The rating officially makes the accident a ‘major’ incident on the International Nuclear and Radiological Event Scale (INES).

The only other time this rating has been used was during the Chernobyl tragedy, however, estimates show the amount of radioactive material released into the atmosphere is approximately 10% of the 1986 accident.

The Japanese Nuclear and Industrial Safety Agency (NISA) issued a new provisional rating due to revised estimates of the amount of radioactivity released, and not because of fears over aftershocks from last month’s earthquakes.

A spokesman for NISA said: “The re-evaluation of the Fukushima Daiichi provisional INES rating resulted from an estimate of the total amount of radioactivity released to the environment from the nuclear plant.

“NISA may revise the INES rating at the Fukushima Daiichi nuclear power plant as further information becomes available.”

Originally, authorities in Japan in mid-March rated the core damage at the Fukushima Daiichi one, two and three reactor units caused by loss of all cooling function to have been at level 5 on the INES scale.

They further assessed that the loss of cooling and water supplying functions in the spent fuel pool of the unit four reactor to have been rated at level 3.

Luke Walsh

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