21 Aug (NucNet): The Japan Nuclear Regulatory Authority (NRA) has revised its rating of the leak of radioactive water from a tank at Fukushima-Daiichi nuclear plant from a Level 1 to a Level 3 on the International Nuclear Event Scale (INES).
The revision took place at a meeting of the NRA’s Regulatory Commission earlier today.
The NRA said it decided to revise the rating of the event due to new information being reported by the plant operator, the Tokyo Electric Power Company (Tepco).
The NRA said it was specifically concerned about the reported high level of beta radioactivity of the leaked water – 80 million becquerels per litre – and the total amount of contaminated water (300 cubic metres), which correspond to the INES level 3 criteria.
The NRA also said that the incident occurred in an area where it was not expected in the design of the installation and therefore sufficient defence in depth is not ensured.
Considering the potential impact, NRA concludes that a level-3 classification (‘serious incident’) is justified for this criterion as well.
The event was first reported on 19 August when water was discovered inside as well as outside the dike surrounding a water tank used for storing contaminated water at Fukushima-Daiichi nuclear plant.
Tepco said today that it has collected the rest of the water from the tank and the dike in a temporary vessel and has started to transfer it to another water tank in the vicinity. No further leaks have been detected.
Tepco also said it has measured the radioactivity of the seawater at a nearby sampling location. The result shows a level of caesium-134 and -137 as well as total beta radioactivity below the detection limit.
This is the first time Japan has declared an event on the INES scale since the March 2011 earthquake and tsunami.
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To contact the editor responsible for this story: Lubomir Mitev at lubomir.mitev@nucnet.org
