ML082740335
| ML082740335 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 09/30/2008 |
| From: | Mudrick C Exelon Generation Co, Exelon Nuclear |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML082740335 (3) | |
Text
TS 6.9.2 September 30, 2008 U.S. Nuclear Regulatory Commission Attn.: Document Control Desk Washington, DC 20555-0001 Limerick Generating Station, Units 1 and 2 Facility Operating License Nos. NPF-39 and NPF-85 NRC Docket Nos. 50-352 and 50-353
Subject:
Special Report - Seismic Monitoring Instrumentation Inoperability, Rev.1
References:
Special Report - Seismic Monitoring Instrumentation Inoperability, Rev.0, dated 7/21/08 This Special Report is being updated and re-submitted pursuant to the requirements of Limerick Generating Station (LGS), Unit 1 and Unit 2 Updated Final Safety Analysis Report (UFSAR) section 3.7.4.5, Technical Specifications 6.9.2, and Technical Requirements Manual (TRM) 3.3.7.2. TRM 3.3.7.2 Seismic Monitoring Instrumentation action "a" states that with one or more of the seismic monitoring instruments inoperable for more than 30 days, a Special Report shall be prepared and submitted to the Nuclear Regulatory Commission pursuant to Specification 6.9.2 of the Technical Specifications within the next ten days outlining the cause of the malfunction and the plans for restoring the instrument(s) to operable status. This revised report describes the restoration of the system computer and the identification of a degraded sensor.
On Wednesday June 11, 2008, both units were operating at full power with functional testing of the seismic monitoring instrumentation system in progress. During the test, the system computer failed to operate as expected and the system was declared inoperable at 1101 hours0.0127 days <br />0.306 hours <br />0.00182 weeks <br />4.189305e-4 months <br />. The system computer performs the function of the man-machine interface and the response spectrum analyzer. The computer was later repaired and returned to service.
However, a sensor in the Unit 1drywell was identified as degraded and will require an outage to perform the required maintenance.
The Seismic Monitoring System consists of two systems. One system is located in the main Control Room (MCR). The MCR Seismic Monitor has 5 tri-axial time-history accelerometer arrays located at various plant locations and elevations, 1 response spectrum analyzer (computer) and 5 digital recorders. If the Limerick Generating Station were to experience a seismic event, appropriate actions would be taken based on inputs from the functional seismic monitoring sensors (14 of 15 channels) inputting into the seismic monitoring computer system along with actions identified in station procedure SE-5. This procedure includes guidance on compensatory actions to be taken when the seismic monitoring instrumentation is out of service.
The second system is a stand-alone system located at the Spray Pond Pump House. The Spray Pond Seismic Monitor is a self-contained system with its own sensor array not
associated with the MCR Seismic Monitor. The Spray Pond Seismic Monitor remains operable.
Cause of the malfunction:
An investigation determined that the cause of the system failure was a degraded computer which has been repaired. However, a sensor has recently been identified as degraded which prevents restoration of the system to operable status.
Plans for restoring the instrument to operable status:
The seismic monitor computer was repaired and was returned to service. The degraded sensor will be repaired during the next Unit 1 refueling outage in Spring 2010.
There are no commitments contained in this letter.
If you have any questions or require additional information, please do not hesitate to contact us.
Sincerely, Original signed by Christopher H. Mudrick Vice President - Limerick Generating Station Exelon Generation Company, LLC cc: S. J. Collins, Administrator, Region I, USNRC E. M. DiPaolo, USNRC Senior Resident Inspector, LGS
bcc: E. Callan GML 5-1 R. Dickinson SSB 3-1 D. Doran SSB 3-2 D. Palena SSB 3-2 D. Trexler SSB 3-2 J. Toro SSB 4-1 R. Kreider SSB 2-4 S. Dixon GML 3-1 P. Colgan GML 3-1