Some of the faults running under the Kashiwazaki-Kariwa atomic plant, the world's biggest, could be considered active under the new nuclear regulator's safety standards, according to documents disclosed by Tokyo Electric Power Co.
If the faults are judged "likely to be active" by the Nuclear Regulation Authority, the nation's top utility will have a difficult time restarting reactors at the massive plant on the coast of Niigata Prefecture.
Under government criteria, active faults are defined as those that have moved in the past 120,000 to 130,000 years. But the NRA, set up in September after its predecessor was discredited over the March 2011 triple-meltdown crisis at Tepco's Fukushima No. 1 plant, plans to move the benchmark to cover the past 400,000 years in new safety standards with teeth set to take effect in July.
A draft of the new standards presented by the NRA on Tuesday stated that utilities won't be allowed to build reactors directly above active faults.
Tepco is conducting a geological survey of the faults under the Kashiwazaki-Kariwa plant's reactors, which produce a combined 8,212,000 kw.
The NRA said it will decide whether to conduct its own probe after the outcome of Tepco's survey becomes clear. Tepco said two faults, "alpha" and "beta," run below reactors 1 and 2. Faults have also been found under reactors 3, 5, 6 and 7.
Tepco denies the faults are active under existing guidelines, but the beta fault, for example, could be categorized as active under the upcoming standards because it has displaced a ground layer that includes volcanic ash dating back 240,000 years.