TOKYO—A remote-controlled “cleaning” robot that entered one of three wrecked Fukushima reactor containment chambers Feb. 9 had to be pulled out before completing its mission due to camera glitches most likely caused by high radiation.
It was the first time a robot entered the chamber inside the Unit 2 reactor since the March 2011 earthquake and tsunami critically damaged the Fukushima Da-ichi nuclear plant.
Tokyo Electric Power Co. said the intent was to inspect and clean a passage before another robot does a fuller examination to assess details of the damage to the structure and fuel inside.
TEPCO needs to know the melted fuel’s exact location and condition and other structural damage in each of the three wrecked reactor in order to figure out the best and safest way to remove them. It is part of the plant’s decommissioning work, which is expected to take decades.
The robot went only partway on a narrow bridge into a space under the core that TEPCO wants to inspect closely. It crawled down the passage while blowing off some debris with a water spray and peeling them with a scraper on its head, and about two hours later, the two cameras on the robot suddenly developed a lot of noise and its image quickly darkened—a sign of a mechanical glitch from high radiation.
The outcome means the second robot will encounter more obstacles and have less time for examination on its mission, currently planned for later this month.
The robot is designed to withstand up to 1,000 Sieverts of radiation, and its two-hour endurance roughly matched the estimated radiation level of 650 Sieverts based on noise analysis of the images transmitted by the robot-mounted cameras. That’s less than 1 per cent of radiation levels inside a running reactor, but still would kill a person almost instantly.
TEPCO officials reassured that despite the dangerously high figures, radiation is not leaking outside of the reactor.
Images recently captured from inside the chamber showed damage and structures coated with molten material, possibly mixed with melted nuclear fuel, and part of a disc platform hanging below the core had been melted through. Similar photographic analysis of radiation levels from the visual data was slightly lower than Thursday’s figure.