IR 05000528/1993021
| ML20045C155 | |
| Person / Time | |
|---|---|
| Site: | Palo Verde  |
| Issue date: | 05/24/1993 |
| From: | Ang W NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | |
| Shared Package | |
| ML20045C154 | List: |
| References | |
| 50-528-93-21, 50-529-93-21, 50-530-93-21, NUDOCS 9306220139 | |
| Download: ML20045C155 (11) | |
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U. S. NUCLEAR REGULATORY COMMISSION
REGION V
f Report No.:
50-528/93-21, 50-529/93-21, and 50-530/93-21 Docket No.:
50-528, 50-529, and 50-530 License No.:
NPF-41, NPF-51, and NPF-74 Licensee:
Arizona Public Sereice Company P. O. Box 53999, Sta dc.' 9012 Phoenix, AZ 85072-3999 Facility Name:
Palo Verde Nuclear Generating Station Units 1, 2, and 3 Inspected at:
Palo Verde Nuclear Generating Station, Wintersburg, Arizona Inspection date: April 27 through May 7, 1993 Inspectors:
C. Myers, Reactor Inspector, Region V C. Clark, Reactor Inspector, Region V Approved by:
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N W. P. Ang, Chief Engineering Section Date Signed Insnection Summary:
Inspection durina the period April 27-May 7. 1993 (Report Nos. 50-528/93-21.
50-529/93-21 and 50-530/93-21)
Areas Inspected: This routine announced inspection reviewed the Inservice Inspection (ISI) activities conducted during the fourth refueling outage for Unit 2 (U2R4).
Special inspection effort was focused on eddy current examination of steam generator tubes.
Inspection Procedure 73753, " Inservice Inspection" was used as guidance during the inspection.
Safety Issues Manaaement System (SIMS) Item:
None 9306220139 930603 PDR ADOCK 05000528=
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Results:
General Conclusions and Specific Findinas:
ISI examinations observed were performed in accordance with licensee
procedures.
Personnel. performing ISI examinations and data evaluations were
knowledgeable and proficient in their activities.
Eddy current examination of staan generator tubes was found to use
current equipment and techniques. However, the threshold of flaw detection and measurement accuracy appeared to be affected by as-manufactured tube conditions.
Sionificant Safety Matters:
Routinely required bobbin coil probe eddy current examinations had not
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identified steam generator tube axial-cracks that were subsequently identified by rotating pancake coil probe eddy current examination. The licensee was
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evaluating high signal noise levels caused by inner diameter surface conditions in steam generator tubes manufactured by the pilgering process that appeared to reduce the flaw detectability and measurement accuracy of eddy-current examination using the bobbin coil probe for primary scanning.
Evaluation of this technical concern is being performed by NRR.
Summary of Violation or Deviations:
None Open Items Summar_y:
One new open item was identified.
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e Details
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1.
Persons Contacted Arizona Public Services Company
- J. Bergstedt, Specialist, Quality Assurance and Monitoring
- R. Bernier, Supervisor, Nuclear Regulatory Affairs R. Bouquot, Supervisor, Quality Assurance and Monitoring T. Bradish, Manager, Nuclear Regulatory Affairs M. Ferguson, Manager, Quality Engineering
- D. Garchow, Manager, Performance Engineering
- D. Hansen, Senior Consulting Engineer, Inservice Inspection
- M. Hodge, Manager, Nuclear Engineering Mechanical D. Kanitz, Nuclear. Regulatory Affairs
- D. Laskos, Supervisor, Quality Control
- D. Leech, Supervisor, Quality Assurance and Monitoring
- A. Morrow, Engineer, Component & Condition Monitoring M. Radspinner, Engineer, Nuclear Engineering
- R. Schaller, Assistant Plant Manager, Unit 1
- E. Simpson, Vice President, Nuclear Engineering
- T. Sundeen, Auditor, Quality Assurance and Monitoring
- J. Young Jr., Engineer, Inservice Examination Others
- F. Gowers, El Paso Electric Site Representative
- R. Henry, Salt River Project Site Representative
- R. Marlow, Vice President, Conam Nuclear /B&W Nuclear Services U. S. Nuclear Regulatory Commission J. Sloan, Senior Resident Inspector A. MacDougall, Resident Inspector
- H. Freeman, Resident Inspector The inspectors also held discussions with other licensee and contractor personnel during the course of the inspection.
