Diablo Canyon's Unit 2 reactor was offline Friday evening as Pacific Gas and Electric Company crews fix recently discovered problems on a couple of the unit's backup generators.
According to PG&E, the reactor was shut down Thursday night so that a couple of parts—described as fasteners or bolts—could be replaced.
Crews decided during routine maintenance that the parts were not performing properly. PG&E is required to keep two out of the unit's three backup generators in good running order at all times in case of a power outage at the plant.
The company says subsequent inspections of Unit 1 did not turn up similar problems, so that reactor continues to operate at full power.
The power plant, located near Avila Beach in San Luis Obispo County, provides 20 percent of the electricity that PG&E delivers to its customers, according to a press statement.