The term ‘nuclear weapon’ refers to any weapon that utilizes energy released from nuclear reactions such as fission/fusion for destructive purposes. Nuclear weapons can be largely categorized according to the type of nuclear reaction involved: nuclear fission (atomic bombs) and nuclear fusion (hydrogen bombs). Advancement of technology has also given birth to the neutron bomb, which utilizes the massive neutron radiation released during nuclear fusion in order to set off a second reaction of nuclear fission.

Atomic Bombs

The nuclei of U235 (Uranium 235), Pu239 (Plutonium 239), and U233 are called ‘fissile’ materials, because they can be used to set off nuclear fission when bombarded by neutrons. When nuclear fission occurs, a large amount of energy and neutrons are released. Therefore, when a certain mass of fissile materials is concentrated at a single spot, a chain reaction of nuclear fission can be set off. The mass at which this is possible is known as the ‘critical mass.’ An atomic bomb is essentially a set of several compartments of sub-critical masses of fissile materials, which are then rapidly combined at the time of detonation. The combined materials then reach a super-critical mass, setting off a rapid chain reaction that releases massive amounts of energy within a short interval of time.

Hydrogen Bombs

The nuclei of U235 (Uranium 235), Pu239 (Plutonium 239), and U233 are called ‘fissile’ materials, because they can be used to set off nuclear fission when bombarded by neutrons. When nuclear fission occurs, a large amount of energy and neutrons are released. Therefore, when a certain mass of fissile materials is concentrated at a single spot, a chain reaction of nuclear fission can be set off. The mass at which this is possible is known as the ‘critical mass.’ An atomic bomb is essentially a set of several compartments of sub-critical masses of fissile materials, which are then rapidly combined at the time of detonation. The combined materials then reach a super-critical mass, setting off a rapid chain reaction that releases massive amounts of energy within a short interval of time.

Neutron Bomb

Neutron bombs utilize the massive amounts of neutron radiation that are released during nuclear fusion to fire a second round of nuclear fission. Thus, it is called the 3F (fission -> fusion -> fission) bomb. The residual radioactive materials generated during the two stages of fission, dubbed ‘ashes of death’, have earned this bomb the nickname ‘dirty hydrogen bomb’.

Nuclear materials are materials that may be used as nuclear fuel. Generally, uranium, plutonium, thorium, or a combination of these is used as nuclear fuel. In the context of nuclear weapons development, the term ‘nuclear materials’ refers to uranium and plutonium.

Uranium

In 1789, German scientist M.H. Klaproth discovered uranium as a part of the mineral uraninite (pitchblende) and named it after Uranus, the planet of the solar system discovered in 1781. A total of 14 artificial isotopes ranging from U227 to U240, all of them radioactive, are currently known. Three isotopes: U234, U235, and U238, all of which have long half-lives, occur in nature. However, more than 99% of these are U238. Uranium ore is mined in Canada, the Republic of South Africa, the United States, Russia, and Australia. A sustained chain of nuclear fission reactions releases massive amounts of energy. This process is known as nuclear power generation. Atomic bombs follow the same principle, but in a much more highly concentrated setting. It is U235 that is used in nuclear power generation, with one gram of uranium 235 yielding the same amount of energy as three tons of coal. However, as its natural concentration is barely 0.7%, uranium ore must first be enriched in order to have a high content of pure U235. 15kg of U235 is needed to fabricate one atomic bomb.

Plutonium

Plutonium is an artificial element first synthesized in 1940 by U.S. scientists G.T Seaborg, E.M. MacMillan, and J.W. Kennedy by bombarding uranium with deuterium. It was known to not occur naturally, but in 1942 a small amount of plutonium was found contained in uranium ore. Similar to the processes within a nuclear power reactor, it seems uranium contained within minerals absorbs neutrons to produce plutonium. Taking on a silvery-white appearance, plutonium is an important fuel material in nuclear fission, and therefore a key ingredient in atomic and hydrogen bombs. International inspection of the manufacturing of plutonium intensified dramatically after 1974, when India extracted and enriched plutonium generated from a civilian nuclear power reactor to create and successfully detonate an atomic bomb. Five to ten kg of highly-enriched plutonium can be used to fabricate one atomic bomb. There is controversy concerning the use of plutonium as an energy source, due to its potential application in nuclear weapons as well as the serious health hazards presented by the element. Highly carcinogenic, when introduced into the human body, plutonium is among the most toxic materials known to man. Heated debate over its use as an energy source continues to this day.

