This occurrence is considered to be of no significance with respect to the health and safety of the public.

Transcription

1 Serial No. MNS September 10, 2015,. DUKESteven Vice D. President Capps, ENERGYMcGuire Nuclear Station Duke Energy MGOIVP Hagers Ferry Road Huntersville, NC : f: Steven.Capps@d u ke-energy. corn U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C K Subject:, Unit 1 Docket No Renewed License No. NPF-9 Selected Licensee Commitment Special Report Nuclear Condition Report No In accordance with Required Action E.1 of Selected Licensee Commitment (SLC) , "Standby Shutdown System," attached is Special Report concerning an occurrence where the Unit 1 Standby Shutdown System was non-functional for a period greater than 7 days. This occurrence is considered to be of no significance with respect to the health and safety of the public. Please contact Lee Hentz at With any questions related to this Special Report. Sincerely, ' S. D. Capps -- i/.;,, j Attachment

2 U.S. Nuclear Regulatory Commission Serial No. MNS Page 2 of 2 cc: V. M. McCree Administrator, Region II U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA G. E. Miller Project Manager (McGuire) U.S. Nuclear Regulatory Commission Rockville Pike Rockville, MD Mail Stop 0-8 G9A J. Zeiler NRC Senior Resident Inspector W. L. Cox, Ill, Section Chief North Carolina Department of Health and Human Services Radiation Protection Section 1645 Mail Service Center Raleigh, NC

3 Attachment Special Report BACKGROUND was designed with a Standby Shutdown System (SSS) to meet 10 CFR 50 Appendix R (Fire Protection Program) and 10 CFR station blackout (SBO) requirements. This SSS is not nuclear safety related. The SSS is designed to mitigate the consequences of certain postulated fire, sabotage incidents, and SBO events by providing the capability to achieve and maintain hot standby conditions from locations external to the control room. This capability is consistent with the requirements in 10 CFR 50 Appendix R, which permits control of safe shutdown outside the control room and at a limited number of local equipment stations. The primary components that support the SSS function are an independent diesel generator, unit specific reactor coolant system (RCS) makeup pumps, unit specific turbine driven auxiliary feedwater (AFW) pumps, and RCS instrumentation. The turbine driven AFW pumps are utilized during an SSS event to maintain adequate secondary side heat removal. The turbine driven AFW pump water supply for the 4 hour SBO event is provided by the AFW Storage Tank (CAST). The water supply for the 72 hour Appendix R event is initially provided by the CAST then later by manual alignment to the Condenser Circulating Water (RC) system. Continuous vents are provided for the Unit 1 RC system water supply due to the potential for air entrainment at a piping high point. For an Appendix R event, an initial CAST inventory is needed to allow time to perform the manual alignment from the CAST to the RC system. Proper operation (passing water flow) of the continuous vents is required for Unit 1 SSS functionality. Selected Licensee Commitment (SLC) "Standby Shutdown System" provides regulatory commitments related to the functionality of the SSS. SLC Table identifies the SSS components required to be functional for the SSS to remain functional. SLC Condition A provides the required actions and completion times when one or more required SSS components are non-functional. As per Required Action A.2, a non-functional SSS component shall be restored to a functional status within 7 days. If Required Action A.2 and its associated Completion Time are not satisfied, the Required Actions and Completion Times of Condition E state that a Special Report shall be submitted to the NRC within 30 days. This Special Report shall outline the cause of the non-functionality, corrective actions taken, and plans for restoring the SSS to a functional status. DESCRIPTION OF OCCURRENCE SSS Scheduled Work On August 5, 2015, the SSS was declared non-functional for scheduled work that included modifications, preventative maintenance, and corrective maintenance on various components and support systems. This work impacted both the Unit 1 and Unit 2 SSS functions. On August 10, 2015, at 14:53, after all applicable functionality tests were performed, Operations declared the SSS functional for both Units and exited the SLC Conditions. This SSS non-functionality was limited to five days. 1

