Nuclear weapon
A nuclear device no larger than a conventional bomb can devastate an entire city by blast, fire, and radiation. Since they are weapons of mass destruction, the proliferation of nuclear weapons is a focus of international relations policy. Nuclear weapons have been deployed twice in war, by the United States against the Japanese cities Hiroshima and Nagasaki in 1945 during World War IIA nuclear weapon (also called an atom bomb, nuke, atomic bomb, nuclear warhead, A-bomb, or nuclear bomb) is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or from a combination of fission and fusion reactions (thermonuclear bomb). Both bomb types release large quantities of energy from relatively small amounts of matter.
The first test of a fission ("atomic") bomb released an amount of energy approximately equal to 20,000 tons of TNT (84 TJ).The first thermonuclear ("hydrogen") bomb test released energy approximately equal to 10 million tons of TNT (42 PJ). Nuclear bombs have had yields between 10 tons TNT (the W54) and 50 megatons for the Tsar Bomba (see TNT equivalent). A thermonuclear weapon weighing little more than 2,400 pounds (1,100 kg) can release energy equal to more than 1.2 million tons of TNT (5.0 PJ).
The first nuclear weapons were bombs delivered by aircraft. Later, warheads were developed for strategic ballistic missiles, which have become by far the most important nuclear weapons. Smaller tactical nuclear weapons have also been developed, including ones for artillery projectiles, land mines, antisubmarine depth charges, torpedoes, and shorter-range ballistic and cruise missiles.
By far the greatest force driving the development of nuclear weapons after World War II (though not by any means the only force) was the Cold War confrontation that pitted the United States and its allies against the Soviet Union and its satellite states. During this period, which lasted roughly from 1945 to 1991, the American stockpile of nuclear weapons reached its peak in 1966, with more than 32,000 warheads of 30 different types. During the 1990s, following the dissolution of the Soviet Union and the end of the Cold War, many types of tactical and strategic weapons were retired and dismantled to comply with arms control negotiations, such as the Strategic Arms Reduction Talks, or as unilateral initiatives. By 2010 the United States had approximately 9,400 warheads of nine types, including two types of bombs, three types for intercontinental ballistic missiles (ICBMs), two types for submarine-launched ballistic missiles (SLBMs), and two types for cruise missiles. Some types existed in several modifications. Of these 9,400 warheads, an estimated 2,468 were operational (that is, mated to a delivery system such as a missile); the rest were either spares held in reserve or retired warheads scheduled to be dismantled. Of the 2,468 operational warheads, approximately 1,968 were deployed on strategic (long-range) delivery systems, and some 500 were deployed on nonstrategic (short-range) systems. Of the 500 nonstrategic warheads in the U.S. arsenal, about 200 were deployed in Europe.
The Soviet nuclear stockpile reached its peak of about 33,000 operational warheads in 1988, with an additional 10,000 previously deployed warheads that had been retired but had not been taken apart. After the disintegration of the Soviet Union, Russia accelerated its warhead dismantlement program, but the status of many of the 12,000 warheads estimated to remain in its stockpile in 2010 was unclear. Given limited Russian resources and lack of legitimate military missions, only about 4,600 of these 12,000 warheads were serviceable and maintained enough to be deployed. Of the 4,600 operational warheads, some 2,600 were deployed on strategic systems and some 2,000 on nonstrategic systems. A global security concern is the safety of Russia’s intact warheads and the security of nuclear materials removed from dismantled warheads.
Treaty on the Prohibition of Nuclear Weapons
| Treaty on the Prohibition of Nuclear Weapons | |
|---|---|
 Parties Signatories | |
| Type | Arms control, nuclear disarmament |
| Signed | 20 September 2017 |
| Location | New York, U.S. |
| Sealed | 7 July 2017 |
| Effective | 22 January 2021 |
| Condition | 90 days after the fiftieth instrument of ratification, acceptance, approval or accession has been deposited |
| Signatories | 86 |
| Parties | 55 (complete list) |
| Depositary | United Nations Secretary-General |
| Languages | Arabic, Chinese, English, French, Russian and Spanish |
| Treaty on the Prohibition of Nuclear Weapons at | |
The Treaty on the Prohibition of Nuclear Weapons (TPNW), or the Nuclear Weapon Ban Treaty, is the first legally binding international agreement to comprehensively prohibit nuclear weapons with the ultimate goal being their total elimination. It was adopted on 7 July 2017, opened for signature on 20 September 2017, and entered into force on 22 January 2021.
