Comprehensive Nuclear-Test-Ban Treaty (CTBT)

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a multilateral agreement that prohibits nuclear explosions by everyone, everywhere – in the atmosphere, underwater, or underground.

The treaty was opened for signature on 24 September 1996 and it has not entered into force yet. To date, it has been signed by 186 States and ratified by 178 States. For the treaty to enter into force, all 44 States listed in Annex 2 are required to ratify it. Eight of these States have yet to sign the Treaty.58

The CTBT prohibits nuclear weapon test explosions or other nuclear explosions.

States Parties commit not to carry out, cause, encourage or participate in any nuclear weapon test explosion or other nuclear explosion, and to prohibit and prevent such explosions in areas under its jurisdiction or control.

The treaty does not define the term “nuclear explosion” explicitly.59

The CTBT does not require declarations.60 As a confidence-building measure (CBM), States provide voluntary notifications of chemical explosions greater than 300 tonnes TNT-equivalent, and should include details such as location, time, quantity and type of explosive used, configuration, and intended purpose of the blast. States Parties may also voluntarily provide annual updates on national use of all other chemical explosions greater than 300 tonnes TNT-equivalent threshold.61

States Parties also commit to data exchange of seismological, radionuclide, hydroacoustic, and infrasound, in accordance with procedures of the International Data Centre (IDC), to support the International Monitoring System (IMS).62

The CTBT provides a mechanism of ad hoc on-site inspections to verify whether a nuclear weapon test explosion or any other nuclear explosion has been carried out.63 On-site inspections occur at the request of a State Party and are based on credible information obtained from the International Monitoring System or by national technical means (NTMs).64

During the inspection, activities and techniques to gather evidence may include:65

• Confirmation of the boundaries and establishment of coordinates of the inspection area;

• Visual observation, video and still photography and multi-spectral imaging (including infrared measurements);

• Measurement of level of radioactivity (gamma radiation monitoring and energy resolution analysis);

• Environmental sampling and analysis of solids, liquids and gases;

• Passive seismological monitoring for aftershocks to localize search area and facilitate determination of the nature of an event;

• Resonance seismometry and active seismic surveys to search for and locate underground anomalies, including cavities and rubble zones;

• Magnetic and gravitational field mapping, ground penetrating radar and electrical conductivity measurements to detect anomalies or artifacts;

• Drilling to obtain radioactive samples.

States Parties have the right to employ managed access to protect sensitive installations and confidential information unrelated to the purpose of the inspection.

States Parties agreed to use national technical means (NTM) and committed not to interfere with the NTM of others.66

The International Monitoring System (IMS) and the International Data Centre (IDC) provide additional information relevant to monitoring. The IMS is comprised of a network of facilities using state-of-the-art technologies for monitoring:67

• Seismological monitoring: detects shockwaves through the ground. The network consists of 50 primary seismological stations that transmit uninterrupted, on-line data to the IDC, supplemented by 120 auxiliary stations that provide data upon request.

• Radionuclide monitoring: detects radioactive particles and noble gases into the atmosphere by a nuclear explosion. The network consists of 80 stations and is supported by certified laboratories that analyze samples and submit results to the IDC.

• Hydroacoustic monitoring: detects sound waves propagating through the oceans. The network consists of 11 stations.

• Infrasound monitoring: detects ultra-low frequency sound waves inaudible to the human ear. The network consists of 60 stations.

All IMS facilities are owned and operated by States Parties, totaling a global network of 337 facilities – including 321 stations and 16 laboratories.68

The IDC receives and processes data from the IMS and applies automatic and expert analysis to detect events of potential relevance under the Treaty. States Parties have a right to access all data made available to the IDC.69

States Parties agreed that compliance concerns would be referred to the multilateral Comprehensive Nuclear Test-Ban Treaty Organization (CTBTO) or addressed directly. These include procedures for consultation and clarification efforts. The treaty additionally includes a dispute settlement procedure of recourse within CTBTO or at the International Court of Justice70.