The goals are part of a two-part plan that represents Tokyo Electric's most concrete timetable yet for controlling the reactors and improving safety conditions at the plant, which was damaged by 15-meter-high tsunami waves on March 11.
At least on paper, the program marks a turning point in the company's struggles to shut down the reactors. For weeks, workers have fought to cool the reactors and spent fuel pools by pouring water on them. The deluge has created other problems, including a flood of contaminated water that seeped into the site and into the ocean.
But conditions have stabilized in recent days, giving the utility, widely known as Tepco, the confidence to unveil its schedule for shutting the reactors.
The first part of the plan would take about three months and include installing a cooling system to lower the temperature in the reactors and spent fuel pools, as well as reducing radiation in the surrounding area, said Tsunehisa Katsumata, the chairman of Tokyo Electric.
The second part, which would take up to six more months, would include more pumping of water, the introduction of a heat removal system and reducing the amount of contaminated water. The wreckage from the three damaged buildings would then be removed and the buildings covered.
"The company has been doing its utmost to prevent a worsening of the situation," Mr. Katsumata told reporters. "We have put together a roadmap," he said, adding, "We will put our full efforts into achieving these goals."
Mr. Katsumata said that he and the company's president, Masataka Shimizu, would consider what's best for the company before deciding whether to resign to take the blame for the crisis. The company said Friday that it plans to distribute $600 million in initial payments to 50,000 people forced to evacuate because of the accident.
On Sunday, Banri Kaieda, the Minister of Economy, Trade and Industry, said that the evacuees who left their homes near the Daiichi plant will be able to return in six to nine months.
Conditions have steadied to the point where the United States and other foreign governments have lowered their warnings for travel in Japan. In a show of support, Secretary of State Hillary Rodham Clinton flew to Japan on Sunday from Seoul, becoming the most senior American official to visit since the disaster.
She expressed support for the relief and reconstruction effort, telling Japan's foreign minister, Takeaki Matsumoto, that her visit reflected "our very strong bonds of friendship that go very deep into the hearts of our people."
Mrs. Clinton called the earthquake, tsunami and nuclear accident "a multi-dimensional crisis of unprecedented scope" and said that the United States is "doing everything we can to support Japan and we have very good cooperation."
Experts from the United States Nuclear Regulatory Commission have been in Japan advising Tokyo Electric and the government. In the days after the crisis began, the N.R.C. said that radiation levels at the Daiichi plant were higher than those reported by the Japanese. The American government also declared a wider evacuation zone than the Japanese.
Asked if the Japanese government had acted transparently enough, Mrs. Clinton said: "We have been very supportive of what Japan is doing to take the appropriate steps."
Mrs. Clinton also met with Emperor Akihito and his wife, Michiko, at the Imperial Palace. The emperor shook her hand, and Mrs. Clinton kissed Michiko on both cheeks. "I'm so, so sorry for everything your country is going through," she told them, before they entered the palace for tea. She added, "if there was anything we can do..."
A short walk from the Imperial Palace, executives at Tokyo Electric's headquarters offered details of their strategy. To prevent radioactive materials from escaping, the company said it plans to put a temporary cover with an air filter over the buildings. Engineers will also start designing a structure with a concrete roofs and sides.
But officials declined to identify the material that they would use to cover the damaged reactor buildings, saying only that it would be similar to the tough fabric used to wrap buildings under construction and would not be comparable to the heavy concrete shell that entombed the damaged reactor at Chernobyl. The company warned that the temporary cover could be damaged in a typhoon.
To keep contaminated water from escaping, the company intends to set up a water processing unit that removes radioactive particles and salt, and store it in tanks. But in a sign of how much improvisation has gone into the plan, company officials said that they will turn a concrete-walled waste treatment building into a large storage tank to hold up to 30,000 tons of contaminated water.
The longer-term goal, they said, was to establish a closed circuit in which radioactive water from the reactors is cooled and pumped back into them.
Michael Friedlander, a former senior operator at three nuclear power plants in the United States, said that waste treatment buildings are specially designed to hold very large volumes of water even if the equipment inside is broken during an earthquake.
During routine operations at a nuclear power plant, the waste treatment building removes low levels of radioactivity from the water and also handles solid waste. Similar equipment will now have to be installed at the site designated today.
"The normal equipment must have been damaged very severely" for the Japanese to have decided to scrap it, Mr. Friedlander said.
Goshi Hosono, a special adviser to the prime minister, identified two risks to the plan. One is that Tokyo Electric could have trouble setting up new equipment to condense steam from the reactors into cool water.
The other, he said, is a serious aftershock or tsunami that could lead to further damage at the site.
Despite its flaws, Tokyo Electric's plan should work, said Hironobu Unesaki, a professor at the Research Reactor Institute at Kyoto University. But the company should try to achieve cold shutdown of the reactors sooner than six to nine months to reduce the risk of radiation being released. He added that "there is no clear scientific explanation" why the plan is divided into two phases.
In the meantime, Tokyo Electric continues to face many tradeoffs. For example, the water being poured to cool the reactors has kept temperatures from rising but not enough to achieve cold shutdown.
To improve cooling, the company would like to restore a closed loop cooling system that recirculates water. But it is hard for workers to enter the plant to install a new system because of the radioactive water in the buildings, basements and trenches. And while efforts are being made to pump out that water and put it into storage, new cooling water has to be poured into the reactors, leading to new radioactive water in the buildings.
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