ML20246L642
| ML20246L642 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 03/14/1989 |
| From: | Hou S Office of Nuclear Reactor Regulation |
| To: | Marsh L Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20245H595 | List: |
| References | |
| IEB-88-011, IEB-88-11, NUDOCS 8905180370 | |
| Download: ML20246L642 (22) | |
Text
.
a
/ p uam\\
~
UNITED STATES
-[
g NUCLEAR REGULATORY COMMISSION
'E WASHINGTON, D. C 20665 p,
%,..../
14 MAR 191E l
MEMORANDUM FOR:
Ledyard B. Marsh, Chief Mechanical Engineering Branch Division of. Engineering & Systems Technology 1
THRU:
Pao-Tsin Kuo, Section Chief Mechanical Engineering Branch Division of Engineering & Sy, stems Technology FROM:
Shou-nien Hou Mechanical Engineering Branch Division of Engineering & Systems Technology
SUBJECT:
AUDIT OF WESTINGHOUSE ACTIVITIES ON BMI THIMBLE TUBE WEAR FOR SOUTH TEXAS PLANT INTRODUCTION The staff of Mechaniccl Engineering Branch and its BNL consultant conducted an audit at a Westinghouse facility in Pittsburgh, PA during January 30 to February 1, 1989. The purpose was to review Westinghouse analytical and experimental activities related to NRC Bulletb 88-11 on the issue of BMI thimble tube wear. Although the audit is specifically for the South Texas 4
plant, the results are mostly generic and equally applicable to all Westinghouse plants.
AUDIT ACTIVITIES During the audit, the staff had several meetings with Westinghouse personnel, visited Westinghouse Waltz Mill test facility, and reviewed calculation packages and supporting documents. The scope of audit consists of thimble wear acceptance criteria, calculations on leakage rate, and results of Westinghouse and European flow tests. Status of Westinghouse and European programs on long term resolution of the Thimble wear problem were also discussed.
FINDINGS A detailed audit trip report is enclosed. The following are highlights of our findings:
1.
The acceptance criterion that thimble wear should not exceed 60% is acceptable for South Texas and for many other Westinghouse plants.
2.
The calculation that determined the maximum leakage rate from a ruptured thimble (35 gpm for South Texas thimbles) is conservative.
89051g[k[h0 [.8 PDR P
i
2 3.
The Westinghouse Waltz Mill flow tests provided important data on thimble vibration behavior. The use of larger thimbles appears a promising long term fix out must be proven in actual reactor operation.
4.
Programs for corrective actions in South Texas plant Unit 1 and 2 includes thimble inspection on a regular basis, reposition or c;;3 ng capen3 i
thimbles per established criteria, removal of flow limiters, replacing all thimbles with larger diameter ones, and installation of ::nu:1
)
i:01:ti:n: Of manual isolation valve and magnetic ball checks valve to 1
each thimble. The program is adequate and ecceptable. We will continue to review the results of program implementation, such as the performance of larger thimbles and adequacy of future inspection intervals.
5.
Although we plan to audit other Westinghouse plants on their plant-specific program per request of NRC Bulletin 88-09, we feel that it is essential to continue our review on the progress of Westinghouse Owners Group and European programs for long term resolution. This audit proves to be very helpful for that purpose.
'/
Shou-nien Hou Mechanical Engineering 8 inch Division of Engineering & Systems Technology
Enclosure:
As stated cc:
L. C. Shao C. Rossi J. E. Richardson J. A. Calvo G. Dick i
C AUDIT TRIP REPORT 1
Purpose:
Audit of Westinghouse Activities on BMI Thimble Tube Wear Location:
Westinghouse R&D Center, Pittsburgh, PA Date:
January 30 - February 1, 1989 Personnel:
S. Hou (NRC), G. DeGrassi (BNL) 1.0 Audit Objectives The purpose of this audit was to review Westinghouse analytical and experimental activities related to the investigation and resolution of the BMI thimble tube wear problem at the South Texas plant.
In addition, work related to addressing the Bulletin 88-09 issues for all Westinghouse plants was also discussed. A copy of the audit agenda is included in Attachment 1.
