メモ ✍ 》 For a precedent for Fukushima’s ice wall you don’t need to look to fantasy, but to the 19th-century mining industry. Digging a mine shaft is a never-ending battle against groundwater, which is constantly flowing into the mine and threatening to collapse the walls and flood the project. You can try to pump it out faster than it comes in, or you can dig another shaft to divert it—or you can freeze everything in place. In 1863 German scientist F.H. Poetsch patented a method of driving metal pipes full of super-cold brine (saltwater can go below 32 degrees without turning to ice) into the soil, freezing the surrounding ground solid as concrete. This allowed miners to dig in peace. The 1905 guide An Elementary Class-Book of Practical Coal-Mining touts its effectiveness in digging mine shafts through quicksand. “The principle of the Poetsch system is to freeze the ground around the shaft into a solid block, the effect of this being to consolidate the sand and hold the water back whilst the shaft is being sunk and lined through the wet ground.” The mining industry uses essentially the same technique today. The reason an ice wall is appealing in Fukushima is because the plant’s most pressing problem right now is groundwater. When the tsunami hit two years ago and the reactors melted down, Tepco cooled the overheating fuel rods by flooding them with millions of gallons of water. That water then became contaminated and had to be stored in tanks, tanks that then began to leak into the soil, and ultimately into the sea. Compounding the problem is the 400 tons of groundwater that flows down the neighboring hillside each day and into the damaged reactor buildings. That water also has to be pumped out and put in tanks, and storage space is running out. There are now about 1,000 tanks at the plant, but water continues to flow in—and, alarmingly, out to sea.
Posted on: Fri, 27 Sep 2013 08:32:02 +0000
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