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“Ice wall” – the effort to contain Fukushima’s radiation

How Fukushima’s underground ice wall keeps nuclear radiation at bay

Think Game of Thrones, but this one is underground and defends against a far more realistic threat.  CNet,

BY ROGER CHENG MARCH 8, 2019 

The intricate network of small metal pipes, capped off by six-foot-high metal scaffolding, shouldn’t stand out amid the numerous pieces of industrial equipment littered throughout the Fukushima Daiichi Nuclear Power Plant. After all, it’s a power plant.

I take a closer look, and notice spheres of ice perched upon the smaller pipes, which line the center of the structure. The facility sits at the water’s edge, and there’s a brisk breeze blowing through.

e intricate network of small metal pipes, capped off by six-foot-high metal scaffolding, shouldn’t stand out amid the numerous pieces of industrial equipment littered throughout the Fukushima Daiichi Nuclear Power Plant. After all, it’s a power plant.

I take a closer look, and notice spheres of ice perched upon the smaller pipes, which line the center of the structure. The facility sits at the water’s edge, and there’s a brisk breeze blowing through

………. The structure, which cost roughly $300 million, paid for by public funds, serves as critical protection, defending the Fukushima area from one of the most radioactive hotspots in the world. While Tokyo Electric Power Co., also known as Tepco, struggles to find a way to remove radioactive material from the facility – a process the government estimates could take more than four decades — the more immediate concern is what to do with the contaminated water leaking out from the facility……….

Ice cold

While the term “ice wall” has a colorful ring to it, engineers use the more academic-sounding term Artificial Ground Freezing.

…… calcium chloride solution is pumped down through a smaller inner pipe, and circulated back up a large outer pipe.

The coolant brings down the temperature of each pipe to -30 degrees Celsius, or -22 degrees Fahrenheit, and the pipes are spaced about three feet apart. The cold emanating from each one hardens the soil around it.

The point of the ice wall is to keep the groundwater that runs down from the mountains to the west from entering Fukushima Daiichi and mixing with the toxic water leaking out of the Unit 1, 2 and 3 reactors. That is,  keep the clean water on the outside of the wall, while the contaminated water stays inside.

Tepco and manufacturing partners, such as Toshiba and Mitsubishi, are working on robots to identify and determine how to clear out the radioactive materials in each of the reactors’ primary containment vessels, essentially the heart of each facility.

Until then, they need a way to slow or stop the flow of water into the facility.

……. With the wall in place, Tepco says it has been able to reduce the level of contaminated water generated from Daiichi. But a Reuters report in March 2018 found that the wall still let a fair amount of clean water in, adding to the volume of toxic water the company needs to deal with. Tepco, however, says it’s been effective in reducing the volume.

“We know this is not the end of our effort,” says a company spokesman. “We will be continuously working hard to reduce the amount of  generation of contaminated water.”

The leaky bucket

Imagine a leaky bucket that constantly needs to be filled with water. At the same time, the water from the leak needs to be collected and stored. And there’s no end in sight to this cycle.

That essentially is the problem that Tepco faces at Daiichi. The fuel rods stored in the three radioactive units constantly have to be cooled with fresh water, but leaks mean the company needs to be vigilant about keeping the tainted liquid from getting out of the facility’s grounds.

Since the accident nearly eight years ago, Tepco has collected 1.1 million tons of contaminated water in 900 tanks stored on the grounds at Daiichi. The company estimates it has enough space in the 37.7-million-square-foot facility to house an additional 270,000 tons of water, which means it would run out sometime in 2020.

“We’re conscious of the fact that we can’t keep storing more and more water,” Kenji Abe, a spokesman for Tepco’s decommissioning and decontamination unit, says through an interpreter.

……. So far, treatment technology from partner companies like Kurion and Sarry have enabled Tepco to remove 62 of the 63 radioactive elements from the water, but one, tritium, remains.

It’s this one element, which is bonded to the water at an atomic level, that means Tepco needs to keep collecting and storing the water.

……..  organizations such as Greenpeace have called for Tepco to keep storing the water, noting that much of the early batches of treated water far exceed safety limits for radioactive elements.

Given the sensitivities around Fukushima, Tepco must continue to store the water. A spokesman said the company isn’t planning to disperse the water. But it is one option being considered by the Japanese government, which ultimately makes the decision.

“Resolving the issue of the contaminated water is something we haven’t yet reached a final solution on,” Yagi says.

…….. The scientist explains that Japan has set a legal radioactivity limit of 60,000 becquerel per liter of tritium. But the treated water is still at 1.7 million Bq per liter, or roughly 30 times what’s deemed safe.

So, for now, Tepco must continue collecting the water. And the ice wall continues to stand, invisible to onlookers, as one of the most important lines of defense. https://www.cnet.com/news/how-fukushimas-underground-ice-wall-keeps-nuclear-radiation-at-bay/

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March 9, 2019 - Posted by | Fukushima continuing

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