Underwater Robot Spots Possible Melted Nuclear Fuel in Fukushima Reactor

Identifying the location of the fuel is a vital step in the decontamination process

Robot finds potential fuel debris in reactor 3 at the Fukushima No. 1 power plant

Since the 2011 meltdown at a nuclear power plant in Fukushima, Japanese authorities have been working to decontaminate the area. A crucial step in the clean up process is locating the nuclear fuel that melted during the disaster—a task easier said than done. Humans can’t safely go near the site, and robots sent to probe the highly toxic reactors have sputtered and died.

But as Kyle Swenson reports for the Washington Post, experts recently made a breakthrough: an underwater robot photographed what appears to be solidified nuclear fuel at the site of the disaster.

The robot, nicknamed “Little Sunfish,” documented icicle-like clusters, clumps and layers of the suspected nuclear material in one of the three reactors that was submerged in water when Japan was hit by a massive earthquake and tsunami six years ago. Some layers are more than three feet thick. According to the Associated Press, the formations were found “inside a main structure called the pedestal that sits underneath the core inside the primary containment vessel of Fukushima’s Unit 3 reactor.”

Takahiro Kimoto, a spokesperson for the Tokyo Electric Power Company (TEPCO), tells Kazuaki Nagata of the Japan Times that “it is possible that the melted objects found this time are melted fuel debris.”

“From the pictures taken today, it is obvious that some melted objects came out of the reactor,” he explains. “This means something of high temperature melted some structural objects and came out. So it is natural to think that melted fuel rods are mixed with them.” 

The lava-like mixture of nuclear fuel rods and other structural materials is known as corium, and finding its location is vital for decontamination efforts. As Lake Barrett, a former official at the U.S. Nuclear Regulatory Commission, tells Nagata, “[i]t is important to know the exact locations and the physical, chemical, radiological forms of the corium to develop the necessary engineering defueling plans for the safe removal of the radioactive materials.”

The possible identification of corium at Fukushima is a promising first step, but there is a long road ahead. Further analysis is needed to confirm that the substance is indeed melted fuel. Then authorities will need to figure out a way to remove it from the area. The process of decommissioning the reactors is expected to take 40 years, and cost about $72 billion, according to an estimate from the Japanese government.

It's not all bad news. With Little Sunfish, scientists may have finally developed a robot that can withstand the highly radioactive bowels of Fukushima’s nuclear reactors, which will help them conduct further investigations of the site.

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