ML102140195

Day Report of Emergency Core Cooling System Model Changes Pursuant to the Requirements of 10 CFR 50.46

ML102140195
Person / Time
Site:	North Anna
Issue date:	07/29/2010
From:	Price A Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
10-440
Download: ML102140195 (7)

Text

VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, V I RGINIA 23261 July 29,2010 U.S. Nuclear Regulatory Commission Serial No.10-440 Attention: Document Control Desk NL&OS/ETS RO Washington, DC 20555 Docket No. 50-339 License No. NPF-7 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

NORTH ANNA POWER STATION UNIT 2 30 DAY REPORT OF EMERGENCY CORE COOLING SYSTEM (ECCS) MODEL CHANGES PURSUANT TO THE REQUIREMENTS OF 10 CFR 50.46 In accordance with 10 CFR 50.46(a)(3)(ii), Dominion hereby submits information regarding cumulative errors in AREVA's large break loss of coolant accident (LBLOCA) Emergency Core Cooling System (ECCS) Evaluation Model and the impact of the Measurement Uncertainty Recapture (MUR) for North Anna Power Station Unit 2 (NAPS 2) on Peak Cladding Temperature (PCT). provides a report describing the changes associated with the Areva LBLOCA ECCS Evaluation Model and impact of the MUR for NAPS 2.

Information regarding the effect of the PCT changes to the reported LBLOCA rack-up is provided for NAPS 2 in Attachment 2. To summarize the information in Attachment 2, the calculated PCT for the LBLOCA analyses is changed by an absolute value of 53°F to a new value of 1874°F for NAPS 2. The current accumulation of changes for these items (sum of absolute magnitudes) since the last 30-day report or reanalysis is greater than 50°F and is significant as defined in 10 CFR 50.46(a)(3)(i).

10 CFR 50.46(a)(3)(ii) requires the licensee to provide a report within 30 days, which includes a proposed schedule for providing a reanalysis or taking other action as may be needed to show compliance with 10 CFR 50.46. Dominion has reviewed the information provided by Areva and determined that the adjusted LBLOCA PCT values and the manner in which they were derived continue to conform to the requirements of 10 CFR 50.46. The identified errors in the LOCA analysis reduce the overall PCT and the positive change in PCT associated with the measurement uncertainty uprate was derived by performing a reanalysis at a bounding power level. Thus, Dominion has no immediate plans to re-perform the LBLOCA analysis since a substantial margin remains between the adjusted PCT (1874 0 F) and the 2200 0 F limit of 10 CFR 50.46.

Dominion routinely tracks adjustments to the LBLOCA calculated PCT values to ensure that reasonable margins to the acceptance value set by 10 CFR 50.46 are maintained.

This information satisfies the 30 day reporting requirements of 10 CFR 50.46(a)(3)(ii) .

Serial Number 10-440 Docket No. 50-339 30-Day ECCS Report Page 2 of 2 If you have any further questions regarding this submittal , please contact Mr. Thomas Shaub at (804) 273-2763.

Very truly yours, J. an rice Vi P esident - Nuclear Engineering Commitments made in this letter: None Attachments: (2)

1) Report of Changes in Areva Large Break LOCA ECCS Evaluation Model - North Anna Power Station Unit 2.

2) 30-Day Reporting of 10 CFR 50.46 Margin Utilization - North Anna Power Station Unit 2.

cc: U.S. Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Avenue , NE, Suite 1200 Atlanta , Georgia 30303-1257 NRC Senior Resident Inspector North Anna Power Station Mr. J. E. Reasor, Jr.

Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.

Suite 300 Glen Allen, Virginia 23060 Dr. V. Sreenivas NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 0-8 G9A Rockville, MD 20852-2738 Ms. K. R. Cotton NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North 11555 Rockville Pike Mail Stop 0-8 G9A Rockville , MD 20852-2738

Serial NO.1 0-440 Docket No. 50-339 ATTACHMENT 1 REPORT OF CHANGES IN AREVA LARGE BREAK LOCA ECCS EVALUATION MODEL NORTH ANNA POWER STATION UNIT 2 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

Serial Number 10-440 Docket No. 50-339 Report of Changes in AREVA LB LOCA ECCS Evaluation Model '

North Anna Power Station Unit 2 Identification of ECCS Evaluation Model Change The current large break loss of coolant accident (LBLOCA) analyses for North Anna Power Station Unit 2 (NAPS 2) were performed using the AREVA Realistic LBLOCA Evaluation Model (EM). AREVA identified two changes and the NAPS MUR also impacted the PCT rackup . The changes are described below and provide the results of an assessment to determine the impact on PCT.

Change: S-RELAP5 Kinetics and Heat Conduction Model changes (-29°F)

Previously, the Idaho National Laboratory (INL) announced an error in the coding of the point kinetics model. The corrections were provided by INL and then installed into S-RELAP5. Recently , INL announced that the previous error corrections were incorrect.

This was captured in an internal AREVA corrective action system item.

The AREVA corrective action item was drafted due to INL announcing that the heat conduction solution is incorrectly programmed. The error is associated with using the incorrect heat capacity when evaluating the right boundary mesh point. Instead of using the last (adjacent) mesh interval heat capacity, the code incorrectly uses the next to last mesh interval heat capacity. The affect of the error is maximized in cylindrical and spherical geometries with few mesh points, which can be minimized with an increased number of mesh points. The effect is further minimized by the S-RELAP5 Realistic LBLOCA, SBLOCA and Non-LOCA methodology guidelines requiring close mesh spacing at the left and right boundaries. This error exists exclusively in the RELAP5 series of codes.

