05000277/FIN-2008007-03
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Finding | |
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| Title | Vital Bus Degraded Voltage Protection (Section 1R21.2.1.8) |
| Description | The team reviewed Exelons load flow and vital bus voltage calculations. The review was performed to verify the minimum vital bus voltage needed to ensure operation of safety related loads required during design basis events was adequate. The team determined that voltages used in these analyses were not based on the trip set point of the Technical Specification Function 4 (LOCA) degraded voltage relay. Exelon had used voltages higher than were afforded by the Function 4 relays based on their belief that minimum expected value, as defined in GL 79-36 Adequacy of Station Electric Distribution Systems Voltage, could be used to calculate adequate voltages to vital loads. In using this assumption Exelon credited voltage improvement due to operation of the non-safety related startup transformer load tap changers in their analysis. The tap changer restores voltage to the vital bus during and following the post accident voltage transient. The team reviewed NRC Letter dated June 2, 1977, which was the basis for the licensing requirement to install the degraded voltage relay protection scheme. This licensing requirement required the set points for the second level reduced-voltage relays provide adequate voltage, from offsite or onsite power sources, for safety related loads at all onsite system distribution levels. The inspectors reviewed the PBAPS licensing records related to degraded voltage protection and did not find where the NRC had allowed Peach Bottom to credit operation of automatic tap changers in lieu of the technical specification reduced voltage relays to provide protection. Exelon stated that their approach was acceptable and the NRC had given this credit when it reviewed and approved certain voltage studies submitted as part of licensing actions related to the degraded voltage relays. This unresolved issue is being opened to determine if the Peach Bottom approved licensing bases includes the use of automatic load tap changers to protect the vital bus from unacceptable low voltage conditions during loss of coolant accidents. (URI 05000277;278/2008007-003, Vital Bus Degraded Voltage Protection) |
| Site: | Peach Bottom  |
|---|---|
| Report | IR 05000277/2008007 Section 1R21 |
| Date counted | Jun 30, 2008 (2008Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.21 |
| Inspectors (proximate) | J Lilliendahl K Mangan G Skinner J Kulp D Orr S Smith L Doerflein M Schlambergj D'Antoniok Mangan P Krohn R Nimitz A Ziedonis E Burket E Torres F Bower |
| INPO aspect | |
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Finding - Peach Bottom - IR 05000277/2008007 | |||||||||||||||||||||||||||||||||
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Finding List (Peach Bottom) @ 2008Q2
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