International Nuclear and Radiological Event Scale

• What is INES?
• Who determines the INES rating?
• How does INES relate to emergency response?
• How does INES apply to emergency exercises?

What is INES?

The International Nuclear and Radiological Event Scale (INES) is a nuclear accident rating tool used by the International Atomic Energy Agency (IAEA), its Member States and the Government of Canada, to classify nuclear accidents.

A nuclear or radiological event, once it has unfolded, is classified by an INES level, where the highest rating is 7. The scale considers impacts on people and the environment, radiological barriers and controls, and the multiple layers of defence built into the design of nuclear reactors.

The scale is designed to classify the size of a radioactive release and its associated public dose. Impacts to people and the environment are measured through calculations of the amounts and type of radiological materials released.

Who determines the INES rating?

The Canadian Nuclear Safety Commission (CNSC) is responsible for assessing and providing provisional and final INES ratings to the IAEA. INES ratings are subject to change as a nuclear event unfolds. Provisional ratings are issued to the IAEA and its Member States once the nuclear event stabilizes to ensure consistent information is communicated within the international nuclear community.

Final INES ratings are issued once the event has ended and adequate information is available to finalize the rating.

How does INES relate to emergency response?

INES ratings are used internationally to record and classify nuclear and radiological events. An INES rating does not inform emergency response actions. The rating is not used by the Province of Ontario or New Brunswick, nor are licensees required by the CNSC to consider INES ratings as part of their emergency exercise planning.

How does INES apply to emergency exercises?

The CNSC requires nuclear power plants to conduct a full-scale emergency exercise every three years to test emergency response plans, decision-making functions, response capabilities and interoperability between organizations. The goal is to test the ability of the licensee, response agencies, and the municipal, provincial and federal government responders to mitigate the impact of a nuclear accident.

Exercises are designed to simulate a potential release. Depending on emergency response player action, the simulated accidents have the potential to result in a (simulated) high-consequence INES Level given the radioactivity available for release according to the scenario and assuming a progression of fuel damage.

The exercise design challenges emergency response plans within the Provinces of Ontario and New Brunswick, and their abilities to implement protective actions such as public sheltering and evacuation.

For more information, read the IAEA International Nuclear and Radiation Events Scale (INES) brochure (PDF)