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Category:Meeting Briefing Package/Handouts
MONTHYEARML24029A1742024-01-30030 January 2024 Constellation Pre-Application January 30, 2024, Meeting Slides - Proposed Alternative to Utilize Code Case N-932, Alternative Requirements for Acceptance of Containment Base Metal Corrosion or Erosion ML23317A0712023-11-14014 November 2023 NRC Pre-Submittal Meeting on November 14th, 2023 - TSTF-591 and Selected 50.69 License Condition Updates (EPID L-2023-LLM-0098) (Slides) ML23262B2602023-09-19019 September 2023 Slides - Constellation - Pre-Application EP 9/25/2023 Meeting Handout ML23255A1042023-08-11011 August 2023 Slides - Constellation - Pre-Application EP 9/18/2023 Draft CEG Presubmittal SG Performance Monitoring Plan Meeting Handout ML23157A0352023-06-0606 June 2023 Annual Assessment Meeting for Pa/Md/Ny/Nj Nuclear Power Plants - NRC Presentation Slides ML23103A4072023-04-13013 April 2023 Presentation Slides for Information Call on 4/13/23 N2E Recirc Discharge Nozzle Weld Repair 2nd Request for Alternative ML22301A0132022-11-0303 November 2022 Pre-Submittal Meeting Presentation Slides - Risk Informed Completion Time (TSTF-505) and Risk Informed Categorization and Treatmentof SSCs (10 CFR 50.69) Proposed License Amendments ML22305A5922022-11-0303 November 2022 Pre-Submittal Meeting Presentation Slides - Risk Informed Completion Time (TSTF-505) and Risk Informed Categorization and Treatmentof SSCs (10 CFR 50.69) Proposed License Amendments-Updated ML22222A1122022-08-0404 August 2022 NMP1 Torus Corrosion Presentation for August 2022 Final ML21314A4472021-11-10010 November 2021 Slides for Presubmittial Meeting for Proposed Alternative to Adopt ASME Code Case N-921 to Extend the Inservice Inspection Interval ML21165A1942021-06-16016 June 2021 Joint Annual Assessment Meeting for Pa/Md/Nj/Ny Nuclear Power Plants - Webinar Presentation ML21165A2882021-06-16016 June 2021 Joint Annual Assessment for Pa/Md/Nj/Ny Nuclear Power Plants - Webinar Presentation (Updated) ML20261G7322020-09-16016 September 2020 Pre-Submittal Slides Extend 120-month Isi/Ist Interval Under 50.55a ML20178A4202020-06-30030 June 2020 NEI Slides for June 30, 2020, Public Meeting on COVID-19 Response ML20170B0212020-06-23023 June 2020 NRC Pre-Submittal Meeting Byron Unit 2 One-Time Deferral of Reactor Pressure Vessel Head Penetration Nozzle (Rpvhpn) Inspections ML20175A8722020-06-23023 June 2020 Risk-Informed Inservice Inspection - U.S Nuclear Regulatory Commission (NRC) - Four Element Risk-Informed Approach ML20163A6552020-06-16016 June 2020 6-16-20 Byron Unit 2 Steam Generator License Amendment Request Pre-Submittal Meeting (NRC) - Byron Unit 2 LAR for One-Time Deferral of Steam Generator Inspections ML20169A5592020-06-16016 June 2020 Steam Generator License Amendment Request Pre-Submittal Meeting (NRC) - Byron Unit 2 LAR for One-Time Deferral of Steam Generator Inspections (Rev 1) ML20098D5082020-04-0909 April 2020 AST LOCA Approach to Elemental Iodine Removal - NRC Public Meeting on RAI 6 - April 9, 2020 ML20022A0262020-01-22022 January 2020 NEI Presentation Status Update for Ropte Short Term Action Plan: Removed Planned Unavailability for Mitigating Systems Performance Index ML19318F9512019-11-20020 November 2019 Presentation Slides for November 20, 2019, Pre-Application Meeting - Request for Revision to Quality Assurance Program Internal Audit Frequency ML19317C9952019-11-12012 November 2019 In-Service Testing Supplemental Position Indication Relief Request NRC Pre-Application Meeting November 18, 2019 ML19158A1202019-06-10010 June 2019 Rict & 50.69 LARs NRC Pre-submittal Meeting ML19161A2572019-06-0404 June 2019 BWR Fleet Msv/Srv - Testing Frequency Relief Request