L-PI-12-095, Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown - Error Identified in ECCS Evaluation Model, 10 CFR 50.46

From kanterella
Jump to navigation Jump to search
Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown - Error Identified in ECCS Evaluation Model, 10 CFR 50.46
ML12291A537
Person / Time
Site: Prairie Island  Xcel Energy icon.png
Issue date: 10/16/2012
From: Sorensen J
Northern States Power Co, Xcel Energy
To:
Office of Nuclear Reactor Regulation, Document Control Desk
References
L-PI-12-095, LTR-LIS-12-414
Download: ML12291A537 (16)
v • d • e


Text

@ Xcel Energym L-PI-12-095 10 CFR 50.46 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington DC 20555-0001 Prairie Island Nuclear Generating Plant, Units 1 and 2 Dockets 50-282 and 50-306 Renewed License Nos. DPR-42 and DPR-60 Fuel Pellet Thermal Conductivitv Degradation and Peaking Factor Burndown - Error Identified in ECCS Evaluation Model, 10 CFR 50.46 As required by 10 CFR 50.46(a)(3)(ii), Northern States Power Company, a Minnesota corporation, doing business as Xcel Energy (hereafter "NSPM") submits this 30-day report due to an error discovered in an emergency core cooling system (ECCS) evaluation model for Prairie Island Nuclear Generating Plant (PINGP) Units 1 and 2.

The affected evaluation model is the 2004 Westinghouse Realistic Large Break Loss of Coolant Accident (LBLOCA) Evaluation Model using Westinghouse Automated Statistical Treatment of Uncertainty Method (ASTRUM), application to Pressurized Water Reactors (PWRs) with upper plenum injection.

The error occurred in the Westinghouse Performance Analysis and Design (PAD) code.

The error is due to the non-explicit modeling of thermal conductivity degradation that occurs in the fuel as it accumulates exposure. The effect of the thermal conductivity degradation is that as the fuel gains exposure it is less able to transfer heat resulting in higher fuel pellet temperatures.

A generic analysis was performed by Westinghouse through the PWR Owners Group using approaches reviewed and accepted by the NRC. The results were used to establish a conservative plant specific peak cladding temperature (PCT) penalty. The plant specific penalty is 227 OF for Unit I , and 340 OF for Unit 2. The current analysis retains considerable margin to the 2200 OF limit. The conservative nature of the PCT penalty coupled with the large amount of margin remaining provides assurance that compliance with 10CFR50.46 has been met, and that no reanalysis is necessary. The technical summary of this condition and updated PCT rack-up sheets are provided in the enclosures to this letter.

1717 Wakonade Drive East Welch, Minnesota 55089-9642 Telephone: 651.388.1121

Document Control Desk Page 2 Summaw of Commitments This letter contains no new commitments and no revisions to existing commitments.

Acting Site Vice-President, Prairie Island Nuclear Generating Plant Northern States Power Company - Minnesota Enclosures (2) cc: Regional Administrator, Region Ill, USNRC Project Manager, Prairie Island Nuclear Generating Plant, USNRC Resident Inspector, Prairie Island Nuclear Generating Plant, USNRC

ENCLOSURE 1 ECCS EVALUATION MODEL CHANGES AND ERRORS Prairie Island Nuclear Generating Plant, UNITS IAND 2 5 pages follow

PCT

SUMMARY

PI1 LBLOCA PI1 SBLOCA PI2 LBLOCA PI2 SBLOCA Analysis of 11/30/07 1/21/08 11130107 1/21/08 Record Date Analysis of 1765 959 1623 965 Record PCT Old Changes 0 0 0 0 and Errors (absolute sum)

Last NRC 6/26/12 (1) 6126112 (1) 06/26/12 ( I ) 6126112 (1)

Notification Date Projected PCT 1765 959 1623 965 From the Last NRC Notification New Errors or 227 0 340 0 Changes (from this Notification Only)

Total of 227 0 340 0 Changes and Errors (absolute Sum)

New Projected 1992 959 1963 1965 PCT (1) These dates reflect the LBLOCA and SBLOCA 201 1 annual report L-PI-12-046.

