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Robot squeezes suspected nuclear fuel debris in Fukushima reactor

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Another step in the long, slow cleanup process

Video: TEPCO

A robot outfitted with remotely controlled pinchers poked at debris that’s suspected to contain molten nuclear fuel at the bottom of one of Fukushima’s nuclear reactors, World Nuclear News reports. The poking and prodding is part of the ongoing cleanup effort at Japan’s Fukushima Daiichi power plant, the site of a major nuclear accident in 2011.

The dextrous robot was dangled into the Unit 2 reactor on February 13th, according to a news release from the plant’s operator, Tokyo Electric Power Company (TEPCO). Unit 2 is one of the reactors at the Fukushima Daiichi power plant that overheated after a massive earthquake and tsunami hit Japan in 2011, which caused the reactor core to melt. TEPCO suspects that radioactive fuel may have melted through the bottom of the reactor vessel to fall into the containment structure surrounding it.

The robot being lowered into the reactor.
Photo: TEPCO

The company has to find the radioactive debris and figure out how to remove them, so TEPCO has been sending in a series of robots to scout out the reactors. It’s a dangerous journey that some of the robots haven’t survived. In January 2017, the TEPCO team sent a robot in to investigate Unit 2. It sent back pictures of rocky chunks at the bottom of the reactor, but the team didn’t know how those deposits felt. Were they solid enough to be picked up and removed, for example, or would they crumble at a touch?

A robot that scooted into the reactor on tank-like treads got stuck in February 2017, so the company decided to try again this week. It sent in a robot about the size of a hefty loaf of bread: a foot long, four inches wide, and a little more than two pounds in weight. It’s equipped with lights, cameras, and sensors that can measure temperature and radiation. And, most importantly, it sports “tong-like fingers” that can pinch and prod the debris, according to an informational video released by TEPCO.

On Wednesday, a team operating the robot remotely lowered it about 10 feet into the bottom of the primary containment vessel. It lifted the solidified gunk at the bottom of the containment vessel, snapping photos as water rained around it. It’s the first time those mysterious deposits have actually been touched, TEPCO’s informational video says.

A preliminary report and a video released by the company show that five of the six deposits the robot tried to grab moved; the other was firmly cemented in place. Those results seem like a decent sign if that’s how TEPCO wants to shift and remove most of the debris. But it’s still early. The company plans to analyze the images as well as the temperature and radiation information that the robot collected, which is key data as TEPCO continues its long, slow cleanup of the destroyed nuclear reactors.

The robot grabs pebbles at the bottom of the Unit 2 reactor.
Video: TEPCO