ML20055E048

Documents Action Taken by Util to Improve Heat Sink Protection Sys & Current Status of Sys.Main Feedwater Logic Circuits Modified Prior to Startup from 8R Outage to Eliminate Potential for Inadvertent Isolation

ML20055E048
Person / Time
Site:	Three Mile Island
Issue date:	07/05/1990
From:	Hukill H GENERAL PUBLIC UTILITIES CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
C311-90-2060, NUDOCS 9007100318
Download: ML20055E048 (2)

Text

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i GPU Nuclost Corporstion N

Post Office Box 480' E M r: Route 441 South - ,

, Middletown, Pennsylvania.17057 0191 7 717 944 7621 TELEX 84 2386 .

9 Writer's Direct Dial Number:

' July 5, 1990 C311-90-2060:

! U. S.JNuclear: Regulatory Commission ",,

l .Attnt. Document ~ Control' Desk-

. Washington, DC 20555 ,

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Dear Sirs:

Three Mil'e Island Nuclear Station,: Unit (THI-1) h p Operating License No. DPR-50 '

9 l Docket No. 50-289 l Heat Sink Protection System  ;

.As discussed with NRC Region I personnel on February 27, 1990, CPUN discovered a condition.during the' Cycle 8 Refueling (8R) Outage which deviates from our- j system description of the Heat Sink Protection: System ~(HSPS) submittal dated April.29,J1985 (Reference-1),where we stated that a single. active failure will' ,

neither inadvertently initiate Emergency Feedwater:(EFW).nor isolate Main) .  !

Feedwater (HFW)'. Inadvertent actuations on partial lous of power were found.

l' sduring post maintenance testing of the system as part of a modification to the .

4

.HSPS.. This letter documents the: action:GPUN has taken to improve'the HSPS ~

system.and the current status of the system. ,- j The HSPS is a safety-grade system that performs the; functions'of MFW. isolation and EFW : initiation'.~ The-system-has four analog channels that provide input to h; two' logic trains.: The normal train logic is 2 out of 4. During the 8R ,

outage, Lt was discovered that a partial-loon of power to the/HSPS could '

e l' actuate one train of:MFW isolation or initiate one train,of!E7Wr: Partial loss:

of power.ia:the' loss of' power to a ningle physical row (nest)Lofisolidl state ,

'g logic printed circuit boardu as; opposed:to a complete. loss;of power to the; '

logic train which is made up of.many such rows.' '

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The probability of partial loss -of power to the HSPS resultinglit a )(PW - ,

11 solation was considered to be low. However,lsince MFW isolation was an~ , t undosirable trancient, the ~MFW logic circuits were modified prior to .startup /  ; >

e from the BR Outage to eliminate the potential for inadvs.rtent MFW isolation.

( s Tests. wore;then' performed which. confirmed:thut:the HSPS now meete the criteria; a?!

of no iinadvertent : isolation of . MFWlon' partia.1 or; total- loss of ) power.L

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i component fetilures or partial loss .of power could f result ,1u.Jinadvertent EPW- Y initiutierr even thoughia total' loss' of power tR the trairr would; not.: Thu

'i= j f potentini for inadvertent EFW initiation in this. manner ;exinted Trior to the Lt r

8R modifications but was' brought: to light d' ' '

J.uringfinstallatioa of!the BPi '

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The potential;foria single failure. actuating one , .

L4 where the:EFW Linitiation signallis 'provideW by> asingle: , traininput of !EPW6 to still the train.-exirts' ' ,

, ; 4' Thu . signals .for: EFH; initiation on '1) Inns .of MFW Pt:mps 'and 2y. Loss 'of RC! Pumps -

T are ' single ' input . uAgnals' which isubject the HSFil toTinndvertent! ~initiationtire 4

l j, .0-W thleLmanner. <0herefore,1 components associated with3these feathree could/fal1< 7

.' Jin-a'utate that would actuate the'tralW. Under' normal' conditions i

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.C311-90-2060 Page 2 of 2 l .-

however, inadvertent EFW actuation would not result in EFW injection into the j

' steam generators because OTSG 1evel would be above the level setpoint. i l

l These design considerations have been evaluated for the TMI-l system and our-  !

? evaluation confirms that the consequences of EFW actuation are acceptab)a. I Partial loss of power does noit result in loss of the safety function and does ,

not result in a safety hazard. The criteria for no inadvertent EFW initiation 1

3) .i resulting.from single failureiwas a GPUN criteria and not a regulatory 1 l

, 'j . requixement. Therefore the system is considered to be operable without l,' meeting this criteria.

Additional modifications of!the HSPS logic to prevent EFW actuation on partial a loan of. power is currently being considered. However, GPUN does not believe L that'EFW actuatione resulting from single-failurer.-represent a concern which on the basis of safety would require further modification.

Sincerely, '.

H. D. Hu 1 l

Vice President'and Director,.THI-1

References:

'l. GPUN Letter, Hukill to Stolz, dated April 29, 1985 l

2. NRC Letter, Stolz to Hukill, dated February 18, 1987 HDil/MRX l' cct' J. Stolz R..Hernan 6 F. Young T.-Martin i

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