05000397/LER-2014-001
On January 9, 2014 at 1743 and 1834 hours0.0212 days <br />0.509 hours <br />0.00303 weeks <br />6.97837e-4 months <br /> secondary containment was declared inoperable during repositioning of the dampers. These two events had durations of 3 and 2 minutes respectively. Control Room operators took manual control of the Reactor Building Exhaust Air flow system to restore secondary containment in the first event, and the controller restored pressure automatically in the second.
On January 15, 2014 at 0907 hours0.0105 days <br />0.252 hours <br />0.0015 weeks <br />3.451135e-4 months <br /> and February 17, 2014 at 0304 hours0.00352 days <br />0.0844 hours <br />5.026455e-4 weeks <br />1.15672e-4 months <br /> secondary containment was declared inoperable during repositioning of the dampers and during high winds respectively. These two events had durations of 6 and 2 minutes respectively. The system controller automatically restored secondary containment differential pressure in both events. In each of these events secondary containment vacuum was not maintained greater than or equal to 0.25 inches of vacuum water gauge as required by Technical Specification 3.6.4.1, due to less than optimal control system tuning for the system. Corrective actions include determining, implementing, and documenting the optimum control system tuning for the system, increasing margin by lowering differential pressure set point, and alerting operations before the Technical Specification limit for secondary containment pressure is reached. 26158 R6 NRC Form 366 (01-2014) Columbia Generating Station APPROVED BY OMB: NO. 3150.0104 EXPIRES: 01131/2017 Reported lessons learned are incorporated into the licensing process and fed beck to industry. Send comments repenting burden estimate to the FOIA, Privacy and Wanton Collections Branch (T.5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by kttemet 0411811 to inixollectsResource@nrc.gov, and to the Desk Met, Office of Information and Regulatory Make, NEOB-10202, (3150-0104), Office of Management and Budget Washington, DC 20503. If a means used to Noose an Infortnation collectbn does not display a currently valid OMB control nunter, the NRC may not conduct or sponsor, and a person Is not required to respond to, the information collection. ContentsPlant ConditionsEvent 1: January 9, 2014 at 1743 hours0.0202 days <br />0.484 hours <br />0.00288 weeks <br />6.632115e-4 months <br /> Event 2: January 9, 2014 at 1834 hours0.0212 days <br />0.509 hours <br />0.00303 weeks <br />6.97837e-4 months <br /> Event 3: January 15, 2014 at 0907 hours0.0105 days <br />0.252 hours <br />0.0015 weeks <br />3.451135e-4 months <br /> Event 4: February 17, 2014 at 0304 hours0.00352 days <br />0.0844 hours <br />5.026455e-4 weeks <br />1.15672e-4 months <br /> At the time of all events, the plant was operating in Mode 1 at 100% power. There were no structures, systems, or components that were inoperable at the start of any of the events that contributed to the events. Event DescriptionEvents 1 & 2 - On January 9, 2014 at 1743 and 1834 hours0.0212 days <br />0.509 hours <br />0.00303 weeks <br />6.97837e-4 months <br /> secondary containment vacuum was not maintained while Reactor Building Outside Air (ROA) heating coil face and bypass dampers were repositioning due to outside ambient temperature fluctuation past the set point. These dampers and heating coil allow for outside air to be heated as it enters the system. These two events had durations of 3 and 2 minutes respectively. In Event 1 control room operators took manual control of the Reactor Building Exhaust Air (REA) flow In-service differential pressure controller (DPIC) (REA-DPIC-1A) to restore secondary containment vacuum to greater than 0.25 inches of vacuum water gauge. In Event 2 the REA in-service controller (REA-DPIC-1A) automatically restored secondary containment vacuum to greater than 0.25 Inches water gauge (inwg). Event 3 - On January 15, 2014 at 0907 hours0.0105 days <br />0.252 hours <br />0.0015 weeks <br />3.451135e-4 months <br /> secondary containment vacuum was not maintained while the ROA heating coil face and bypass dampers were repositioning due to outside ambient temperature fluctuation past the set point. This event had duration of 6 minutes. In this event the REA in-service controller (REA-DPIC-1A) automatically restored secondary containment vacuum to greater than 0.25 inwg. Event 4 - On February 17, 2014 at 0304 hours0.00352 days <br />0.0844 hours <br />5.026455e-4 weeks <br />1.15672e-4 months <br /> secondary containment vacuum was not maintained during a period of high winds. This event had duration of 2 minutes. In this event the REA in-service controller (REA-DPIC-1B) automatically restored secondary containment vacuum to greater than 0.25 inwg. In each event described above, because Reactor Building [NG] vacuum decreased below 0.25 inches of water gauge, secondary containment was logged as inoperable in the surveillance log and Technical Specification 3.6.4.1 Action A was entered. Extent of Condition This condition of Reactor Building vacuum momentarily dropping below the prescribed limit is specific to the Reactor Building Heating Ventilation and Air Cooling (HVAC) [VA] and Standby Gas Treatment (SGT) [BH] systems, and their capability to establish and maintain secondary containment vacuum. No other systems were affected as a result of this condition. 2$158A R3 NRC FORM 386A (01.2014) During an extent of condition review performed to determine past operability, it was determined that there were multiple instances where secondary containment vacuum was less than the TS required value of 0.25 inwg. In these instances secondary containment vacuum went below the TS required value of 0.25 inwg and went unnoticed by operators as the annunciator alarm comes in at 0.0 inwg. This alarm value has been identified as Incorrect to alert operators to secondary containment vacuum below the TS required value af 0.25 inwg and the condition has been documented in the corrective action process to be aligned with the TS value of 0.25 inwg. In each of these events the REA in-service controller automatically restored secondary containment vacuum to greater than 0.25 inwg. Immediate Corrective Action In Event 1 Operators took manual control of the REA differential pressure (dP) controller (PDC] and quickly adjusted REA flow to restore secondary containment vacuum to greater than 0.25 