- Denotes those attending the exit meeting on May 7,1993.
2.
Inservice Inspection - Observation of Work Activities (73753)
A.
Purpose The purpose of this inspection was to review a sample of completed
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Inservice Inspection (ISI) work and to observe work activities in progress in Unit 2 to determine if the inspection, repair and replacement-of Class 1, 2 and 3 pressure retaining components were being performed in accordance with applicable requirements.
Eddy current examination for steam generator tubes was reviewed in detail.
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B.
Backaround During this inspection the licensee was conducting the Unit 2 fourth refueling outage (U2R4).
Section 4.0.5 of the Palo Verde Unit 2 Technical Specifications requires
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that Inservice Inspection (ISI) be performed in accordance with Section
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XI of the American Society of Mechanical Engineers (ASME) Boiler and
. Pressure Vessel Code (Code) and applicable Addenda.
In NRC letter dated October 21, 1987, the NRC accepted the licensee's ISI program, which was based on the 1980 Edition of the ASME Code,Section XI, with Addenda through Winter 1981. The Code inspection requirements are the basis for inservice examinations and tests conducted during the initial 120-month of commercial operation inspection interval, which began on September 19,
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1986.
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C.
Schedulino of Work The inspectors reviewed licensee ISI plans and schedules for the current ISI interval to determine if changes to the inspection plan had been properly documented and approved.
The inspectors found that all changes to the ISI plan had been properly documented and approved.
D.
Review of Personnel Qualifications and Certifications The inspectors reviewed the qualifications and certifications of personnel observed to be conducting ISI examinations during this inspection.
These personnel were certified for Level I and 11 examination activities under American Society for Nondestructive Testing Standard SNT-TC-1A. The inspectors also reviewed a sample of the qualifications and certifications of licensee and contractor Level III examiners. The inspectors verified that the records contained the required information, such as:
employer's name, person certified and activity qualified to perform.
E.
Observation of Work
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The inspectors observed portions of the following examinations:
Volumetric examination of reactor coolant pump 2A flywheel by
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ultrasonic testing (UT) using procedure No. 73TI-9ZZ23, Rev. 2,
" Ultrasonic Examination of Reactor Coolant Pump Flywheels."
Surface examination of pressurizer nozzle weld No. 001 by liquid
penetrant testing (PT) using procedure No. 73-9ZZ07, Rev. 3. " Liquid Penetrant Examination."
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Volumetric examination of pressurizer nozzle weld No. 5-33 by
ultrasonic testing (UT) using procedure No. 73TI-9ZZO9, Rev. 06.00,
" Ultrasonic Examination of Pipe Welds."
For each of the examination methods observed, the inspectors verified the following :
Approved procedures were available and followed. Nondestructive
examination (NDE) equipment specified in the procedures was used.
Personnel were knowledgeable of the examination methods and proper
operation of the equipment.
Personnel were qualified and certified for the examination
activities which they performed. These activities included designation of examination method, calibration of equipment, examination, and evaluation and acceptance of test results.
Required documentation was complete. Examination results,
evaluations, and any corrective actions, repairs or replacements were recorded as specified in the ISI program and NDE procedures.
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F.
Eddy Current Examination of Steam Generator Tubes (1)
Backround Palo Verde Technical Specification 4.4.4.0 requires periodic inservice inspection of a sample of steam generator tubes to demonstrate the operability of the steam generators. This surveillance requirement assures that the structural integrity of this portion of the reactor coolant boundary is maintained.
