IRSN, Institut de radioprotection et de sûreté nucléaire

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Enhancing Nuclear Safety


3- Inspection of nuclear materials

Nuclear materials are materials that could be used to manufacture a nuclear explosive device. Their definition is based on their fissile (for a fission device), fusible (for a thermonuclear bomb) or fertile (ability to produce fissile or fusible materials) characteristics. Accordingly, these materials are subject to extremely rigorous checks at both international level (for fissile or fertile materials) and national level.

The risks of proliferation are picked up firstly at the state level, but secondly at international level. In the case of nuclear power, the IAEA is responsible for verifying that countries that have pledged not to develop nuclear weapons are honouring their commitments.

For states with nuclear weapons, the audits focus on the civil nuclear industry, which is subject to the same constraints as for other countries. This is the case for France, which submits its nuclear material to IAEA and EURATOM inspections.

At international level

International inspections are intended to detect any possible violation of commitments made by a state to only use nuclear materials for peaceful purposes. Signing up to a treaty or convention on non-proliferation, and to its corresponding system of verification, is always a voluntary act undertaken by a sovereign state. The underlying motivation behind becoming a signatory may lie in a desire for greater international security or in order to take advantage of international measures for assistance and technical cooperation provided to states ratifying such treaties. It may also be the result of pressure such as trade or diplomatic sanctions taken against those states that refuse to sign such treaties.

At an international level, inspections are carried out by the IAEA and EURATOM. These inspections involve both the declaration and monitoring of the movement of nuclear materials (plutonium, uranium and thorium) between countries and declarations regarding the flow and socks of materials held at a national level which do not relate to materials concerned with national security. International inspections also involve inspections of French facilities by EURATOM inspectors and to a lesser extent by the IAEA.

At national level

At a national level, protection and inspection of nuclear materials is subject to specific regulations which fall under the Code of Defence and associated regulatory documentation. Given the importance of its nuclear industry and aware of its responsibilities regarding non-proliferation, France has adopted some of the most comprehensive regulations and organization in the world, covering both civil nuclear materials as well as those relevant for national security.

There are six materials covered by French legislation: plutonium, uranium, thorium, tritium, deuterium and lithium 6 (deuterium and lithium 6 are not radioactive). Their definition is subject to periodic reviews based on the advancement of knowledge and techniques.

Classification of nuclear materials for national inspection purposes

Declaration threshold

Licensing threshold

Uranium 233

Uranium enriched by more than 20%

Uranium enriched by less than 20%

Natural/depleted uranium



Lithium 6

1 gram

1 gram

1 gram

1 kilogram

1 kilogram

0.01 gram

1 gram

3 gram

15 gram

250 gram

500 kilogram

200 kilogram

2 gram

1 kilogram


This regulation aims to prevent the loss, theft or diversion of nuclear materials and to protect these materials and related facilities or transport against malicious activities.

In this context, the regulations require operators and industrial facilities holding these materials to comply with a number of provisions that complement each other, such as:

  • physical protection measures to protect the materials against malicious action or sabotage by placing barriers and other devices between publicly accessible areas and the premises holding the materials
  • monitoring of the materials such that the location and use of the materials is known at all times
  • accounting measures such that the exact quantity of the materials is known at all times [2]. Each operator must keep their own accounts, which is regularly compared to centralized accounts held by the IRSN. For plutonium, such accounts shall be kept to the nearest gram
  • containment measures to prevent unauthorised movement of materials
  • surveillance measures which aim to ensure the integrity of containment and to verify that no material has been released illegally.

Possession of plutonium by an operator requires prior authorisation by the relevant authorities, which in France is the Senior Defence and Security Official (HFDS) of the Ministry for Energy. This authorisation is issued only after analysis of a file provided by the operator detailing physical protection, monitoring, accounting... This analysis is performed by the IRSN, which is authorised to act on behalf of the ministry.

The granting of authorisation for the most sensitive nuclear materials, such as plutonium, requires the operator to undertake a safety study in order to assess the effectiveness and relevance of the protection against key threats defined by the government. These threats include both an internal threat to the facility (from a malicious member of staff) and the threat of a group of heavily armed assailants seeking to enter the facility. The threats are reviewed periodically by specialised state agencies to reflect the changing national and international situation.

The regulations also require operators to conduct periodic inventories of all the materials they hold in order to detect possible discrepancies between the physical reality on the ground and the inventories of stock held. The authorities can then require the operator to produce a crisis inventory to confirm or deny information or any suspicion of theft of material. For this purpose, exercises to produce crisis inventories are regularly conducted by the operators concerned, the IRSN and the competent authorities.

Technical methods of inspection

  • Inspection measures : Most inspections concern organizational, administrative or regulatory aspects. The physical follow-up of nuclear materials is checked by means of ‘reinforced’ inspections including physical measurements. These inspections may concern any phase within the fuel cycle. Inspectors take measurements (of the volume and quality of materials) to produce results that can be compared with those obtained by operators, thereby checking the quality of facility measuring systems and the accuracy of results used for monitoring purposes. Inspectors must ensure that their measurement results are relevant in order to be credible with regards to authorities and operators.
    The measurement methods used by inspectors are based on conventional non-destructive measurement methods (gamma spectrometry, neutron measurement) adapted to the specific constraints imposed by the inspection context. First of all, the measuring devices used must be transportable. If the premises where the measurements are made are not adequate or barely so, this may affect the quality of results: the measurement area is often the storage area itself, or a nearby room.
  • "Containment monitoring" of nuclear materials : "Containment" refers to all measures taken to prevent unauthorised or unjustified movement of nuclear materials, and "monitoring" to all those actions that ensure complete containment, confirm no abnormal release, no falsification and correct operation of the equipment used.
    Initially, inspection bodies analyse records of operators describing the systems in place in their facilities. The devices most commonly used include video cameras, nuclear sensors (gamma or neutron), seals, movement sensors (radar, infrared sensor) and also door opening detectors. They then check during inspections, that the expected materials have been properly positioned, are working correctly and have not been fraudulently used.

2 More information on the protection and inspection of nuclear materials in France : see our specific documentation.

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