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Nuclear weapons tests are experiments carried out to determine the effectiveness, yield, and explosive capability of nuclear weapons. Throughout the 20th century, most nations that developed nuclear weapons tested them. Testing nuclear weapons can yield information about how the weapons work, as well as how the weapons behave under various conditions and how structures behave when subjected to nuclear explosions. Nuclear testing has often been used as an indicator of scientific and military strength, and many tests have been overtly political in their intention; most nuclear weapons states publicly declared their nuclear status by means of a nuclear test.

The first nuclear weapon was detonated as a test by the United States at the Trinity site on July 16, 1945, with a yield approximately equivalent to 20 kilotons. The first hydrogen bomb, codenamed "Mike", was tested at the Enewetak atoll in the Marshall Islands on November 1, 1952 (local date), also by the United States. The largest nuclear weapon ever tested was the "Tsar Bomba" of the Soviet Union at Novaya Zemlya on October 30, 1961, with the largest yield ever seen (as of September 2013), an estimated 50–58 megatons.

In 1963, three (UK, US, Soviet Union) of the four nuclear and many non-nuclear states signed the Limited Test Ban Treaty, pledging to refrain from testing nuclear weapons in the atmosphere, underwater, or in outer space. The treaty permitted underground nuclear testing. France continued atmospheric testing until 1974, and China continued until 1980. Neither has signed the treaty.[1]

Underground tests in the United States continued until 1992 (its last nuclear test), the Soviet Union until 1990, the United Kingdom until 1991, and both China and France until 1996. After signing the Comprehensive Test Ban Treaty in 1996 (which has as of 2012 not yet entered into force), these states have pledged to discontinue all nuclear testing. Non-signatories India and Pakistan last tested nuclear weapons in 1998.

The most recent nuclear test occurred in February 2013 in North Korea. In January 2013, it was announced by North Korea that it plans to conduct further tests involving rockets that can carry satellites as well as nuclear warheads.[2]


Four major types of nuclear testing: 1. atmospheric, 2. underground, 3. exoatmospheric, and 4. underwater

Nuclear weapons tests have historically been divided into four categories reflecting the medium or location of the test.

  • Atmospheric testing designates explosions that take place in the atmosphere. Generally these have occurred as devices detonated on towers, balloons, barges, islands, or dropped from airplanes. Nuclear explosions that are close enough to the ground to draw dirt and debris into their mushroom cloud can generate large amounts of nuclear fallout due to irradiation of the debris.
  • Underground testing refers to nuclear tests conducted under the surface of the earth, at varying depths. Underground nuclear testing made up the majority of nuclear tests by the United States and the Soviet Union during the Cold War; other forms of nuclear testing were banned by the Limited Test Ban Treaty in 1963. When the explosion is fully contained, underground nuclear testing emits a negligible amount of fallout. Underground nuclear tests can "vent" to the surface, producing considerable amounts of radioactive debris as a consequence. Underground testing can result in seismic activity depending on the yield of the nuclear device and the composition of the medium it is detonated in, and generally result in the creation of subsidence craters.[3] In 1976, the United States and the USSR agreed to limit the maximum yield of underground tests to 150 kt with the Threshold Test Ban Treaty.
  • Exoatmospheric testing refers to nuclear tests conducted above the atmosphere. The test devices are lifted on rockets. These high altitude nuclear explosions can generate a nuclear electromagnetic pulse (NEMP), and charged particles resulting from the blast can cross hemispheres to create an auroral display.
  • Underwater testing results from nuclear devices being detonated underwater, usually moored to a ship or a barge (which is subsequently destroyed by the explosion). Tests of this nature have usually been conducted to evaluate the effects of nuclear weapons against naval vessels (such as in Operation Crossroads), or to evaluate potential sea-based nuclear weapons (such as nuclear torpedoes or depth-charges). Underwater tests close to the surface can disperse large amounts of radioactive particles in water and steam, contaminating nearby ships or structures.


Separately from these designations, nuclear tests are also often categorized by the purpose of the test itself.

