ML17058A484
| ML17058A484 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 03/02/2017 |
| From: | Xcel Energy Inc |
| To: | Office of Nuclear Material Safety and Safeguards |
| Jacobs C, 301-415-6825 | |
| References | |
| CAC L25174 | |
| Download: ML17058A484 (23) | |
Text
Exemption Request for Restoring Dry Shielded Canister (DSC) 11 - 15 Compliance to 10 CFR Part 72 Pre-Submittal Meeting Monticello Nuclear Generating Plant Independent Spent Fuel Storage Installation (ISFSI)
Xcel Energy March 2, 2017 1
Introduction Xcel Energy
Pat Burke - Vice President Engineering and Technical Services
Kent Scott - Director Site Operations, MNGP
Mike Baumann - Director, Nuclear Fuels
Marty Murphy - Director, Nuclear Licensing, Regulatory Affairs
Scott Marty - Director, Dry Fuel Storage
Mark McKeown - Manager, Spent Nuclear Fuel
Glenn Adams - Project Licensing
Jay Silberg - Pillsbury Law TN Americas, LLC Raheel Haroon - Engineering Manager 2
Introduction Meeting Purpose Pre-Application presentation and feedback Review Basis for Proposed Exemption Request
Safety assured through design, material quality, welding and examination processes
Processes confirmed through inspection of DSC-16
Requested exemption balances consequences and risks
DSC 11 - 15 are in storage; transfer risks are eliminated
Additional examination would increase risk w/o significant increase in confidence Review Schedule 3
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Background===
Timeline 10/2013 Discovered PT examinations were non-compliant 7/2014 Submitted Exemption Request (ER) for DSC 11 - 16 12/2014 Withdrew ER for DSC 11 - 16 2/2015 Performed Phased Array Ultrasonic Exam (PAUT) DSC 16 9/2015 Submitted ER for DSC 16 (based on PAUT) 12/2015 Confirmatory Order to restore compliance within 5 years 6/2016 Exemption granted for DSC 16 10/2016 DSC 16 placed in Horizontal Storage Module (HSM) 12/2016 Submitted Project Plan 4
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Background===
CoC 1004 Dye Penetrant Exam (PT)
PT in accordance with TS 1.2.5 Based on ISG-4 Rev. 1 and ISG-15 TS 1.1.12.4, Alternatives to Codes and Standards PT at each layer is alternative to volumetric examination 5
Principles Balance Risks Nuclear Safety Industrial Safety Radiological safety Timely restoration to compliance Optimize NMSS staff review effort Leverage previously docketed information 6
Safety Basis Determination of Safety o Design o Material Quality o Weld Process o Examination 7
Normal TS Compliance ITCP He Leak Testing TS 1.2.4a QC PT QC VT Welder Inspect AWS Weld Experience - OE Welder Qualification Weld Process Qualification Weld Filler Quality Shell Fabrication Quality Lid Fabrication Quality Nominal material strength Weld layer < Critical Flaw Multiple-Layer Weld No NDT for Austenitic SS Weld Process Quality Design Examination
Safety Basis - Design Design Critical weld flaws are considered in the design Stress reduction factors are imposed to account for imperfections or flaws Creep is not plausible Cyclic loading has been considered and is below the threshold of ASME Code 8
Normal TS Compliance ITCP He Leak Testing TS 1.2.4a QC PT QC VT Welder Inspect AWS Weld Experience - OE Welder Qualification Weld Process Qualification Weld Filler Quality Shell Fabrication Quality Lid Fabrication Quality Nominal material strength Weld layer < Critical Flaw Multiple-Layer Weld No NDT for Austenitic SS Weld Process Quality Design Examination
Safety Basis - Design Design Multiple layer welds effectively eliminate pinhole leaks Flaws in austenitic stainless steels are not expected to exceed one weld bead Austenitic stainless steels are ductile and can withstand large flaws Use of nominal material strength in design
(<actual) 9
Safety Basis - Material QA Material Quality Lid fabrication quality Shell fabrication quality Weld filler quality Quality validated by Nuclear Oversight 10
Safety Basis - Weld Process Welding Process Welding program elements met requirements Experienced and qualified welders employed OEM Automated Welding System utilized Welding demonstrations performed Flat welding orientation is forgiving Ductile and easily weld-able base materials Evidence of good welding practices Process provided excellent results in 2008 11
Safety Basis - Examinations Examinations Welders performed visual inspection QC performed VT NDE Regarding the non-compliant PT exams:
Progressive PT exam does not preclude flaws 12
