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Frequently Asked Questions (FAQs)

Nuclear Testing

Nuclear weapons tests are experiments carried out to determine nuclear weapons' effectiveness, yield, and explosive capability. Banning nuclear testing will prevent the development of nuclear weapons by countries that do not currently have them, upgrades to current nuclear arsenals or the creation of new, more advanced generations of nuclear weapons.

There are four different types of nuclear tests: (1) atmospheric tests; (2) underground tests; (3) upper atmospheric tests; and (4) underwater tests. Atmospheric testing is the process of testing a nuclear weapon in or above the atmosphere. Underground testing refers to when nuclear explosions are detonated at various levels under the Earth’s surface. Upper atmospheric testing is when a nuclear weapons test or explosion is conducted at altitudes above 30 kilometres within the Earth’s atmosphere. Underwater testing is when a nuclear test or explosion occurs underwater or close to the surface.

The five nuclear-weapon States, as defined under the 1968 Nuclear Non-Proliferation Treaty (NPT) are: China, France, the Soviet Union/the Russian Federation, the United Kingdom and the United States. The United States was the first country to commence testing in 1945. The former Soviet Union was second to test in 1949, the United Kingdom was third in 1952, France was fourth in 1960 and China fifth in 1964.

The United States was the first country to test on 16 July 1945. The former Soviet Union was second to test on 29 August 1949. This was followed by a test by the United Kingdom on 3 October 1952, France on 13 February 1960, and China on 16 October 1964.

The Soviet Union last tested on 24 October 1990, the United Kingdom on 26 November 1991, the United States on 23 September 1992, France on 27 January 1996 and China on 29 July 1996, just a few months before the Comprehensive Nuclear-Test-Ban Treaty (CTBT) opened for signature

Three out of the five nuclear-weapon States have ratified the CTBT. France and the United Kingdom were the first nuclear-weapon States to ratify the Treaty on 6 April 1998. The Russian Federation ratified it on 30 June 2000. Both China and the United States signed the CTBT on 24 September 1996, but both States have yet to ratify it

Between 1945 and 1996, more than 2,000 nuclear tests—over 1,000 by the United States, more than 700 by the Soviet Union, 210 by France, 45 by the United Kingdom, and 45 by China—were conducted at over 60 test sites around the world.

The “Manhattan Project” began as a small research programme in 1939. The World War II project was transferred to the authority of the United States Army and operated from 1941 to 1946.

The scientific research was directed by American physicist J. Robert Oppenheimer who was credited with developing the world’s first atomic bomb. Eventually, the Manhattan Project employed more than 130,000 people and cost nearly US$ 2 billion (equivalent to US$ 32 billion in 2022). It maintained control over the United States’ weapons production until formation of the U.S. Atomic Energy Commission in January 1947.

The United States dropped two atomic bombs on Japan during World War II: on 6 August 1945, the first bomb, code-named ‘Little Boy’, was dropped on the city of Hiroshima. It had an explosive yield of around 13 kilotons, and at the moment of detonation, a fireball was generated that raised temperatures to 4,000 degrees Celsius, turning Hiroshima – where many buildings were made of wood and paper - into an inferno. Three days later, on the morning of 9 August, a second nuclear bomb, code-named ‘Fat Man’, yielding 21 kilotons was prepared for detonation. While casualty figures vary greatly, in Hiroshima it is estimated some 90,000 to 166,000 people died within the first four months, while in Nagasaki the immediate deaths range from 60,000 to 80,000, according to the U.S.-Japanese Radiation Effects Research Foundation.

On 30 October 1961, the Soviet Union dropped its so-called “Tsar Bomba”—or "Emperor Bomb"—from an altitude of 10,500 metres to detonate at a height of 4,000 metres above the island of Novaya Zemlya. At about 50 megatons, “Tsar Bomba” was the largest, most powerful nuclear explosive ever detonated anywhere in the world.

From 1965 to 1974, a total of 621 nuclear tests were conducted by the five nuclear-weapon States: the United States (366), the Soviet Union (186), France (51), China (15) and the United Kingdom (2). India also conducted 1 nuclear test during that period.

The single year with the most nuclear tests (178) was 1962, the same year as the Cuban Missile Crisis.

Nuclear weapons have been tested in the following countries: Algeria, Australia, China, French Polynesia, India, Kazakhstan, Kiribati, the Marshall Islands, Democratic People’s Republic of Korea (DPRK), Pakistan, Russia, Turkmenistan, Ukraine, the United States, and Uzbekistan.

The Nevada Test Site in the United States was the site of the largest number of tests (over 900), followed by Semipalatinsk, Kazakhstan in the USSR with over 450 tests. Over 190 tests were conducted in French Polynesia in the South Pacific, and the Soviet test-site Novaya Zemlya in the Arctic Ocean hosted 130 tests.

Testing has also been conducted in the South Pacific’s Marshall Islands (United States), Christmas Island (United States and United Kingdom), at Lop Nur in Western China, in Australia (United Kingdom), Algeria (France) and in many other locations scattered over the globe.