  • Weapons-related tests are designed to garner information about how (and if) the weapons themselves work. Some serve to develop and validate a specific weapon type. Others test experimental concepts or are physics experiments meant to gain fundamental knowledge of the processes and materials involved in nuclear detonations.
  • Weapons effects tests are designed to gain information about the effects of the weapons on structures, equipment, organisms and the environment. They are mainly used to assess and improve survivability to nuclear explosions in civilian and military contexts, tailor weapons to their targets, and develop the tactics of nuclear warfare.
  • Safety experiments are designed to study the behavior of weapons in simulated accident scenarios. In particular, they are used to verify that a (significant) nuclear detonation cannot happen by accident. They include one-point safety tests and simulations of storage and transportation accidents.
  • Nuclear test detection experiments are designed to improve the capabilities to detect, locate, and identify nuclear detonations, in particular to monitor compliance with test-ban treaties.
  • Peaceful nuclear explosions were conducted to investigate non-military applications of nuclear explosives.

Aside from these technical considerations, tests have been conducted for political and training purposes. Tests also often serve multiple purposes.

Alternatives to full-scale testing[]

Sub-critical experiment at the Nevada Test Site.

Hydronuclear tests study nuclear materials under the conditions of explosive shock compression. They can create sub-critical conditions, or supercritical conditions with yields ranging from negligible all the way up to a substantial fraction of full weapon yield.[4]

Critical mass experiments determine the quantity of fissile material required for criticality with a variety of fissile material compositions, densities, shapes, and reflectors. They can be sub-critical or super-critical, in which case significant radiation fluxes can be produced. This type of test resulted in several criticality accidents.

Sub-critical (or cold) tests are any type of tests involving nuclear materials and possibly high-explosives (like those mentioned above) that purposefully result in no yield. The name refers to the lack of creation of a critical mass of fissile material. They are the only type of tests allowed under the Comprehensive Nuclear-Test-Ban Treaty.[5] Sub-critical tests continue to be performed by the nuclear powers.[6][7]

There have also been simulations of the effects of nuclear detonations using conventional explosives (such as the Minor Scale U.S. test in 1985). The explosives might be spiked with radioactive materials to simulate fallout dispersal.


File:Phoenix en route to North Vietnam, 1967.jpg

The Phoenix of Hiroshima (foreground) in Hong Kong Harbor in 1967, was involved in several famous anti-nuclear protest voyages against nuclear testing in the Pacific.

The 18,000 km2 expanse of the Semipalatinsk Test Site (indicated in red), attached to Kurchatov (along the Irtysh river). The site comprised an area the size of Wales.[8]

The first atomic weapons test was conducted near Alamogordo, New Mexico, on July 16, 1945, during the Manhattan Project, and given the codename "Trinity". The test was originally to confirm that the implosion-type nuclear weapon design was feasible, and to give an idea of what the actual size and effects of a nuclear explosion would be before they were used in combat against Japan. While the test gave a good approximation of many of the explosion's effects, it did not give an appreciable understanding of nuclear fallout, which was not well understood by the project scientists until well after the atomic bombings of Hiroshima and Nagasaki.

The United States conducted six atomic tests before the Soviet Union developed their first atomic bomb (RDS-1) and tested it on August 29, 1949. Neither country had very many atomic weapons to spare at first, and so testing was relatively infrequent (when the U.S. used two weapons for Operation Crossroads in 1946, they were detonating over 20% of their current arsenal). However, by the 1950s the United States had established a dedicated test site on its own territory (Nevada Test Site) and was also using a site in the Marshall Islands (Pacific Proving Grounds) for extensive atomic and nuclear testing.

The early tests were used primarily to discern the military effects of atomic weapons (Crossroads had involved the effect of atomic weapons on a navy, and how they functioned underwater) and to test new weapon designs. During the 1950s, these included new hydrogen bomb designs, which were tested in the Pacific, and also new and improved fission weapon designs. The Soviet Union also began testing on a limited scale, primarily in Kazakhstan. During the later phases of the Cold War, though, both countries developed accelerated testing programs, testing many hundreds of bombs over the last half of the 20th century.

