A group of researchers has found traces of a tsunami believed to date back to between the 14th and 16th centuries near Takahama nuclear power plant in Fukui prefecture, western Japan.
The plant's operator, Kansai Electric Power Co, said the finding did not affect its evaluation of the risk of a tsunami at the plant or its countermeasures. The Nuclear Regulation Authority, however, said it planned to ask the utility to look into the research.
The idled reactors No 3 and 4 at the Takahama plant obtained safety clearance from the regulator in February, clearing a key hurdle towards resumption.
An official with the regulator said on the finding: "We will examine the information without preconceptions, and will note whether it may relate to a threat to safety."
Hirofumi Yamamoto, professor of geology at Fukui University, and other researchers found a layer of sand containing seashells in shallow ground at a location more than 500 metres from the shore of the bay.
Age measurement via carbon-isotope analysis has dated the layer to between the 14th and 16th centuries.