The determination is likely to delay the restart of the plant's reactors, Yomiuri Shimbun reported Tuesday.
The Nuclear Regulation Authority made the assessment in a draft report of an on-site inspection of the Higashidori nuclear power plant in Aomori prefecture that is operated by Tohoku Electric Power Co.
The report means Tohoku will probably not be able to restart the plant's reactors in July 2015 as hoped. Several crush zones run near the plant's reactor building and the plant operator will have to review predictions about possible earthquake intensities and the facility's ability to withstand a tremor.
The agency is expected to ask other experts to evaluate the findings of the draft report.
The NRA previously issued a separate assessment that the Tsuruga nuclear power plant in Fukui prefecture confirming that crush zones at the site were active faults.
Both plants may have to permanently shut down if investigations agree with the assessments.
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