ML20009D065

Part 21 Rept Re Apparent Degradation of Rosemount,Inc Resistance Temp Detectors.Thirteen safety-related Detectors & Five nonsafety-related Detectors for Unit 3 Have Been Refurbished

ML20009D065
Person / Time
Site:	Millstone
Issue date:	07/10/1981
From:	Counsil W NORTHEAST NUCLEAR ENERGY CO.
To:	Stello V NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
REF-PT21-81-477-000 PT21-81-477-000, TAC-47841, NUDOCS 8107230083
Download: ML20009D065 (3)

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ONNECTICUT 06101

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fA}'lh O O July 10,1981 Docket Nos. 50-245 6

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B10232 tl Mr. V. Stello, Jr., Director Tf Office of Inspection and Enforcement g

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U. S. Nuclear Regulatory Commission Hh oO g Washington, D.C.

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Gentlemen:

Millstone Nuclear Power Station, Unit No. 2 Resistance Temperature Detectors Pursuant to the reporting requirements of 10CFR Part 21, Northeast Nuclear Energy Company (NNECO) is hereby advising the NRC Staff of the apparent degradation of certain resistance temperature d3tectors (RTD). The RTDs are supplied by Rosemont, Incorporated.

NNECO identified two (2) reactor coolant system cold leg RTDs which had been providing unreliable temperature signals to the reactor pro-tection system (RPS). The temperaturc sigtils from the affected RTDs vere found to deviate from the average of the signals from the other cold leg RTDs.

As the RCS cold leg temperature is utilized as input to calculate the thermal margin / low p mssure (TM/LP) trip set-point, inaccurate RTD readings could result in a non-conservative TM/LP trio setpoint. A non-conservative TM/LP trip setpoint could potentially result in the exceeding of DNB limits.

Therefore, in accordance with 10CFR Part 21.3 (d) (4), NNECO has determined this defect to be a potential substantial safety hazard. This deter-mination was completed on July 8, 1981. The basis for this deter-mination is that the unreliable temperature.ignals from the affected RTDs could result in a non-conservative TM/LP trip setpoint which could contribute to the exceeding of a safety limit. At no time was the operability of the RPS compromised.

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usur4 has determined the'cause of?the erroneous ~RTD temperature signals

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, to ;befresistance changes in the. RTD circuitry; as ' a rest It of. corrosion J-Lofithe.RTDileads'at a terminal block connection in:the head of~the'RTD

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Jassemblies. [At-this time, fit.is judged that the corrosion is a result of

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1; Ja reactionibetween dissimilar metals in the RTD leads' and terminal' M

Iblocksilocatediinithe;RTD head: assembly.-

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- Sixteen (16) /Rosemont, Incorporatied, RTDs' are utilized in' safety-related-

- applications' at Millstone Unit:No.' 2.-

An additional.'six. (6) Lare used in L

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non-safety-relatediapplications. : Thirteen (13) " safety-telated R1Ds 'and -

., - five

(5) non-safety-related RTDs have been refurbished. We remaining-n threeL(3) safety-related RTDs and'the non-safety-related RTD are in-l accessible.due to-temperature or radiation.. %ese four RTDs are oper-

{ating satisfactorily and.there is currently no indication of any de--

ygradation,in'the temperature signals.: NNECO has increased surveillance ion' the :three. (3)- safety-related1RTDs which have' not' been refurbished.

sThe' refurbishment of the Rm assemblies consisted of replacing all icomponents:in.the head'ofithe RTD assemblies _ including the crimp type-

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terminals on;the RTD field' leads

and terminal' blocks.

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NNECO'is currently. planning:to' replace ~all RTDs atl Millstone Unit No. 2-

' with RTDs :of a _different manufacturer. during the next refueling outage ~

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scheduled.to commence,in.early December 1981.

y NNECOIhas.~ appraised 5the Nuclear' Steam Supply System vendor of'the

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H Lpotential substantial. safety hazard described herein.

As. licensee'for-Millstone' Unit.Nos. 1 and 3 also, NNECO has determined

that 'no :Rosemont:RTDs are utilized in : safety-related ~ applications at

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. Millstone-Uriit No. -l and none are planned for use at Millstone Unit No.

3,;which-is currently lunder. construction.

iWe. trust _ youifind-this information sufficient to fulfill the notification

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requirements of 10CFR Part 21.

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY NA/N W.' G. Counsil Senior Vice President s

.cc: 'See following page i---

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!.Mr. ~ Boyce: H.'.Grier, Director

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. Region I Office of Inspection and Enforcement U. 'S.':. Nuclear Regulatory ' Conmission -

631. Park Avenue King of. Prussia, PA 19406 s

Director.of. Nuclear Reactor Regulation fAttn:

Mr. Robert A. Clark, Chief Operating. Reactors. Branch #3 U. S. Nuclear. Regulatory Consission Washington, D.C.

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