The audit covered the following topics:
1.
Basis for 60% wear acceptance criterion.
2.
Thimble tube leakage rate calculations.
3.
Framatome/EdF/ Westinghouse European Flow Tests.
4.
Westinghouse Waltz Mill Flow Tests.
5.
Mol hot cell inspections of Tihange 3 thimble tubes and flow limiters.
6.
Status of European programs on long term resolution of tube wear issue.
7.
Status of Westinghouse programs on long term resolution.
2.0 Audit Summary Dave Boyle of Westinghouse gave a brief overview of the major topics. A meeting attendance list is included in Attachment 2.
The audit proceeded with a review of the documentation related to each topic and discussions with appropriate Westinghouse personnel. Audit work sheets are included as.
The following is a summary of the items reviewed and the findings.
2.1 Basis for 60% Wear Acceptance Criterion The Westinghouse calculation supporting the adequacy of the 60% wall thickness wear allowable for South Texas was reviewed. Westinghouse had I
I performed a finite element analysis of a worn thimble tube section subjected to 2500 psi external pressure. The assumed wear scar was 20 mm long with the ends tapered at a 45' angle based on wear measurements on Tihange plant thimble tubes. The model was developed on the WECAN program and used three-dimensional, elastic, 20-node isoparametric solid elements. The model L
had two elements through the wall thickness in unworn areas and one element 1
I 1
I
f 1
through the wall in the wear scar area. Four cases of wear depth were analyzed - 54%, 70%, 85% and 94% wear of the tube wall. Westinghouse stated that the stress evaluation was based on comparing calculated peak stress to rupture strength which was assumed to be the minimum tensile strength.
By interpolating stress results from the cases analyzed, for 60% wear, the maximum stress was 32 ksi compared to the tensile strength of 95.7 ksi, resulting in safety margin of 3.
l A concern was raised that true peak stresses were not being calculated I
because the finite element mesh was not fine enough to address the effect of stress concentrations in the wear area. To support their model, Westinghouse j
provided additional calculations for two other plants - McGuire and Robinson.
j The McGuire tube model had a similar mesh size as the STP model. The Robinson model had a finer mesh with twice the number of elements through the wall thickness. The tube geometries were similar although not identical. The results showed a peak stress of 26.3 ksi for Robinson and 19.8 kai for McGuire. Therefore, Westinghouse argued that peak stresses may be somewhat higher but not significantly higher.
Based on the stress margin for STP tubes, it was concluded that although peak stresses may be higher than those calculated, 9.ere is no safety concern.
In addition to the margin, peak stresser are normally associated with f atigue failure rather than rupture. Since the number of full pressure cycles is not expected to be very large, this does not appear to be a f atigue concern. Therefore, comparing " peak" stress to rupture strength was conservative.
The review of the McGuire and Robinson analyses also indicated refinements in the methodology. More conservative stress allowables were used. For McGuire, " peak" stress was compared to Sm and also to the fatigue endurance limit.
For Robinson, maximum linearized stress was compared to Sm and " peak" stress was compared to the f atigue endurance limit. Westinghouse indicated that each plant will have its own unique analysis.
2.2 Thimble Tube Leakage Rate Calculation The Westinghouse leakage rate calculation for thimble tube wear-through at South Texas was reviewed. The methodology was based on a paper by F.J.
Moody, " Maximum Flow Rate of a Single Component, Two Phase Mixture," published in 1965. The calculation contained several conservative assumptions. The f ailure was assumed to be an instantaneous guillotine break. The effect of the cable inside the tube was neglected (although the cable is only inserted during flux mapping). To maximize flow, a low water quality (.05) was assumed. Friccional losses through the tube were neglected. Based on normal operating canditions in the lower core plate area, the leakage rate was calculated to be 35 gpm. Westinghouse compared this to the normal charging pump capacity of 120 gpm and concluded that the leakage from a single tube f ailure is well below the system's normal make-up capacity. Based on the conservatism in the calculation, this is a reasonable conclusion.