Attachment Ito LTR-LIS-12-414 September 20, 2012 Page 2 of 3 Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown

Background

~ u e pellet i thermal conductivity degradation (TCD) and peaking factor burndown were not explicitly considered in the Prairie lsland Unit 1 Best Estimate Large Break Loss-of-Coolant Accident (BE LBLOCA) Analysis of Record (AOR). Nuclear Regulatory Commission (NRC) lnformation Notice 2011-21 (Reference I ) notified addressees of recent information obtained concerning the impact of irradiation on fuel thermal conductivity and its potential to cause significantly higher predicted peak cladding temperature (PCT) results in realistic emergency core cooling system (ECCS) evaluation models. This evaluation provides an estimated effect of fuel pellet TCD and peaking factor burndown on the PCT calculation for the Prairie Island Unit 1 BE LBLOCA AOR. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-I 3451 (Reference 2).

~ f f e c t e dEvaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect A quantitative evaluation, as discussed in Reference 3, was performed to assess the PCT effect of fuel pellet TCD and peaking factor burndown on the Prairie Island Unit 1 BE LBLOCA analysis and concluded that the estimated PCT impact is 227°F for 10 CFR 50.46 reporting purposes. The peaking factor burndown, included in the evaluation, is provided in Table 1 and is conservative for the current cycle. Xcel Energy, Inc. and its vendor, Westinghouse Electric Company LLC, utilize processes which ensure that the LOCA analysis input values conservatively bound the as-operated plant values for those parameters and will be validated as part of the reload design process.

Table I:Peaking Factors Assumed i n the Evaluation of TCD c I (1) Includes uncertainties.

(2) Hot assembly average power follows the same burndown, since it is a function of FdH.

References I.NRC lnformation Notice 201 1-21, McGinty, T. J., and Dudes, L. A., "Realistic Emergency Core Cooling System Evaluation Model Effects Resulting From Nuclear Fuel Thermal Conductivity Degradation," December 13,201 1. (NRC ADAMS # MLI 13430785)

2. WCAP-13451, "Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting,"

October 1992.

3. 0G-12-386, "For lnformation Only - Input Supporting the PWROG LBLOCA Program Regarding Nuclear Fuel Thermal Conductivity Degradation (PA-ASC-1073, Revision 0)

(ProprietarylNon-Proprietary)," September 18, 2012.

Attachment I to LTR-LIS-12-414 September 20, 2012 Page 3 of 3 Westinghouse LOCA Peak Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Prairie Island Unit 1 Utility Name: Xcel Energy, Inc Revision Date: 9/20/2012 Analvsis Information EM: ASTRUM (2004) Analysis Date: 11/30/2007 Limiting Brealc Size: Split FQ: 2.5 FdH: 1.77 Fuel: 422 Vantage + SGTP (%): 10 Notes:

Clad Temp (OF) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT PCT ASSESSMENTS (Delta PCT)

A. PRIOR ECCS MODEL ASSESSMENTS 1 .None B..PLANNED PLANT MODIFICATION EVALUATIONS 1 . None 0 C. 2012 ECCS MODEL ASSESSMENTS 1 Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown D. OTHER*

1 .None LICENSING BASIS PCT + PCT ASSESSMENTS PCT = 1992

  • It is recommended that the licensee determine if these PCT allocations should be considered with respect to 10 CFR 50.46 reporting requirements.

References:

I . WCAP-16890-P, Revision 1, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 1 Using ASTRUM Methodology," June 2008.

2 . LTR-LIS-12-4 14, "Prairie Island Units 1 and 2, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown," September 20,2012.

