ML20206B400

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Annual & 30-Day Rept of ECCS Evaluation Model Changes & Errors for Byron & Braidwood Stations
ML20206B400
Person / Time
Site: Byron, Braidwood  Constellation icon.png
Issue date: 12/31/1998
From:
COMMONWEALTH EDISON CO.
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ML20206B396 List:
References
NUDOCS 9904290235
Download: ML20206B400 (21)
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Text

r Attachment 1 10 CFR 50.46 Annual and 30-Day Report of the Emergency Core Cooling System Evaluation Model Changes and Errors Assessments as of March 22,1999

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  • PLANT NAME: Braidwood Station Unit 1

. ECCS EVALUATION MODEL: Small Break Loss of Coolant Accident (SBLOCA)

REPORT REVISION DATE: 3/22/99

. CURRENT OPERATING CYCLE: B NALYSIS OF RECORD (AOR)

Evaluation Model: NOTRUMP~

Calculation: Westinghouse SEC-LIS-5314-CO, October,1997 Fuel: VANTAGE 5NANTAGE+ 17 x 17 Heat Flux Hot Channel Factor (FQ) = 2.60 Nuclear Enthalpy Rise Hot Channel Factor (FNAH) = 1.70 Steam Generator Tube Plugging (SGTP) = 30%

Reference Peak Cladding Temperature (PCT) PCT = 1695.0*F '

MARGIN ALLOCATION A. PRIOR LOSS OF COOLANT ACCIDENT (LOCA) MODEL ASSESSMENTS None B. CURRENT LOCA MODEL ASCESSMENTS None NET PCT PCT = 1695.0*F l

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' PLANT NAME: Braidwood Station Unit 1 ECCS EVALUATION MODEL: Laroe Break Loss of Coolant Accident (LBLOCA)

REPORT REVISION DATE: 3/22/99 l CURRENT OPERATING CYCLE: 3 OR Evaluation Model: BASH Calculation: Westinghouse SEC-SAll-4747-C2, May,1996 Fuel: VANTAGE 5/ VANTAGE + 17 x 17 FQ = 2.60 FNAH = 1.70 SGTP = 30%

Reference PCT PCT = 1968.0'F MARGIN ALLOCATION l

A. PRIOR LOCA MODEL ASSESSMENTS Translation of Fluid Conditions from SATAN to LOCTA (Note 8) _ APCT = 15.0*F Reactor Coolant System (RCS) Crossover Leg Volume (Note 9) APCT = 3.0*F )

B. CURRENT LOCA MODEL ASSESSMENTS Replacement Steam Generator (RSG) (SGTP 20%, Note 10) APCT = 21.0*F !

Passive Heat Sink Increase (Note 11) APCT = 16.0*F i Reactor Coolant Fan Cooler (RCFC) Performance (Note 11) APCT = 1.0*F )

LOCBART Fuel Rod Outside Diameter (FOD) Input Error (Note 13) apt. T = 2.0*F l Initial Containment Pressure (Note 11) APCT = -5.0*F LBLOCA Burst Location Change (Note 12) APCT = 94.0*F Removal of Translation of Fluid Conditions from SATAN to LOCTA (Note 8) APCT = -15.0*F NET PCT PCT = 2100.0'F

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' PLANT NAME: 'Braidwood Station' Unit 2 ECCS EVALUATION MODEL: SBLOCA

- REPORT REVISION DATE: 3/22/99'-

CURRENT OPERATING CYCLE: Z*

AOR Eva!uation Model: NOTRUMP-Calculation: Westinghouse SEC-SAll-4730-CO, May,1995 Fuel: VANTAGF5NANTAGE+ 17 x 17-FQ = 2.60 FNAH = 1.70 -

SGTP = 30%

Reference PCT PCT = 1723.0*F

. MARGIN ALLOCATION A.- PRIOR LOCA MODEL ASSESSMENTS NOTRUMP Specific Enthalpy Error (Note 5) APCT = 20.0*F SALIBRARY Double Precision Error (Note 6) APCT = -15.0'F SBLOCTA Fuel Rod initialization Error (Note 7) APCT = 10.0*F Burst and Blockage / Time in Life (Note 3) APCT = ' 30.0*F I

8. ' CURRENT LOCA MODEL ASSESSMENTS None NET PCT PCT = .1768.0*F
  • lt is expected that Braidwood Station Unit 2 Cycle 7 operation will end by the end of April 1999 and Braidwood Station Unit 2 Cycle 8 operation will start on June 1,1999.

