Nuclear accidents worldwide rated by the INES scale 1957-2011

The nuclear accident that occurred in Fukushima in 2011 received a score of seven on the INES scale, and was thus rated as a major accident.

Nuclear events and the INES scale

In 1990, the International Atomic Energy Agency (IAEA) introduced the International Nuclear Event Scale (INES) to act as a tool for prompt communication with the public in case of a nuclear event. Its intention is to act as a standard guideline that can bridge understanding of the safety significance of these events between the technical community, the public, and the media. In fact, the INES scale can be implemented in any event that is associated with the use, storage, and transport of radioactive materials and sources, including loss or theft, and the discovery of virgin materials.

The INES scale is logarithmic, where each increasing level represents an accident that is ten times more severe than the previous rating. The disasters in Fukushima, Japan in 2011 and Chernobyl, Ukraine in 1986 received a 7 on the INES scale, the highest classification on the scale. Ratings between 4 and 7 are classified as accidents, with 4 representing an accident with local consequences and a 7 representing a major accident. A major accident represents a major release of radioactive material, indicating widespread health and environmental impacts. A lethal dose of radioactive radiation among humans is 7,000 millisievert. Chernobyl reactors still emit radiation that has been measured at 6,000 millisievert. The UN estimates that the average individual receives an annual average dose of about 2.4 millisievert.

After the Fukushima accident, an estimated 52 billion yen was paid to households that were victims of the event. Opposition to nuclear energy rose rapidly in Japan and South Korea after the event, reaching some 52 percent and 66 percent, respectively.