Masao Yoshida – whose actions as manager of the Fukushima Daiichi power plant during its triple meltdown averted an even greater disaster – has died. 
 
 Yoshida, 58, took early retirement from the plant's operator, Tepco, in late 2011 after being diagnosed with oesophageal cancer. He died in a Tokyo hospital on Tuesday, reports said. 
 
 Tepco and Yoshida, a heavy smoker, said the cancer was not related to the nuclear accident caused by the March 2011 tsunami that hit Japan. 
 
 Although Tepco has been widely criticised for its handling of the accident, Yoshida's courage and refusal to follow orders from the firm's headquarters after the plant was struck by a 42-foot tsunami on the afternoon on 11 March 2011 have been credited with preventing a catastrophic release of radiation that could have forced the evacuation of Tokyo. 
 
 The 58-year-old stayed on at the plant to direct the perilous operation to cool its crippled reactors amid frequent aftershocks and hydrogen explosions inside reactor buildings. 
 
 He will be remembered most of all for defying an order from senior Tepco officials in Tokyo to stop pumping seawater into one of the damaged reactors in a frantic effort to keep it cool. Tepco officials were concerned that pumping seawater into the reactors would render them commercially useless. 
 
 His death will deprive experts of an important source of information for future investigations into the accident. More than two years after the triple meltdown radiation levels in key areas of Fukushima Daiichi are still far too high for on-site inspections. 
 
 Workers at the plant are also struggling to treat huge amounts of contaminated water used to cool melted fuel deep inside three of the plant's six reactors. 
 
 This week Tepco said it had detected a dramatic spike in radioactive caesium levels in groundwater in an area of the plant close to the sea. 
 
 The discovery is another blow to efforts to clean up the site; the operation to remove melted fuel from the reactors and decommission the facility is expected to take about 40 years. 
 
 Tepco officials said they had found levels of caesium-134, which has a half life of about two years, at 9,000 becquerels per litre inside a well on Tuesday – about 90 times higher than levels three days earlier and 150 times higher than Japan's safety standard. 
 
 The company said it had yet to determine the cause of the radiation spike. 
 
 The tsunami killed more than 18,000 people along Japan's north-east coast and forced the evacuation of 150,000 residents from villages and towns close to the Fukushima Daiichi plant. 
 
 Yoshida, who had been manager of the plant for just nine months when the tsunami knocked out its regular and emergency power supplies, was reprimanded but later hailed as a hero as it became clear that his actions had saved the plant from a nuclear fission chain reaction – a potentially far more devastating scenario than a fuel meltdown. 
 
 "I bow deeply out of respect for his leadership and decisiveness," the prime minister of the time, Naoto Kan, wrote on Twitter after Yoshida's death was reported. "I wish I had had the chance to talk to him at length about the nuclear disaster once again." 
 
 Video footage from the earthquake-proof bunker from which Yoshida directed the mission to save the plant shows him occasionally apologising to colleagues for sending them out to connect water supplies to dangerously overheating reactors. 
 
 He is later persuaded to abandon a "suicide" mission, which he offered to lead, to cool another reactor. 
 
 Despite his largely calm demeanour at the time, Yoshida would later admit that he feared he and his colleagues would perish inside the plant. "During the first week of the accident I thought several times that we were all going to die," he told journalists shortly before he retired. 
 
 Yoshida insisted he had never once considered a total withdrawal from the plant, a prospect that brought him into conflict Kan, who had warned Tepco bosses that a total evacuation of the plant would spell the end of the utility. 
 
 The company's president, Naomi Hirose, paid tribute to Yoshida's contribution and his ability to encourage the other engineers and emergency workers – nicknamed the Fukushima 50 – who braved high levels of radiation in the early days of the crisis. 
 
 "We deeply appreciate his contribution and the way he handled the accident," Hirose said in a statement. "He literally put his life at risk in dealing with the accident. 
 
 "We keep his wishes in our hearts and will do the utmost to rebuild Fukushima, which he tried to save at all costs." 

 TOKYO â€” Masao Yoshida, a nuclear engineer who took charge of the Fukushima Daiichi power plant two years ago as multiple reactors spiraled out of control after a tsunami, but who ultimately failed to prevent the worldâ€™s worst nuclear disaster since Chernobyl, died here on Tuesday. He was 58. 
 
 The cause was cancer, said the Fukushima plantâ€™s operator, Tokyo Electric Power. 
 
 Mr. Yoshida had been chief manager at Fukushima Daiichi for just nine months when a 42-foot tsunami inundated the site on March 11, 2011, knocking out vital cooling systems to the plantâ€™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 companyâ€™s nuclear power plants when he was head of nuclear facilities. Mr. Yoshida later apologized to reporters, saying he had been â€œtoo laxâ€? in his assumptions of how big a tsunami might hit the coastal plant. 
 
 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, given how quickly it came on. 
 
 Survivors include 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 an order that he is told comes directly from Prime Minister Naoto Kan to stop injecting seawater into one of the reactors, a last-ditch measure taken by plant workers to try to cool it. (Mr. Kan later denied that he had given such an order, and suggested that Tokyo Electric officials had probably misunderstood.) 
 
 He later offers to lead a â€œsuicide missionâ€? 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. 
 
 â€œI fear we are in acute danger,â€? Mr. Yoshida is heard saying in the video shortly after yet another blast rocks the command room. â€œBut letâ€™s calm down a little. Letâ€™s all take a deep breath. Inhale, exhale.â€? 
 
 Masao Yoshida was born on Feb. 17, 1955, in Osaka, Japan, to a family that ran a small advertising firm. An only child, he spent much of his middle and high school years practicing the Japanese martial art kendo. He went on to study nuclear engineering at the Tokyo Institute of Technology and joined Tokyo Electric after graduate school. 
 
 He worked his way up through the companyâ€™s nuclear power division, overseeing its nuclear plants from 2007 until being appointed chief of Fukushima Daiichi in June 2010. The tsunami that struck the plant was the largest in recent memory. He led the disaster response for eight months before going on sick leave. 
 
 On his last day at Fukushima Daiichi in December 2011, according to a book on Mr. Yoshida by Kadota Ryusho, he again rallied his troops. 
 
 â€œYou still have a difficult road ahead, but I know you will overcome,â€? Mr. Yoshida is quoted as saying. â€œI promise to do my best to return.â€?
– The Fukushima nuclear plant manager hailed as a hero for defying orders and putting public safety ahead of the company's bottom line has died of cancer at the age of 58. Masao Yoshida stayed at the plant to try to stabilize it after the March 2011 quake and tsunami and prevented Japan's worst nuclear disaster from getting even worse by ignoring orders to cease pumping seawater into a damaged reactor at the plant he managed, the Guardian reports. Company officials didn't want to render the reactor unusable, but if Yoshida had obeyed orders, it could have resulted in a chain reaction causing a radiation leak big enough to force the evacuation of Tokyo. In video footage of the plant's command room after the tsunami struck, Yoshida is seen offering to lead a "suicide mission" to cool another reactor, reports the New York Times, which notes that Yoshida apologized after the disaster for failing to invest in adequate tsunami walls. He retired in 2011 after being diagnosed with esophageal cancer, which was not believed to be the result of radiation exposure: He was a heavy smoker and the disease would normally take between five and 10 years to develop if it was the result of radiation.