Images taken by a robotic probe inside one of the three melted reactors at the tsunami-devastated facility raised concerns about the Fukushima nuclear power plant’s earthquake resistance in the event of another major disaster.
These images showed exposed steel bars in the main supporting structure and parts of its thick external concrete wall missing.
Since last year, the primary containment chamber of Unit 1 has been visited by robotic probes sent by the plant’s operator, Tokyo Electric Power Company Holdings. The most recent investigation, finished at the end of March, produced new results announced Tuesday.
Below the core, in a supporting structure known as the Unit 1 pedestal, a remotely controlled underwater vehicle, or ROV-A2, was sent.
Images not seen since a tsunami and earthquake devastated the plant 12 years prior were returned. The most likely location to find remnants of the melted fuel is inside the pedestal.
The pedestal’s 120-centimeter (3.9-foot) thick concrete exterior was severely broken towards its bottom, revealing the steel reinforcement inside, according to an approximately five-minute video included in 39 hours of footage the robot took.
The steel reinforcement is generally intact, according to TEPCO spokesperson Keisuke Matsuo, but the company plans further to examine data and photographs over the ensuing few months to determine whether and how the reactor’s earthquake resistance may be increased.
Photographs of the exposed steel reinforcing have raised concerns about the reactor’s safety.
Masao Uchibori, the governor of Fukushima, pleaded with TEPCO to “quickly analyze levels of earthquake resistance and disseminate information in a way prefectural inhabitants can easily grasp and relieve the fear of the locals and people around the country.”
According to company officials, the footage captured by the robot also showed equipment that had fallen and other kinds of debris, including piles of debris that rose as high as 40-50 centimeters (1.3-1.6 feet) from the bottom of the primary containment chamber.
This debris may have included nuclear fuel falling from the core and hardening.
According to Matsuo, the information gathered from the most recent investigation will enable specialists to devise strategies for clearing debris and deciphering the 2011 meltdowns.
TEPCO will also use the information to produce a three-dimensional map of the specifics of the melted fuel and debris, which will take around a year.
Experts have concluded that most of the melted fuel inside Unit 1 fell to the bottom of the primary containment chamber, but some of it may have even fallen through into the concrete foundation, which makes the already challenging task of decommissioning even more difficult.
This conclusion is based on data gathered from earlier probes and simulations.
Three reactors still contain almost 880 tons of deadly radioactive melted nuclear fuel. Robotic probes have provided some data, but it is mainly unknown how the molten debris is doing.
The quantity is around ten times what was taken out of Three Mile Island’s contaminated fuel during cleanup efforts after its partial core melt in 1979.
After a delay of nearly two years, a trial removal of melted debris is anticipated to start in Unit 2 later this year.
After a 10-year wait, spent fuel removal from the cooling pool of the Unit 1 reactor will begin in 2027.
In 2031, the emphasis will shift to getting melted fuel out of the reactors when all the spent fuel has been removed from the pools.
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