Tohoku Electric Power Co. and Chubu Electric Power Co. admitted Friday they failed to report structural faults in their nuclear plants to the government.
Four minor cracks in pipes carrying primary cooling water were found at Tohoku Electric's Onagawa No. 1 plant in Miyagi Prefecture during regular checks in 1998 and 2001, officials at the utility said.
They failed to report the cracks because they thought they were not problematic, they said.