2
_l
- s 2.3 FRAMATOME/EdF/ Westinghouse European Flow Tests Information on the early European flow tests was documented primarily in progress reports and meeting minutes between Westinghouse and Framatome/EdF which were provided for review. The French have been performing flow tests at their Arny and Cadarache facilities since May, 1985. The early tests identified flow-induced vibration due to axial flow in the annulus of the thimble tube and column as the cause of the problem.
Based on the early test results, it was concluded that the corrective measure is to reduce flow in that area. Most of the flow tests were related to the development of flow limiting devices including those installed in South Texas.
The4 reporto provided interesting historical background information.
However, since South Texas and Westinghouse have no further plans to use flow limiters, most data was not directly relevant to the long term resolution of the thimble tube wear problem for U.S. plants. Due to time constraints, this documentation was not reviewed in detail.
. 2.4 Westinghouse Waltz Mill Flow Tests The Westinghouse report on the Waltz Mill flow tests, WCAP-11919, " Flow Induced Vibration and Wear of PWR In-core Flux Detector Guide Thimbles,"
January 1989, was provided for review. These tests provided information on the flow induced vibration response of three different size thimble tubes under va*ying flow conditions. The test hardware included a thimble tube, a simulated core support plate section, a thimble tube guide column, a lower fuel assembly nozzle, and a tube above the nozzle simulating a fuel assembly instrument guide tube. The thimble tube was supported at elevations corresponding to the reactor vessel penetration and at various elevations in the instrument guide tube. Two flow paths were set up so that flow through the core support plate (main flow) and flow through the thimble tube guide column (thimble flow) could be simulated and controlled independently. The thimble tube was instrumented with accelerometers. Proximity probes were installed on the core support plate to measure vibrations in the region above the plate. A tour of the Waltz Mill test facility was conducted. Although the test setup had been disassembled, some of the test hardware was still available for inspection.
The tests measured the thimble tube vibration response subjected to a range of flows. Various configurations were tested including.313 inch (original thimble size used in STP Units 1 & 2),.339 inch, and.385 inch (the size of future replacement tubes at STP Units 1 & 2) thimble tubes, various tube support conditions, main flow only, thimble flow only, and balanced flow. Tests were performed both with and without flow limiters. Flow limiter off-design conditions were tested including reduced preloads, gaps, misaligned and tilted configurations.
The tests provided useful comparative information on the vibration performance of the various thimble tube configurations. From the data, Westinghouse concluded that thimble tube excitation is derived f rom two sources:
main flow and thimble flow. Main flow excitation is turbulent.
Thimble flow excitation is turbulent (but small) up to a certain flow rate, 3
a
i
~
and then develops fluid-elastic characteristics. The fluid-elastic behavior is characterized by a significant reduction in damping and a sudden increase in vibration levels. The tests demonstrated that a properly functioning flow limiter was effective in reducing vibration. However, it was noted that flow limiter vibration was observed when the preload was removed. Westinghouse concluded that the best performers were the.313 and.339 thimbles with flow limiters and the.385 thimble without a flow limiter.
Westinghouse also developed analytical correlations to estimate fluid elastic instability levels as a percentage of STP best estimate flow. For a
.313 inch thimble, the instability was predicted at 75% of best estimate flow. For the.385 inch thimble, the instability level increased to at least 140%. There are a number of factors, however, shich are difficult to predict with confidence. The tube support condition significantly affects the vibration response.
In the test, it was decided to support the tube at known locations to f acilitate the development of analytical models. In actual reactor service, each tube is supported in an ill-defined fashion. The support condition for the same. tube may change each time when it is withdrawn and reinserted during refueling due to uncertainty of contact points.
The Waltz Mill flow tests provioed valuable information on the relative vibration behavior of various thimble tube configurations. The tests showed that the.385 inch thimble tube should perform better than the original.313 inch tube. However, as evidenced by the Tihange tube failures and the STP wear indications, the thimble tube performance must be proven in the actual reactor service environment.