A mandate adopted by the United Nations General Assembly on 23 December 2016 scheduled two sessions for negotiations: 27 to 31 March and from 15 June to 7 July, 2017.The treaty passed on schedule on 7 July with 122 in favour, 1 against (Netherlands), and 1 official abstention (Singapore). 69 nations did not vote, among them all of the nuclear weapon states and all NATO members except the Netherlands.
Principles of atomic (fission) weapons
The fission process
When bombarded by neutrons, certain isotopes of uranium and plutonium (and some other heavier elements) will split into atoms of lighter elements, a process known as nuclear fission. In addition to this formation of lighter atoms, on average between 2.5 and 3 free neutrons are emitted in the fission process, along with considerable energy. As a rule of thumb, the complete fission of 1 kg (2.2 pounds) of uranium or plutonium produces about 17.5 kilotons of TNT-equivalent explosive energy.
Nuclear Weapons
At the dawn of the nuclear age, the United States hoped to maintain a monopoly on its new weapon, but the secrets and the technology for building the atomic bomb soon spread. The United States conducted its first nuclear test explosion in July 1945 and dropped two atomic bombs on the cities of Hiroshima and Nagasaki, Japan, in August 1945. Just four years later, the Soviet Union conducted its first nuclear test explosion. The United Kingdom (1952), France (1960), and China (1964) followed. Seeking to prevent the nuclear weapon ranks from expanding further, the United States and other like-minded countries negotiated the nuclear Nonproliferation Treaty (NPT) in 1968 and the Comprehensive Nuclear Test Ban Treaty (CTBT) in 1996.
India, Israel, and Pakistan never signed the NPT and possess nuclear arsenals. Iraq initiated a secret nuclear program under Saddam Hussein before the 1991 Persian Gulf War. North Korea announced its withdrawal from the NPT in January 2003 and has successfully tested advanced nuclear devices since that time. Iran and Libya have pursued secret nuclear activities in violation of the treaty’s terms, and Syria is suspected of having done the same. Still, nuclear nonproliferation successes outnumber failures, and dire decades-old forecasts that the world would soon be home to dozens of nuclear-armed have not come to pass.
At the time the NPT was concluded, the nuclear stockpiles of both the United States and the Soviet Union/Russia numbered in the tens of thousands. Beginning in the 1970s, U.S. and Soviet/Russian leaders negotiated a series of bilateral arms control agreements and initiatives that limited, and later helped to reduce, the size of their nuclear arsenals.
Today, the United States and Russia each deploy roughly 1,350 strategic warheads on several hundred bombers and missiles, and are modernizing their nuclear delivery systems. These warheads are counted using the provisions of the New START agreement, which caps each country at 1,550 strategic deployed warheads and attributes one deployed warhead per deployed heavy bomber, no matter how many warheads each bomber carries. Warheads on deployed ICBMs and SLBMs are counted by the number of re-entry vehicles on the missile. Each re-entry vehicle can carry one warhead.
Both Russia and China also possess smaller numbers of non-strategic (a.k.a. tactical) nuclear warheads, which are not subject to any treaty limits.
China, India, and Pakistan are all pursuing new ballistic missile, cruise missile, and sea-based nuclear delivery systems. In addition, Pakistan has lowered the threshold for nuclear weapons use by developing tactical nuclear weapons capabilities to counter perceived Indian conventional military threats. North Korea continues its nuclear pursuits in violation of its earlier denuclearization pledges.