From 1960 to 1966, France conducted 17 atmospheric and underground nuclear tests in Algeria. From 1966 to 1996, France conducted 193 atmospheric and underground nuclear tests in French Polynesia on the atolls of Mururoa and Fangataufa, located some 1,000 kilometres from Tahiti in the South Pacific.

The most recent nuclear test was conducted on 3 September 2017 in the Democratic People’s Republic of Korea (DPRK) at the Punggye-ri test site. This was also the location of the 2006, 2009, 2013, January 2016 and September 2016 nuclear tests.

South Africa began building its own nuclear-weapons arsenal in 1982 but dismantled it by June 1991. It then acceded to the 1968 NPT as a non-nuclear-weapon State in July 1991.

Belarus, Kazakhstan, and Ukraine inherited nuclear weapons from the Soviet Union (USSR). When the USSR collapsed in December 1991, its nuclear arsenal was scattered over four newly independent countries: the Russian Federation, Belarus, Kazakhstan, and Ukraine. In assuming the USSR’s legacy, including its status as a nuclear-weapon state under the 1968 NPT, Ukraine, Kazakhstan, and Belarus gave up their newly inherited nuclear weapons. Russia eventually consolidated all nuclear weapons and delivery systems on its own territory (many were voluntarily destroyed in the process).

The 1958 bilateral Mutual Defense Agreement on nuclear weapons cooperation is a bilateral treaty between the United Kingdom and the United States and is the most comprehensive agreement that either country has in this area. It enables the parties to exchange classified defense information on nuclear weapons, naval nuclear propulsion, and nuclear threat reduction to enhance each State's "atomic weapon design, development and fabrication capability." It also provides for the exchange of special nuclear material (e.g. plutonium, highly enriched uranium), components and equipment between the two countries, as well as the transfer of "non-nuclear parts of atomic weapons" to the UK

In 1996, the nuclear armed States had approximately 27,454 nuclear warheads worldwide. Russia had the most nuclear warheads amounting to 15,572, followed by the United States (10,931), France (450), China (233), the United Kingdom (203), and Israel (65).

According to the Stockholm International Peace Research Institute (SIPRI), the nine nuclear-armed weapon states – the United States, Russia, the United Kingdom, France, China, India, Pakistan, Israel and Democratic People’s Republic of Korea (DPRK) – have a total inventory of 12,705 nuclear

weapons, 9,440 of which comprises of the total stockpile of warheads intended for military use. The U.S. and Russia have the largest stockpiles of 3,708 and 4,477 warheads respectively. China has approximately 350 nuclear warheads, followed by France (290), the UK (180), Pakistan (165), India (160), Israel (90), and Democratic People’s Republic of Korea (DPRK) (20).

China adopted a universal no-first-use pledge in 1964. This is a pledge that a nuclear-weapon State will not be the first party to use nuclear weapons in a conflict or crisis.

China also provides non-nuclear-weapon States with unconditional “negative security assurances.” This is a pledge by a nuclear-weapon State that it will not use nuclear weapons against a non-nuclear-weapon State.

About 75 percent of these tests (1,517 total) were conducted underground. The remaining 25 percent were carried out in the atmosphere (530 total tests, a few of which were conducted underwater), sometimes near inhabited areas.

The announced nuclear test by Democratic People’s Republic of Korea (DPRK) on 9 October 2006 broke an eight-year-long de-facto moratorium on nuclear testing. However, it also provided the first real-life test case for the CTBTO’s global alarm system.

Although only partially completed and operating in test mode, the CTBTO’s Verification Regime proved that it was capable of meeting expectations. Over 20 International Monitoring System (IMS) seismic stations throughout the world detected the explosion. Data on the time, location, and magnitude of the event was transmitted to all Signatory States within two hours.

A detailed analysis was provided by the International Data Centre (IDC) within two days. Within two weeks of the test, the radionuclide noble gas station at Yellowknife, Canada was able to detect elevated amounts of Xenon 133 in the atmosphere. Only radionuclide findings can provide ultimate proof that an explosion is nuclear in nature. By applying atmospheric transport models to backtrack the gas dispersion, its registration was found to be consistent with the hypothesized release from the DPRK’s announced test.

All the data and analyses were provided to Signatory States, enabling them to make their own judgements.

Former U.S. President Bill Clinton described the CTBT as the “longest sought, hardest fought prize in the history of arms control negotiations.”

India conducted two sets of underground tests, code-named “Shakti (Power) ‘98”, on 11 and 13 May 1998 at its Pokhran underground testing site. In contrast to its initial nuclear test in 1974, there were

no claims that these were “peaceful tests.” Pakistan responded 15 days later when it conducted two sets of underground tests at its Ras Koh range on 28 and 30 May 1998, respectively.

Treaty History

The “Nuclear Age”, also referred to as the atomic age, began with the first nuclear test conducted by the United States of America on 16 July 1945 at Alamogordo, New Mexico. Less than a month later, the U.S. dropped two atomic bombs on Japan – on Hiroshima on 6 August and on Nagasaki on 9 August 1945. Japan surrendered on 15 August 1945, bringing an end to World War II. However, nuclear testing did not end there. It took five more decades, until the 1996 opening for signature of the Comprehensive Nuclear-Test-Ban Treaty (CTBT), that efforts to “put the nuclear genie back in the bottle” really began to bear fruit.