For Byron Station Unit 2 and Braidwood Station Unit 2 a new SBLOCA analysis was performed taking into account the Auxiliary Feedwater (AFW) modification, increased

. peaking factor, and additional conservatism in the Emergency Core Coolant System l (ECCS) flow. This new analysis will be the SBLOCA AOR for Braidwood Station Unit  ;

2 Cycle 8c ' Note:- There are two separate SBLOCA analyses, one for RSGs  !

(Byron /Braidwood Unit 1) and one' for Old Steam Generators (OSGs) i (Byron /Braidwood Unit 2). There is only one LBLOCA analysis for all four units.

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PLANT NAME: Braidwood Station Unit 2 l ECCC EVALUATION MODEL: SBLOCA  !

REPORT REVISION DATE: 3/22/99 CURRENT OPERATING CYCLE: 8*

AOR  ;

Evaluation Model: NOTRUMP Calculation: Westinghouse SEC-LIS-5396-CO, January,1999 l

Fuel: VANTAGE 5/ VANTAGE + 17 x 17  !

FQ = 2.70 4 FNAH = 1.75 SGTP = 30%

l Reference PCT- PCT = 1806.0*F '

MARGIN ALLOCATION A.. PRIOR LOCA MODEL ASSESSMENTS None

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l B. CURRENT LOCA MODEL ASSESSMENTS  :

Burst and Blockage / Time in Life (Note 3) APCT = 19.0*F NET PCT PCT = 1825.0*F 1

  • lt is expected that Braidwood Station Unit 2 Cycle 7 operation will end by the end of .

April 1999 and Braidwood Station Unit 2 Cycle 8 operation will start on June 1,1999. i For Byron Station Unit 2 and Braidwood Station Unit 2 a new SBLOCA analysis was i performed taking into account the AFW modification, increased peaking factor, and additional conservatism in the ECCS flow. This new analysis will be the SBLOCA AOR for Braidwood Station Unit 2 Cycle 8. Note: There are two separate SBLOCA analyses, one for RSGs (Byron /Braidwood Unit 1) and one for OSGs (Byron /Braidwood Unit.2).There is only one LBLOCA analysis for all four units. l

" PLANT NAME: Braidwood Station Unit 2 ECCS EVALUATION MODEL: LBLOCA REPORT REVISION DATE: 3/22/99 CURRENT OPERATING CYCLE: I kOR Evaluation Model: BASH '

' Calculation: Westinghouse SEC-SAll-4747-C2, May,1996 j Fuel: VANTAGE 5NANTAGE+ 17 x 17 i FQ = 2.60 FNAH = 1.70 l SGTP = 30%

l Reference PCT PCT = 1968.0*F .l MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS I Translation of Fluid Conditions from SATAN to LOCTA (Note 8) APCT = 15.0'F RCS Crossover Leg Volume (Note 9)' APCT = 3.0*F B. CURRENT LOCA MODEL ASSESSMENTS Passive Heat Sink Increase (Note 11) APCT = 16.0*F RCFC Performance (Note 11) APCT = 1.0*F LOCBART FOD Input Error (Note 13) APCT = 2.0*F Initial Containment Pressure (Note 11) APCT = -5.0*F LBLOCA Burst Location Change (Note 12) APCT = 94.0*F Removal of Translation of Fluid Conditions from SATAN to LOCTA (Note 8) APCT = -15.0*F NET PCT PCT = 2079.0'F

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' PLANT NAME: Byron Station Unit 1 ECCS EVALUATION MODEL: SBLOCA REPORT REVISION DATE: 3/22/99 CURRENT _ OPERATING CYCLE: 9 AOR Evaluation Model: NOTRUMP Calculation: Westinghouse SEC-LIS-5314-CO, October,1997 l

~

Fuel: VANTAGE 5NANTAGE+ 17 x 17 FQ = 2.60 FNAH = 1.70  !

