Less than 12 hours after the quake-triggered tsunami hit the Fukushima Daiichi nuclear complex on March 11, 2011, Tokyo Electric Power Co. sought government approval for the unprecedented step of releasing radioactive steam from troubled reactors to reduce a dangerous buildup of pressure.
Prime Minister Naoto Kan, however, would soon become increasingly distrustful of TEPCO because of delays in starting the so-called venting operations, which were aimed at preventing damage to the reactor containment vessels.
"TEPCO said it wanted to do venting. So I told TEPCO to do it, but it didn't," Kan recalled. "I asked why, but there wasn't a reply. I thought things would go wrong if they kept going on like this."
Frustrated by TEPCO's response, the 64-year-old prime minister said in front of reporters early in the morning on March 12 that he planned to speak directly with the person responsible at the Fukushima Daiichi plant to find out exactly what was going on.
On his way to the plant on board a Self-Defense Forces helicopter, Kan bombarded Haruki Madarame, 62, a nuclear adviser to the government, with questions, such as what would happen if a reactor core melted and whether there could be an explosion.
Kan arrived at the plant shortly after 7 a.m. But he had no idea at the time that fuel was already melting in the No. 1 reactor.
"What is going on?" Kan heatedly asked plant chief Masao Yoshida, 56, at a meeting room of the emergency response office building.
Yoshida explained that the power to remotely operate valves for venting the No. 1 reactor had been lost and that workers would quickly need to manually operate the valves because of the rising radiation level inside the reactor building.
"We will do the venting. We will do it even if we have to form a suicide corps," Yoshida said.
For Kan, the 24-minute meeting with Yoshida helped reassure him to an extent.
Following Yoshida's order, at 9:04 a.m., the first batch of workers left the No. 1 reactor's main control room and headed to the No. 1 reactor building to make a valve, located outside the containment vessel, 25 percent open.
As the next team prepared for its job, 51-year-old Hideyoshi Endo, who joined the second team, recalled the words of a former operator he met about 25 years ago. The operator had told him how shift supervisors, who lead teams of reactor operators when they are on duty, should behave.
"A shift supervisor appears bossy, but he is the one who must first enter places where radiation levels are high when something happens," the operator had said.
Endo, now a supervisor himself, was taking a nap at home when the quake hit and had been due to start work at 9 p.m. that day. He walked 13 kilometers from his home to the plant that night to help. "Now is my time," he thought.
Wearing fire-proof clothing and carrying an air tank on his back, Endo hung a radiation meter from his neck capable of measuring up to 1,000 millisieverts per hour. His team had to open another valve by hand and return before the air in his tank, due to last 20 minutes, ran out.
When Endo's team was ready to go, the two workers in the first team returned to the main control room, having completed their job successfully. They had been exposed to up to 25 millisieverts of radiation.
Endo's team had to go to the bottom area of the reactor's containment vessel, where radiation levels were expected to be much higher.
At 9:24 a.m., the second team departed.
"I thought it was a battle against radiation as much as it was against time," Endo said.
Endo's team was tasked with three missions -- to open the valve, to measure the radiation level inside the reactor building, and to return safely.
After opening the door to the reactor's building, the reading on Endo's radiation measurement device jumped to 500 millisieverts per hour. As he lit up the inside of the building with a flashlight, he saw it was filled with what looked like steam or dust.
Endo and another member of the team then went downstairs to a room housing a doughnut-shaped suppression chamber at the bottom of the reactor's containment vessel. They heard a series of large bangs in the dark -- a type of noise Endo had never heard before. The radiation meter went back and forth between 900 and 1,000 millisieverts per hour.
"I thought we had to move ahead as long as we could see the number on the meter," Endo said.
When Endo was some 30 meters away from the valve, however, he saw the radiation meter reading surpass 1,000 millisieverts. He stared at the meter for a few seconds, but it had gone up all the way and did not come back down.
If the radiation level was 1,000 millisieverts per hour, Endo would have exceeded the 100-millisievert radiation dose limit a nuclear power plant worker is allowed to be exposed to in five years in just six minutes. But Endo no longer had a way of knowing how high the radiation level was.
Endo only needed a few seconds to decide to return. His colleague did not seem to understand the situation, but Endo pulled his arm and urged him to head back.
When Endo tried to leave the reactor building, he looked back and found that his colleague was not with him. His colleague caught up with him before long and Endo gestured to him to move faster as he was continuing to walk slowly. Endo could not blame him. He was shocked that he could not complete the valve operation, not to mention the fact that he was very tired.
When the two returned to the main control room, all eyes turned to them.
"It failed. The radiation meter scaled out," reported Endo. As Endo unloaded his air tank and took off his mask, he found that he was drenched with sweat all over. During the 8-minute journey, Endo was exposed to 89 millisieverts of radiation, while his colleague was exposed to 95 millisieverts.
Ikuo Izawa, 52, the head of the Nos. 1 and 2 reactor operators on duty at the time, told the two that they had to leave the control room because of their high exposure.
"I'm sorry that I couldn't help," Endo told Izawa. "It's okay. I really appreciate it," Izawa replied.
Endo thought about his fellow workers in the room as he walked away. "There were people in their 20s and 30s who had newborn babies," he recalled.
Working without knowing the radiation level is a frightening situation for workers. In June 2012, TEPCO found the radiation level near the No. 1 reactor's suppression chamber stood at up to 10,300 millisieverts per hour, a level highly likely to be fatal if a person stays there for an hour.
(Reported by Hideki Takahashi and Hisashi Ota)