Using nuclear reactions to generate electric power and developing nuclear weapons follow the same scientific process, using the same materials. Therefore, nuclear power generation for peaceful purposes can always be used for wartime purposes. That is, nuclear fuels used for power generation can be collected and then be reprocessed to yield ingredients of nuclear weapons. (nuclear reprocessing) This is the very reason the international community is bent on monitoring the usage of nuclear materials. (NPT, IAEA)

Once ignited, conventional fuels such as oil or coal keep burning as long as oxygen is present. However, nuclear fuels can combust only inside special equipment: nuclear reactors. Also, while conventional fuels can only be used once, nuclear fuels can be used as fuel several times by being re-enriched. Therefore, used nuclear fuel can either be disposed of or re-enriched for repeated use. This is called reprocessing. Because nuclear fuels emit radiation, the disposal of nuclear fuels requires special equipment to contain the radiation. Also, special facilities are needed in order to reprocess nuclear fuels for further use. Such reprocessing facilities are strictly regulated and inspected by the international community. This is because reprocessing facilities are able to produce plutonium and HEU, which can be used as ingredients of nuclear weapons. Used peacefully, reprocessing facilities are productive. However, if used for warlike purposes, these facilities are capable of causing catastrophic destruction. This is why South Korea (Republic of Korea) has announced that it will not build or operate reprocessing facilities, following its stated commitment to being a non-nuclear weapons state.

The nuclear-fuel cycle refers to the process of burning nuclear fuels in a reactor and then recovering re-usable materials from spent fuel. The process involves refining and extracting nuclear fuels such as uranium and thorium from mineral ore, burning the fuel in nuclear reactors, and then finally reprocessing the spent fuel for further use. Natural uranium ore contains only 0.7% of the fissile material U235, which can be used for nuclear fission. The remainder of the ore usually consists of U238. When used in a reactor, U238 absorbs neutrons to produce Pu239, which is a fissile material. While Pu239 is an ingredient of the atomic bomb, it is also stored for future use in integral fast reactors. As not all of the U235 is burned up during the power generation process in reactors, used fuel can be reprocessed and manufactured to produce nuclear fuel. While completing the nuclear-fuel cycle has many economic advantages in that it secures a stable supply of fuel for nuclear power generation purposes, it also has the effect of accumulating the ingredients of nuclear weapons. Therefore, nations that complete the nuclear-fuel cycle are closely watched by the international community.

HEU is an artificial material synthesized by concentrating U235, which is used in nuclear fission. Natural uranium ore contains only about 0.7% of pure U235, so its level of concentration must first be increased before it can be used as a nuclear fuel. This process is known as enrichment, which involves gradually concentrating U235 several times over. Methods for producing HEU include gas diffusion, centrifuge processing, and laser processing. Details of such methods are highly classified, according to nuclear nonproliferation guidelines. A three to five percent concentration of U235 within the nuclear reactor is needed for a sustained chain of nuclear fission. Meanwhile, HEU usually refers to materials with a 20% or higher concentration of U235. Therefore, it is natural to regard a nation holding HEU as harboring intentions to develop nuclear weapons.

The Nuclear Club refers to the five nations that have been approved by the international community to possess nuclear weapons: the U.S., the U.K., France, Russia, and China. Naturally, the Nuclear Club is not a formal organization. Nations not belonging to the Club are prohibited by international law from developing or holding nuclear weapons. Nations such as India, Pakistan, and Israel are regarded as de facto nuclear weapon states, despite the lack of official announcements or approvals. Therefore, a total of eight nations are believed to possess nuclear weapons. The Republic of South Africa was formerly a nuclear weapons nation. Nations such as Kazakhstan, Uzbekistan, and Belarus, which gained independence as well as nuclear capabilities following the fall of the USSR, have ceded all nuclear weapons to Russia and are being closely monitored by the international community. The members of the Nuclear Club, in order to prevent non-nuclear weapons nations from gaining nuclear weapons capabilities, have organized the IAEA (International Atomic Energy Agency) to carry out on-site inspections on the use of nuclear materials by non-nuclear weapons states. Also, the Nuclear Club nations drew up the NPT (Nuclear Nonproliferation Treaty), which prohibits non-nuclear weapons nations from acquiring or developing nuclear weapons. Meanwhile, some nations that have not been officially approved to hold nuclear weapons are critical of the current unbalanced structure and are continually striving to acquire nuclear weapons capabilities. (Current Nuclear Weapons Nations of the World)