SGTP = 30%

Reference PCT PCT = 1695.0*F MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS i l

None ,

4 B. CURRENT LOCA MODEL ASSESSMENTS Reconstituted Fuel Rod (Note 1) APCT = 0*F NET PCT PCT = 1695.0*F

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  • PLANT NAME: Byron Station Unit 1 ECCS EVALUATION MODEL: LBLOCA REPORT REVISION DATE: '3/22/99 CURRENT OPERATING CYCLE: 2

~ OR' Evaluation Model: BASH I Calculation: Westinghouse SEC-SAll-4747-C2, May,1996 j Fuel:. VANTAGE 5NANTAGE+ 17 x 17

~

FQ = 2.60 -

FNAH = 1.70 -

SGTP = 30%-

Reference PCT - PCT = 1968.0*F i

MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS - <

I Removed Upper internal Assembly Alignment Pins (Note 2) APCT = 5.0*F I Assembly Guide Pin Flakes (Note 4) APCT = 6.0*F i Translation of Fluid Conditions from SATAN to '

LOCTA (Note 8) APCT = 15.0*F - l RCS Crossover Leg Volume (Note 9) APCT = 3.0*F l Replacement Steam Generator (RSG) (SGTP 20%, Note 10) APCT = 21.0*F  ;

- B. CURRENT LOCA MODEL ASSESSMENTS j 1

Passive Heat Sink Increase (Note 11) APCT = 16.0*F l RCFC Performance (Note 11) APCT = 1.0*F )

LOCBART FOD input Error (Note 13) APCT = 2.0*F - j initial Containment Pressure (Note 11) APCT = -5.0*F  !

LBLOCA Burst Location Change (Note 12) APCT = 94.0*F  !

i Removal of Translation of Fluid Conditions from SATAN

' to LOCTA (Note 8) APCT = -15.0*F Reconstituted Fuel Rod (Note 1) APCT = 0*F l

NET PCT- PCT = 2111.0*F

' PLANT NAME: Byron Station Unit 2 ECCS EVALUATION MODEL: SBLOCA 3 REPORT REVISION DATE: 3/22/99 I

' CURRENT OPERATING CYCLE: B* ]

AOR Evaluation Model: NOTRUMP Calculation: Westinghouse SEC-SAll-4730-CO, May,1995 Fuel: VANTAGE 5NANTAGE+ 17 x 17 FQ = 2.60 FNAH = 1.70 I SGTP = 30%

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Reference PCT PCT = 1723.0*F

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MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS i

NOTRUMP Specific Enthalpy Error (Note 5) APCT = 20.0*F l SALIBRARY Double Precision Error (Note 6) APCT = -15.0*F SBLOCTA Fuel Rod initialization Error (Note 7) APCT = 10.0*F )

Burst and Blockage / Time in Life (Note 3) APCT = 30.0*F i B. CURRENT LOCA MODEL ASSESSMENTS None i NET PCT PCT = 1768.0*F l

  • It is expected that Byron Station Unit 2 Cycle 8 operation will end by the end of October 1999 and Byron Station Unit 2 Cycle 9 operation will start by the end of November 1999. For Byron Station Unit 2 and Braidwood Station Unit 2 a new SBLOCA analysis was performed taking into account the AFV! modification, increased peaking factor, and additional conservatism in the ECCS flow. This new analysis will be the SBLOCA AOR for Byron Station Unit 2 Cycle 9. Note: There are '

two separate SBLOCA analyses, one for RSGs (Byron /Braidwood Unit 1) and ona for OSGs (Byron /Braidwood Unit 2). There is only one LBLOCA analysis for all four units.

