Tokyo (AFP) – Pictures taken by a robotic probe inside one of the three melted-down reactors at Japan’s wrecked Fukushima nuclear power plant. It showed exposed steel rods in the main supporting structure and parts of its thick outer concrete wall missing, raising concerns about its earthquake resistance in the event of another major disaster.
The station’s operator, Tokyo Electric Power Holdings Corporation, has been sending robotic probes inside the Unit 1 primary containment chamber since last year. The new findings, published on Tuesday, are from the most recent investigation conducted at the end of March.
A remotely operated underwater vehicle called ROV-A2 has been sent inside the base of Unit 1, a supporting structure just below the core. She’s back with images seen for the first time since an earthquake and tsunami crippled the factory 12 years ago. The area inside the base of the statue It is where traces of molten fuel are most likely to be found.
A nearly five-minute video — part of 39 hours of images captured by the robot — showed that the concrete outside of the 120-centimetre (3.9-foot) base had been badly damaged near its bottom, exposing the rebar inside. .
TEPCO spokesman Keisuke Matsuo told reporters Tuesday that the rebar remains largely intact, but the company plans to do more data and image analysis over the next two months to see if and how the reactor’s earthquake resistance can be improved.
Images of exposed steel reinforcement raised concerns about reactor safety.
Still inside the three reactors are about 880 tons of highly radioactive molten nuclear fuel. Robotic probes provided some information, but the state of the melted debris remains largely unknown. The amount is about 10 times as much as the damaged fuel removed in the cleanup of the Three Mile Island nuclear plant in the United States after the 1979 partial meltdown.
Fukushima Governor Masao Oshibori urged TEPCO to “rapidly assess earthquake resistance levels and provide information in such a way that prefectural residents can easily understand and alleviate the anxiety of residents and people across the country.”
Video taken by the robot also showed equipment that slid as well as other types of debris, possibly nuclear fuel that fell from the core and solidified, piling up to a height of 40-50 cm (1.3-1.6 ft) from below the primary containment chamber, said Matsuo. Company officials said the mound is lower than the mounds seen in images taken in previous internal investigations at two other reactors, indicating that meltdowns at each reactor may have progressed differently.
Matsu said data gathered from the latest probe will help experts come up with ways to remove debris and analyze meltdowns in 2011. TEPCO also plans to use the data to create a 3D map of the molten fuel and debris details, which could take about a year.
Based on data gathered from previous investigations and simulations, experts said most of the molten fuel inside Unit 1 fell to the bottom of the primary containment chamber, but some may have fallen into the concrete foundation — a situation that makes it really scary. The shutdown task is very difficult.
The process of removing dissolved debris in the second unit is expected to begin later this year after a delay of nearly two years. Removal of spent fuel from the Unit 1 reactor coolant is scheduled to begin in 2027 after a 10-year delay. Once all spent fuel has been removed from the pools, the focus in 2031 is to remove melted debris from the reactors.
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