05000387/LER-2015-003

LER-2015-003, Secondary Containment Inoperability Due to Failure to Meet Technical Specification Surveillance Requirement 3.6.4.1.1

Susquehanna Steam Electric Station Unit 1
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material
Initial Reporting
ENS 51001	10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material
3872015003R01 - NRC Website

LER 15-003-01 for Susquehanna, Unit 1, Regarding Secondary Containment Inoperability Due to Failure to Meet Technical Specification Surveillance Requirement 3.6.4.1.1

ML16026A576
Person / Time
Site:	Susquehanna
Issue date:	01/26/2016
From:	Franke J A Susquehanna, Talen Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
PLA-7430 LER 15-003-01
Download: ML16026A576 (6)

the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503.1f 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 not required to resoond to. the information collection.

Susquehanna Steam Electric Station, Unit 1 05000387

CONDITIONS PRIOR TO THE EVENT

Unit 1 — Mode 1, 100 percent Rated Thermal Power Unit 2 — Mode 5, Refueling There were no systems, structures, or components that were inoperable at the start of the event and contributed to the event. On April 21, 2015, a procedure was in progress on Unit 2 for planned performance of Surveillance Requirements (SR). The procedure and SRs use a simulated loss of offsite power (LOOP) event, and load shedding from an Engineered Safeguards System (ESS) bus, and auto start of diesel generators from standby conditions. This procedure directs the use of a test alignment for the hand switch for the lead Reactor Building (RB) Secondary Containment Zone III supply fan for performance of the required surveillance testing. The test alignment for the hand switch defeats the low flow trip logic of operating supply fans and the auto start of the standby supply fans upon a loss and restoration of power to an ESS bus.

EVENT DESCRIPTION

On April 21, 2015, at 2258 hours0.0261 days <br />0.627 hours <br />0.00373 weeks <br />8.59169e-4 months <br />, the ventilation system that maintains Secondary Containment was unable to maintain a negative pressure requiring entry into the Action Statement for Technical Specification (TS) 3.6.4.1, Condition A, for the failure to meet Surveillance Requirement (SR) 3.6.4.1.1 for Susquehanna Steam Electric Station (SSES) Unit 1 and Unit 2. The Reactor Building (RB) Zone III differential pressure fell below the TS requirement of 0.25 inches water column (in. w.c.) while Zone III fans were in the test alignment for the hand switch, [EllS System Code VA]. A wind gust of approximately 30 mph had been previously recorded at the station. The Zone III ventilation system is designed to shut down if the sensed differential pressure between the zone and the outside atmosphere is too high or too low, as can occur during winds. After the ventilation shuts down, the sensed differential pressure lowers and the system is designed to restart when operating properly. The RB ventilation was restored when the handswitch for the lead Zone III supply fan was returned to the START position, enabling the low flow trip logic of operating RB supply fans, and the auto start of the standby RB supply fans. When the fans restarted, differential pressure was restored to meet the TS requirement of 0.25 in. w.c. at 2314 hours0.0268 days <br />0.643 hours <br />0.00383 weeks <br />8.80477e-4 months <br />. TS 3.6.4.1, Condition A, was later exited on April 22, at 0015 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br />.

On April 22, 2015, at 0158 hours0.00183 days <br />0.0439 hours <br />2.612434e-4 weeks <br />6.0119e-5 months <br />, this condition was reported as an 8-hour Event Notification #51001 in accordance with 10 CFR 50.72(b)(3)(v)(C) for any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the release of radioactive material.

SSES has no redundant Secondary Containment system. In accordance with 10 CFR 50.73(a)(2)(v)(C), this LER is being submitted for an event or condition that at the time of discovery, could have prevented the fulfillment of the safety function of Secondary Containment to control the release of radioactive material.

CAUSE OF THE EVENT

The combination of the equipment line up and high winds caused the Zone III supply fans to trip, resulting in the inability to maintain the vacuum required by TS 3.6.4.1. Since the loss would not have occurred in the absence of high winds, high winds were determined to be the direct cause.

CAUSE OF THE EVENT (contd.) The apparent cause was determined to be inadequate risk assessment of the test alignment with respect to Secondary Containment operability. This equipment configuration had not affected testing in the past, which allowed the risk to become latent. If risk of the alignment had been properly assessed prior to being incorporated into the test procedure, the event would have been prevented either through voluntary LCO entry or via the use of an alternative equipment alignment.

ANALYSIS/SAFETY SIGNIFICANCE

Potential consequences of this event include:

• Unit 1 shutdown per TS 3.6.4.1 action statements if the Completion Time of Condition A was not met

• An unmonitored release of radioactivity to the environment The actual consequence of this event was a degradation of the Secondary Containment differential pressure, which led to an unplanned entry into the Action Statement for TS 3.6.4.1, Condition A, for Unit 1 and Unit 2. An Engineering evaluation was performed, which concluded that Secondary Containment could have performed its safety function of isolating as assumed in the SSES accident analysis and also of re-establishing 0.25 in. w.c.

differential pressure within the assumed accident analysis time of 10 minutes (i.e., drawdown time). Therefore, the safety function of the Secondary Containment boundary and Standby Gas Treatment systems were unaffected and capable of performing their safety function during this event. As such, there were no actual consequences to the health and safety of the public.

Additionally, this event will not be counted as a safety system functional failure (SSFF) for the NRC performance indicator based on the engineering evaluation that was done in accordance with the Nuclear Energy Institute 99-02, Rev. 7, "Regulatory Assessment Performance Indicator Guideline" that concluded there was no loss of Secondary Containment's ability to fulfill its safety function.

CORRECTIVE ACTIONS

Spent Fuel Pool and cavity. Corrective action was taken to restore the RB Zone III ventilation, and exit the TS 3.6.4.1, Condition A, when differential pressure for Secondary Containment was restored to meet the TS requirement in SR 3.6.4.1.1.

Corrective actions included reassessment of the hand switch alignment method from procedures known to use it and departmental reviews of test procedures that fall within the Extent of Condition to ensure no other procedures use inadequately assessed reactor building fan manipulations. All corrective actions to address the event are complete.

Completed Actions:

• Test procedures involved in this event were revised to preclude future occurrences

• A cross-departmental review of procedures was performed to identify any procedures that may utilize alternate positioning of Secondary Containment (Zone I, II and III HVAC) fan exhaust dampers to identify if similar events could occur using the alignment. The action required revision of any identified procedures to prevent challenges to Secondary Containment differential pressure.

PREVIOUS SIMILAR EVENTS

This event is similar to the following events involving the use of procedures that had an impact on maintaining the RB Secondary Containment ventilation.

• LER 50-387(388)/2014-007-00, Loss of Secondary Containment Pressure During RPS Transfer, issued June 12, 2014.

• LER 50-387(388)2013-006-01, Loss of Secondary Containment due to Differential Pressure not Meeting Technical Specification 3.6.4.1, issued July 30, 2014