In 1954 the Castle Bravo fallout plume spread dangerous levels of radiation over an area over 100 miles long, including inhabited islands.

Atomic and nuclear tests can involve many hazards. Some of these were illustrated in the U.S. Castle Bravo test in 1954. The weapon design tested was a new form of hydrogen bomb, and the scientists underestimated how vigorously some of the weapon materials would react. As a result, the explosion—with a yield of 15 Mt—was over twice what was predicted. Aside from this problem, the weapon also generated a large amount of radioactive nuclear fallout, more than had been anticipated, and a change in the weather pattern caused the fallout to be spread in a direction which had not been cleared in advance. The fallout plume spread high levels of radiation for over a hundred miles, contaminating a number of populated islands in nearby atoll formations (though they were soon evacuated, many of the islands' inhabitants suffered from radiation burns and later from other effects such as increased cancer rate and birth defects), as did the crew of the Japanese fishing boat Daigo Fukuryū Maru. One crewman died from radiation sickness after returning to port, and it was feared that the radioactive fish they had been carrying had made it into the Japanese food supply.

Because of concerns about worldwide fallout levels, the Partial Test Ban Treaty was signed in 1963. Above are the per capita thyroid doses (in rads) in the continental United States resulting from all exposure routes from all atmospheric nuclear tests conducted at the Nevada Test Site from 1951–1962.

Bravo was the worst U.S. nuclear accident, but many of its component problems—unpredictably large yields, changing weather patterns, unexpected fallout contamination of populations and the food supply—occurred during other atmospheric nuclear weapons tests by other countries as well. Concerns over worldwide fallout rates eventually led to the Partial Test Ban Treaty in 1963, which limited signatories to underground testing. Not all countries stopped atmospheric testing, but because the United States and the Soviet Union were responsible for roughly 86% of all nuclear tests their compliance cut the overall level substantially. France continued atmospheric testing until 1974, and China until 1980.

Almost all new nuclear powers have announced their possession of nuclear weapons with a nuclear test. The only acknowledged nuclear power which claims never to have conducted a test was South Africa (see Vela Incident), which has since dismantled all of its weapons. Israel is widely thought to possess a sizable nuclear arsenal, though it has never tested, unless they were involved in Vela. Experts disagree on whether states can have reliable nuclear arsenals—especially ones using advanced warhead designs, such as hydrogen bombs and miniaturized weapons—without testing, though all agree that it is very unlikely to develop significant nuclear innovations without testing. One other approach is to use supercomputers to conduct "virtual" testing, but codes need to be validated against test data.

There have been many attempts to limit the number and size of nuclear tests; the most far-reaching is the Comprehensive Test Ban Treaty of 1996, which has not yet been ratified by the United States. Nuclear testing has since become a controversial issue in the United States, with a number of politicians saying that future testing might be necessary to maintain the aging warheads from the Cold War. Because nuclear testing is seen as furthering nuclear arms development, many are also opposed to future testing as an acceleration of the arms race.

Nuclear testing by country[]

Over 2,000 nuclear explosions have been conducted, in over a dozen different sites around the world. Red Russia/Soviet Union, blue France, light blue United States, violet Britain, black Israel, orange China, yellow India, brown Pakistan, green North Korea and light green (territories exposed to nuclear bombs)

"Baker Shot", part of Operation Crossroads, a nuclear test by the United States at Bikini Atoll in 1946

The nuclear powers have conducted more than 2,000 nuclear test explosions (numbers are approximated, as some test results have been disputed):

