ML20005E236

Forwards 10CFR50.46 Annual Rept of ECCS Model Revs

ML20005E236
Person / Time
Site:	South Texas
Issue date:	12/26/1989
From:	Mcburnett M HOUSTON LIGHTING & POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ST-HL-AE-3327, NUDOCS 9001040140
Download: ML20005E236 (8)

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The Light P.O. Box 1700 Houston, Texas 77001 (713) 228 9211 Houston Lighting ae Power m- - , _ _ . - - - - - - - - - ~ ~ - - - - - -

December 26, 1989 ST-HL-AE-3327 File No.:G03.11, 003.17 10CFR50.46

,o U. S. Nuclear Regulatory Commission Attention: Docun.~. introl Desk

. Washington, DC 20555 South Texas Project Electric Generating Station Units 1 and 2 Dockets No STN 50 498,'STN 50-499 10CFR50.46 Reauired Annual Reoort of ECCS Model Revisions In accordance with 10CFR50.46(a)(ii), HL&P is submitting the attached information regarding ECCS model revisions affecting South Texas Project (STP)

Units 1 and 2.

The cumulative revisions to the Westinghouse Small Break LOCA ECCS Evaluation model~are provided for your review. The STP Small Break LOCA-analyses remain conservative when the effects of the revision are considered.

If there are any questions, please contact Mr. A. W. Harrison at (512) 972 7298 or myself at (512) 972-8530.

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. FILt M. A. McBurnett

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Manager S'.tpport Licensing MAR;. f.Wl/n1

-Attachments: Effects of Westinghouse ECCS Evaluation Model Modifications on the South Texas Units 1 and 2 LOCA Analysis Results:

Chapter 15 of the Fiual Safety Analysis Report r9001040140_891226 jDR - ADOCK-osooo49g g3

?DC A1/040.N10 A Subsidiary of Houston Industries incorporated

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"f ST-HL AE- 3327 Houston Lighting & Power Company File No. : C03. it , C03,17 i

South Texas Proj,ect Electric Generating Station Page 2 7

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Regional-Administrator, Region IV Rufus S. Scott Nuclear Regulatory Commission Associate General Counsel

, 611 Ryan Plaza Drive, Suite 1000 Houston Lighting & Power Company

Arlington, TX 76011 P. O. Box 61867 Houston, TX 77208 Ceorge Dick, Project Manager U.S. Nuclear Regulatory Commission INPO. .'

Washington, DC 20555 Records Center 1100 circle 75 Parkway

.. J. I. Tapia Atlanta, CA 30339-3064 F

Senior Resident Inspector

• c/o U. S. Nuclear Regulatory Dr. . Joseph M. Hendrie Commission 50 Be11 port Lane-P. O. Box 910 Be11 port, NY 11713 Bay City, TX 77414 D. K. iacker J. R. Newman, Esquire Bureau of Radiation Control Newman & Holtzinger, P.C. Texas Department of Health

.1615 L Street, N.W. 1100 West 49th Street- -

Washington, DC 20036 Austin, TX 78704

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.- Ward /R. F. Verret Central Power & Light Company P. 0. Rox 2121

Corpus Christi, TX 78403

'J. C. Lanier Director of Generation-

l. City of Austin Electric Utility

-721 Barton Springs Road +

Austin, TX 78704 L R. J., Costello/M. T. Hardt City.Public Servi.-a Board P.;O.-Box 1771 >

San Antonio, TX 78296 l

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I' Revised 12/15/89 l

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i EFFECT OF WESTINGHOUSE ECCS EVALUATION MODEL MODIF7. CATIONS ON Tr!E SOUTH TEXAS UNITS 1 & 2 LOCA ANALYSIS RESULTS CHAPTER IS OF THE FINAL SAFETY ANALYSIS RFPORT The October 17, 1988 revision to 10CFR50.46 required applicants and holders of operating licenses or construction permits to notify the Nuclear Regulatory (

Commission (NRC) of errors and changes in the ECCS Evaluation Models on an i annual basis, when the errors and changes were not significant. Reference 1 l defines a significant error or change as one which results in a calculated peak fuel cladding temperature different by more than 50'F from the i temperature calculated for the limiting transient using the last acceptable )

model .or is a cumulation of changes and errors such that the sum of the j ebsolute magnitudes of the respective temperature changes is greater than  !

