05000265/LER-2005-002
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| Event date: | |
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| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 2652005002R01 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Quad Cities Nuclear Power Station Unit 2 05000265 NUMBER NUMBER (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
Main Steam Relief Valve Actuator Degradation Due to Failure to Correct Vibration Levels Exceeding Equipment Design Capacities CONDITION PRIOR TO EVENT A.
Unit: 1 Event Date: January 6, 2006 Event Time: 1900 hours0.022 days <br />0.528 hours <br />0.00314 weeks <br />7.2295e-4 months <br /> Reactor Mode: 1 Mode Name: Power Operation Power Level: 085% Unit: 2 Event Date: December 30, 2005 Event Time: 0900 hours0.0104 days <br />0.25 hours <br />0.00149 weeks <br />3.4245e-4 months <br /> Reactor Mode: 1 Mode Name: Power Operation Power Level: 024% DESCRIPTION OF EVENT B.C On December 21, 2005, the 2-0203-3D Main Steam Electromatic Relief Valve (ERV) [RV] [SB] was declared inoperable due to the inability to determine whether or not a 125 VDC negative ground was affecting the valve control circuit. Operations personnel entered Technical Specification Limiting Condition of Operation (LCO) 3.4.3 Condition A and 3.5.1 Condition G for an inoperable safety relief valve, which placed Unit 2 in a 14-day allowed outage time (AOT). Station personnel continued troubleshooting efforts to determine the effect and precise circuit location of the negative ground.
On December 30, 2005, a load drop was initiated to allow personnel to enter the Unit 2 drywell to conduct an inspection of the 3D ERV. The inspection team found internal damage in the 3D ERV solenoid [SOL] actuator, and a unit shutdown was initiated at 0900 hours0.0104 days <br />0.25 hours <br />0.00149 weeks <br />3.4245e-4 months <br />.
Inspections of the other three Unit 2 ERV solenoid actuators were conducted.
Significant wear and some loose parts were identified on the 3B, 3C and 3E ERV actuators. These ERV actuators were electrically stroked from the main control room one time prior to the initial inspections and two more times after the initial inspections, with personnel in attendance to verify operation of the actuators; however indications of an open valve via control room annunciation and sequence of event recorder (SER) computer points were not received for the 3C and 3E valves.
All four ERV solenoid actuators were replaced with rebuilt actuators and Unit 2 was synchronized to the grid on January 1, 2006, and returned to pre-Extended Power Uprate (pre-EPU) power (approximately 2511 MWt) on January 3, 2006.
On December 31, 2006, power was decreased on Unit 1 to pre-EPU power as a conservative measure. On January 6, 2006, based on the results of the Unit 2 ERV actuator inspections, a Unit 1 shutdown was initiated to perform an extent of condition (EOC) review. Unit 1 was taken off line at 0001 on January 7, 2006.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) Quad Cities Nuclear Power Station Unit 2 05000265 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17) Three of the four Unit 1 ERVs were declared inoperable based on unsuccessful actuator stroke tests or inspection results. Loose hardware and spring guidepost wear were noted on all four of the ERV solenoid actuators. All four Unit 1 ERV actuators were removed and quarantined for further evaluation. Rebuilt actuators were installed and stroke tested satisfactorily. Unit 1 was synchronized to the grid on January 8, 2006, and returned to pre-EPU power on January 9, 2006.
During inspections of the quarantined Unit 1 ERV actuators, it was noted that the actuator pivot plate bolting was worn. This condition created the potential for failure of the actuator to function as designed. Procedure reviews conducted in light of this information determined that the pivot plate bolts were not normally inspected. This brought into question the continued operability of the refurbished and currently installed Unit 2 ERV actuators. Unit 1 was not immediately called into question because new pivot plate bolts had just been installed during the January 7, 2006, shutdown.
On January 14, 2006, Unit 2 was shut down for inspection of the ERV actuator pivot plate bolts. During the as-found stroke testing, the 3D ERV actuator stroked once and then became bound. The cause of this condition was determined to be over tightening of the roller plunger and ERV actuator equipment tolerances. Changes were made to the guidance for rebuilding the actuators, and the removed Unit 2 ERV actuators were then rebuilt using the new rebuild criteria and reinstalled.
Also during the Unit 2 shutdown, an inspection was conducted on the support between the ERV main valve and the ERV pilot valve. This support is referred to as the turnbuckle. The inspection identified that both valve and pilot side turnbuckle tack welds had cracked on the 3D ERV. Because cracked turnbuckle tack welds might be a precursor to fretting wear of the turnbuckle threads, the turnbuckle was removed and further analyzed on site, and fretting wear was identified.
As a result of the roller-plunger over-tightening issue identified on Unit 2, the Unit 1 ERVs were declared inoperable. On January 15, 2006, Unit 1 was shut down and the Unit 1 ERV actuators were satisfactorily stroke tested in place. The Unit 1 ERV turnbuckles were inspected with no cracks found on the tack welds. The Unit 1 ERV actuators were replaced with actuators rebuilt in accordance with the new criteria developed in response to the Unit 2 issues. Also, the Unit 1 3D ERV was replaced due to high tailpipe temperatures experienced during the previous start up.
