Tokyo Electric Power Co. said Dec. 12 a bent water rod caused two fuel rods to come into contact inside a fuel rod assembly stored in a spent fuel storage pool for the No. 5 reactor of the Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture.
No damage to nuclear fuel or other anomalies have been reported, but the two fuel rods may have been in contact with each other when they were burning inside the reactor.
The situation had the potential to cause a serious fuel failure accident.
A fuel rod assembly is a bundle of 60 fuel rods. A water rod, or a passage for coolant water, runs through its center.
Water rods were found to be bending in 18 fuel rod assemblies in the storage pool. Closer studies found that in one fuel rod assembly, the bending water rod pushed one nearby fuel rod into contact with another.
At the Kashiwazaki-Kariwa plant, a number of unspent fuel rod assemblies had been exposed to excessive loads due to sloppy work procedures when they were encased in metal covers.
The two fuel rods in question may have come into contact during such work procedures, TEPCO officials said.
The fuel rod assembly was encased in a cover in 1994 and burned in the nuclear reactor from 1995 to 2000.
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