Nuclear-Weapon States:
The nuclear-weapon states (NWS) are the five states—China, France, Russia, United Kingdom, and the United States—officially recognized as possessing nuclear weapons by the NPT. The treaty recognizes these states’ nuclear arsenals, but under Article VI of the NPT they are not supposed to build and maintain such weapons in perpetuity. In 2000, the NWS committed themselves to an “unequivocal undertaking…to accomplish the total elimination of their nuclear arsenals.” Because of the secretive nature with which most governments treat information about their nuclear arsenals, most of the figures below are best estimates of each nuclear-weapon state’s nuclear holdings, including both strategic warheads and shorter-range and lower-yield nuclear bombs, generally referred to as tactical nuclear weapons.
China
- About 320 total warheads.
France:
- About 290 total warheads.
Russia:
- March 2020 New START declaration: 1,326 strategic warheads deployed on 485 intercontinental ballistic missiles, submarine-launched ballistic missiles, and strategic bombers
- The Federation of American Scientists (FAS) estimates approximately 4,315 nuclear warheads, including 1,570 deployed offensive strategic warheads (with 870 in storage), 1,875 non-strategic warheads, and 2,060 additional retired warheads awaiting dismantlement, as of January 2020.
United Kingdom:
- About 215 strategic warheads, of which an estimated 120 are deployed and 95 are in storage. The United Kingdom possesses a total of four Vanguard class Trident nuclear-powered ballistic missile submarines, which together form its exclusively sea-based nuclear deterrent.
United States:
- March 2020 New START declaration: 1,373 strategic nuclear warheads deployed on 655 intercontinental ballistic missiles, submarine-launched ballistic missiles, and strategic bombers.
- The United States also has an estimated 150 B-61 nuclear gravity bombs that are forward-deployed at six NATO bases in five European countries: Aviano and Ghedi in Italy; Büchel in Germany; Incirlik in Turkey; Kleine Brogel in Belgium; and Volkel in the Netherlands. The total estimated U.S. B-61 stockpile amounts to 230.
- FAS estimates approximately 3,800 stockpiled warheads and 2,000 retired warheads awaiting dismantlement, for a total of 5,800 warheads as of early 2020.
Non-NPT Nuclear Weapons Possessors:
- India, Israel, and Pakistan never joined the NPT and are known to possess nuclear weapons.
- India first tested a nuclear explosive device in 1974. That test spurred Pakistan to ramp up work on its secret nuclear weapons program.
- India and Pakistan both publicly demonstrated their nuclear weapon capabilities with a round of tit-for-tat nuclear tests in May 1998.
- Israel has not publicly conducted a nuclear test, does not admit or deny having nuclear weapons, and states that it will not be the first to introduce nuclear weapons in the Middle East. Nevertheless, Israel is universally believed to possess nuclear arms, although it is unclear exactly how many.
The following arsenal estimates are based on the amount of fissile material—highly enriched uranium and plutonium—that each of the states is estimated to have produced. Fissile material is the key element for making nuclear weapons. India and Israel are believed to use plutonium in their weapons, while Pakistan is thought to use highly enriched uranium.
India: Approximately 150 nuclear warheads.
Israel: An estimated 90 nuclear warheads, with fissile material for up to 200.
Pakistan: Approximately 160 nuclear warheads.
States that Declared Their Withdrawal from the NPT:
North Korea joined the NPT as a non-nuclear weapon state but announced its withdrawal from the NPT in 2003 --a move that has not been legally recognized by the other NPT member states. North Korea has tested nuclear devices and nuclear-capable ballistic missiles. Uncertainty persists about how many nuclear devices North Korea has assembled.
North Korea:
- Estimated as of January 2020 to have approximately 30-40 warheads.
- While there is a high degree of uncertainty surrounding North Korea's fissile material stockpile and production, particularly on the uranium enrichment side, North Korea is estimated to have 20-40 kilograms of plutonium and 250-500 kilograms of highly enriched uranium. The estimated annual production of fissile material is enough for 6-7 weapons.
