05000265/LER-2003-005
| Event date: | |
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| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2652003005R00 - NRC Website | |
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6
- Pi (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
Technical Specification Allowable Value Exceeded for Main Steam Flow Switches due to Inadequate Drift Allowance used in Setpoint Calculation
A. CONDITION PRIOR TO EVENT
Unit: 2 � Event Date: July 17, 2003 � Event Time: 1059 hours0.0123 days <br />0.294 hours <br />0.00175 weeks <br />4.029495e-4 months <br /> Reactor Mode: 1 � Mode Name: Power Operation � Power Level: 085% Power Operation (1) - Mode switch in the RUN position with average reactor coolant temperature at any temperature.
B. DESCRIPTION OF EVENT
On July 17, 2003, at 1059 hours0.0123 days <br />0.294 hours <br />0.00175 weeks <br />4.029495e-4 months <br />, during performance of the Unit 2 Division II Main Steam Line High Flow Switch Calibration and Functional Test, two main steam [SB] flow instruments [FS] were determined to have as-found setpoints that exceeded the Technical Specification (TS) Allowable Value. The instruments were calibrated to be within the TS allowable range. A total of 16 switches, four per steam line, are installed on the Unit 2 main steam lines. The switches feed into the Primary Containment Isolation System [JM], with 'one out of two twice' logic.
C. CAUSE OF EVENT
The root cause of this event was the use of inadequate drift allowance in engineering setpoint calculations.
The main steam flow switches were installed in February 2002. Because the main steam flow switches were newly installed at the time the setpoint calculations were performed, there was no historical drift data available. Therefore, the Technical Specification allowable value was calculated using the applicable calibration uncertainty values provided by the manufacturer along with an assumed drift term in accordance with procedural guidance. Based on the historical data that is now available, the drift that has been experienced exceeds the values assumed.
D. SAFETY ANALYSIS
The safety significance of this event was minimal. Although the instruments were found to have setpoints outside the TS allowable values, the instruments would have provided the trip signal within the analytical values assumed in the accident analysis. Therefore, the safety function would have been met. This event is being FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 (If more space is required, use additional copies of NRC Form 366A)(17) reported as operation prohibited by TS due to the fact that multiple instruments were found out of calibration during the same surveillance, providing sufficient evidence that the situation existed longer than allowed by TS.
E. CORRECTIVE ACTIONS
Immediate Actions
The main steam flow switches were recalibrated.
Corrective Actions to be Completed A drift analysis will be performed for the Unit 1 and Unit 2 main steam flow switches and current calibration frequencies will be evaluated. Additional actions will be taken as appropriate based on this evaluation.
The Unit 1 and Unit 2 Barton main steam flow switches will be replaced with differential pressure transmitters.
F. PREVIOUS OCCURRENCES
No instances of multiple main steam flow switches being outside of the Technical Specification Allowable Value were identified in the last two years. However, there was one instance (not reportable) of a single main steam flow switch on Unit 1 where the as-found setpoint exceeded the Technical Specification Allowable Value.
G. COMPONENT FAILURE DATA
The main steam flow switches are Barton Model 288A Differential Pressure Indicating Switches, with a setting range of 0 to 400 paid.