05000498/FIN-2016007-02
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Finding | |
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Title | Failure to Verify the Adequacy Calculations Associated with Direct Current Circuit Breakers |
Description | The team identified two examples of a Green, non-cited violation of 10 CFR Part 50, Appendix B, Criterion III, Design Control, which states, in part, the design control measures shall provide for verifying or checking the adequacy of design, such as by the performance of design reviews, by the use of alternate or simplified calculational methods, or by the performance of a suitable testing program. Specifically, since March 22, 1988, the licensee failed to verify the adequacy of the molded case circuit breakers to perform their design basis function using appropriate time-current curves and tolerances or Class 1E 125 Vdc molded case circuit breakers to assure adequate trip response times, instantaneous trip accuracies, and rates of change of the sensed variable (the short circuit current). In response to this issue, the licensee determined that the 125 Vdc system would remain operable while implementing corrective actions to revise their design calculations to incorporate the appropriate time-current curves and current tolerances in design calculations. This violation was entered into licensees corrective action program as Condition Reports CR 16-2196 and CR 16-2117. The team determined that the failure to verify the adequacy of the design of Class 1E 125 Vdc molded case circuit breakers was a performance deficiency. The performance deficiency was determined to be more than minor, and therefore a finding, because it was associated with the design control attribute of the Mitigating Systems cornerstone and adversely affected the cornerstone objective of ensuring the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences. Specifically, the failure to verify the adequacy of the molded case circuit breakers to perform their design basis function using appropriate time-current curves and tolerances adversely affected the capability of the 125 Vdc systems. Additionally, independent inspector calculations confirmed that the calculation errors resulted in a reasonable doubt on the operability of the 125 Vdc molded case circuit breakers. In accordance with Inspection Manual Chapter 0609, Appendix A, The Significance Determination Process (SDP) for Findings At-Power, dated June 19, 2012, Exhibit 2, Mitigating Systems Screening Questions, the team determined the finding to be of very low safety significance (Green) because the finding was a deficiency affecting the design or qualification of a structure, system, or component, and the structure, system, or component maintained its operability or functionality. The team determined that this finding did not have a cross-cutting aspect because the most significant contributor did not reflect present licensee performance. |
Site: | South Texas |
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Report | IR 05000498/2016007 Section 1R21 |
Date counted | Mar 31, 2016 (2016Q1) |
Type: | NCV: Green |
cornerstone | Mitigating Systems |
Identified by: | NRC identified |
Inspection Procedure: | IP 71111.21M |
Inspectors (proximate) | C Baron C Stott G Gardner J Kirkland M Williams S Hedger T Fanelli T Farnholtz |
Violation of: | 10 CFR 50 Appendix B Criterion III, Design Control |
INPO aspect | |
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Finding - South Texas - IR 05000498/2016007 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (South Texas) @ 2016Q1
Self-Identified List (South Texas)
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