NRC Pre-Application Meeting June 4, 2019 ML19151A6602019-05-31031 May 2019 BWR Fleet Mssv/Srv Testing Frequency Relief Request NRC Pre-Application Meeting June 4, 2019 ML19133A0912019-04-22022 April 2019 Supplement to Containment Oxygen Concentration License Amendment Request ML19022A2002019-01-23023 January 2019 Request for Use of ASME Code Case N-879 for Exelon Nuclear Power Plants ML18347B3142018-12-19019 December 2018 Bwrvip/Asme Relief Request Discussion December 19, 2018 ML18334A2162018-11-30030 November 2018 Presentation Slides: Exelon BWR MSIV (Boiling-Water Reactor - Main Steam Isolation Valve) Leakage Optimization for NRC Pre-Submittal Meeting of December 6, 2018 ML18319A1272018-11-19019 November 2018 Slides for 11/19/18 Public Meeting - Exelon Fleet LAR for Common Language for TS 5.7 High Radiation Areas ML18054B3592018-02-27027 February 2018 Slide: NRC Pre-Submittal Meeting for Exelon Fleet LAR to Relocate TS Unit Staff Qualification ANSI Requirements to the QATR, February 27, 2018, Profile Info: Submitted by Frank Mascitelli ML17325A2772017-11-28028 November 2017 November 28, 2017 Pre-Submittal Teleconference Re Planned TSTF-542 LAR Presentation ML17306A0842017-11-0606 November 2017 Meeting Slide for Teleconference with Exelon Generation Company, LLC - Criticality Analysis for NMP1 Boraflex Racks: No Boraflex Credit, 3 Out of 4 Loading, and Cell Blockers ML17142A2382017-05-25025 May 2017 OEDO-17-00280 - Briefing Package for Drop-In Visit on June 9, 2017, by Senior Management of Exelon Generation Company, LLC with Chairman Svinicki, Commissioner Baran, and Commissioner Burns ML16153A3452016-06-0101 June 2016 Sign in Sheet and Handout ML16077A1562016-03-22022 March 2016 Fleet: Pre-application Teleconference with Exelon to Discuss a Potential License Amendment Request Regarding Operating Training Standards ML16075A3292016-03-16016 March 2016 OEDO-16-00165 - Briefing Package for Drop-In Visit on March 23, 2016, by Senior Management of Exelon Generation Company, LLC with the NRC Executive Director for Operations ML14084A5342014-03-26026 March 2014 Nrc/Nei Presentation Slides: 13-02 OIP Template Update ML13340A0912013-11-0101 November 2013 Regulatory Conference/Public Meeting - Loss of Shutdown Cooling - Ceng Presentation/Slides ML13059A3742013-03-13013 March 2013 Summary of Category 1 Public Meeting with Nine Mile Point Nuclear Station, Unit 2 Representatives to Discus Planned Amendment Request on Implementation of Mellla+ ML1212100442012-04-0303 April 2012 Meeting Slides - NFPA-805 Pre-Application Meeting with NRC Staff April 3, 2012 ML1113605612011-05-16016 May 2011 NRC Meeting Slides, Nine Mile Point & Fitzpatrick 2011 Annual Assessment Meeting ML0926506592009-09-15015 September 2009 Slides from the Public Meeting with Constellation Energy - Nine Mile Point ISFSI Presentation ML0913400442009-05-14014 May 2009 Annual Assessment Meeting Sign-in Sheet, April 30, 2009 ML0827705652008-10-27027 October 2008 Extended Power Uprate Pre-Application Meeting Slides ML0634800282006-12-0404 December 2006 Slides, Nine Mile Point 1 Alternate Source Term, from Nrc/Constellation Energy Meeting ML0619102902006-03-27027 March 2006 03/27/2006 Powerpoint Presentation - Nine Mile Point License Renewal NMP1 Drywell ML0609402022006-01-27027 January 2006 Rathje C 2000, Website Reference Used in Chapter 2 NMP FSEIS ML0534601142005-11-17017 November 2005 Preliminary Results of Environmental Review Nine Mile Point Power Station, Units 1 and 2, U.S. Nuclear Regulatory Commission, November 17, 2005 ML0509401192005-03-30030 March 2005 Handout Used in Meeting Held on March 30, 2005 Between the U.S. Nuclear Regulatory Commission Staff and the Constellation Energy Group, Inc. Representatives 2024-01-30
