|Susquehanna Steam Electric Station Unit 2 05000-387|
|Reporting criterion:||10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material|
|3872017003R00 - NRC Website|
|Person / Time|
|Site:||Susquehanna Steam Electric Station Unit 2 05000-387, Susquehanna|
Susquehanna, Talen Energy
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17125A013 (4)|
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclenr Regulatory Commission, Washington, DC 20555-0001, or by e-mail to NEON 10202: (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is riot required to respond to, the information collection.
Susquehanna Steam Electric Station Unit 2 05000-387 YI-AR SEQUEN1 lAm. REV
CONDITIONS PRIOR TO EVENT
Unit 1 — Mode 1, approximately 100 percent Rated Thermal Power Unit 2 — Mode 5, approximately 0 percent Rated Thermal Power There were no structures, systems, or components that were inoperable at the start of the event that contributed to the event. Unit 2 was in a refueling outage and Zone II was relaxed.
On March 8 at approximately 0239, during work to replace Load Center Breaker 2B240-021 (supply breaker to 2B246) [EIIS: BKR] and inspect MCC Breaker 2B246-023 [EllS: BKR], both units Zone III HVAC [EIIS:NA] differential pressure was lost when Operations commenced the restoration phase prematurely. The error occurred when Load Center Breaker 2B240-021 (supply breaker to 2B246) [EIIS: BKR] was returned to service without MCC Breaker 2B246-023 [EIIS: BKR] restored. Unit 2 Zone Ill isolation dampers [El IS:DMP] were temporarily aligned to an alternate power supply during the work. When Operations attempted to restore Zone 3 HVAC damper control power to normal, there was no power available from Distribution Panel 2Y246. The Unit 2 division II Zone III isolation dampers [EIIS: DMP] failed to their safety "closed" position causing a low flow trip of all Unit 2 Zone III fans [EIIS:FAN].
This resulted in Zone III differential pressure lowering to less than the TS 184.108.40.206 allowable limit of 0.25 in w.g.
A timeline of events is as follows:
0235: Commenced MCC 26246 bus restoration.
0239: Operations place the Control Power Supply to Unit 2 RB Dampers to normal. Unit 2 Zone III Division II dampers [EIIS: DMP] closed due to loss of control power causing Unit 2 Zone III fans [EIIS:FAN] to trip on low flow.
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.
Susquehanna Steam Electric Station Unit 2 05000-387 - 00 2017 - 003
CAUSE OF EVENT
The cause of the event was less than adequate procedure use and adherence.
Secondary Containment Zone III pressure was not maintained above the TS 220.127.116.11 required vacuum of 0.25 in w.g. with respect to outside atmosphere. The event was caused by a loss of power to the Unit 2 Zone III isolation dampers, which caused them to close. This resulted in the shutdown of the Unit 2 Reactor Building fans and a loss of Zone III vacuum. This event is being reported pursuant to 10 CFR 50.73(a)(2)(v)(C) as a condition that could have prevented fulfillment of a safety function to mitigate the consequences of an accident by controlling the release of radioactive material.
There was no actual safety consequence as a result of this event. Engineering analysis of this event has determined that secondary containment could have performed its safety function of isolating, as assumed in the accident analysis, and also of re-establishing 0.25 in w.g. vacuum (drawdown) within the assumed accident analysis time (10 minutes). This event will not be counted as a safety system functional failure (SSFF) for the NRC performance indicator.
Corrective actions included a communication to Operators and a revision to the Procedure and Work Instructions Use and Adherence procedure to perform a second check for non-conditional procedure steps.
PREVIOUS SIMILAR EVENTS
2016 (PLA-7459) 10, 2015 (PLA-7329)