By Martin Fackler | NYT | Aug. 2, 2011

TOKYO — The operator of the Fukushima Daiichi nuclear plant said Monday that it measured the highest radiation levels within the plant since it was crippled by a devastating earthquake. However, it said the discovery would not slow continuing efforts to bring the plant’s damaged reactors under control.

The operator, Tokyo Electric Power, said that workers on Monday afternoon had found an area near Reactors No. 1 and 2, where radiation levels exceeded their measuring device’s maximum reading of 10 sieverts per hour — a fatal dose for humans.

The company said the reading was taken near a ventilation tower, suggesting that the contamination happened in the days immediately after the March 11 earthquake and tsunami, when workers desperately tried to release flammable hydrogen gas that was then building up inside the reactor buildings. The release, known as venting, failed to prevent crippling explosions that destroyed the reactor buildings.

The company said the workers who found the reading were safely protected by antiradiation clothing. Tokyo Electric said it has closed off an area of several yards around where the lethal radiation level was found. The company said this would not hamper efforts to build a new cooling system and remove contaminated water.

The plant has continued to spew radiation since the disaster, though levels have been dropping. The operator is working to install a new makeshift cooling system by early next year that will allow it to finally shut down the plant’s three damaged reactors.

That effort includes removing thousands of tons of highly contaminated water from the reactor buildings. On Monday, Tokyo Electric also said it will begin constructing a new wall that will extend some 60 feet underground to prevent radioactive groundwater from seeping into the nearby Pacific Ocean.