Remembering Masao Yoshida, Nuclear Engineer, Fukushima Plant Chief

Masao Yoshida, a nuclear engineer who served as plant chief during the March 11, 2011, catastrophe at Tokyo Electric Power Co.’s (TEPCO’s) Fukushima Daiichi nuclear plant, died on Tuesday from esophageal cancer. He was 58.

"The situation went way beyond any severe accident that I had considered until then, and for an instant I had no idea what to do," Yoshida said, as documented in a December 2011 interim government report, about his thoughts after realizing the massive 42-foot-high tsunami that followed the 9.0-magnitude Great Tohoku earthquake had inundated the plant’s power sources. "I was overwhelmed from the information that kept coming in continuously, and I had lost the luxury of making a comprehensive judgment about related important information," he was quoted as saying.

Video footage (in Japanese) released by TEPCO last August of the fortified emergency command bunker from which Yoshida and a small group of staff known as the Fukushima 50 monitored the plant at the height of the crisis shows the distressed plant chief instructing workers to prepare for venting to reduce the pressure in the containment vessel at Unit 1 just after midnight on March 12, after realizing core cooling equipment at the unit was not working. Unit 1 suffered a hydrogen explosion (see accident timeline here) later that day.

The clip also records the instants after a more violent explosion—one which was heard 40 miles away and injured six workers—rattled Unit 3 on March 14,with Yoshida yelling amidst ensuing panic, "Headquarters, headquarters! We have a big problem!" his voice cracking as he reports the time: 11.01 a.m. JST. Just hours later, at about 5 p.m., under tremendous time pressure after reports that workers were struggling to connect vent lines to Unit 2—which was dangerously overheating—Yoshida is seen juggling demands from TEPCO, the prime minister’s office, and a number of experts including from the Nuclear Safety Commission. An anonymous voice from TEPCO’s head office remarks, "It’s such a waste to inject seawater into Reactor 2 because it corrodes the reactor. Can you inject fresh water to the limit?" Yoshida says impatiently, in his characteristic booming voice: “You want to reuse the reactor but it would be too late if we use freshwater. Fresh water is not an option. Now we need plenty supply of coolant water. We have to take seawater.” Yoshida was later reportedly reprimanded for disobeying orders but then praised for his judgment.

Of the three days following the devastating tsunami, after four of the plant’s six units saw hydrogen explosions and core meltdowns, Yoshida reportedly recalled: "There were several instances when I thought we were all going to die here. I feared the plant was getting out of control and we would be finished." The footage captures his desperation: At one point, he raises a suicide squad comprised of himself and other elderly workers to restore cooling if the situation worsens, only to be dissuaded from carrying out the death mission.

Despite being pushed to their physical limits, Yoshida said in later interviews that his subordinates and other workers continued toil at the accident sites, often returning ashen-faced as they reported the gravity of the situation. At an August symposium on the Fukushima accident, Yoshida likened workers to Buddhist saints, thanking them for their frantic efforts to bring the crisis under control.

On Tuesday, TEPCO President Naomi Hirose said Yoshida "led workers to take action against the accident, literally prepared to give his life." Following Yoshida’s esophageal cancer diagnosis at the end of 2011—reportedly unrelated to his duties—the former plant chief was forced to "dedicate himself to battling his disease," Hirose said.

Born in Osaka, Japan, on Feb. 17, 1955, Yoshida studied nuclear engineering at the Tokyo Institute of Technology and joined TEPCO after graduate school. He oversaw the utility’s nuclear facilities from 2007 until being appointed head of the six-reactor Fukushima Daiichi plant in June 2010. He led the disaster response for eight months before going on sick leave.

"He had directly expressed to me his strong desire to dedicate himself to the restoration of Fukushima with us. I was looking forward to the day when I would see him leading the way with his energetic, booming voice. I am filled with deep regret that we are no longer able to work together towards the rebirth of TEPCO," Hirose said.

Sources: POWERnews, POWER, TEPCO

—Sonal Patel, Senior Writer (@POWERmagazine, @sonalcpatel)