Mounting obstacles, missteps and confusion at the Fukushima Dai-ichi nuclear complex have stymied emergency workers struggling to cool down the overheating plant and avert a disaster with global implications.
The coastal power plant, located 140 miles (220 kilometers) northeast of Tokyo, has been leaking radiation since a magnitude-9.0 quake on March 11 triggered a tsunami that engulfed the complex. The wave knocked out power to the system that cools the dangerously hot nuclear fuel rods.
Contaminated water in Unit 2 tested at radiation levels some 100,000 times normal amounts, plant operator Tokyo Electric Power Co. said.
As officials scrambled to determine the source of the radioactive water, chief Cabinet Secretary Yukio Edano said Monday that the contaminated water in Unit 2 appeared to be due to a partial meltdown of the reactor core.
A TEPCO spokesman said the presence of radioactive chemicals such as iodine and cesium point to damaged fuel rods as the source. However, pressure inside the containers holding the reactors was stable, indicating any meltdown was only partial, spokesman Kaoru Yoshida said.
New readings show contamination in the ocean has spread about a mile (1.6 kilometers) farther north of the nuclear site than before. Radioactive iodine-131 was discovered just offshore from Unit 5 and Unit 6 at a level 1,150 times higher than normal, Hidehiko Nishiyama, a spokesman for the Nuclear and Industrial Safety Agency, told reporters.
Closer to the plant, radioactivity in seawater tested about 1,250 times higher than normal last week and climbed to 1,850 times normal over the weekend. Nishiyama said the increase was a concern but the area was not a source of seafood.
Tsunami Relief: Network for Good
It could take weeks to clear out the radioactive water, said Gary Was, a nuclear engineering professor at the University of Michigan.
"Battling the contamination so workers can work there is going to be an ongoing problem," he said.
Japan's nuclear watchdog, the Nuclear Safety Commission, said Monday that its members -- government-appointed experts who monitor the atomic industry -- believe that the highly radioactive water came from the containment vessel. It did not clearly state that the primary containment vessel, which protects the core, had been breached.
The commission warned that radioactive water was seeping from the plant into soil and seawater, NISA official Kenji Kinjo said.
Edano, the government spokesman, urged residents to stay out of the 12-mile (20-kilometer) evacuation zone around the plant, saying contaminants posed a "big" health risk. He was responding to reports that people had been sneaking back in without government approval.
Meanwhile, a strong earthquake shook the region and prompted a brief tsunami alert early Monday. The quake off the battered coast of Miyagi prefecture in the northeast was measured as a magnitude 6.5, the Japan Meteorological Agency said.No damage or injuries were reported, and TEPCO said the quake would not affect work to stabilize the plant.
Scores of strong earthquakes have rattled Japan over the past two weeks, adding to the sense of unease across Japan, where the final death toll from the March 11 disasters is expected to top 18,000.
Confusion at the plant has intensified fears that the nuclear crisis will last weeks, months or years amid alarms over radiation making its way into produce, raw milk and even tap water as far away as Tokyo.
TEPCO officials said Sunday that radiation in leaking water in the Unit 2 reactor was 10 million times above normal - an apparent spike that sent employees fleeing the unit. The day ended with officials saying the huge figure had been miscalculated and offering apologies.
"The number is not credible," TEPCO spokesman Takashi Kurita said hours later. "We are very sorry."
The government and nuclear safety agency chastised TEPCO for the latest in a series of missteps.
"This sort of mistake is not something that can be forgiven," Edano said sternly Monday.
The crisis did not interrupt a yearly rite much loved by the Japanese: the blooming of cherry trees at Tokyo's Yasukuni Shrine.
Cherry trees typically begin blooming in the south in March, in the capital days later, and in the chilly north in April.
Trees at the Yasukuni Shrine in Tokyo began blooming Monday, the country's meteorological agency said.
Associated Press writers Tomoko A. Hosaka, Mayumi Saito, Mari Yamaguchi and Jeff Donn contributed to this report.