U.S. President Dwight D. Eisenhower introduced the “Atoms for Peace” programme in a speech on 8 December 1953, marking one of the first calls to halt the nuclear arms race and setting up an atomic energy agency. Eisenhower was concerned about the prospect of nuclear technology proliferating around the world and the increasing number of States with atomic bomb-making capabilities. The “Atoms for Peace” programme proposed that the U.S. would share non-military nuclear technology, training, and materials with other nations. As a result, as of 1954, the U.S. could export nuclear technology and material, provided that the recipient countries agreed not to use it for military purposes. Under the Atoms for Peace programme, in 1956, the International Atomic Energy Agency (IAEA) was formed.

Concerned over the threat posed by the escalation of nuclear testing around the world and the increasing yields of these tests, the Prime Minister of India, Jawaharlal Nehru, was the first Head of State to call for a “standstill agreement” to halt nuclear testing in 1954.

Following the Hiroshima and Nagasaki bombings in 1945, peace organizations became highly active in protesting against nuclear weapons. By the time the United Kingdom conducted its first hydrogen bomb test in 1957, nuclear testing was considered an important public issue.

The international peace movement played an essential role throughout the Cold War in keeping the public informed on disarmament issues, while pressuring governments to negotiate arms control treaties. This movement was instrumental in various attempts to negotiate a comprehensive nuclear-test-ban. It was particularly active around the negotiations of the 1968 Treaty on the Non-Proliferation of Nuclear Weapons (NPT), the 1991 Partial Test Ban Treaty amendment conference, the NPT Review Conferences in 1995 and 2000, and finally the 1996 CTBT.

The first such meeting of scientific experts from Canada, France, Poland, Romania, the Soviet Union, the United Kingdom, and the United States was organized by the United Nations in 1958 to analyze the problems associated with nuclear test ban verification.

In 1958, the UK, U.S., and USSR started negotiations, with the aim to establish a comprehensive test-ban-treaty to prevent all nuclear explosions, everywhere. The question of implementing a verification system continuously came up and posed challenges to the negotiations based on political will to conclude a treaty.

On 31 March 1958, the USSR passed a decree to ban nuclear tests, and urged the U.S. and UK to sign it. Former U.S. President Dwight Eisenhower agreed to a temporary testing suspension and proposed to form a “Group of Experts” (GSE) which resulted in the Conference of Experts to Study the Possibility of Detecting Violations of a Possible Agreement on Suspension of Nuclear Tests, also known as the “Conference of Experts”. Comprised of specialists from Canada, Czechoslovakia, France, Poland, Romania, the UK, the U.S., and the USSR, the Conference of Experts discussed and provided the first UN report on establishing a nuclear-test-ban verification regime. Against the backdrop of the Cold War, the GSE spent twenty years designing and testing elements of a verification system that has now been implemented by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO).

Following the October 1962 Cuban Missile Crisis, the signing of the Partial Test Ban Treaty (PTBT) marked the first time the world witnessed real progress on negotiations for a nuclear- test-ban.

Signed by the U.S., UK and the Soviet Union on 5 August 1963 in Moscow, the PTBT banned nuclear testing in the atmosphere, underwater and in space, stating that Signatory States could not “carry out any nuclear weapon explosion, or any other nuclear explosion…in the atmosphere; beyond its limits, including outer space; or underwater, including territorial waters or high seas.” Although it signalled progress towards a comprehensive test ban treaty, the main effect of the PTBT was that environmental issues were addressed rather than a decrease in testing activities: testing went underground, which was not prohibited by the PTBT.

On 1 July 1968, the Nuclear Non-Proliferation Treaty (NPT) opened for signature. It was signed that same day by the United States, the United Kingdom, the Soviet Union and 58 other countries. At present, 191 States have joined the NPT.

The Treaty defined nuclear-weapon States (NWS) as those five countries that tested nuclear weapons before 1968: China, France, the Soviet Union, the United Kingdom and the United States —and defined all others as non-nuclear-weapon States (NNWS).

The NPT is built upon three “pillars”: nuclear non-proliferation, nuclear disarmament and the peaceful use of nuclear energy. It is also based upon a so-called “grand bargain”; namely, that the non-nuclear-weapon states agreed to not develop nuclear weapons, and in return, the nuclear-weapon states agreed to disarm their nuclear weapons. The non-nuclear weapon states would also receive assistance in developing nuclear power for peaceful purposes.

In addition to the five NWS, there are four other nuclear-armed states: India, Pakistan, Israel, and Democratic People’s Republic of Korea (DPRK). India first tested in 1974 and Pakistan in 1998. Israel has a policy of nuclear opacity and has not reported testing nor conducted any nuclear test to public knowledge but is a nuclear-armed state according to research institutions such as the Stockholm International Peace and Research Institute, Natural Resources Defence Council and the Nuclear Threat Initiative. DPRK has conducted six nuclear tests in 2006, 2009, 2013, two in 2016, 2017, all of which were detected by CTBTO’s International Monitoring System.

