A leak of highly radioactive water at the crippled Fukushima nuclear power plant could be the beginning of a new disaster, Japan’s nuclear watchdog said.
The plant operator has built hundreds of steel tanks to store massive amounts of radioactive water coming from three melted reactors, as well as underground water running into reactor and turbine basements.
Tokyo Electric Power Co says about 300 tons of contaminated water leaked from one of the tanks, possibly through a seam.
The leak is the fifth, and the worst, since last year involving tanks of the same design at the wrecked Fukushima Dai-ichi plant, raising concerns that contaminated water could begin leaking from storage tanks one after another.
“That’s what we fear the most. We must remain alert. We should assume that what has happened once could happen again, and prepare for more,” Nuclear Regulation Authority Chairman Shunichi Tanaka said.
The watchdog also proposed at a weekly meeting on Wednesday to raise the rating of the seriousness of the leak to level three, a “serious incident,” from level one, “an anomaly”, on an International Nuclear and Radiological event scale from zero to seven.
The watchdog urged TEPCO to step up monitoring for leaks and take precautionary measures.
During the meeting, officials also revealed that plant workers apparently have overlooked several signs of leaks, suggesting that their twice-daily patrols were largely just a walk.
They have not monitored water levels inside tanks, obviously missed a puddle forming at the bottom of the tank earlier, and kept open a valve on an anti-leakage barrier around the tanks.
TEPCO said the leaked water is believed to have mostly seeped into the ground after escaping from the barrier around the tank. It acknowledged a possible leak to the sea.
The plant suffered multiple meltdowns following a massive earthquake and tsunami in 2011.