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' PLANT NAME: B_yron Station Unit.2 ECCS EVALUATION MODEL: SBLOCA REPORT REVISION DATE: 3/22/99 CURRENT OPERATING CYCLE: B*

AOR' Evaluation Model: NOTRUMP Calculation: Westinghouse SEC-LIS-5396-C0, January,1999 Fuel: VANTAGE 5/ VANTAGE + 17 x 17 FQ = 2.70 FNAH = 1.75 SGTP = 30%

Reference PCT PCT = 1806.0*F MARGlN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS 1

None B. CURRENT LOCA MODEL ASSESSMENTS Burst and Blockage / Time in Life (Note 3) APCT = 19.0'F NET PCT PCT = 1825.0*F l

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  • lt is expected that Byron Station Unit 2 Cycle 8 operation will end by the end of l October 1999 and Byron Station Unit 2 Cycle 9 operation will start by the end of i

. November 1999. For Byron Station Unit 2 and Braidwood Station Unit 2 a new SBLOCA analysis was performed taking into account the AFW modification, increased peaking factor, and additional conservatism in the ECCS flow. This r'ew analysis will be the SBLOCA AOR for Byron Station Unit 2 Cycle 9. Note: There are two separate SBLOCA analyses, one for RSGs (Byron /Braidwood Unit 1) and one for OSGs (Byron /Braidwood Unit 2). There is only one LBLOCA analysis for all four units.

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' PLANT NAME: Byron Sttion Unit 2 ECCS EVS.UATION MODEL: LBLOCA REPORT hEVISION DATE: 3/22/99 j CL8RRENT OPERATING CYCLE: a l l AOR Evaluation Model: BASH I Calculation: Westinghouse SEC-SAll-4747-C2, May,1996 Fuel: VANTAGE 5/ VANTAGE + 17 x 17 FQ = 2.60 FNAH = 1.70 SGTP = 30%

Reference PCT ' PCT = 1968.0*F MARGIN ALLOCATION l l

A. PRIOR LOCA MODEL ASSESSMENTS I l

Removed Upper Internal Assembly Alignment Pins (Note 2) APCT = 28.0*F Translation of Fluid Conditions from SATAN to LOCTA (Note 8) APCT = 15.0*F RCS Crossover Leg Volume (Note 9) APCT = 3.0*F B. CURRENT LOCA MODEL ASSESSMENTS Passive Heat Sink Increase (Note 11) APCT = 16.0*F RCFC Performance (Note 11) APCT = 1.0*F l LOCBART FOD Input Error (Note 13). APCT = 2.0*F I initial Containment Pressure (Note 11) APCT = -5.0*F LBLOCA Burst Location Change (Note 12) APCT = 94.0*F Removal of Translation of Fluid Conditions from SATAN to LOCTA (Note 8) APCT = -15.0'F NET PCT PCT = 2107.0*F

O t Attachment 2 10 CFR 50.46 Annual and 30-Day Report of the Emergency Core Cooling System Evaluation Model Changes and Errors Assessment Notes

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1. Reconstituted Fuel Rod There is one reconstituted fuel rod in the Byron Station Unit 1 Cycle 9 core. The reconstituted fuel assembly containing a stainless steel rod was evaluated in accordance with guidance described in NRC Generic Letter 90-02, " Alternative Requirements for Fuel Assemblies in the Design Features Section of Technical Specifications,"

Supplement 1, to determine if Loss of Coolant Accident (LOCA) Peak Cladding Temperature (PCT) penalties apply. The methodology utilized is described in  !

Westinghouse Fuel Assembly Reconstitution Evaluation Methodology, WCAP-13060-P-A, dated July 1993. Since only one stainless steel rod is involved, the PCT is inconsequential and will be assigneo c 0 F PCT penalty for both the Small Break Loss of j Coolant Accident (SBLOCA) and the Large Break Loss of Coolant Accident (LBLOCA). i No other units have any reconstituted fuel rods in the core.

2. Removed Upper Internal Assembly Alianment Pins l

'This penalty addresses the removal of upper intemal alignment pins at the Byron Station. Two pins have been removed from Byron Station Unit 1 and six pins have been removed from Byron Station Unit 2. Removal of the alignment pins resulted in a LBLOCA PCT penalty of +5.0 F for Byron Station Unit 1. Byron Station Unit 2 previously accounted for the cut pins by penalizing Heat Flux Hot Channel Factor (FQ). Starting with Byron Station Unit 2 Cycle 6 a LBLOCA PCT penalty of +28.0*F was assessed instesd of the FQ penalty. This will establish consistent treatment of the cut alignment pins for both units at Byron Station.

3. Burst and Blockaae/ Time in Life Typically the SBLOCA was performed using Beginning of Life (BOL) fuel perfonnance data (i.e., PAD) and evaluated at other burnups using the SPIKE computer code.