  • United States United States: 1,054 tests by official count (involving at least 1,151 devices, 331 atmospheric tests), most at Nevada Test Site and the Pacific Proving Grounds in the Marshall Islands, with 10 other tests taking place at various locations in the United States, including Amchitka Alaska, Colorado, Mississippi, and New Mexico (see Nuclear weapons and the United States for details).[9]
  • Soviet Union Soviet Union: 715 tests (involving 969 devices) by official count,[10] most at Semipalatinsk Test Site and Novaya Zemlya, and a few more at various sites in Russia, Kazakhstan, Turkmenistan, and Ukraine.
  • France France: 210 tests by official count (50 atmospheric, 160 underground[11]), four atomic atmospheric tests at C.E.S.M. near Reggane, 13 atomic underground tests at C.E.M.O. near In Ekker in the French Algerian Sahara, and nuclear atmospheric tests at Fangataufa and nuclear undersea tests Moruroa in French Polynesia. Additional atomic and chemical warfare tests took place in the secret base B2-Namous, near Ben Wenif, other tests involving rockets and missiles at C.I.E.E.S, near Hammaguir, both in the Sahara.
  • United Kingdom United Kingdom: 45 tests (21 in Australian territory, including nine in mainland South Australia at Maralinga and Emu Field, some at Christmas Island in the Pacific Ocean, plus many others in the United States at the Nevada Test Site as part of joint test series)[12]
  • China China: 45 tests (23 atmospheric and 22 underground, at Lop Nur Nuclear Weapons Test Base, in Malan, Xinjiang)[13][14]
  • India India: Six underground tests (including the first one in 1974), at Pokhran[citation needed].
  • Pakistan Pakistan: Six underground tests, at Ras Koh Hills, Chagai District and Kharan Desert, Kharan District in Balochistan Province.[15]
  • North Korea North Korea: Three underground tests at the Punggye-ri Nuclear Test Site[citation needed].

There may also have been at least three alleged but unacknowledged nuclear explosions (see list of alleged nuclear tests). Of these, the only one taken seriously as a possible nuclear test is the Vela Incident, a possible detection of a nuclear explosion in the Indian Ocean in 1979.

From the first nuclear test in 1945 until tests by Pakistan in 1998, there was never a period of more than 22 months with no nuclear testing. June 1998 to October 2006 was the longest period since 1945 with no acknowledged nuclear tests.

Graph of nuclear testing

Treaties against testing[]

There are many proposed anti-nuclear explosion treaties, such as the Partial Nuclear Test Ban Treaty, and the Comprehensive Nuclear Test Ban Treaty. Most of these treaties were passed because scientists in many different countries noticed spikes in radiation levels in civilian areas. Human nuclear testing also contributed to the formation of the treaties, and examples can be seen in the following articles:

The Partial Nuclear Test Ban treaty makes it illegal to detonate any nuclear explosion anywhere except underground, in order to reduce atmospheric fallout. Most countries have signed and ratified the Partial Nuclear Test Ban which went into effect in October 1963. Of the nuclear states, France, China, and North Korea have never signed the Partial Nuclear Test Ban Treaty.[16] The 1996 Comprehensive Nuclear-Test-Ban Treaty (CTBT) bans all nuclear explosions everywhere, including underground. For that purpose, the Preparatory Commission of the Comprehensive Nuclear-Test-Ban Treaty Organization is building an international monitoring system with 337 facilities located all over the globe. 85% of these facilities are already operational.[17] As of May 2012, the CTBT has been signed by 183 States, of which 157 have also ratified. However, for the Treaty to enter into force it needs to be ratified by 44 specific nuclear technology-holder countries. These "Annex 2 States" participated in the negotiations on the CTBT between 1994 and 1996 and possessed nuclear power or research reactors at that time. The ratification of eight Annex 2 states is still missing: China, Egypt, Iran, Israel and the United States have signed but not ratified the Treaty; India, North Korea and Pakistan have not signed it.[18]

Compensation for victims[]

Over 500 atmospheric nuclear weapons tests were conducted at various sites around the world from 1945 to 1980. As public awareness and concern mounted over the possible health hazards associated with exposure to the nuclear fallout, various studies were done to assess the extent of the hazard. A Centers for Disease Control and Prevention/ National Cancer Institute study claims that nuclear fallout might have led to approximately 11,000 excess deaths, most caused by thyroid cancer linked to exposure to iodine-131.[19]

