ML12073A354

30-Day Report Pursuant to 10 CFR 50.46, Changes to or Errors in an Evaluation Model

ML12073A354
Person / Time
Site:	Oconee
Issue date:	03/09/2012
From:	Culp D Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
Download: ML12073A354 (10)

Text

David C. Culp Duke 10 CFR 50.46 Manager Energy.

Nuclear Engineering Duke Energy Corporation 526 South Church Street Charlotte, NC 28202 Mailing Address:

March 9,2012 EC08H / P. 0. Box 1006 Charlotte, NC 28201-1006 U. S. Nuclear Regulatory Commission 7043828833 Washington, D. C. 20555-001 704 382 7852 fax Attention: Document Control Desk David. Culp@duke-energy.com

Subject:

Duke Energy Carolinas, LLC (Duke Energy)

Oconee Nuclear Station, Units 1, 2, and 3 Docket Numbers 50-269, 50-270, and 50-287 30-Day Report Pursuant to 10 CFR 50.46, Changes to or Errors in an Evaluation Model 10 CFR 50.46 (a)(3)(ii) requires the reporting of changes to or errors in Emergency Core Cooling System (ECCS) evaluation models (EMs), or in the application of such models that affect the temperature calculation. On February 23, 2012, Duke Energy received a letter from AREVA identifying two changes which affect the large break loss of coolant accident (LBLOCA) analysis of record for Oconee Units 1, 2, and 3. The first change is an EM application error, and the second change is an EM modeling change. The Oconee small break LOCA (SBLOCA) analyses are not affected by these issues.

The enclosed Attachments provide a description of each LBLOCA EM Error Correction, and the associated impact to the Oconee LBLOCA analysis of record. AREVA identified the first item as an error in the determination of the end of ECCS bypass. Based on information supplied by AREVA, an assessment of this error results in a peak cladding temperature (PCT) decrease of 800F. AREVA identified the second item as an EM modeling change to include the effects of the upper plenum column weldments. Based on information supplied by AREVA, an assessment of this error results in a PCT increase of 80'F. Therefore, these two changes offset each other, resulting in no net change to the PCT results for the Oconee LBLOCA analysis of record.

An evaluation of the two changes identified above was performed by AREVA for the Oconee SBLOCA analyses. It was concluded that there is no change on the limiting SBLOCA analysis results. This conclusion is valid for the SBLOCA analyses performed at full-power, 75% partial-power, and 50% partial-power. Since there is no net change in the LOCA PCTs for these two changes, there are no plans for future reanalysis. This issue has been entered into Oconee's corrective action program as PIP 0-12-2225.

Included in this report are Mk-B1 1 fuel LOCA PCT summary tables and Mk-B-HTP mixed-core LOCA PCT summary tables for Units 1 and 3, and a full-core Mk-B-HTP LOCA PCT summary table for Unit 2. The LOCA results for Units 1, 2 and 3 remain unchanged from those previously reported. Since the PCTs are unchanged, the oxidation and whole core hydrogen generation are similarly unaffected, and remain acceptable.

www.duke-energy.com r

U.S. Nuclear Regulatory Commission March 9, 2012 Page 2 This information satisfies the 30-day reporting requirements of 10 CFR 50.46 (a)(3)(ii).

There are no regulatory commitments associated with this letter.

Please address any comments or questions regarding this matter to Jeff Thomas at (704) 382-3438 (Jeff. Thomas@duke-energy.corn).

Sincerely, David C. Culp Acting Vice President Nuclear Engineering Attachment Report of Error Corrections on AREVA LBLOCA ECCS Evaluation Model Table 1: Mk-B1 1 Peak Cladding Temperature Summary - Oconee Units 1 and 3 Table 2: Mk-B-HTP Mixed Core Peak Cladding Temperature Summary - Oconee Units 1 and 3 Table 3: Mk-B-HTP Full Core Peak Cladding Temperature Summary - Oconee Unit 2

U.S. Nuclear Regulatory Commission March 9, 2012 Page 3 xc:

V. M. McCree, Region II Administrator U.S. Nuclear Regulatory Commission Marquis One Tower 245 Peachtree Center Avenue NE, Suite 1200 Atlanta, GA 30303-1257 J. F. Stang, Senior Project Manager (ONS)

