MONTICELLO - SAFETY SYSTEM OVERPRESSURE PROTECTION FAILURE DUE TO CLOSED VALVES

At 2045 [CDT] on 8/14/12, MNGP [Monticello Nuclear Generating Plant] Operations determined that valves RHR-82 and RHR-84 had been inappropriately closed as part of an isolation clearance order for work on shutdown cooling suction piping. These valves are required to be open to provide overpressure protection for RHR piping passing through primary containment penetration X-12.
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