2.5 Tihange Hot Cell Inspections at Mol Westinghouse provided correspondence documents on the Mol hot cell inspections of Tihange 3 thimble tubes and flow limiters. The final report has not yet been issued. Four tubes and their corresponding flow limiters were removed from the Tihange reactor and examined. The sample included the tube that had worn through the wall as well as tubes with varying degrees of wear. The flow limiters were checked for leak tightness, force-deflection characteristics and dimensional changes. The inspection indicated no changes in force-deflection characteristics and no leaks up to 2 bars of pressure.
However, there were changes in height dimensions. Wear was observed on the top and bottom surfaces. Maximum wear of 4 mm was seen at the bottom of one flow limiter. In addition, one retaining ring was broken.
Photographs of the thimble tubes showed that the tubes wore predominately on one side. The J15 tube had three holes at different elevations where the wall had worn through. The L14 tube had a wear scar exceeding 80% of the wall thickness. A cross section of the tube showed that the tube deformed but had not ruptured.
The hot cell inspection results support the theory that the flow limiters were vibrating and contributing to tube wear. They also demonstrated that the assumed wear scar used in the stress analysis is reasonable and that a tube can sustain significant wall wear without rupture.
4 n
p
~
2.6 Status of European Programs on Long Term Resolution
.=
Westinghouse provided a trip report on the June 1988 Westinghouse /EdF status meeting. The report summarized the ongoing EdF R&D program studies as follovs:
1.
Analytical Studies o minimum velocity of flow necessary for flutter-type instability of tube o dynamic response of tube subjected to annular flow impact points and forces 2.
Experimental Studies o determination of the sources of fluid induced vibrations o optimization of nozzle geometry o determination of:
a) wear mechanisms + coatings, surf ace treatments b) wear law + expected life of tubes + replacement I
3.
Statistical Studies o Correlation between wear ' damage and several parameters (vibration monitoring results, geometry of guide and support columns, flow velocities, etc.)
2.7 Status of Westinghouse Programs on Long Term Resolution Westinghouse gave a short presentation on the Westinghouse Owners Group (WOG) program on thimble tube wtar. This is a recent program which started in October 1988 and is scheduled for completion by the end of 1989. The objective of the WOG program is to establish plant criteria for accurately measuring, predicting and dealing with BMI thimble tube wear. The program should assist utilities in meeting the Bulletin 88-09 requirements, respond to open NRC' concerns, and prevent forced outages due to thimble leaks. Maj or tasks include the following:
o Establish accurate Eddy current wear scar standards (By using hot cell examinations to determine actual scar shape).
o Establish criteria and guidelines to categorize plants based on thimble wear rate and maintenance programs.
o Provide thimble wear rate estimates for each category of plant.
o Provide a finite element analysis to determine maximum allottable thimble wall loss.
5 ni
1
^
Determine an accurate value for a worst case leak through a worn o
thimble.
'l Determine the actual rupture strength for worn thimble tubes by test.
e Westinghouse also indicated that they are investigating the use of l
special coatings to minimize tube wear. They are continuing to investigate the use of larger tubes and sleeves and have approached several utilities to j
test a few modified tubes in their reactors.
I
'3.0 Conclusions l1.
The calculation which established the 60% wear criterion for South Texas is acceptable.
' j I
2.
The calculation that determined the maximum leakage rate from a ruptured 1
thimble tube is acceptable.
3.
The hot cell examinations of flow limitere from Tihange support the theory that they were vibrating and contributed to the thimble tube wear.
1 4.
The hot cell examinations of the Tihange thimble tubes support the f
adequacy of the assumed wear scar shape and demonstrate that the tubes can sustain significant wear prior to rupture.
5.
The Westinghouse Waltz Mill flow tests provided important data on thimble tube vibration behavior and demonstrated the improved vibration performance of the larger thimble tubes. The tests also demonstrated excellent flow limiter performance for the smaller tubes.
6.
Based on European and South Texas experience with flow limiter performance, it is clear that flow test loop results may not always be reliable to predict thimble tube behavior in a reactor. It appears that the adequacy of a long term solution can only be verified in a reactor operating environment.
4.0 Recommendations for Future Audits 4.1 South Texas HL&P had previously committed to take the following corrective actions:
o Inspect thimbles on a regular basis.
o Reposition or cap thinbles per established criteria.
o Remove flow limiters and replace.313" thimbles with.385" thimbles.
o Install manual thimble isolation valves.
o Install magnetic ball check valves.
