W3P85-0338, Final Part 21 & Const Deficiency Rept SCD-37 Re Unreliable Temp Signals from Resistance Temp Detectors (Rtd).Initially Reported on 810710.Safety-related RTDs Replaced or Environmentally Sealed.Design Change Notice Issued

Final Part 21 & Const Deficiency Rept SCD-37 Re Unreliable Temp Signals from Resistance Temp Detectors (Rtd).Initially Reported on 810710.Safety-related RTDs Replaced or Environmentally Sealed.Design Change Notice Issued

ML20107M843
Person / Time
Site:	Waterford
Issue date:	02/21/1985
From:	Cook K LOUISIANA POWER & LIGHT CO.
To:	Martin R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
References
REF-PT21-85-212-000 PT21-85-212, PT21-85-212-000, SCD-37, W3P85-0338, W3P85-338, NUDOCS 8503060022
Download: ML20107M843 (3)

Text

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Louisiama / 44 ace-o~m. 7 er POWER & L1GHT / NEW CALEANS LOUIS %NA

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70174-e000 . (504)388-2345

$1UE$YS February 21, 1985 W3P85-0338 0-3-A35.07.37 3-A1.01.04 A4.05 Mr. Robert D. Martin Regional Administrator, Region IV U.S. Nuclear Regulatory Commission 611 Ro n Plaza Drive, Suite 1000 1 @'@

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Arlin on, TX 76011 k)/f l , FEB 2 5 l985

Dear Mr. Martin:

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Subject:

Waterford 3 SES Docket No. 50-382 SIGNIFICANT CONSTRUCTION DEFICIENCY No. 37

" Temperature Detectors (RDTs) Failure" Final Report

Reference:

LP&L letter W3K84-2957 dated October 31, 1984 The referenced letter provided an interim report on SCD-37 with the Justification for Interim Operation. It stated that the final report would be submitted upon the completion of response time testing.

In accordance with the requirements of 10CFR50.55(e)(3), enclosed are two copies of the Final Report of SCD-37.

Very truly yours, K.W. Cook Nuclear Support & Licensing Manager KWC:GEW:sms cc. NRC, Director, Office of I&E G.W. Knighton, NRC-NRR D.M. Crutchfield, NRC-NRR NRC Resident Inspectors Office INPO Records Center (D.L. Gillispie) l E.L. Blake ) ij W.M. Stevenson _

8503060022 850221

~t h '<f I PDR ADOCK 05000382 S PDR

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• W3P85-0338 FINAL REPORT OF

SIGNIFICANT CONSTRUCTION DEFICIENCY NO. 37 l l TEMPERATURE DETECTORS (RTD'S) FAILURE i i

INTRODUCTION i i

, This report is submitted pursuant to 10CFR50.55(e). It describes a deficiency i

regarding unreliable temperature signals from Rosemount, Inc., resistance i temperature detectors (RTD's). The RTD's supply reactor coolant system (RCS) cold leg temperature signals to the reactor protection system. This problem is i considered reportable under the requirements of 10CFR50.55(e). This problem was

! identified to the Nuclear Regulatory Commission on July 10, 1981, by a utility I 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 RCS T-cold signal could result in. .a non-conservative thermal margin / low pressure (TM/LP) trip setpoint and could permit possible 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 I not deemed credible. The utility has determined that the cause of the erroneous RTD signals was due to resistance changes in the RTD circuitry as a result of corrosion degradation of the RTD leads as the terminal block connection in the head of the RTD assembly. The corrosion was believed to be caused by a galvanic reaction between the dissimilar metals in the RTD leads and the terminal blocks.

CE stated that the affected 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. .

SAFETY IMPLICATIONS The galvanic corrosion in RTD's head introduces parasitic resistance into the instrumentation loop. This results in unreliable signals which would essentially indicate lower than actual temperature and adversely affect protective system response. Thus the safety of the plar.t could be compromised, if left uncorrected.

CORRECTIVE ACTION A total of 33 Rosemount RTD's were utilized at Waterford 3. Of these 33, sixteen (16) are safety related RTD's installed in steam generator's hot and cold legs which provide input to the Plant Protection System. Eight (8) of these sixteen (16) Rosemount RTD's were replaced with Weed RTD's which leaves eight (8) dual-element Rosemount RTD's which were required to be environmentally sealed. The remaining seventeen (17) are non safety related and are not included in the scope of SCD 37.

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.g W3P85-0338 SCD 37 Design Change Notice (DCN-NYC-IC-654 R2) was issued to implement the corrective action, and LP&L Condition Identification and Work Authorization (CIWA) 008032 performed this DCN instruction. CIWA 008032 was closed January 8, 1985, based on implementaion and documentation completion.

The corrective action consisted of applying two coats of Carboline 1340 clear to all exposed metal surfaces connected or forming part of the terminal strip, top and bottom after connections are made.

Carboline 1340 was preferred over silver soldering since it provided a moisture resistant seal over all exposed metal parts, as well as reducing chances of galvanic corrosion.

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SCD-37/SCD4