INES Scale

In case of an accident in a nuclear power plant or during the handling of radioactive material, the public must be informed clearly and promptly. For this purpose, the international nuclear and radiological event scale, INES, has been formulated. This scale was developed by the International Atomic Energy Agency (IAEA) and has been used since 1990 to assess nuclear power plant accidents. In 2006, this scale was extended to handle all radioactive sources. The INES scale has seven levels and is divided, like the Richter scale: each accident classified in the next level is 10 times more severe.

Levels 1—3 are called incidents, level 1 is also referred to as an anomaly, levels 4—7 are accidents. Events without any safety significance are called deviations from the operating limits and are classified below the scale and labeled 0.

The INES scale considers three areas of impact:

People and the environment

Evaluates if radioactive material has been released to the environment or if people were exposed to elevated radiation including the impacts.

Radiological barriers

Evaluates the breach of barriers and release of radioactive material in areas where it should not be present, but there is no impact on people or the environment.

Defense-in-depth

Exposure of shortcoming of the safety systems that were supposed to prevent the accident.

An accident is classified by the country where the accident occurred. If the actual circumstances of the accident are unknown or the danger is still present, a temporary classification is reported; it can be changed later to the final classification.

The INES scale is used for precise communication with the public about an accident, making sure that there is no misunderstanding, exaggeration or misrepresentation of the accident resulting in a possible panic.

 

INES scale pyramid (The International Nuclear and Radiological Event Scale).

INES scale pyramid (The International Nuclear and Radiological Event Scale).

General Description of INES Levels

INES Level People and Environment Radiological Barriers and Control Defence-in-Depth

Major Accident

LEVEL 7

Major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures.

 

 

Serious Accident

LEVEL 6

Significant release of radioactive material likely to require implementation of planned countermeasures.

 

 

Accident with Wider Consequences

LEVEL 5

Limited release of radioactive material likely to require implementation of some planned countermeasures.

Several deaths from radiation.

Severe damage to reactor core.

Release of large quantities of radioactive material within an installation with a high probability of significant public exposure. This could arise from a major criticality accident or fire.

 

Accident with Local Consequences

LEVEL 4

Minor release of radioactive material unlikely to result in implementation of planned countermeasures other than local food controls.

At least one death from radiation.

Fuel melt or damage to fuel resulting in more than 0.1% release of core inventory.

Release of significant quantities of radioactive material within an installation with a high probability of significant public exposure.

 

Serious Incident

LEVEL 3

Exposure in excess of ten times the statutory annual limit for workers.

Non-lethal deterministic health effect (e.g., burns) from radiation.

Exposure rates of more than 1 Sv/h in an operating area.

Severe contamination in an area not expected by design, with a low probability of significant public exposure.

Near accident at a nuclear power plant with no safety provisions remaining.

Lost or stolen highly radioactive sealed source.

Misdelivered highly radioactive sealed source without adequate procedures in place to handle it.

Incident

LEVEL 2

Exposure of a member of the public in excess of 10 mSv.

Exposure of a worker in excess of the statutory annual limits.

Radiation levels in an operating area of more than 50 mSv/h.

Significant contamination within the facility into an area not expected by design.

Significant failures in safety provisions but with no actual consequences.

Found highly radioactive sealed orphan source, device or transport package with safety provisions intact.

Inadequate packaging of a highly radioactive sealed source.

Anomaly

LEVEL 1

 

 

Overexposure of a member of the public in excess of statutory annual limits.

Minor problems with safety components with significant defence-in-depth remaining.

Low activity lost or stolen radioactive source, device or transport package.

 

detail