05000390/FIN-2010003-03
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Finding | |
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| Title | B-train Main Control Room Chiller Temperature Control Valve Failure |
| Description | The inspectors identified an issue associated with the B-train Main Control Room Chiller temperature control valve. This issue is being characterized as an unresolved item (URI). Licensee procedure 0-SI-82-4, 18 Month Loss of Offsite Power with Safety Injection Test Diesel Generator 1B-B, provides the detailed steps to verify the operability of Diesel Generator 1B-B and 6.9 kV Shutdown Board 1B-B load shed logic during loss of offsite power with and without safety injection (SI) actuation. 0-SI-82-4 also simulates a loss of offsite power and the subsequent recovery of shutdown board power from the 1B-B diesel generator. One of the components affected during surveillance 0-SI-82-4 was the B-train main control room chiller. During the test, the chiller was initially in service with normal ERCW cooling flow supplied. When shutdown board voltage was lost during the test, the B-train main control room chiller stopped and B-train ERCW header flow ceased and ERCW pressure lowered to atmospheric pressure. The main control room chiller temperature control valve (TCV), 0-TCV-67-1053-B, was a hydraulically operated valve that used ERCW pressure for operation. Due to valve design, the TCV opened on the loss of ERCW pressure. When the shutdown board was re-energized from the diesel, the diesel load sequencer started the associated ERCW pumps and the main control room chiller. During the performance of 0-SI-82-4 on March 10, 2008, the B-train MCR chiller tripped on low suction pressure. Subsequent licensee investigation revealed that the chillers TCV had failed in the open position. The licensee initiated a work order to repair the TCV and PER 139875 to document the chiller trip during testing. During TCV disassembly, the licensee discovered that the valves internal stem guide had become misaligned which prevented the valve from closing. No valve internal parts were found damaged in the valve body or actuator. The corrective actions for PER 139875 included completion of the work order to rebuild the TCV and completion of the maintenance rule cause determination evaluation (CDE). CDE 914 determined that the apparent cause of the shift of the TCVs valve stem guide was due to an ERCW header pressure surge which occurred when the ERCW pumps restarted after the simulated loss of offsite power during 0-SI-82-4. The CDE also determined that no actions to prevent recurrence were necessary since the testing on March 10, 2008, was considered to be a unique, isolated event that was caused by a peculiar ERCW transient which is unlikely to be repeated in future testing or any other anticipated plant condition. During the performance of 0-SI-82-4 on October 9, 2009, the B-train MCR chillers TCV failed open. The licensee initiated a work order to repair the TCV and PER 204181 to document the chiller trip during testing. During TCV disassembly, the licensee discovered that the valves internals had shifted therefore preventing the valve from closing. No valve internal parts were found damaged in the valve body or actuator. On December 23, 2009, the functional evaluation for PER 205438 determined that the B-train MCR chiller TCV was operable, but non-conforming, and that manual compensatory actions were required. The manual compensatory actions prescribed by the functional evaluation were implemented by revision to licensee procedure AOI-40, Station Blackout. The inspectors questioned the licensees compensatory action implementation and past operability of the MCR chillers. Pending additional information from the licensee regarding the past operability determinations and further review of the maintenance on the TCVs by the NRC, this issue will be identified as URI 05000296/2010003-01, B-train Main Control Room Chiller Temperature Control Valve Failure. |
| Site: | Watts Bar  |
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| Report | IR 05000390/2010003 Section 4OA2 |
| Date counted | Jun 30, 2010 (2010Q2) |
| Type: | URI: |
| cornerstone | Mitigating Systems |
| Identified by: | NRC identified |
| Inspection Procedure: | IP 71152 |
| Inspectors (proximate) | R Monk E Guthrie K Miller M Schwiegr Monke Guthrie M Pribish |
| INPO aspect | |
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Finding - Watts Bar - IR 05000390/2010003 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Finding List (Watts Bar) @ 2010Q2
Self-Identified List (Watts Bar)
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