05000374/LER-2001-002
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3742001002R00 - NRC Website | |
PLANT AND SYSTEM Identification General Electric - Boiling Water Reactor, 3489 Megawatts Thermal Rated Core Power
A. CONDITION PRIOR TO EVENT
Unit(s): 2 � Event Date: 05/27/01 � Event Time: 0618 Hours Reactor Mode(s): 1 � Power Level(s): 80 Mode(s) Name: Run
B. DESCRIPTION OF EVENT
On May 27, 2001, Unit 2 was operating at 80 percent reactor power. Procedure LOS-RP-M5, "Turbine Control Valve Monthly Surveillance," was in progress to test the main turbine control valves (TCV) [TA). During the performance of LOS-RP-M5 on TCV #1 , an automatic reactor scram occurred at 0618 hours0.00715 days <br />0.172 hours <br />0.00102 weeks <br />2.35149e-4 months <br /> due to turbine stop valve closure which was caused by high vibration on the main turbine with reactor power above 25 percent power. Vibration on turbine bearing #1 exceeded the main turbine trip set point of 12 mils for greater than three seconds.
All systems operated as designed, and there were no ECCS actuations. The lowest reactor water level reached was minus 10 inches, after which level recovered to the normal band. Reactor pressure responded normally. No safety relief valves actuated. All control rods fully inserted.
This event is reportable pursuant to 10CFR50.73(a)(2)(iv)(A) as an event that resulted in an automatic actuation of the reactor protection system. An Emergency Notification System call was made at 0740 hours0.00856 days <br />0.206 hours <br />0.00122 weeks <br />2.8157e-4 months <br /> on May 27, 2001.
C. CAUSE OF EVENT
The root cause of this event was that a connector on the linear variable differential transformer (LVDT) for TCV #3 was contaminated with Electrohydraulic Control (EHC)[JJ] fluid in combination with higher than normal baseline vibration during TCV testing. This resulted in a high resistance connection, which produced an incorrect position indication on TCV #3. This resulted in a feedback signal, which throttled flow through the TCV #3 compared to the remaining TCVs.
As a result of this feedback, the remaining TCVs opened further to maintain pressure.
The closure of TCV #1 for testing in combination with the abnormal position of the remaining control valves created an unbalanced steam load across the high pressure turbine. This change in steam flow unloaded the #1 and #2 high pressure turbine bearings, and resulted in increased vibration, which reached the trip setpoint of 12 mils for greater than three seconds.
Contributing to this event was a less than optimal alignment of the main turbine "A" coupling. This misalignment was recognized during the last refueling outage but was evaluated as acceptable for continued operation. This misalignment could not cause a high vibration trip individually. However, this increased base load vibration during TCV testing in combination with the problem on TCV #3, contributed to the transient high vibrations that caused the trip.
D. C SAFETY ANALYSIS The safety consequences of this event were minimal. The turbine generator trip is described as an event of moderate frequency in Chapter 15 of the Updated Final Safety Analysis Report (UFSAR). The plant responded consistent with the referenced UFSAR chapter, taking into account the lower power level which mitigated some of the assumed transient responses (e.g., SRV lifting, loss of feedwater, and RCIC/HPCS initiation). The reactor was safely shut down and recovery performed without incident. There were no safety system functional failures. This event would have been more severe at full power. The power level was reduced for the performance of the turbine control valve testing.
E. C CORRECTIVE ACTIONS 1. Unit 2 main turbine "A" coupling will be aligned to within GE Specifications in L2R09. (ATM# 52841) 2. LOS-RP-M5 will be revised to bypass the high vibration trips on Turbine Bearings #1 and #2 during TCV testing. (ATM# 52841) Corrective Action to Prevent Recurrence:
1. The fouled TCV connector was cleaned and the seal replaced during the forced outage. (complete) 2. The remaining TCV connector seals in Unit 1 and 2 will be replaced in future outages. (ATM# 52841) F. C PREVIOUS OCCURRENCES A review of Licensee Event Reports over the previous five years found no previous or similar occurrences.
G. C COMPONENT FAILURE DATA Since no component failure occurred, this section is not applicable.