ML13330B549
| ML13330B549 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 08/16/1991 |
| From: | Rosenblum R Southern California Edison Co |
| To: | NRC/IRM |
| References | |
| NUDOCS 9108220127 | |
| Download: ML13330B549 (5) | |
Text
Southern California Edison Company 23 PARKER STREET IRVINE, CALIFORNIA 92718 R. M. ROSENBLUM TELEPHONE MANAGER OF August 16, 1991 (714) 454-4505 NUCLEAR REGULATORY AFFAIRS U. S. Nuclear Regulatory Commission Attention:
Document Control Desk Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 Thermal Shield, Loose Parts Monitoring System San Onofre Nuclear Generating Station Unit 1 This letter describes improvements made to our system for monitoring loose parts in the reactor vessel and was developed in response to your letter dated December 19, 1990 (open item (g)) which approved the design of the thermal shield replacement supports. The improvements and modifications we have made to the electronics and software used in the Loose Parts Monitoring (LPM)
System have made a significant improvement in our ability to detect loose parts. Our Loose Parts Monitoring System now meets the sensitivity criteria of Regulatory Guide 1.133.
Cycle 10 Operation For operation during Cycle 10, SCE installed a loose parts monitoring system consisting of four accelerometers installed at 90 degree intervals around the reactor vessel flange. The accelerometer signals were available at an amplifier located in the Unit 1 chemical feed area. Capability was provided for the plant personnel to select and listen to any one of the four accelerometers through a set of earphones.
A jack was provided to allow recording of the signal on magnetic tape. The required weekly recording was done with portable equipment and the daily readings were logged and trended manually.
Improvements for Cycl.e 11 Operation The improvements made during the Cycle 11 refueling outage allow for continuous electronic monitoring, improved audio monitoring, improved recording technology and electronic analysis capability, simultaneous data acquisition capability from all four accelerometer channels, improved data retention, immediate graphical data representation, and the capability for future software modification. A more detailed explanation of the improvements is contained in Enclosure 1 to this letter.
9108,2 27 910816 PDR ADOCK 05000206 p
Document Control Desk
-2 With these improvements, the present LPM system can detect a 0.5 ft-lb impact up to 30 feet away from the sensor. The sensitivity of the present LPM system exceeds the requirement of Reg Guide 1.133 and assures that a loose part in the bottom of the vessel (which is approximately 29 ft. from the sensors) will be detected. The sensitivity of the LPM system will be demonstrated and discussed in more detail in our submittal providing the acceptance criteria levels for thermal shield acoustical and neutron noise (scheduled for September 20, 1991).
Section 8.1 of the Safety Evaluation enclosed with your December 19, 1990 letter and previous conversations with the NRC staff suggest that the accelerometers should be relocated to provide improved LPM system performance.
However, because of the changes described in this letter, the performance of the LPM system has been significantly improved and the system provides reliable early warning of loose parts activity. For these reasons we do not plan to modify the location of the accelerometers.
If you have any questions, please do not hesitate to call.
Very truly yours, R. M. Rosenblum Manager of Nuclear Regulatory Affairs Enclosures cc:
J. B. Martin, Regional Administrator, NRC Region V George Kalman, NRC Senior Project Manager, San Onofre Unit 1 J. 0. Bradfute, NRC Project Manager, San Onofre Unit 1 C. W. Caldwell, NRC Senior Resident Inspector, San Onofre Units 1, 2&3 DESCRIPTION OF IMPROVEMENTS TO THE LOOSE PARTS MONITORING SYSTEM SINCE CYCLE 10 OPERATION SAN ONOFRE NUCLEAR GENERATING STATION, UNIT 1 Page 1 of 2 LOOSE PARTS MONITORING (LPM) SYSTEM IMPROVEMENTS Filter/Amplifier We have installed a new computer controlled conditioning filter/amplifier in the control room. The new filter/amplifier has 16 input channels. Four of the channels are dedicated to the loose parts monitoring system accelerometers, eight are used for the neutron noise monitoring system and four channels are spares. This new device allows continuous simultaneous monitoring of all four accelerometer channels.
Computer and Software The output signals from the filter/amplifier are routed to a new computer with a software system for monitoring. The new software, combined with the new filter/amplifier, offers several additional capabilities over the previous system, including:
Continuous simultaneous monitoring of all 4 accelerometer channels.(1)
Audio option, for monitoring by operators.
Remote alert function at the computer in the Control Room to provide early warning to technical personnel.
Improved data retention.
Improved data analysis capabilities.
Automatic 500 K data retention upon exceeding the threshold value.
Immediate data processing and graphical display capability.
Automatic trending to compare to previous 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
Note (1)
License Condition 3.M requires at least two of the four LPM channels to be operable. One of the accelerometers is currently inoperable.
Page 2 of 2 Operation Methods The LPM system is currently operated with the software system continuously monitoring the LPM input data. During each shift, the operators spend at least 5 minutes listening to the signals over a loud speaker to determine qualitatively if the sound levels have changed. The data samples are periodically analyzed using a modified logarithmic amplitude probability density technique. This technique produces a clear graphical representation of the loose parts noise and can also provide a reliable early warning of loose parts activity. This analysis effort, which previously required up to a week to complete, can now be done immediately.
The software package also records a 500 K data sample and actuates an acoustic alert whenever the signal level exceeds a preselected value. The criteria for the acoustic alert and alarm is currently in preparation and will be provided by September 20, 1991 as scheduled in our letter dated July 16, 1991. In the interim, an alert level has been chosen based on review of the accelerometer activity during Cycle 10 operation. The alert level is used solely to inform plant technical personnel of an early trend.
The data files are also automatically trended and compared to the data from the previous four hours.
NRC-ACST.MG2 ENCLOSURE 1