ML20134G154

Provides 30 Day Rept Re PCT of Limiting Small Break & Large Break LOCA Analysis Evaluation for Plant

ML20134G154
Person / Time
Site:	Byron
Issue date:	11/04/1996
From:	Lesniak M COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9611130061
Download: ML20134G154 (5)

Text

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1 Commonwealth Ik!ison Company

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,1400 Opus Place 8

Iknvners Grove, IL 60515-5701 November 4,1996 Oflice of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attention: Document Control Desk

Subject:

Byron Station Unit 2 30 Day 10 CFR 50.46 Report NRC Docket No. 50-455

Reference:

Commonwealth Edison Letter, D. M. Saccomando to US NRC, "Braidwood Station Units 1 and 2, Byron Station Units 1 and 2, Zion Station Units 1 and 2,30 Day 10 CFR 50.46 Report, NRC Docket Nos. 50-456/457,50-454/455, and 50-295/304,"

dated April 25,1996.

This letter fulfills the 30 day reporting requirement of 10 CFR 50.46(a)(3)(ii) for Byron Nuclear Power Station Unit 2. The Reference transmitted to the NRC the most recent report for Braidwood, Byron, and Zion Stations. provides updated information regarding the Peak Clad Temperature (PCT) of the limiting Small Break and Large Break Loss of Coolant Accident analysis evaluation for ByTon Station Unit 2. Attachment 1 includes all assessments as of Nov.1,1996. Attachment 2 contains a detailed description for each change or error reported, Westinghouse has notified Comed of several issues which have resulted in PCT assessments to both the large and small break LOCA analyses for Braidwood, Byron, and Zion Stations. Comed has reviewed the Westinghouse notifications and concurs with Westinghouse's conclusions that Comed has no reporting obligations under 10 CFR 21. For all the discrepancies contained in this report, Westinghouse and Comed have determined that these issues do not constitute substantial safety hazards, and that all Comed plants continue to comply with the requirements of 10 CFR 50.46 and 10 CFR 50 Appendix K acceptance criteria. Because compliance with 10 CFR 50.46 is maintained with existing PCT penalties, no near term reanalysis is planned for these Units.

t Please direct any questions to this office.

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Marcia T. Lesniak Nuclear Licensing Administrator Attachments po0\\ /l/#

cc:

A. B. Beach, Regional Administrator - Region III G. Dick, Byron Project Manager - NRR S. Burgess, Senior Resident inspector - ByTon Office of Nuclear Safety -IDNS nonn44 9611130061 961104 PDR ADOCK 05000455 S

PDR k:nla:5046by2 doc:2 A Unicom Company J

i PLANT NAME:

Byron Station Unit 2 ECCS EVALUATION MODEL:

Small Break LOCA REPORT REVISION DATE:

11/1/96 CURRENT OPERATING CYCLE: 2 ANALYSIS OF RECORD Evaluation Model: NOTRUMP Calculation: Westinghouse SEC-SAll-4730-CO, May,1995 Fuel: VANTAGE 517 x 17 FQ = 2.50 FNAH = 1.65 SGTP = 30%

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Reference PCT PCT = 1723.0 F MARGIN ALLOCAT]ON A. PRIOR LOCA MODEL ASSESSMENTS NOTRUMP Specific Enthalpy Error (Note 3)

APCT =

20.0 F SALIBRARY Double Precision Error (Note 4)

APCT =

-15.0 F j

B. CURRENT LOCA MODEL ASSESSMENTS SBLOCTA Fuel Rod Initialization Error (Note 5)

APCT =

10.0 F Burst and Blockage / Time in Life (Note 2)

APCT =

30.0 F NET PCT PCT = 1768.0oF l

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PLANT NAME:

Byron Station Unit 2 ECCS EVALUATION MODEL:

Large Break LOCA REPORT REVISION DATE:

11/1/96 CURRENT OPERATING CYCLE: 2 ANALYSIS OF RECORD Evaluation Model: BASH Calculation: Westinghouse SEC-SAII-4747-C0, May,1995 Fuel: VANTAGE 517 x 17 FQ = 2.50 FNAH = 1.65 SGTP = 30%

Reference PCT PCT = 1915.0 F MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS Removed Upper Internal Assembly Alignment APCT =

28.0 F Pins (Note 1)

B. CURRENT LOCA MODEL ASSESSMENTS 100 psig IFBA., Use ofZIRLO fuel materials and futre increased peaking factors (Note 6)

APCT =

53.0 F NET PCT PCT = 1996.0 F kala.3046by2. doc:4

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Comed 10 CFR 50.46 Report Westinghouse Assessments Not Included in Rack-Ups

1. Removed Upper Internal Assembly Alignment Pins This penalty addresses the removal of upper internals alignment pins at Byron Station.

