This 60-day telephone notification is being made under reporting requirements specified by
10 CFR 50.73(a)(2)(iv)(A) to describe an invalid actuation of a containment isolation signal affecting more than one system.
At 2230 CST on November 30, 2017, with the Duane Arnold Energy Center (DAEC) operating at 100 percent power, an invalid Group 3 isolation on the 'B' side of the Primary Containment Isolation System [PCIS] occurred. Group 3 isolation signals were generated for Primary Containment Isolation Valves for Drywell and Torus Ventilation and Purge, Containment Nitrogen Compressor Suction and Discharge, Recirculation Pump Seals, and Post Accident Sample System.
This event was caused by a fault on the 1D25 Instrument AC Inverter. The fault was caused by an insufficient design clearance to ground and was corrected by increasing the clearance.
All equipment responded in accordance with the plant design. Specifically, all actuations were complete and successful.
There were no safety consequences or impacts on the health and safety of the public. The event was entered into DAEC's corrective action program for resolution.
The NRC Resident Inspector has been notified.
