Treaty on the Prohibition of Nuclear Weapons (TPNW)

The Treaty on the Prohibition of Nuclear Weapons (TPNW) is a multilateral treaty with 74 States Parties. The Treaty prohibits the development, possession, use, and threat of use of nuclear weapons, with the ultimate goal of their total elimination.

The Treaty was signed on 7 July 2017 and entered into force on 22 January 2021, following the deposit of the 50th instrument of ratification. The First Review Conference is expected to be held in November-December 2026.

The TPNW prohibits States Parties from developing, testing, producing, manufacturing, acquiring, possessing, stockpiling, transferring, using, or threatening to use nuclear weapons or other nuclear explosive devices. It also prohibits providing any assistance, encouragement, or inducement for such activities. The Treaty further prohibits the stationing, installation or deployment of nuclear weapons or other nuclear explosive devices in the territory or under jurisdiction or control of the States Parties.39

States Parties that have possessed or hosted nuclear weapons are required to eliminate their arsenals or remove foreign nuclear weapons from their territories in accordance with verified, time-bound plans.40

The TPNW stipulates that verification measures for States Parties that have eliminated or still possess nuclear weapons are to be agreed upon with a competent international authority, in cooperation with the IAEA, to ensure the irreversible elimination of their nuclear-weapon programmes.41

The TPNW requires States Parties to adhere to International Atomic Energy Agency (IAEA)’s comprehensive safeguards agreement (CSA) (INFCIRC/153 (Corrected)). States Parties are required to maintain their existing safeguards agreements or, if they have not done so, bring into force a CSA. States Parties that have owned, possessed, or controlled nuclear weapons or other nuclear explosive devices, once they have completed the irreversible elimination of their nuclear-weapon programmes, are required to conclude a safeguards agreement with the IAEA to ensure the non-diversion of declared nuclear material from peaceful nuclear activities and the absence of undeclared nuclear material or activities.42

The TPNW does not provide a definition of nuclear weapons or nuclear explosive devices.

States Parties are required to submit initial declarations containing information on:

• whether they have owned, possessed, or controlled nuclear weapons or nuclear explosive devices and if it has irreversibly eliminated its nuclear-weapon programme prior to the Treaty’s entry into force.43

• whether they currently own, possess, or control any nuclear weapons or other nuclear explosive devices.44

• whether any nuclear weapons or nuclear explosive devices owned, possessed, or controlled by another State are located within their territory or under their jurisdiction or control.45

States Parties that own, possess, or control nuclear weapons and other nuclear explosive devices are required to submit a plan (legally-binding and time-bound) for the verified and irreversible elimination of their nuclear-weapon programme. Once the elimination has been concluded and a safeguards agreement has entered into force, the States Parties are required to submit a final declaration that it has fulfilled its obligations.46

States Parties hosting nuclear weapons or other nuclear explosive devices owned, possessed, or controlled by another State, upon the removal of such weapons, are required to submit a declaration that it has fulfilled its obligations.47

States Parties that owned, possessed, or controlled nuclear weapons or other nuclear explosive devices and eliminated their nuclear-weapon programme prior to the entry into force of the treaty are required to cooperate with the international authority designated to verify the irreversible elimination of its nuclear-weapon programme. The competent authority reports its findings to the States Parties.48

States Parties that have owned, possessed, or controlled nuclear weapons or other nuclear explosive devices are required to submit regular reports to each Meeting of States Parties or Review Conference on the progress made towards elimination of their nuclear-weapon programme until it has been fulfilled.49

The TPNW provides for the designation of a competent authority to negotiate and verify the irreversible elimination of the nuclear-weapon programme and related facilities. The verification process may include:

• Irreversible elimination of nuclear-weapon programme, including the elimination or conversion of all nuclear- weapons-related facilities;50

• Removal from operational status and destruction of nuclear weapons or nuclear explosive devices, within a deadline of a maximum period of 10 years with a maximum extension period of five years.51

• Removal of hosted nuclear weapons or nuclear explosive devices, within a period of 90 days. 52

No details are provided regarding specific inspection provisions or procedures.

Under the CSA, the IAEA has the right to conduct different types of inspections: ad hoc, routine, and special. 

Ad hoc inspections are used to verify the information contained in initial reports, identify and verify any subsequent changes, and verify the quantity and composition of nuclear material prior to its transfer into or out of the State.11 

Routine inspections verify, on an ongoing basis, the consistency between reports and records, the location, identity, quantity, and composition of all nuclear material subject to safeguards, and investigate discrepancies such as unaccounted-for material, shipper–receiver differences, and book inventory uncertainties.12 These inspections may also be of unannounced character.13 

Special inspections are conducted in exceptional cases to verify information in special reports or when the information provided by a State, including that obtained through routine inspections, is insufficient to enable the Agency to fulfill its safeguards responsibilities. These may involve accessing additional information or locations beyond the scope of routine inspections.14 

In addition, Safeguards visits are conducted at declared facilities at appropriate times during the lifecycle for verifying the safeguards relevant design information.15  

The frequency and intensity of inspections vary based on facility type, material quantity, and form. Specific formulas define maximum inspection efforts, such as man-days or man-years, depending on factors like enrichment levels and throughput.16

No details are provided regarding specific monitoring measures or procedures for verifying the irreversible elimination of the nuclear-weapon programme and facilities.

Under the CSA, verification measures rely on nuclear material accountancy and are complemented by containment and surveillance measures.

For nuclear material accountancy, IAEA inspectors, inter alia, audit the records kept and perform independent measurements to verify the quantity and composition of nuclear material declared in the State’s report. Inspectors count items, measure attributes, and compare findings with the declared figures. Measurement methods include non-destructive assay (NDA) – used to verify the location, identity, quantity, and composition of nuclear material without destroying the item – and Destructive Analysis (DA) – collection and analysis of representative samples using chemical and physical techniques used for detecting bias defects (i.e., small quantities of material are diverted over time).53

Containment and surveillance measures are used to maintain continuity of knowledge of nuclear material between inspection visits. These efforts aim to detect undeclared movement or tampering. The IAEA uses a range of tools: (1) tags and seals, with single-use or verifiable seals, to secure containers and equipment; (2) sensors and data recorders to monitor access and integrity in real time; and (3) optical surveillance systems, including underwater cameras, high intensity lighting, short-term setups, other monitoring equipment.

There are provisions for continuous monitoring, if necessary, using unattended and remote equipment, transmitting authenticated and encrypted safeguards-relevant data off-site and enabling real-time monitoring.54

Environmental sampling is also used in facilities and at locations where inspectors have access during inspections and design information verification55 to detect undeclared nuclear activities or materials or concealment efforts by analysing trace isotopes or particles in air, water, soil, or surfaces.

The TPNW established a six-year review conference cycle, supported by regular biennial Meetings of States Parties (MSP), to consider and take decisions regarding the application and implementation of the Treaty, in accordance with its provisions. An extraordinary MSP may be convened when deemed necessary, upon the written request of any State Party, provided that the request is supported by at least one third of the States Parties.56

The Treaty also addresses the settlement of disputes arising between two or more States Parties concerning its interpretation or application. In such cases, the parties involved are required to consult with one another to resolve the dispute through negotiation or by other peaceful means of their choosing, in accordance with Article 33 of the Charter of the UN. Furthermore, the MSP may assist in the resolution of such disputes by offering its good offices, encouraging the parties concerned to initiate a settlement procedure of their choice, and recommending a time frame for any agreed procedure, consistent with the Treaty and the UN Charter.57