05000263/FIN-2012002-04
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Finding | |
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| Title | Monticello Susceptibility to Degraded Voltage and Under Voltage Conditions Identified by January 30, 2012, Event at the Byron Station |
| Description | The licensees position, as documented in OPR 01325199-01 is as follows. The failure of phase C insulator at Byron Station that resulted in an open circuit condition caused an imbalanced voltage condition at their essential buses. At both Byron Station and MNGP, neither the degraded bus voltage nor the loss of voltage logic was designed to provide isolation due to an open phase connection resulting from a component failure. The degraded voltage logic is designed to monitor voltage at the 4kV essential buses to ensure that when connected to the offsite source, the voltage is adequate to provide for proper operation of safety-related components. The design and licensing bases requirements do not require analysis of imbalanced voltage conditions resulting from equipment or component failures. Therefore, the degraded voltage relaying scheme is capable of responding to degraded grid conditions as described in the Monticello TS 3.3.8.1, Amendment 147, LOP Instrumentation. Also, in conclusion, the licensee documented the following, The degraded voltage relays and loss of voltage relays are operable. The vulnerability is not considered to impact the operability of the specified design basis automatic functions of the various relays described in Technical Specification 3.3.8.1 (Loss of Power Instrumentation) and in accordance with applicable design requirements. The NRC inspectors plan to further review the licensees position that the condition is not required to be evaluated by their licensing and design basis. Since this evaluation will require additional review by subject matter experts located at both the Regional Office and Headquarters, this issue will be treated as an Unresolved Item |
| Site: | Monticello  |
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| Report | IR 05000263/2012002 Section 1R15 |
| Date counted | Mar 31, 2012 (2012Q1) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71111.15 |
| Inspectors (proximate) | K Riemer M Phalen S Thomas P Voss S Bell M Ziolkowskip Vossm Learn D Mcneil K Riemer M Phalen S Thomas J Laughlin J Bozga M Jones |
| INPO aspect | |
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Finding - Monticello - IR 05000263/2012002 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Monticello) @ 2012Q1
Self-Identified List (Monticello)
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