ML20149G562

Nonproprietary Evaluation of Margin to Steam Generator Overfill for Millstone Unit 3

ML20149G562
Person / Time
Site:	Millstone
Issue date:	01/31/1988
From:	Huang P WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML19341D864	List: ML20148S356 ML20149G562
References
WCAP-11718, NUDOCS 8802180309
Download: ML20149G562 (14)

Text

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WESTINGHOUSE CLASS 3 WCAP-11718 s

f EVALUATION OF THE MARGIN TO STEAM GENERATOR OVERFILL FOR MILLSTONE UNIT 3 P. H. Huang

. JANUARY 1988 Nuclear Safety Department d

Westinghouse Electric Corporation Nuclear Energy Systems P.O. Box 355 Pittsburgh, Penn:ylvania 15230 I,)1988byWestinghouseElectric.orporation h

L 8802100309 880122 3 PDR ADOCK 050 P

TABLE OF CONTENTS Paces I. INTRODUCTION / BACKGROUND 1 II. COMPARISONS FOR MILLSTONE 3 AND THE REFERENCE PLANT 2 A. Design Basis SGTR Analysis for the Reference Plant 2 B. Comparisons of the Plant Systems and Equipments 3 Used for SGTR Recovery C. Comparisont of the Emergency Operating Procedures, 6 Operator Action Times and the Worst Single Failure D. Comparisons of SGTR Transient and Margin to Overfill 8 for Millstone 3 and the Reference Plant E. Evaluation of Margin to Overfill for the Millstone 3 10 III. REFERENCES 11 O

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Evaluation of the Margin to Steam Generator Overfill for Millstone 3 I. Introduction / Background s

one of the requirements for plant specific information listed in the NRC safety 4 evaluations for WCAP 10698, "SGTR Analysis Methodology to Determine the Margin to Steam Generator Overfill", is an assessment of the individual plant relative to the reference plant analyzed in WCAP 10698 to demonstrate shrgin to steam generator overfill for a design basis SGTR.

This report provides a survey of the Millstone 3 primayy and balance of plant system, designs relativ: to the reference plant. L

[hnassessmentis then performed to evaluate the effects of the system differences on the margin to overfill. The evaluations are based on the following assumptions: -

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II. Comparisons for Millstone 3 and the Reference Plant A. Design Basis SGTR Analysis for the Reference Plant The design basis SGTR analysis for the reference plant was performed using the LOFTTR1 program. The analysis was performed for a

' double-ended rupture of one steam generator tube using Itconservative was assumed parameters and assumptions with respect to overfill.

that a loss of offsite power occurred at the time of reactor trip, and the highest worth rod was assumed to be stuck at reactor trip.

The major operatt! &ctions for SGTR recovery which are included in the E-3 guideline of the WOG ERGS were explicitly modelled in the analysis. The operator actions modelled include identification and isolation of the ruptured steam generator, cooldown of the RCS to establish subcooling margin, depressurization of the RCS to restore inventory, and termination of SI tc stop primary to secondary leakage.

1. Identify and Isolate the Rupture Steam Generator:

Recovery actionb of a tube rupture begin by isolating steam flow from the ruptured steam generator and throttling the auxiliary feedwater flow to the ruptured steam generator. The ruptured steam generator is assumed to be identified and isolated when the narrow rance evelreappps(

69 at[ jdlnute af ter initiation of the SGTR, whichever is onger.

Cooldown of the RCS to Establish Subcooling Margin:

. 2.

Afterisolationoftherupturedsteamgenerator,thereisa[)g,e minute operator action time imposed prior to cooldown. The RCS is cooled by dumping steam from the PORV on one intact steam generator to the atmosphere. The cooldown is continued until RCS subcooling at the ruptured steam generator pressure is 20 F plus i an allowance for subcooling uncertainty.

3. Depressurize the RCS to Restore Inventor AftertheRCScooldowniscompleted,a[yj1nuteoperatoraction W

l time is imposed prior to depressurization. The RCS is '

depressurized to assure adequate coolant inventory prior to terminating SI flow. With the RCPs stopped, normal pressurizer spray is not available and thus the RCS is depressurized by opening a pressurizer PORV. The depressurization is continued until any of the following conditions are satisfied: RCS pressure is less than the ruptured steam generator pressure and the pressurizer level is greater than the level uncertainty, or pressurizer level is greater than 80% minus level uncertainty, or RCS subcooling is less than the subcooling uncertainty.