[Table view] Category:Slides and Viewgraphs
MONTHYEARML24029A1742024-01-30030 January 2024 Constellation Pre-Application January 30, 2024, Meeting Slides - Proposed Alternative to Utilize Code Case N-932, Alternative Requirements for Acceptance of Containment Base Metal Corrosion or Erosion ML23317A0712023-11-14014 November 2023 NRC Pre-Submittal Meeting on November 14th, 2023 - TSTF-591 and Selected 50.69 License Condition Updates (EPID L-2023-LLM-0098) (Slides) ML23262B2602023-09-19019 September 2023 Slides - Constellation - Pre-Application EP 9/25/2023 Meeting Handout ML23255A1042023-08-11011 August 2023 Slides - Constellation - Pre-Application EP 9/18/2023 Draft CEG Presubmittal SG Performance Monitoring Plan Meeting Handout ML23157A0352023-06-0606 June 2023 Annual Assessment Meeting for Pa/Md/Ny/Nj Nuclear Power Plants - NRC Presentation Slides ML23103A4072023-04-13013 April 2023 Presentation Slides for Information Call on 4/13/23 N2E Recirc Discharge Nozzle Weld Repair 2nd Request for Alternative ML23080A2972023-03-21021 March 2023 Presentation Slides for Information Call on 3/21/23 N2E Recirc Discharge Nozzle Weld Repair Request for Alternative NEI 99-01, Slides - Constellation - Pre-Application EP 2/23/2023 Meeting Slides2023-02-21021 February 2023 Slides - Constellation - Pre-Application EP 2/23/2023 Meeting Slides ML22301A0132022-11-0303 November 2022 Pre-Submittal Meeting Presentation Slides - Risk Informed Completion Time (TSTF-505) and Risk Informed Categorization and Treatmentof SSCs (10 CFR 50.69) Proposed License Amendments ML22305A5922022-11-0303 November 2022 Pre-Submittal Meeting Presentation Slides - Risk Informed Completion Time (TSTF-505) and Risk Informed Categorization and Treatmentof SSCs (10 CFR 50.69) Proposed License Amendments-Updated ML22222A1122022-08-0404 August 2022 NMP1 Torus Corrosion Presentation for August 2022 Final ML21314A4472021-11-10010 November 2021 Slides for Presubmittial Meeting for Proposed Alternative to Adopt ASME Code Case N-921 to Extend the Inservice Inspection Interval ML21165A1942021-06-16016 June 2021 Joint Annual Assessment Meeting for Pa/Md/Nj/Ny Nuclear Power Plants - Webinar Presentation ML21165A2882021-06-16016 June 2021 Joint Annual Assessment for Pa/Md/Nj/Ny Nuclear Power Plants - Webinar Presentation (Updated) ML21162A3322021-06-11011 June 2021 BWR Fleet Relief Request Associated with RPV Instrument Nozzle Repairs ML20261G7322020-09-16016 September 2020 Pre-Submittal Slides Extend 120-month Isi/Ist Interval Under 50.55a ML20178A4202020-06-30030 June 2020 NEI Slides for June 30, 2020, Public Meeting on COVID-19 Response ML20170B0212020-06-23023 June 2020 NRC Pre-Submittal Meeting Byron Unit 2 One-Time Deferral of Reactor Pressure Vessel Head Penetration Nozzle (Rpvhpn) Inspections ML20175A8722020-06-23023 June 2020 Risk-Informed Inservice Inspection - U.S Nuclear Regulatory Commission (NRC) - Four Element Risk-Informed Approach ML20169A5592020-06-16016 June 2020 Steam Generator License Amendment Request Pre-Submittal Meeting (NRC) - Byron Unit 2 LAR for One-Time Deferral of Steam Generator Inspections (Rev 1) ML20163A6552020-06-16016 June 2020 6-16-20 Byron Unit 2 Steam Generator License Amendment Request Pre-Submittal Meeting (NRC) - Byron Unit 2 LAR for One-Time Deferral of Steam Generator Inspections ML20098D5082020-04-0909 April 2020 AST LOCA Approach to Elemental Iodine Removal - NRC Public Meeting on RAI 6 - April 9, 2020 ML20022A0262020-01-22022 January 2020 NEI Presentation Status Update for Ropte Short Term Action Plan: Removed Planned Unavailability for Mitigating Systems Performance Index ML19158A1202019-06-10010 June 2019 Rict & 50.69 LARs NRC Pre-submittal Meeting ML19133A0912019-04-22022 April 2019 