Safety Basis - Examinations Examinations ITCP, siphon port and vent port passed the helium leak test; this demonstrates the confinement function ITCP passed the vacuum test and pressure test, which support a determination of structural integrity OTCP root pass served as the barrier to in-leakage during the ITCP helium test and therefore provides some measure OTCP weld integrity 13
Safety Basis - Confirmation Processes Confirmed Through PAUT PAUT examination and analysis of DSC-16 confirmed processes produce acceptable welds Conservative flaw sets and application of design loads create margin to safety DSC 16 representative of the campaign DSC 16 Exemption PAUT Pressure Testing 1.2.3a Vacuum Testing TS 1.2.2 He Leak Testing TS 1.2.4a QC PT QC VT Welder Inspect AWS Weld Experience - OE Welder Qualification Weld Process Qualification Weld Filler Quality Shell Fabrication Quality Lid Fabrication Quality Nominal material strength Weld layer < Critical Flaw Multiple-Layer Weld No NDT for Austenitic SS Examination Weld Process Quality Design 14
- 1. Authorized by law
- 2. Not endanger life, property or the common defense and security
- 3. Otherwise in the public interest 15
Exemption Request 10 CFR 72.7 - Not endanger life or property Assurance of weld integrity as previously discussed Design, material quality, weld process, exams Confirmed by PAUT and analysis of DSC-16 Recognize DSCs 11 - 15 in Storage Mode at MNGP Site specific load cases allow additional margin Even in the case of loss of confinement, consequences are minimal
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Conclusion:==
Therefore the selected approach, to not do any more examinations, does not endanger life or property 16
Exemption Request 10 CFR 72.7 - Otherwise in the public interest Alternatives offer higher dose, greater risk, little increase in confidence Safety Safety Licensing Technological Alternative Dose / DSC Risk Confidence Challenges Challenges Proposed ER Null Null Null Null Null Unload - Reload 1.5 R High Nominal Increase Zero Zero Repair ITCP Weld 1.4 R High Nominal Increase Med High Lid Augmentation 1 R Med Nominal Increase High High PAUT DSC 11 in Rx Bldg 1 R Med Nominal Increase Med Zero PAUT DSC 11 - 16 in Rx Bldg 1R High Nominal Increase Null Zero In Situ PAUT - HSM Med Low Nominal Increase Null High In Situ PAUT - Drill HSM Low Med Nominal Increase Med High In Situ PAUT - TC Med Med Nominal Increase Med High Incremental Change Compared to Proposed Exemption Request 17
Exemption Request 10 CFR 72.7 - Otherwise in the public interest Significant Effort for transfer Obtain transfer cask, equipment and crew Mobilize, train and qualify crews Execute work Risks of Canister Transfer from HSM Stress of extraction (bottom welds)
Risk of binding and gouging during extraction Exposure of TC/DSC to more significant external events Risk of TC drop from Transfer Trailer (TT)
Risk of cask handling accident with Reactor Building Crane Radiological dose to workers 18
Exemption Request 10 CFR 72.7 - Otherwise in the public interest NUREG 1864 and EPRI 1009691 provide risk insights for dry fuel storage The transfer phase carries the highest risk Transfer also increases industrial risk 19 EPRI 1009691 Figure 3-1, Summary of Total Cask Lifecycle Risk by Phase
Exemption Request 10 CFR 72.7 - Otherwise in the public interest Certain radiological dose with any of the alternative Radiological risk of handling >> Radiological risk in Storage Theoretical risk in Storage described in UFSAR 8.2.8.3 No mechanism for such a release
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Conclusion:==
Therefore the selected approach, to not do any more examinations, is the least dose and least risk alternative, and therefore in the public interest 20
Examples Examples VSC-24 Confirmatory Action Letter (ca 1997): Inner shield (confinement) welds, subject to known cracking, were not subject to additional examination HI-STORM Enforcement Discretion (ca 2009): Canisters were loaded without fabrication welds being adequately leak tested Oconee DSC Exemption (ca 2014): Canisters were loaded without field welds being subject to a compliant helium leak test ANO HI-STORM Exemption (ca 2014): Applied safety risk of a retrieval operation to accept a canister loaded with a failed fission product barrier 21
Exemption Request - DSCs 11 - 15 Tentative Schedule o June 2017 Xcel Energy Submit ER o June 2018 NRC approve exemption o July 2018 Xcel Energy report Order satisfied Proposed plan meets deadline 3 years early o June 2021 Confirmatory Order deadline 22
Questions 23