Presently this is explicitly modeled using a " time in life study." The burst and blockage model does not have any effect on the PCT if the PCT is less than 1700 F. As a result of the NOTRUMP specific enthalpy error described in Note 5, the Small Break LOCTA computer code fuel rod initialization error described in Note 7, and the SALIBRARY double precision error described in Note 6, a 30 F burst and blockage / time in life penalty is applicable to the SBLOCA for Byron Station Unit 2 and Braidwood Station Unit 2.

For the revised Byron Station Unit 2 and Braidwood Station Unit 2 analysis the burst and blockage penalty is 19 F. For Byron Station Unit 1 and Braidwood Station Unit 1 analysis there is no burst and blockage penalty because the PCT is less than 1700 F.

4. Assembly Guide Pin Flakes Bending of fuel assembly alignment pins to angles greater than 5 degrees may result in the generation of pin flakes or fragments. The flakes could potentially lodge themselves in an assembly and locally reduce assembly flow. The flakes could increase blockage of the hot rod subchannel during the reflood period and increase the PCT. This penalty of 6 F is only applicable to Byron Station Unit 1.

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5. NOTRUMP Specific Enthalov Error A typographical error was found in a line of coding in the NOTRUMP computer code.

This line of coding was intended to model the calculation found in Equation L-127 of i NOTRUMP - A Nodal Transient Small Break and General Network Code,

'_WCAP-10079P-A, dated August 1985. Although the equation in the topical report is j correct, the coding represented the last term as a partial derivative with respect to the '

fluid node mixture region total energy instead of the mixture region total mass. This 20 F penalty only applies to the SBLOCA analyses for Braidwood Station Unit 2 Cycle 7 and Byron Station Unit 2 Cycle 8. i

6. SALIBRARY Double Precision Errors During migration of the LOCA computer codes from the CRAY computer to UNIX-based i platforms, programming errors were made in two library routines related to improper l specification of double precision variables. These errors were found and fixed during later computer code maintenance. Test cases with individual computer codes in the models demonstrated very small differences in only the SATAN and NOTRUMP i computer code results, with correspondingly minor effects on final PCT predictions. i Because the error only affects a very limited number of LBLOCA analyses which were i performed on the UNIX-based platform prior to correcting the codes, the evaluation of  !

effects for LBLOCA analyses were assessed on a plant-specific basis. The LBLOCA l analyses for the Byron and Braidwood Stations were not affected. For SBLOCA analyses performed on the UNIX-based platform, representative plant calculations resulted in an estimated generic effect of-15 F for affected analyses. This 15 F penalty only applies to the SBLOCA analyses for Braidwood Station Unit 2 Cycle 7 and Byron Station Unit 2 Cycle 8.

7. Small Break LOCTA Computer Code Fuel Rod initialization i 1

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- An error was discovered in the Small Break LOCTA computer code related adjustments which are made as part of the fuel rod initialization process used to obtain agreement between the Small Break LOCTA model and the fuel data supplied from the fuel thermal-hydraulic design calculations at full power, steady-state conditions. Specifically, an j adjustment to the power, which is made to compensate for adjustments to the assumed  !

pellet diameter was incorrect. Additionally, updates were made to the fuel rod cladding

, creep and strain model to correct logic errors that could occur in certain transient conditions. These model revisions also had a small affect on the fuel rod initialization

_ process, and can produce small affects during the transient. Due to the small magnitude of the affects, and the interaction between the two items, they are being evaluated as a l single, closely related affect. Calculations with the corrected model resulted in an i increase of 10 F in the PCT for the SBLOCA. This 10 F penalty only applies to the SBLOCA analyses for Braidwood Station Unit 2 Cycle 7 and Byron Station Unit 2 Cycle 8. '

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- 8. Translation of Fluid Conditions from SATAN to LOCTA

' An error was discovered in the coding related to the translation of fluid conditions between the SATAN blowdown hydraulics computer code and the LOCTA computer l code used for subchannel analysis of the fuel rods. In performing axial interpolations to l translate the SATAN fluid conditions onto the mesh nodalization used by the LOCTA l computer code, the length of the lower core channel fluid connection to the lower plenum node was incorrectly calculated. Calculations with the corrected model resulted in an l increase of 15'F in the PCT for the LBLOCA. This penalty applies to both the Byron and l

- Braidwood Station LBLOCA analyses.

