The accident at the Fukushima-Daiichi nuclear power plant in Japan has been provisionally increased from Level 5 to Level 7 – a “major threat” – on the International Atomic Energy Agency’s International Nuclear Event and Radiological Scale (INES).
Level 7 is the most serious level on INES and is used to describe an event comprised of “a major release of radioactive material with widespread health and environmental effects requiring implementation of planned and extended countermeasures”.
This is only the second Level 7 accident in the nuclear industry. The first was at Chernobyl in 1986.
In a report to the IAEA, Japan’s Nuclear and Industrial Safety Agency (NISA) said the accident had been re-evaluated based on data showing the total amount of radioactivity released to the environment from the plant since it was hit by an earthquake and tsunami on 11 March 2011.
The report said figures show the total amount of iodine-131 discharged is estimated at 130 petabequerels (PBq) and caesium-137 at 6.1 PBq.
NISA said it estimates that the amount of radioactive material released to the atmosphere is approximately 10 percent of the Chernobyl accident.
NISA had initially rated the accident at Fukushima-Daiichi as Level 5, which means “accident with wider consequences”.
The new provisional Level 7 rating considers the accidents that occurred at units 1, 2 and 3 as a single event on INES.
Previously, separate INES Level 5 ratings had been applied for units 1, 2 and 3.
The provisional INES Level 3 rating assigned for unit 4 still applies.
>>Related reports in the NucNet database (available to subscribers)
Fukushima-Daiichi Events Provisionally Rated INES Level 5 (News in Brief No. 73, 18 March 2011)
Japan Update: Work Begins To Remove Contaminated Water (News in Brief No. 82, 27 March 2011)
Removing Contaminated Water Might Take Another Week, NISA Says (World Nuclear Review No. 14, 8 April 2011)
