Robot probes sent to one of Japan's wrecked Fukushima nuclear reactors have suggested worse-than-anticipated challenges for the plant's ongoing cleanup. The plant's operator, Tokyo Electric Power Co., said the remote-controlled "scorpion" robot was sent into Unit 2's containment vessel Thursday to investigate the area around the core that melted in 2011, but its crawling function failed while climbing over highly radioactive debris, the AP reports. The robot transmitted some data and visuals but couldn't locate melted fuel—key info to determine how to remove debris out of the reactor. The robot was abandoned inside the vessel at a location where it won't block a future probe.
Preliminary exams over the past few weeks have detected structural damage to planned robot routes and higher-than-expected radiation inside Unit 2's chamber, suggesting the need to revise robot designs and probes. TEPCO needs to know the melted fuel's exact location, condition, and other structural damage in each of the three wrecked reactors to figure out the best and safest ways to remove the fuel. Earlier this month, another robot, made for cleaning debris for the main "scorpion" probe, had to return midway through because two of its cameras became inoperable after two hours when its radiation exposure reached a maximum tolerance of 1,000 sievert—a level that can kill within seconds. The robot's original planned duration was 10 hours, or 100 sievert per hour. (Read more Fukushima Dai-ichi stories.)