Treaty on the Non-Proliferation of Nuclear Weapons (NPT)

The Treaty on the Non-Proliferation of Nuclear Weapons (NPT) is a multilateral treaty with 191 States Parties. The treaty prohibits the development and acquisition of nuclear weapons and other nuclear explosive devices. The treaty further obligates all its Parties to pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race and to nuclear disarmament, and to a treaty on general and complete disarmament under strict and effective international control.

The NPT was opened for signature on 1 July 1968 and entered into force on 5 March 1970. In May 1995, during the Fifth NPT Review and Extension Conference, the Treaty was extended indefinitely.

Under the NPT, nuclear weapon states (NWS) are defined as those that “manufactured and exploded a nuclear weapon or other nuclear explosive device prior to 1 January 1967”.1 There are five NWS parties to the NPT: China, France, the Russian Federation (the Soviet Union when the Treaty entered into force), the United Kingdom, and the United States of America. All other States Parties are considered non-nuclear weapons states (NNWS).

The Treaty requires non-nuclear-weapon States (NNWS) to place all source and special fissionable material under International Atomic Energy Agency (IAEA) safeguards “to prevent diversion of nuclear energy from peaceful uses to nuclear weapons or other nuclear explosive devices”. Each NNWS is required to conclude a comprehensive safeguards agreement (CSA), based on document INFCIRC/153, with the IAEA.2 Additionally, the NPT prohibits NWS from transferring nuclear weapons or other nuclear explosive devices to NNWS, and to assisting, encouraging or inducing NNWS to acquire such weapons or devices. NNWS are not required to conclude a CSA, although they have voluntarily concluded Voluntary Offer Agreements (VOAs).

The IAEA Statute defines source material as “Uranium containing the mixture of isotopes occurring in nature; uranium depleted in the isotope 235; thorium; any of the foregoing in the form of metal, alloy, chemical compound, or concentrate; any other material containing one or more of the foregoing in such concentration as the Board of Governors shall from time to time determine; and such other material as the Board of Governors shall from time to time determine”.4

Special fissionable material is defined as “Plutonium-239; uranium-233; uranium enriched in the isotopes 235 or 233; any material containing one or more of the foregoing; and such other fissionable material as the Board of Governors shall from time to time determine; but the term ‘special fissionable material’ does not include source material”.5

States Parties are required to establish and maintain a system of accounting for and control of all nuclear material subject to safeguards under the CSA.

States Parties are required to provide detailed baseline declarations on the numbers, locations, and technical data of nuclear material subject to safeguards, and on the design information of new and existing facilities.6 The initial reports allow the IAEA to establish a unified national inventory.

States Parties are required to subsequently submit routine data updates regarding inventory change reports, reflecting any adjustments to nuclear material, and physical inventory reports each time a material balance is taken.7 Any changes to nuclear facilities and inventories, including material unaccounted for (MUF) has tobe updated as well.

States Parties are also required to submit special reports in the event of any unusual incident or circumstance that could indicate the possibility of unauthorized removal or diversion.8

States Parties are also required to provide notifications about transferring nuclear material in and out of the State, including information on the quantity and composition of the nuclear material, the material balance area, the dates and locations of shipment, the approximate date of arrival, and the transfer of responsibility for the nuclear material.9

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.10

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.11 These inspections may also be of unannounced character.12

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.13

In addition, Safeguards visits are conducted at declared facilities at appropriate times during the lifecycle for verifying the safeguards relevant design information.14

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.15

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).16

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.17

Environmental sampling is also used in facilities and at locations where inspectors have access during inspections and design information verification,18 to detect undeclared nuclear activities or materials or concealment efforts by analyzing trace isotopes or particles in air, water, soil, or surfaces.

The NPT established a five-year Review Conference (RevCon) cycle, supported by annual Preparatory Committees (PrepComs) in the three years preceding each conference. The purpose is to assess the implementation of the Treaty’s provisions, review progress toward its objectives—particularly nuclear disarmament, non-proliferation, and the peaceful uses of nuclear energy—and to strengthen the Treaty’s effectiveness in light of evolving international security dynamics.

Regarding safeguards compliance, in practice, the IAEA Secretariat normally attempts to resolve anomalies and compliance concerns directly with the state in question. If necessary, concerns are referred to the IAEA Board of Governors. The Board makes a determination of non-compliance if appropriate and reports its findings to IAEA Member States, the United Nations Security Council (UNSC), and the United Nations General Assembly (UNGA). Furthermore, INFCIRC/153 provides a dispute settlement procedure creating an arbitral tribunal at the International Court of Justice, another avenue for dispute settlement.19