The IAEA and the OECD Nuclear Energy Agency (OECD/NEA) have published updated guidance for rating the safety significance of nuclear and radiological events and communicating them clearly to the public. The 2026 edition of INES: The International Nuclear and Radiological Event Scale User's Manual , which replaces the 2008 edition, reflects the latest experience and practices in effective communication on nuclear or radiological incidents.
About INES
Like the Richter scale for earthquakes, INES distils a complex event into a single number on a logarithmic scale. The INES scale was created in the aftermath of the 1986 accident at the Chornobyl nuclear power plant, when international experts convened by the IAEA and the OECD/NEA proposed a rating scale similar to those used for earthquakes and hurricanes. INES was introduced in 1990.
"INES provides a clear and consistent way to communicate the safety significance and associated radiation risk of nuclear and radiological events," said Simon Coenen, Senior Expert for Nuclear Safety at Belgium's Federal Agency for Nuclear Control and former Co-Chair of the INES Advisory Committee. "It supports a common understanding of the nature and severity of an event among technical experts, the media and the public. The scale applies to events at facilities and during activities involving sources of ionizing radiation, including the use of radioactive sources and the transport of radioactive material."
Participation in INES is voluntary. Currently, over 80 countries have a designated INES National Officer, who is responsible for communicating events occurring in their country to the IAEA.
How INES Rates Events
While the Richter magnitude measures the physical size of an earthquake from instrument readings, INES provides perspective on the safety significance of events. It rates them on a scale from Level 0 to Level 7, with Level 7 assigned to events with the highest safety significance. Events without safety significance are rated at Level 0. Events are rated by assessing their actual and potential consequences against defined criteria in three areas, with the highest level derived from these assessments determining the event level:
- the impact on people and the environment, such as received radiation doses and releases of radioactive material into the environment;
- the impact on radiological barriers and controls at facilities, such as damage to reactor fuel;
- the impact on defence in depth, meaning the measures put in place to prevent or cope with accidents.
The Chornobyl accident and the 2011 accident at the Fukushima Daiichi nuclear power plant were both rated at Level 7.
Where a country so decides, the rating of an event is shared with the IAEA through the Unified System for Information Exchange in Incidents and Emergencies (USIE). It is then published on the IAEA's publicly accessible Nuclear Events Web-based System (NEWS) .
Updates in the 2026 Edition
The 2026 edition of the INES Manual presents refined rating criteria and clarifies the scope of the scale and the responsibility for assigning ratings. It reflects lessons learned from past events, in particular the Fukushima Daiichi accident. It includes guidance on events involving multiple facilities or units at one site: where a single external event, such as an earthquake, leads to releases from several units, the total activity released from all units is considered in the rating.
The Manual distinguishes between provisional and final ratings and addresses the use of INES in evolving severe emergencies, prioritizing public communication ahead of the rating process.
"The value of INES depends on the consistent, harmonized and credible application of the scale across Member States," said Amgad Shokr, Director of the IAEA Incident and Emergency Centre. "The 2026 edition of the INES User's Manual provides Member States with updated guidance to support its consistent application. In addition, we are strengthening the INES National Officer network, enhancing training and guidance, and further developing the tools and platforms used for event rating and communication."