U. S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop 0-8 G9A Rockville, MD 20852-2738 A. T. Sabisch, NRC Senior Resident Inspector Oconee Nuclear Station

ATTACHMENT Report of Error Corrections on AREVA LBLOCA ECCS Evaluation Model Table 1:

Mk-B11 Peak Cladding Temperature Summary-Oconee Units I and 3 Table 2:

Mk-B-HTP Mixed Core Peak Cladding Temperature Summary - Oconee Units I and 3 Table 3:

Mk-B-HTP Full Core Peak Cladding Temperature Summary - Oconee Unit 2

Report of Error Corrections on AREVA LBLOCA ECCS Evaluation Model By letter dated February 23, 2012 (Reference 2), AREVA notified Duke Energy of two changes which affect the large break loss of coolant accident (LBLOCA) analysis of record for Oconee Units 1, 2, and 3. The first change is an EM application error, and the second change is an EM modeling change. The small break LOCA analyses are not affected by these issues.

AREVA identified the first item as an error in the determination of the end of ECCS bypass.

This issue is identified in AREVA Condition Report WebCAP 2012-165 as an error in the ECCS bypass calculational model that determines the end of total ECCS bypass. A mathematical error was discovered in the RELAP5/MOD2-B&W blowdown model control variables that calculate the time for total end of bypass. AREVA identified in the BWNT LOCA Evaluation Model (EM) BAW-1 01 92PA Rev. 0 (Reference 1) that the end of bypass calculations determine when an 80 percent condensation efficiency on the core flood tank (CFT) injected liquid could condense all the steam reaching the upper downcomer region. The control variables incorrectly calculated the steam energy flowing into the upper downcomer region. When the control variables were corrected, the end of bypass time was predicted approximately 2 seconds earlier, resulting in a shorter lower plenum refill period with a quicker onset of lower core quench and lower PCT. Based on information supplied by AREVA, an assessment of this error results in a peak cladding temperature (PCT) decrease of 800F.

AREVA identified the second item as an EM modeling change to include the effects of the upper plenum column weldments. This issue, identified in AREVA Condition Report WebCAP 2012-757, was discovered as part of a LBLOCA sensitivity study was being performed for the 205 FA Bellefonte plant with a revised upper plenum and upper head modeling that considered the changes in core cooling when upper plenum column weldments are explicitly modeled. This revised modeling reflects a more detailed noding arrangement in the reactor vessel upper plenum than was used and approved for application in the BWNT LOCA Evaluation Model (EM)

BAW-10192P-A Rev. 0 (Reference 1). A simplified column weldment model was developed for the 177 FA Oconee model based on approximations from the 205 FA Bellefonte model. When this simplified model was used, the scoping case with the column weldment modeled over the top of the hot channel resulted in reduced cooling during portions of the blowdown phase. As a result, the end of blowdown fuel temperatures increased and these changes translate into roughly a 40 F increase in the unruptured segment PCTs, while the ruptured segment is increases by roughly 80 F. The more limiting temperature change for the ruptured segment is used by AREVA for assessing the EM modeling change PCT increase as 80 F.

Based on information supplied by AREVA, the scoping analyses indicated little change from the currently reported LBLOCA PCT prior to either error correction. In other words, the net decrease in PCT from the ECCS bypass error correction is roughly equivalent to the PCT increase when the column weldments are modeled in the 177 FA plants. Therefore, these two errors offset each other with no net change to the current LBLOCA PCTs for the ONS-1, ONS-2 and ONS-3 plants.

The ECCS bypass calculation is not applicable to the Oconee SBLOCA analyses. The upper plenum column weldment modeling change was considered for SBLOCA and it was concluded that it will not affect the limiting results because the SBLOCA is a slower evolving transient with up flows in the core hot bundles such that there is no net change from the presence of a column weldment in the upper plenum. Therefore, there is no change to the current SBLOCA PCTs for the ONS-1, ONS-2 and ONS-3 plants.

Page 1 of 6

References

1. AREVA NP Topical Report BAW-10192P-A, Rev. 0, "BWNT LOCA - BWNT Loss-of-Coolant Accident Evaluation Model for Once-Through Steam Generator Plants,"

June 1998.

