Cherenkov radiation usually occurs in radioactive materials immersed in water. Nuclear materials, of which radioactive materials are a by-product, can be used for peaceful purposes (such as energy production), but also for nuclear weapons.
The IAEA’s mandate includes verifying that nuclear materials and facilities continue to be used for peaceful purposes. States report to the IAEA the location, quantity, chemical composition, physical form and use of their nuclear material under their safeguards agreements, and the IAEA verifies that the information provided by the State are complete and accurate.
Using specialized equipment, namely Next Generation Cherenkov Viewing Devices (XCVD) or Digital Cherenkov Viewing Devices (DCVD), which capture emitted light, nuclear safeguards inspectors can analyze nuclear material at nuclear facilities and other locations and compare this data to information reported by the state. For example, they can measure the Cherenkov radiation present in the ponds where spent fuel from nuclear reactors is stored and determine whether the amount of spent nuclear fuel reported is accurate or not. In this way, they can detect whether nuclear material from spent nuclear fuel has been diverted from peaceful use.