The Nuclear Regulation Authority said Wednesday it has raised the severity assessment of a recent radioactive water leak incident at the Fukushima No. 1 power plant to level 3 on an international scale.
The NRA decided to rate the incident two notches higher than its initial assessment after Tokyo Electric Power Co. said an estimated 300 tons of highly radioactive water escaped from one of the huge steel tanks there, making it the worst leak yet involving the containers.
Level 3 on the International Nuclear and Radiological Event Scale is defined as a “serious incident.”
The overall Fukushima nuclear crisis has been rated at the maximum level of 7, on par with the 1986 Chernobyl disaster.
Based on data provided by Tepco, regulators have said the amount of the leaked radioactive substances totaled several thousand terabecquerels when converted into radioactive molybdenum 99.
The NRA has been consulting with the International Atomic Energy Agency on whether it is appropriate to apply the so-called INES scale to the facilities as they were built as an emergency response to a nuclear crisis, and that crisis already rates a level 7.
The international group said the INES is applicable but noted that frequent changes of rating will not help to communicate the actual situation in a clear manner, according to the IAEA answer sheet provided by the NRA.
The IAEA has urged Japan to explain more clearly what is happening at Fukushima and avoid sending “confusing messages” about the disaster, the NRA said.
Last week’s spill was “the most recent of a number of events that involved leakage of contaminated water,” the IAEA said in a document submitted to the NRA.
“Previous similar events were not rated on the INES scale. The Japanese (authorities) may wish to prepare an explanation for the media and the public on why they want to rate this event, while previous similar events have not been rated.”
NRA Chairman Shunichi Tanaka said during a meeting of other commissioners that the NRA should not be too quick to evaluate the problems at the Fukushima plant hereafter and should consider ways to efficiently disseminate information on what is happening and how the problems could affect the environment.