50'F. l In Reference 2, information regarding modifications to the Westinghouse large break and small break LOCA ECCS Evaluation Models was submitted to the NRC. f The following presents an assessment of the effect of the modifications to the Westinghouse ECCS Evaluation Models on the loss-of-coola t accident (LOCA) analysis results found in Chapter 15 of the South Texas Units 1 & 2 Final Safety Analysis Report. ,

i Large Break LOCA The large break LOCA analysis for South Texas Units 1 & 2 were examined to assess the:effect of the. applicable modifications to the Westinghouse large j break LOCA ECCS Evaluation Model on peak cladding temperature (PCT) results <

reported in Chapter 15 of the FSAR, The large break LOCA analysis results were calculated using the 1981 version of the Westinghouse large break LOCA ECCS Evaluation Model incorporating the BART analysis technology. The ,

analysis assumed the following information important to the large break LOCA l analyses:

NSSS power level of 102% of 3800 Mwt.

17x17XL STD fuel Steam Generator Tube Plugging Level of 5% Uniform among the four steam generators, j Nuclear Peaking Factors of 2.50 for the total peaking factor and 1.52 for the Enthalpy Rise peaking factor.

t The limiting break resulted from the double ended guillotine rupture of the cold leg piping with a discharge coefficient of CD - 0.6 and maximum safeguards assumptions. The calculated peak cladding temperature was 2122 F.

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5 CODE MODIFICATION RELATED TO THE 1981 ECCS EVALUATION MODEL INCORPORATING BART ANALYSIS TECHNOLOGY:

In the 1981 version of the Westinghouse ECCS Evaluation Model which incorporates the BART analysis technology, a modification was made to delay downcomer overfilling. The delay corresponds to backfilling of the intact

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-cold legs, Data from tests simulating cold leg injection during the post-  !

large break LOCA reflood phase which have adequate safety injection flow to condense all of the available steam flow show a significant amount of subcooled liquid to be present in the cold leg pipe test section. This situation corresponds to the so-called maximum safety injection scenario of ECCS Evaluation Model analyses.

For maximum safety injection scenarios, the reflooding model in the

-Westinghouse 1981 ECCS Evaluation Model incorporating the BART analysis technology uses a WREFLOOD code version which predicts the downcomer to overfill. Flow through the vessel _ side of the break is computed based upon the available head of water in the downcomer in VREFLOOD using a method with incompressible flow in an open channel. A modification to the WREFLOOD computer code was made to consider the cold leg inventory which would be present in conjunction with the enhanced downcomer level in the non-faulted loops. .

VREFLOOD code logic was altered to consider the filling of the cold legs together with downcomer overfilling. With this coding update, when the downcomer level exceeds its maximum value, as input to WREFLOOD, liquid flow ,

into the intact cold leg, as well as spillage out the break, is considered.  !

This logic modification stabilizes the overfilling of the vessel downcomer as it approaches the equilibrium level. In some cases this change could delay the downcomer overfilling process, which could in turn result in a peak cladding temperature (PCT) penalty. The magnitude of the possible PCT penalty was assessed by reanalyzing a plant which is maximum safeguards limited (CD-0.6 DECLG case) and which is most sensitive to the changes in~the WREFLOOD code using the 1981 ECCS Evaluation Model without including the BART analysis technology. methods. The PCT penalty of 16*F which resulted represents the maximum _ PCT penalty which could be exhibited for any plant due to the WREFLOOD logic change and is a conservative estimate for the BART analysis technology.

This' change represents a model enhancement in terms of consistency of the approach in the WREFLOOD code and the actual response of the downcomer level.

Since Appendix K to 10CFR50 does not require the explicit treatment of the mass storage feature, this modification represents an enhancement rather than an error.- However, to assess the margin available for accommodating potential plant changes, a 16 F penalty in the peak cladding temperature will be tracked for this code modification.