The Peaceful Nuclear Explosions Treaty (PNET) was negotiated and signed by the Soviet Union and the United States in 1976, but not ratified until 1990, to address the challenge of peaceful nuclear explosions (PNEs). The PNET obligated these two states parties inter alia not to carry out any individual nuclear explosions with a yield exceeding 150 kilotons.

The purpose of the PNET was to regulate the peaceful nuclear testing that was being carried out by both the Soviet Union and the United States for economic reasons during the 1970s and 1980s. For example, during this period, the Soviet Union used a nuclear test to create a dam, while the United States considered, but did not implement, using several hydrogen bombs to create an artificial harbour at Cape Thompson, Alaska.

In 1990, the Soviet Union proposed a moratorium on nuclear testing that the United States and United Kingdom agreed to. The Soviet Union then declared a moratorium on nuclear testing in 1991, which was followed by U.S. legislation that imposed a moratorium until 1993 and subsequently through 1994, provided that no other country tested. The United States announced its commitment to concluding a comprehensive nuclear-test-ban treaty early in 1993. Prospects for negotiating such a treaty increased significantly during this time because the Russian Federation, the United Kingdom and the United States all had a moratorium on nuclear testing in place. This set the stage for the successful CTBT negotiations that hosted 44 countries and took place from 1994 through 1996

The CTBT opened for signature on 24 September 1996. Following the United States, the remaining four nuclear-weapon states - China, France, the United Kingdom, and the Russian Federation - all signed the Treaty that same day in New York. By the end of the day, another 66 States signed the Treaty and took the first steps toward making the full commitment never to conduct nuclear tests of any kind on Earth. In September 1996, the CTBT began its long journey towards becoming a global, legally binding Treaty.

The CTBT will enter into force 180 days (six months) after all 44 Annex 2 States have deposited their instruments of ratification with the United Nations Secretary-General who is the Depositary of the Treaty. These “Annex 2” States were compiled from the IAEA’s April 1996 edition of “Nuclear Power Reactors in the World”, which identified countries that possessed nuclear research and/or power reactors at that time. These countries had also participated in the Conference on Disarmament and in CTBT negotiations in 1996.

The Comprehensive Nuclear-Test-Ban Treaty (CTBT), Signature and Ratification

The 1963 Partial Test Ban Treaty (PTBT) prohibits nuclear explosions in the atmosphere, outer space and underwater, but it does not prohibit underground nuclear explosions. The 1996 CTBT prohibits all nuclear explosions on Earth, including underground nuclear testing.

The Nuclear Non-Proliferation Treaty (NPT) lays the foundation of the international nuclear non-proliferation regime. When it was being negotiated in the late 1960s, a permanent ban on nuclear testing was seen as an important element of such a regime.

The CTBT was a part of the package when the NPT was extended indefinitely in 1995. States Parties to the NPT agreed to achieve a comprehensive test ban treaty no later than the end of 1996 in exchange for the NPT being extended indefinitely. The CTBT was also part of the agreement to pursue nuclear disarmament at the 2000 NPT Review Conference in 2000.

The NPT and the CTBT are complementary regarding the control and limitation of nuclear arms activities and relevant technologies. With the NPT as its legal basis, the IAEA monitors the “upstream” dimension of nuclear weapons development (i.e. uranium enrichment, plutonium reprocessing and fuel fabrication), while the CTBT is meant to monitor the “downstream” final proof of a State’s intention to develop nuclear weapons, the nuclear test explosion.

The Conference on Disarmament (CD), and its predecessors—the Ten-Nation Committee on Disarmament (1960), the Eighteen-Nation Committee on Disarmament (1962-1968) and the Conference of the Committee on Disarmament (1969-1978)—is the international community’s sole multilateral disarmament negotiations forum. Major disarmament treaties, such as the NPT and the Chemical Weapons Convention (CWC), were negotiated at the CD. Thus, the precedent was established for the CTBT to also be negotiated in this forum. In 1982, the CD established a subsidiary body to launch negotiations on a comprehensive nuclear-test-ban treaty. In January 1994, an ad hoc Committee was formed to host the negotiations. Negotiations took place between 1994 and 1996, at the conclusion of which the CTBT opened for signature on 24 September 1996 at the United Nations General Assembly in New York.

A State deposits its instrument of ratification by hand or via mail with the UN Secretary-General who is the Depositary of the Treaty. The instrument of ratification is a document that must be signed by an appropriate official of the respective national government such as the Head of State, the Head of Government, the Minister of Foreign Affairs, or an official with full powers to sign the instrument. It is the responsibility of the Secretary-General to promptly inform all Signatory States of the ratification.

A State becomes a member of the CTBTO when it signs the Treaty. By signing the CTBT, the State is allowed to actively participate in the decision-making process of the CTBTO Preparatory Commission and is also involved in its activities.

To become an observer state, a non-Signatory State must be listed in the CTBT as a host for an International Monitoring System (IMS) facility. These States can attend meetings and workshops and engage in activities of the two Working Groups. Working Group A deals with budgetary, legal and administrative matters, while Working Group B deals with verification matters pertaining to the Provisional Technical Secretariat (PTS).

