05000237/FIN-2011004-03
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Finding | |
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| Title | Inadequate Relay Preventative Maintenance |
| Description | A finding of very low safety significance was self-revealed for the failure to follow the preventive maintenance program which resulted in the failure of the Unit 3 303241-52A GE HFA relay. This relay gives a start permissive signal for all three reactor feed pumps (RFPs). The licensees corrective actions included restoring the correct preventive maintenance item (replace the relay), including adding a preventive maintenance item for the associated Unit 2 relay. The licensee also included a review of relays in multiple systems to ensure that the proper preventive maintenance items were identified and scheduled. The finding was determined to be more than minor because it was associated with the Mitigating Systems Cornerstone attribute of equipment performance and affected the cornerstone objective of ensuring the availability, reliability, and capability of a system that responds to an initiating event to prevent undesirable consequences. The inspectors determined the finding could be evaluated using the SDP in accordance with IMC 0609, Significance Determination Process, Attachment 0609.04, Phase 1 - Initial Screening and Characterization of Findings, Table, 4a, for the Mitigating Systems Cornerstone for the reasons stated in the previous paragraph. The inspectors answered question 4 YES. The finding represented an actual loss of safety function of one or more trains of equipment designated as risk-significant per 10 CFR 50.65 for >24 hours. The inspectors verified that Feedwater Level Control was a high safety significant function per the licensees Maintenance Rule database and that the inability to restart any of the Unit 3 RFPs lasted longer than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The Senior Reactor Analysts (SRAs) performed SDP phases 2 and 3 analyses of this finding. The exposure period was determined to be approximately 5 months, the time between the last known successful operation of the relay and the failure. For the phase 2 evaluation, the SRAs solved the transient (TRANS), small loss of coolant accident (SLOCA), and loss of direct current bus (LODC) worksheets in the Risk-Informed Inspection Notebook for Dresden Nuclear Power Station Units 2 and 3 (Revision 2.1a) assuming that the power conversion system (PCS) was unavailable for greater than 30 days. Using the counting rule for adding sequences described in IMC 0609 Appendix A, Determining the Significance of Reactor Inspection Findings for At-Power Situations, the SDP result was a 6 or a finding of low to moderate safety significance. The SRAs determined that a phase 3 SDP was necessary because the phase 2 result assumed that the main feedwater (MFW) pumps would always be unavailable and because the exposure period was 5 months rather than 1 year assumed by the phase 2 SDP process. For the phase 3 evaluation, the SRA modified the Standardized Plant Analysis Risk Model (SPAR) for Dresden to add basic events modeling the potential for MFW to trip. The SRAs assumed MFW would trip in response to a reactor trip approximately 6 percent of the time and that MFW would not be recoverable. The estimated delta CDF over the exposure period was 9.0E-8/yr, which is a finding of low to moderate safety significance (Green). The dominant sequence was a manual shutdown followed by the trip of MFW and the inability to restart the pumps. Random failures of the isolation condenser, high pressure coolant injection and low pressure coolant injection were also part of the dominant sequence. There were no cross-cutting aspects to this finding. |
| Site: | Dresden  |
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| Report | IR 05000237/2011004 Section 1R18 |
| Date counted | Sep 30, 2011 (2011Q3) |
| Type: | Finding: Green |
| cornerstone | Mitigating Systems |
| Identified by: | Self-revealing |
| Inspection Procedure: | IP 71111.18 |
| Inspectors (proximate) | J Draper L Jones J Corujo-Sandin R Orlikowski D Melendez-Colon C Phillips M Ring |
| INPO aspect | |
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Finding - Dresden - IR 05000237/2011004 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Dresden) @ 2011Q3
Self-Identified List (Dresden)
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