Supplement to Containment Oxygen Concentration License Amendment Request ML18347B3142018-12-19019 December 2018 Bwrvip/Asme Relief Request Discussion December 19, 2018 ML18334A2162018-11-30030 November 2018 Presentation Slides: Exelon BWR MSIV (Boiling-Water Reactor - Main Steam Isolation Valve) Leakage Optimization for NRC Pre-Submittal Meeting of December 6, 2018 ML18319A1272018-11-19019 November 2018 Slides for 11/19/18 Public Meeting - Exelon Fleet LAR for Common Language for TS 5.7 High Radiation Areas ML18054B3592018-02-27027 February 2018 Slide: NRC Pre-Submittal Meeting for Exelon Fleet LAR to Relocate TS Unit Staff Qualification ANSI Requirements to the QATR, February 27, 2018, Profile Info: Submitted by Frank Mascitelli ML17325A2772017-11-28028 November 2017 November 28, 2017 Pre-Submittal Teleconference Re Planned TSTF-542 LAR Presentation ML17306A0842017-11-0606 November 2017 Meeting Slide for Teleconference with Exelon Generation Company, LLC - Criticality Analysis for NMP1 Boraflex Racks: No Boraflex Credit, 3 Out of 4 Loading, and Cell Blockers ML16153A3442016-06-0101 June 2016 Oswego Chamber of Commerce Assessment Meeting Presentation ML16077A1562016-03-22022 March 2016 Fleet: Pre-application Teleconference with Exelon to Discuss a Potential License Amendment Request Regarding Operating Training Standards ML14084A5342014-03-26026 March 2014 Nrc/Nei Presentation Slides: 13-02 OIP Template Update ML13340A0912013-11-0101 November 2013 Regulatory Conference/Public Meeting - Loss of Shutdown Cooling - Ceng Presentation/Slides ML13059A3742013-03-13013 March 2013 Summary of Category 1 Public Meeting with Nine Mile Point Nuclear Station, Unit 2 Representatives to Discus Planned Amendment Request on Implementation of Mellla+ ML1212100442012-04-0303 April 2012 Meeting Slides - NFPA-805 Pre-Application Meeting with NRC Staff April 3, 2012 ML1113605612011-05-16016 May 2011 NRC Meeting Slides, Nine Mile Point & Fitzpatrick 2011 Annual Assessment Meeting ML0926506592009-09-15015 September 2009 Slides from the Public Meeting with Constellation Energy - Nine Mile Point ISFSI Presentation ML0827705652008-10-27027 October 2008 Extended Power Uprate Pre-Application Meeting Slides ML0827503872008-09-29029 September 2008 Enclosure 2 Meeting Slides ML0811403012008-04-23023 April 2008 NRC Annual Performance Assessment Meeting ML0807901872008-03-18018 March 2008 NRC Annual Performance Assessment Slides, 2007 Reactor Oversight Program ML0712704232007-04-24024 April 2007 Constellation Slides - Nine Mile Point Meeting Annual Assessment Summary 2006-07 ML0710100842007-04-10010 April 2007 Slides for 04/24/2007 Nine Mile Point Annual Assessment Meeting ML0634800282006-12-0404 December 2006 Slides, Nine Mile Point 1 Alternate Source Term, from Nrc/Constellation Energy Meeting ML0630003542006-09-26026 September 2006 Slides for Constellation Energy Nine Mile Point 2 Extended Power Uprate Meeting ML0615106012006-05-23023 May 2006 EPRI HRA Users Group Review of Draft NUREG-1842 ML0609500372006-04-0505 April 2006 Public Meeting, Nine Mile Point Nuclear Station, Slides ML0619102902006-03-27027 March 2006 03/27/2006 Powerpoint Presentation - Nine Mile Point License Renewal NMP1 Drywell 2024-01-30
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NMP1 Torus Corrosion As of 1R26 - April 2021
Disclaimer This training session is being recorded for future use in the NRCs knowledge management program. The recorded contents of the session, including any questions posted by audience members, will be preserved in accordance with the NRCs record management program and are subject to FOIA disclosure. Please refrain from including any sensitive information (i.e., SUNSI) in any questions that you may ask.