  • United States: As of March 2009, the U.S. is the only nation that compensates nuclear test victims. Since the Radiation Exposure Compensation Act of 1990, more than $1.38 billion in compensation has been approved. The money is going to people who took part in the tests, notably at the Nevada Test Site, and to others exposed to the radiation.[20][21]
  • France: In March 2009, the French Government offered to compensate victims for the first time and legislation is being drafted which would allow payments to people who suffered health problems related to the tests. The payouts would be available to victims' descendants and would include Algerians, who were exposed to nuclear testing in the Sahara in 1960. However, victims say the eligibility requirements for compensation are too narrow.[20]
  • United Kingdom: There is no formal British government compensation program. However, nearly 1,000 veterans of Christmas Island nuclear tests in the 1950s are engaged in legal action against the Ministry of Defense for negligence. They say they suffered health problems and were not warned of potential dangers before the experiments.[20]
  • Russia: Decades later, Russia offered compensation to veterans who were part of the 1954 Totsk test. However, there was no compensation to civilians sickened by the Totsk test. Anti-nuclear groups say there has been no government compensation for other nuclear tests.[20]
  • China: China has undertaken highly secretive atomic tests in remote deserts in a Central Asian border province. Anti-nuclear activists say there is no known government program for compensating victims.[20]

Milestone nuclear explosions[]

The following list is of milestone nuclear explosions. In addition to the atomic bombings of Hiroshima and Nagasaki, the first nuclear test of a given weapon type for a country is included, and tests which were otherwise notable (such as the largest test ever). All yields (explosive power) are given in their estimated energy equivalents in kilotons of TNT (see TNT equivalent). Putative tests (like Vela Incident) have not been included.

Date Name Yield (kT) Country Significance
1945-07-16 Trinity 18–20 USA First fission device test, first plutonium implosion detonation
1945-08-06 Little Boy 12–18 USA Bombing of Hiroshima, Japan, first detonation of an enriched uranium gun-type device, first use of a nuclear device in military combat.
1945-08-09 Fat Man 18–23 USA Bombing of Nagasaki, Japan, second and last use of a nuclear device in military combat.
1949-08-29 RDS-1 22 USSR First fission weapon test by the USSR
1952-10-03 Hurricane 25 UK First fission weapon test by the UK
1952-11-01 Ivy Mike 10,400 USA First cryogenic fusion fuel "staged" thermonuclear weapon, primarily a test device and not weaponized
1952-11-16 Ivy King 500 USA Largest pure-fission weapon ever tested
1953-08-12 Joe 4 400 USSR First fusion weapon test by the USSR (not "staged")
1954-03-01 Castle Bravo 15,000 USA First dry fusion fuel "staged" thermonuclear weapon; a serious nuclear fallout accident occurred; largest nuclear detonation conducted by United States
1955-11-22 RDS-37 1,600 USSR First "staged" thermonuclear weapon test by the USSR (deployable)
1957-05-31 Orange Herald 720 UK Largest boosted fission weapon ever tested. Intended as a fallback "in megaton range" in case British thermonuclear development failed.
1957-11-08 Grapple X 1,800 UK First (successful) "staged" thermonuclear weapon test by the UK
1960-02-13 Gerboise Bleue 70 France First fission weapon test by France
1961-10-31 Tsar Bomba 50,000 USSR Largest thermonuclear weapon ever tested—scaled down from its initial 100 Mt design by 50%
1964-10-16 596 22 PR China First fission weapon test by the People's Republic of China
1967-06-17 Test No. 6 3,300 PR China First "staged" thermonuclear weapon test by the People's Republic of China
1968-08-24 Canopus 2,600 France First "staged" thermonuclear weapon test by France
1974-05-18 Smiling Buddha 12 India First fission nuclear explosive test by India
1998-05-11 Pokhran-II 60[22] India First potential fusion/boosted weapon test by India; first deployable fission weapon test by India
1998-05-28 Chagai-I 40[23] Pakistan First fission weapon (boosted) test by Pakistan
1998-05-30 Chagai-II 20[23] Pakistan Second fission weapon (boosted) test by Pakistan
2006-10-09 2006 North Korean nuclear test 2-12 North Korea First fission plutonium-based device tested by North Korea
2009-05-25 2009 North Korean nuclear test 1-20 North Korea Successful fission device tested by North Korea
2013-02-16 2013 North Korean nuclear test 9 North Korea
2016-01-06 2016 North Korean nuclear test 6-9 North Korea Most recent nuclear test

"Staging" refers to whether it was a "true" hydrogen bomb of the so-called Teller-Ulam configuration or simply a form of a boosted fission weapon. For a more complete list of nuclear test series, see List of nuclear tests. Some exact yield estimates, such as that of the Tsar Bomba and the tests by India and Pakistan in 1998, are somewhat contested among specialists.

