ML050490124

11/5/04: (27 Pages -Slides) U3R11 SG Loose Part

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: ML050490053 ML050490124 ML050490197
References
TAC MC4292
Download: ML050490124 (27)

Text

VERDE PALO U3R11 SG Loose Part Kevin Sweeney System Engineering 11/5/2004 1

Loose Part removed from SG 32 11/5/2004 2

Tubesheet FOSAR - Affected Tubes 11/5/2004 3

PLP/PLI Affected Tubes Centerline of Screw #5 11/5/2004 4

Economizer Elevation View Tube Bundle Shroud Center Support Cylinder Location of High Flow resulting in Cold Leg Corner Wear Eggcrate Tube Support Feedwater Box 02C Flow Distribution Baffle 11/5/2004 5

11/5/2004 6 8

7 6

5 Deflector Plate 4

3 2

1 11/5/2004 7

Feedbox cutout BE SG 11/5/2004 8

Brooks Robot/Camera Camera &

Light to look up FW box holes Magnetic If needed to confirm Wheels -

presence of screws Robot to an articulating camera roll along can be extended the shell 11/5/2004 9

Inspection Results - Set Screw #4 Evidence of erosion or skewness 11/5/2004 10

Inspection Results - Set Screw #5 Set Screw missing 11/5/2004 11

Inspection Results - Proper Installation 11/5/2004 12

Set Screw #12 (SG 31) 11/5/2004 13

Feedring Flow Holes Deflector Plate 11/5/2004 14

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 15

Analysis/Evaluation Approach

• Four (4) impact assessment areas addressed

- Feedwater box integrity

- Streaming Flow through screw hole

• Tube wear

• FIV

• SG Performance

- Loose Part Wear

• Transport Probability

• Projected Wear Rates

• Impact Damage

- Active and Inactive tubes

- Unit 1 Operability 11/5/2004 16

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 17

FEA Model Feedwater Box with screws missing 11/5/2004 18

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 19

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 20

Tube Pattern - Streaming Flow 11/5/2004 21

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 22

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 23

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 24

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 25

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 26

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 11/5/2004 27