Sensitivity studies to rebaseline the Analysis of Record (AOR) using updated computer code versions / methodology and minor input changes, described in Note 12, resulted in a PCT of 20frF, a 94*F increase relative to AOR. These results incorporate the SATAN /LOCTA error included in the letter from R. M. Krich (Comed) to U.S. NRC, 4

" Annual 10 CFR 50.46 Report," dated April 23,1998. Therefore, this 15 F penalty is '

removed in this report.

9. Reactor Coolant System (RCS) Crossover Leo Volume IMP is an electronic database containing a variety of plant geometry data whose primary l purpose is to interactively support the LOCA Evaluation Model input preprocessors.

Secondary purposes are to provide a convenient repository and ready reference for j Nuclear Steam Supply System (NSSS) geometry information for a variety of functional '

groups that generally utilize the database simply for limited hand data extractions.

Westinghouse discovered an error in a recent edition of the Byron /Braidwood IMP l Database associated with the crossover leg volume. The IMP Database has been subsequently updated. l The impact of the error is a 3 F increase in PCT la the LBLOCA. The SBLOCA AOR l bounds the increased crossover leg volume configuration and there is no adverse impact i to SBLOCA PCT. This item applies to the Byron and Braidwood Stations.

,10. Replacement Steam Generator (RS.G_) i 1

Westinghouse performed an evaluation to (emonstrate the applicability of the current LBLOCA AOR to the Babcock & Wilcox International (BWI) RSGs. The evaluation consisted of evaluating the differences between the BWI and Westinghouse designed steam generators and the impact on the PCT. The evaluation resulted in a 21 F PCT i penalty for the BWI RSGs, The RSG supports a steam generator plugging level of up to ,

20% This is applicable to Byron Station Unit 1 and Braidwood Station Unit 1. 1 4

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L 11, Passive Heat Sink / Reactor Containment Fan Cooler (RCFC) Performance Data / initial j Containment Pressure Assumption in the LBLOCA analysis it is conservative to assume data which minimizes the containment pressure during the transient, such as the assumption of the total amount of passive heat sinks, the performance of RCFCs, the assumption of initial containment pressure, containment spray flows, etc.

a) Passive Heat Sink l The amount of passive heat sinks assumed in the AOR LOCA analysis is documented in the Updated Final Safety Analysis Report (UFSAR) Table 6.2-55. Subsequent to the AOR analysis, numerous modifications were done inside the containment. To perform the modifications materials such as steel were installed inside the containment.

Increased steel results in a decrease in the containment pressure during the LOCA transient and is potentially non-conservative.

Anytime modifications such as replacing the steam generators, addition of Safety i injection (SI) Tank Access Galleries, etc. are done inside the containment, evaluations are performed to determine the impact of these modifications on the LOCA analysis.

Westinghouse ' representatives performed an evaluation to determine the impact on the PCT due to the addition of various passive heat sinks. The Westinghouse evaluation .

i addressed the addition of increased steel due to RSGs, SI Tank Access Gallery steel, and an assumed miscellaneous containment metal mass corresponding to 20,000 sq. ft.

at 0.2083 ft. thickness for future modifications. This evaluation determined a PCT penalty of 16 F for these additional passive heat sinks.

l b) RCFC Performance Data l The RCFC Performance data assumed in the AOR analysis was determined to be incorrect. Revised corrected data was provided to Westinghouse to evaluate the impact on the LOCA analysis. The Westinghouse evaluation determined a PCT penalty of 1 F  ;

for the corrected data. i l_

c) initial Containment Pressure Assumption . j The AOR assumed a very conservative initial containment pressure of -1.0 psig. To partially offset the penalty associated due to the above items (a) and (b), the assumption of initial containment pressure was revised. The revised assumption of initial containment pressure is -0.5 psig. This revised assumption for the initial containment pressure resulted in a PCT benefit of 5 F.

