Japan suspended operations to prevent the stricken Fukushima Dai-ichi nuclear plant from melting down Wednesday after a surge in radiation forced workers to take cover indoors.
Chief Cabinet Secretary Yukio Edano said work on dousing reactors with water was disrupted by the high radiation levels.
"The workers cannot carry out even minimal work at the plant now," Edano said. "Because of the radiation risk we are on standby," he said.
A spokesman from Tokyo Electric Power Co., the owner of the facility, said workers were told to remain inside until it was safe.
The country has ordered a nearby 140,000 people to seal themselves indoors after a series of explosions and fires at the plant. The latest fire, at the plant's No. 4 reactor, is under control, according to TEPCO, which blamed it on an earlier fire that hadn't been fully extinguished. But Japan's nuclear agency was unable to confirm that the blaze had been put out, and clouds of white smoke were billowing from the reactor, according to live video footage of the plant.
The agency also reported that damage to the fuel rods at the No. 1 reactor were at 70 percent. Kyodo News added that 33 percent of the second reactor's fuel rods were also damaged.
Tuesday’s fire at the fourth reactor is thought to have damaged the reactor's suppression chamber, a water-filled pipe outside the nuclear core that is part of the emergency cooling system.
Officials said radiation levels in areas around the nuclear plant rose early Tuesday afternoon but appeared to subside by evening.
Early Wednesday, Japan abandoned plans to spray water from helicopters into an overheating spent fuel storage pool at the facility. A TEPCO spokesman said that helicopters were deemed impractical, but other options were under consideration, including fire engines. There were later reports that a boric acid drop was being considered.
Boric acid is "important because it captures radiation and helps prevent radiation from leaking," said Masami Nishimura, the nuclear safety agency spokesman.
He said the government had also ordered the utility company to immediately spray water on Unit 4.
Both units 1 and 3 have no roof after earlier blasts, making it easy to dump water onto them, he said. Unit 4 has holes in the building, allowing fire trucks to spray water inside, he said.
Boric acid contains boron, which helps slow nuclear reactions by absorbing neutrons, said Naj Meshkati, a nuclear power plant safety expert at the University of Southern California.
The International Atomic Energy Agency has established a 19-mile no-fly zone around the plant's perimeter -- a move that comes as the U.S. Navy said Tuesday they detected low levels of airborne radiation at Yokosuka and Atsugi bases, 200 miles away from the nuclear plant, according to Newscore.