Japan finds evidence that Fukushima Daiichi may have been caused by human error

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Tokyo Electric Power Company (TEPCO), operator of the stricken Fukushima nuclear plant, has claimed that it had “taken various measures to prevent nuclear disaster” and that the tsunami that hit the plant following the Great East Japan Earthquake on March 11 “far exceeded predictions.”

However, a government committee investigating the nuclear crisis has found that the utility had been ill-prepared, even pointing to evidence that the ongoing disaster may have been caused by human error.

The committee’s findings suggest that a lack of disaster readiness led to confusion in the chain of command, and ultimately a failure to take the best course of action.

Masao Yoshida, the former chief of the damaged Fukushima No. 1 nuclear plant, had supervised emergency efforts immediately after the crisis began without knowing that the isolation condenser of the No. 1 reactor had shut down.

According to the committee’s most recent findings, workers on site had shut down the No. 3 reactor’s high-pressure coolant injection (HPCI) system on March 13  — which was the final chance at cooling the reactor — without authorization from higher ups, and found later that they could not restart the system. The reactor suffered a hydrogen explosion the following day.

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The HPCI system is a type of emergency core cooling system (ECCS) that is activated when reactor water levels dip unusually low, injecting water into the reactor. It utilizes the steam given off by a reactor’s residual heat to run a turbine-driven pump, vigorously pushing water from the top of the reactor to the reactor core, where nuclear fuel is located. Its biggest advantage is that it can operate on batteries in the case of a power outage.

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According to the committee’s most recent findings, engineers operating the Fukushima No. 1 plant had stopped the high-pressure coolant injection (HPCI) system of the No. 3 reactor

This comes on the heels of revelations that Masao Yoshida, then chief of the plant, had overseen emergency efforts under the assumption that the isolation condenser (IC) of the No. 1 reactor was still running when it actually wasn’t.

The main issue here is that TEPCO was not adequately prepared for such a crisis, forcing engineers to take such action based on their own judgment.

A coolant injection system meant to serve as a last defense against an explosion at the Fukushima No. 1 nuclear plant’s No. 3 reactor had been disabled at the discretion of workers on site, suggesting that a possible breakdown in the chain of command led to the severity of the ongoing nuclear crisis.

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Source: Mainichi

Source: Mainichi 

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