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l l 12. PCT Assessment for the LBLOCA for the Byron and Braidwood Stations Due to Burst  !

l Location Chanoe The LBLOCA AOR for the Byron and Braidwood Stations is presented in Chapter 15 of the UFSAR, Revision 7, and has a limiting case PCT of 1968 F. Westinghouse performed a series of sensitivity studies to rebaseline the AOR. One of the sensitivity cases using minor input changes indicated a PCT increase from 1968 F to 2062 F, a 94'F increase. Since the minor input changes and computer code version / methodology .

changes did not appear significant enough to account fo.- the 94 F change, a non-

! conformance report was opened, and an investigation was undertaken to determine the cause of the PCT increase.

it was determined that the PCT increase was largely attributed to the change in the predicted location of the hot rod burst. Nodes just downstream of fuel assembly grids are typically non-limiting due to the enhanced cooling afforded by the grid. In the AOR, hot rod burst occurred just downstream of a spacer grid, hence the cladding temperature at the burst elevation remained relatively low. In the sensitivity case, the thermal-hydraulic results, though not significantly changed, were sufficiently different to move the location of the rod burst by one node (i.e., 3 inches), and the cladding temperature at the burst node was not influenced by the presence of a grid.

Investigation subsequently performed has concluded that there is no valid reason to discredit the 3-inch shift in the hot rod burst. Therefore, the plant-specific 94 F analytical PCT penalty will be assigned to the Byron Station and Braidwood Station cumulative PCT at this time. ,

This is not considered to be an error in the Evaluation Model nor an error in the application of the Model, but merely a consequence of the discretization of the thermal-hydraulic process that is fundamental to the Model. Westinghouse continues to consider the ramifications of the burst location behavior relative to the ability to obtain stable results and may introduce discretionary changes to the Modelin the future.

Application of the 94 F analytical PCT penalty allows removal of the 15 F PCT penalty for SATAN /LOCTA Translation that was introduced in the 199710 CFR 50.46 Annual Report, submitted to the NRC by Comed on April 23,1997, because the computer code versions utilized in the sensitivity study incorporate the associated model corrections.

~ 13. LOCBART laout Fuel Rod Outside Diameter (FOD) Error An input calculational error in the Large Break AOR for the Byron and Braidwood Stations was discovered in the LOCBART computer code input FOD corresponding to j the fuel rod outside diameter. LOCBART is the rod heatup computer code of the BASH I Evaluation Model. This constitutes an error in the application of the Evaluation Model as defined in 10 CFR 50.46. A plant specific LOCBART sensitivity study was made which corrected the input FOD to its correct value, resulting in a 2 F PCT penalty.

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Attachment 3 10 CFR 50.46 Annual and 30-Day Report of the Emergency Core Cooling System Evaluation Model Changes and Errors Assessment Notes Not included in Rack-ups

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The following is a brief description of other Loss of Coolant Accident (LOCA) l assessments that reflect changes to the Evaluation Models, which are not included in the rack-up sheets. These assessments, in all cases, resulted in benefits to the calculated Peak Cladding Temperature (PCT). However, we have conservatively chosen not to cradit these PCT benefits, i.e., for each change a delta PCT of zero degrees Fahrenheit is assigned. Evaluations of these changes are based upon conservative generic studies for Westinghouse designed Nuclear Steam Supply Systems (NSSSs) or engineering judgment. They do not constitute a change to the application of the Evaluation Models in the current licensing basis for the Byron and l Braidwood Stations. If a re-analysis or an evaluation is obtained from Westinghouse, the impact of these changes will be included and the effect of these changes will be reported as applicable, Emeroency Diesel Generator (EDG) Underfreauency Evaluation l

The safety analyses are performed assuming the EDG operates at the steady state frequency. Recent EDG loading sequence tests and modeling indicate that the underfrequency reduction can be as much as 2 Hz (i.e., from 55 to 57 Hz) for a period of 4 seconds. The impact of the frequency swing during EDG loading sequences was evaluated and was determined to have insignificant impact on the PCT.

