Tokyo (Platts)--25Mar2011/752 am EDT/1152 GMT

Japan's Nuclear and Industrial Safety Agency said Friday that the government now does not rule out the possibility that Tokyo Electric Power Company's Fukushima-1 No 3 reactor container may be damaged, after it detected higher radiation levels than normal inside the reactor building.

A NISA official said the government was looking at whether the No. 3 reactor container or pipelines inside the reactor building have been damaged after three workers were exposed to high radiation late Thursday.

NISA has measured the radiation inside the No. 3 building at 400 millisieverts/hour, the official said. Radiation detected in water inside the reactor building where the workers were exposed was measured at 10,000 times the usual level, he added.

"When we look at the composition of the water, the source of the water seems to be the reactor core," said the official. However, he added that "core reactor damage such as cracks has not been conclusively discovered."

He said it was also possible that the contaminated water could have come from the spent fuel storage pool.

On Thursday, at least two workers suffered radiation exposure while working in the basement of the building to connect power cables to restore the cooling system. A third may have been exposed and all three have been taken to the National Institute of Radiological Sciences for testing and treatment, he said.

The workers were exposed to about 170 millisieverts/hour of radiation, a Tepco official told public broadcaster NHK Thursday. Meanwhile, although work inside of the No. 3 reactor has been suspended, spraying and water injection operations have been conducted again at reactors No. 2, 3 and 4 using seawater.

Some preparations are underway, however, to start switching to freshwater to limit the corrosive effect of seawater on reactor equipment, and the US military is providing support.

"A US military ship is presently on its way to the plant full of [fresh] water that we will use as a backup," said Defense Minister Toshimi Kitazawa.

Also, the national government has started warning local governments in the areas surrounding the Fukushima-1 plant to prepare for a possible expansion of the evacuation zone.

An evacuation zone of a 20-km radius has been established around the stricken nuclear plant, while resident living between 20 km and 30 km of the plant have been advised to remain indoors.

Many people have already evacuated from the 20-30-km zone already, said Chief Cabinet Secretary Yukio Edano because "life in the community has become increasingly difficult."

He said it has become increasing difficult to deliver food and other goods to the area.

He added that local governments should start preparing in case radiation levels increase and evacuation from the larger area becomes necessary.

"There is no immediate likelihood that the plant will stop emitting radiation," he said.

Separately, Tepco told news agency AFP that it may take a month to achieve cold shutdown of the Fukushima-1 plant.

AFP also said NISA was considering raising the nuclear event level higher than the current 5 out of 7, which is the same level as the 1979 accident at Three Mile Island, Pennsylvania, in the US.

Japan's nuclear power regulator indicated Friday, said the AFP, that it may raise its assessment of the crisis at the nuclear plant to level six, or "serious accident."

An NISA official was quoted as saying: "We can't rule out the possibility of raising the disaster level to six. Depending on how the situation unfolds, it's still possible for the level to be raised." The Fukushima-1 plant's power and cooling systems were knocked out by the massive earthquake and tsunami which devastated northeastern Japan on March 11. That led to a series of fires and explosions that crippled the plant and resulted in radiation being emitted.

Elevated radiation levels have been detected in vegetables and milk produced in areas surrounding Fukushima-1, and radioactive substances have been detected in tap water as far away as Tokyo.

--Takeo Kumagai, takeo_kumagai@platts.com

--Christine Forster, christine_forster@platts.com

--Thomas Hogue, thomas_hogue@platts.com

Similar stories appear in Nucleonics Week. See more information at http://bit.ly/NucleonicsWeek