Tohoku Electric Power Co. said Monday it detected cracks in 12 places in a reactor at its nuclear power plant in Miyagi Prefecture during a regular inspection early this month.
The cracks were found in the shroud of a pressurizer in the Onagawa plant's No. 1 reactor. There was no radiation leakage or impact on the external environment, company officials said.
The cracks -- the largest some 14 cm long -- were discovered during an inspection that began Sept. 8, the company said at a news conference in the afternoon.
They were found running along the center part of the shroud, with other cracklike lines found near the bottom. Company inspectors are trying to confirm whether these, too, are cracks.
The top and middle sections of the shroud were checked during a regular inspection in 1994, while the bottom portion was inspected in 1995. Neither of the inspections showed any irregularities, the officials said.
Tohoku Electric Power supplies power in northeast Japan.
Miyagi Gov. Shiro Asano expressed concern over the latest findings at the Onagawa plant.
"If (the cracks) pose a serious problem to operations, the issue will be whether there were any prior indications," he said. "All records of previous inspections should be scrutinized."