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One of the fears of utility operators in Southern California is coming true and that is the two-unit San Onofre nuclear plant will be down through the end of August, straining electric supply during the state’s high-demand summer period, Southern California Edison (SCE) said.

The utility said it will submit a plan to regulators by the end of July to outline a schedule to restart San Onofre Unit 2, but the plan requires approval of nuclear regulators which will take additional time, the spokeswoman said.

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The 2,150-megawatt nuclear station is halfway between Los Angeles and San Diego and is critical to the grid to import electricity into Southern California, the state independent system operator has said.

San Onofre’s extended shutdown raises the possibility of rolling power outages as warmer temperatures boost demand for power over the summer, the California Independent System Operator said.

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A plan to restart Unit 3 will take longer to file with nuclear regulators, the spokeswoman said, due to the type of damage found there.

The five-month outage began following the discovery of premature tube wear in steam generators made by Mitsubishi Heavy Industries and installed within the past two years.

The Nuclear Regulatory Commission (NRC) said San Onofre’s tube degradation was serious enough that the utility must identify the root cause and find ways to manage it before seeking NRC approval to restart either reactor.

SCE has plugged more than 1,300 worn tubes inside four giant steam generators. The utility has blamed accelerated tube wear on vibration that allows the tubes to rub against each other and support structures inside the steam generators, but is still working to understand the cause.

SCE has said it may have to operate the reactors at a reduced output of between 50 percent and 80 percent for several months, then perform inspections to look for additional wear.

The NRC will hold a public meeting June 18 in California to discuss results of a two-month special inspection of Unit 3, according to a notice.

The NRC staff will summarize the findings of an “augmented inspection team” and SCE officials will respond to the report.

The NRC said the meeting will be the first in a series to keep the public informed on the agency’s oversight activity.

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