05000373/LER-2003-003

LER-2003-003,

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
3732003003R00 - NRC Website

PLANT AND SYSTEM IDENTIFICATION

General Electric - Boiling Water Reactor, 3489 Megawatts Thermal Rated Core Power

A. CONDITION PRIOR TO EVENT

Unit(s) : 1 Event Date: 7/10/03 Event Time 1110 Reactor Mode(s): 1 Power Level(s): 100 Mode(s) Name: Run

B. DESCRIPTION OF EVENT

On 7/7/03, during the performance of surveillance LIS-RI-101, "Unit 1 RCIC Steam Line High Flow Isolation Calibration," differential pressure (D/P) switch 1E31- NO13AA failed its diaphragm integrity test, such that no switch as-found setpoint could be obtained. The surveillance was stopped, and the switch was replaced.

The new switch was tested acceptably and returned to service.

On 7/10/03, during the continuation of surveillance LIS-RI-101, D/P switch 1E31- NO13BA failed its diaphragm integrity test. The surveillance was stopped, and the switch was replaced.

At the time of discovery of the failure of switch 1531-N013BA, switch 1E31-N013AA had been replaced and calibrated. However, because both switches were found with diaphragm failures during the same surveillance, this condition was determined to be reportable under 10 CFR 50.73 (a)(2)(vii) as a condition where a single cause _caused two independent trains or channels to become inoperable in a single system designed to mitigate the consequences of an accident. Because these failures would have prevented a Reactor Core Isolation Cooling (RCIC)(BN) Steam Line High Flow isolation in the event of a break, it is also reportable under 10 CFR 50.73(a)(2)(v)(D) as a condition that could have prevented the fulfillment of the safety function of systems needed to mitigate the consequences of an accident.

C. CAUSE OF EVENT

The root cause of the diaphragm failures was not determined; however, Static 0- Ring, Inc. (SOR) D/P switches have historically experienced ruptures of the Kapton diaphragm material. The switches that failed have been in service since 12/98 (1B31-N013AA) and 12/99 (1E31-N013BA), which are typical life spans for these switches in this application.

The use of SOR D/P switches at LaSalle has been documented in IE Bulletin 86-02 (7/18/86) and a Safety Evaluation Report (4/1/87) *Continued Use of SOR DP Switches at LaSalle County Station." LaSalle elected to replace the SOR switches for the reactor water level trip functions with Rosemount trip units. Due to coot considerations, SOR switches were retained in less critical applications, including the RCIC Steam Line Flow - High isolation. A quarterly (92 day) channel calibration surveillance interval was established and incorporated into Technical Specification Surveillance Requirement 3.3.6.1.3 for these switches, to ensure early detection of failures. This was the first reportable event related to the failure of an SOR switch since 1995.

Efforts to identify a suitable replacement for these switches continue, but have not been successful to date.

D. SAFETY ANALYSIS

The safety significance of this event was minimal. The RCIC Steam Line Flow—High function detects a break of the RCIC steam supply lines and closes the steam line isolation valves to prevent inventory loss and potential core uncovery. No credit in the UFSAR accident analysis is taken for this function, since the bounding analysis is performed for large breaks such as recirculation and MSL breaks. However, the isolation function prevents the RCIC steam line break from becoming bounding.

With both divisions inoperable at the same time, the RCIC equipment room Area and Differential Temperature instrumentation is diverse to the high flow isolation function and would have closed the steam line isolation valves in the event of a break or leak in the steam supply lines.

This event constitutes a safety system functional failure.

E. CORRECTIVE ACTIONS

L The failed switches were replaced with like-for-like SOR DIP switches.

2. Efforts to identify, qualify and install an acceptable replacement for the SOR switches are in-progress (AT# 154202-6).

LER NUMBER

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TITLE

Cooling Isolation due to Personnel Error This LER involved an inadvertent isolation of the RCIC inboard steam line isolation valve that occurred following discovery of a ruptured diaphragm on D/P switch 2E314F013SA. The isolation was due to a personnel error, in that the circuit breaker to the isolation valve was closed prior to resetting the high flow isolation logic signal. The corrective actions were to replace the failed DIP switch and to address the personnel error issues. These corrective actions would not have prevented this event.

to a Torn Diaphragm This LER documented the failure of DIP switch 2831-N013AA due to a torn diaphragm. Corrective actions were to replace the switch, and would not have prevented this event.

G. COMPONENT FAILURE DATA

Static 0-Ring, D/P Switch, Model # 103AS-E203-NX-C1A-MTTX6