(Reuters) - Japanese engineers conceded on Friday that burying a crippled nuclear plant in sand and concrete may be a last resort to prevent a catastrophic radiation release, the method used to seal huge leakages from Chernobyl in 1986.
But they still hoped to solve the crisis by fixing a power cable to two reactors by Saturday to restart water pumps needed to cool overheating nuclear fuel rods. Workers also sprayed water on the No.3 reactor, the most critical of the plant's six.
It was the first time the facility operator had acknowledged burying the sprawling 40-year-old complex was possible, a sign that piecemeal actions such as dumping water from military helicopters or scrambling to restart cooling pumps may not work.
"It is not impossible to encase the reactors in concrete. But our priority right now is to try and cool them down first," an official from the plant operator, Tokyo Electric Power Co, told a news conference.
As Japan entered its second week after a 9.0-magnitude earthquake and 10-meter (33-foot) tsunami flattened coastal cities and killed thousands, the world's worst nuclear crisis since Chernobyl and Japan's worst humanitarian crisis since World War Two looked far from over.
Around 6,500 people have been confirmed dead from the earthquake and tsunami while 10,300 are missing, many feared dead.
Some 390,000 people including many elderly are homeless and battling near-freezing temperatures in makeshift shelters in northeast coastal areas. Food, water, medicine and heating fuel is in short supply.
The government signaled it could have moved faster in dealing with the multiple disasters.
"An unprecedented huge earthquake and huge tsunami hit Japan. As a result, things that had not been anticipated in terms of the general disaster response took place," Chief Cabinet Secretary Yukio Edano told a news conference.
Japan also raised the severity rating of the nuclear crisis from Level 4 to Level 5 on the seven-level INES international scale, putting it on a par with America's Three Mile Island accident in 1979, although some experts say it is more serious.
Chernobyl was a 7 on the INES scale.
Tourists, expatriates and many Japanese continue to leave Tokyo, fearing a blast of radioactive material from the nuclear complex 240 km (150 miles) to the north, even though health officials and the U.N. atomic watchdog have said radiation levels in the capital were not harmful.
That is little solace for about 300 nuclear plant workers toiling in the radioactive wreckage, wearing masks, goggles and protective suits with seams sealed off by duct tape to keep out radioactive particles. "My eyes well with tears at the thought of the work they are doing," Kazuya Aoki, a safety official at Japan's Nuclear and Industrial Safety Agency, told Reuters.
Even if engineers restore power at the Fukushima Daiichi plant, the pumps may be too damaged from the earthquake, tsunami or subsequent explosions to work.
The first step is to restore power to pumps for reactors No. 1 and 2, and possibly 4, by Saturday, said Hidehiko Nishiyama, Japan's nuclear safety agency spokesman.