Anti-nuclear activists are expected to protest a meeting Monday night with the Nuclear Regulatory Commission.
Federal regulators have found that design flaws appear to be the cause of excessive wear in tubing that carries radioactive water at San Onofre.
Nuclear Regulatory Commission Regional Administrator Elmo Collins told The Associated Press in an interview that missteps in fabrication or installation are considered as possible sources of the rapid tube decay but "it looks primarily we are pointed toward the design" of the plant's steam generators.
The NRC is scheduled to discuss its findings Monday evening at a meeting near the plant. Anti-nuclear activists plan to attend the meeting in protest. One of those groups includes Friends of the Earth, which filed a petition with the NRC asking for a public hearing on its problems.
Edison did not immediately comment on the NRC findings.
The company said in a statement the Unit 2 reactor likely would remain offline at least through August, pending NRC approval for a restart.
The facility has been off-line since January 31, after problems in a large number of tubes in the nuclear generator. Investigators said the tubes experienced excessive wear, but could not determine the cause of the wear.
Check back for updates on the meeting and protests.