The Nuclear Regulation Authority proposed Wednesday raising the severity status of the recent radioactive water leak from a tank at Tokyo Electric Power Co.’s Fukushima No. 1 nuclear plant to level 3 from an earlier level 1 on the International Nuclear and Radiological Event Scale (INES).
The level 3 rating corresponds to a “serious accident” while the level 1 designation means an “anomaly,” according to the eight-level rating system.
The NRA said about 300 tons of highly radioactive water has leaked from tank No. 5 in the H4 area of the damaged plant. In total, it said, the nuclear materials released into the environment has been estimated at several thousand terabecquerels, converted into radioactive molybdenum 99.
“This is comparable to level 3, given the standards for the radiation barriers and management of a facility,” the NRA said in a document released Wednesday.
Raising the severity rating would be one of the most serious actions taken since the March 11, 2011, mega-quake and tsunami led to three reactor meltdowns.
The NRA will consult with the International Atomic Energy Agency to determine if its level assessment is appropriate since the leak occurred in the wake of the meltdown crisis, which has already been classified as level 7, or “major accident.”
INES ratings are usually applied after accidents at undamaged nuclear-related facilities.
NRA chief Shunichi Tanaka voiced deep worry Wednesday about the plant, which now has about 1,060 massive tanks containing highly radioactive water.
“I’m concerned most about how such tanks with high levels (of radioactive water) are increasing rapidly,” Tanaka said, adding that if large tsunami were to again hit, many of the tanks would be destroyed at once.
The water in the tanks had been used to cool the three melted reactors. Some of the tanks are temporary, including the leaking one. It is just sheet metal bolted together with its seams sealed.
Tanaka urged Tepco to quickly repair and resume operations of ALPS, the filtering equipment that can remove all radioactive materials except for tritium from tainted water at the facility.
“If (the tainted water) is processed with ALPS, risks would be greatly reduced,” Tanaka said.
Tepco initially planned to start full-fledged ALPS operations in mid-August but stopped tests of the system after finding corrosion holes on a tank. The operations are not expected to resume until December.
Also Wednesday, NRA members agreed to set up an expert panel to monitor marine conditions and effects on sea creatures, fish in particular, in waters near the wrecked plant.
The panel, which is scheduled to hold its first session Sept. 6, will provide “trustful and meaningful figures” to reduce “harmful rumors and misunderstandings,” NRA member Kayoko Nakamura said during a meeting.
Tepco has denied that water from the leaking tank No. 5 flowed directly into the Pacific Ocean. But separately, about 300 tons of radioactive groundwater is believed flowing into the ocean every day.
The groundwater is contaminated with radioactive tritium, which is believed to be about 1/1000 as harmful to humans as cesium-134 and -137, but remains a source of public concern given the massive amount of tainted water reaching the sea.
The Fisheries Agency regularly conducts sampling surveys on radioactive materials from fish caught along the coast. But the agency’s checks mainly focus on radioactive cesium and strontium, not tritium.
Fishermen have halted operations off Fukushima since the catastrophe started, except for sampling surveys of radioactive materials.
Sampling survey results up to August show no significant increase in fish containing radioactive cesium, with only some caught off Fukushima exceeding the government safety standard of 100 becquerels per kilogram.