When a State signs a Treaty, it implies that a State will take steps to consent to be bound by the Treaty. A signature is achieved when the authorised representative of a State signs the Treaty at United Nations Headquarters in New York. An appointment must be made with the Chief of the Treaty Section at the Office of Legal Affairs at the United Nations Secretariat to sign the Treaty.

Approval is required by the legislature, the executive of a state, or both. To be accepted at the international level, the instrument of ratification must be signed either by the Head of State, Head of Government, and Minister for Foreign Affairs or by an official with full powers to sign the instrument. The signature validates the instrument of ratification. The ratification process is completed by depositing the instrument of ratification with the Secretary-General of the United Nations.

Under Article 18 of the 1969 Vienna Convention on the Law of Treaties, signatory States have an obligation to desist from any acts which would defeat the objective and purpose of the treaty that they have signed.

By signing the Treaty, States underscore their support for a world free of nuclear testing and explosions. Signatory States become members of the CTBTO Preparatory Commission where they make decisions pertaining to the work and activities of the Commission. Signatory States may benefit from the establishment of IMS facilities and National Data Centres (NDCs) on their territories

International Data Centre (IDC) in Vienna. They may also benefit from the scientific and technological research opportunities provided by IMS’s verification data. Read more in Membership Benefits.

A ratifying State shows that it is committed to the CTBT and its entry into force. Its ratification demonstrates that it is dedicated to achieving a world free of nuclear testing, while contributing to the global nuclear disarmament and non-proliferation regime.

Only a ratifying State, together with a majority of other ratifying States, can request that conferences on facilitating the entry into force of the CTBT be convened. After entry into force of the Treaty, only the ratifying States, the so-called States Parties, are full members of the CTBTO and can participate in the decision-making processes related to the mandate and the activities of the organization.

The instrument of ratification is a document, which must be signed by an appropriate official of the respective national government, including the title of the person who has signed it and its date and place of issue. The instrument of ratification must be signed either by the Head of State, Head of Government, the Minister of Foreign Affairs or an official with full powers to sign the instrument. This signature validates the instrument of ratification.

Annex 2 States are the 44 States that formally participated in the 1996 session of the Conference on Disarmament and possessed nuclear power or research reactors at the time. All the Annex 2 States must ratify the Treaty in order for it to enter into force. Of the 44 Annex 2 States, only Democratic People’s Republic of Korea (DPRK), India, and Pakistan have not signed the CTBT. There are five of the 44 Annex 2 States that have signed but are yet to ratify the CTBT, which are: China, Egypt, the Islamic Republic of Iran, Israel, and the United States.

The Organization

The Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) is an international organization. It was established on 19 November 1996. The CTBTO exists to prepare for the Treaty’s entry into force. It has two main tasks:

- promoting universal recognition of the Treaty; and

- building up the CTBT verification regime to ensure no nuclear explosion can go undetected.

The CTBTO Preparatory Commission lays the groundwork for the future when the Treaty enters into force and the CTBTO is established. The main task of the Commission is to establish the global verification regime so that it will be fully operational once the Treaty enters into force. The main task of the CTBTO will be to ensure international verification of compliance with the CTBT and to provide a forum for consultation and cooperation among States Parties.

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) was adopted by the UN General Assembly on 10 September 1996 and opened for signature on 24 September 1996. The UN Secretary-General is the Depositary of the Treaty, and upon the request of a majority of ratifying States, convenes the conferences on facilitating the entry into force of the Treaty (the so-called Article XIV Conferences after the article in the Treaty which stipulates they should be held every two years).

The CTBTO is an independent international organization with its own membership and budget, but it has had a Relationship Agreement with the United Nations since 2000 which provides a framework for cooperation between the two organizations. For example, the Commission may participate in UN meetings in the same capacity as the International Atomic Energy Agency (IAEA), which is also not part of the UN Economic and Social Council (ECOSOC).

The CTBTO and the UN can also cooperate and maintain close working relationships on matters of mutual interest and concern.

Regarding financial matters, the CTBTO uses the UN scale of assessed contributions as a basis for how Member States pay their scaled annual dues to the organization. The CTBTO is located at the Vienna International Centre where all UN organizations in Vienna also have their offices.

According to Article XIV of the CTBT, the Treaty will enter into force 180 days after all 44 of the States mentioned in Annex 2 of the Treaty have ratified it. These “Annex 2” States were compiled from the IAEA’s April 1996 edition of “Nuclear Power Reactors in the World”, which identified countries that possessed nuclear research and/or power reactors at that time. These countries had also participated in the Conference on Disarmament and in CTBT negotiations in 1996.

The CTBTO is expected to contribute to the timely resolution of any compliance concerns arising from possible misinterpretation of verification data relating to chemical explosions, for instance, the CTBTO provides data on large mining explosions, and assists in the calibration of stations that are part of the International Monitoring System (IMS).