inwg. In Events 2, 3, and 4 the REA flow in-service controller automatically restored secondary containment vacuum to greater than 0.25 inwg. CauseIn accordance with NUREG-1022 Revision 3 Section 2.3 these four events are being reported together as these have all occurred in the 60 day LER reporting period and appear to have similar cause(s) for each event. Events 1 & 2 were reported together as they were related and occurred within an hour of each other. Events 3 and 4 were reported under individual ENS notifications. Secondary vacuum dropping below the TS required value of 0.25 inwg happened in four separate events in this LER reporting period. All four of these events were similar in that an external weather related event, three temperature related transients and one wind related transient, occurred that required the exhaust ventilation fan to adjust its flow to maintain a vacuum above the TS required value of 0.25 inwg. The cause of secondary containment vacuum not being maintained greater than or equal to 0.25 inwg was due to improper tuning of the Reactor Building Outside Air (ROA) differential pressure controllers. The transient response of the controllers were not properly tuned to compensate for sudden pressure changes that are expected during operation of the pressure control system. Operating Experience & Previous Occurrences A loss of the ability to maintain secondary containment vacuum greater than required has occurred and was reported at Columbia Generating Station (Columbia) three times in the past two years. On August 25, 2013, reported under LER 2013-007-00, secondary containment was declared inoperable during a sudden thunderstorm when secondary containment vacuum was not maintained greater than or equal to 0.25 inwg. On July 24, 2012, reported under LER 2012-003-00, secondary containment vacuum was not maintained due to an inadvertent trip of one set of the redundant Reactor Building HVAC fans FAN), during ongoing maintenance on the SGT system. On December 10, 2011, reported under LER 2011-004-00, secondary containment vacuum was not maintained and the cause was determined to be ice buildup and subsequent release on exterior equipment supplying the Reactor Building HVAC system. The first Operating Experience (OE) event is similar in cause as the four events reported in this LER. Due to the single occurrence and the extreme weather conditions at the time, multiple causal factors were not considered. A corrective action which could have prevented recurrence of this event, to alert operations to a potential issue with secondary containment before the Technical Specification, LCO 3.6.4.1A for secondary containment vacuum is reached, was in 26158A R3 NRC FORM 366A (01-2014) 8. LER NUMBER 3. PAGE 2. DOCKET Columbia Generating Station 05000 397 aft. NRC FORM 3118A (014814) LICENSEE EVENT REPORT (LER) U.S. NUCLEAR REGULATORY COMMISSION CONTINUATION SHEETNARRATNEprogress at the time of the four events reported in this LER. The last two OE events have associated corrective actions, and the causes are not applicable to the current cause of weather related secondary containment vacuum changes, nor would corrective actions from these past two events prevented occurrence of these four events reported in this LER. As discussed in the Reactor Oversight Process working group public meeting held on January 15, 2014 the Industry has experienced an increase in reports of safety system functional failures (SSFF) in where there is not a true loss of safety function, but momentary conditions in which Technical Specification operability criteria are not satisfied. Specifically temporary losses of secondary containment vacuum have increased In the industry. The four events described In this LER fall into this increase in number of reports. Further Corrective Actions The potential for these momentary pressure excursions will continue to occur as there has been no change in the design of the equipment To minimize recurrence actions are being taken to update the current calibration procedures to reflect the optimum control system tuning for the REA/ROA system, and increasing margin in secondary containment by lowering the differential pressure set point on the REA controllers. Columbia is also investigating methods to alert operations to a potential issue with secondary containment before the Technical Specification secondary containment pressure is reached. Assessment of Safety ConsequencesThis event resulted in an unplanned entry into LCO 3.6.4.1.A. Secondary containment vacuum was less than 0.25 inwg for between 2 and 6 minutes. While the actual vacuum was beyond the range allowed by Technical Specifications, the Reactor Building HVAC system is designed to, among other things; maintain the reactor building during normal operating at a negative pressure with respect to atmosphere to minimize the release of airborne radioactive material. During emergency operation, the SGT system maintains the reactor building at a negative pressure. During each of the events described in this LER at least one train of SGT was In standby condition and available to restore the reactor building to a vacuum above the TS required value of 0.25 inwg. An engineering safety function analysis was performed which demonstrated that the ability for SGT to achieve secondary containment vacuum to above 0.25 inwg, credited in the accident response analysis, could have been attained using either of the two available trains of the SGT system at the time of each of the events, thus there were no potential safety consequences. There was no actual safety consequence associated with this event since no event involving radiological hazards were experienced during the event. NEI 99-02 allows the licensee to perform an engineering analysis to determine if the event is reportable as a SSFF performance indicator occurrence. The engineering analysis has shown that these events did not result in a SSFF; therefore this event does not affect the NRC Regulatory Oversight Process Indicators. Energy Industry Identification System (EIIS) Information Energy Industry Identification System (EIIS) Information codes from IEEE Standards 805-1984 and 803-1983 are represented in brackets as (XXI and pooq throughout the body of the narrative. 26158A R3 NRC FORM 388A (01-2014) |
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| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
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