Members of Japan’s Nuclear Regulation Authority NRA are now urging Tokyo Electric Power Company (Tepco) to find new technology and methods to aid in the cleanup of the Fukushima Daiichi NPP, Asahi Shimbun reported on 24 March.
Robots are repeatedly damaged on their missions, either from radiation damage, or by becoming stranded on-site. The suggestion is that the clean up may move faster if Tepco’s energy and the government’s money is redirected to chemistry, biology, and a “safe containment,” by building some sort of structure around Fukushima Daiichi similar to the sarcophagus around Chernobyl. Alternatively, artificial intelligence should be used to move robots through some of their tasks. All of the robots deployed so far have been remotely controlled by humans operators.
The comments followed the most recent robot failure. On 23 March Tepco attempted to send a survey robot into the containment vessel of the unit 1 reactor to find fuel debris, information needed to plan decommissioning. However, the PMORPH survey robot, developed by Hitachi-GE Nuclear Energy and the International Research Institute for Nuclear Decommissioning (IRID), was unable to get its cameras to the predetermined location and only sent back a partial report.
A month earlier, Tepco aborted a mission using a Toshiba Scorpion robot that was built to scramble over rubble, capture images and data inside the plant’s facilities. The robot could tolerate up to 1000 Sieverts of radiation but could not withstand the hostile environment inside the unit 2 reactor where it was dispatched.
These followed a string of earlier robot losses at the plant going back to the Quince 1, the first robot to enter the facility after the disaster. Quince, developed by the Chiba Institute of Technology, the International Rescue System Institute, and Tohoku University in Japan, went into the unit 2 reactor building where it measured radiation levels, collected dust samples and video footage. It ran several missions but eventually disconnected from its communications cable and was stranded inside the building.
Earlier, iRobot’s ground-based PackBot and Warrior robots, and Honeywell’s T-Hawk drones helped Tepco get to better understand the radioactivity and conditions around its facilities, including around damaged reactors within weeks of the disaster. Swimming and crawling robots, also developed by Hitachi and GE Nuclear energy, were used in a 2014 mission to capture images and readings inside a damaged reactor.
While useful data has been collected using cameras and robots, there is now some doubt about their future. “We should come up with a method that will allow us to investigate in a short period of time and in a more sensible way,” a senior NRA member was quoted as saying by Asahi Shimbun.
The search for melted fuel in the reactors has so far been unsuccessful.
Naohiro Masuda, president of Tepco's Fukushima Daiichi Decommissioning project, told reporters the company had to rethink its methods in order to examine and extract the hazardous material in the unit 2 reactor. “We should think out of the box so we can examine the bottom of the core and how melted fuel debris spread out,” Masuda said, according to the Japan Times.
Photo: PMORPH was the latest robot to enter Fukushima reactor (Photo: IRID)