4 Ultimate Heat Sink Cooling Evolution Attachment Special Report The Standby Nuclear Service Water Pond (SNSWP) functions as the McGuire Ultimate Heat Sink and is governed by Technical Specification (TS) During the summer months, the SNSWP can approach its TS temperature limit of 820 F. Prior to reaching this limit, a cooling evolution is initiated. Lake Norman functions as the normal, nonseismic heat sink for the Nuclear Service Water (RN) system and the RC system. On August 5, the SNSWP temperature reached 78 F. Procedural guidance requires Operations to locally monitor SNSWP temperature once per night and to evaluate cooling the SNSWP. On August 6, an alignment was made to cool the SNSWP through an operating RN pump. This alignment does not affect functionality of the SSS. The Operating Procedure has a note that states this alignment may prevent the RN piping high point continuous vents from operating properly (passing flow). The procedure goes on to state the continuous vent flow will selfrestore upon restoring an RN system normal alignment. This alignment was secured on August 9. Water flow was verified from the high point continuous vent by a night shift Auxiliary Operator (AO) at approximately 04:00 AM on August 10. Loss of Flow from the Unit 1 Continuous Vent Line At approximately 08:50 AM on Monday, August 10, the day shift AO determined that the continuous vent was not passing flow. Per SLC , the lack of continuous vent flow makes the SSS non-functional. However, the electronic surveillance rounds tool was still carrying a note that read "Cooling SNSWP with 2A RN Pump" as the reason for this surveillance item being UNSAT. This electronic note was incorrectly carried as part of the surveillance rounds through Tuesday, August 11. The note for the UNSAT condition was then changed to read "Control Room Informed" on Wednesday, August 12 and carried through the day shift of Thursday, August 13. On day shift August 13, Operations realized this was not a valid reason for no flow through the continuous vents because the SNSWP was not in a cooling alignment. Later that day, it was determined that the continuous vent line was clogged. Also on August 13, it was realized the SSS was non-functional after the SNSWP cooling alignment was secured on August 10. In summary, the SSS scheduled work started on August 5 and completed on August 10 at 14:53. On August 10 at 08:50, the continuous vent line that supports Unit 1 SSS functionality was not passing flow. It was later determined this condition was not associated with the SNSWP cooling evolution; rather the vent line was clogged. As such, the non-functionalities overlapped on August 10. The overlapping non-functionalities exceeded the SLC Required Action A.2 Completion Time of 7 days on August 12. The continuous vent line was not returned to functional status until August 16. Total SSS non-functionality time was 11 days. 2

5 CAUSE OF THE NON-FUNCTIONALITY Attachment Special Report Three factors contributed to exceeding the SLC 7 day Completion Time of Required Action A.2: 1. Concurrent issues (scheduled maintenance and emergent issue) caused the SSS to be non-functional for greater than 7 days. 2. The continuous vent line became clogged and would not pass flow. 3. Operators failed to promptly identify (and correct) the continuous vent line being clogged following the RN system alignment change. CORRECTIVE ACTIONS Immediate: 1. Unit 1 SSS was logged non-functional on August 13, 2015, due to no flow from the Subsequent: continuous vent line. Actual non-functionality started on August 10 at 08:50 am. 1. The clogged continuous vent line was cleared using a chemical cleaning process, and the vent and SSS were declared functional on August 16. Planned: 1. Create an awareness communications message to emphasize the importance of the turnover process between surveillance rounds AOs and Plant Senior Reactor OPerators (SROs) to ensure rigorous, accurate validation of information. 2. Revise the SNSWP cooling procedure, OP/11AI6400/O06 Endl (Cooling SNSWP Via RN Strainers), to include a functionality assessment of the SSS and any associated equipment prior to entering a SNSWP cooling alignment. SAFETY SIGNIFICANCE The loss of the continuous vent is considered to have very low safety significance for several reasons. An Engineering evaluation determined there was a high likelihood that the Unit 1 turbine driven AFW pump would have had adequate suction sources at all times during the period of time the continuous vent was non-functional if needed during an Appendix R event. This conclusion is based on the large volume of the condensate sources (CAST) which can supply the turbine driven AFW pump for many hours before requiring makeup or the alignment to an alternate suction source such as the RN or RC systems. Thus, in the timeframe that the RC source might have been required, AFW system flow rates would have already been reduced to pump minimum flow requirements and likely be insufficient to transport a large air void to the turbine driven AFW pump suction, even if present. 3

6 Attachment Special Report Additionally, the McGuire PRA model includes the RC system suction source to the turbine driven AFW pump and the associated risk results were reviewed for risk insights for this issue. An assumed loss of the turbine driven AFW pump due to failure of the RC system suction has a very low conditional core damage probability when the brief exposure period is considered. The low risk impact stems from both the passive nature of the CAST suction source and the reliability of the IRN system assured source for accident sequence where the CAST may fail due to external events such as severe tornado strikes or earthquakes. The important accident sequences for the RO system suction source involve loss of all AC power (e.g., LOOP, Tornado, Fire, Seismic events) where the RN system assured source is unavailable because of a loss power to the associated motor-operated valves. 4