KORIYAMA // Japan's nuclear crisis intensified yesterday as authorities raced to combat the threat of multiple reactor meltdowns and more than 170,000 people evacuated the quake and tsunami-savaged coast where fears spread over possible radioactive contamination.
Nuclear plant operators were frantically trying to keep temperatures down in a series of nuclear reactors - including one where officials feared a partial meltdown could be happening yesterday - to prevent the disaster from growing worse.
Yukio Edano, the chief cabinet secretary, also said yesterday that a hydrogen explosion could occur at unit three of the Fukushima Dai-ichi nuclear complex, the latest reactor to face a possible meltdown. That follows a blast the day before in the power plant's unit one, and operators attempted to prevent a meltdown there by injecting sea water into it.
"At the risk of raising further public concern, we cannot rule out the possibility of an explosion," Mr Edano said. "If there is an explosion, however, there would be no significant impact on human health."
More than 170,000 people had been evacuated as a precaution, though Mr Edano said the radioactivity released into the environment so far was so small it didn't pose any health threats.
Mr Edano said none of the Fukushima Dai-ichi reactors was near the point of complete meltdown, and he was confident of escaping the worst scenarios.
A complete meltdown - the collapse of a power plant's ability to keep temperatures under control - could release uranium and dangerous contaminants into the environment and pose major, widespread health risks.
Mr Edano said operators were trying to cool and decrease the pressure in the unit three reactor, just as they had the day before at unit one.
"We're taking measures on unit three based on a similar possibility" of a partial meltdown, Mr Edano said.
unit three at the Fukushima plant is one of three reactors there that had automatically shut down and lost cooling functions necessary to keep fuel rods working properly due to a power outage from the quake. The facility's unit one is also in trouble, but unit two has been less affected.
On Saturday, an explosion destroyed the walls of unit one as operators desperately tried to prevent it from overheating and melting down.
Without power, and with its valves and pumps damaged by the tsunami, authorities resorted to drawing sea water mixed with boron in an attempt to cool the unit's overheated uranium fuel rods. Boron disrupts nuclear chain reactions.
The move will likely render the 40-year-old reactor unusable, said a foreign ministry official briefing reporters. Officials said the sea water will remain inside the unit, possibly for several months.
Robert Alvarez, a scholar at the Institute for Policy Studies and former senior policy adviser to the US secretary of energy, told reporters that the sea water was a desperate measure.
He said the success of using sea water and boron to cool the reactor will depend on the volume and rate of their distribution. He said the dousing would need to continue nonstop for days.
Another key, he said, was the restoration of electrical power, so that normal cooling systems can operate.
Mr Edano said the cooling operation at unit one was going smoothly after the sea water was pumped in.
Operators released slightly radioactive air from unit three yesterday, while injecting water into it hoping to reduce pressure and temperature to prevent a possible meltdown, Mr Edano said. He said radiation levels just outside the plant briefly rose above legal limits, but since had declined significantly. Also, fuel rods were exposed briefly, he said, indicating that coolant water didn't cover the rods for some time. That would have contributed further to raising the temperature in the reactor vessel. Officials placed five reactors, including units one and three at Dai-ichi, under states of emergency Friday after operators lost the ability to cool the reactors using usual procedures.
An additional reactor was added to the list early yesterday, for a total of six - three at the Dai-ichi complex and three at another nearby complex. Evacuations have been ordered at each location. Japan has a total of 55 reactors spread across 17 complexes nationwide.
Officials began venting radioactive steam at Fukushima Dai-ichi's unit one to relieve pressure inside the reactor vessel, which houses the overheated uranium fuel.
Concerns escalated dramatically on Saturday when that unit's containment building exploded.
Officials were aware that the steam contained hydrogen and were risking an explosion by venting it, acknowledged Shinji Kinjo, spokesman for the government's Nuclear and Industrial Safety Agency, but chose to do so because they needed to keep circulating cool water on the fuel rods to prevent a meltdown.
Officials insisted there was no significant radioactive leak after the explosion.
If the reactor core became exposed to the outside, officials would likely begin pouring cement and sand over the entire facility, as was done at the 1986 Chernobyl nuclear accident in the Ukraine, Peter Bradford, a former commissioner of the US Nuclear Regulatory Commission, told reporters.
Another expert, physicist Ken Bergeron, told reporters that as a result of such a meltdown the surrounding land would be off-limits for a long time and "a lot of first responders would die."
Yesterday, the UN's nuclear agency said excessive levels of radiation at a second Japanese nuclear facility had led authorities to report a state of emergency there.