Once the Treaty enters into force, several things will occur. Most importantly, the verification regime will become fully operational and ready to be used for verification purposes as foreseen in the Treaty.

On an organizational level, the Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) as it is currently known will cease to exist, and the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) will be established in its place. Ratifying States will become States Parties to the Treaty, the Provisional Technical Secretariat (PTS) will become the Technical Secretariat, and the Executive Secretary will become a Director-General.

The Commission is made up of a plenary body, composed of all the States Signatories and the Provisional Technical Secretariat (PTS), which assists the Commission in conducting its activities. The plenary body is comprised of the following policy-making organs: Working Group A, Working Group B, the Advisory Group, and the Advisory Group. Working Group A handles budgetary and administrative items, Working Group B deals with verification examination issues, and the Advisory Group advises both Working Groups A and B on relevant financial, budgetary, and associated administrative matters. The PTS carries out the activities of the organization mandated by the Treaty, including the build-up of the verification regime and the promotion of the Treaty.

The Provisional Technical Secretariat (PTS) assists the CTBTO Preparatory Commission and prepares for the implementation of the provisions of the Treaty. The PTS promotes the Treaty and is responsible for the build-up of the verification regime. It is tasked with supervising and coordinating the provisional operation of the International Monitoring System (IMS) and the International Data Centre (IDC). The PTS receives, processes, analyses and reports on IMS data, and enhances the on-site inspection mechanism so that it will be operational once the Treaty enters into force.

The PTS is mainly a technical organization because up to 80% of its budget is allocated to the establishment of the global verification regime.

As the PTS is primarily technical in nature, it employs mostly staff with scientific and technical skills. Examples of technical PTS jobs include work as seismologists, engineers, computer analysts, data analysts, infrasound, radionuclide and hydroacoustic officers and methodology officers, as well as an array of technicians.

The CTBTO is financed by its Member States. The activities of the organization are funded by assessed contributions levied annually on all States Signatories to the Treaty. Activities of the organization may also be funded by voluntary contributions in cash or in-kind.

Since 2005, the CTBTO’s budget has been administered through a split currency system. The split currency system was introduced as a measure to mitigate the adverse effects of currency fluctuations. Therefore, State Signatories’ assessed contributions are now split between U.S. dollars and euros in accordance with the projected expenses of the Commission in each of these currencies. The CTBTO’s total budget is the combination of the euro and US dollar amounts.

What are the main criteria for working at the PTS? In addition to possessing the required educational qualifications, one has to be a national of a State that has signed the Treaty. Besides having a well-balanced personality and good communication skills, experience in a cross-cultural work environment is always considered an asset. Knowledge of German is an additional asset because the PTS is based in Vienna, Austria.

The working language of the CTBTO is English, while the official languages are Arabic, Chinese, English, French, Russian and Spanish, just as in the United Nations. The working language means that the daily work of the CTBTO is performed in English while reference to the official languages means

that formal proceedings are conducted in all those languages. Additionally, the Treaty and other key documents are available or will be provided in all the official UN languages.

The International Monitoring System (IMS)

According to Article IV, Point B.16 of the CTBT, the original concept of a verification system was envisioned as a global monitoring system equipped with “facilities for seismological monitoring, radionuclide monitoring including certified laboratories, hydroacoustic monitoring, infrasound monitoring, and respective means of communication supported by the International Data Centre (IDC.)” CTBTO has established a unique global monitoring system that includes almost every item outlined in the CTBT. The CTBT proposed that the IMS will include 337 facilities (321 stations and 16 radionuclide labs) once complete, located in 89 countries across the globe. Over 92 percent of those stations and laboratories have been established to date, making it almost 100% compliant with the original concept as outlined in the CTBT. Using infrasound, seismic, radionuclide, and hydroacoustic technologies, the IMS facilities are designed to detect atmospheric and underwater nuclear tests and explosions with yields greater than one kiloton, and underground nuclear tests with yields greater than five kilotons.

The International Monitoring System (IMS) monitors the Earth for any sign of a nuclear explosion. International Data Centre (IDC) analyses the data relayed from the monitoring stations 24/7, and upon entry into force, on-site inspections (OSI) can be requested by States Parties in case of a suspected nuclear test. The verification regime is currently operated provisionally and will become fully operational once the CTBT enters into force.

Once the Treaty enters into force, three additional components of the verification regime will be activated: consultation and clarification, on-site inspections and confidence-building measures.

The consultation and clarification process is intended to clarify and resolve matters concerning possible non-compliance with the Treaty’s basic obligations. On-site inspections are used to determine whether a nuclear-weapon test or any other nuclear explosion has been carried out and to collect evidence that might assist in identifying any potential violator of the Treaty.

Confidence-building measures help resolve compliance concerns arising from possible misinterpretation of verification data relating to chemical explosions (e.g. large mining explosions) and assisting in the calibration of stations that are part of the IMS.

The International Monitoring System (IMS) is a unique global network using four state-of-the-art technologies: seismic to monitor shockwaves through the ground; hydroacoustic to detect sound waves in the oceans; infrasound to listen for ultra-low-frequency sound waves inaudible to the human ear; and radionuclide to monitor the atmosphere for radioactive particles and gases from a nuclear explosion.

