The latest disclosures add to a long list of recent mishaps, leaks and breakdowns that have underscored grave vulnerabilities at the Fukushima Daiichi nuclear power plant site more than two years after a powerful earthquake and tsunami set off meltdowns at three reactors.
They come two weeks after the prime minister, Shinzo Abe, promised that his government would take a more active role in the site's cleanup, raising questions over how seriously he has taken that pledge. Abe's government has continued to push for a restart of the country's nuclear power program, and he heads to the Middle East on Saturday to promote Japanese exports to the region, including nuclear technology.
Abe also plans to lead Tokyo's delegation to Argentina for the International Olympic Committee's final vote, set for Sept. 7, on the host city for the 2020 Olympics. Tokyo, 150 miles south of the stricken nuclear power plant, is one of three finalists competing to host the games. The others are Istanbul and Madrid.
Opposition lawmakers here have demanded that Abe stay home and declare a state of emergency.
"The nuclear crisis is real and ongoing, yet the government continues to look the other way," said Yoshiko Kira of the opposition Japan Communist Party, which made significant gains in parliamentary elections last month.
"The government should declare a state of emergency right now, and intervene to stop the outflow of contaminated water," Kira said at an anti-nuclear rally outside Abe's office in Tokyo.
Abe remains popular, and it is uncertain how large a liability the crisis at the Fukushima plant will become for him. But it has become increasingly clear that the latest problems may be too large for the plant's operator, the Tokyo Electric Power Co., or TEPCO, to handle.
TEPCO has built nearly 1,000 tanks at the sprawling complex to store as many as 335,000 tons of contaminated water, the product of coolant pumped into the reactors to keep their cores from overheating, and groundwater pouring into their breached basements at a rate of 400 tons a day. This week, TEPCO said one tank had sprung a huge leak.
On Friday, TEPCO presented an even starker view of the situation, acknowledging that as many as 220,000 tons of that water is stored in makeshift steel tanks similar to the one that is leaking. The operator said the 36-foot-tall cylindrical tanks, meant as a temporary repository for the growing amount of radiated water at the complex, used vulnerable rubber sealing and that their ability to withstand radiation was not tested.
The tanks are susceptible to leaks at the seams and through their concrete base, said Noriyuki Imaizumi, the acting general manager of TEPCO's nuclear power division. A nearby drain can carry any leaked water to the sea, Imaizumi said, and high radiation readings along a section suggest that water has already traveled through the drain to the ocean.
The makeshift tanks also lack water level gauges, making it difficult to detect leaks. Only two workers are assigned to checking nearly 1,000 tanks on two-hour patrols twice a day, Imaizumi said.
The Nuclear Regulation Authority, which the Japanese government ordered to more actively advise and monitor TEPCO's activities at the plant, had told the company to begin transferring the water from the makeshift tanks to better-built vessels. But after visiting the plant on Friday, an authority commissioner, Toyoshi Fuketa, said the vast quantities made doing so quickly "unrealistic."
A series of pits TEPCO dug to store some of the water also began leaking earlier this year, forcing workers to transfer the water into the steel tanks.
Experts have said they suspect that more contaminated water is seeping out from under the melted-down reactors into the groundwater and the Pacific. Elevated levels of radioactive cesium in surrounding waters seem to confirm those suspicions.
TEPCO has said those leaks are not directly from beneath the reactors, but from maintenance tunnels that run along the coast and remain contaminated from the early days of the disaster.
But it also acknowledges that the water beneath the reactors is extremely contaminated, and experts say that that if it does get into the ocean, it will surpass even the leaks that occurred in the disaster's early days.
"That prospect scares me," Michio Aoyama, a senior scientist in the Oceanography and Geochemistry Research Department at the government-affiliated Meteorological Research Institute, said in an interview this month.
"It's the ultimate, worst-case scenario," Aoyama said.