05000301/LER-2011-002
| Point Beach Nuclear Plant, Unit 2 | |
| Event date: | 03-07-2011 |
|---|---|
| Report date: | 05-03-2011 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(vii), Common Cause Inoperability |
| 3012011002R00 - NRC Website | |
Event Description
Between March 4, 2011 and March 16, 2011, during the Unit 2 Refueling 31 outage (MODE 6) performance of 2ICP 04.001E, Reactor Protection and Safeguards Analog Racks Steam Pressure Refueling Calibration, it was discovered on March 7, 2011, that the as-found values for four of the six Unit 2 engineered safety feature (ESF) steam line pressure (SLP) instrument channel dynamic compensation module lead time constants were outside required technical specification (TS) values. The event does not constitute a safety system functional failure.
Cause of the Event
The drift calculation to address the static and dynamic settings was not performed in a timely manner. The drift calculation later showed the modules did contain a positive bias but the setpoint was too low for the potential drift.
Analysis of the Event
TS LCO 3.3.2, ESFAS Instrumentation, Table 3.3.2-1, Function 1.e requires that three channels are required per steam line to be operable to provide safety injection (SI) during MODES 1 and 2, and in MODE 3 when pressurizer pressure is greater than 1800 psig where a secondary side break or stuck open valve could result in rapid depressurization of the steam lines. The function is not required to be operable in MODES 4, 5 or 6.
Steam line pressure-low provides protection against the main steam line break (MSLB), feed line break and inadvertent opening of a steam generator (SG) relief or safety valve. The steam line pressure-low provides a signal for control of the main steam atmospheric steam dump valves. A failure of a steam line pressure channel will not create a control failure that would result in a low steam line pressure SI event.
The lead constant value is required to be greater than or equal to 12 seconds, and the lag value is required to be less than or equal to 2 seconds. The ESFAS steam line pressure instruments monitor main steam line pressure and actuate on a 2-out-of 3 (2/3) steam line pressure-low condition to provide protection against a MSLB, main feedwater line break, or an inadvertent opening of a SG relief or safety valve.
The results of an evaluation determined that the dynamic response for all six of the compensation modules lead time constants had drifted low after being set within 0.037 seconds of their ideal setting. None of the Unit 2 modules exceeded the required TS lag value.
All six channels were found to be within the static calibration as-found tolerances. Therefore, the module outputs were able to reach the allowable field trip setpoint of 530 psig when actual process pressure was 743 psig, providing an actual margin of 408 psig to the safety limit of 335 psig. The downstream bistables would have tripped to produce the steam line pressure low SI actuations that are required prior to reaching the TS-required value of 500 psig within 1.125 seconds, which would provide a minimum margin of 165 psig to the analyzed safety limit of 335 psig. Accordingly, the safety significance of this event is low.
Failed Components
None ESFAS instrumentation, Lead/Lag Time Constants for Steam Line Pressure outside Technical Specification Values Engineered Safety Feature Steam Line Pressure Dynamics Modules Discovered Outside of Technical Specification Values
Corrective Actions
The drift calculation for the SLP compensation modules was revised and a performance monitoring plan was implemented. The modules are currently being refurbished and will be installed with new setpoints and tolerances during the ongoing refueling outage.
Similar Events A review of recent LERs identified the following previous conditions that involved lead/lag time constants for steam line pressure outside technical specification Values:
LER Number Title