ML20033A943
| ML20033A943 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 11/20/1981 |
| From: | Aswell D LOUISIANA POWER & LIGHT CO. |
| To: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, LW3-1121-81, W3K-81-0420, W3K-81-420, NUDOCS 8111300195 | |
| Download: ML20033A943 (4) | |
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LOUISIANA 242 OEunONOe sincer POWER & LIGHT P O 80x 6008
- NEW ORLEANS. LOUISIANA 70174 * (504) 366 2345 E uS O EsYE November 20, 1981
,,g*y W3K-81 0420 Q-3-A35.07.37 Mr. K. V. Seyfrit, Director, Region IV U. S. Nuclear Regulatory Commission Office of Inspection and Enforcement 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76012
Subject:
Waterford SES Unit No. 3 Docket No. 50-382 Interim Report of Significant Construction Deficiency No. 37
" Temperature Detectors (RTD's) Failure"
Dear Mr. Seyfrit:
In accordance with the requirements of 10CFR50.55(e), we are hereby providing two copies of the Interim Report of Significant Construction Deficiency No. 37, " Temperature Detectors (RTD's) Failure."
If you have any questions, please advise.
Very truly yours,
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Attachment
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- 1) Director
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I Office of Inspection & Enforcement l
U. S. Nuclear Regulatory Commission l
Washington, D. C.
20555 (with 15 copies of report) 1
- 2) Director l
Office of Management Information and Program Control U. S. Nuclear Regulatory Commission Washington, D. C.
20555 (with 1 copy of report) l E L '1 3
8111300195 811120 PDR ADOCK 05000
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LW3-ll21-81 LOUISIANA POWER AND LIGHT COMPANY WATERFORD SES UNIT NO. 3 INTERIM REPORT OF SIGNIFICANT CONSTRUCTION DEFICIENCY No. 37 "ROSEMOUNT RTD FAILURES" Or.k 03 liS /
Reviewed by J P Padalino - Project Engineer Date Reviewed by M
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P Fredricks - Supervising Engineer Date Reviewed by
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K Foj t - Licensinf Engineer Date lfff Boviewed by J '(sp/- Lead Engineer (NSSS)
Date Reviewed by k.
- bnt, 10 / Z 3 } Of A Beninati - Qldlity Assurance Engineer Dale
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INTERIM REPORT OF SIGNIFICANT CONSTRUCTION DEFICIENCY No. 37 TEMPERATURE DETECTORS (RTD'S) FAILURE INTRODUCTION-This report is submitted pursuant to 10CFR50.55(e).
It describes a deficiency regarding unreliable temperature signals from Rosemount, In c.,
resistance temperature detectors (RTD's).
The RTD's supply reactor coolant system (RCS) cold leg temperature signals to the reactor protec-tion system. This problem is considered reportable under the require-ments of 10CFR50.55(e). This problem was identified' to the Nuclear Regu-latory Commission on July 10, 1981, by.a utility owner of a C-E NSSS.
DESCRIPTION OF PROBLEM On July 27, 1981, C-E Power Systems notified Ebasco Services, Incorporated, that errors in the RC5 T-cold signal could result in a non-conservative thermal margin / low pressure (TM/LP) trip setpoint and could permit pos-sible operation in excess of departure from nucleate boiling (DNB) limits.
C-E does not believe that such operation is likely to occur because the RTD drift is easily detectable by cross channel comparison and simultaneous multiple failures are not deemed credible. The utility has determined that the cause of the erraneous RTD signals was due to resistance changes in the RTD circuitry as a result of corrosion degradation of the RTD leads at the terminal block connection in the head of the RTD assembly. The corro-sion was believed to be caused by a galvanic reaction between the dissimilar metals in the FTD leads and the terminal blocks.
The utility placed the plant in hot standby for approximately twenty-four hours while all accessible safety and non-safety related Rosemount RTD's were refurbished.
This refurbishment consisted of replacing all components in the head of the RTD assemblies including the crimp type terminals on the RTD field leads and the terminal block. A gasket was also added to each of the RTD assembly heads to limit ingress of water vapor into the RTD head assembly, and surveillance of the inaccessible safety related RTD's was increased. The utility is planning to replace all Rosemount RTD's with com-parable equipment f rom an alternate vendor during the next unit refueling outage.
SAFETY IMPLICATIONS The documents referenced together with NY I&C's evaluation recognize that the failure of subject RTD's is significant and could compromise the safe opera-tion of NSSS.
The subject RTD's are used predominantly in safety related systems.
Sixteen are installed in steam generator's hot and cold leg and provide inout to Plant Protection System; four of these will be used for subcooled margin calculator.
Six additional are used for display.
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The galvanic corrosion in RTD's head introduces parasitic resistance into the instrument ation loop.
This results in unreliable signals which would essentially indicate lower than actual temperature and adversely af fect protective system response.
Thus the safety of the plant could be compro-j mised, if left uncerrected.
CORRECTIVE ACTION i
RTD leads are being silver soldered at the terminal strip to eliminate any resistance changes due to galvanic corrosion.
1 New York Instrument & Controls (ISC) has issued a Design Change Notice (DCN-NYC-1C-654) to implement the corrective action.
Corrective action will be accomplished and a Final Report submitted on or before liarch 31, 1982.
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