ML20038B080
| ML20038B080 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 11/04/1981 |
| From: | Papay L SOUTHERN CALIFORNIA EDISON CO. |
| To: | Engelken R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8111240687 | |
| Download: ML20038B080 (3) | |
Text
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s Docket Nos. 50-361/362 50 55(e) Report Southern California Edison Company g6 RO. SOX 800 2244 WALNUT GROVE AVENUE ROSEM EAD, CALirORNIA 91770 November 4, 1981 v.a..aaa' n> me
- f Mr. R. H. Engelken, Director
- f' Efb Offica of Inspection and Enforcement f
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U. S. Nuclear Regulatory Commission NOV2 31985 F-a ia Lane, Suite 210
" *E S ilic P Walnut Creek, California 94596 Q,,f,
Dear Mr. Engelken:
' c57T T M "
Subj ect :
Docket Nos. 50-361 and 50-362 San Onofre Nuclear Generating Station, Units 2 and 3 i
In a letter to your office dated October 7, 1981, we identified a condition which we considered potentially report-
?
able in accordance with 10CFR50.55(e).
The condition concerns malfunction of Pressurizer Level Indicators due to collection of condensate in low points of flexible interconnecting tubing.
i Enclosed are twenty-five (25) copies of a final report entitled, " FINAL REPORT ON MALFUNCTION OF PRESSURIZER LEVEL INDICATORS-San Onofre Nuclear Generating Station, Units 2 and 3."
If you have any questions regarding this report, we would be pleased to discuss them with you at your convenience.
Very truly yours, 4
l fp Enclosures i
cc:
Victor Stello (NRC, Director I&E) l A.
E. Chaffee (NRC, San Onofre Units 2 and 3)
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,s FINAL REPORT ON MAL 1 UNCTION OF PRESSURIZER LEVEL INDICATORS San Onofre Nuclear Generating Station,_ Units 2 and 3 INTRODUCTION This report is submitted pursuant to 10CFR50.55(e)(3).
It describes a condition in which the condensing pots on the pressurizer level transmitter (2LT-0110-1 and -2) were mounted in such a way that the functioning of the condensing pot was reduced, and. water loss from the reference leg could not be adequately replenished.
This report includes a description of the deficiency, analysis of the safety implications and a summary of the corrective action taken.
By letter dated October 7, 1981, Edison confirmed notification to the NRC of this potentially reportable condition.
BACKGROUND Level transmitters 2LT-0110-1 and 2LT 0110-2 are differential pressure transmitters employed in pressurizer level measurements.
The transmitter outputs are used for control of the charging pumps and back-up heaters, and for indication for post. accident monitoring.
These transmitters utilize a ' wet' or liquid filled reference leg in which a constant level is important for proper instrument. operation.
During hot _ functional testing, disagreements of 5 to 20% were noted between level transmitters 2LT-0110-1 and -2; these were reported-in Startup Problem Report (SPR 1596).
Filling the reference legs at the transmitter installations caused the level indications to converge, indicating that-the problem was attributable to non-constant level in the reference legs.
DISCUSSION The following discussion is responsive to 10CFR50.55(e)(3).
Description Of The Deficiency l
The line connecting.the steaa space of the pressurizer to the condensing pot consisted of the following segments:
A short length of pipe welded to the upper side of the pressurizer, a root valve, a length of flexible tubing, and a section of rigid 3/8 inch tubing to the condensing pot.
The steam from the pressurizer steam space condensed in the flexible f
tubing:and caused it to sag and form a loop seal.
The flexible tubing was also positioned lower than the condensing pot and the excess condensate returned to the pressurizer.
i
s The depleting of reference leg water reduced the pressure to the line section downstream of-the loop se.tl.
This resulted in the introduction of non-condensibles into the condensing pot, further blocking the flow of steam into this region.
Analysis Of Safety Implications The inability of the original condensate chamber installations to maintain a constant reference leg resulted in erroneously high pressurizer level measurement.
Incorrect pressurizer level measurement affects charging pump and pressurizer back-up heater control, both of which have safety related functions.
In addition, erroneous post accident monitoring instrumentation indication could be displayed.
Corrective Actions Resciution of SPR 1596 involved issuance of Design Change Package (DCP) 140J which relocated the condensate chambers to the outlet of the root valves, eliminating the flexible tubing which formed the loop seal.
This configuration will maintain a constant liquid level in the reference leg and maintain accuracy of pressurizer level indication.
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