RS-20-125, Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station

Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station

ML20283A568
Person / Time
Site:	Clinton
Issue date:	10/09/2020
From:	Simpson P Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
RS-20-125
Download: ML20283A568 (6)

Text

4300 Winfield Road Warrenville, IL 60555 630 657 2000 Office RS-20-125 10 CFR 50.46 October 9, 2020 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Clinton Power Station, Unit 1 Facility Operating License No. NPF-62 NRC Docket No. 50-461

Subject:

Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station

Reference:

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S. NRC, "Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station," dated October 10, 2019 This letter provides the annual report required by 10 CFR 50.46, "Acceptance criteria for emergency core cooling systems for light-water nuclear power reactors," for Clinton Power Station, Unit 1. The attachments describe the changes in accumulated peak cladding temperature since the previous annual report submitted in the referenced letter.

There are no regulatory commitments contained in this letter. Should you have any questions concerning this letter, please contact Mr. Kenneth M. Nicely at (630) 657-2803.

Respectfully, Patrick R. Simpson Sr. Manager Licensing Exelon Generation Company, LLC Attachments:

1. 10 CFR 50.46 Report

2. 10 CFR 50.46 Report Assessment Notes cc: NRC Regional Administrator, Region III NRC Senior Resident Inspector, Clinton Power Station

ATTACHMENT 1 Clinton Power Station, Unit 1 l SAFER/GESTR-LOCA l GNF2 Fuel 10 CFR 50.46 Report PLANT NAME: Clinton Power Station, Unit 1 ECCS EVALUATION MODEL: SAFER/GESTR-LOCA EVALUATION MODEL VENDOR: GNF/GEH REPORT REVISION DATE: October 9, 2020 CURRENT OPERATING CYCLE: 20 ANALYSIS OF RECORD CALCULATIONS

1. GEH Report 0000-0121-9100-R0, Clinton Power Station, GNF2 ECCS-LOCA Evaluation, October 2011 Fuel Analyzed in Calculation and in Operation: GNF21 Limiting Fuel Type: GNF2 Limiting Single Failure: High Pressure Core Spray Diesel Generator Limiting Break Size/Location: Double-Ended Guillotine Break of Recirculation-Pump Suction Piping Reference Peak Cladding Temperature (PCT): 1880 °F MARGIN ALLOCATION A. PRIOR LOCA MODEL ASSESSMENTS:

10 CFR 50.46 report dated October 26, 2012 (Note 1) PCT = 0 °F 10 CFR 50.46 report dated October 25, 2013 (Note 2) PCT = 40 °F 10 CFR 50.46 report dated October 24, 2014 (Note 3) PCT = -15 °F 10 CFR 50.46 report dated October 23, 2015 (Note 4) PCT = 0 °F 10 CFR 50.46 report dated October 21, 2016 (Note 5) PCT = 0 °F 10 CFR 50.46 report dated October 18, 2017 (Note 6) PCT = 30 °F 10 CFR 50.46 report dated October 18, 2018 (Note 7) PCT = 0 °F 10 CFR 50.46 report dated October 10, 2019 (Note 8) PCT = 0 °F Net PCT 1935 °F 1 Clinton Power Station (CPS) Cycle 20 operation is utilizing IronClad and ARMOR Accident Tolerant Fuel (ATF) Lead Test Rods (LTRs). As documented in GNF Report 005N2294 Rev. 1, these LTRs and LTAs are similar to the existing GNF2 fuel type in use at CPS and their LOCA response is bounded by the Reference 1 analysis.

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ATTACHMENT 1 Clinton Power Station, Unit 1 l SAFER/GESTR-LOCA l GNF2 Fuel 10 CFR 50.46 Report B. CURRENT LOCA MODEL ASSESSMENTS:

Notification 2019-05 (Note 9) PCT = 0 °F Notification 2020-01 (Note 9) PCT = 0 °F Total PCT change from current assessments PCT = 0 °F Cumulative PCT change from current assessments lPCTl = 0 °F Net PCT 1935 °F Page 2

ATTACHMENT 2 Clinton Power Station, Unit 1 10 CFR 50.46 Report Assessment Notes

1. Prior LOCA Model Assessment (2012)

The referenced letter reported that the GNF2 fuel design was introduced into the Clinton Power Station (CPS) core during the Reload 13 (Cycle 14) outage. There were no Emergency Core Cooling System (ECCS) related changes or modifications that affected the assumptions in the CPS Loss-of-Coolant Accident (LOCA) analysis of record.

[

Reference:

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S.

