LER 05000289/2014-001-00 describes an
unanalyzed condition in which Exelon identified
DC motor control circuits were unfused. Specifically, Exelon did not provide overcurrent protection for wiring associated with 250VDC full-voltage control circuits for four non-safety emergency bearing oil pumps in the turbine building to prevent wires from overheating due to fire-induced faults and excessive currents flowing through the cable. With enough current flowing through the cable, the potential exists that the overloaded motor control wiring could damage adjacent control circuit wiring for both instrument air compressors (IA-P-1A/B), which are needed to achieve and maintain post-fire
safe shutdown for a fire in the cable spreading room. This condition could result in a loss of the associated
safe shutdown components or a secondary fire in another fire area. The failure to protect
safe shutdown cables from the effect of postulated fires was a performance deficiency. This performance deficiency was a violation of
TMI Operating License Condition 2.C.(4), which requires, in part, post-fire
safe shutdown cables remain free of the effects of fire-induced cable faults during postulated fires. Contrary to the above, Exelon identified they failed to meet this requirement and the condition existed since initial construction. The issue was more than minor because it was associated with the protection against external events (fire) attribute of the
mitigating systems cornerstone and it adversely affected the cornerstone objective of ensuring the availability, reliability, and capability of systems that respond to
initiating events to prevent undesirable consequences. The inspectors determined that the finding was of very low safety significance (Green), based on
IMC 0609, Appendix F, Fire Protection
Significance Determination Process, Phase 2 screening criteria. The finding screened to Green based upon task number 2.3.5, and because no credible fire ignition source was determined to adversely affect the motor control circuits of concern as determined. Additionally, a fire area of concern (cable spreading area) is an alternate shutdown fire area protected by detection and an automatic suppression system. The cables in the other fire area of concern (turbine building) are Institute of Electrical and Electronics Engineers 383 (
thermoset) construction with steel armor and tied to station ground which decreases the likelihood of inter-cable and intra-cable interactions. Because this finding is of very low safety significance and had been entered into Exelons corrective action program (IRs 1651702, 1658837, 1658842), this violation is being treated as a Green, licensee-identified
NCV consistent with the NRCs
Enforcement Policy.