Notes:

(a) This evaluation credits peaking factor burndown, see Reference 2.

to LTR-LIS-12-414 September 20,2012 Page 2 of 3 Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown

Background

Fuel pellet thermal conductivity degradation (TCD) and peaking factor burndown were not explicitly considered in the Prairie lsland Unit 2 Best Estimate Large Break Loss-of-Coolant Accident (BE LBLOCA) Analysis of Record (AOR). Nuclear Regulatory Commission (NRC) lnformation Notice 2011-21 (Reference 1) notified addressees of recent information obtained concerning the impact of irradiation on fuel thermal conductivity and its potential to cause significantly higher predicted peak cladding temperature (PCT) results in realistic emergency core cooling system (ECCS) evaluation models. This evaluation provides an estimated effect of fuel pellet TCD and peaking factor burndown on the PCT calculation for the Prairie lsland Unit 2 BE LBLOCA AOR. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-I3451 (Reference 2).

Affected Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect A quantitative evaluation, as discussed in Reference 3, was performed to assess the PCT effect of fuel pellet TCD and peaking factor burndown on the Prairie lsland Unit 2 BE LBLOCA analysis and concluded that the estimated PCT impact is 340°F for 10 CFR 50.46 reporting purposes. The peaking factor burndown, included in the evaluation, is provided in Table 1 and is conservative for the current cycle. Xcel Energy, Inc, and its vendor, Westinghouse Electric Company LLC, utilize processes which ensure that the LOCA analysis input values conservatively bound the as-operated plant values for those parameters and will be validated as part of the reload design process.

(1) Includes uncertainties.

(2) Hot assembly average power follows the same burndown, since it is a function of FdH.

References

1. NRC lnformation Notice 201 1-21, McGinty, T. J., and Dudes, L. A., "Realistic Emergency Core Cooling System Evaluation Model Effects Resulting From Nuclear Fuel Thermal Conductivity Degradation," December 13, 2011. (NRC ADAMS # MLI 13430785)
2. WCAP-13451, "Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting,"

October 1992.

3. OG-12-386, "For lnformation Only - Input Supporting the PWROG LB,LOCA Program Regarding Nuclear Fuel Thermal Conductivity Degradation (PA-ASC-1073, Revision 0)

(ProprietaryINon-Proprietary)," September 18, 2012.

to LTR-LIS-12-414 September 20,2012 Page 3 of 3 Westinghouse LOCA Peak Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Prairie Island Unit 2 Utility Name: Xcel Energy, Inc Revision Date: 9/20/20 12 Analvsis Information EM: ASTRUM (2004) Analysis Date: 11/30/2007 Limiting Brealc Size: Split FQ: 2.5 FdH: 1.77 Fuel: 422 Vantage + SGTP (%): 25 Notes:

Clad Temp (OF) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT PCT ASSESSMENTS (Delta PCT)

A. PRIOR ECCS MODEL ASSESSMENTS 1 .None B. PLANNED PLANT MODIFICATION EVALUATIONS 1 None C. 2012 ECCS MODEL ASSESSMENTS 1 . Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bumdown D. OTHERQ 1 . None LICENSING BASIS PCT + PCT ASSESSMENTS PCT= 1963

  • It is recommended that the licensee determine if these PCT allocations should be considered with respect to 10 CFR 50.46 reporting requirements.

References:

1 . WCAP-16891-P, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 2 Using ASTRUM Methodology," June 2008.

2 LTR-LIS-12-414, "Prairie Island Units 1 and 2, 10 CFR50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bumdown," September 20,2012.

Notes:

(a) This evaluation credits peaking factor burndown, see Reference 2.

