear weapons.
Japan is as far advanced as Germany and also operates a reprocessing plant. Either
nation could construct nuclear weapons in a short time.
Many other states have capabilities in some or all of the relevant technologies and
could assemble a nuclear weapons program in a short time.