05000456/FIN-2012002-06
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Finding | |
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Title | Inadequate Safety-Related 4kV Undervoltage Protection |
Description | TS 3.3.5, Loss of Power Diesel Generator Start Instrumentation, required that in Modes 1-4 two channels per bus of the loss of voltage (undervoltage) function and two channels per bus of the degraded voltage function shall be operable. In addition, TS Surveillance Requirement 3.3.5.2 stated that the acceptable channel calibration values for the undervoltage setpoint was greater than 2730 volts with a time delay of less than or equal to 1.9 seconds; and for the degraded voltage setpoint, the value was greater than 3930 volts with a time delay of 310 plus or minus 30 seconds. Upon actuation of the undervoltage or degraded voltage function, the EDGs were designed to start and provide power to all engineered safety feature loads. However, because the engineered safety feature undervoltage and degraded voltage protection schemes was comprised of two contacts in series that monitored differential voltages between the A-B and B-C phases, upon the loss of only the A or C phase, only one protective relay was actuated and therefore did not satisfy the coincidence logic necessary to initiate an undervoltage or degraded voltage protection signal. The Byron and Braidwood licensee concluded that this event was not within the facilitys CLB and that because the NRC had reviewed and approved the design, that the undervoltage protection design inadequacies did not impact operability and that the requirements of TS 3.3.5 were met. The licensee implemented compensatory actions consisting of a dedicated operator station for each operating unit in the main control room to ensure that manual action would be taken to separate the TS preferred power source following a loss of A or C phase to the station auxiliary transformers (SATs). At the end of this inspection, a detailed review of the CLB was in progress. This URI will remain open pending the completion of this review and a determination of whether the undervoltage and degraded voltage protection design vulnerability was within the stations CLB. |
Site: | Braidwood ![]() |
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Report | IR 05000456/2012002 Section 1R15 |
Date counted | Mar 31, 2012 (2012Q1) |
Type: | URI: |
cornerstone | Mitigating Systems |
Identified by: | NRC identified |
Inspection Procedure: | IP 71111.15 |
Inspectors (proximate) | A Garmoe B Jose E Duncan J Benjamin J Gilliam M Holmberg M Perry |
INPO aspect | |
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Finding - Braidwood - IR 05000456/2012002 | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Braidwood) @ 2012Q1
Self-Identified List (Braidwood)
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