Yes. By the mid-1990s, there was consensus that the IMS would have seismological stations at its core and be reinforced by other complementary monitoring technologies. There was also consensus that it was only through using these complementary technologies that the capability of detecting all nuclear testing on Earth can be guaranteed.

The CTBTO Verification Regime is one of the most ambitious global projects ever undertaken and there were many political, environmental, and administrative challenges. For example, there were technical challenges with establishing the radionuclide network, as it was the first of its kind to be created on a global scale and robust equipment had to be designed to operate reliably in remote and isolated locations, where technical expertise was scarce. There were also logistical challenges, namely that special procedures had to be designed to send sensitive samples from radionuclide stations to IMS network laboratories for evaluation.

Yes. Only the Signatory States of the CTBT can request IMS data on other States.

As set out in Annex 1 to the Protocol of the Treaty, the IMS’s 321 stations and 16 radionuclide laboratories are located all over the world, altogether in 89 countries. Many stations are situated in remote and hard-to-reach areas in order to provide global coverage of any nuclear test activity.

The United States is the country with the most IMS designated installations (38), followed by the Russian Federation (32). Then, in descending order, Australia (21), France (17), Canada (16), the UK (12), China (12) and Japan (10).

The following countries have one designated radionuclide lab each, making a total of 16: Argentina, Australia, Austria, Brazil, Canada, China, Finland, France, Israel, Italy, Japan, New Zealand, the Russian Federation, South Africa, the United Kingdom and the United States. The laboratories have not carried out any verification analyses to date.

The IMS monitoring stations are operated by various local institutions under contract with the CTBTO. The post-certification operation and maintenance contract between the CTBTO and the station operator references the station’s operation manual, which contains a station-specific annex defining the operational standards. This information includes items such as station inventory, preventive maintenance schedules, procedures for reporting problems, availability of spare parts and lists of contacts.

Seismologists can tell the difference between naturally occurring earthquakes and man-made explosions with some key indicators. Most earthquakes are straightforward “shear dislocations”, meaning that geological stress causes the rock to fracture along its plane of weakness. The earthquake generates “P” and “S” waves on certain planes in a recognisable four-lobed pattern. The timeframe depends upon the strength of the earthquake, but usually takes several seconds to propagate over the entire fault plane.

With man-made explosions, nuclear or otherwise, the dynamics are different. “P” waves extend radially outward, generating equal force in all directions. In principle, there are no initial “S” waves. Energy release in an explosion occurs within a fraction of a second—far faster than in an earthquake.

The IMS hydroacoustic monitoring network comprises eleven stations, covering the world’s oceans, which make up 70 percent of the surface area of the Earth. Low frequency underwater sound, such as ones produced by nuclear tests, travel efficiently through water. These sounds can be detected at great distances.

The IMS infrasound network uses micro-barometers (i.e. acoustic pressure sensors) to detect very low-frequency sound waves in the atmosphere. It can differentiate between atmospheric explosions, natural phenomena (e.g. volcanic eruptions), and man-made phenomena, such as aircraft in supersonic flight and rocket launches.

Radionuclide stations use air samplers to detect radioactive particles released from atmospheric explosions or noble gases vented from underground and underwater explosions. The radionuclide laboratories then analyse those samples that are suspected of containing radionuclide material, which may have been produced by a nuclear explosion.

When a nuclear explosion occurs, a great deal of energy is instantaneously released and physical products are created. The energy interacts with the environment and propagates sound vibrations through the solid earth, the ocean, or the atmosphere. Physical products (e.g. radioactive particles and/or gases) are released into the surrounding medium and can leak into the atmosphere, even if the actual explosion occurred underground or underwater.

The IMS uses the aforementioned three “wave-form technologies”—seismic, hydroacoustic and infrasound—with sophisticated sensors to detect the transient signals created when this explosive energy is released. At the same time, radionuclide stations collect and analyse air samples for evidence of the physical products created and carried by the prevailing winds. The radionuclide technology can show whether an explosion has been nuclear in nature.

Many States have identified a number of potential civil and scientific applications and benefits emanating from the Treaty’s verification technologies. These include enhanced meteorological and environmental monitoring, which contribute to sustainable development and human welfare goals. The data are already used for tsunami warning purposes.

CTBTO's state-of-the-art network can also identify earthquakes or other seismic events that could cause a tsunami. The data are recorded by 164 seismic and hydroacoustic stations that monitor underground and the oceans round-the-clock, using cutting-edge technologies. This information is sent in near real-time to National Tsunami Warning Centres (NTWC) of Member States to help them issue more timely and precise alerts -- saving more lives and minimizing risk. At present, 19 warning

centres in 18 countries, which are Treaty signatories, have signed a Tsunami Warning Agreement with the CTBTO.

Not only is it legal, but it is also compulsory under Article IV of the CTBT, which states that the verification regime and its IMS must be fully operational when the Treaty comes into force.

