The US Nuclear Regulatory Commission hit Southern California Edison’s San Onofre Nuclear Generating Station (SONGS) with a violation for what it called a lapse in plant security, the agency announced late Thursday.

The NRC noted the violation during a four-day inspection in May. SONGS has been completely offline since January, when a radioactive leak led to the discovery of severely degraded heat exchanger tubes in both of the plant’s (nominally) operating reactors. (In July, the NRC released its report on the tube failures, saying that although plant operators had made major design changes that affected the stability of the tubes, they had not violated any laws.)
Regulators said Edison “failed to develop procedures to monitor electronic devices related to security,” but the NRC has withheld most of the details of the violation.