The following information was provided by the licensee via phone and email:
This 60-day telephone notification is being made in accordance with 10 CFR 50.73(a)(1) and 10 CFR 50.73(a)(2)(iv)(A).
On August 8, 2023, at 1107 hours0.0128 days <br />0.308 hours <br />0.00183 weeks <br />4.212135e-4 months <br /> pacific daylight time (PDT) with Unit 1 in Mode 1 at 100 percent power, an invalid actuation occurred when Unit 1 4-kV vital bus 'G' was automatically transferred from auxiliary power to startup power due to an invalid bus under voltage signal, which occurred during planned maintenance activities.
As a result of the actuation signal, auxiliary salt water and containment fan cooling units transferred automatically and started as designed. Plant systems responded as expected. This event was entered into the Diablo Canyon Power Plant corrective action program for resolution.
There was no plant or public safety impact.
The NRC Senior Resident Inspector has been notified.