Prime Minister Naoto Kan has called for the closure of a nuclear plant in central Japan, citing the risk of another disastrous quake after the Fukushima Daiichi plant, in the northeast of the country, was destroyed by the March 11 earthquake and tsunami.
Nearly 26,000 people were killed or are still missing after the quake and tsunami which triggered the world's biggest nuclear disaster since Chernobyl in 1986. The plant is still leaking radiation.
The call to shut down the Hamaoka plant signaled a potential shift in energy policy, and while the government says other plants will be unaffected, it could embolden anti-nuclear movements.
Several thousand protesters marched through central Tokyo on Saturday to welcome Kan's call to shut down Hamaoka and urging him to push for further closures.
Deputy Chief Cabinet Secretary Yoshito Sengoku said that Japan would remain committed to nuclear power, although Trade Minister Banri Kaieda, who oversees energy policy, said Japan's target must be reviewed.
"With regard to energy policy, we set the target last June of increasing nuclear power to 50 percent by 2030, but we will have to rethink this," Kaieda said on Fuji TV.
"We must put more effort into renewable energy, and that will become one trigger for (economic) growth."
Chubu Electric Power Co is leaning toward closing the plant as requested and could make the decision at a board meeting as early as Monday, media said.
Asked whether he would seek the closure of other nuclear plants, Kan told reporters on Sunday: "That won't be the case," adding that Hamaoka had an especially high risk of being hit by a massive earthquake.
Japan last year vowed to boost the share of electricity generation through nuclear power to 50 percent by 2030 from the current 30 percent by building at least 14 new reactors.
Government experts put the chance of a magnitude 8.0 quake hitting the Hamaoka area in the next 30 years at 87 percent, which raises questions over why it was built there in the first place.
The magnitude 9.0 quake on March 11 crippled cooling systems at Fukushima Daiichi, operated by Tokyo Electric Power.
Of 54 reactors in commercial use in Japan, 32 are under planned or unplanned maintenance and operators may face resistance to restarting them.
Board members of Chubu, which serves major manufacturers, including Toyota Motor Corp, postponed a decision on Saturday on whether to temporarily close Hamaoka.
Chubu spokesman Akio Miyazaki said another board meeting would be held on or after Monday. The Nikkei business daily said the board would meet on Monday.
Yomiuri newspaper said Chubu was likely to comply with Kan's request to close Hamaoka, with a capacity of 3,617 megawatts, pending introduction of quake and tsunami safety measures -- but only after it finds ways to supply power in a stable fashion. Two of the plant's three working reactors are in operation.
Chubu says it can meet this fiscal year's peak demand of 25,600 MW even if Hamaoka shuts. But the Yomiuri newspaper, quoting a company executive, says the company may have to consider "rolling blackouts" in very hot weather.
Miyazaki said relying on thermal plants to make up shortfalls if Hamaoka closes would push up costs by 700 million yen ($8.7 million) per day -- or about 256 billion yen a year. That could overturn the firm's projected profit of 130 billion yen in the year to March 31, 2012.
Chubu chairman Toshio Mita was in Qatar to discuss possible procurement of liquefied natural gas, Miyazaki said.