6 L
At a result of this audit, South Texas plant-specific calculations were found acceptable. Westinghouse flow tests showed that the larger tubes should i
perform better than the original thimble tubes. The addition of isolation
)
valves will provide confidence that potential leaks can be isolated.
Future NRC reviews should focus on the performance of the larger thimbles and adequacy of future inspection intervals.
4.2 Bulletin 88-09 This bulletin requires all Westinghouse plants to establish and implement a thimble tube inspection program. The program shall define an appropriate inspection method, inspection frequency and tub 9 wear acceptance criterion.
Future NRC reviews of selected plant programs can focus on plant-specific calculations defining wear acceptance criteria, justification of inspection f requency and uncertainties in inspection methods. Another important area to review is methods and procedures for isolation of leaking tubes. Short term corrective action procedures and long term plans should be discussed. A 4
continued NRC review of the progress of the Westinghouse Owners Group and the European programs for long term resolution is recommended.
4
)
7 fL
ATTACHMENT 1 Audit Agenda e
b e
G
p AGENDA L
SOUTH TEXAS PLANT BMI WEAR ISSUE MEETING (1-30-89)
PURPOSE:
PROVIDE NRC ACCESS T0 PERTINENT ANALYTICAL AND TEST DATA WHICH LED.T0 WESTINGHOUSE CONCl.USIONS FOR WEAR MITIGATION, TOPICS:
1)
CALCULATIONS CONFIRMING THE ACCEPTABILITY OF 60% WEAR, 2)
TUBE LEAKAGE CALCULATIONS.
3)
WEAR CAUSE ANALYSIS INCLUDING FRAMATOME, EDF AND
~
WESTINGHOUSE TEST RESULTS, 4)
TEST REPORT ON WALTZ MILL FLOW LIMITER AND THIMBLE
- TUBES, 5)
REPORT ON MOL HOT CELL INSPECTION RESULTS ON THIMBLES /
FLOW LIMITERS.
6)
WOG - PROGRAM DISCUSSION, 7)
TOUR OF WALTZ MILL FLOW TEST FACILITY.
a2
4 ATTACHMENT 2 l
Thimble Tube Meeting Attendance List.
l 1/30/89-Thimble Tube Meeting - Westinghouse NAME ORGANIZATION George Dick NRC Wes Schulz HL&P Engineering A.W. Harrison
, HL&P Licensing R.V. Chavez ji - Nuclear Safety D. Merkovsky
}[ - Mech. Equip. Design John Irons ji-Project Dept.
Dave Boyle
}[ - Primary Components Eng.
Claudia Abbate NRC Ciuliano DeGrassi BNL/NRC Shou-nien Hou NRC Michael Plunkett EAS/NRC Ching Yu W - Mech. Equip. Design D. Forsyth
}[ - Mech. Equip. Design N.R. Singleton
}[ - Mech. Equip. Design R. Schwirlan
}[ - Mech. Equip. Design l
l l
n
l r
1 ATTACHMENT 3 Audit Work Sheets t
^
-_m_-_mm_.__.m__,_,._
NRC AUDIT ON SOUTH TEXAS PLANT January 30.to February 2, 1989 SUBJECT A:
BMI TH1MBLE TUBE WEAR (BULLETIN 88-09)
AUDIT ITEM OR CONCERN (Item No.:
1)
Discuss technical basis for the 60% wear acceptance criterion and audit calculations.
EVALUATION Reviewed STP thimble tube calculation that established wear criterion. An elastic, finite element model of a tube with an assumed wear scar was developed using the WECAN program. The model used 20 node isoparametric brick elements. The model assumed a flat wear scar, 20 mm long with the ends tapered at about a 45' angle (based on measurements at Tihange). The applied load was an external pressure of 2500 psi. Four wear cases were considered -
54%, 70%, 85% and 94% wear of the tube wall. Peak stresses were compared to a stress limit of 95.7 ksi - ultimate strength at 650*F.
