ML12031A147

Day Report for Emergency Core Cooling System Model Changes of 10 CFR 50.46

ML12031A147
Person / Time
Site:	Millstone
Issue date:	01/25/2012
From:	Price J Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML12031A147 (7)

Text

--w Dominion Nuclear Connecticut, Inc.

5000 Dominion Boulevard, Glen Allen, Virginia 23060 om inio Web Address: www.dom.com January 25, 2012 U.S. Nuclear Regulatory Commission Serial No.11-708 Attention: Document Control Desk NL&OS/MAE RO Washington, DC 20555 Docket No. 50-336 License No. DPR-65 DOMINION NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION UNIT 2 30-DAY REPORT FOR EMERGENCY CORE COOLING SYSTEM MODEL CHANGES PURSUANT TO THE REQUIREMENTS OF 10 CFR 50.46 In accordance with 10 CFR 50.46(a)(3)(ii), Dominion Nuclear Connecticut, Inc. (DNC) hereby submits information regarding cumulative errors in AREVA's Small Break Loss of Coolant Accident (SBLOCA) Emergency Core Cooling System (ECCS) Evaluation Model that impacts peak clad temperature (PCT) for Millstone Power Station Unit 2 (MPS2). provides a report describing the changes associated with the AREVA SBLOCA ECCS evaluation model for MPS2.

Information regarding the effect of the PCT changes to the reported SBLOCA margin utilization is provided for MPS2 in Attachment 2. To summarize the information in , the calculated PCT for the SBLOCA analyses is changed by an absolute value of 87 0 F to a new value of 1801OF. This result represents a significant change in PCT, 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. DNC has reviewed the information provided by AREVA and determined that the adjusted SBLOCA PCT values and the manner in which they were derived continue to conform to the requirements of 10 CFR 50.46. As such, DNC considers the requirement for reconsideration for reanalysis specified in 10 CFR 50.46(a)(3)(ii) to be satisfied with the submission of this notification. DNC routinely tracks adjustments to the SBLOCA 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). If you have any further questions regarding this submittal, please contact Wanda Craft at (804) 273-4687.

Sincerely, J. an rice Vi e Pr sident -Nuclear Engineering

Serial No.11-708 Docket No. 50-336 ECCS Model Changes Page 2 of 2 Commitments made in this letter: None Attachments:

1) Report of Changes in AREVA Small Break LOCA ECCS Evaluation Model - Millstone Power Station Unit 2.

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

cc: US. Nuclear Regulatory Commission Region 1 475 Allendale Road King of Prussia, PA 19406-1415 C. J. Sanders Project Manager - Millstone Power Station U.S. Nuclear Regulatory Commission One White flint North 11555 Rockville Pike Mail Stop 08-B3 Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station

Serial No.11-708 Docket No. 50-336 ATTACHMENT 1 REPORT OF CHANGES IN AREVA SMALL BREAK LOCA ECCS EVALUATION MODEL MILLSTONE POWER STATION UNIT 2 DOMINION NUCLEAR CONNECTICUT, INC.

Serial No.11-708 Docket No. 50-336 ECCS Model Changes Attachment 1, Page 1 of 2 Report of Changes in AREVA Small Break LOCA ECCS Evaluation Model Millstone Power Station Unit 2 Identification of ECCS Evaluation Model Change The current small break loss of coolant accident (SBLOCA) analyses for Millstone Power Station Unit 2 (MPS2) was performed using the AREVA S-RELAP5 computer code. Since the last 30-day report, AREVA has identified two changes impacting peak clad temperature (PCT). 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 (+40 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 and that the recommended convergence criteria supplied with those corrections should be retained. This was captured in an internal AREVA corrective action system item.

A second AREVA corrective action item was drafted due to INL announcing that the heat conduction solution was 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 used 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 SBLOCA 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 10 CFR 50.46 evaluations were performed. MPS2 has a PCT impact of

+4 OF.

Change: Sleicher-Rouse single phase vapor heat transfer correlation (+83 0 F)

An internal AREVA corrective action item was written to evaluate the impact of modifying the formulation of the Sleicher-Rouse single phase vapor heat transfer correlation in the S-RELAP5 code. In developing a boiling water reactor loss of coolant accident analysis methodology using S-RELAP5, AREVA noticed that the behavior of

Serial No.11-708 Docket No. 50-336 ECCS Model Changes Attachment 1, Page 2 of 2 the Sleicher-Rouse single phase vapor heat transfer correlation differed from other correlations. Additionally, it was discovered that the formulation of the correlation in the S-RELAP5 code was different from the formulation of the correlation used in other industry codes. AREVA prepared an S-RELAP5 code version with the alternative formulation. The alternative formulation of the Sleicher-Rouse agreed more closely with the formulation of the correlation used in the other industry codes.

The results of plant sample problems indicate that the predicted SBLOCA PCT for MPS2 should be increased by 83 0F.

Conclusion DNC has performed an evaluation of MPS2 PCT for comparison to 10 CFR 50.46 requirements. The analysis of record PCT for MPS2 is 1941°F. Considering the current PCT changes, as well as the previously reported changes and errors, the licensing basis SBLOCA PCT is 1801OF for MPS2. The SBLOCA results have sufficient margin to the 2200OF limit specified in 10 CFR 50.46(b)(1). The current PCT assessment of 87 0 F is greater than the 50°F limit for reporting as defined in 10 CFR 50.46(a)(3)(i);

hence, the change is significant and submittal of this 30-day report to the NRC is required.

Serial Number 11-708 Docket No. 50-336 ATTACHMENT 2 30-DAY REPORTING OF 10 CFR 50.46 MARGIN UTILIZATION MILLSTONE POWER STATION UNIT 2 DOMINION NUCLEAR CONNECTICUT, INC.

Serial Number 11-708 Docket No. 50-336 ECCS Model Changes Attachment 2, Page 1 of 1 10 CFR 50.46 MARGIN UTILIZATION - SMALL BREAK LOCA Plant Name: Millstone Power Station, Unit 2 Utility Name: Dominion Nuclear Connecticut, Inc.

Analysis Information EM: PWR SBLOCA, S-RELAP5 Based Limiting Break Size: 0.08 ft2 Analysis Date: 01/02 Vendor: AREVA Peak Linear Power: 15.1 kW/ft Notes: None PCT (OF) Delta PCT (OF)

LICENSING BASIS Analysis of Record PCT 1941 PCT ASSESSMENTS (Delta PCT)

A. Prior ECCS Model Assessments

1. Decay Heat Model Error -133

2. Revised SBLOCA Guideline 0

3. Core Exit Modeling-Upper Tie Plate Flow Area -22

4. Point Kinetics Programming Issue with RELAP5-Based Computer Codes -8

5. S-RELAP5 Choked Flow Error with Non-Condensables Present 0

6. Radiation to Fluid Heat Transfer Model Change -64 B. Planned Plant Modification Evaluations

1. None 0 C. Current ECCS Model Assessments

1. RELAP5 Kinetics and Heat Conduction Model(1' 4

2. RODEX2 Thermal Conductivity Degradation{') 0

3. Sleicher-Rouse Correlation Modeling{'1 83 D. Other

1. None 0 LICENSING BASIS PCT + PCT ASSESSMENTS PCT = 1801 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 or equal to 50°F and is significant, as defined in 10CFR50.46(a)(3)(i).