Please leave your chat box open to view all questions and answers posed during the session.
Safety Issues and Best Inspector Practices
- Licensee Evaluation was not Technically Justified
- Time between examinations (20 years) was excessive
- In depth independent safety review and analysis can be time consuming - Take the time
71111.08 Inservice Inspection Activities
- If applicable, review at least one volumetric or surface examination from the previous outage with relevant indications that the licensee analytically evaluated and accepted for continued service. The licensees acceptance needs to be in accordance with the ASME Code or an NRC-approved alternative. Confirm that any indications were examined for acceptability for continued service.
10CFR55a.(g)(4)- ASME Section XI
- Requirements for examination (component, methods, boundaries),
components), acceptance criteria, frequency of examination, qualifications, repair
- 10-year inspection interval. Each interval divided into 3 periods.
- Section IWE - Requirements for Class MC and Metallic Liners of Concrete Containments
- If ASME Section XI Indication that doesnt meet acceptance criteria. 3 options (IWE-3122):
- Reexamine it and it meets acceptance criteria.
- Evaluate and accept it for further service
Section XI IWE Examination Requirements
- Item E.12 - Wetted Surfaces of Submerged Areas
- General Visual Examination
- Once per 10-year interval
- IWE-3510 Acceptance Criteria
2019 1R25 Owners Activity Report (OAR)
- Sometimes referred to as the 90 Day report
- Summary of Repair Activities
- Listing of items with flaws or relevant conditions that exceeded acceptance criteria and required evaluation to determine acceptability for continued service.
- Selected the Torus evaluation as it is primary containment, the last of the fission product barriers. (Risk Informed)
Nine Mile Point Unit 1
- License extended to 2029.
- Mk-1 Containment, Isolation Condenser, no HPCI or RCIC.
MK-1 Containment Terminology and Area of Interest Non-Vent Bay Vent Bay 8 Downcomers 4 Downcomers Area of Interest
Vent Header 1R24 (2019) Torus Examination Results
- Indications reported by divers.
- Tiger Striping - vertical stripes of black oxide covered steel and bare steel
- Black oxide stripes approximately 1 inch wide
- Bare metal stripes approximately 1/2 inch wide
- Vertical stripes extend to at most 9 feet below waterline.
- 1 large area of bare metal, could not be measured (Bay 8)
- 2 large pits (.08 inches deep by 0.5 inch dia. and 0.1 inches deep by 3 inch dia.) (Bay 4)
- Bays 1-20 examined and recorded separately
Tiger Stripe Corrosion
- Measured by divers using gauges in 2019 during Section XI, IWE Exams
- 4-6 feet from surface of water along inside and outside diameter walls of torus.
- Dark oxide high points, bare metal low points
- Appears in photographs taken in 1999 when torus was drained (next slide)
- Area of tightly adherent rust scale
- Bay 8 had conditions similar to bare metal low points without dark oxide high points.
