05000282/LER-2016-001
| 02-18-2016 | On 12/21/2015 with Unit 1 (U1) in Mode 1 at 100% power and Unit 2 (U2) in Mode 3, a technical review of a new weak link calculation as part of the transition to National Fire Protection Association's Performance Based Standard for Fire Protection for Light Water Reactor Electronic Generating Plants (NFPA 805) identified a non-emergency unanalyzed condition reportable under 10 CFR 50.72(b)(3)(ii)(B). Specifically, several motor operated valves (MOVs) credited to be manually operated from outside the control room in the event of a fire in the control room or relay room could be damaged in a postulated fire if hot shorts were to bypass the torque and limit switches. Also, MOVs associated with the Gland Steam system of both U1 and U2 had been added to F5 Appendix B but never analyzed in the event of a hot short. These conditions could impact the ability of plant operators to implement procedure F5 Appendix B, Control Room Evacuation (Fire). The identified MOVs are located in Fire Area (FA) 13 (Control Room) and FA 18 (Relay and Cable Spreading Room). New hourly fire watch impairments were created in these areas as compensatory measures. The fire detection systems in the control room and relay room remain in service. The site submitted Event Notification (EN) 51616.
Reviews of the list of MOVs susceptible to hot shorts bypassing the torque and limit switches continued and additional valves were noted to be affected by this failure mechanism. As a compensatory measure, new hourly fire watch impairments were created for FA 31 ("A" Train Hot Shutdown Panel & Air Compressor/Auxiliary 695 Feedwater Room), FA 32 ("B" Train Hot Shutdown Panel & Air Compressor/Auxiliary 695 Feedwater Room), FA 58 (Auxiliary Building Ground Floor U1) and FA 73 (Auxiliary Building Ground Floor U2). EN 51616 was updated on 01/14/2016. The public health and safety was not impacted. ContentsEvent DescriptionDuring technical review for a new calculation as part of the transition to NFPA-805, the station reviewed MOVs identified in the Appendix R program to ensure they had been analyzed correctly. In this review it was determined several MOVs had been added to the program but had not been analyzed for a weak link. Further, several MOVs would not survive a hot short condition, although they were credited in the Appendix R program to meet programmatic requirements for survivability from a hot short condition. Also, MOVs associated with the Gland Steam system of both U1 and U2 had been added to F5 Appendix B but never analyzed in the event of a hot short. These MOVs could be affected by a fire in FA 13 (Control Room) and FA 18 (Relay and Cable Spreading Room). This unanalyzed condition could impact the ability of plant operators to implement procedure F5 Appendix B. Therefore, the station reported this unanalyzed condition under 10 CFR 50.72(b)(3)(ii)(B) on 12/21/2015 as EN 51616. New hourly fire watch impairments were created in these fire areas as compensatory measures. After submittal of EN 51616, the review was further expanded for all credited MOVs which resulted in identifying additional MOVs that would not survive a hot short condition if a fire were to occur in the following fire areas: FA 31 ("A" Train Hot Shutdown Panel & Air Compressor/Auxiliary Feedwater Room, 695), FA 32 ("B" Train Hot Shutdown Panel & Air Compressor/ Auxiliary Feedwater Room, 695), FA 58 (Auxiliary Building Ground Floor U1), and FA 73 (Auxiliary Building Ground Floor U2). EN 51616 was updated on 01/14/2016 listing the additional fire areas and the compensatory actions of new hourly fire watch impairments. Event AnalysisOn February 28, 1992 the NRC released Information Notice 92-18 (IN 92-18), Potential for Loss of Remote Shutdown Capability During a Control Room Fire, addressing the potential for a control room fire causing electrical short circuits ("hot shorts") between normally energized conductors and conductors associated with the control circuitry of motor-operated valves (MOVs) required for achieving and maintaining post-fire safe shutdown conditions. This could result in a loss of capability to achieve or maintain safe shutdown conditions 2 CONTINUATION SHEETprompted the 12/15/2015 event notification, and the updated notification on 01/14/2016, for an unanalyzed condition due to non-compliant fire protection manual operator actions reportable under 10 CFR 50.72(b)(3)(ii)(B). Compensatory measures were initiated in affected fire areas. EN 51616 was submitted to the NRC. During the causal evaluation for the LER, PINGP reviewed its response to a 1997 Unresolved Issue (URI) regarding the review of MOVs in accordance with IN 92-18 (Accession Number 9710200112). The response stated PINGP would use IN 92-18 as guidance to perform additional reviews of the hot short problem following the completion of the Appendix R safe shutdown analysis and create an accurate list of MOVs susceptible to hot shorts (ADAMS Accession Number 9711200012). On August 7, 1998, calculation ENG-ME-353, Mechanical MOV Analysis to support IN 92-18 determined the valve and operator thrust and torque values that may occur during a hot short that bypasses the limit switches and torque switches. The calculation addressed 46 Appendix R related valves and found 32 could potentially be damaged during a fire induced hot short requiring modifications and revision to the Appendix R safe shutdown analysis. During a fire, a hot short could cause the MOV to operate without its torque/limit