On-Site Inspections (OSI)

An on-site inspection represents the final verification measure under the CTBT. It is launched to determine whether a nuclear explosion has taken place in violation of the Treaty. A team consisting of specially trained inspectors is sent to the site of a suspected nuclear explosion to gather facts that will help States Parties establish whether the Treaty has been violated.

An on-site inspection is preceded by the analysis of International Monitoring System (IMS) data at the International Data Centre (IDC), which may point to the possibility of a nuclear explosion. The only way to gather conclusive evidence as to whether a nuclear explosion occurred is by conducting an on-site inspection at the site of a suspected nuclear explosion.

No, on-site inspections can only be invoked once the Treaty has entered into force

Under the terms of the Treaty, a State Party cannot refuse an on-site inspection on its territory. A refusal of an on-site inspection constitutes a violation of the Treaty since a State Party – by signing and ratifying the CTBT– has accepted all its provisions. In the case of a refusal, the matter would be referred to the Conference of the States Parties, who will then decide on measures to be taken to ensure compliance with the Treaty, considering the recommendations by the Executive Council. The Conference or the Executive Council may bring the case to the attention of the United Nations.

The length of an on-site inspection depends on the inspection activities approved by the Executive Council. The inspection team must submit its first report within 25 days after the approval of the inspection. Unless the majority of the Executive Council decides to discontinue the on-site inspection, it can last up to 60 days.

During that second phase, which is called the continuation phase, mostly geophysical inspection techniques are used. According to Part II of the Protocol of the CTBT, on-site inspections can be further prolonged by another 70 days should the inspection team consider this extension necessary. Therefore, in total, an on-site inspection can last up to 130 days.

Each State Party has the right to request an on-site inspection in the case of a suspicious event. Such a request can be submitted independently from a consultation and clarification process. Requests for on-site inspections are simultaneously presented to the Executive Council and to the Director-General of the Technical Secretariat of the CTBTO.

An on-site inspection request should be based on information about the suspicious event that triggered the request. This information can be drawn from data gathered by the IMS, as well as from data generated by national monitoring systems. Regardless of the source, a request for an on-site inspection must contain detailed information about the event, including estimated time and location, as well as details about the probable physical environment of the event (i.e., whether it has taken place underground, underwater or in the atmosphere) and, which State Party or State Parties would be inspected. If a State Party requests an on-site inspection on another territory that is not a Party to the CTBT, the State Party must ensure that the on-site inspection is in line with the Protocol of the CTBT.

A request for an on-site inspection is sent to the Director General and the Executive Council of the CTBTO. The Director General forwards the request to the State Party or Parties that are the subject of the inspection request and seeks their clarification. The resulting information, as well as relevant IMS monitoring data, is then made available to the Executive Council. At least 30 of the 51 Council members need to support the request for it to be approved.

The size of the inspection team is limited and should not exceed 40 persons. The team consists of inspectors and assistant inspectors, who will be appointed, based on a list managed by the Technical Secretariat. Inspectors and assistant inspectors are nominated by States Parties or, in the case of staff of the Technical Secretariat, by the Director-General based on their expertise and experience. No national of the requesting State Party can be a part of the on-site inspection team. In a dedicated procedure following the Treaty’s entry into force, inspectors and assistant inspectors are approved in their functions by States Parties.

The Protocol of the Treaty defines the inspection area as a continuous area of no more than 1,000 km², and there should not be a linear distance exceeding 50 km in any direction. Based on IMS monitoring data and their analysis by the IDC, the location of this inspection area can be identified. The aim is to reduce the uncertainty in the location estimate to a level accepted under the Treaty (i.e., to an area of no more than 1,000 km²).

Yes. The managed-access regulation allows an inspected State Party to restrict the inspection team’s access to certain parts within the inspection area. This measure allows the inspected State Party to protect its national security interests and to prevent the disclosure of confidential information unrelated to the purpose of the inspection.

Several areas of no more than 4 km² can be subjected to the managed-access regulation, but the total cannot exceed 50 km². If the inspected State Party restricts the access to certain areas, it is required by the Treaty to provide alternatives for the inspection team to carry out its mandate.

Observers are not specifically required as part of an on-site inspection, but the State Party requesting the inspection may send a representative to observe it. Observers may be nationals of the requesting State Party or of third State Parties. The Treaty stipulates that there should be no more than three observers and that they should be subject to the inspected State Party’s acceptance. During the on-site inspection, the observers have the right to be informed about all activities and findings, and to make recommendations to the inspection team.

The inspection team must submit an initial report on the on-site inspection no later than 25 days after the inspection has been approved. Based on this report, the Executive Council determines

whether the inspection will be continued. In case the inspection does continue, a final inspection report will be required following the conclusion of the inspection. This report contains all information relevant to inspection activities and the respective findings. It also gives an account of the cooperation with the inspected State Party and a description of the access provided to the inspection team.

Based on the report, the Executive Council reaches a final assessment as to whether non-compliance with the Treaty has occurred. If the Council concludes that the inspected State Party has indeed violated the provisions of the Treaty, the Council may recommend that the Conference takes measures to ensure compliance with the Treaty. The Conference and the Council both have the option to bring a case of Treaty violation to the attention of the UN Security Council.