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Page 2 South Texas Units 1 & 2 large break LOCA analysis results could be affected by the modifications specified above. While there may be no adverse effect on

- the PCT calculation for the change, a conservative estimate of 16*F will be j assessed and tracked for use in determining the available margin to the limits of-10CFR50.46.

A. Analysis calculated result __2122 *F B. Modifications to Westinghouse ECCS Evaluation + 16 'F Model ECCS Evaluation Model Modifications Resultant PCT - 2138 'F Small Break LOCA The small break LOCA analyses for South Texas Units 1 & 2 were also examined to assess the effect of the applicable modifications to the Westinghouse ECCS Evaluation Models on peak cladding temperature (PCT) results reported in

• Chapter 15 of the FSAR. The small break LOCA analyses results were calculated  ;

using' the 1985 version of the Westinghouse small break LOCA ECCS Evaluation

~Model incorporating the NOTRUMP analysis technology.- The limiting size small break resulted from a 4-inch equivalent diamater break in the cold leg. The calculated peak cladding temperature was 1367#F. The analysis assumed the following information important to the small break LOCA analyses:

NSSS power level of 102% of 3800 Mwt.

17x17XL STD fuel i

Steam Generator Tube Plugging Level of 5% Uniform among the four steam generators.

Nuclear Peaking Factors of 2.50 for the total peaking factor and 1.52 for the Enthalpy Rise peaking factor.

The Westinghouse small break LOCA ECCS Evaluation Model analyses for South Texas Units 1 & 2 were performed with a version of the NOTRUMP computer which existed prior to the identification of the following potentially significant modifications noted in Reference 3:

1) The modification to preclude changing the region designation (upper, lower) for a node in a stack which does not contain the mixture-vapor interface was not incorporated in the small break LOCA analyses. The purpose of the modification was to enhance tracking of the mixture-vapor interface in a stacked series of fluid nodes and to preclude a node in a l stack, which does not contain the mixture-vapor interface, from changing the region designation. The update does not affect the fluid conditions p

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-t 8 w Page 3 in.the nodes representing the reactor coolant system, only the designation of_the region of the node. The region designation does not typically affect the calculations, except for the nodes representing the core fluid volume (core nodes). In core nodes which are designated as containing vapor regions,-the use of the steam cooling heat transfer correlation is forced on the calculation in compliance with the requirements of Appendix K to 10CFR50, even if the node conditions would indicate otherwise. This modification could affect the heat transfer calculation if the region designation was improperly reflected, but is expected-to result in a small decrease in the PCT if the correction was taken into account.

2) Tho modification to correct typographical errors in the equatiens which calculate the heat transfe- rate derivatives for subcooled, aaturated, and superheated natural nnvection conditions for the upper region of interior fluid nodes 7as not taJ uded in the small break LOCA analyses.

The her* rranrfer rate decivativos for subcooled, saturated, and y:perheeted natural convection conditions ior the upper re3 ten of tate;ior fluid nodas used the 1cuer region heat trcnsfer area instcad of the z.pper res.an heat transfer area. which could in rare instances, affect the amounc of heat that coulo i+ transferred to the fluid.

Incorporating the notification into the small break LOCA analyses could result in an increaso i.n the PCT of 36.lPF.

- 3) The modification to correct typographical errors in equations.which

- calculate the derivatives of the natural convection mode of heat transfer in the subroutine HEAT were not included in the small break LOCAL analyses. However, incorporating the correction into the analyses would have no effect on the analysis results.

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4) The modification to correct a typographical error in an equation which calculates the internal energy for nodes associated with the reactor coolant pump model when the associated reactor coolant pump flow links are found to be in critical flow was not included in the small break LOCAL analyses. Since the small break LOCA Evaluation Model calculations did not encounter critical flow in the reactor coolant pump flow links, including this modification would have no effect on the analysis results.

5) The modification to correct an error in the implementation of equation 5-33 of Reference 5 was not included in the small break LOCAL analyses.

