05000317/FIN-2015007-01
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Finding | |
|---|---|
| Title | Inadequate Verification of Offsite Power Operability Limit |
| Description | The team identified a finding of very low safety significance involving a non-cited violation of Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Appendix B, Criterion III, "Design Control," because Exelon did not ensure the operability of offsite power in design calculations. The team determined that non-conservative assumptions caused the results of the voltage calculation to predict higher 4160 Volts, Alternating Current (VAC) switchgear post-trip voltage levels than those which could occur with existing controls. Specifically, the team found that Exelons calculation assumed a 3.2 percent switchyard voltage drop upon main generator trip, which did not bound the 5 percent alarm setting provided by the Transmission System Operator Security Analysis application. The team also determined that Exelon used a non-quantitative evaluation, which could not be verified, to adjust design basis calculation results in order to show that during a design basis event the 4160 VAC bus voltage would recover in time to reset the degraded voltage relay prior to the transient degraded voltage relay (TUR) tripping (causing a loss of offsite power). The team could not determine if offsite power would be lost during the event because these assumptions could not be validated. Exelon entered the issue into the corrective action program and performed preliminary computer modeling of the current plant configuration that showed offsite power was operable. The finding was determined to be more than minor because it was associated with the Mitigating Systems Cornerstone design control attribute and adversely affected the cornerstone objective of ensuring the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences and was similar to Example 3j in Appendix E of the NRC IMC 0612. Using the NRC IMC 0609, Significance Determination Process, Appendix A, The Significance Determination Process (SDP) for Findings At-Power, Exhibit 2, Mitigating Systems Screening Questions, the finding was determined to be of very low safety significance (Green) because it was a design deficiency confirmed not to result in the loss of operability or functionality. This finding was not assigned a cross-cutting aspect because it was a historical design issue not indicative of current performance. |
| Site: | Calvert Cliffs  |
|---|---|
| Report | IR 05000317/2015007 Section 1R21 |
| Date counted | Dec 31, 2015 (2015Q4) |
| Type: | NCV: Green |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.21M |
| Inspectors (proximate) | H Leake J Kulp K Mangan M Orr S Makor S Pindale W Sherbin |
| Violation of: | 10 CFR 50 Appendix B Criterion III, Design Control |
| INPO aspect | |
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Finding - Calvert Cliffs - IR 05000317/2015007 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Calvert Cliffs) @ 2015Q4
Self-Identified List (Calvert Cliffs)
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