05000416/FIN-2017007-02
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Finding | |
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Title | Failure to Correct Standby Diesel Generator Trip |
Description | The team identified a Green, self -revealed, non -cited violation of 10 CFR 50 Appendix B, Criterion XVI, Corrective Actions, which states, in part, Conditions adverse to quality are promptly identified and corrected. On June 22, 2016, the station identified a condition adverse to quality affecting the standby diesel generators, but did not promptly correct the issue until September 22, 2017. Specifically, the actions described in Standing Order 17 -0011 were not appropriate for restoring full capability during a design basis tornado event, which could affect the capability of the Division I and II standby diesel generators. In response to this issue the licensee revised the standing order to have the operator press the diesel generator manual start button while the diesel is running to eliminate the associated non- safety trips. The finding was entered into the corrective action program as Condition Report CR -GGN -2017 -09751. The team determined that the failure to promptly correct a condition adverse to quality, regarding diesel generator capability during a design basis tornado is a performance deficiency. The performance deficiency was more than minor, and therefore a finding, because it was associated with the design control attribute of the Mitigating Systems Cornerstone. Specifically, the failure to correct an identified condition adverse to quality resulted in a prolonged design challenge to the Division I and II standby diesel generator capability, which adversely affected the cornerstone objective to ensure the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences. In accordance with Inspection Manual Chapter 0609, Appendix A, Exhibit 2, dated June 19, 2012, the team determined that the finding required a detailed risk evaluation, per Exhibit 4 screening question number 1, for external event mitigation systems. According to the tornado analysis database prepared by the Office of Reactor Research, the frequency of an F -2 tornado or stronger at Grand Gulf Nuclear Station (GGNS) is 4.71E -4/year. The design basis tornado at GGNS has a maximum wind velocity of 360 mph which correlates to a strong F- 5 tornado. The design basis tornado generates a differential pressure of 3 psi. The pressure of concern is the 1.5 psi that could affect operation of the Division I and II diesel generators. Given that pressure is proportional to the square of the velocity, the wind speed affecting the diesel generators would be approximately 250 mph. 250 mph is in the range of an F- 4 tornado. Using generic distributions of the frequency of varying tornado strengths, the analyst estimated that the frequency of an F- 4 tornado or stronger at GGNS is 3.93E -6/year. Using the site- specific SPAR model, the analyst quantified the conditional core damage probability for a tornado- induced loss of offsite power with the failure of both Division I and II diesel generators. The conditional core damage probability was 6.35E -2. Therefore, the incremental conditional core damage probability of the performance deficiency, using the bounding assumption that all F -4 or stronger tornados striking the site would fail both diesel generators, was 2.50E -7. Qualitatively, given this bounding assumption, and the potential to recover the diesels after failure, the analyst determined that the CDF was less than 1E -7. This results in a finding of very low safety significance (Green). This finding had a cross -cutting aspect in the area of human performance associated with procedure adherence because the licensee failed to follow the operability evaluation process to properly determine operability [H.8]. |
Site: | Grand Gulf |
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Report | IR 05000416/2017007 Section 1R21 |
Date counted | Dec 31, 2017 (2017Q4) |
Type: | NCV: Green |
cornerstone | Mitigating Systems |
Identified by: | Self-revealing |
Inspection Procedure: | IP 71111.21M |
Inspectors (proximate) | W Sifre C Stott N Okonkwo N Day S Hedger C Baron S Gardner T Farnholtz |
Violation of: | 10 CFR 50 Appendix B Criterion XVI |
CCA | H.8, Procedure Adherence |
INPO aspect | WP.4 |
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Finding - Grand Gulf - IR 05000416/2017007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Grand Gulf) @ 2017Q4
Self-Identified List (Grand Gulf)
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