The licensee's program for inservice inspection of steam generator tubing is based on a modification of Regulatory Guide 1.83, Revision 1, " Inservice Inspection of Pressurized Water Reactor Steam Generator Tubes." RG 1.83 identifies that the inservice inspection program should include nondestructive examination by eddy current testing (ECT), capable of locating and identifying stress corrosion cracks and tube wall thinning by chemical wastage, mechanical damage
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or other causes.
Technical specification 4.4.4.4.a.6 requires that a steam generator tube be removed from service when a tube defect is determined to be equal to or greater than 40% of the nominal wall thickness.
The bases for this technical specification states that tube inspections of operating plants have demonstrated the capability to reliably detect degradation that has penetrated 20% of the original wall thickness.
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The CE System 80 steam generators are vertical, U-tube recirculating steam generators containing 11,012 Inconel 600 tubes (ASME SB-163),
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0.750" 00, 0.666" ID with 0.042" average wall. thickness.
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(2) Jnspection Activity
The inspectors reviewed the eddy current examination technique utilized by the licensee for steam generator tube inspections. The licensee documents used for this review are identified in Appendix A along with background references for. regulatory requirements.
The inspectors reviewed the licensee's procedures and held discussions with licensee ISI personnel and contractors.
The inspectors reviewed ECT data from recent examinations of tubing in Unit 2.
The inspectors observed several analysts perform ECT data evaluations.
The inspectors noted in particular the following features of the licensee's program.
a.
Examination Plan
- The licensee's examination plan for each steam generator during this refueling outage consisted of the following:
- 100% of the tubes, full length with bobbin probe examination.
- 10% of the tubes at the expansion transition and the first support location on the hot leg with rotating pancake coil (RPC)
examination.
- Supplemental RPC examination as required for characterization of non-quantifiable indications from the bobbin examinations.
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The inspectors found the licensee's examination plan to exceed technical specification requirements and to incorporate industry recommendations.
b.
Use of Independent Contract Data Analysts The licensee utilized independent contractors for the primary.
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(CONAM/B&W) and the secondary (CE/ABB) data evaluations. Automated data analysis was also utilized. Discrepancies between any flaw depth calls greater than 10% were resolved by a third ;ndependent analyst. The inspectors found the d:pth of independence and experience in the licensee's' data analysis to be a strength in the licensee's program.
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c.
Site Specific Trainina Onsite orientation training was conducted by Performance Engineering
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for all licensee and contractor personnel involved in ECT
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examinations. The inspectors found that the licensee used prepared material for the training. The training included a written examination and a practical demonstration of data evaluation.
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inspectors concluded that the training was adequate.
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Analyst Performance Trendina In addition to the initial performance demonstration, continuing analyst performance was monitored informally by trending the frequency of defect call discrepancies between analysts.
The inspectors found the performance trending to be a strength in the licensee's program.
c.
ECT Technique Summary
The licensee utilized Eddynet (a Trade name) data evaluation equipment supplied and operated by a contractor (Conam Nuclear).
Primary tube scanning was performed using a 0.610" OD magnetic bias bobbin probe (ZETEC ULC) at a scanning speed of 26"/sec with a data sampling rate of 800 samples /sec.
Smaller probes (0.590" and 0.540") were also used for short radius tube examinations and where obstructions were encountered., Supplemental tube examination was
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performed using a rotating pancake coil probe (RPC) consisting of three axis coils scanning at a linear speed of 0.1"/sec.
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The licensee used multifrequency analysis and frequency mixing for
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data analysis to characterize indications. The licensee utilized 20, i
100, 550 (Primary) and 990 KHZ frequencies with the following mixes:
Mix 1:
550-100 KHZ Differential, for detection and sizing Mix 2:
550-100 KHZ Absolute, for sizing wear
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Mix 3:
550-100 KHZ Differential (high span), for detection at roll transition Mix 4:
550-990-100 KHZ Differential, for detection at geometry changes j
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The licensee employed two standards for equipment calibration. The ASME standard consisted of 100%, 60%, 20% through wall holes as specified in ASME Section V.