ENCLOSURE 2 LBLOCA and SBLOCA Peak Clad Temperature Assessment Sheets 7 pages follow

Westinghouse Non-Proprietary Class 3 Westinghouse Electric Company

@~ e m i n ~ h a u s e Nuclear Sewices 1000 Westinghouse Drive Cranberry Township, Pennsylvania 16066 USA September 20,2012 Direct tel: (412) 374-2202 Direct fax: (724) 720-0857 e-mail: teoliscd@westinghouse.com Our ref: LTR-LIS-12-414 Prairie lsland Units I and 2 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown

Dear Sir or Madam:

The information documented in this letter is for Xcel Energy, Inc.'s use in making a determination relative to the reporting requirements of 10 CFR 50.46.

Attachments 1 and 2 to this letter document 10 CFR 50.46 reporting text and the estimated effects for the evaluations of burnup effects due to fuel pellet thermal conductivity degradation (TCD) and peaking factor burndown on the Prairie lsland Units I and 2 Best Estimate Large Break Loss-of-Coolant Accident (BE LBLOCA) analyses of record, respectively. The evaluations use the method described in Reference 1. A revised LBLOCA Peak Cladding Temperature (PCT) rackup sheet for each unit is included in the attachments. Note that the "Future" rackup sheets remain unchanged from the previously transmitted sheets since evaluating Prairie lsland Units I and 2 at Extended Power Uprate (EPU) conditions is outside the scope of the PWR Owners Group program (PA-ASC-1073).

Author: (Electronically Approved)* Co-author: (Electronically Approved)"

Carmen D. Teolis Aaron M. Everhard LOCA Integrated Services I LOCA Integrated Services I Verified: (Electronically Approved)" Verified: (Electronically Approved)*

Kevin J. Barber Katsuhiro Ohkawa, EM Lead LOCA Integrated Services I (50.46 reports only)

LOCA lntegrated Services I Approved: (Electronically Approved)"

Eric P. Husser, on behalf of Amy J. Colussy, Manager LOCA lntegrated Services I Reference 1: OG-12-386, "For Information Only - Input Supporting the PWROG LBLOCA Program Regarding Nuclear Fuel Thermal Conductivity Degradation (PA-ASC-1073, Revision 0) (ProprietaryINon-Proprietary)," September 18, 2012.

Attachment I: Prairie lsland Unit I,10 CFR 50.46 Reporting Text and Peak Cladding Temperature Rackup Sheet : Prairie lsland Unit 2, 10 CFR 50.46 Reporting Text and Peak Cladding Temperature Rackup Sheet

  • Electronically approved documents are authenticated in the electronic document management system.

O 2012 Wesfinghouse Electric Company LLC All Rights Reserved

Westinghouse Non-Proprietary Class 3 to LTR-LIS-12-414 September 20,2012 Page 1 of 3 Attachment I Prairie Island Unit I I 10 CFR 50.46 Reporting Text and Peak Cladding Temperature Rackup Sheets (3 pages, including cover page)

O 2012 Westinghouse Electric Company LLC All Rights Reserved to LTR-LIS-12-414 September 20,2012 Page 2 of 3 Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown

Background

Fuel pellet thermal conductivity degradation (TCD) and peaking factor burndown were not explicitly considered in the Prairie Island Unit I Best Estimate Large Break Loss-of-Coolant Accident (BE LBLOCA) Analysis of Record (AOR). Nuclear Regulatory Commission (NRC) lnformation Notice 2011-21 (Reference 1) notified addressees of recent information obtained concerning the impact of irradiation on fuel thermal conductivity and its potential to cause significantly higher predicted peak cladding temperature (PCT) results in realistic emergency core cooling' system (ECCS) evaluation models. This evaluation provides an estimated effect of fuel pellet TCD and peaking factor burndown on the PCT calculation for the Prairie Island Unit I BE LBLOCA AOR. This change represents a Non-Discretionary Change in accordance with Section 4.1.2 of WCAP-I 3451 (Reference 2).

