The operator of a troubled nuclear power plant in north-eastern Japan started to transfer highly radioactive water to a nearby storage vessel, news reports said on Wednesday.

A series of strong temblors on Monday and Tuesday caused a delay in the pumping operation, but Tokyo Electric Power Co, which runs the Fukushima Daiichi Nuclear Power Station, started at 7:30 pm (10:30 GMT) Tuesday to pump out of a reactor building, where the radiation-contaminated water has hindered workers’ efforts to contain the crisis.

Some 700 tons are to be moved into a condenser where, in normal operations, steam created from the reactor is cooled down. The pumping is expected to take 40 hours, Kyodo News reported.

The operations require considerable time as workers need to transfer some 60,000 tons of contaminated water, collected in the basements of the turbine buildings of reactors 1, 2 and 3, as well as the trenches linked to them.

The Japanese government decided Tuesday to raise the severity of the ongoing nuclear crisis from level 5 to level 7, the worst on the International Nuclear and Radiological Event Scale (INES).

While both the 1986 Chernobyl disaster and the Fukushima nuclear accident are now both rated at the highest level of the 7-step INES scale, the International Atomic Energy Agency (IAEA) said the Japanese accident is far less severe than the Soviet nuclear disaster.

Japan’s Jiji Press reported that Gregory Jaczko, chairman of the United States Nuclear Regulatory Commission, said the plant was not yet stable.

“We don’t see significant changes on a day-to-day basis with the reactors” of the Fukushima Daiichi plant, Jaczko told a hearing of the Senate Environment and Public Works Committee. “It is not yet, however, what we believe to be stable.” Referring to the fact that external power sources to water pumps at reactors were lost about 50 minutes after a strong quake on Monday, Jaczko said, “What we want to see is to move into a situation in which that kind of situation would be dealt with in a more predictable manner and with less possibility for the loss of the cooling system.” Jaczko warned that if the ability to cool the reactor cores is lost, Japan will have to face the possibility of “a further degradation in the fuel, which could lead to possibly a greater release (of radioactive substances) than what’s going on.”

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