Two pins have been removed from Byron Unit I and six pins have been removed from Byron Unit 2. Removal of the alignment pins resulted in a LBLOCA PCT penalty of 5.0 F for Byron Unit 1. Byron Unit 2 previously accounted for the cut pins by penalizing FQ. Starting with Byron Unit 2 Cycle 6 a LBLOCA PCT penalty of 28.0 F was assessed instead of the FQ penalty. This will establish consistent treatment of the cut alignment pins for both Byron units.

2. Burst and Blockagefrime in Life Typically the Small Break LOCA was performed using BOL fuel performance data (PAD) and evaluated at other burnups using the SPIKE 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. The analysis of record for Zion already incorporated the penalty due to burst and blockage (a time m life study was performed). However, the axial nodalization error and the revised rod internal pressure model had synergistic effects in the burst and blockage model which result in a SBLOCA PCT penalty of 83 F for Zion.

As a result of the NOTRUMP specific enthalpy error, an additional 20 F penalty is applicable to Zion resulting in a total penalty of 103 F. As a result of the NOTRUMP specific enthalpy error and SALIBRARY double precision error, a 30 F burst and blockage / time in life penalty is r.ow applicable to the SBLOCA for Braidwood and Byron.

3. NOTRUMP Specific Enthalpy Error A typographical error was found in a line of coding in the NOTRUMP code. This line of coding was intended to model the calculation found in Equation L-127 of WCAP-10230P-A. Although the equation in the topical report is correct, the codmg 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 applies to j

the SBLOCA analyses for Braidwood, Byron, and Zion.

4. SALIBRARY Double Precision Errors During migration of the LOCA codes from the CRAY computer to UNIX-based platforms, programming errors were mr.de in two library routines related to improper specification of double precision variables. These errors were found and fixed during later code maintenance. Test cases with individual codes in the models demonstrated very small differences in only the SATAN and NOTRUMP code results, with correspondingly minor effects on final peak clad temperature 3redictions. Because the error only affects a very limited number of LBLOCA analyses w 1ich were performed on the UNIX platform prior to correcting the codes, the evaluation of effects for LBLOCA analyses were assessed on a plant-specific basis. The LBLOCA analyses for Byron, Braidwood, and Zion were not affected. For SBLOCA analyses performed on the UNIX platform, representative plant calculations resulted in an estimated generic effect of-15 F for affected analyses. This error only applies to the SBLOCA analyses for Braidwood and Byron since the Zion analyses were performed on the CRAY platform.

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Comed 10 CFR 50.46 Report

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Westinghouse Assessments Not Included in Rack-Ups

5. SBLOCTA Fuel Rod Initialization An error was discovered in the SBLOCTA code related to adjustments which are made as part of the fuel rod initialization process which is used to obtain agreement between the SBLOCTA model and the fuel data supplied from the fuel therma,-hydraulic design calculations at full power, steady-state conditions. Specifically, an adjustment to the pc * :r, which is made to compensate for adjustments to the assumed pellet diameter was incorrect. Additionally, updates were made to the fuel rod clad creep and strain model to 4

correct logic errors that could occur in certain transient conditions. These model revisions had a small effect on the fuel rod initialization process and could produce small effects during the transient. Due to the small magnitude of effects, and the interaction between l

the two times, they are being evaluated as a single, closely related effect, The error affects the model NOTRUMP. Representative plant calculations with the corrected model i

demonstrated that these revisions result in a predicted peak clad temperature increase on the order of 10 F. This 10 F penalty is applicable to Byron, Braidwood and Zion.

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6. 100 osig Backfill Pressure. Use of ZIRLO Fuel Materials and Increased Peaking Factors.

I Byron Unit 2 Cycle 7 reload fuel contains fuel rods initially pressurized to 100 psig. The previous cycle was pressurized to 200 psig. The reload fuel also contains ZIRLO 1

cladding, mid-grids and intermediate flow mixing grids. The arevious cycle used Zirc-4.

Future cycles analysis will contain increased peaking factors, lowever the current cycle does not make use of the analysis. The conservative combination of the effects is estimated at 53*F.

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