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A Robot Commences Retrieval of Melted Fuel at Fukushima Nuclear Plant
A robot has entered a damaged reactor at Fukushima to extract melted fuel debris. The mission is a crucial step in the plant's decommissioning process. Tokyo Electric Power Company estimates 880 tons of molten fuel debris across three reactors.
The primary objective is to extract a small quantity of melted fuel debris from the reactor's base for the first time.
This operation marks the initial step in a complex and lengthy process aimed at decommissioning the plant and addressing substantial amounts of highly radioactive melted fuel within three reactors damaged during the 2011 earthquake and tsunami. Experts anticipate that insights gained from this robot mission will enhance their understanding of the cores and fuel debris.
Following the 2011 earthquake and tsunami, the nuclear fuel within the reactor cores liquefied when the cooling systems at the Fukushima Daiichi nuclear plant failed. The resulting melted fuel combined with various internal reactor components, such as zirconium, stainless steel, electrical cables, and concrete, posing a formidable challenge for cleanup efforts due to its highly radioactive nature.
Tokyo Electric Power Company Holdings (TEPCO), the plant operator, estimates that approximately 880 tons of molten fuel debris are still present in the three reactors, although some specialists suggest the quantity could be higher. To facilitate the robot's movement within the Unit 2 reactor, workers will employ a series of five 1.5-metre-long pipes, with the robot itself capable of extending up to 6 metres inside the vessel.
Equipped with tongs, a light, and a camera, the robot will be remotely operated from a separate building at the plant due to the hazardous radiation levels emitted by the melted debris. Its task involves delicately snipping off and collecting a minute amount of debris, less than 3 grams, to mitigate radiation risks.
The intricate manoeuvres required for the robot's safe navigation, avoiding obstacles and potential entrapment, necessitate a two-week timeframe for the mission. Daily operations are limited to two hours to reduce radiation exposure for workers, with eight teams scheduled to rotate shifts, each permitted a maximum of around 15 minutes in the reactor building.
Lake Barrett, who oversaw the cleanup at the U.S. Three Mile Island nuclear plant post the 1979 disaster, emphasised the significance of sampling the melted fuel debris. Now advising TEPCO on Fukushima's decommissioning, Barrett highlights the urgent need to relocate the stabilised but aging melted fuel to ensure long-term safety.
The Japan Atomic Energy Agency stresses the importance of understanding the melted fuel debris to facilitate its safe removal, storage, and disposal. Experts anticipate that analysing the sample will unveil crucial details about the 13-year-old meltdown, shedding light on previously unknown aspects.
The extracted melted fuel sample will undergo thorough analysis in multiple laboratories. In case of radiation surpassing safety limits, a robot will retract the sample back into the reactor. Barrett underscores that this sampling marks just the beginning of a complex process with the ultimate goal of transferring the highly radioactive material into secure canisters for storage.
The current robot's limitations allow it to access only the debris's upper surface, hinting at the need for more advanced robots in the future. TEPCO faces the challenge of delving deeper into the over a metre thick debris pile to gather diverse samples for comprehensive analysis and equipment development.
While the removal of spent fuel rods from Unit 3 has been completed, the task of extracting the melted fuel faces delays due to technical hurdles. The decommissioning timeline is estimated at 30-40 years by the government, with some experts suggesting it could extend up to a century.
Unlike Chernobyl's entombment post its 1986 explosion, Barrett dismisses this approach for Fukushima due to its seismic and coastal location, posing unpredictable risks. The complex nature of the Fukushima plant demands an active decommissioning strategy rather than a passive entombment solution.
A robot has entered a damaged reactor at Fukushima to extract melted fuel debris.
The mission is a crucial step in the plant's decommissioning process.
Tokyo Electric Power Company estimates 880 tons of molten fuel debris across three reactors.
Source: AP NEWS