ML032090144
| ML032090144 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 07/17/2003 |
| From: | South Texas |
| To: | Office of Nuclear Reactor Regulation |
| Thadani M, NRR/DLPM, 415-1476 | |
| References | |
| TAC MB8435 | |
| Download: ML032090144 (27) | |
Text
7/17/03 1
Bottom Mounted Instrument Penetration Condition Resolution
7/17/03 2
STP Participants Tom Jordan VP, Engineering & Tech Services Mark McBurnett Manager, Quality & Licensing Steve Thomas Manager, Plant Design Tim Bowman Unit 1 Operations Manager Michael Lashley Test Engineering Supervisor Bill Humble NSSS Supervisor Wayne Harrison Licensing Engineer Ulhas Patil Design Engineer
7/17/03 3
INTRODUCTORY REMARKS Mark McBurnett Manager, Quality & Licensing
7/17/03 4
Agenda Introductory Remarks Mark McBurnett Summary Tom Jordan Root Cause Process and Monitoring / Inspection Plan Steve Thomas Return to Service Tim Bowman
7/17/03 5
Desired Meeting Outcome NRC has sufficient information to complete their assessment
7/17/03 6
SUMMARY
Tom Jordan Vice President, Engineering & Technical Services
7/17/03 7
Evidence of Very Small Leakage Found in Routine Inspection
7/17/03 8
BMI Guide Tube Penetration
7/17/03 9
Extensive NDE Campaign Conducted
7/17/03 10 Eddy Current J-Groove Probe
7/17/03 11 Developed Technology to Identify Wastage
7/17/03 12 Comprehensive Examination Performed Using Industry Experts
- UT from penetration tube ID
- Enhanced visual exam of J-groove weld surface
- Volumetrically interrogate vessel base metal for wastage
- ET from penetration tube ID
- Profilometry
- Borescope examinations
- Helium tests
- Metallurgical analyses of removed nozzle remnants
- Boat sample analyses
7/17/03 13 Examination Results
- Penetration #1
- Three axial indications, one leak path
- Penetration #46
- Two axial indications, one leak path
7/17/03 14 Permanent Half-Nozzle Repair Alloy 690 replacement nozzle Alloy 52 weld pad Alloy 52 J-Groove weld Original BMI Thimble Guide Tube Original structural weld Mechanical plug used during repairs (not shown)
Existing BMI nozzle NiCrFe socket weld
7/17/03 15 Repair of Both Nozzles Complete
7/17/03 16 Remaining Activities Boat sample analysis Sep 21 Nozzle remnants analysis Sep 21 LER supplement Oct 12
7/17/03 17 Condition Limited to the Two Identified Nozzles
- Routine inspection identified very low leakage
- Extensive NDE confirmed condition limited to two penetrations
- Axial cracks in tubes
- No wastage
- Substantial safety margin existed
- Repairs are complete
- Monitoring / inspection plan developed
7/17/03 18 ROOT CAUSE PROCESS and MONITORING / INSPECTION PLAN Steve Thomas Manager, Plant Design
7/17/03 19
7/17/03 20 Comprehensive NDE Narrows Consequences
- No circumferential cracks
- No cracks above or below J-groove weld
- No wastage
- UT examination
- Visual examination
- No iron in residue
- Very small deposits and leak rates
==
Conclusion:==
Leakage is the only expected and observed consequence
7/17/03 21 Two Possible Causes Leak Axial Crack in Nozzle and/or Weld PWSCC Nozzle and/or Weld Low-Cycle Fatigue Nozzle or Weld PWSCC Nozzle and/or Weld Fabrication Flaw Over-Stress Nozzle and/or Weld Crack Initiation Crack Propagation Consequences STP Unit 1 BMI Flaw Investigation July 8, 2003 Results
7/17/03 22 Facts Inconsistent with PWSCC
- No cracks identified except in #1 and #46
- Cracks relatively old (3-5 yrs), about same age
- Cracks not ID initiated
7/17/03 23 What Might be Expected Assuming PWSCC The industry has inspected 543 upper head CRDM nozzles and found 114 TW or partial TW defects.
Therefore, if PWSCC were the cause and STP inspected 58 nozzles, we would expect to find 12 nozzles with TW or partial TW defects.
7/17/03 24 Facts Suggesting Fabrication Flaws
- Cracks not at highest residual stress locations
- Penetrations #1 and #46 are different in terms of residual stress
- Some cracks do not appear to be in contact with primary water
7/17/03 25 Crack Propagation Scenario J-groove Weld Crack initiates at tube/weld interface due to high residual stresses and thermal fatigue.
Crack propagates due to thermal fatigue.
Crack contacts primary water. Growth continues by fatigue or PWSCC.
Crack grows to the point of leakage into annulus.
Tube wall
7/17/03 26 Boat Sample Objectives Nozzle 1
- Capture portion of leaking crack including part of nozzle wall, part of weld, and site of observed helium leakage Nozzle 46
- Capture portion of crack shown by UT not to connect with the surface
7/17/03 27 Mock-up Penetration #46 Boat Sample
7/17/03 28 Monitoring / Inspection Plan Confirms Effective Corrective Action
- Continue bare metal visual inspections under boric acid control program
- Perform UT and EVT of penetrations at next Unit 1 vessel inservice inspection
- Perform periodic UT of vessel base material around repaired penetrations
- Perform volumetric examination of Unit 2 penetrations at next refueling outage with core barrel removal
7/17/03 29 Condition Limited to the Two Identified Nozzles
- Routine inspection identified very low leakage
- Extensive NDE confirmed condition limited to two penetrations
- Axial cracks in tubes
- No wastage
- Substantial safety margin existed
- Repairs are complete
- Monitoring / inspection plan developed
7/17/03 30 RETURN to SERVICE Tim Bowman Unit 1 Operations Manager
7/17/03 31 Unit 1 is Ready to Return to Service
- Extent of condition known
- Probable causes identified
- Engineering work complete
- Condition corrected
- Confidence in repair
- Plant staff prepared