switch protection, damaging the valve and preventing manual operation of the valve. All credited MOVs for safe shut-down were reviewed for this condition and seventeen MOVs were found susceptible. Susceptible MOVs Eleven (11) MOVs require modification to re-wire the torque and limit switches to prevent damage to the actuator: 3 infocollects.Resource@nrc.goy, and to the Desk Officer, Office of Information and Regulatory Affairs, Prairie Island 05000282 1) MV-32006, 1 TURB GLND STM SL SPLY UPSTRM SO MV 2) MV-32010, 1 TURB GLND STM SL SPLY B-P MV 3) MV-32016, 11 SG MS SPLY TO 11 TD AFW PMP MV 4) MV-32017, 12 SG MS SPLY TO 12 TD AFW PMP MV 5) MV-32019, 21 SG MS SPLY TO22 TD AFW PMP MV 6) MV-32020, 22 SG MS SPLY TO 22 TD AFW PMP MV 7) MV-32021, 2 TURB GLND STM SL SPLY UPSTRM SO MV 8) MV-32022, 2 TURB GLND STM SL SPLY B-P MV 9) MV-32238, 11 AFW TO 11 SG MV 10) MV-32246, 22 AFW TO 21 SG MV 11) MV-32333, 11 TD AFW PMP SUCT FROM CST MV Six (6) MOVs require PINGP to revise the Appendix R safe shutdown analysis to credit actions to isolate other valves or to credit check valves. 1) MV-32115, 122 SFP HX INLT HDR MV B 2) MV-32117, 121 SFP HX INLT HDR MV A 3) MV-32166, 1 REAC EXCS LTDN LINE ISOL MV A 4) MV-32194, 2 REAC EXCS LTDN LINE ISOL MV A 5) MV-32335, 12 MD AFW PMP SUCT FROM CST MV 6) MV-32336, 21 MD AFW PMP SUCT FROM CST MV The causal evaluation for this event determined the cause was the failure to include ENG-ME- 353 as an input to the Appendix R safe shutdown analysis. Because of this exclusion, the site did not update ENG-ME-353 to include new weak link data to support the Appendix R safe shutdown analysis. Additionally, the causal evaluation identified inadequate supervisory oversight during the transition to NFPA 805 that contributed to the event. When one engineer was assigned to both the Appendix R program and the transition to NFPA 805 resulting in untimely responses, in a 4 CONTINUATION SHEETInfocollects,Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, 05000282 Prairie Island NOmanner commensurate with their safety significance, to previously identified deficiencies for compliance with IN 92-18. Safety SignificanceThe NFPA 805 License Amendment identified the need to revise ENG-ME-353 to incorporate updated vendor information (ADAMS Accession Number ML12278405). During the revision of ENG-ME-353, this issue was identified, There were no structures, components or systems that were inoperable at the start of the event that contributed to the event. There was no nuclear, environmental, radiological or industrial safety consequences related to this event. PINGP has procedures and controls in places to minimize the likelihood and severity of fires occurring, and a significant fire impacting the ability to safely shutdown did not occur. This postulated fire scenario requires that a significant fire of sufficient size and intensity to damage MOV control cables and bypass torque and limit switches to cause spurious operation and damage to MOVs. The frequency of fires large enough to damage control cables is much lower than the generic fire ignition frequency that includes fires of all intensities. To damage the MOV, the fire must cause damage to cable insulation to the point that an energized conductor shorts around the torque and limit switches to the MOV control circuit for sufficient time for the MOV to stroke to the opposite position without open circuit or short to ground. Causes PINGP failed to include ENG-ME-353 as an input to the Appendix R safe shutdown analysis which led to failure to update ENG-ME-353 to include new weak link data. During the original analysis for IN 92-18, only a specified list of MOVs was reviewed to be credited; however, additional MOVs were added without the required analysis to support survivability. 5 Corrective Actions
o Eleven (11) MOVs require modification to re-wire the torque and limit switches to prevent damage to the actuator: ® MV-32006, 1 TURB GLND STM SL SPLY UPSTRM SO MV ® MV-32010, 1 TURB GLND STM SL SPLY B-P MV ® MV-32016, 11 SG MS SPLY TO 11 TD AFW PMP MV ® MV-32017, 12 SG MS SPLY TO 12 TD AFW PMP MV
0 ® MV-32115, 122 SFP HX INLT HDR MV B ® MV-32117, 121 SFP HX INLT HDR MV A ® MV-32166, 1 REAC EXCS LTDN LINE ISOL MV A ® MV-32194, 2 REAC EXCS LTDN LINE ISOL MV A ® MV-32335, 12 MD AFW PMP SUCT FROM CST MV ® MV-32336, 21 MD AFW PMP SUCT FROM CST MV 6 Previous Similar EventsDamage by Fire Induced Hot Shorts" was submitted on September 7, 1998 (ADAMS Accession Number 9809150244). Corrective Actions
a. Re-evaluate MOVs to identify alternate shutdown systems, components, or flow paths that are not susceptible to damage and revise the Safe Shutdown Analysis accordingly, or b. Modify MOV's mechanically to prevent mechanical damage (e.g. smaller motor), or c. Modify MOV's electrically to prevent hot short susceptibility (e.g. hold the MOV circuit breaker open or rewire the MOV control circuit).
submitted on October 26, 1998 (ADAMS Accession Number 9810300149). Corrective Actions
7 NRC with a schedule of the corrective actions as committed to in the original submittal (ADAMS Accession Number 9904150006). 8 |
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| Prairie Island Nuclear Generating Plant | |
| Event date: | 12-21-2015 |
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| Report date: | 02-18-2016 |
| Initial Reporting | |
| ENS 51616 | 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition |
| 2822016001R00 - NRC Website | |
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