Fukushima alert level may be raised
on 21/08/2013 16:40:08
The operator of the plant said about 300 tons of contaminated water has leaked from one of hundreds of steel tanks around the wrecked Fukushima Dai-ichi plant. Tokyo Electric Power has not worked out how or where the water leaked, but suspects it did so through a seam on the tank.
The leak, the fifth since last year involving tanks of the same design, also raised concerns that this could be the beginning a new disaster - contaminated water 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," watchdog chairman Shunichi Tanaka said. "We are in a situation where there is no time to waste."
The watchdog proposed to raise the rating of the leak to level 3 from an earlier level 1 on an International Nuclear and Radiological event scale of eight. However it plans to consult the UN nuclear agency over whether it is appropriate to use the evaluation scale on the already wrecked Fukushima plant.
The watchdog urged TEPCO to step up monitoring for leaks and take precautionary measures.
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 initially said the leaked water is believed to have mostly seeped into the ground after escaping from the barrier around the tank. It initially said the leak did not pose an immediate threat to the sea because of its distance - about 500 yards from the coastline.But it later reversed that view and acknowledged a possible leak to the sea after detecting high radioactivity inside a gutter extending to the ocean.
The company also said the tank may have been leaking slowly for weeks through a possible flaw on its bottom. That could create extensive soil contamination and a blow to plans to release untainted underground water into the sea as part of efforts to reduce the amount of radioactive water.
Four other tanks of the same design have had similar leaks since last year. The incidents have shaken confidence in the reliability of hundreds of tanks that are crucial for storing water that has been funneled into the broken reactors to keep melted radioactive fuel cool.
The plant suffered multiple meltdowns following a massive earthquake and tsunami in March 2011 - a level 7 "major accident," the highest on the INES rating and the worst since Chernobyl in 1986.
About 350 of some 1,000 steel tanks built across the plant complex containing nearly 300,000 tons of partially treated contaminated water are less-durable ones with rubber seams.
TEPCO says the tanks that have leaked use rubber seams that were intended to last about five years.
Contaminated water that TEPCO has been unable to contain continues to enter the Pacific Ocean at a rate of hundreds of tons per day. Much of that is ground water that has mixed with untreated radioactive water at the plant.