Photo/Illutration This panoramic photograph released by Tokyo Electric Power Co. shows damage to the inner areas of the concrete pedestal that supports the pressure vessel inside the No. 1 reactor at its Fukushima No. 1 nuclear power plant. (Provided by the International Research Institute for Nuclear Decommissioning and Tokyo Electric Power Co.)

Damage to a pedestal inside the No. 1 reactor at the crippled Fukushima No. 1 nuclear power plant is more extensive than previously believed, forcing a more intensive look at its resistance to a major earthquake. 

Tokyo Electric Power Co. released a panoramic photograph of the area inside the reactor taken by a robotic probe in late March showing the damage. 

The investigation found that the metal framework has been exposed along the inner side of the pedestal’s wall for about 1 meter from its bottom and for the entire inner circumference, the company said.

TEPCO had previously said that its videos showed the metal framework was exposed for only half of the inner circumference.

However, company officials found it was exposed for the entire inner circumference after analyzing the footage.

The officials combined photos taken in the investigation together to create the panoramic image showing the extent of the damage.

An 8.5-meter-tall cylindrical pedestal made of concrete supports the reactor’s 440-ton pressure vessel. Its external diameter is 7.4 meters.

The lower portion of the pedestal wall is around 1.2 meters thick, according to TEPCO.

The company is not sure how much of the lower portion of the wall is damaged.

However, because the investigation found an iron board that is in the middle of the wall partly exposed, TEPCO assumes the wall might have lost concrete that is 0.6 meter thick, or half of the 1.2 meters.

The company will re-evaluate the pedestal’s ability to withstand an earthquake based on this assumption.

At a meeting of the Nuclear Regulation Authority on April 14, a TEPCO official said that the plant “has experienced strong earthquakes,” such as the one in March last year that registered up to an upper 6 on the Japanese seismic intensity scale of 7 and whose epicenter was off the coast of Fukushima Prefecture, when speaking about the pedestal’s ability to withstand an earthquake.

“It is a fact that the pedestal’s ability to support (the nuclear reactor) has been maintained,” the official said.

Still, the company can’t deny the possibility that the pressure vessel would tilt or sink in the event of a major tremor, the official said.

However, TEPCO believes such an occurrence would only have a limited impact on the plant and none on the outside world, the official said.

An NRA’s secretariat official said at the meeting that TEPCO has not provided a detailed basis for believing that any impact would be minimal.

The official demanded that TEPCO report detailed results of its analysis.

The Fukushima plant went into triple meltdown after the Great East Japan Earthquake and tsunami struck in March 2011, causing nuclear fuel to melt through the bottom of the pressure vessel.

It is believed the concrete of the pedestal has melted after coming into contact with molten fuel debris.

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