After more than 40 years, the San Onofre nuclear plant in San Clemente, Calif. will be closing permanently.

The announcement that the plant’s Units 2 and 3 would be retired was made by majority owner Southern California Edison (SCE) on June 7. SCE said that the continuing uncertainty about when or if Unit 2 might return to service was not good for customers, investors or the need to plan for the region’s long-term electricity needs.

“With this decision, SCE is now focused on looking ahead to planning for California’s energy future,” said Ron Litzinger, SCE president.

When Units 2 and 3 were operating, the reactors were capable of producing enough power to serve 1.4 million average homes.

The Nuclear Regulatory Commission (NRC) will continue to provide oversight of the San Onofre nuclear plant during the decommissioning process. The NRC has a well-defined, decommissioning procedure that involves transferring the used fuel into safe storage, followed by the removal and disposal of radioactive components and materials. Longer term, this process calls for reducing residual radioactivity to a level that supports termination of the NRC license.

Nuclear plants are required by the NRC to put aside funds for decommissioning while the plant is operating. The California Public Utilities Commission regulates utilities that own nuclear plants in the state and has allowed SCE to collect those funds during the operating years of the nuclear plant. The money is collected from customers and invested in dedicated trusts.

The cost to decommission Units 2 and 3 is about $4.1 billion. SCE, as majority owner, must provide $3 billion, of which $2.7 billion has been collected through March 31. Other co-owners have collected more than $927 million through last December.

Within two years of SCE’s June 7 decision to permanently close the San Onofre nuclear plant, the utility will submit to the NRC and state officials a detailed plan that spells out specific decommissioning activities and schedules, cost estimates and potential environmental impacts. As part of this process, there will be public review and comments.

For more information, the NRC has addressed some frequently asked questions.