On February 2, 2011, while Unit 2 was operating at 100% power, the C loop
RCS cold leg loop isolation valve, 2-RC-MOV-2595, experienced stem to disc separation resulting in a low
RCS flow condition in the C
RCS loop and subsequent
automatic reactor trip. The licensee decided to repair the valve in Cold Shutdown by draining the
RCS to mid-loop. The
RCS standpipe is relied upon to provide both local and remote indication of
RCS level during reduced inventory and mid-loop configurations. The licensee drained to reduced inventory and was forced to re-fill the
RCS due to the unreliable level indication of 2-RC-LR-200A. Troubleshooting was performed on the 13 Enclosure electronics of the level recorder and associated circuitry and the instrument was tested before a second attempt at draining to mid-loop was commenced. During the second attempt 2-RC-LR-200A again became unreliable and operators were again forced to refill the
RCS. The licensee then performed more in-depth troubleshooting of the instrumentation and performed a third drain down to mid-loop conditions once it had been returned to service. The third attempt was successful, although the instruments still experienced several instances of erratic indication. The licensee entered this issue into their
CAP as CR413227, and initiated Apparent Cause Evaluation (
ACE) 018543. The inspectors require additional information, including the licensees completed investigation in ACE018543 to determine if there is a performance deficiency which is more than minor. This issue is identified as
URI 05000281/2011002-01,
Reactor Coolant System Instrumentation Erratic Level Indication.
