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Masao Yoshida; directed Fukushima disaster efforts

Mr. Yoshida led the disaster response at Fukushima.

Associated Press/FIle 2011

Mr. Yoshida led the disaster response at Fukushima.

TOKYO — Masao Yoshida, a nuclear engineer who took charge of the Fukushima Dai’ichi power plant two years ago as multiple reactors spiraled out of control after a tsunami, but who ultimately failed to prevent the world’s worst nuclear disaster since Chernobyl, died here Tuesday. He was 58.

The cause was cancer, said the Fukushima plant’s operator, Tokyo Electric Power Company.

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Mr. Yoshida had been chief manager at Fukushima Dai’ichi for just nine months when a massive earthquake generated a tsunami that inundated the site March 11, 2011, knocking out vital cooling systems to the plant’s six reactors. Eventually hydrogen explosions and fuel meltdowns occurred at three reactors, releasing vast amounts of radioactive matter into the environment.

Although the company was widely criticized for its handling of the disaster, which forced more than 100,000 people from their homes, Mr. Yoshida won praise for his effort to minimize the damage.

He has been faulted, however, for failing to invest in adequate tsunami walls at the company’s nuclear power plants when he was head of nuclear facilities. Mr. Yoshida later apologized to reporters, saying he had been “too lax” in his assumptions of how big a tsunami could be.

Mr. Yoshida took a leave from Tokyo Electric in late 2011 after receiving a diagnosis of esophageal cancer. Experts have said his illness was not a result of radiation exposure from the accident. He leaves his wife, Yoko, and three sons.

When the tsunami hit, Mr. Yoshida took command from inside a fortified bunker at the plant. In video footage of the command room released by Tokyo Electric last year, Mr. Yoshida can be seen at times pushing his workers to hook up water hoses or procure fuel, at times tearfully apologizing to teams he sent out to check on the stricken reactors.

At one point, he ignores orders that he is told come from Prime Minister Naoto Kan to stop injecting seawater into one of the reactors, a last-ditch measure by plant workers to try to cool it. (Kan later denied that he had given such orders.)

Mr. Yoshida later offers to lead a “suicide mission” with other older officials to try pumping water into another reactor but is dissuaded. And as officials warn that core meltdowns have most likely started, he directs men to leave the reactors but stays put in the bunker. Mr. Yoshida later said that the thought of abandoning the plant never occurred to him.

Masao Yoshida was born on Feb. 17, 1955, in Osaka, Japan. He studied nuclear engineering at the Tokyo Institute of Technology and joined Tokyo Electric after graduate school.

He worked his way up through the company’s nuclear power division, overseeing its nuclear facilities from 2007 until being appointed chief of Fukushima Dai’ichi in June 2010.

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