A wear scar standard consisted of 50%,
30%, 0% (noise) simulated wear marks.
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Defect depth was determined by phase angle measurement of the differential bobbin coil signal calibrated to the ASME standard.
Wear depth was determined by voltage amplitude of the absolute bobbin coil signal calibrated to the wear standard.
The data analysts characterized and recorded all indications which met the following criteria:
Wear >10% through wall e
All quantifiable degradations >1% through wall e
Voltage amplitude criteria were not used for the identification of tube defects.
The licensee typically used the following plugging criteria:
>20% for stay cylinder, batwing and cold leg corner wear e
>35% for all other tubes previously examined with no indications detected or not inspected
>40% for tubes that had previous indications >10%
All possible loose parts with any detectable wear
All suspected cracks
f.
Pilgering Noise Level During eddy current examinations of the Unit 2 steam generators following the recent tube rupture event, the licensee made extensive use of rotatirig pancake coil (RPC) probes to examine suspect tube areas.
The RPC probe examinations identified 13 axial indications which had not been identified during prior bobbin coil probe examinations of the tubes. The licensee was evaluating the significance of the additional indications as part of their root
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cause evaluation of the tube rupture.
The NRC review of recent ECT examinations of the Unit 2 steam.
generators noted that the licensee's data analysts had identified i
extensive ID chatter.
This condition was defined by the licensee's procedure as bobbin signals caused by the tube manufacturing process (pilgering, ID variations, etc.) and characterized by long areas of horizontal motion in the impedance plane display of the signal. The data analysts considered these signals to represent the noise level in the bobbin signal for these tubes. According to the data analysts, this horizontal signal noise leve. ranged from 1.7 to 3.4 volts and resulted in a vertical signal amplitude in the range of 0.1 to 0.2 volts. The inspectors found that this vertical signal i
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amplitude was approximately the same level at which flaw indications were considered identifiable by the licensee.
The inspectors were concerned that the signal-to-noise ratio may be inadequate to discriminate actual flaws. The inspectors noted that RPC examination of the tubing was unaffected by the pilgering condition.
The licensee provided the following information to the inspectors.
All steam generator tubing in all Units had been procured as pilgered tubing.
The pilger tube reducing process involves incremental roll reduction of sections of the tubing, resulting in circumferential bands of slight surface variations on the ID of the tubing.
The inspectors noted that the circumferential bands are identifiable by visual as well as ECT bobbin examination. For the steam generators in Units 1 and 2, the tubing had been obtained from the same manufacturer (Noranda), while the tubing for the Unit 3 steam generators was obtained from a different manufacturer (Sandvik). According to the ECT data analysts, the pilgering noise levels appeared highest in the Unit 2 steam generators, followed by Unit 3 and finally Unit 1.
The inspectors sampled the ECT data tapes and observed no indications which had not been identified by the licensee.
However, the inspectors noted that the pilgering noise level in the tapes appeared to be more significant than had been experienced in general by the industry.
The licensee's ECT contractor also acknowledged the unusually high degree of signal noise level attributed to pilgering which necessitated careful interpretation by the data analysts.
The licensee stated that they were evaluating the minimum level of flaw detectability and their confidence level in the probability of flaw detection for their ECT technique as part of their root cause evaluation of the recent tube rupture in Unit 2.
The inspectors encouraged the licensee to evaluate ECT techniques such as rotating field probes, multi-pancake coil RPC probes and pilger-compensating data analysis software to improve the reliability of its ECT flaw detection capability.
The licensee indicated that they were pursuing utilization of advanced techniques to further improve their examination technique.