The corrections for these two errors were installed into a new code version of S-RELAP5 and 50.46 evaluations were performed. North Anna Unit 2 has a PCT impact of -29°F.

Change: Steam Generator Entrainment bias factor (FIJ) change (-4°F)

An internal AREVA corrective action item was written to evaluate the impact of not entraining the appropriate amount of liquid into the steam generator tubes during a LBLOCA event. The Realistic LBLOCA methodology uses a bias on interphase friction at the steam generator tube sheet entrance to insure an acceptable amount of liquid is entrained into the steam generator tubes during a large break. The bias determination was performed by comparing calculated results from S-RELAP5 with measured data from the Upper Plenum Test Facility (UPTF) tests. The UPTF test facility represents a full scale, four loop PWR complete with the necessary hardware that can be used to represent geometry specific phenomena that occurs during a large or small break LOCA. The S-RELAP5 parameter that controls entrainment is interphase friction. The range of interphase friction spans several orders of magnitude between the flow regimes occurring in the hot leg, hot leg riser, steam generator inlet plenum and steam generator tube sheet. Consequently, determining the uncertainty in interphase friction Page 1 of 2

Serial Number 10-440 Docket No. 50-339 is not feasible so a conservative bias is used instead. The magnitude of the bias is determined by adjusting the S-RELAP5 Realistic LBLOCA Multiplier "FIJ" until S-RELAP5 over-predicts the entrainment observed in UPTF tests by an amount which is conservative although arbitrary. With the S-RELAP5 Kinetics and Heat Conduction Model changes mentioned previously, the FIJ multiplier of 1.75 is invalid and under-predicts the measured entrainment. The re-evaluation of the S-RELAP5 entrainment yielded a value of 5.0 for the FIJ multiplier, which is appropriate with a modeling change to the steam generator riser angle, greater than 30-degrees, and with the horizontal stratification flag set to off in the hot leg.

The corrections for this error were implemented and the PCT impact to North Anna Unit 2 is assessed to be - 4 OF.

Change: Impact of Measurement Uncertainty Recapture (MUR) (+20 OF)

North Anna evaluated the PCT impact of a 1.7% increase in core power for the MUR power uprate on Unit 2. For the MUR power uprate, an explicit Realistic LBLOCA analysis was performed by AREVA by performing an analysis with 59 cases being run with increased nominal core power from 2893 MWt to 2942.2 MWt, which bounds the MUR rated thermal power of 2940 MWt.

The resulting evaluation by AREVA identified a +20°F change to the PCT for NAPS 2.

Conclusion Dominion has performed an evaluation of PCT for comparison to 10 CFR 50.46 requirements. The Analysis of Record PCT for NAPS 2 is 1789°F. Considering the current PCT changes as well as all previously reported changes and errors, the licensing basis LBLOCA PCT is 1874°F for NAPS 2. The LBLOCA results have sufficient margin to the 2200°F limit specified in 10 CFR 50.46(b)(1). The current PCT assessment of 53°F is greater than the 50°F limit for reporting as defined in 10 CFR 50.46(a)(3)(i); hence, the change is considered significant and submittal of this 30 day report to the NRC is required.

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Serial Number 10-440 Docket No. 50-339 ATTACHMENT 2 30 DAY REPORTING OF 10 CFR 50.46 MARGIN UTILIZATION NORTH ANNA POWER STATION UNIT 2 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

Serial Number 10-440 Docket No. 50-339 10 CFR 50.46 MARGIN UTILIZATION - AREVA LARGE BREAK LOCA Plant Name: North Anna Power Station, Unit 2 Utility Name: Virginia Electric and Power Company Analysis Information EM: AREVA RLBLOCA EM Limiting Break Size: DEGB Analysis Date: 2004 Vendor: AREVA FQ: 2.32 F~H: 1.65 Fuel: Mixed: SGTP (%): 12 NAIF/Advanced Mark-BW Notes: Only AREVA Fuel in Plant, Analysis Covers Both Types Clad Temp COF) Notes LICENSING BASIS Analysis of Record PCT 1789 PCT ASSESSMENTS (Delta PCT)

A. Prior ECCS Model Assessments

1. Forslund-Rohsenow Correlation Modeling 64

2. RWST Temperature Assumption 8

3. LBLOCA/Seism ic SG Tube Collapse 0 ICECON Code Errors 0

4. RLBLOCA Choked Flow Disposition 22

5. RLBLOCA Changes in Uncertainty Parameters 10

6. Mixture Level Model Limitation in the S-RELAP5 Code -19

7. Point Kinetics Programming Issue with RELAP5-Based Computer Codes -20

8. Cold Leg Condensation Under Predicted by S-RELAP5 Following Accumulator Injection 0

9. Cross-Flow Junction Area in S-RELAP Model 0

10. Radiation to Fluid Heat Transfer Model Change -32 B. Planned Plant Modification Evaluations

1. Advanced Mark-BW Top Nozzle Modification 65

2. GSI-191 Sump Strainer 0

3. MUR Implementation 20 {1 }

C. 2009/2010 ECCS Model Assessments

1. S-RELAP5 Kinetics and Heat Conduction Model -29 {1 }

2. RODEX3A - Thermal Conductivity Degradation 0 {1 }

3. SG entrainment bias factor (FIJ) change -4 {1 }

D. Other

1. None 0 LICENSING BASIS PCT + PCT ASSESSMENTS PCT = 1874 NOTES:

{1} The current accumulation of changes for these items (sum of absolute magnitudes) since the last 30-day report or reanalysis is greater than 50°F and is significant as defined in 10CFR50.46(a)(3)(i).

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