The Nuclear Regulation Authority has confirmed that trouble with nuclear fuel rods stored in the spent-fuel pool of reactor 5 at the Kashiwazaki-Kariwa plant in Niigata Prefecture should be designated as a level 1 incident based on a globally recognized scale, the watchdog's officials said.
A pair of fuel rods at Tokyo Electric Power Co.'s massive atomic power complex were found to be touching after the bundle of rods they are stored in became overheated and deformed, leading the NRA to determine that the fuel had likely been loaded to the reactor core "in an abnormal situation," the officials said.
This assessment is only provisional, and the NRA added that no leakage of radioactive substances was observed, the officials said.
The flow of coolant water through the bundle of fuel rods could be hampered if they stick together, making it easier for heat to accumulate, the NRA said.
Level 1 on the International Nuclear and Radiological Event Scale is a stage defined as an "anomaly." The Fukushima No. 1 meltdowns last year and the 1986 Chernobyl catastrophe were classed as level 7 incidents.
Tepco reported Oct. 16 that it had discovered deformed sections of spent nuclear fuel assemblies in reactor 5's spent-fuel tank at the Kashiwazaki-Kariwa plant, on the Sea of Japan coast.