ML20099C812

Application for Amend to License NPF-12,changing Tech Specs to Define Required Shutdown Margin in Terms of RCS Boron Concentration.Fee Paid

ML20099C812
Person / Time
Site:	Summer
Issue date:	03/06/1985
From:	Dixon O SOUTH CAROLINA ELECTRIC & GAS CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
Shared Package
ML20099C815	List: ML20099C812 ML20099C836
References
NUDOCS 8503110435
Download: ML20099C812 (3)

Text

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SOUTH CAROLINA ELECTRIC & GAS COMPANY Post OFFICE M4 COLuualA. SouYH CAROLINA 29218

0. W. Osmom. Ja.

Vice PatssotNT sucts. o... Tion. March 6, 1985 Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission (NRC)

Washington, D.C. 20555

Subject:

Virgil C. Summer Nuclear Station Docket No. 50/395 Operating License No. NPF-12 Shutdown Margin-Modes 3, 4 and 5

Dear Mr. Denton:

So2th Carolina Electric and Gas Company (SCE&G) hereby requests an amendment to Section 3/4.1.1.2, " Reactivity Control System," of the Virgil C. Summer Nuclear Station Technical Specifications. The proposed _ hange, as shown on the attached marked-up Technical Specification pages, defines the required shutdown margin in terms of Reactor Coolant System (RCS) boron concentration. This amendment is requested for use in Cycle 3 to ensure that operators will have at least fif teen (15) minutes to terminate an inadvertent boron dilution in Modes 3, 4, and 5 following receipt of a high flux at shutdown alarm.

During NRC review of the plant Final Safety' Analysis Report (FSAR), SCE&G was requested by the Staf f to address the boron dilution event, considering Regulatory Guide 1.70, Revision 2 guidelines. This guidance stated that the dilution event should be addressed in all shutdown modes, and that operator action time to prevent loss of shutdown margin should start from receipt of a signal alerting him to the event. Therefore, SCE&G provided an analysis for the dilution event for Cycle I conditions and included the results in Section 15.2.4 of the FSAR. With an increase in the shutdown margin to 2% for Modes 3, 4, and 5, this analysis showed that at least 13.4 minutes existed for the operator to take action to halt the dilution. These results were used to form the licensing basis for the plant for Cycle 1.

A detailed cycle specific analysis for the boron dilution event was performed for Cycle 2. The method of analysis was based on that used for Cycle 1, and the dilution flowrates and RCS volumes assumed in the analysis were the same as those f ound in the FSAR. The high flux at shutdown alarm was again assumed to be set at twice background. This analysis confirmed that the Cycle 1 analysis presented in the FSAR was conservative for Cycle 2 and ensured that the operator had suf ficient time to terminate an inadvertent boron dilution before the shutdown margin was lost.

In Cycle 3, SCE&G plans to begin transition to an 18 month low-leakage fuel management scheme. Accordingly, a bounding analysis of the dilution event has been performed for all operating modes using conservative assumptions based on 1

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-Mr. Harold .R. Denton, Director -

- Shutdown Margin-Modes 3, 4, and 5 March 6,-1985:

Page #2 18 month low-leakage core designs. An important fact'or in.the analysis is the initial boron concentration because higher boron concentrations can be more easily diluted, resulting in a more rapid loss of shutdown margin.

Therefore, as the initial boron concentration increases, the shutdown

' margin required to preserve's fixed operator action time also increases.

The required shutdown margin is also shown to vary with operating mode making the transient more limiting in some modes than others. The results

-of the bounding analysis show that Technical Specification changes are not required in Modes 1, 2 and 6 because at all times suf ficient time exists for the operator to locate the source of and terminate a dilution before

~s hutdown margin -is- lost. -However, for modes 3, 4 and 5, revisions are necessary in order to allow the operator 15 minutes from the time of the alarm until the margin is lost to take any necessary actions. -Therefore, f SCE&G is making 'the proposed Technical Specification change defining the n required shutdown margin as a function of the RCS' boron concentration for Modes 3, 4:and 5.1By comparing the actual RCS boron concentration to the figure, the operator can determine what shutdown margin is required in L

~

order _ to be within the bounds of the safety analysis. The lowest values of the shutdown margin contained in the Technical Specification are consistent 7

with those in the current Westinghouse Standard Technical Specifications for three loop plants. This approach is being proposed based on the

!  : factors 'of ' the analysis as noted above.

4 SCE&G has determined that a finding of. no significant hazards is appropriate because of the following:

.The amendment does not. involve's significant increase in the probability. or consequences of an accident previously evaluated because the. high flux at shutdown alarm continues to be set at twice.

7

-background, . and ' Regulatory Guida 1.70, Revision 2 requiresents and the

design-basis continue to be met.

l

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The amendment-does-not ' create the possibility of a new or different I kind of accident because the' physical plant design is not being l'

changed.

b The' amendment ,does not involve a significant reduction in a margin of safety. To the contrary, the amendment is being requested to maintain

. the margin. of safety duriag the transition to 18 month cycles by g ' holding the ' time for operator action in the event of an inadvertent

boron dilution at or in excess of t)at stated in the FSAR.

M

a Mr. Harold R. Denton, Director Shutdown Margin-Modes 3, 4, and 5 March 6, 1985 Page #3 This revision has been reviewed and approved by both the Plant Safety Review Committee and - the Nuclear Safety Review Committee. Please find enclosed the application fee of one hundred fif ty dollars ($150.00) required by Title 10 of the Code of Fed.eral Regulations, Part 170. .

If you have any questions, please advise.

Very truly yours,

/

0. W. D* on, Jr.

AMM/0WD/gj

. At tachment:

cc: V. C. Summer C. A. Price.

T. C. Nichols, Jr./0. W. Dixon, Jr. . C. L. Ligon (NSRC)

E. H. Crews, Jr. K. E. Nodland E. C. Roberts R. A. St ough W. A. Williams , Jr. G. Percival D. A. Nauman C. W. Hehl J. N. Grace J. B. Knotts, Jr.

Group Managers H. G. Shealy O. S. Bradham NPCF File E _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ , _,