Fukushima Update & Explanation of International Atomic Energy Agency INES Scale

The IAEA is reporting that INES ratings have been issued for some of the events relating to the nuclear emergency at the Fukushima Daiichi and Daini nuclear power plants.

Japanese authorities have assessed that the core damage at the Fukushima Daiichi 2 and 3 reactor units caused by loss of all cooling function has been rated as 5 on the INES scale. The loss of cooling and water supplying functions in the spent fuel pool of the unit 4 reactor has been rated as 3.

The loss of cooling functions in the reactor units 1, 2 and 4 of the Fukushima Daini nuclear power plant has also been rated as 3. All reactor units at Fukushima Daini nuclear power plant are now in a cold shut down condition.

INES Scale- INES, to facilitate understanding, uses a numerical rating to explain the significance of nuclear or radiological events. This is just like using ratings for earthquakes or temperature, which would be difficult to understand without the Richter or Celsius scales. INES applies to any event associated with the transport, storage and use of radioactive material and radiation sources. Such events can include industrial and medical uses of radiation sources, operations at nuclear facilities, or the transport of radioactive material.

Events are classified at seven levels: Levels 1–3 are “incidents” and Levels 4–7 “accidents”. These levels consider three areas of impact: people and the environment, radiological barriers and control, and defence in depth. The scale is designed so that the severity of an event is about ten times greater for each increase in level on the scale. Events without safety significance are called “deviations” and are classified Below Scale/Level 0.