Fukushima shutdown could take a month
Osaka - Fukushima nuclear plant operator Tepco on Friday said it may take a month to achieve cold shutdown, as Japan mulled hiking the crisis to a notch under Chernobyl on an atomic accident scale.
The Nuclear and Industrial Safety Agency (Nisa) currently rates Fukushima at 5 out of 7, making it the worst ever in Japan, putting it on the same level as the 1979 accident at Three Mile Island in Pennsylvania.
Tokyo Electric Power Co (Tepco) admitted on Friday it may take at least another month to achieve a cold shutdown of all reactors - when temperatures inside fall below boiling point and its cooling systems are back at atmospheric pressure.
"We are still in the process of assessing the damage at the plant, so we can't put a deadline on when the cooling operations will work again. It may take more than a month, who knows," a Tepco spokesperson told AFP.
Temperatures at one reactor spiked at one point to 400ºC this week before stabilising. Temperatures inside reactors one to four remain around boiling point, a nuclear safety agency official said.
Progress has been slow in efforts to restore the plant's cooling systems that were knocked out after Japan's biggest recorded earthquake and a subsequent tsunami that devastated swathes of the northeast.
Firefighters have been dousing stricken reactors with seawater in an effort to cool damaged reactors and fuel rods, with radioactive particles emitted into the air, contaminating tap water, the sea and food products.
Japan's nuclear power regulator indicated on Friday it may raise its assessment of the crisis at the quake-hit Fukushima Daiichi nuclear plant to level 6 or "serious accident", after gathering data on radiation levels in surrounding regions.
A Nisa official said: "We can't rule out the possibility of raising the disaster level to 6. Depending on how the situation unfolds, it's still possible for the level to be raised."
Among the six reactors at the power plant, reactors one, two and three were operating at the time of the magnitude-9.0 quake and halted automatically.
But the cores are believed to have partially melted after the cooling systems failed, sparking a series of explosions and fires.
Authorities have since struggled to keep fuel rods inside reactors and fuel storage containment pools underwater. If they are exposed to air, they could degrade further and emit large amounts of dangerous radioactive material.
France's Nuclear Safety Authority already rates the Fukushima crisis at 6 on the scale. The 1986 Chernobyl disaster was put at 7, the highest.
Such ratings are issued based on the International Nuclear and Radiological Event Scale, or INES.