Tokyo Electric Power Co. said March 19 it has uncovered a second instance of fuel rods coming into contact with each other at its Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture.
According to TEPCO, the rods in question were found in a fuel assembly stored in a spent fuel storage pool for the No. 1 reactor.
The company has been surveying all seven reactors at the plant after rods were found in contact with each other inside the spent fuel storage pool for the No. 5 reactor in December.
The Nuclear Regulation Authority provisionally rated the latest incident a Level 1 on the seven-level International Nuclear and Radiological Event Scale the same day.
A fuel assembly is a bundle of 60 fuel rods. A metal water rod, or a passage for coolant water, runs through its center.
According to TEPCO, bent water rods were found in six fuel assemblies in the storage pool for the No. 1 reactor. One of those water rods had bent a fuel rod and pushed it into contact with one next to it.
The six fuel assemblies were used in the reactor between 1997 and 2002.
TEPCO said that under methods used until 1998, fuel assemblies were subjected to intense pressure when they were placed into metal casings. That pressure may have deformed the water rods, TEPCO officials said.
TEPCO and other nuclear plant operators have been checking whether similar instances have occurred at their facilities, but no such cases have been found so far.
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