The troubled San Onofre nuclear power plant will remain dark through the hot summer months when energy demand is at its highest in Southern California.

The top official at Edison International said Thursday that the plant will not restart any time soon and that, instead, the utility will lean on a pair of mothballed generating units in Huntington Beach and will implement alerts and incentives for customers to conserve power.

When running at full capacity, San Onofre supplies about 19% of the power to Edison customers in Southern California.

Officials said the contingency plans should be sufficient to get customers through the summer without power shortages under all but the most extreme circumstances.

The plant, located on the coast just south of San Clemente, has been shuttered since Jan. 31, while officials probe the extent and cause of unusual wear on tubes that carry radioactive water in the plant’s newly replaced steam generators.

The Nuclear Regulatory Commission has ordered the plant to stay offline until Edison can identify the exact cause of the wear and determine how to fix it.

Ted Craver, chief executive of Edison, parent company of plant operator Southern California Edison, said the earliest that the Unit 2 reactor could restart would be the end of summer, and Unit 3, which showed more troubling wear, may take longer.

“I don’t see how we could submit [a restart plan] to the NRC before the end of July, and their process is maybe another month, so that’s the end of August,” Craver said.

Making the call on when it is safe to restart the plant will be a “huge decision,” he said: “I’m not sure there’s going to be a bigger decision I make in my time as CEO here.”

The NRC will have final say on when and under what conditions the plant can fire up again. The agency announced Thursday that it has scheduled a public meeting in San Juan Capistrano on June 18 to discuss the initial findings of a special inspection team it dispatched to the plant.

Edison officials believe the perplexing wear is happening because the rate of steam flow among the tubes is causing excessive vibration, leading the tubes to rub against each other. But they still have not pinpointed exactly what led to those conditions.

Reports by environmental group Friends of the Earth have blamed design changes in the replacement steam generators for causing the wear issues. Craver said the steam generators were designed to prevent vibration issues but “the implementation of the design doesn’t appear to be meeting the specification.”

To date, 1,317 tubes in the plant’s two working reactor units have been taken out of service, representing a little more than 3% of all the plant’s tubes. About one-third of those were plugged because of excessive wear and the others were plugged as a preventive measure, Craver said.

The short-term plan to restart San Onofre could involve running at lower power to decrease the rate of steam flow. In the longer term, Craver said other options could include adding supports for the tubes or replacing the steam generators entirely. The latter is a costly proposition since the last steam generator replacement came in at an estimated $671 million.

Edison officials have said they will seek to recover the inspection and repair costs under the warranty with steam generator manufacturer Mitsubishi Heavy Industries, but ratepayers could end up on the hook for the costs to buy replacement power.

The steam generator problems and other issues at the plant have led some environmental groups and local residents to say the plant can’t be operated safely and should be decommissioned. San Onofre is one of two nuclear plants in California. The other is the Diablo Canyon nuclear plant in San Luis Obispo County.

abby.sewell@latimes.com