05000395/FIN-2011003-01
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Finding | |
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Title | Failure to Adequately Assess and Manage Risk of Switchyard Maintenance Activities During Lowered RCS Inventory Conditions |
Description | The inspectors identified a Green non-cited violation (NCV) of 10 CFR 50.65(a)(4), Requirements for Monitoring the Effectiveness of Maintenance at Nuclear Power Plants, for the failure to perform an adequate risk assessment and implement approved high risk management contingency plans for work in the stations electrical switchyard. Specifically, on April 21, 2011, operations work control personnel failed to adequately assess the impact of work activities in the switchyard involving the use of vehicles, resulting in outage high risk management actions that prohibited the movement of vehicles during lowered reactor coolant system (RCS) inventory conditions from being implemented. Following the inspectors identification of this issue, the licensee adequately assessed and managed the increase in risk for the activities. The issue was entered into the licensees corrective action program as condition report CR-11-01908. The failure to perform an adequate risk assessment and implement high risk evolution contingency plans for work in the stations switchyard was a performance deficiency within the licensees ability to foresee and correct. This finding was associated with the Initiating Events Cornerstone and affected the cornerstone objective for limiting the likelihood of those events that upset plant stability and challenge critical safety functions during shutdown, such as, loss of offsite power (LOOP) due to trucks damaging critical electrical components in the switchyard. The inspectors determined that the finding is more than minor because it was similar to both the more than minor examples 7.e and 7.g in NRC Inspection Manual Chapter (IMC) 0612, Appendix E, Examples of Minor Issues, because the risk assessment for the switchyard work activity failed to consider the impact of vehicle movements resulting in outage high risk management actions that prohibited the movement of vehicles during lowered RCS inventory conditions from being implemented. A Significance Determination Process (SDP), Phase 1 screening determined that the performance deficiency represented an increase in the likelihood of a LOOP during shutdown and therefore the risk was estimated using NRC IMC 0609, Appendix G, Shutdown Operations Significance Determination Process. A Phase 2 SDP risk evaluation was done by a regional senior risk analyst using IMC 0609, Appendix G, Attachment 2. The major assumptions of the analysis were that the plant was in plant operating state (POS-2) in Mode 6, with the RCS vented and the residual heat removal (RHR) system in service for decay heat removal. Time to boil was estimated at 35 minutes with an estimated time to core damage of 8.8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />. The exposure period was approximately 2.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />. The LOOP initiating event likelihood was increased by one order of magnitude due to the impact of the performance deficiency. Multiple (i.e., three) qualified sources of offsite power and both onsite emergency diesel generators were available when the vehicles were moved into the switchyard. Recovery credit for restoration of offsite power was included. The dominant sequence was a LOOP with failure of emergency power sources causing a loss of RHR and failure to recover offsite power or emergency power prior to core damage ensuing. The risk was mitigated by the short exposure period and the availability of mitigating system equipment. The result of the analysis was a core damage frequency risk increase of <1E-6/year, a finding of very low safety significance (Green). The inspectors determined that this finding had a cross-cutting aspect in the area of Human Performance, because personnel did not appropriately plan and coordinate switchyard work activities consistent with nuclear safety by incorporating appropriate outage risk insights and risk management contingency plans |
Site: | Summer ![]() |
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Report | IR 05000395/2011003 Section 1R13 |
Date counted | Jun 30, 2011 (2011Q2) |
Type: | NCV: Green |
cornerstone | Initiating Events |
Identified by: | NRC identified |
Inspection Procedure: | IP 71111.13 |
Inspectors (proximate) | A Sengupta E Coffman G Mccoy J Zeiler R Hamilton |
CCA | H.5, Work Management |
INPO aspect | WP.1 |
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Finding - Summer - IR 05000395/2011003 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Summer) @ 2011Q2
Self-Identified List (Summer)
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