Tokyo Electric Power Co. (9501) suspended the removal of spent nuclear fuel rods at its wrecked Fukushima plant after a cooling system failed due to a damaged power cable, the company said in an e-mailed statement.
The cooling system at reactor No. 4 was halted at about 9:45 a.m. local time and it would take around two hours for it to be replaced by a backup system, the company known as Tepco said. The water is cool enough to remain at a safe temperature until the backup system is operating, it said.
The failure occurred after a power cable was damaged during excavation work at another building at the plant, Tepco said. No abnormalities were found at the spent fuel pools at the other three reactors, or at the plant’s shared pool.
Tepco began removal of 1,331 spent fuel assemblies in the No. 4 unit’s pool on Nov. 18 in what it described as a major milestone toward the plant’s decommissioning.
The No. 4 reactor building was heavily damaged by an explosion and fire in the days following the March 11 earthquake and tsunami in 2011. This led to concerns the nuclear rods in the spent fuel pool may have been damaged, adding to the risk of removal, a process that will continue until the end of this year.
Were the rods to break, it could release krypton-85, which may increase the risk of cancer to those who come in contact with the radioactive gas, according to Arnie Gundersen, chief engineer at Burlington, Vermont-based energy consultant Fairewinds Associates Inc.
Another risk is if two assemblies come too close together during removal. If the chemical protection around the fuel pods was compromised during the 2011 accident, contact could result in a self-sustained nuclear chain reaction that might boil off the water in the spent fuel pool within days, Gundersen said.
Without that cooling water, a fuel fire could result in the spread of radiation on a similar scale to that after the meltdowns at the three Fukushima reactors in 2011, he said.
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