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Daunting obstacles t o Fukushima cleanup, even as evacuees move back

text-what-radiationAs evacuees move back, Fukushima cleanup faces daunting obstacles, Science, By Dennis Normile Mar. 2, 2017 TOKYOSix years into a decommissioning effort expected to last into the 2050s, an official leading the work on the stricken Fukushima Daiichi Nuclear Power Plant claims that cleanup crews are making “steadfast progress.” But thorny technical obstacles must be overcome.

Stemming ocean contamination has been a thorny challenge. Since early in the crisis, crews have circulated water through the damaged reactors to prevent overheating that could lead to further fuel melting. That water, and groundwater flowing through the site, is heavily contaminated and TEPCO has struggled to keep it from seeping into the Pacific. Schemes to divert groundwater away from the plant and freeze a wall of soil around the reactors down to bedrock—to contain contaminated water—have minimized leaks, Masuda said.

In the meantime, TEPCO has accumulated 960,000 tons of contaminated water stored in 1000 10-meter-tall tanks at the site. TEPCO has removed cesium, strontium, and more than 50 other radionuclides from that water. But they have been stymied by tritium, a radioactive hydrogen isotope in the water. Several experimental approaches to removing the tritium “were judged to be impractical,” Masuda said……

Another major hurdle is determining the condition and location of the melted fuel, much of which is believed to have dropped to the bottoms of the containment vessels where high radiation levels preclude human entry. Robotic investigations are proving problematic. In January, the camera on a robotic probe sent into the Unit 2 containment vessel was fried by radiation, though it did return important images before its demise. Then last month, a small robot on tanklike treads was sent through a 10-centimeter-diameter pipe into the vessel to investigate the presumed location of the damaged fuel. But it got tangled up in debris and was abandoned.

TEPCO is now thinking it might need a robot able to jump over debris. And they are planning robotic investigations of the units 1 and 3 containment vessels in preparation for a planning session this summer to set a policy for recovering the melted fuel. http://www.sciencemag.org/news/2017/03/evacuees-move-back-fukushima-cleanup-faces-daunting-obstacles

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March 4, 2017 - Posted by | Fukushima continuing

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