FUKUSHIMA, Japan (AP) — Emergency workers racing to cool dangerously overheated nuclear fuel scrambled Saturday to connect Japan's crippled reactors to a new power line, as a safety official suggested faulty planning at the complex helped trigger the crisis.
Backup power systems at the Fukushima Dai-ichi plant had been improperly protected, said Hidehiko Nishiyama of Japan's Nuclear and Industrial Safety Agency, leaving them vulnerable to the tsunami that savaged the northeastern coast on March 11 and set off the nuclear emergency.
The failure of Fukushima's backup power systems, which were supposed to keep cooling systems going in the aftermath of the massive 9.0-magnitude earthquake, let uranium fuel overheat and were a "main cause" of the crisis, Nishiyama said.
"I cannot say whether it was a human error, but we should examine the case closely," he told reporters.
A spokesman for Tokyo Electric Power Co., which owns and runs the plants, said that while the generators themselves were not directly exposed to the waves, some of the electrical support equipment was outside. The complex was designed to protect against tsunamis of up to 5 meters (16 feet), he said. Media reports say the tsunami was at least 6 meters (20 feet) high when it struck Fukushima.
Motoyasu Tamaki also acknowledged that the complex was old, and might not have been as well-equipped as newer facilities.
Meanwhile, plant operators said they would reconnect four of the plant's six reactor units to a power grid Saturday. Although a replacement power line reached the complex Friday, workers had to methodically work through badly damaged and deeply complex electrical systems to make the final linkups without setting of a spark and potentially an explosion.
"Most of the motors and switchboards were submerged by the tsunami and they cannot be used," Nishiyama said.
Even once the power is reconnected, it is not clear if the cooling systems will still work.
The storage pools need a constant source of cooling water. Even when removed from reactors, uranium rods are still extremely hot and must be cooled for months, possibly longer, to prevent them from heating up again and emitting radioactivity.
As Japan crossed the one-week mark since the twin natural disasters spawned the nuclear crisis, the Japanese government conceded Friday it was slow to respond and welcomed ever-growing help from the United States in hopes of preventing a complete meltdown.
"In hindsight, we could have moved a little quicker in assessing the situation and coordinating all that information and provided it faster," Chief Cabinet Secretary Yukio Edano said Friday.
The earthquake and the tsunami it spawned killed more than 7,200 people and obliterated entire villages along the northeast coast. Thousands more people were missing.
Rescuers pulled a man alive from a wrecked house Saturday, but reports later said he had returned the building after the disaster and only had been trapped for one day. He was too weak to talk and transferred immediately to a hospital, a military official said, declining to be named because he was not authorized to speak with reporters.
Emergency crews at the nuclear plant faced two continuing challenges: cooling the nuclear fuel in reactors where energy is generated and cooling the adjacent pools where thousands of used nuclear fuel rods are stored in water.
Japan's government on Friday raised the accident classification for the nuclear crisis from Level 4 to Level 5 on a seven-level international scale. That put it on a par with the Three Mile Island accident in Pennsylvania in 1979, and signified its consequences went beyond the local area.
Edano also said Tokyo was asking Washington for additional help, a change from a few days ago, when Japanese officials disagreed with American assessments of the severity of the problem.
A U.S. military fire truck was among a fleet of Japanese vehicles that sprayed water into Unit 3, according to air force Chief of Staff Shigeru Iwasaki, sending tons of water arcing over the facility in an attempt to prevent nuclear fuel from overheating and emitting dangerous levels of radiation.
Additionally, the United States also conducted overflights of the reactor site, strapping sophisticated pods onto aircraft to measure radiation aloft. Two tests conducted Thursday gave readings that U.S. Deputy Energy Secretary Daniel B. Poneman said reinforced the U.S. recommendation that people stay 50 miles (80 kilometers) away from the Fukushima plant. Japan has ordered only a 12-mile (20-kilometer) evacuation zone around the plant.
American technical experts also are exchanging information with officials from the Tokyo Electric Power Co. which owns the plants, as well as with Japanese government agencies.
The tsunami knocked out power to cooling systems at the nuclear plant and its six reactors. In the week since, four have been hit by fires, explosions or partial meltdowns. The events have led to power shortages and factory closures, hurt global manufacturing and triggered a plunge in Japanese stock prices.
Most of Japan's auto industry is shut down. Factories from Louisiana to Thailand are low on Japanese-made parts. Idled plants are costing companies hundreds of millions of dollars. And U.S. car dealers may not get the cars they order this spring.
But Prime Minister Naoto Kan vowed that the disasters would not defeat Japan.
"We will rebuild Japan from scratch," he said in a nationally televised address, comparing the work with the country's emergence as a global power from the wreckage of World War II.
While nuclear experts have been saying for days that Japan was underplaying the crisis' severity, Hidehiko Nishiyama of the nuclear safety agency said the rating was raised when officials realized that at least 3 percent of the fuel in three of the complex's reactors had been severely damaged. That suggests those reactor cores have partially melted down and thrown radioactivity into the environment.
Low levels of radiation have been detected well beyond Tokyo, which is 140 miles (220 kilometers) south of the plant, but hazardous levels have been limited to the plant itself.
The Science Ministry said radiation levels about 30 kilometers (19 miles) northwest of the Fukushima Dai-ichi plant briefly spiked Friday to 0.15 millisieverts per hour, about the amount absorbed in a chest X-ray. While levels fluctuate, radiation at most points at that distance from the facility have been far below that. The ministry did not have an explanation for the rise.
Police said more than 452,000 people made homeless by the quake and tsunami were staying in schools and other shelters, as supplies of fuel, medicine and other necessities ran short.
Talmadge reported from Yamagata, Japan. Associated Press writers Foster Klug in Hirota, Japan, and Elaine Kurtenbach, Tim Sullivan, Shino Yuasa and Jeff Donn in Tokyo contributed to this report.
© Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.