1999 Inspection of Torus (Drained)
Licensee Use As-Is Evaluation
- ASME Requires Evaluation but doesnt specify how to do it
- Lowest average wall thickness reading - Bay 8 - 0.448 inches (TCMP - discussed later)
- Deepest measured valley - 0.070 inches
- Acceptance Criteria - Required minimum wall in area of degradation - 0.397 inches
- Calculation of remaining wall thickness
- Remaining wall: 0.448 - 0.070 = 0.378 inches - Below minimum required wall.
- Average remaining wall = [0.448 + 2*(0.378)]/3 = 0.401 with a required 0.397 at that location.
Inspector Questions
- Evaluation seemed simplistic.
- Does the evaluation justify structural integrity to the next examination?
- Is the calculation technically justifiable?
- Where did the remaining wall thickness values come from?
- What is the required minimum wall thickness?
- What is the corrosion mechanism?
- What is the corrosion rate of the tiger strip areas?
- How long will the evaluation be good for?
- Are there any reinspection requirements?
Inspector Mapping of Licensees Data Inside Bay Outside Bay Waterline 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 AVG Values Waterline 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 0 Waterline Tightly Adherent Rust Scale 0 5 5 10 Tigers Stripes 10 15 15 20 Special Area TCMP Monitored 20 25 Pits/Other Degradation 25 30 General 30 35 35 40 40 45 45 50 50 55 55 60 60 65 65 70 70 75 .397 Required Min Wall 75 80 80 85 Non-Vent Bay 85 90 90 95 95 100 100 105 105 110 Non-Vent 110 115 Vent Bay 115 120 120 125 125 130 130 135 135 140 140 145 145 150 150 155 155 160 160 165 165 170 Vent Bay 170 175 175 180 180 185 185 190 190 195 195 200 200 205 205 210 210 215 215 220 220 225 225
Evaluation
- The calculation method seemed very simplistic, and the basis wasnt discussed in the evaluation.
- Deriving design equations is not my specialty.
- Best practice: Ask for help when you need it.
- NRC has lots of specialists. They can save you lots of time.
- Contacted NRR Staff from DNRL/DEX for expertise.
- Determined that the basis was in design hoop stress calculations and use of average remaining wall thickness was adequate for showing structural integrity of the torus.
Inspector Concerns with Evaluation
- Engineering evaluation did not demonstrate integrity to next exam.
- Licensee showed 4 mils margin.
- No corrosion rate determined
- Evaluation used old data. (2017 vice 2019 data)
- Result was 1 mil margin vice 4 mils in original evaluation in 2019.
- Did not update as new data received - Using 2020 data, zero mils margin.
- Licensee reevaluated in response to inspector concerns
- Used weighted average of typical (average) tiger stripe depth and thinnest remaining wall average wall thickness in each bay.
- Generated a corrosion rate to show structural integrity to next required examination with little margin.
- Pitting in Bay 4 - Used approved method.
- Bay 8 Intermediate Area - Licensee took UT thickness measurements to determine adequate thickness.
Inspector Concerns with Exam Frequency
- Examinations completed in 1989, 1999 and 2019
- 10-year frequency required by IWE
- Where is the 2009 examination?
Inspector Retrieved Examination History Dec Aug Aug Aug 1999 2009 2019 2029 ISI Plans 1st CISI Interval 2nd CISI Interval 3rd CISI Interval July 2003 - Letter forwarding RFO April 2019 - Torus Examination - Divers 15/16/17 OARs states taking credit for April 99 inspection for 1st Interval Issues April 1999 - RFO-15 Torus Drained for
- 10 CFR 50.55a (g)(6)(ii)(B)(3) addresses the use of Expedited Examination an expedited examination to satisfy a required interval examination (1997 version of 10CFR)
September 1996 - 50.55a requires inspection of Class MC and CC Components by September 2001
- Sec XI - Should be scheduled in same period
- No inspection occurred between April 1999 and April 2019
Inspection Results *NMP Resident Report 2021002 (ML21222A021)*
- Green finding and associated NCV of ASME Section XI, paragraph IWE-3122.3, Acceptance by Engineering Evaluation, when Exelon performed an engineering evaluation that did not meet the applicable requirements in ASME Section XI, subsection IWE as required by 10 CFR Part 50.55a(g)(4)(v). Specifically, the engineering evaluation did not demonstrate that the torus wall thickness satisfied the minimum wall thickness requirements in their design specification through the period the evaluation applied which ends in 2023.