Affected Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect A quantitative evaluation, as discussed in Reference 3, was performed to assess the PCT effect of fuel pellet TCD and peaking factor burndown on the Prairie Island Unit I BE LBLOCA analysis and concluded that the estimated PCT impact is 227°F for 10 CFR 50.46 reporting purposes. The peaking factor burndown, included in the evaluation, is provided in Table 1 and is conservative for the current cycle. Xcel Energy, Inc. and its vendor, Westinghouse Electric Company LLC, utilize processes which ensure that the LOCA ,analysis input values conservatively bound the as-operated plant values for those parameters and will be validated as part of the reload design process.

Table I: Peaking Factors Assumed i n the Evaluation of TCD II (1 \ Includes uncertainties.

i2j Hot assembly average power follows the same burndown, since it is a function of FdH.

References

1. NRC lnformation Notice 201 1-21, McGinty, T. J., and Dudes, L. A., "Realistic Emergency Core Cooling System Evaluation Model Effects Resulting From Nuclear Fuel Thermal Conductivity Degradation," December 13,2011. (NRC ADAMS # MLI 13430785)
2. WCAP-13451, "Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting,"

October 1992.

3. 06-12-386, "For lnformation Only - Input Supporting the PWROG LBLOCA Program Regarding Nuclear Fuel Thermal Conductivity Degradation (PA-ASC-1073, Revision 0)

(Proprietary/Non-Proprietary)," September 18, 2012.

to LTR-LIS-12-414 September 20, 2012 Page 3 of 3 Westinghouse LOCA Peak Clad Temperature Summary for ASTRUM Best Estimate Large Break Plant Name: Prairie Island Unit 1 Utility Name: Xcel Energy, Inc Revision Date: 9/20/2012 Analysis Information EM: ASTRUM (2004) Analysis Date: 11/30/2007 Limiting Brealc Size: Split PQ: 2.5 FdH: 1.77 Fuel: 422 Vantage + SGTP (%): 10 Notes:

Clad Temp (OF) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 1765 I PCT ASSESSMENTS (Delta PCT)

A. PRIOR ECCS MODEL ASSESSMENTS 1 None B. PLANNED PLANT MODIFICATION EVALUATIONS 1 None 0 C. 2012 ECCS MODEL ASSESSMENTS 1 . Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bumdown D. OTHER*

1 . None LICENSING BASIS PCT + PCT ASSESSMENTS PCT= 1992

  • It is recommended that the licensee determine if these PCT allocations should be considered with respect to 10 CFR 50.46 reporting requirements.

References:

I . WCAP-16890-P, Revision 1, "Best-Estimate Analysis of the Large-Break Loss-of-Coolant Accident for the Prairie Island Nuclear Plant Unit 1 Using ASTRUM Methodology," June 2008.

2 . LTR-LIS-12-414, "Prairie Island Units 1 and 2, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Bumdown," September 20,2012.

Notes:

(a) This evaluation credits peaking factor burndown, see Reference 2.

Westinghouse Non-Proprietary Class 3 to LTR-LIS-92-414 September 20,2012 Page 1 of 3 Attachment 2 Prairie Island Unit 2 10 CFR 50.46 Reporting Text and Peak Cladding Temperature Raekup Sheets (3 pages, including cover page)

O 2012 Westinghouse Electric Company LLC All Rights Reserved to LTR-LIS-12-414 September 20,2012 Page 2 of 3 Evaluation of Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown

Background

Fuel pellet thermal conductivity degradation (TCD) and peaking factor burndown were not explicitly considered in the Prairie Island Unit 2 Best Estimate Large Break Loss-of-Coolant Accident (BE LBLOCA) Analysis of Record (AOR). Nuclear Regulatory Commission (NRC) lnformation Notice 2011-21 (deference 1) notified addressees of recent information obtained concerning the impact of irradiation on fuel thermal conductivity and its potential to cause significantly higher predicted peak cladding temperature (PCT) results in realistic emergency core cooling system (ECCS) evaluation models. This evaluation provides an estimated effect of fuel pellet TCD and peaking factor burndown on the PCT calculation for the Prairie Island Unit 2 BE LBLOCA AOR. This change represents a Non-Discretionary Change in accordance with Section 4. I.2 of WCAP-13451 (Reference 2).

