The accidents at Three Mile Island and Chernobyl highlighted the difficulties the nuclear energy sector has in communicating with the press and the public at large. Nuclear specialists have seen the need to come up with an information tool they can use in the event of a nuclear incident or accident. The INES scale was devised to fill that need.
The International Nuclear Event Scale (INES) is based on the same principle as the Richter scale used to measure the strength of earthquakes. The INES consists of seven levels distributed over two categories. The lower levels (1 to 3) concern incidents and the higher levels (4 to 7) indicate accidents. Incidents and accidents are evaluated using three safety attributes: consequences for the population and the environment (off-site impact), consequences on the site and, thirdly, defence in depth degradation. Only those events that have an impact, even a potential one, on the nuclear safety of facilities, are included in this scale. By way of example, Three Mile Island was categorized at level 5 and Chernobyl at level 7 on the INES scale.
It should be noted that the INES scale is used exclusively as a communication tool and that the number of INES incidents must not be used on its own to assess the safety of a nuclear facility.