4. Terminate SI to stop Primary to Secondary Imakage:

After the ACS depressurization is completed, an operator action time of ,)TinuteisimposedpriortoSItermination. The SI flow is tern:,nated when the RCS pressure increases, minimum ATW flow l

is available or at least one intact steam generator level is in the narrow range, RCS subcooling is greater than the subcooling l

l uncertainty, and the pressurizer level is greater than the level uncertainty.

2

B. Comparisons of the Plant Systems and Equipment Used for SGTR Recovery The major RCS and SG parameters, and systems / equipment used for SGTRand recovery for Millstone 3 (NEU)

Table 1.

mes narameters _ g sc narameters _

SI System -

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me AFW System 0.. C l

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SG PORV canacity a,C e

Przr PORV cacacity 0,, C O

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Table 1 Comparison of the major RCS and SG parameters, and systems / equipment used ' '

for SGTR Recovery for Millstone 3 (NEU) and the reference plant.

Millstone 3 (NEU) Reference Plant of WCAP 10698 A,C i

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c. comparisons of the Emergency operating Procedures, Operator Action Times and the Worst Single Failure Emeraanev onaratina Procedure -' a, C e

onarator Action Times '

Q. , C Worst sincie Failure Assumetion ~

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TABLE 2 OPikATOR ACTION TIMES 'FOR DEsl&N EA315 54Tt ANALYSIS

- 4, C Atlisa Identify and isolate ruptured 54 Operator action time to initiate cooldown Cooldown Operator action time to initiate depressurization Depressurization Operator action time to initiate

$1 termination

$1 termination and pressure equalization i .,

• These times are dependent upon the plant design and parametert and the equipment used to perform the operations, and therefore are calculated with the LOFTTR) analysis program.

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I D. Comparisons of SGTR Transient and Margin to ov0rfill for Mil 10tena 3 f and the Reference Plant The SGTR transient for Millstone 3 is expected to be different fro.-

• thetransientforthereferenceplant.{ l 1

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]'ihe following are the evaluations of the effects of the system designs on the transient recovery times and margin to t

overfill for each of the four major recovery periods.

1. Time to isolation of the ruptured SG a,g i

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2. Time to complete cooldown

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3. Time to complete depressurization ~

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4. Time to terminate the primary to secondary leakage a,t l

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5. Comparison of Margin to overfill for Millstone 3 and the Reference Plant Based on the above evaluation, the tima at which safety injection flow is terminated for Millstone 3 is expected to be approximately the sar.e as the reference plant. However, the tint at whicn primary to secondary leakage is terminated for Millstone 3 could be significantly longer than for the reference plant.

The following system responses / parameters will increase the margin to__

overfill for Millstone 3:

l The following system responses / parameters will decrease the margin to l -

overfill for Millstone 3: A., C l

9 ,

F

overall, the margin to overfill for the Millstone 3 is expected to be greater than for the reference plant since the break flow rate for Millstone 3 is expected to be lower than the break flow rate for the reference plant. However, it is not possible to quantify the difference without an explict analysis since there are negatives as well as positives in the above comparisons.

E. Evaluation of Margin to overfill for the Millstone 3 The margin to overfill for the Millstone 3 has also begg estimated

]sith some based on the[

simple assumpt ions on[ ,,The results indicated that margin to overfill can not be dem]onstrated since overly conservative assumptions were necessary when hand calculation were Those assumptions include the following: ,

g,e 3[ sed.

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It is expected that a significant increase in margin to SG overfill could be demonstrated such that margin to overfill would be demonstrated if a detailed analysis utilizing the computer program and methodology described in WCAP 10693 is performed.

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III. REFERENCES

1. Lewis, Huang, Behnke, Fittante, Gelman, "SGTR Analysis Methodology to

• Determine the Margin to Steam Generator overfill," WCAP-10698-P-A, August 1987. (PROPRIETARY)

2. Lewis, Huang, Rubin, "Evaluation of offsite Radiation Doses for a Steam Generator Tube Rupture Accident," Supplement 1 to WCAP-10698-P-A, March 1986. (PROPRIETARY)

3. J. A. Camp, Letter from NEU to Westinghouse Concerning Plant Specific Information for Millstone 3 for the Evaluation of Margin to overfill, January 7, 1988.

4. E-3 Procedure for Millstone 3 ,

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