Equation 5-33 describes the calculation of the flow link friction parameter cm for single phase flow in a non critical flow link k. In the erroneous implementation, equation 5 33 was replaced by equation 5-34 which is used for all flow conditions. This modification could affect the small break LOCA calculation, but is expected to result in a decrease in the PCT if the correctic ~- N into account through a new analysis, l

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6) The' modification made to prevent code aborts resulting from implementation of a new FORTRAN compiler en the Westinghouse CRAY computer system was not included in the small break LOCA analyses. Due to the different treatments of the precision of numbers between the FORTRAN compilers, the-subtraction of two large, but'close numbers j resulted in zero. The zero value was used in the denominator of a derivative equation, which resulted in the code aborts.- Implementing this modification for cases which did not abort has the potential to result in an increase in the PCT of approximately 4.8'F.

7) The modification to properly call some double-dimensioned variables in subroutines INIT and TRANSNT was not included in the small break LOCA >

analyses. However, all of the doubly dimensioned variables used a 1 as the second dimension in.all of the erroneous calls, and therefore this moditication would have no effect on the PCT.

8) The modification to correct an error in implementing equations L-28, L-52 and L-29, L 53 of Reference 5 was not included in the small break LOCA analyses. The two pairs of equations respectively describe the partial derivatives of F# with respect to pressure and specific enthalpy. F* is an interpolation parameter that is defined by equations L-27, L-51 of Reference 6. This modification could affect the small break LOCA calculation,but is expected to result in a decrease in the PCT if the correction were taken into account through a new analysis.

Modifications were also made to the small break LOCTA-IV computer code used in i

-the 'small break LOCA ECCS Evaluation Model. Since the small break LOCTA-IV code modifications could, at most, result in-a very small benefit the offect of modification'to the small break LOCTA IV code modifications do not need to be assessed or tracked.

The effect of the ECCS Evaluation Model modifications on the small break LOCA

, analyses for South Texas Units 1 & 2 could result in a penalty in the peak L cladding temperature calculation if taken into accouat. For conservatism in estimateing the available margin, a peak cladding temperature penalty'of

- approximately 42 F should be added to the analysis calculation as a result of

! ECCS Evaluation Model changes when determining the avilable margin to the

-limits of 10CFR50.46.

As discussed above, modifications to the Westinghouse small break LOCA ESSC Evaluation Model could affect the small break LOCA analysis results by altering the PCT.

A. Analysis calculated result __1367 *F B. Modifications to Westinghouse ECCS Evaluation + 42 F E

Model

'ECCS Evaluation Model Modifications Resultant PCT __1409 F A1/040.N10

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e 39 REFERENCES-1.. " Emergency Core Cooling Systems; Revisions to Acceptance Criteria,: - Federal Register, Vol. 53, No.180, pp. 35996-36005, Dated September 16, 1988.

2. NS-NRC-89 3463, "10CFR50.46 Annual Notification for 1989 of Modifications in the Westinghouse ECCS Evaluation Modeis,"

Letter from W. J. Johnson (Westinghouse) to T. E. Murley (NRC),

dated October 5, 1989.

3. NS NRC 89 3464, " Correction of Errors and Modifications to the NOTRUMP Code in the Westinghouse Small Break LOCA ECCS Evaluation Model Which Are Potentially Significant," Letter from W. J. Johnson

-(Westinghouse) to T. E. Murley (NRC), Dated October 5, 1989.

4 WCAP-9561-P-A, Addendum 3 (Proprietary), WCAP-9562 A, Addendum 3 (Non-Proprietary),- Young, M. Y. , " Addendum to: BART-1A: A Computer Code for the Best Estimate Analysis of Reflood Transients.(Special

_ Report: Thimble Modeling in Westinghouse ECCS Evaluation Model)," 1986.

5 .- "NOTRUHF - A Nodal Transient Small Break and General Network Code,"

WCAP-10079-P A (Proprietary), WCAP-10080-A (Non-Proprietary),

Meyer, P. E., et. al. , August 1985.

6. " Westinghouse Small Break ECCS Evaluation Model Using the NOTRUMP Code,"

WCAP-10054-P-A (Proprietary), WCAP-10081 A (Non-Proprietary), Lee, N.,

et. al., August 1985.

7. " Westinghouse Small Break ECCS Evaluation Model Ceneric Study with the NOTRUMP Code,' WCAP-11145, Rupprecht, S. D., et', al., August 1985.

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