Just a month before a powerful earthquake and tsunami crippled the Fukushima Daiichi plant at the center of Japan’s nuclear crisis, government regulators approved a 10-year extension for the oldest of the six reactors at the power station despite warnings about its safety.

The regulatory committee reviewing extensions pointed to stress cracks in the backup diesel-powered generators at Reactor No. 1 at the Daiichi plant, according to a summary of its deliberations that was posted on the Web site of Japan’s nuclear regulatory agency after each meeting. The cracks made the engines vulnerable to corrosion from seawater and rainwater. The generators are thought to have been knocked out by the tsunami, shutting down the reactor’s vital cooling system.