ML050490124
| ML050490124 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 11/05/2004 |
| From: | Sweeney K Arizona Public Service Co |
| To: | Office of Nuclear Reactor Regulation |
| Fields M B ,NRR/DLPM,415-3062 | |
| Shared Package | |
| ML050490137 | List: |
| References | |
| TAC MC4292 | |
| Download: ML050490124 (27) | |
Text
11/5/2004 1
U3R11 SG Loose Part Kevin Sweeney System Engineering P
A L
O V
E R D
E
11/5/2004 2
Loose Part removed from SG 32
11/5/2004 3
Tubesheet FOSAR - Affected Tubes
11/5/2004 4
PLP/PLI Affected Tubes Centerline of Screw #5
11/5/2004 5
Tube Bundle Shroud Eggcrate Tube Support Center Support Cylinder Flow Distribution Baffle Feedwater Box Economizer Elevation View Location of High Flow resulting in Cold Leg Corner Wear 02C
11/5/2004 6
11/5/2004 7
1 2
3 4
5 6
7 8
Deflector Plate
11/5/2004 8
Feedbox cutout BE SG
11/5/2004 9
Brooks Robot/Camera Magnetic Wheels -
Robot to roll along the shell Camera &
Light to look up FW box holes If needed to confirm presence of screws an articulating camera can be extended
11/5/2004 10 Inspection Results - Set Screw #4 Evidence of erosion or skewness
11/5/2004 11 Inspection Results - Set Screw #5 Set Screw missing
11/5/2004 12 Inspection Results - Proper Installation
11/5/2004 13 Set Screw #12 (SG 31)
11/5/2004 14 Feedring Flow Holes Deflector Plate
11/5/2004 15 Rereview of Eddy Current
- Eddy current results from U3R11 reviewed after FW Box FOSAR Findings
- All calls from TSC to 03C
- Three (3) tubes found with wear at 02C
- R127C40 - 10% wear
- R129C40 - 20% wear
- R130C41 - 25% wear
- Historical review indicated no previous wear or precursors
- Further review indicated tubes directly inline with #5 hole
- Confirmed by Westinghouse
11/5/2004 16 Analysis/Evaluation Approach
- Four (4) impact assessment areas addressed
- Feedwater box integrity
- Streaming Flow through screw hole
- Tube wear
- SG Performance
- Loose Part Wear
- Transport Probability
- Projected Wear Rates
- Impact Damage
- Active and Inactive tubes
- Unit 1 Operability
11/5/2004 17 Feedwater Box Integrity
- Set Screw Design Function
- Prevent Feedwater Box collapse during FWLB
- Feedwater Box/Economizer not credited during FWLB
- Assure negative impact to tubing not generated
- Analysis
- Westinghouse developed 3-D FEA model
- Assumed two (2) set screws per 90 degree section missing
- Results
- Insignificant increase in elastically calculated stresses
- Box deflects outwards away from tube bundle
- Maximum displacement less than 1/4 inch
11/5/2004 18 FEA Model Feedwater Box with screws missing
11/5/2004 19 Streaming Flow
- Analysis Approach
- FIV analysis
- Similar to analytical effort performed for SG mods
- Calculate stability ratio
- Acceptance criteria - <= 1.0
- Ratio > 1 - increased potential for fluid-elastic instability and wear
- ATHOS model used
- Results
- Stability ratio slightly greater than 1
- Consistent with observed wear
- Flow rates much less than cold leg corner phenomenon
- 27 ft/sec vs 46 ft/sec
- Negligible impact on SG performance (<1 psi)
11/5/2004 20 Streaming Flow
- Recommended Actions - Unit 3
- Three tubes with indicated wear
- Plugged and Staked
- Develop preventative plugging strategy for screw locations adjacent to deflector plates
- Determined that five (5) tubes per location affected
- Recommend plugging and staking each location in both steam generators
- Twenty tubes (minimum) per SG
- Reviewed ECT data in U2 OSGs and Unit 1
- No indication of wear or wear precursor at any locations
11/5/2004 21 Tube Pattern - Streaming Flow
11/5/2004 22 Loose Part Wear
- Analysis Approach
- Address wear potential
- Transport probability
- Geometric Probability
- Wear rate analysis
- Archard Theory
- Impact analysis
- Active tubes
- Inactive tubes
- Loose part wear approach consistent with Engineering Study 02-MS-A76
11/5/2004 23 Loose Part Wear
- Transport Probability
- Factors
- Diameter of Screw relative to feedring hole diameter
- Both two (2) inch
>> Set Screw has chamfered end
>> Flow holes may be slightly enlarged (erosion)
>> Probability estimate
- Flow hole must be aligned
- Unlikely
>> Inspection indicates mis-alignment (cold condition)
- Cross flow and drop angle make vertical alignment unlikely
- Cross Flow force 10 lb vs 4 lb set screw
- Conclusion -
- Most likely location - lying on feedwater ring with no access to tube bundle - flows and flow direction insufficient to upright screw
11/5/2004 24 Loose Part Wear
- Wear Rate Analysis
- Archard Theory of Wear V = KFND
- Wear Rates projected to be low
- Weight/Shape of screw in expected low flow field (1.5 ft/sec) results in low contact force
- Fixity of tubes at the tubesheet minimizes sliding motion
- Expected position to be horizontal
- Consistent with U3R11 findings
- No operating cycle restrictions for Units 3 or 1 with respect to loose part wear
11/5/2004 25 Loose Part Wear
- Impact damage
- Active tubes
- Condition is pure impact without sliding
- Based on combination of flow and weight, test data indicates that resulting dents would be slightly greater than 1 mil
- Inactive tubes
- Industry experience (Ginna) of loose part impact interaction resulting in collapse of plugged, unpressurized tube
- Despite minimal impact load - Engineering elected to provide caging of plugged, unstaked tubes on tube bundle periphery in regions considered within expected transport range
- 15 rows from hole locations
- Action taken in both SGs
11/5/2004 26 Unit 1 Operability Operability evaluation
- Design of Feedwater Box - no difference
- Similar erosion/corrosion can not be ruled out
- Wear Review
- ECT Data from U1R11 and U2R10 (OSGs) shows no indication of wear in the affected regions
- Condition (streaming flow) assumed not to exist at end of Cycle 11
- FOSAR
- FOSAR exam performed in both SGs
- No evidence of loose part
- Analysis
- Analysis in support of Unit 3 indicates no expected impact to tube integrity
- Tube plugging in Unit 3 preventative in nature
- Integrity
- Leak and burst testing/industry experience validate leak stability for wear indications - should leak occur timely, orderly shutdown would result
- PVNGS shutdown limits more conservative than EPRI limits
11/5/2004 27 Remaining Actions Complete Plugging and Staking in Unit 3
- 30 tubes total in SG 32
- 37 tubes total in SG 31
- Expected completion - 11/7 Westinghouse to provide final QAd analysis reports
- FEA Analysis
- Wear Analysis
- Expected 11/12 DFWO
- DFWO to include Condition Monitoring (CM) Report per NEI 97-06
- CM will document all the actions and analyses to conclude no impacts on tube integrity - Mode 4 restraint CRDR
- Document all actions taken and address transportability
- No corrective measure for Unit 1 - last cycle of operation for OSG
- Evaluate potential need for future inspections in RSG