05000265/LER-2002-003
| Quad Cities Nuclear Power Station Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| 2652002003R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Quad Cities Nuclear Power Station Unit 2 05000265 (If more space is required, use additional copies of NRC Form 366A)(17)
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor, 2957 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
EVENT IDENTIFICATION
Reactor Shutdown due to Failure of Reactor Steam Dryer from Flow-Induced Vibrations as a Result of Extended Power Uprate (EPU)
A. CONDITION PRIOR TO EVENT
Unit: 2 � Event Date: July 11, 2002 � Event Time: 1417 hours0.0164 days <br />0.394 hours <br />0.00234 weeks <br />5.391685e-4 months <br /> Reactor Mode: 1 � Mode Name: Power Operation � Power Level: 083% Power Operation (1) - Mode switch in the RUN position with average reactor coolant temperature at any temperature.
B. DESCRIPTION OF EVENT
Over a period of approximately 30 days, Quad Cities Unit 2 experienced several anomalous readings related to reactor pressure, reactor level, steam flow, and moisture carryover. When the first anomalous reading occurred on June 7, 2002, an evaluation was made that concluded that the only component that could cause such readings was a degraded Steam Dryer [DRY]. An operability determination was completed that supported continued operation of the unit. A key element of the operability determination was that no loose parts could migrate such that they would affect emergency equipment.
Based on analyses of additional plant data from June 18, 2002, to July 10, 2002, it was determined that there no longer was reasonable assurance that the operability determination supported continued operation with a degraded Steam Dryer because Steam Dryer fragments were potentially migrating from the Reactor [AC] and entering the Main Steam lines [SB]. Since these fragments could potentially impact multiple safety systems, Technical Specification 3.0.3 was conservatively entered and a Unit 2 shutdown was initiated on July 11, 2002.
An inspection of the Unit 2 Reactor internals on July 13, 2002, revealed that a Steam Dryer cover plate had failed, which allowed steam to bypass the dryer. Steam Dryer cover plate fragments were found in a Main Steam line flow venturi [FE] and Main Turbine [TA] stop valve [V] inlet screen. However, based on the magnitude of the actual Steam Dryer failure and the actual migration of its broken parts, it was concluded that all of the Unit 2 safety systems would have responded as designed had a design basis event occurred, and that the entry into TS 3.0.3 was not a required entry.
FACILITY NAME (1) LER NUMBER (6 DOCKET NUMBER (2) PAGE (3) (If more space is required, use additional copies of NRC Form 366A)(17)
C. CAUSE OF EVENT
The root cause of the Steam Dryer failure was a lack of industry experience and knowledge of flow-induced vibration dryer failures.
An examination of the cracked Steam Dryer cover plate by metallurgical experts and a study of a scale model at the General Electric San Jose facility resulted in the determination that the cause of the Steam Dryer cover plate failure was high cycle mechanical fatigue caused by flow-induced vibrations. The flow-induced vibration coincided with the natural frequency of the failed 1/4" thick cover plate, creating a resonance condition. The flow-induced vibration frequency was created by pressure pulsations whose magnitude increased with higher steam flows due to the EPU conditions. Unit 2 reached EPU conditions (-117% of pre-EPU Power) for the first time in March 2002. This condition was not identified during the EPU evaluations performed due to the lack of industry experience and knowledge of flow-induced vibration dryer failures.
D. SAFETY ANALYSIS
The safety significance of the Steam Dryer failure was minimal. The changes in sensed and actual Reactor water level and pressure, moisture carry-over, and increased Main Steam flows had no adverse effect on plant operation during all normal and potential accident modes. The accidents and transients described in Updated Final Safety Analysis Report Section 15.0 remained bounding and there were no effects on the Technical Specifications or the TRM due to the actual event.
Based on the magnitude of the actual Steam Dryer failure and the actual migration of its broken parts, it can be concluded that all of the Unit 2 safety systems would have responded as designed, had a design basis event occurred. Therefore, although the unit was conservatively shut down using TS 3.0.3, the Unit 2 safety systems were capable of performing their safety functions throughout the event and entry into TS 3.0.3 was not a required entry. This report is submitted as a voluntary report of an event that might be of generic interest or concern.
E. CORRECTIVE ACTIONS
Immediate Actions:
- The damaged 1/4" Unit 2 Steam Dryer outer bank cover plate was replaced with a 1/2" thick plate.
- The undamaged side 1/4" outer bank cover plate on the Unit 2 Steam Dryer was replaced with a 1/2" plate.
- All Steam Dryer foreign material from the Reactor Vessel, Main Steam system, and other interconnected systems was identified and retrieved.
- The Steam Dryer was inspected for additional damage and repair/disposition.
- All collateral damage due to the damaged Steam Dryer was identified and repaired/dispositioned.
- Temporary acoustic monitoring of the Unit 2 Steam Dryer was installed to obtain data to identify the power level (steam flow) at which the frequency of concern significantly increases.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 (If more space is required, use additional copies of NRC Form 366A)(17) Corrective Actions to be Completed:
- Evaluations will be performed of other components in the dryer assembly and in the steam flow path to determine any additional vulnerability to steam flow induced vibration failures. Recommendations will be provided for monitoring and/or future modifications to alleviate any identified problem areas.
- The Quad Cities Unit 1 1/4" dryer cover plate will be replaced with a 1/2" plate to remove vulnerability to failure.
F. PREVIOUS OCCURRENCES
No previous occurrences of Steam Dryer failure at Quad Cities were identified.
G. COMPONENT FAILURE DATA
The Steam Dryer was manufactured by Stearns-Roger.