Affected Evaluation Model 2004 Westinghouse Realistic Large Break LOCA Evaluation Model Using ASTRUM Estimated Effect A quantitative evaluation, as discussed in Reference 3, was performed to assess the PCT effect of fuel pellet TCD and peaking factor burndown on the Prairie Island Unit 2 BE LBLOCA analysis and concluded that the estimated PCT impact is 340°F for 10 CFR 50.46 reporting purposes. The peaking factor burndown, included in the evaluation, is provided in Table Iand is conservative for the current cycle. Xcel Energy, lnc. and its vendor, Westinghouse Electric Company LLC, utilize processes which ensure that the LOCA analysis input values conservatively bound the as-operated plant values for those parameters and will be validated as part of the reload design process.

(1) Includes uncertainties.

(2) Hot assembly average power follows the same burndown, since it is a function of FdH.

References I.NRC lnformation Notice 2011-21, McGinty, T. J., and Dudes, L. A., "Realistic Emergency Core Cooling System Evaluation Model Effects Resulting From Nuclear Fuel Thermal Conductivity Degradation," December 13,2011. (NRC ADAMS # MLI 13430785)

2. WCAP-13451, "Westinghouse Methodology for Implementation of 10 CFR 50.46 Reporting,"

October 1992.

3. OG-12-386, "For lnformation Only - Input Supporting the PWROG LBLOCA Program Regarding Nuclear Fuel Thermal Conductivity Degradation (PA-ASC-1073, Revision 0)

(ProprietarylNon-Proprietary)," September 18, 2012.

to LTR-LIS-12-414 September 20, 2012 Page 3 of 3 Westinghouse LOCA Peak Clad Temperature Summnrjr for ASTRUM Best Estimate Large Break Plant Name: Prairie Island Unit 2 Utility Name: Xcel Energy, Inc Revision Date: 912012012 Analvsis Information EM: ASTRUM (2004) Analysis Date: 11/30/2007 Limiting Brealc Size: Split PQ: 2.5 PdH: 1.77 Fuel: 422 Vantage + SGTP (%): 25 Notes:

Clad Temp (OF) Ref. Notes LICENSING BASIS Analysis-Of-Record PCT 1623 1 PCT ASSESSMENTS (Delta PCT)

A. PRIOR ECCS MODEL ASSESSMENTS 1 . None B. PLANNED PLANTMODIFICATION EVALUATIONS 1 . None C. 2012 ECCS MODEL ASSESSMENTS 1 . Evaluation of Fuel Pellet Thermal ConductivityDegradation and Peaking Factor Burndown D. OTHER*

1 None LICENSING BASIS PCT + PCT ASSESSMENTS PCT- 1963

  • It is recommended that the licensee determine if these PCT allocations should be considered with respect to I0 CFR 50.46 reporting requirements.

References:

1 . WCAP-16891-P, "Best-Estimate Analysis of the Large-Break Loss-of-CoolantAccident for the Prairie Island Nuclear Plant Unit 2 Using ASTRUM Methodology," June 2008.

2 . LTR-LIS-12-414, "Prairie Island Units I and 2, 10 CFR 50.46 Notification and Reporting for Fuel Pellet Thermal Conductivity Degradation and Peaking Factor Burndown," September 20,2012.

Notes; (a) This evaluation credits peaking factor burndown, see Reference 2.

Retrieved from "https://kanterella.com/w/index.php?title=L-PI-12-095,_Fuel_Pellet_Thermal_Conductivity_Degradation_and_Peaking_Factor_Burndown_-_Error_Identified_in_ECCS_Evaluation_Model,_10_CFR_50.46&oldid=2460322"