- Green finding and associated non-cited violation (NCV) of ASME Section XI Subparagraph IWE-2412(a), Inspection Program B when Nine Mile Point did not perform an inspection for wetted surfaces of submerged areas (ASME Item E1.12) at Unit 1 in the first containment inservice inspection interval which spanned between December 26, 1999, and August 22, 2009.
Next Steps
- Licensee is performing a new finite element analysis with hopes to recover some margin and refining minimum wall requirements.
- Examination is due during 2023 outage.
- Licensee to sample the tiger stripe area to determine corrosion mechanism and corrosion rate.
Questions?
Backup Slides Minimum Wall Requirements Location Dependent Vent Bay Non-Vent Bay
Minimum Wall Thickness Requirements
- Dependent on Bay type and location on torus shell
- Accounts for hydrodynamic effects on shell due to LOCA and SRV lifts
- 0.460 - As Built Thickness
- 0.431 - Minimum required wall due to hydrodynamic effects
- Min required wall at most stressed location.
- Torus Corrosion Monitoring Program
- 0.397 - Accident Pressure only
- Min required wall for pressure of 35 psi
What is the corrosion mechanism?
- TCMP - determines and trends the degradation in the wall thickness due to general corrosion.
- Requires presence of oxygen and since torus is inerted, corrosion rate is low.
- Cause and mechanism is not known at this time.
- Potential causes - based upon internet research
- Sulphur reducing bacteria (internet research)
- Anaerobic - flourishes in oxygen deficient environments (Inerted)
- Dormant when oxygen is present
- Licensee will be sampling the tiger stripe area in the upcoming outage to identify the mechanism.
What is the corrosion rate of the tiger stripe area?
- Depends on when you start the clock.
- Can see the stripes in 1999
- Licensee started the clock in 1989 based upon examination reports done in an outage
- Done by examiners in an IBRB.
- Could only see 2-3 feet below water surface due to murkiness of water and lighting.
- My read was that the description fit the tightly adhered rust scale region identified in 2019.
- Licensee claimed it identified the tiger stripes.
- Licensees responsibility. Adamant to start in 1989.
- Why is this important? Tiger strip corrosion rate determines how long the evaluation is good for.
- Cause and mechanism is not known at this time.
- Potential causes - based upon internet research
- Sulphur reducing bacteria (internet research)
- Anaerobic - flourishes in oxygen deficient environments (Inerted)
- Dormant when oxygen is present
- Licensee will be sampling the tiger stripe area in the upcoming outage to identify the mechanism.
How long is the evaluation good for?
- Worst case thinnest plate from TCMP in whole torus.
- Worst case deepest tiger stripe in whole torus.
- The 2019 evaluation used TCMP results from 2017 when results from 2018 and 2019 were available.
- Substitute 2019 data in - less than 1 mil margin
- Substitute 2020 data - at minimum wall
- 2021 data - below minimum wall
- General Corrosion - TCMP - 5 mils/year
- Tiger stripe corrosion rate
- Updated evaluation method
- Evaluated bay by bay using TCMP data and actual tiger stripe data for the bay being evaluated.
- Using 30 year tiger strip corrosion rate - evaluation is good until 2024.
How did we get here?
How did we make it to 2021 and the first indications there was a problem was when minimum wall and containment operability was being questioned?
Where did the data come from?
- Torus Corrosion Monitoring Program - General Corrosion
- Annual Ultrasonic Thickness Tests taken at 6 worst case locations in Torus since 1995.
- Determines an Average minimum remaining wall thickness at those 6 locations
- Divers measurement of depth of tiger stripes.
- How accurate were the measurements?
Next Week:
Vogtle AP1000 an Overview