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Thursday, 12 March 2015

Fukushima No. 1's never-ending battle with radioactive water : Japan Times


MAR 11, 2015

The disaster that struck four years ago may have abated for most of the Tohoku region, but the nightmare continues at Tokyo Electric Power Co.’s Fukushima No. 1 nuclear plant, which suffered three reactor core meltdowns and is plagued daily by increasing amounts of radioactive water.

Tepco hopes to improve the situation via two key measures: a 1.5-km-long sunken wall of frozen soil encircling stricken reactors 1, 2 and 3 and the damaged reactor 4 building to keep groundwater from entering and mixing with coolant water leaking in the reactor building basements, and “subdrain” wells around the buildings to pump up the tainted groundwater for treatment and ultimate discharge into the Pacific.

The utility hopes these steps will drastically reduce the amount of radioactive water, which is currently some 300 tons each day.

Many experts, however, say Tepco can’t expect smooth sailing as a wall of underground ice of such magnitude has never before been attempted.

And Tepco’s plans to pump up tainted groundwater via the subdrains and discharge it into the sea after removing most of its radioactive components also appears iffy. The company has already lost the trust of fishermen over its failure to disclose the extent of the radioactive water flowing into the Pacific.

The crippled complex has to contend with some 300 tons of new tainted groundwater every day, and part of the process has entailed a nonstop effort to build steel storage tanks. The groundwater, mainly rain that seeps into the soil both at the complex and at locations farther inland, flows toward the sea, including into the basements of the buildings housing the three wrecked reactors.

There, the groundwater mixes with radioactive water that is leaking from cracks in the reactors. Tepco must keep pumping new water into the reactors to cool the melted fuel rods within. The basements are too radioactive to enter.

The problematic groundwater flow used to amount to 400 tons daily, but the utility has taken some steps, including paving over part of the complex with asphalt to keep rainwater from seeping underground.

To stop the increase of tainted water, Tepco must keep all, or at least nearly all, groundwater from flowing into the basements.

The sunken ice wall is considered critical to this goal and Tepco has been setting up pipes to run coolant underground to freeze the soil — a process the utility hopes to start at the end of this month if it receives approval from the Nuclear Regulation Authority.

Although Tepco said it will take several months to completely freeze the soil into a solid ice wall, it expects the wall to reduce the amount of groundwater flowing into the reactor buildings to 50 tons a day from 300 at present.

One “problem will be how long it will take to freeze soil evenly (to make an ice wall without holes), and we have already seen this problem when Tepco attempted to make ice walls inside the underground trench (connected to the reactor turbine buildings),” said Shigeaki Tsunoyama, an education and research special adviser at the University of Aizu.

“I’m worried that the same thing might happen with the ice wall (encircling the reactor buildings),” said Tsunoyama, who sits on a panel formed by the NRA to oversee the decommissioning of the nuclear plant.

Fukushima No. 1 has a maze of underground trenches connected to the reactor turbine buildings to run cables and pipes, and they are now filled with highly radioactive water leaking from the turbine buildings.

To remove the water in the trenches, Tepco tried for months to block the tainted water running from the buildings by freezing it before abandoning the effort last year.

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