05000388/LER-2016-003

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LER-2016-003, Secondary Containment Inoperability due to Failure to Meet Surveillance Requirement 3.6.4.1.1
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 51872 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material
3882016003R00 - NRC Website
v • d • e

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by interne( e-mail to Int ocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, 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.

CONDITIONS PRIOR TO EVENT

Unit 1 — Mode 4, 0 percent Rated Thermal Power Unit 2 — Mode 1, 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.

On April 19, at 1606 hours0.0186 days <br />0.446 hours <br />0.00266 weeks <br />6.11083e-4 months <br />, supply and exhaust fan swaps were completed for the Reactor Building (RB) Heating Ventilation and Air Conditioning (HVAC) systems [EIIS System Identifier: VA]. The fan swaps were associated with equipment maintaining Zone II of Secondary Containment (Unit 2 RB [EMS System Identifier: NG]).

EVENT DESCRIPTION

On April 19, 2016 at 2159 hours0.025 days <br />0.6 hours <br />0.00357 weeks <br />8.214995e-4 months <br />, Secondary Containment became inoperable, requiring an action of Technical Specification (TS) 3.6.4.1 to restore the system to an operable status in four hours. The TS 3.6.4.1, Condition A for an inoperable Secondary Containment was entered because RB Zone II differential pressure (dP) was below the required TS required limit of >1= 0.25 inches of vacuum water gauge (in. w.g.), which does not meet the Surveillance Requirement (SR) 3.6.4.1.1. The Zone II supply system outside air (intake) louver XD-27586 [EIIS Identifier: LV] was then adjusted and the Zone II dP returned to a steady 0.29 in. w.g. of vacuum, which was above the required TS limit. The TS 3.6.4.1, Condition A for inoperable Secondary Containment was exited at 2222 hours0.0257 days <br />0.617 hours <br />0.00367 weeks <br />8.45471e-4 months <br />.

The event was reported to the NRC on April 20, 2016 in accordance with 10 CFR 50.72(b)(3)(v)(C) under Event Notification 51872, and per the guidance of NUREG-1022, Revision 3, Section 3.2.7, for applicable reporting criteria on the loss of a safety function. There is no redundant Secondary Containment system.

This LER is being submitted in accordance with 10 CFR 50.73(a)(2)(v)(C), for an event or condition that could have prevented the fulfillment of the safety function of Secondary Containment to control the release of radioactive material.

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet 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.

CAUSE OF EVENT

The cause of this event was determined to be less than adequate Operating Procedure (OP) instructions for the RB HVAC systems. Specifically, a final step in the OP after swapping fans is only to ensure that dP is >1= to the required 0.25 in. w.g. of vacuum. As a result, the pressure (demand) on the zone controller was not being checked following fan swaps. If the pressure (demand) for the controller is out of the control band of 10 to 14 psi, it then leaves the zone vulnerable to changes that occur in dP, as may occur with changing ambient conditions. In order to ensure the dP will continue to meet the required SR acceptance criteria, a step will be added to the OP to ensure that controller demand is within the desired control band after swapping fans.

ANALYSIS/SAFETY SIGNIFICANCE

If the condition had not resolved within four hours, the unit would be required by TS to initiate actions to shutdown. The actual consequence was the degradation of the required Secondary Containment vacuum, and a resulting inability to meet the SR acceptance criteria for a brief period of time, approximately 23 minutes. This led to the unplanned need to take the Required Action of TS 3.6.4.1 to restore Secondary Containment to an operable status. An engineering evaluation was performed that concluded Secondary Containment could have still performed its safety function of isolating as assumed in the accident analysis and also of re-establishing 0.25 in. w.g. of vacuum (i.e., drawdown time) within the assumed accident analysis time of 10 minutes. Therefore, the safety function of the Secondary Containment boundary and Standby Gas Treatment systems were unaffected and capable of performing their safety functions during this event. As such, there were no actual consequences to the health and safety of the public. Based on an engineering evaluation to show there to be no loss of the Secondary Containment safety function, this event will not be counted as a safety system functional failure (SSFF) for the NRC performance indicator.

CORRECTIVE ACTIONS

Immediate action completed on April 19, 2016, restored Secondary Containment to an Operable status.

The planned corrective action includes:

  • The Operating Procedure (OP) instructions for the Units 1 and 2 RB HVAC systems will be revised to include a step that requires checking the pressure gauge on the RB exhaust fan controllers, (e.g., PDC-27581 and PDC-17581) for their respective zones.

comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet 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.

PREVIOUS SIMILAR EVENTS

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

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