See also[]


  1. "The Treaty has not been signed by France or by the Peoples Republic of China." U.S. Department of State, Limited Test Ban Treaty.
  2. KIM, HYUNG-JIN (24 January 2013). "N. Korea Warns of Nuke Test, More Rocket Launches". U.S. News and World Report. Retrieved January 24, 2013. 
  3. For an overview of the preparations and considerations used in underground nuclear testing, see ""Underground Nuclear Weapons Testing" (". Retrieved 2006-10-19.  For a longer and more technical discussion, see U.S. Congress, Office of Technology Assessment (October 1989) (PDF). The Containment of Underground Nuclear Explosions. Washington, D.C.: U.S. Government Printing Office. 
  4. Carey Sublette (9 August 2001). "Nuclear Weapons Frequently Asked Questions". section 4.1.9. Retrieved 10 April 2011. 
  5. Jonathan Medalia (12 March 2008). "Comprehensive Nuclear-Test-Ban Treaty: Issues and Arguments". Congressional Research Service. p. 20. Retrieved 10 April 2011. 
  6. "US conducts 'subcritical' nuclear test". 2012-12-07. Retrieved 2013-05-28. 
  7. "Subcritical nuke tests may be resumed at Novaya Zemlya". 
  8. Togzhan Kassenova (28 September 2009). "The lasting toll of Semipalatinsk's nuclear testing". Bulletin of the Atomic Scientists. 
  9. "Gallery of U.S. Nuclear Tests". Retrieved 2010-10-21. 
  10. "Soviet Nuclear Test Summary". Retrieved 2010-10-21. 
  11. "N° 3571.- Rapport de MM. Christian Bataille et Henri Revol sur les incidences environnementales et sanitaires des essais nucléaires effectués par la France entre 1960 et 1996 (Office d'évaluation des choix scientifiques et technologiques)". Retrieved 2010-10-21. 
  12. "UK/US Agreement". Archived from the original on 2007-06-07. Retrieved 2010-10-21. 
  13. Nuclear Weapons, see also Nuclear Weapons Test List
  14. "Chinese Nuclear Tests Allegedly Cause 750,000 Deaths" Epoch Times. March 30, 2009.
  16. U.S. Department of State, Limited Test Ban Treaty.
  17. "CTBTO Factsheet: Ending Nuclear Explosions". Retrieved 2012-05-23. 
  18. "Status of signature and ratification". Retrieved 2012-05-23. 
  19. Exposure of the American Population to Radioactive Fallout from Nuclear Weapons Tests
  20. 20.0 20.1 20.2 20.3 20.4 What governments offer to victims of nuclear tests
  21. Radiation Exposure Compensation System: Claims to Date Summary of Claims Received by 06/11/2009
  22. [2010 test] Kakodkar says Pokhran-II tests fully successful], 24 September 2009
  23. 23.0 23.1 Pakistan Nuclear Weapons. Federation of American Scientists. December 11, 2002


  • Gusterson, Hugh. Nuclear Rites: A Weapons Laboratory at the End of the Cold War. Berkeley, CA: University of California Press, 1996.
  • Hacker, Barton C. Elements of Controversy: The Atomic Energy Commission and Radiation Safety in Nuclear Weapons Testing, 1947–1974. Berkeley, CA: University of California Press, 1994.
  • Schwartz, Stephen I. Atomic Audit: The Costs and Consequences of U.S. Nuclear Weapons. Washington, D.C.: Brookings Institution Press, 1998.
  • Weart, Spencer R. Nuclear Fear: A History of Images. Cambridge, MA: Harvard University Press, 1985.

External links[]

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