At least 45 tons of highly radioactive water have leaked from a purification facility at the Fukushima Daiichi nuclear power station, and some of it may have reached the Pacific Ocean, the plant's operator said on Sunday.

Nearly nine months after Fukushima Daiichi was ravaged by an earthquake and tsunami, the plant continues to pose a major environmental threat. Before the latest leak, the Fukushima accident had been responsible for the largest single release of radioactivity into the ocean, threatening wildlife and fisheries in the region, experts have said.

Molten nuclear fuel may have bored into the floor of at least one of the reactors at the stricken Fukushima Daiichi nuclear power plant, the complex’s operator said Wednesday, citing a new simulation of the accident that crippled the plant in March.

The simulation suggested that the meltdown may have been more severe than had previously been thought.

Even as Japan plans to phase out nuclear power as too risky for domestic use, the government is supporting a new push by Japanese industry to sell nuclear power technology to other countries.

Japanese industrial conglomerates, with the cooperation of the government in Tokyo, are renewing their pursuit of multibillion-dollar projects, particularly in smaller energy-hungry countries like Vietnam and Turkey. The effort comes despite criticism within Japan by environmental groups and opposition politicians.

In an effort to track the long-term health effects of the nuclear disaster at Fukushima, Japan has begun a survey of local children for thyroid abnormalities, a problem associated with exposure to radiation.

Despite continued fears over radiation levels, Japan lifted evacuation advisories for an area spanning five towns and cities around a tsunami-ravaged nuclear power plant on Friday, the first such move since multiple fuel meltdowns at the site led to a substantial radiation leak and forced more than 100,000 surrounding residents to flee.

Japan’s new prime minister, Yoshihiko Noda, promised on Friday to keep Japan on its path of phasing out nuclear power, saying it was “unrealistic” to build any new reactors in the wake of the Fukushima nuclear crisis or to extend those at the end of their life spans.

In his first speech to the nation as prime minister, Mr. Noda, Japan’s former finance minister and a fiscal conservative, also said Japan would seek to rebuild its tattered finances even as it pays for reconstruction after the country’s devastating earthquake, tsunami and nuclear accident in March.

Despite continuing fears over the safety of food from the area of the disaster-stricken Fukushima Daiichi nuclear power plant, Japan has lifted a ban on beef shipments from there that it had imposed just a month ago, when meat contaminated with radioactive material was found to have reached Japanese supermarkets.

The half-century-old, oil-fueled power generators here had been idle for more than a year when, a day after the nuclear accident in March, orders came from Tokyo Electric Power headquarters to fire them up.

Workers at the Yokosuka power plant, whose turbine is a half-century old.

“They asked me how long it would take,” said Masatake Koseki, head of the Yokosuka plant, which is 40 miles south of Tokyo and run by Tokyo Electric. “The facilities are old, so I told them six months. But they said, ‘No, you must ready them by summer to prepare for an energy shortage.’ ”

Japan’s Parliament passed a law on Wednesday that will allow the use of public funds to shore up the company operating the crippled Fukushima Daiichi nuclear plant, and help it pay what is expected to amount to billions of dollars in compensation claims.

Japan on Friday proposed an aggressive plan to spend 13 trillion yen ($167 billion) over five years in hopes of bringing about a swift recovery after its recent natural and nuclear disasters.

The Japanese government is desperate to pull the economy out of a recession stemming from the March 11 earthquake and tsunami as well as the problems related to the Fukushima nuclear plant. The catastrophes damaged factories, disrupted supply chains, caused a crippling power shortage and curtailed consumer spending.