EDG Freauency Evaluation Currently, all safety analyses are performed assuming the EDG operates at the steady state frequency. However, the Technical Specifications allow EDG

( frequency to be within ! 1.2 Hz of the steady state frequency of 60 Hz. In the letter from R. M. Krich (Comed) to U.S. NRC, " Annual 10 CFR 50.46 Report,"

dated April 23,1998, it was stated that Westinghouse would perform a formal assessment of any PCT impact associated with this EDG frequency band. After further review, evaluation, and discussion, it was decided that the current assumption of EDG operation at steady state frequency is appropriate and that it is not necessary for Westinghouse to perform a formal PCT assessment. As stated in the 1998 Annual 10 CFR 50.46 Report, dated April 23,1998, the impact on PCT has been determined to be small. There is sufficient inherent I conservatism in the Westinghouse LOCA Emergency Core Cooling System (ECCS) Evaluation Models to bound uncertainty associated with EDG frequency uncertainty, and therefore the overall change to PCT is expected to be zero.'

Therefore, the utilization of steady state EDG frequency in the LOCA analysis is ,

judged to be appropriate.  !

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' Earliest Actuation Time for the Reactor Containment Fan Coolers (RCFCs) durina a LOCA l

The earliest actuation time of the RCFCs assumed in the Large Break Loss of Coolant Accident (LBLOCA) Analysis of Record (AOR) for the Byron and

Braidwood Stations is 25 seconds with the full heat removal capacity for the RCFCs. Prior to 25 seconds it was assumed that no heat is removed by the RCFCs. Braidwood Station reviewed the RCFC operation during normal and accident conditions and determined that the RCFC initiation and the heat removal capacity of the RCFC can vary depending on different conditions.

Based on this review of the RCFC operation during various normal and accident conditions, Braidwood Station provided the RCFC heat removal capacities and initiation times to Nuclear Fuel Management (NFM) for review and assessment of its impact on the LBLOCA analysis. NFM evaluated the RCFC data and determined that it had no significant impact on the AOR. This RCFC data and its assessment on the LBLOCA AOR are also applicable to Byron station.

Fuel Rod Desian and 10 CFR 50.46 Acceptance Criteria Westinghouse representatives recently informed Comed representatives that fuel rod corrosion and its associated feedback effect on rod internal pressure and the pressure stress limit have led to a potential violation of fuel rod design criteria and 10 CFR 50.46 acceptance criteria. Violation of the "no gap reopening" fuel -

rod criterion does not automatically result in a 10 CFR 50.46 acceptance criterion violation. This issue was first addressed in Westinghouse letter NSD-NRC 97-5404, dated October 28,1997.- This letter concluded that a substantial safety hazard as defined in 10 CFR 21 does not exist, and that the same levels of -

safety as considered in the design basis evaluations were maintained .

Plant specific evaluations are performed every reload cycle using Westinghouse methodology to ensure that the reload design does not violate the 17% total  :

localized corrosion criterion of 10 CFR 50.46. Specifically, evaluations have been performed for Braidwood Station Unit 1 Cycle 7 and 8, Braidwood Station Unit 2 Cycle 7, Byron Station Unit 1 Cycle 9, and Byron Station Unit 2 Cycle 7.

These evaluations have shown that the 17% total localized corrosion criterion of 10 CFR 50.46 is not violated.

l

.LBLOCA Power Distribution Appendix K to 10 CFR 50 requires that the power distribution, which results in the most severe calculated consequences, be used in the ECCS Evaluation Model calculations. The current basis for all Westinghouse LBLOCA evaluations is the chopped cosine power distribution. Calculations were performed with BASH, which examined peak power locations and power distributions that were not considered in the original analysis. Under some circumstances, these evaluations lead to PCTs greater than those calculated with the cosine

, distribution. Previously, the Byron and Braidwood Stations included a conservative temporary PCT penalty of 100*F to bound the effects of other power shapes.

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l To address the power shape issue, Westinghouse has developed an alternate axial power shape methodology, ESHAPE (Explicit Shape Analysis for PCT Effects). The ESHAPE methodology is based on explicit analysis of a set of skewed axial power shapes. The NRC as part of the Westinghouse LBLOCA Evaluation Model has previously approved the explicit use of skewed power {

shapes. Westinghouse has performed evaluations for the Byron and Braidwood  !

Stations using ESHAPE and has determined that the cosine power shape used in the Analysis of Record remains limiting. Therefore, the PCT penalty of 100 F !

was removed. I

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