The maximum stress at 60% wear was approximately 32 ksi, so there was a significant margin.
The calculation applied to STP only. Each p ant will have its own analysis.
Dif ferent wear scar shapes may be used for different plants.
The adequacy of the model mesh for determining peak stresses was questioned.
The model had two elements through thickness at unworn areas and only one element through thickness at worn area. W provided two additional cales for two other plants, McGuire and Robinson to justify the model. The Robinson model was more refined with four elements through unworn wall and two elements at worn section. Although the geometries were not identical, a stress comparison showed peak stress of 26.3 kai for Robinson and 19.8 ksi for McGuire. Therefore the refined model gave higher stresses but not a great deal higher. Based on the STP model stress margin, there is no safety concern.
The McGuire and Robinson analyses also used a different stress allowable Sm for peak stress for McGuire and Sm for maximum linearized stress for Robinson.
Both calculations also considered fatigue.
CONCLUSION Based on the significant margin between calculated stress and tensile stress, the 60% acceptance criteria is acceptable for STP.
Westinghouse will perform plant specific analysis for each plant probably using different methodologies and acceptance criteria. We should review on a case-by-case basis.
Ri
i z.,
NRC AUDIT ON. SOUTH TEXAS PLANT January 30 to February 2,1989 SUBJECT A:
BMI THIMBLE TUBE WEAR (BULLETIN 88-09)
AUDIT ITEM OR CONCERN (Item No.:
2)
Audit calculations on thimble tube leakage rate estimation.
EVALUATION STP leakage rate calculation was reviewed. A number of conservative assumptions were made. The break was assumed to be an instantaneous guillotine break. The effect of the cable inside the tube was neglected (although this cable is in the tube for a small perce'ntage of time). The calculation was based on a-paper by F.J. Moody, " Maximum Flow Rate of a Single Component, two phase mixture." A low water quality of.05 was assumed to.
maximize leakage flow. Frictional losses through the tube were not considered. A lower core plate area pressure of 2232 psi and temperature of 560*F were used. The' leakage rate was calculated to be 35 gpm which is well below the normal charging pump capacity of 120 gpm.
CONCLUSION The calculation is conservative and acceptable.
i
d NRC AUDIT ON SOUTH TEXAS PLANT January 30 to February 2,1989 1
i l
. SUBJECT A:
BMI THIMBLE TUBE WEAR (BULLETIN 88-09)
AUDIT ITEM OR CONCERN (Item No.:
3)
Audit reports on root cause analysis of wear, including Framatone/EdF/W tests conducted'since 1985.
i EVALUATION The French have been performing flow tests at their Arny and Cadarache facilities since 1985. Westinghouse has been involved in a number of these tests. A number of reports and correspondence documents were made available for review. The work was primarily related to the development of flow limiters. Since flow limiters will not be used at STP or other U.S. plants, the reports were not reviewed in detail.
CONCLUSION The reports provide good background information but since flow limiters will not be used in U.S. plants, most data was not relevant to long term resolution.
h
[
NRC AUDIT ON SOUTH TEXAS PLANT
\\
January 30 to February 2,1989 SUBJECT A:
BKI THIMBLE TUBE WEAR (BULLETIN 88-09) l l
AUDIT ITEM OR CONCERN (Item No.:
4)
Audit reports of W flow tests at Waltz Mill Lab on flow limiters and various size thimble tubes.
EVALUATION Test reports were reviewed. Various configurations were flow tested
.313,
.339 and.385 thimbles, with and without flow limiters, flow limiters with off-design conditions (no preload, misaligned, etc.).
Test results provided valuable comparative information on vibration performance. The tests suggest that tubes are excited by random flow turbulence and that at 1700 gpm and higher a fluid-elastic excitation due to thimble flow exists. The data showed that the best performers are any thimble with a properly functioning flow limiter and the.385 thimble without a flow limiter. Tests with off-design flow limiter conditions such as no preload showed that flow limiter vibration can occur.
CONCLUSION Tests provided valuable data on thimble tube vibration behavior. The use of
.385 thimbles looks like a promising long term fix but must be proven in actual reactor operation.
