Damage to a pedestal inside the No. 1 reactor at the crippled Fukushima No. 1 nuclear power plant is more critical than previously believed, triggering a more intricate assessment of its resistance to a major earthquake.
Plant operator Tokyo Electric Power Co. (TEPCO) has no time to waste in confronting the issue. It must swiftly assess the damage and take effective action to prevent an accident or leak of radioactive materials.
An underwater robotic probe detected the damage in late March. It found that the metal framework lies exposed along the inner side of the pedestal’s wall for about 1 meter from its bottom and for the entire inner circumference as concrete in these areas has been lost.
There are fears the containment vessel that houses the pressure vessel could crack if the pedestal collapses in a severe earthquake. That could cause radioactive materials to leak.
Referring to the structure’s current earthquake resistance, TEPCO stressed that the pedestal has managed to support the reactor vessel even though the plant “has experienced strong earthquakes.” The utility cited one last year that registered lower 6 on the Japanese seismic intensity scale of 7.
Although the possibility of the pressure vessel tilting or sinking cannot be ruled out, the company asserts the impact will be limited with no risk of radioactive material leaking to the outside.
However, the Nuclear Regulation Authority (NRA) said last week it could not decide whether the assumptions underlying TEPCO’s risk assessment are accurate as the extent of damage and condition of the structural materials are not yet fully understood. The nuclear safety watchdog also said it would be difficult to reinforce the pedestal because of high radiation levels inside the containment vessel.[…]