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Thursday, Dec. 22, 2011

Fukushima fuel removal deadline set at 10 years

Staff writer

Tepco aims to start removing spent fuel rods from the Fukushima plant's wrecked reactors within two years, and extracting the melted fuel in the containment vessels within 10 years, according to a medium- to long-term road map for decommissioning the facility released Wednesday.

Four of the reactors at the Fukushima No. 1 plant will be scrapped over the next 30 to 40 years, the plan drafted by the government and Tokyo Electric Power Co. says.

But the plan's feasibility remains in serious doubt as the sky-high radiation levels in the reactor units will prevent workers from getting anywhere near them.

Instead, Tepco will have to devise or commission remote-controlled machines able to identify and plug cracks in the containment vessels, and use machines to remove the melted fuel inside — a task that requires technologies the world has never seen.

Nevertheless, Tepco Vice President Zengo Aizawa tried to sound upbeat at a Wednesday evening news conference, telling reporters the utility will research and harness technologies from around the world to successfully decommission the crippled reactors.

"We think the plan is achievable," he said.

But Aizawa conceded that huge challenges lie ahead, especially when it comes to extracting the melted fuel.

On Friday, the government declared that a "cold shutdown condition" had been achieved at three of the wrecked reactors, and announced that the Fukushima disaster had entered a new phase that would ultimately result in its decommissioning.

Based on a computer simulation, Tepco believes reactors 1, 2 and 3 suffered meltdowns in the immediate aftermath of the March 11 earthquake and tsunami, and that the fuel rods inside melted through the pressure vessels and stopped just short of breaching their containment vessels.

"Plugging the leaks in the containment vessels will be the first major challenge," Tepco spokesman Kazuhiro Takei said during the same news conference.

After plugging the leaks, Tepco will flood the reactors with water in an attempt to get its first glimpse inside, and then start removing the fuel from the cores, according to the road map.

Once the cracks in the containment vessels are sealed, the utility will also start pumping out the enormous quantity of tainted water that has flooded the basement floors of the reactor buildings.

This, however, means the contaminated water could remain in the units for as long as 9 years. Tepco plans to complete work on sealing the cracks and holes in the containment vessels for reactors 1 to 3 in five to six years.

But before removing the fuel rods from the spent-fuel pools of units 1 to 4, Tepco said it will have to remove debris caused by the March 11 quake and tsunami, as well as the hydrogen explosions they triggered, and also create casks to store the spent rods.

The spent-fuel pools of units 1 to 4 contain 3,108 nuclear fuel assemblies, according to a government panel, including some that contain MOX, a hybrid fuel that contains enriched plutonium.

The three crippled reactors, meanwhile, contain 1,496 active fuel assemblies, although many are believed to have melted or suffered severe damage.

All of the fuel in the No. 4 reactor, which was undergoing a regular inspection when the March 11 disasters struck, had already been transferred to its spent fuel pool.

Information from Kyodo added

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The Japan Times

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