2. AREVA Letter FAB12-120 to S. B. Thomas (Duke Energy), "10 CFR 50.46 LOCA Report of Two EM Error Corrections (AREVA CR 2012-165: ECCS Bypass Mathematical Error and AREVA CR 2012-757: Upper Plenum Column Weldment EM Change),"

February 23, 2012.

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Report of Error Corrections on AREVA LBLOCA ECCS Evaluation Model Table 1: Mk-B11 I Peak Cladding Temperature Summary Oconee Units 1 and 3 Table 2: Mk-B-HTP Mixed Core Peak Cladding Temperature Summary Oconee Units I and 3 Table 3: Mk-B-HTP Full Core Peak Cladding Temperature Summary Oconee Unit 2 References for Tables 1, 2, & 3 A)

Letter, T. C. Geer (Duke) to USNRC, "Report Pursuant to 10 CFR 50.46, Changes to or Errors in an Evaluation Model", December 18, 2007. [ADAMS ML073580171]

B) Letter, T. C. Geer (Duke) to USNRC, "Report Pursuant to 10 CFR 50.46, Changes to or Errors in an Evaluation Model", July 29, 2008. [ADAMS ML0821300961 C) Letter, T. C. Geer (Duke) to USNRC, "30-Day Report Pursuant to 10 CFR 50.46, Changes to or Errors in an Evaluation Model", August 19, 2010. [ADAMS ML102360485]

D) Letter, G. J. St.Clair (AREVA) to S. B. Thomas (Duke), "10 CFR 50.46 LOCA Report of Two EM Error Corrections (AREVA CR 20120165: ECCS Bypass Mathematical Error and AREVA CR 2012-757: Upper Plenum Column Weldment EM Change)", Dated February 23, 2012, AREVA Letter FAB12-120.

E)

Letter, R. M. Glover (Duke) to USNRC, "30-Day Report Pursuant to 10 CFR 50.46, Changes to or Errors in an Evaluation Model", December 8, 2011. [ADAMS ML11347A193]

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Table 1: Mk-B1 1 Peak Cladding Temperature Summary - Oconee Units 1 and 3 LBLOCA PCT(°F)

Comments Evaluation model: RELAP5/MOD2-B&W Analysis of record POT 2035 Mark-B1 1 (M5), 17.7 kW/ft at 6.021 ft elevation Prior errors (APCT)

References A and B

1. Various 0

Prior evaluation model changes (APCT)

1. None 0

Errors (APCT)

Reference D

1. Error in ECCS Bypass Calculation

-80 Evaluation model changes (APCT)

Reference D

1. Upper Plenum Column Weldment Modeling

+80 Absolute value of errors/changes for this report (APCT) 0 Net change in PCT for this report 0

Final PCT 2035 SBLOCA Full Power -100% FP PCT(0F)

Comments Evaluation model: RELAP5/MOD2-B&W Analysis of record PCT 1461 (2 HPI Case) 0.15 ft2 break Prior errors (APCT)

1. None 0

Prior evaluation model changes (APCT)

1. None 0

Errors (APCT)

Reference C

1. EOC SBLOCA Axial Power Shape Error

+225 Evaluation model changes (APCT)

Reference D

1. Upper Plenum Column Weldment Modeling 0

Absolute value of errors/changes for this report (APCT) 225 Net change in PCT for this report

+225 Final PCT 1686 SBLOCA Reduced Power - 75% FP [1]

PCT(°F)

Comments Analysis of record PCT 1774 (1 HPI case) 0.075 ft2 break Prior errors (APCT)

1. None 0

Prior evaluation model changes (APCT)

1. None 0

Errors (APCT)

Reference C

1. EOC SBLOCA Axial Power Shape Error Unknown Evaluation model changes (APCT)

Reference D

1. Upper Plenum Column Weldment Modeling 0

Absolute value of errors/changes for this report (APCT)

Unknown Net change in PCT for this report Unknown Final PCT Unknown Operation Not Justified [2]

Notes

1. Partial power SBLOCA analysis with one HPI pump out of service, supports 30 day LCO for TS 3.5.2 Condition B. Also supports TS 3.5.2 Condition C1 and C2.

2. Entry to LCO window administratively not allowed. Refer to Oconee corrective action program item PIP 0-10-6229 for details.