R
NRC AUDIT ON SOUTH TEXAS PLANT Janunty 30 to February 2, 1989 SUBJECT A:
BMI THIMBLE TUBE WEAR (BULLETIN 88-09)
AUDIT ITEM OR CONCERN (Item No.:
5)
Discuss Tihange 3 inspection results on thimble tubes and flow limiters, and review final report from Moi, Belgium Center of Nuclear Studies.
EVALUATION Reviewed Hol test correspondence and test data. The final report was not available.
It should be available next month. The tests consisted of hot cell examinations of four Tihange thimble tubes and corresponding flow limiters. Findings - on flow limiters: wear observed on top and bottom surf aces - up to 4 mm wear on one FL bottom surf ace. No leaks up to 2 bars pressure.
No change in force-deflection curve. One retaining ring was broken. On thimble tubes:
photos show wear predominately on one side. J15 tube had 3 holes where the wall was worn through, L14 had wear of approximately 80% of wall. A cross-section of L14 showed deformation but no rupture.
CONCLUSION Results support the theory that the Tihange flow limiters were vibrating.
Tube inspections support adequacy of wear scar models and conservatism of 60%
wear criterion.
l l
L__----___-_.
R
~NRC AUDIT ON SOUTH TEXAS PLANT January 30 to February 2, 1989 SUBJECT A:
BMI THIMBLE TUBE WEAR (BULLETIN 88-09)
AUDIT ITEM OR CONCERN (Item No.:
6)
Discuss European programs on long term resolution on thimble tube wear issue.
EVALUATION l
Reviewed trip report f rom 6/88 Westinghouse /EDF status neeting. EDF ongoing l
R&D program studies:
1.
Analytical studies
- minimum velocity of flow necessary for flutter-type instability of tube
- dynamic response of tube subjected to annular flow - impact points and forces 2.
Experimental studies determination of the sources of the fluid induced vibration optimization of nozzle geometry determination of wear mechanisu - coatings, surf ace treatment, wear law - expected life of tube - replacement 3.
Statistical studies Correlation between wear damage and several parameters (vibration monitoring results, geometry of guide and support columns, flow velocities, etc.).
CONCLUSION European programs may provide more information on long term problem resolution.
R
- l-C NRC AUDIT ON SOUTH TEXAS PLANT January 30 to February 2, 1989 L
SUBJECT A:
BMI THIMBLE TU E WEAR (BULLETIN 88-09)
AUDIT ITEM OR CONCERN (Item No.:
7)
Review STP and W studies and test programs _ for long term resolution.
EVALUATION Westinghouse owners group (WOG) program started in October 1988. To be i
completed by end of 1989. Program will:
- Establish accurate eddy current wear scar standards.
- Establish criteria and guidelines to categorize plants based on thimble wear rate and maintenance programs.
- P-ovide wear rate. estimates for each category of plant.
- Provide a FE analysis to determine maximum allowable wall loss.
- Determine an accurate value for a worst. case leak through a worn thimble.
- Determine actual rupture strength for worn thimble tubes by test.
Westinghouse is also conducting its own R&D to' investigate tube coatings, use of larger tubes, use.of sleeves. Some utilities have been approached to test fixes on specific tubes in reactor.
CONCLUSION WOG program is on the right track to provide information necessary to address bulletin concerns.
We should follow progress of WOG and Westinghouse R&D program.
l l
e
-- -_ - - _ _ _ _. _- L
South Texas Project Pressurizer Surge Line Meeting January 31 and February 1,1989 Ncme Organization George Dick
'NRC Claudia Abbate NRC Shou-nien Hou NRC Michael Plunkett EAS Jack Bailey HL&P W. Harrison HL&P Sam Patel HL&P E. L. Cranford Westinghouse i
B. J. Coslow Westinghouse John Irons Westinghouse K. C. Chang Westinghouse R. L. Brice-Nash Westinghouse S. A. Swamy Westinghouse Warren Bamford Westinghouse Gary Ells Westinghouse Dave Roarty Westinghouse Anthony Marvray Texas Utilities David Rencher Texas Utilities
l-
_