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TEPCO failed to predict hydrogen explosion

17 August 2011

The operator of the tsunami-hit Fukushima number one nuclear power plant failed to predict the hydrogen explosion that occurred on 12 March following the disaster. That is what sources involved in the investigation into the crisis have said.

The damaged number one reactor building, centre left, at the Fukushima number one Nuclear Power Plant is pictured on 12 March
The damaged number one reactor building, centre left, at the Fukushima number one Nuclear Power Plant is pictured on 12 March

"Nobody was able to predict the explosion," an employee at Tokyo Electric Power Co. (TEPCO) was quoted as telling members of the government's fact-finding panel on the Fukushima nuclear crisis.

Plant Manager Masao Yoshida said to the panel: "We made a serious mistake as we failed to grasp important information on the power station.”

The investigation has also revealed that TEPCO did not prepare an instruction manual on procedures for venting to protect reactors' containment vessels when external power sources are lost.

As part of its investigation into the crisis, the fact-finding panel has questioned Yoshida and other TEPCO employees as well as officials with government regulators. It will closely examine the answers as well as data on the accident in order to get to the bottom of the crisis.

The hydrogen explosion occurred at the plant's number one reactor on 12 March 2011, the day after the Great East Japan Earthquake and tsunami hit the plant. The blast blew off the upper part of the building housing the reactor.

Experts suspect that the hydrogen was generated after zirconium contained in fuel rods was heated and reacted with water.

TEPCO officials told the fact-finding panel that workers had never imagined that hydrogen would fill the reactor building and eventually explode because they were preoccupied with checking the conditions of the reactor and its containment vessel.

Because the plant had no instruction manual on venting, workers were forced to consider a procedure for venting by closely examining the blueprint of the reactor.

Since all the external power sources had been lost, workers at the plant procured batteries and other equipment to secure power sources. However, due to insufficient communications between workers on the types of devices that were needed, various machines were brought into the plant, forcing workers to take time to select usable devices from among them.

Furthermore, the panel has discovered that Yoshida and other top officials with the plant failed to notice the isolation condenser (IC), necessary to cool down the core of the number one reactor in case of emergency, had stopped working, and considered countermeasures on the assumption that the IC was functioning properly.

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