- North Korea operates its 5-megawatt heavy-water graphite-moderated reactor to extract plutonium for its nuclear warheads and has done so on an intermittent basis since August 2013. There has also been intermittent activity at North Korea's reprocessing facility since 2016, indicating that Pyongyang has likely separated plutonium from the reactor's spent fuel.
- North Korea unveiled a centrifuge facility in 2010. It is likely that Pyongyang is using that facility to produce highly-enriched uranium for weapons. U.S. intelligence suggests that there are several additional centrifuge facilities in North Korea.
States of Immediate Proliferation Concern:
Prior to the implementation of the Joint Comprehensive Plan of Action, Iran pursued a uranium enrichment program and other projects that provided it with the capability to produce bomb-grade fissile material and develop nuclear weapons, if it chose to do so. Iran’s uranium enrichment program continues, but it is restricted by the nuclear deal. Iran has taken steps to breach those limits in response to the U.S. withdrawal from the JCPOA and reimposition of sanctions but maintains that it does not intend to pursue nuclear weapons. Iran’s nuclear program remains subjected to safeguards by the IAEA, including continuous surveillance at certain facilities, put in place by the JCPOA.
In 2007, Israel bombed a site in Syria that was widely assessed to be a nuclear reactor being constructed with North Korea's assistance. Syria has refused to cooperate with the International Atomic Energy Agency's attempts to investigate.
Iran:
- No known weapons or sufficient fissile material stockpiles to build weapons.
- The International Atomic Energy Agency (IAEA), the institution charged with verifying that states are not illicitly building nuclear weapons, concluded in 2003 that Iran had undertaken covert nuclear activities to establish the capacity to indigenously produce fissile material.
- July 2015: Iran and six world powers negotiated a long-term agreement to verify and significantly reduce Iran's capacity to produce material for nuclear weapons.
- As part of this agreement, the IAEA and Iran concluded an investigation into Iran’s past nuclear weapons-related activities. The agency concluded that Iran had an organized program to pursue nuclear weapons prior to 2003. Some of these activities continued through 2009, but there were no indications of weaponization activities taking place after that date.
- In 2020, the IAEA launched a new investigation into Iran’s possible undeclared nuclear activities. While the investigation concerns materials and activities from the pre-2003 period, the Agency remains tasked with determining what, if any, materials or activities were omitted from Iran’s initial declarations to the IAEA. At the June 2020 Board of Governors meeting, IAEA member states passed a resolution calling on Iran to comply fully with the ongoing investigation into its past nuclear activities.
Syria:
- September 2007: Israel conducted an airstrike on what U.S. officials alleged was the construction site of a nuclear research reactor similar to North Korea’s Yongbyon reactor.
- The extent of Syrian-North Korean nuclear cooperation is unclear but is believed to have begun in 1997.
- Investigations into the U.S. claims uncovered traces of undeclared man-made uranium particles at both the site of the destroyed facility and Syria’s declared research reactor.
- Syria has not adequately cooperated with the IAEA to clarify the nature of the destroyed facility and procurement efforts that could be related to a nuclear program.
States That Had Nuclear Weapons or Nuclear Weapons Programs at One Time:
- Belarus, Kazakhstan, and Ukraine inherited nuclear weapons following the Soviet Union’s 1991 collapse, but returned them to Russia and joined the NPT as non-nuclear-weapon states.
- South Africa secretly developed but subsequently dismantled its small number of nuclear warheads and also joined the NPT in 1991.
- Iraq had an active nuclear weapons program prior to the 1991 Persian Gulf War but was forced to verifiably dismantle it under the supervision of UN inspectors. The U.S.-led March 2003 invasion of Iraq and subsequent capture of Iraqi leader Saddam Hussein definitively ended his regime’s pursuit of nuclear weapons.
- Libya voluntarily renounced its secret nuclear weapons efforts in December 2003.
- Argentina, Brazil, South Korea, and Taiwan also shelved nuclear weapons programs.
