The following information was provided by the licensee via email:
The following event description is based on information currently available. If, through subsequent reviews of this event, additional information is identified that is pertinent to this event or alters the information being provided at this time, a follow-up notification will be made via the ENS or under the reporting requirements of 10 CFR 50.73.
This telephone notification is being made pursuant to the reporting requirements of 10 CFR 50.73(a)(1) and 10 CFR 50.73(a)(2)(iv)(A) to describe invalid actuations of the Palo Verde Nuclear Generating Station (PVNGS) Unit 1 B Train Auxiliary Feedwater (AF) system and Essential Spray Pond (ESP) system that occurred while in a refueling outage.
On April 11, 2022, at approximately 2045 Mountain Standard Time, an automatic start of the Unit 1 B Train AF and ESP systems occurred during restoration from a surveillance test. The station was conducting a surveillance test during a Unit 1 refueling outage to verify the proper responses of the Engineered Safety Features Actuation Systems to simulated design basis events. The test portion was completed satisfactorily; however, during the restoration portion, the load sequencer inadvertently cycled between Mode 0 and Mode 1 three times in immediate succession.
At the time of the system actuations, one of the actuation signals associated with this portion of the test had been reset per procedure. Another actuation signal was still in while restoration steps were ongoing, but the sequencer was not expected to cycle between Modes. The system actuations did not occur as a result of actual plant conditions or parameters and are therefore invalid.
The Unit 1 B Train AF and ESP system actuations were complete and the systems started and functioned successfully. For the systems that did not actuate, the reasons are clearly understood as those systems were in an overridden condition due to test configuration.
The spurious actuation was not able to be replicated and a direct cause was not identified. There were no adverse impacts to public health and safety nor to plant employees.