24 Mai 2014
May 23, 2014
Fukushima plant chief admitted mishandling of reactor cooling system
THE ASAHI SHIMBUN
A wrong instruction issued by the manager of the Fukushima No. 1 nuclear plant after an emergency cooling system failed possibly led to an early meltdown at the No. 1 reactor, documents show.
Before his death from cancer last year, Masao Yoshida told a government committee that he felt “regret” for making a “wrong presumption” in handling the critical situation in the wake of the Great East Japan Earthquake and tsunami.
According to a copy of Yoshida’s testimony, recently obtained by The Asahi Shimbun, a worker at the plant’s central control room noticed that the cooling system, an isolation condenser (IC) attached to the No. 1 reactor, was losing its functions on the evening of March 11, 2011.
Suspecting that the condenser was losing cooling water, the worker requested that Yoshida, who was in the emergency response center, take steps to refill the condenser with water using a light oil-powered pump.
The No. 1 reactor lost electric power at 3:37 p.m., about an hour after the magnitude-9.0 quake jolted the plant compound.
The isolation condenser serves as a last-ditch measure to cool the reactor when ordinary pumps cannot operate due to a lack of outside power supplies and emergency generators.
Placed above the reactor vessel, it cools steam from the pressure vessel, condenses it into water and returns water into the reactor.
Steam is cooled as it passes through piping in a water-filled tank, which needs to be refilled after water evaporates in the process.
But Yoshida was unaware of how the mechanism worked, because it was the first time that an isolation condenser was operated at the plant in 20 years.
Not realizing that the worker’s request meant the isolation condenser was losing functions, Yoshida only instructed workers to continue preparations to pour water into the reactor vessel--an order that should have been given when the emergency cooling system was functioning.
In its report, the Investigation Committee on the Accident at the Fukushima Nuclear Power Stations of Tokyo Electric Power Co. concluded that “at the time there was nobody present in the plant who had years of experience in IC operations, not even training or experience in IC inspections.”
In his testimony, Yoshida said he “knew almost nothing about how to control IC,” adding that the condenser is “a unique system.” The lack of knowledge about the condenser made it difficult for him to grasp meaning of the request from the central control room, he added.
The testimony also showed that while Yoshida was widely hailed by the media as the “man who saved Japan,” he had a number of regrets in his response to the nuclear crisis. As for his response to the isolation condenser on the No. 1 reactor, he admitted he had an “overwhelming sense of regret” for not realizing what was an “SOS” from frontline workers.
He also testified that there was no “suggestion” of any kind from the headquarters of TEPCO, the operator of the plant, as to how the plant workers should manage the isolation condenser.
If Yoshida had been aware of the condenser’s mechanism and realized it had become dysfunctional, he could have taken steps to prevent the early meltdown at the No. 1 reactor, such as venting to handle the rising pressure in the reactor vessel and restoring the functions of the isolation condenser.
Yoshida only realized that the isolation condenser was possibly not functioning after reports showed a rise in radiation levels inside the No. 1 reactor building at around 10 p.m. on March 11, 2011.
The government’s analysis estimates that the core of the No. 1 reactor became damaged at around 6 p.m., and the reactor went into meltdown two hours later.
(This article was compiled from reports by Hideaki Kimura and Kyoko Horiuchi.)