UPDATE 3:53 p.m.: A preliminary investigation into the cause of an unexpected shutdown of Unit 2 at Diablo Canyon nuclear power plant indicates that the electrical disturbance that triggered the shutdown was a result of a flashover event on a lightning arrester located on the non-nuclear side of the plant, said Blair Jones, PG&E spokesman.
A flashover is an unintended arc between two pieces of electrical equipment. The flashover occurred during routine maintenance that involved pressure washing, known as hot washing, of electrical insulators near the lightning arrester. Upon sensing the disturbance, the unit performed as designed and automatically went offline to protect equipment.
The unit remains in a safe condition. PG&E has informed the U.S. Nuclear Regulatory Commission and appropriate local and state officials.
Original story: Unit 2 at Diablo Canyon nuclear power plant was unexpectedly shut down Wednesday morning.
The cause of the shutdown was a disturbance in equipment that moves electricity from the plant to the states electrical grid, said Blair Jones, Pacific Gas and Electric Co. spokesman.
The unit was shut down safely, and plant operators are working to determine the exact cause of the incident. The plants other nuclear reactor continues to generate power.
The unit will be restarted after the cause of the incident is fully understood and equipment is tested, Jones said.