Embattled operator Tokyo Electric Power Company faces compensation payments worth tens of billions of dollars for victims of the world's worst nuclear accident since Chernobyl a quarter of a century ago.
More than 80,000 people have been forced from homes, farms and businesses in a 20-kilometre (12-mile) zone around the plant which was hit by a tsunami on March 11 and has since leaked radiation into the air, ground and sea.
To help TEPCO, Asia's biggest electric power company, meet its obligations, the centre-left government of Prime Minister Naoto Kan decided on a financial aid plan paid for mostly with new government bonds.
The scheme will give the government a stronger hand in supervising TEPCO, save the biggest of Japan's 10 utilities from bankruptcy, and prevent turmoil on financial markets in the world's third-largest economy.
The firm, which supplies power to Tokyo and the wider Kanto region, is also Japan's largest corporate bond issuer, accounting for eight per cent of the country's 62 trillion yen ($765 billion) corporate bond market.
The plan is subject to parliamentary approval, which is not certain as some lawmakers have called for stronger measures to ensure the public does not foot the cost, amid criticism the scheme protects shareholders and bondholders.
The government in a statement cited its "social responsibility in having promoted nuclear power" and said it would "support Tokyo Electric Power... under the principle of minimising the burden on the people".
To win public support for the plan, the government may also ask banks to waive some of their pre-quake loans to TEPCO, said the top government spokesman Yukio Edano, in comments that sent banking shares tumbling.
Under the plan the government will create a body to handle claims made against TEPCO and act as an insurance body for the nuclear industry. The body would also be funded by contributions from other power companies.
TEPCO and the government have yet to release estimates for the payout bill, but analysts say it could range from four trillion yen ($50 billion) to 10 trillion yen depending on how long the nuclear crisis lasts.
To allay the risk of a second quake-triggered nuclear disaster, another power company, Chubu Electric, on Friday shut down a reactor at another coastal nuclear plant, as requested by the Kan government.
Chubu lowered control rods into the number four reactor vessel of its Hamaoka power plant, located in the tectonic high-risk region of Tokai, about 200 kilometres southwest of Tokyo.
Kan said the plant should stay shut while a higher sea wall is built and other measures are taken to guard it against a major tsunami.
"The reactor has come to a halt," Chubu spokesman Mikio Inomata said. "There was no problem and everything went as scheduled," he said, adding that the reactor would soon enter stable "cold shutdown" status.
The firm planned to begin shutting down the plant's only other operational reactor, number five, on Saturday, the spokesman said.
Nine weeks after the quake-tsunami disaster, TEPCO gave a snapshot Thursday of the Fukushima plant that confirmed experts' fears, saying that the fuel rods inside reactor one had been fully exposed to the air and had melted.
However, it said that relatively low temperatures indicated that the fuel was now submerged under water at the bottom of the vessel, preventing it from reaching critical stage and going into full meltdown.
TEPCO has said it targets cold shutdowns of all reactors at Fukushima between October and January.
But trade and industry minister Banri Kaieda said the latest news was "a big factor that may require a change in the roadmap".
The company on Thursday also reported another leak of highly radioactive runoff water from its emergency dousing operations into the Pacific Ocean, leading the government to apologise to Japan's Asian neighbours.
Kan earlier this week announced a full review of Japan's national energy policy, scrapping a previous plan to build 14 new reactors to meet half of the country's energy demand with nuclear power by 2030.
While Japan would not abandon nuclear energy, which now meets a third of its demand, the premier stressed that renewables such as solar and wind power would become "key pillars" of the nation's new energy strategy.
What the stars mean:
★ Poor ★ ★ Promising ★★★ Good ★★★★ Very good ★★★★★ Exceptional