TOKYO - The Japanese government announced Tuesday that it is funding a costly, untested subterranean ice wall in a desperate step to stop leaks of radioactive water from the crippled Fukushima nuclear plant after repeated failures by the plant's operator.

The decision is widely seen as a safety appeal just days before the International Olympic Committee chooses between Tokyo, Istanbul and Madrid on which city will host the 2020 Olympics.

The Fukushima Dai-ichi plant has been leaking hundreds of tons of contaminated underground water into the sea since the 2011 earthquake and tsunami damaged the complex. Several leaks from tanks storing tainted water in recent weeks have heightened the sense of crisis that the utility's owner, Tokyo Electric Power Co., isn't able to contain the problem.

"Instead of leaving this up to TEPCO, the government will step forward and take charge," said Prime Minister Shinzo Abe said after adopting the outline. "The world is watching if we can properly handle the contaminated water but also the entire decommissioning of the plant."

The government plans to spend an estimated 47 billion yen ($470 million) through the end of 2014 on two projects — the ice wall and upgraded water treatment units that is supposed to remove all radioactive elements but tritium — according to energy agency official Tatsuya Shinkawa.

The government is not paying for urgently needed water tanks and other equipment that TEPCO is using to stop leaks.

The ice wall would freeze the ground to a depth of up to 30 metres (100 feet) through a system of thin pipes carrying a coolant as cold as minus 40 degrees Celsius (minus 40 Fahrenheit). It would thus block contaminated water from escaping the facility's immediate surroundings, as well as keep underground water from entering the reactor and turbine buildings, where most contaminated radioactive water has collected.

The project, which TEPCO and the government proposed in May, is set for completion by March 2015.

Similar methods have been used to block water from parts of tunnels and subways, but building a wall that surrounds four reactor buildings and their related facilities is unprecedented. The wall could cost 30 billion to 40 billion yen ($300 million to $400 million) for initial installation, plus an annual running and maintenance cost.

TEPCO has been pumping water into the wrecked reactors to keep cool nuclear fuel that melted when the March 2011 earthquake and tsunami knocked out the plant's power and cooling system. TEPCO has built more than 1,000 tanks holding 335,000 tons of contaminated water at the plant, and the amount grows by 400 tons daily.

TEPCO is also constructing an offshore wall of steel panels along the coast to keep contaminants from spreading further into the sea. The utility says radioactive elements have mostly remained near the embankment inside the bay, but experts have reported offshore "hot spots" of sediments contaminated with high levels of cesium.

The leaks came at a worst time as Tokyo headed into the final days of the contest to host the 2020 Olympics. With anti-government demonstrations plaguing Istanbul, Turkey's bid and a recession and high Spanish unemployment hanging over Madrid's candidacy, Tokyo is pushing its bid as the safe choice in uncertain times.

The IOC will select the 2020 host on Sept. 7 in Buenos Aires, Argentina.

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  • In this Monday, Aug. 26, 2013 photo, fisherman Fumio Suzuki stands on his boat Ebisu Maru before the start of fishing in the waters off Iwaki, about 40 kilometers (25 miles) south of the tsunami-crippled Fukushima Dai-ichi nuclear power plant, Japan. (AP Photo/Koji Ueda)

  • In this Monday, Aug. 26, 2013 photo, fisherman Choji Suzuki stands on the Ebisu Maru before the start of fishing in the waters off Iwaki, about 40 kilometers (25 miles) south of the tsunami-crippled Fukushima Dai-ichi nuclear power plant, Japan. (AP Photo/Koji Ueda)

  • In this Monday, Aug. 26, 2013 photo, fisherman Fumio Suzuki cleans the deck of his boat Ebisu Maru before the start of fishing in the waters off Iwaki, about 40 kilometers (25 miles) south of the tsunami-crippled Fukushima Dai-ichi nuclear power plant, Japan. (AP Photo/Koji Ueda)

  • In this Aug. 26, 2013 photo, fishermen Choji Suzuki, left, and his son Fumio sort out fish they caught aboard their boat Ebisu Maru in the waters off Iwaki, about 40 kilometers (25 miles) south of the tsunami-crippled Fukushima Dai-ichi nuclear power plant, Japan. (AP Photo/Koji Ueda)

  • In this Aug. 26, 2013 photo, fisherman Fumio Suzuki watches the sunrise aboard his boat Ebisu Maru before the star of fishing in the waters off Iwaki, about 40 kilometers (25 miles) south of the tsunami-crippled Fukushima Dai-ichi nuclear power plant, Japan. (AP Photo/Koji Ueda)

  • In this Aug. 26, 2013 photo, fisherman Fumio Suzuki sorts out fish he caught aboard his boat Ebisu Maru in the waters off Iwaki, about 40 kilometers (25 miles) south of the tsunami-crippled Fukushima Dai-ichi nuclear power plant, Japan. (AP Photo/Koji Ueda)

  • In this Aug. 26, 2013 photo, fisherman Choji Suzuki navigates the Ebisu Maru before fishing in the waters off Iwaki, about 40 kilometers (25 miles) south of the tsunami-crippled Fukushima Dai-ichi nuclear power plant, Japan. (AP Photo/Koji Ueda)

  • Fisherman Choji Suzuki sorts out fish he caught aboard his boat Ebisu Maru in the waters off Iwaki, about 40 kilometers (25 miles) south of the tsunami-crippled Fukushima Dai-ichi nuclear power plant, Monday, Aug. 26, 2013. (AP Photo/Koji Ueda)