We can’t see inside Fukushima Daiichi because all our robots keep dying

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Tepco, the utility company tasked with overseeing cleanup and waste processing for the former Fukushima Daiichi nuclear plant, hit another snag this week. Last month, we reported on new findings about Reactor #2 that showed it was far more radioactive inside than previously measured. At the time, we noted that Tepco was working on a new robot that could handle up to 73 sieverts of radiation, but the measured level of 530 sieverts vastly exceeded that tolerance.

Now, Tepco has admitted that repeated robot failure is hampering its plan to search the bottom of the reactor, and find the estimated 600 tons of fuel and debris that may have poured out of the reactor and into the concrete lining below it. Initial attempts to see into Reactor #2 via robotic probe have all failed. We’ve only been able to estimate contamination levels by checking the amount of interference in the video feed the robot relays. The new hardened robot built by Toshiba and meant to give Tepco a much-improved ability to survey the damage reactor died 5x faster than expected and stalled 10 feet from the grate it needed to inspect.

A composite photo of the metal grate and the hole in it, directly below the Reactor Pressure Vessel.

In the wake of this setback, Naohiro Masuda, president of the Fukushima Daiichi Decommissioning, has called for imaginative thinking. “We should think out of the box so we can examine the bottom of the core and how melted fuel debris spread out,” Masuda told reporters.

Robots have been dying in Fukushima reactors since the disaster, but this is a higher-profile failure. The new robot Toshiba built (it’s been described as scorpion-like) was meant to solve this problem. The fact that it failed so quickly just underscores how much trouble Tepco is likely to have in further improving its design.

Why is radiation so bad for robots?

Radiation has different effects on robots than it does on people. The exact effects differ depending on what type of radiation it is (alpha, beta, gamma) and the composition of the inorganic substance. But radiation has a well-known tendency to interfere with or destroy electronics. Gamma rays will turn wiring brittle, which is a real issue when attempting to build a mobile robot. It can also damage electronic circuits (again, this depends on the type of radiation and the materials used to construct the necessary components). Presumably Tepco and Toshiba already chose to build their robot with radiation-hardened chips and shielded the vital parts of the robot as best they could. Wikipedia has an extensive article on radiation hardening and how it’s done, for those who would like more information on the topic.

There’s no practical way to shield humans from the amount of radiation coming off Fukushima Daiichi’s Reactor #2, and existing robot designs aren’t working well, despite relying on a minimum number of electronic parts. Building chips and robots that are radiation-hardened enough to perform their intended duties without being weighed down by heavy shielding could be extremely difficult and expensive to develop.

Tepco continues to insist it can meet a 2021 goal of beginning actual site clean-up. This will require enormous investments in the field of robotics and may require the company to create entirely new designs to ensure their hardware doesn’t die in a matter of minutes. If the company’s survey robots keep dying, how are they going to field robots that can cut and gather the nuclear fuel that melted into concrete?

Now read: How does nuclear energy work?



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