White polyester box covers Unit 1 of Japan’s stricken Fukushima Daiichi nuclear plant
A Circus Tent for Fukushima Daiichi? WSJ, DECEMBER 15, 2011, The polyester cover erected over Unit 1 of Japan’s stricken Fukushima Daiichi nuclear power station was fashioned in the shape of atight-fitting, non-descript, white box.
It could have looked very different.
At first, planners from plant operator Tokyo Electric Power Co. and
general contractor Shimizu Corp. say they considered something that
looked like a circus tent, when they sat down in mid-March to discuss
how to stop the spread of radioactive materials from the plant’s four
damaged reactor buildings.
Constructing a tent was fast, and Tepco was in a hurry to stop the
spread of radiation – particularly from Units 1 and 3, where hydrogen
explosions after the nuclear accident in March had blown away the
reactor buildings. The engineers finally decided the boxy shape, with
panels fastened to a steel frame, would be more durable…. “The
cover we built is expected to last at least a few years, but in the
future, we probably need a more robust structure,” said Masahiro Indo.
“The cover isn’t exactly air-tight; air can leak through gaps between
The Wall Street Journal describes some of the civil-engineering
heroics Shimizu went through to get the cover in place.
But even before the construction began, there were challenges. There
was no detailed plant blueprint, for one. That information was trapped
in a computer in the reactor building and inaccessible. The only
layout available was one produced 40 years ago, which didn’t include
any of the stacks, pipes and buildings added later.
Shimizu ended up doing a laser scan of the entire building and
creating a 3-D image, then building a 1/100-scale model of Unit 1,
complete with surrounding debris. “We rebuilt the model three or four
times until we were satisfied with it,” Mr. Indo said.
The cover is made up of 20-meter-square polyester sheets, with each
sheet held down by two weights weighing 7 and 12 tons. The panels were
lifted by two cranes capable of carrying 750-ton loads, out of only 14
such machines in all of Japan.
During the construction, those cranes got dosed with high levels of
radiation, particularly the one working closest to Unit 1. So where
are the contaminated cranes now? Tepco says they’re still sitting in
the plant complex, waiting for their next mission.
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