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.