05000424/LER-2004-001
| Vogtle Electric Generating Plant - Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| 4242004001R00 - NRC Website | |
A. REQUIREMENT FOR REPORT
This event is reportable per 10 CFR 50.73 (a)(2)(iv) because an unplanned reactor protection system actuation occurred.
B. UNIT STATUS AT TIME OF EVENT
At the time of this event, Unit 1 was in power ascension in Mode 1 (power operations) at 35 percent of rated thermal power. The generator was tied to the grid and the Main Feedwater system was supplying water to all four steam generators. Other than that described herein, there was no inoperable equipment that contributed to the occurrence of this event.
C. DESCRIPTION OF EVENT
On March 27, 2004, at 2110 EST, control room operators tied the generator to the grid. At 2150 EST, an operator observed steam flow / feed flow mismatch alarms and noticed that the speed of the inservice main feed pump, MFP B, was increasing. The feed pump speed control was switched from automatic to manual, but to no effect. Operators then changed speed control systems. This also had no effect on the increasing speed, and steam generator (SG) water levels began to fluctuate. Operators manually tripped the reactor at 2205 EST. The operators then tripped MFP B and the auxiliary feedwater system (AFW) actuated. The unit was stabilized in Mode 3 (Hot Standby) at 2209 EST.
D. CAUSE OF EVENT
The cause of this event was a control valve hydraulic operating cylinder sticking in the open position so that the speed of the feed pump turbine could not be controlled. The valve stuck open due to misalignment of the hydraulic cylinder shaft with bushings in the cylinder cover. Discussions with vendor personnel determined that a technique exists to ensure the alignment of the upper and lower bushings on the hydraulic cylinder shaft following bushing installation. However, this technique was not utilized in the site instruction for rebuilding the valve. Previously, vendor personnel had been contracted to perform the valve rebuilding. The vendor considered the bushing alignment technique that was used to be a "skill-of-the-craft." More recently, site personnel had begun to perform the valve rebuilding, but the site instruction did not adequately address the necessity for using a bushing alignment technique.
1 U.S. NUCLEAR REGULATORY COMMISSION FACILITY NAME (1)
DOCKET
05000-424 LER NUMBER (6) A contributing cause of this event was the failure of control room personnel to recognize a higher-than- normal MFP B differential pressure prior to the start of the event. Had this been recognized, the control valve problem may have been diagnosed earlier and MFP B swapped for MFP A.
E. ANALYSIS OF EVENT
As the steam flow / feed flow mismatch problem continued, control room personnel acted appropriately to trip the reactor and prevent a challenge to the automatic trip actuation circuitry.
They also performed appropriately in tripping MFP B, which initiated the auxiliary feedwater system actuation, as designed. Based on these considerations, there was no adverse effect on plant safety or on the health and safety of the public as a result of this event.
The event does not represent a safety system functional failure.
F. CORRECTIVE ACTIONS
1) The MFP B control valve hydraulic operating cylinder bushings were properly aligned, the control valve returned to service, and the reactor returned to normal power operations.
2) The valve rebuilding site instruction has been revised to incorporate the proper bushing alignment technique.
3) The Unit 2 MFP control valve hydraulic operating cylinders were assembled utilizing the proper bushing alignment technique. The Unit 1 MFP A control valve hydraulic operating cylinder will be inspected during the Spring 2005 refueling outage.
4) Maintenance and engineering personnel are evaluating the scope and extent of site instruction and procedure development for activities that were previously performed by turbine-generator vendor personnel. The key activities are expected to be identified by June 30, 2004, and a schedule for procedure changes will be developed by December 31, 2004.
5) Licensed operators will review this event in continuing training, emphasizing the importance of maintaining a questioning attitude when abnormal conditions or parameters are encountered.
05000-424 DOCKET PAGE (3) LER NUMBER (6) FACILITY NAME (1)
G. ADDITIONAL INFORMATION
1) Failed Components:
Control valve hydraulic cylinder manufactured by General Electric Corporation, Type DEV631, 6 stage dual inlet turbine, secondary operating cylinder 501E431DY-63.
2) Previous Similar Events:
None 3) Energy Industry Identification System Code:
Main Feedwater System — SJ Auxiliary Feedwater System — BA