The unimaginable toxicity of Fukushima reactor’s molten nuclear debris – robots the only hope for cleanup
For Fukushima’s nuclear disaster, robots may be the only hopeThe 2011 meltdown in Japan is still too hot for humans to handle. Send in the machines. CNet BY ROGER CHENG, MARCH 4, 2019 ………. I’m inside the cavernous top of the Unit 3 reactor in the Fukushima Daiichi Nuclear Power Plant. Yes, that Fukushima Daiichi, site of the world’s worst nuclear disaster.
Unit 3 was one of three reactors crippled on March 11, 2011, after a 9.0 earthquake struck 80 miles off the coast of Japan. (Units 4, 5 and 6 at Daiichi weren’t operating at the time.) The temblor shook so violently it shifted the Earth’s axis by nearly 4 inches and moved the coast of Japan by 8 feet. Eleven reactors at four nuclear power plants throughout the region were operating at the time. All shut down automatically. All reported no significant damage.
An hour later, the tsunami reached shore.
Two 50-foot-high waves barreled straight at Fukushima Daiichi, washing over coastal seawalls and disabling the diesel generators powering the plant’s seawater cooling systems. Temperatures inside the reactors skyrocketed to as high as 5,000 degrees Fahrenheit.
Fuel rods became molten puddles of uranium that chewed through the floors below, leaving a radioactive cocktail of fuel rods, concrete, steel and melted debris. Molten fuel ultimately sank into the three reactors’ primary containment vessels, designed to catch and secure contaminated material.
Next Monday marks the eighth anniversary of the earthquake. Since then, Japanese energy giant Tokyo Electric Power Company, or Tepco, has cleared enough of the rubble on the top floor of the Unit 3 building to allow for my 10-minute visit.
I gaze up at the massive barrel vault ceiling, trying to get a handle on the sheer scale of everything. Radiation levels are too high for me to linger. My quickening pace and breath are betrayed by rapid flapping noises coming from the purple filters on both sides of my respirator mask.
At the far end of the room, there’s an enormous orange platform known as a fuel-handling machine. It has four giant metal legs that taper down, giving the structure a sort of animalistic look. Thin steel cables suspend a chrome robot in the center of the frame. The robot, largely obscured by a pink plastic wrapper, is equipped with so-called manipulators that can cut rubble and grab fuel rods. The robot will eventually pull radioactive wreckage out of a 39-foot-deep pool in the center of the room.
It’s just one of the many robots Tepco is using to clean up the power plant. It’s why I came to Japan this past November — to see how robots are working in one of the most extreme situations imaginable.
The Japanese government estimates it will cost $75.7 billion and take 40 years to fully decommission and tear down the facility. The Japan Atomic Energy Agency even built a research center nearby to mock up conditions inside the power plant, allowing experts from around the country to try out new robot designs for clearing away the wreckage.
The hope is that the research facility — along with a drone-testing field an hour away — can clean up Daiichi and revitalize Fukushima Prefecture, once known for everything from seafood to sake. The effort will take so long that Tepco and government organizations are grooming the next generation of robotics experts to finish the job. …….
Two years ago, Tepco erected a dome over the Unit 3 reactor and fuel pool so that engineers could bring in heavy equipment and now, us.
Roughly 60 feet below me, radiation is being emitted at 1 sievert per hour. A single dose at that level is enough to cause radiation sickness such as nausea, vomiting and hemorrhaging. One dose of 5 sieverts an hour would kill about half of those exposed to it within a month, while exposure to 10 sieverts in an hour would be fatal within weeks.
Unit 3 is the least contaminated of the three destroyed reactors.
Radiation in Unit 1 has been measured at 4.1 to 9.7 sieverts per hour. And two years ago, a reading taken at the deepest level of Unit 2 was an “unimaginable” 530 sieverts, according to The Guardian. Readings elsewhere in Unit 2 are typically closer to 70 sieverts an hour, still making it the hottest of Daiichi’s hotspots.
The reactors’ hostile environments brought most of the early robots to their figurative knees: High gamma radiation levels scrambled the electrons within the semiconductors serving as the robots’ brains — ruling out machines that are too sophisticated. Autonomous robots would either shut down or get snared by misshapen obstacles in unexpected places.
The robots also had to be nimble enough to avoid disturbing the volatile melted fuel rods, essentially playing the world’s deadliest game of “Operation.” At least initially, they weren’t. “Fukushima was a humbling moment,” says Rian Whitton, an analyst at ABI Research. “It showed the limits of robot technologies.”………….. https://www.cnet.com/news/for-fukushimas-nuclear-disaster-robots-may-be-the-only-hope/
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