Event Notification Report for August 22, 2024

CONTROL ROOM VENTILATION INOPERABLE

The following information was provided by the licensee via email and phone:

"At 2001 EDT on 8/20/2024, it was discovered that both trains of the control room ventilation system were simultaneously inoperable. Due to this inoperability, the system was in a condition that could have prevented the fulfillment of a safety function; therefore, this condition is being reported as an eight-hour notification per 10 CFR 50.72(b)(3)(v).

"There is no impact on the health and safety of the public or plant personnel. The NRC resident inspector has been notified.

"One train of control room ventilation was restored to operable status at 2107 EDT on 8/20/2024."

The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance:

While performing canister maintenance on train B, it was discovered that the dampener for train A failed to close. Train B was restored at the conclusion of maintenance.


* * * UPDATE ON 08/21/24 AT 1648 EDT FROM LAUREN ANDERSON TO JOSUE RAMIREZ * * *

The following information was provided by the licensee via email and phone:

"This event is also reportable per 10 CFR 50.72(b)(3)(xiii), loss of emergency assessment capability, as the technical support center facility is located inside the control room envelope."

Notified R2DO (Masters)

CONTROL ROOM FILTRATION SYSTEMS INOPERABLE

The following information was provided by the licensee via fax or email:

"At 2010 CDT on 08/20/2024, with Unit 2 in Mode 1 at 100% power, Train B Essential Chiller was unable to maintain the Chilled Water Outlet Temperature in the required band. Train B Essential Chilled Water and the associated cooled components were declared inoperable. Train B Control Room Makeup and Cleanup Filtration System was declared inoperable due to the unavailability of cooling. Train C Control Room Makeup and Cleanup Filtration System was previously inoperable for planned maintenance for reasons other than loss of cooling. This resulted in the inoperability of two of the three 50-percent capacity safety trains required for accident mitigation.

"This event is reportable under 10 CFR 50.72(b)(3)(v)(D) as a condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.

"There was no impact on the health and safety of the public or plant personnel. The NRC Resident Inspector has been notified."

The following additional information was obtained from the licensee in accordance with Headquarters Operations Officers Report Guidance:

Train C has been placed back in service and is awaiting testing to verify its ability to perform its safety function. Testing is expected to be completed by 1500 CDT on 08/21/2024. Plant is on a 72 hr S/D clock until restoration is verified.

SECONDARY CONTAINMENT BOUNDARY INOPERABLE

The following information was provided by the licensee via fax and phone:

"At 1200 EDT on 8/21/2024, with Millstone unit 3 in mode 1 at 100 percent power, it was discovered that the secondary containment boundary was inoperable while maintenance activities on the system were in progress. Therefore, this condition is being reported as an eight-hour, non-emergency notification per 10 CFR 50.72(b)(3)(v)(C) and (D).
"There is no impact on the health and safety of the public and plant personnel. The NRC Resident Inspector has been notified.
"Unit 3 continues to operate in mode 1 at 100 percent power with actions in progress to restore the system to operable within the technical specification allowed outage time. There has been no impact to unit 2, which remains at 100 percent power.

"The state of Connecticut and local towns were notified."