The adequacy of the licensee's EC1 examination plan and technique is being evaluated by NRR.
Pending review and resolution of the concern for ECT flaw detection reliability, this was identified as a followup item (FOLLOWUP ITEM 50-529/93-21-01).
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(3)
Quality Assurance involvement in ECT Examinations The inspectors reviewed the activities conducted by the of the
licensee's Quality Assurance and Monitoring (QA&M) Department during ECT examinations.
The inspectors found that QA&M performed
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surveillance of work activities, observed the performance of the data analysts and conducted audits of ECT vendors.
The inspectors found that the licen:ee's Independent' Safety Evaluation Group (ISEG) had also reviewed the ISI program to incorporate industry experience.
The inspectors found the licensee's QA ' involvement to be adequate.
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(4)
Inspection Personnel Oualifications The inspectors sampled 12 personnel qualifications and certifications for ECT examiners and found them to be adequate to satisfy the requirements of qualification standard SNT-TC-1A.
G.
Conclusions The inspectors concluded that the licensee was adequately implementing their approved ISI program.
Licensee personnel. were knowledgeable and proficient in their examination activities. The NDE examinations methods, in particular eddy current examination of steam generator tubes, employed current equipment for data acquisition and analysis.
No violations or deviations from NRC requirements were identified in the areas reviewed.
3.
Exit Meeting An interim exit meeting was held on April 30, 1993, with the Manager of Regulatory Compliance to discuss the findings of the inspection of the overall ISI program. An exit meeting at the conclusion of the inspection j
was conducted on May 7,1993, with the licensee representatives
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identified in paragraph 3 of this report. The licensee did not identify as proprietary any of the materials discussed, provided to or reviewed by
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the inspectors during this inspection.
The inspectors summarized the findings of the inspection as described in this report. The inspectors emphasized.that the signal noise levels conditions due to pilgering in the Unit 2 steam generator tubes exceeded
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general industry experience and posed a significant concern for masking
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defects. The licensee acknowledged the inspectors' concerns.
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Appendix A 1.
Licensee Documents Reviewed:
a.
Nuclear Administrative and Technical Manual (NATM) 73TI-9RC01, Revision 7. " Steam Generator Eddy Current Examinations," dated 10/4/92 b.
Eddy Current Data Analysis Course, PVNGS Steam Generators, dated 3/29/93 c.
NATM 73AC-0XI01, ASME Section XI Inservice Inspection, Rev. 01.03, dated 8/22/92 d.
QA Audit of Conam Nuclear, Inc., April 1993 e.
Work Request 804973, Tube Plugging f.
Work Request 000604748, Tube Pulling g.
QA Audit Report 92-002, Maintenance, 6/92 h.
QA&M Audit Scoping Matrix, Special Processes /ASME, Matrix 1, Rev.1, 2/16/91 i.
ISEG Audit Report 92-0062, dated 10/30/92.
2.
Background References:
a.
EPRI "PWR Steam Generator Examination Guidelines", Revision 2, including draft Appendices G and H dated 7-15-92 b.
American Society for Nondestructive Testing, Recommended Practice No. SNT-TC-1A,1980 Edition, Personnel Qualification and Certification in Nondestructive Testing c.
Palo Verde Technical Specification 3/4.4.4 d.
Palo Verde Updated Safety Analysis Report (USAR), Paragraph 5.2.4 Inservice Inspection and Testing of Reactor Coolant Pressure Boundary e.
Regulatory Guide 1.83, Rev.1, 7/75, Inservice Inspection of Pressurized Water Reactor Steam Generator Tubes
f.
ASME Section XI, " Rules for Inservice Inspection of Nuclear Power Plant Components," 1980 Edition including Addenda through-the Winter.
1981 and Article IV of the 1989 Edition including Addenda through 1990 g.
ASME Section V, " Nondestructive Examination," 1980 Edition' including Addenda through the Winter 1981
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