ML19350B703

Responds to SER Item 1.7.11 of Confirmatory Issue Re Steam Generator Level Measurement Errors.Mod Will Limit Increase in low-low Steam Generator Water Level Setpoint Due to Ref Leg Heatup to 2%

ML19350B703
Person / Time
Site:	Summer
Issue date:	03/18/1981
From:	Nichols T SOUTH CAROLINA ELECTRIC & GAS CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
NUDOCS 8103230444
Download: ML19350B703 (2)

Text

__

j , ..

south CAROLINA ELECTRIC & gas COMPANY postorncenonre.

?

!hCJ .,

COLUMe:A, south CAROLINA 29218 /

T C. NicMots.Ja. /

VeCE Passesnt a=0 Geove (arce.svg

=cca.. o.ie... March 18, 1981 , ,';. 4 A

Mr. Harold R. Denton, Director y Office of Nuclear Reactor Regulation /

U. S. . Nuclear Regulatory Commission Y N Washington, D. C. 20555

Subject:

Virgil C. Summer Nuclear Station Docket No. 50/395 Steam Generator Level Indication Dear Mr. Dentoni In the Virgil C. Summer Nuclear Station Safety Evaluation Report (SER) item 1.7.11 of the Confirmatory Issues identified a required response regarding level measurement errors. This letter provides that response.

High energy line breaks inside containment could result in heatup of the steam generator level measurement reference leg. Increased reference leg water column temperature will result in a decrease of the water column density with consequent apparent increase in the indicated steam generator water level (i.e., apparent level exceeding actual level). This potential level bias could result in delayed protection signals (reactor trip and emergency feedwater initiation) which are based on low-low steam generator water level.

The Virgil C. Summer Nuclear Station has an automatic steamline isolation system on low steam line pressure. It has been determined j that boiling will not occur in the reference legs of the intact steam generators. These steam generator level impulse lines, however, are being thermally insulated to minimize their heatup during the time required to perform a trip function af ter a high energy line break inside the containment. This modification will limit the increase in the low low steam' generator' water level setpoint due to reference leg heatup to 2% and is based on conservative estimates of containment conditions following an event.

This insulation is considered a solution to ensure proper accuracies without requiring a large increase in the trip setpoint that might interfere with normal operation. SCE&G is aware of another solution currently under development. This solution will use some form of temperature compensation or modification to eliminate or reduce temperature errors. When this solution is finalized, SCE&G J

i 8103230444

0 Mr. Harold R. Denton Page Two j '

will evaluate it. If our evaluation of this or another solution indicates the need for further modifications, SCE&G will take appro-priate action to obtain NRC approval and to modify the system, as required.

This letter should provide you with sufficient information to resolve this SER confirmatory issue. If you have any questions, please let us know.

Very truly yours, j

. T. C. Nichols, Jr.

RBC:TCN:rh cc: V. C. Summer.

G. H. Fischer T. C. Nichols, Jr.

C. A. Price D. A. Nauman W. A.- Williams, Jr.

. R. B. Clary A. R. Koon A..A. Smith H. N. Cyrus J. B. Knotts,Jr.

J. L. Skolds B. A. Bursey O. S. Bradham ISEG NPCF PRS File 3

rey-- ,+m t=*- y , 94 g -se c w ,e, , .-a4 -ge - -,e;e ...n.- ---.-,,y.,.,-+y-wqe-r ,%--.~ e,e g w. -.e e. .w., e > - - , - - e.,,- ,.,a- , -,--et--,- -. -r-w--