ML20039B317
| ML20039B317 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 12/16/1981 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| IEIN-79-22, NUDOCS 8112220517 | |
| Download: ML20039B317 (3) | |
Text
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Mr. Harold R. Dm tal, Director s
Office of Nuclear Beactor Regulatials
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U. S. Nuclear Regulatory Coninissial I
Washingtm, D. C.
20555
Subject:
Virgil C. SunIner Nuclear Statim Docket No. 50/395 Caltrol System Failures Caused By High Blergy Line Breaks NRC IE Informatial Notice 79-22
Dear Mr. Dental:
On November 10, 1981 a discussicn was held with ibn Dunning of the Instrummtatial Ccntrol Systems Branch regarding the four coltrol system failure scenarios caused by high mergy line breaks which are identified in NBC IE Informatial Notice 79-22. Another plant, currettly under liceicising review, had recently reported that castrol systen nodificatims would be required to eliminate postulated interactials. The discussicn celtered around SCE&G providing sane assurance that the sann scalarios had bem reviewed.
As indicated in our letter dated May 18, 1981 SCE&G is reviewing ca1 trol systems failures as requested in your letter dated April 30, 1981 and will provide you with a report by March 1,1982. The following respcnses are preliminary and reflect the currett status of that review for the four items discussed.
Steam Gmerator Pr+.r Operated Relief Valve Ccntrol System The Virgil C. Suniner Nuclear Statial Solid State Protecticn Systen (SSPS) includes a block of all castrol actial to opm the steam gelerator Power Operated Relief Valves (PORV's) at LoIo Tavg (P-12 at 553'F). 7his block is designed to prevelt excessive cooldown if the coltrol system were to fail in the "opel" nude. She block is implenalted cn each fail closed PORV with qualified A&B train soleioids and IE circuits and power supplies.
Pressurizer Power Wated Relief Valve Ccntrol System The Virgil C. Sunmer Nuclear Statial SSPS also includes a block of all coltrol acticn to open the pressurizer PORV's cn 104 pressurizer pressure (P-11 at 1985 PSIG). 1his block is designed to prevelt excessive depressurizaticn of the reactor coolant systen if
] C)O j the PORV ccntrol systen were to fail in the "open" node. She block is implemented cn eadi fail closed PORV with a qualified solcioid and j
IE circuits and power supply.
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Mr. Harold R. Dentcn Page two December 16, 1981 Main Feedwater Ccntrol System
'Ihis scalario involves a san 11 feedline rupture between the steam gmerator nozzle and the feedline check valve which effects the main feedwater cnitrol system of all three loops. A failure in all three nuin feedwater ccntrol systems initiates a spurious signal to close the feedwater a21 trol valves causing all stem generators to reach the IoIo level setpoint at the sarre time.
A preliminamf review indicates that the postulated break will not effect the ccntrol grade porticn c,f the nuin feedwater ccntrol systen due to the locaticn of our feedwater check valves. Further study of this inprcbable scalario and other related analyses alcng with a review of the qualificaticn of effected equipcnt is being dcne to assure there is no p tm tial interactial.
Autcmatic Rod Ccntrol Systen
'Ihis scalario involves an intermediate steamline rupture inside ccntainnuit which effects the power range neutrcn detectors, their ct.bling or crnnectors. '1he system nust fail low such that the rods step out prior to receipt of a reactor trip cn negative flux rate, high neutrcn flux or overpower Delta-T.
Preliminary review indicates that this improbable scalario is possible at the Virgil C. Sumer Nuclear Staticn if the power range neutrcn dectors can fail as described. Westinghouse is in the process of attempting to qualify the detectors aid we are cialyzing then to deternune if they cat fail as postulated in the time required.
If you have any further questicns, please contact us.
Very truly yours,
.O T. C. Nichols, Jr.
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Mr. Harold R. Dmtcn Page three Decenber 16, 1981 cc:
H. R. Dentcn V. C. Sumner T. C. Nichols, Jr.
G. H. Fisher H. N. Cyrus H. T. Rahh D. A. Naunan M. B. M1itaker, Jr.
W. A. Williams, Jr.
O. S. Bradham-l R. B. Clary M. N. Browne A. R. Koan G. J. Braddick J. K. Skolds
'J.
B. Knotts, Jr.
B. A. Bursey J. C. Ruoff NPCF File