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Table 2: Mk-B-HTP Mixed Core Peak Cladding Te perature Summary - Oconee Units 1 & 3 LBLOCA PCT(°F)

Comments Evaluation model: RELAP5/MOD2-B&W Analysis of record PCT 2020 Prior errors (APCT)

1. None 0

Prior evaluation model changes (APCT)

1. None 0

Errors (APCT)

Reference D

1. Error in ECCS Bypass Calculation

-80 Evaluation model changes (APCT)

Reference D

1. Upper Plenum Column Weldment Modeling

+80 Absolute value of errors/changes for this report (APCT) 0 Net change in PCT for this report 0

Final PCT 2020 SBLOCA Full Power -100% FP PCT(°F)

Comments Evaluation model: RELAP5/MOD2-B&W Analysis of record PCT 1397 (2 HPI Case) 0.15 ft2 break Prior errors (APCT)

1. None 0

Prior evaluation model changes (APCT)

1. None 0

Errors (APCT)

Reference C

1. EOC SBLOCA Axial Power Shape Error

+225 Evaluation model changes (APCT)

Reference D

1. Upper Plenum Column Weldment Modeling 0

Absolute value of errors/changes for this report (APCT) 225 Net change in PCT for this report

+225 Final PCT 1622 SBLOCA Reduced Power - 75% FP [1]

PCT(°F)

Comments Analysis of record PCT 1788 (1 HPI case) 0.075 ft2 break Prior errors (APCT)

1. Not Applicable (New Analysis performed in 2008)

N/A Prior evaluation model changes (APCT)

1. Not Applicable (New Analysis performed in 2008)

N/A Errors (APCT)

Reference C

1. EOC SBLOCA Axial Power Shape Error Unknown Evaluation model changes (APCT)

Reference D

1. Upper Plenum Column Weldment Modeling 0

Absolute value of errors/changes for this report (APCT)

Unknown Net change in PCT for this report Unknown Final PCT Unknown Operation Not Justified [2]

Notes

1. Partial power SBLOCA analysis with one HPI pump out of service, supports 30 day LCO for TS 3.5.2 Condition B. Also supports TS 3.5.2 Condition C1 and C2.

2. Entry to LCO window administratively not allowed. Refer to Oconee corrective action program item PIP 0-10-6229 for details.

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Table 3: Mk-B-HTP Full Core Peak Cladding Te perature Summary - Oconee Unit 2 LBLOCA PCT(°F)

Comments Evaluation model: RELAP5/MOD2-B&W Analysis of record POT 1913 Prior errors (APCT)

1. None 0

Prior evaluation model changes (APCT)

1. None 0

Errors (APCT)

Reference D

1. Error in ECCS Bypass Calculation

-80 Evaluation model changes (APOT)

Reference D

1. Upper Plenum Column Weldment Modeling

+80 Absolute value of errors/changes for this report (APCT) 0 Net change in POT for this report 0

Final POT 1913 SBLOCA Full Power -100% FP PCT(-F)

Comments Evaluation model: RELAP5/MOD2-B&W Analysis of record POT 1598 (2 HPI Case) 0.15 ft2 break Prior errors (APCT)

1. None 0

Prior evaluation model changes (APCT)

1. None 0

Errors (APCT)

1. None 0

Evaluation model changes (APCT)

Reference D

1. Upper Plenum Column Weldment Modeling 0

Absolute value of errors/changes for this report (APCT) 0 Net change in POT for this report 0

Final POT 1598 SBLOCA Reduced Power - 50% FP [1]

PCT(°F)

Comments Analysis of record POT N/A Will be reported under a separate LAR (Reference E)

Prior errors (APCT)

1.

N/A Prior evaluation model changes (APOT)

1.

N/A Errors (APCT)

1.

N/A Evaluation model changes (APCT)

Reference D

1. Upper Plenum Column Weldment Modeling 0

Absolute value of errors/changes for this report (APCT)

N/A Net change in POT for this report N/A Final POT N/A Operation Not Justified [2]

Notes

1. Partial power SBLOCA analysis with one HPI pump out of service, supports 30 day LCO for TS 3.5.2 Condition B. Also supports TS 3.5.2 Condition C1 and C2.

2. Pending review and approval of separate LAR. Refer to Reference E for additional details.

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