NRC, "Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station," dated October 26, 2012]

2. Prior LOCA Model Assessment (2013)

To address inaccuracies in thermal conductivity degradation, GEH replaced the GESTR-LOCA model with a newer model, PRIME. The dominant Peak Cladding Temperature (PCT) effect is from the PRIME thermal conductivity which produces higher fuel stored energy. The PCT impact identified in the referenced letter reflects the difference between the existing GESTR analysis PCT and a conservatively postulated PCT if the analysis were performed with the PRIME model. The CPS ECCS-LOCA analysis methodology remains GESTR based, and it will not be PRIME based until the ECCS-LOCA analysis is re-performed using PRIME. The notification resulted in a

+40 °F PCT impact to GNF2 fuel.

[

Reference:

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S.

NRC, "Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station," dated October 25, 2013]

3. Prior LOCA Model Assessment (2014)

The referenced letter identified four vendor notifications.

• The first notification addressed several accumulated updates to the SAFER04A model. These code maintenance changes had an individually and collectively insignificant effect on calculated PCT.

• The second notification corrected a logic error that was isolated, occurring with an indication that the expected system mass diverges from the calculated actual system mass. This error affects the ECCS flow credited as reaching the core. Correction of this error did not impact the PCT for GNF2 fuel.

• The third notification addressed an error with the imposed minimum pressure differential (P) for droplet flow above a two-phase level in the core. This error can create an inappropriate steam cooling benefit above the core two phase level. To correct this error, an explicit core P calculation was applied without regard to droplet condition resulting in a PCT of -15 °F to GNF2.

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ATTACHMENT 2 Clinton Power Station, Unit 1 10 CFR 50.46 Report Assessment Notes

• The fourth notification addressed an incorrect pressure head representation when defining the counter current flow limitation. Correction of this error did not impact the PCT for GNF2 fuel.

[

Reference:

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S.

NRC, "Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station," dated October 24, 2014]

4. Prior LOCA Model Assessment (2015)

Per the referenced letter, no vendor notifications of ECCS model errors/changes applicable to CPS were issued. There were no ECCS related changes or modifications at CPS that affect the LOCA analysis of record.

[

Reference:

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S.

NRC, "Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station," dated October 23, 2015]

5. Prior LOCA Model Assessment (2016)

Per the referenced letter, no vendor notifications of ECCS model errors/changes applicable to CPS were issued. There were no ECCS related changes or modifications at CPS that affect the LOCA analysis of record.

[

Reference:

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S.

NRC, "Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station," dated October 21, 2016]

6. Prior LOCA Model Assessment (2017)

Per the referenced letter, there were two vendor notifications of ECCS model errors/changes applicable to CPS.

• The first notification identifies that GNF2 leakage flow paths between the bundle and the bypass were incorrectly modeled. The correction to the model had an impact of

+30 °F.

• The second notification identifies that fuel rod plenum region was not modeled consistent with GNF2s 10 x 10 design. Plenum inputs were updated to reflect the current design with a 0 °F impact to PCT.

[

Reference:

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S.

NRC, "Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station," dated October 18, 2017]

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ATTACHMENT 2 Clinton Power Station, Unit 1 10 CFR 50.46 Report Assessment Notes

7. Prior LOCA Model Assessment (2018)

Per the referenced letter, no vendor notifications of ECCS model errors/changes applicable to CPS were issued. There were no ECCS related changes or modifications at CPS that affect the LOCA analysis of record.

[

Reference:

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S.

NRC, "Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station," dated October 18, 2018]

8. Prior LOCA Model Assessment (2019)

Per the referenced letter, no vendor notifications of ECCS model errors/changes applicable to CPS were issued. There were no ECCS related changes or modifications at CPS that affect the LOCA analysis of record.

[

Reference:

Letter from P. R. Simpson (Exelon Generation Company, LLC) to U.S.

NRC, "Annual Report of Emergency Core Cooling System Evaluation Model Changes and Errors for Clinton Power Station," dated October 10, 2019]

9. Current LOCA Model Assessment (2020)

Notification 2019-05 identifies that the upper and lower limits for the SAFER code forward and backward bypass leakage were coded incorrectly for the control rod guide tube to control rod drive housing interface backward leakage path. The error was estimated to have a zero-degree impact upon the GNF2 licensing basis PCT.

Notification 2020-01 identifies that the PRIME code contained errors in irradiation growth after a breakaway neutron fluence, thermal conductivity applied to the zirconium barrier for cladding temperature drop, and gap conductance during pellet-cladding gap closure.

The errors were estimated to have a zero-degree impact upon the GNF2 licensing basis PCT.

CPS Cycle 20 operation is utilizing IronClad and ARMOR Accident Tolerant Fuel (ATF)

Lead Test Rods (LTRs). These LTRs and LTAs are similar to the existing GNF2 fuel type in use at CPS and their LOCA PCT response is bounded by the standard GNF2 fuel analyzed in the analyses of record.

[

Reference:

GNF Report 005N2294 Rev. 1, "Technical Evaluation Report to Support ARMOR and IronClad Lead Test Assemblies at Clinton Power Station," dated August 2019]

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