For more than 40 years, Japan Atomic Power Co. used erroneous data regarding the location of nuclear fuel rods within the reactor at its Tokai No. 2 power plant in Ibaraki Prefecture, the company has said.

The information — which is used to plan for severe accidents — is necessary for regulatory safety screenings before the reactor’s restart can be approved.

Japan Atomic Power said Monday it will examine whether the data mishap has affected safety screenings.

The company said the data in question pertains to the distance between the top of the fuel rods and the bottom of the reactor. The distance was initially set to be 9,152 millimeters, but it was changed to 9,203 millimeters due to a change to fuel rod specifications during the design and construction process.

But the original figures were used since 1974. The problem was discovered on Jan. 11 by the Nuclear Regulation Authority, a government watchdog.

The plant, which started operations in November 1978, reached the standard operating life of 40 years this year.

Japan Atomic Power has filed for a 20-year extension. The plant must clear safety screening by November to be approved by the NRA for an extension.