The official name of the NPT is the ‘Treaty for the Nonproliferation of Nuclear Weapons’. It prohibits the five ‘nuclear weapons nations’ from providing any form of support or transfers that may contribute to ‘non-nuclear weapons nations’ gaining nuclear weapons capabilities, while also prohibiting non-nuclear weapons nations from developing, assembling, testing, or acquiring nuclear weapons. The basic aim of the NPT is to limit the number of nations with nuclear weapons capabilities. In accordance with this goal, non-nuclear weapons nations are obliged to sign a safeguards agreement that stipulates duties such as receiving IAEA inspections on nuclear materials and their usage. Only the U.S. and the Soviet Union originally held nuclear weapons. However, France and China started testing nuclear weapons from 1960, which became a trend in other nations as well. This led to the sentiment that the trend could very well bring about the extinction of humanity. A draft of the NPT was drawn up after negotiations by the U.S. and the Soviet Union, and the NPT was opened for signing following negotiations with non-nuclear weapons nations at the U.N. General Assembly on the 12th of June, 1968. The NPT finally entered into force in \ March of 1970. Most of the world’s sovereign nations have ratified the treaty. However, nations, including France and China, who opposed the U.S.- and Soviet-led nature of the treaty from its inception, have not ratified it. Other nations such as India, Pakistan, Israel, and Cuba also have not ratified the NPT. South Korea officially ratified the treaty on the 23rd of April, 1975. While North Korea did sign the treaty in December of 1985, it withdrew in 1993 in protest of special nuclear inspections, only to suspend this withdrawal shortly thereafter. In January of 2003, North Korea again withdrew from the NPT as tensions over its nuclear weapons program intensified.

The IAEA is an international organization whose stated objective is to limit the use of nuclear energy to purposes serving the well being of humanity. It was first proposed by U.S. president Eisenhower at the eighth U.N. General Assembly held on the 8th of December, 1953.
A statute was signed in 1956 by 80 nations, and the IAEA was finally established on the 29th of July, 1957. The IAEA aims to limit the use of nuclear energy to purposes contributing to the peace, well being, and prosperity of mankind while prohibiting its use for any military purposes. In accordance with such goals, it pursues such activities as:

△promoting the peaceful use of nuclear energy,
△setting health security guidelines,
△providing underdeveloped nations with technological aid,
△exchanging scientific and technological information and personnel, and
△building and maintaining radioactivity-safe facilities.

As stipulated by NPT regulations, the IAEA signs safeguards agreements with member nations and then conducts inspections, monitoring, and maintenance in these nations. Although the IAEA promotes U.N. policies and also submits reports to the world body, it is not an official affiliate organization of the U.N. South Korea became an IAEA member nation in 1957, and North Korea in 1974. The IAEA’s headquarters are located in Vienna, Austria.

The term ‘nuclear inspection’ refers to inspections and related activity on the current status of nuclear materials and facilities, which are carried out by the IAEA in nations that have ratified the NPT. Inspections usually fall into three categories: temporary, regular, and special.

Temporary Inspection

Temporary inspections are held in order to verify the current status of the nuclear materials and facilities as reported by NPT member nations to the IAEA.

Regular Inspection

Regular inspections are held periodically in order to update and account for changes in the status of a nation’s nuclear materials and facilities, and are only carried out when a nation’s report has been verified through temporary inspections. The inspection includes the compiling of an inventory of nuclear materials and the testing of sealant and security devices. Regular inspections are carried out three to four times a year.

Special Inspection

Special inspections are ordered when temporary and regular inspections are deemed insufficient to dissolve suspicions of a nation’s possession of nuclear weapons. That is, if a nation declines to modify its report despite discrepancies discovered during temporary inspections or if sufficient evidence to suspect illicit usage has been gathered through regular inspections, a special inspection is carried out in order to ascertain the status of nuclear weapons development or possession. A representative case is the special inspection the IAEA requested of North Korea in 1992. This happened because, contrary to North Korea report that it had extracted only 90 grams of plutonium, inspections revealed sufficient evidence to suspect that several kilograms of the material had been extracted. In resistance to the move by the IAEA, North Korea withdrew from the NPT in 1993, sparking the 1st North Korean nuclear crisis.