05000395/FIN-2013003-03
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Finding | |
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| Title | Failure to Adequately Design, Install and Maintain Oil Collection Devices for Reactor Coolant Pump Motors |
| Description | The inspectors identified three examples of a non-cited violation of the Virgil C. Summer Nuclear Station, Unit No. 1, Renewed Facility Operating Licensee No. NPF-12, Condition 2.C(18), Fire Protection System, associated with 10 CFR 50, Appendix R, Section III.O, for problems associated with reactor coolant pump (RCP) motor oil collection system. Specifically, the inspectors identified (1) a split in the sealing boot for the B RCP motor oil cooler enclosure, (2) a failure to ensure an adequate design for the oil lift pump enclosure, and (3) a failure to have oil collection components for internally leaked oil escaping the RCP motor discharge air ductwork flange area. The licensee entered the problem into their corrective action program as condition reports 12-05736 and 12-05756. The inspectors determined that the aforementioned problems with RCP motor oil enclosures and ductwork were performance deficiencies (PD). The inspectors reviewed inspector manual chapter (IMC) 0612 and determined that the PDs were more than minor and therefore a finding because they impacted the mitigating systems cornerstone objective to ensure the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences, and the related attribute of protection against external factors such as fire. This finding has a credible impact on safety because the failure to adequately install, maintain and design the oil collection system presented a degradation of a fire confinement component which has a fire prevention function of not allowing an oil leak to reach hot surfaces. The inspectors reviewed IMC0609, Attachment 4, and Appendix F and determined the following for each example: Example 1 was assigned a high degradation rating because the split in the boot on the bottom of the oil enclosure would allow significant leakage to occur. The duration was greater than thirty days because the condition had existed for the previous operating cycle and this yields a duration factor of 1.0. Combining this with a generic fire frequency for a pressurized water reactor (PWR) containment or 1E-2 results in a fire frequency of 1E-2 which requires a phase 2 evaluation. Example 2 was assigned a moderate degradation rating due to openings which would allow the escape of high pressure oil based on the location and orientation of the leak within the enclosure on each of the three RCPs. However, since the oil lift pumps are only operated for approximately five minutes before the start of a RCP, the duration is less than three days yielding a duration factor of .02. Combining this with a generic fire frequency for a PWR containment or 1E-2 results in a fire frequency of 2E-4 which requires a phase 2 evaluation. Example 3 was assigned a low degradation rating due to minimal leakage potential which screens to a Green or very low safety significance. A phase 2 Significance Determination Process (SDP) risk evaluation was performed by a regional senior risk analyst for PD examples 1 and 2 using IMC 0609 Appendix F, with data from NUREG/CR 6850, the licensees fire protection engineering report and the latest NRC VC Summer SPAR PRA risk model. The major assumptions for example 1 included: a one year exposure period, the ignition frequency from NUREG /CR 6850 for reactor coolant pump oil fires increased by one order of magnitude to account for the PD, the probability of non-suppression (PNS) from NUREG/CR 6850 for containment with detection at 5 minutes and damage at 10 minutes, and a base reactor trip transient conditional core damage probability (CCDP). The Example 2 assumptions included: a one hour exposure period to account for oil lift system operation for all three RCPs, the ignition frequency from NUREG/CR 6850 for reactor coolant pump oil fires increased by an order of magnitude to account for the PD, the PNS from NUREG/CR 6850 for containment with detection at 5 minutes and damage at 10 minutes, and a CCDP assumed for a small loss of coolant accident (LOCA) given the potential target cables in the RCP enclosures. The dominant sequence for example 1 was an oil leak in the B RCP oil cooler enclosure which leaked onto hot surfaces causing an oil fire on B RCP which was assumed to lead to a reactor trip if not rapidly suppressed. The dominant sequence for example 2 was an oil fire in any of the 3 RCPs upon startup due to spray from the oil lift system enclosure causing a fire on contact with hot surfaces. The fire is assumed to damage cables associated with reactor coolant system boundary valves if not rapidly suppressed leading to a small LOCA. For PD example 1 the risk was mitigated by the absence of safe shutdown equipment in the vicinity of the B RCP and PD example 2 risk was mitigated by the short exposure period. The risk of the three examples together represented an increase in core damage frequency of <1E-6/year a GREEN finding of very low safety significance. The cause of example 1 relating to ensuring collection devices are leak-free involved the cross-cutting area of human performance, the component of resources, and the aspect of complete and accurate procedures, H.2(c), because the procedure for inspection of the oil collection enclosures was inadequate to detect the degraded condition. The other examples were not indicative of current licensee performance. |
| Site: | Summer  |
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| Report | IR 05000395/2013003 Section 4OA5 |
| Date counted | Jun 30, 2013 (2013Q2) |
| Type: | NCV: Green |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | |
| Inspectors (proximate) | E Coffman G Mccoy J Reece |
| Violation of: | 10 CFR 50 Appendix R Section III.O 10 CFR 50 Appendix R |
| CCA | H.7, Documentation |
| INPO aspect | WP.3 |
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Finding - Summer - IR 05000395/2013003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Summer) @ 2013Q2
Self-Identified List (Summer)
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