Does closing San Onofre plant raise blackout concerns?

A little bit, but barring unusual problems this summer Southern California Edison should be all right. The utility's reserve margins could drop to as low as 6 percent during peak demand, which is still above the 3 percent level at which disruptions start to occur, according to the publication Power. That assumes power supplies aren't reduced by outages at other plants or transmission problems due to wildfires. If that happens, the story could change. Last summer, Socal Edison made up for the loss of San Onofre by bringing back two gas-fired units at the Huntington Beach Power Plant. But those units are not longer available. The decision to shut down the plant permanently was not unexpected - the operation has been out of service for a year and a half amid all sorts of back-and-forth between regulatory officials and the utility. From Power:

The California Independent System Operator said the absences of San Onofre Nuclear Generating Station and the Huntington Beach units, as well as reduced hydroelectric generation as a result of an ongoing drought, mean reliability risks to southern Orange and San Diego counties are "marginally more challenging" this summer, but still within planning standards. Several new combined cycle plants in the Los Angeles area that came online recently have eased pressure further north.

From the LAT:

A long-range future without the plant is a more complicated scenario, largely because the state is also implementing new regulations on the way coastal power plants use seawater for cooling. San Onofre will loom large in upcoming discussions on whether to retire, retrofit or repower 11 gas-fired coastal plants that supply about 11,000 megawatts of power -- nearly five times what San Onofre generates. The nuclear plant, which once supplied enough power for about 1.4 million homes in Southern California, has been shuttered for 15 months because of unusual deterioration of tubes in its replacement steam generators.