05000388/LER-2017-009

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LER-2017-009, Secondary Containment Declared Inoperable Due to Trip of Zone II Equipment Exhaust Fan
Susquehanna Steam Electric Station Unit 2
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 52973 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material
3882017009R01 - NRC Website

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.

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3. LER NUMBER

CONDITIONS PRIOR TO EVENT

Unit 1 — Mode 1, approximately 100 percent Rated Thermal Power Unit 2 — Mode 1, approximately 100 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.

EVENT DESCRIPTION

On September 16, 2017, a plant operator identified belts associated with the Unit 2 "B" Reactor Building Equipment Compartment Exhaust fan (2V206B) [EIIS System/Component Identifier: VA/FAN] slipping and a hot burnt rubber smell in the area. The operator recommended swapping fans to place the "A" fan (2V206A) in service.

At approximately 13:30, when performing the swap to place the 2V206A fan in service, the 2V206A fan tripped unexpectedly after being placed in service. Reactor Building [EIIS System Code: NG] differential pressure lowered to Surveillance Requirement 3.6.4.1.1 was not met due to loss of Secondary Containment differential pressure. The 2V206B fan was placed back in service and Reactor Building differential pressure was restored to above 0.25 inches WG.

On September 16, 2017, at 15:53, this condition was reported (ENS #52973) in accordance with 10 CFR 50.72(b)(3)(v)(C) as an event or condition that, at the time of discovery, could have prevented the fulfillment of the safety function to mitigate the consequences of an accident by controlling the release of radioactive material. Susquehanna Steam Electric Station (SSES) has no redundant Secondary Containment System.

CAUSE OF EVENT

The failure was not able to be replicated during investigation. The direct cause is inconclusive.

A failure modes analysis was completed to identify the likely cause of the fan trip. Potential causes include the following:

1. Linkages on Flow Control Damper PDD27522A [EIIS System/Component Identifier: VA/CDMP] could have been binding and prevented the damper from going open.

2. Low Flow Switch FSL27522A [EllS System/Component Identifier: VA/FS] could have failed to reset during the 2V206A start.

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.

3. LER NUMBER

2017 - 009 - 01 44)

CONTINUATION SHEET

The procedure section for performing a fan swap includes the following caution statement: "Minimizing time between start of standby fan and subsequent shutdown of running fan will prevent low flow trip to occur. Low flow trip will occur if fans remain in parallel for approx. 30 seconds". Operator interviews indicated the discharge damper took longer than expected to open. The fans may have been running in parallel for longer than 30 seconds.

ANALYSIS/SAFETY SIGNIFICANCE

Based on engineering analysis of the event, secondary containment could have performed its safety function of isolating as assumed in the accident analysis and of re-establishing 0.25 inches of vacuum WG (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 based on the engineering analysis supporting the system's ability to fulfill the safety function.

CORRECTIVE ACTIONS

Due to the definitive cause being inconclusive, the remaining potential failure modes identified as unlikely are being addressed to minimize or eliminate an event similar to this. Corrective actions include the following:

1. Linkages on Flow Control Damper PDD27522A will be greased to reduce the probability of binding from occurring 2. The reset for the Low Flow Switch FSL27522A will be tested to address the potential of an intermittent failure. If the reset test is unsatisfactory, the low flow switch will be replaced.

3. The caution statement in the applicable Unit 1 and 2 procedures will be revised to state "Leaving fans operating in parallel may cause a low flow trip. Securing a fan should be performed as soon as the discharge damper indicates dual position. Low flow trip will occur if flow remains below trip setpoint of 18,000 scfm for approximately 30 seconds.

COMPONENT FAILURE INFORMATION

Information for Flow Control Damper PDD27522A:

Manufacturer: Trane Model: CF40A3SW3CCUBSX Information for Low Flow Switch FSL27522A Manufacturer: United Electric Controls Model: J-6-142-9515 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, file information collection.