Both Unit 1 and Unit 2 were returned to power operation on January 19, 2006.
CAUSE OF EVENT C.� The ERV actuator damage was caused by main steam line (MSL) vibration levels that exceeded the design capabilities of the components during operation at EPU power levels. The root cause was the adoption of a maintenance strategy to minimize the effects of the vibration on MSL attached components rather than correcting the source of the MSL vibrations soon after original startup of the plant.
Although ERV actuator problems had been encountered early in the life of the plant, the actions taken involved increasing the frequency of maintenance. This strategy supported ERV actuator response at pre-EPU power levels; however it did not address operation of the actuator in an increasing vibration environment. Failure to recognize this as a potential issue associated with operation at EPU power resulted in the 2006 Unit 1 and Unit 2 forced outages.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) � (If more space is required, use additional copies of NRC Form 366A)(17) (CDF), internal events Large Early Release Frequency (LERF), and external events.
This LER is being submitted in accordance with:
- 10 CFR 50.73(a)(2)(i)(A), Completion of shutdown required by TS, (January 15, 2006, Unit 1 shutdown - ENS call made January 15, 2006, at 1136 hours0.0131 days <br />0.316 hours <br />0.00188 weeks <br />4.32248e-4 months <br />, in accordance with 10 CFR 50.72(b)(2)(i))
- 10 CFR 50.73(a)(2)(i)(B), Operation or condition prohibited by TS, (December 30, 2005, Unit 2 shutdown, and January 6, 2006, Unit 1 shutdown)
- 10 CFR 50.73(a)(2)(v)(D), Any event or condition that could have prevented the fulfillment of a safety function, (January 6, 2006, Unit 1 shutdown)
- 10 CFR 50.73(a)(2)(vii), Single cause inoperability of independent trains or channels, (January 6, 2006, Unit 1 shutdown) E.� CORRECTIVE ACTIONS Following the event, the ERV actuators on Unit 1 and Unit 2 were rebuilt in accordance with guidance incorporating the results of the inspections.
Unit 1 and Unit 2 remained limited to pre-EPU power until the Acoustic Side Branches were installed.
Acoustic Side Branches (ASBs) have been designed for and installed on the main steam system for both Unit 1 and Unit 2. Subsequent testing has shown that overall MSL vibrations have been reduced to a level to support safe and reliable operation of the MSLs and attached components during future operating cycles at EPU.
The ERV actuators for both Unit 1 and Unit 2 have been replaced with actuators with a more robust design.
Guidance has been provided concerning how to process recommendations and conclusions affecting system/equipment operation from contracted studies/projects. This process includes requirements to track reports and recommendations to ensure disposition is documented.
The Operational and Technical Decision Making Process procedure and the Technical Task Risk/Rigor Assessment, Pre-Job Brief, Independent Third Party Review and Post- Job Brief procedure have been revised to add the rigor and documentation necessary to ensure proper evaluation of complex engineering decisions and risk analysis products.
Corrective Action to be Completed:
The test control process is being revised to address failure modes and effects analysis and also requirements for owner reviews of test plans and test reports.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Quad Cities Nuclear Power Station Unit 2 05000265 NUMBER NUMBER (If more space is required, use additional copies of NRC Form 366A)(17)
F. PREVIOUS OCCURRENCES
The following instances of ERV actuator failure due to vibration were identified:
August 11, 1990 (Quad Cities Unit 1) - The 3C ERV failed to open manually due to a worn solenoid spring bracket bushing. A worn bushing permitted a spring to work its way up around the bushing.
March 1, 1993 (Quad Cities Unit 1) - The 3C ERV showed unusual wear. Excessive wear noted on the plunger guides of the actuator was attributed to vibration.
October 20, 2003 (Dresden Unit 2) - The 3D ERV was discovered with a missing limit switch screw, damaged housing, and a broken wire.
November 21, 2003 (Quad Cities Unit 1) - Inspection of the 3C, 3D, and 3E ERVs revealed degraded components, which was attributed to vibration.
April 27, 2005 (Dresden Unit 3) - The 3E ERV was found with loose mounting hardware for the microswitch. Both switches were found in their expected position; however, one screw was found missing on one switch and one mounting screw was found loose on the other switch. Several other actuators were inspected with no problems found.
These five events include findings of loose parts, worn bushings, worn springs and worn posts. The corrective actions taken in response to the January shutdowns at Quad Cities address each of these events. They include redesign/replacement of the actuator and reduction in the source of the vibration. The earlier corrective actions taken to prevent these events included increased preventive maintenance performance and addition of thread lock on certain components. No action was taken to reduce the source of the damaging vibration.
G. COMPONENT FAILURE DATA
The valves are 6 inch, model 1525VX relief valves manufactured by Dresser Industries.