ML20044F600

Ultrasonic Insp of Feedwater Nozzles.

ML20044F600
Person / Time
Site:	Hatch
Issue date:	04/29/1993
From:	Dykes E, Mortenson S GENERAL ELECTRIC CO.
To:
Shared Package
ML20044F598	List: ML20044F597 ML20044F600
References
GE-NE-508-031-0, GE-NE-508-031-0493, GE-NE-508-31, GE-NE-508-31-493, NUDOCS 9305280299
Download: ML20044F600 (14)

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O GE-Ne508-031-0493 O

O O

ULTRASONIC INSPECTION OF FEEDWATER NOZZi ES O

April 29,1993 O

S.C. Mortenson O

GENERAL ELECTRIC NUCLEAR ENERGY 175 CURTNER AVE SAN JOSE, CALIFORNIA 95125 O

O Approved: nf e s

E.R. Dykes, M$ager O NDE Developm5ht O

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IMPORTANT NOTICE REGARDING  ;

CONTENTS OF THIS DOCUMENT

.I Please Read Carefully The on'y undertakings of General Electric Company respecting ,

information in this document are contained in the contract between i O Southern Nuclear Operating Company and General Electric 1 Company, as identified in the purchase order for this report and

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i nothing contained in this document shall be construed as j changing the contract. The use of this information by anyone  !

i other than the Southern Nuclear Operating Con. bny or for any i purpose other than that for which it is intended, is not authorized; j O' and with respect to any unauthorized use, General Electric - 1 Company makes no representation or warranty, and assumes no ,

liability as to the completeness, accuracy, or usefulness of the j information contained in this document. i O.

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G E-NE-508-023-0193 O

ABSTRACT O As a result of feedwater nozzle cracking observed in Boiling Water l Reactor (BWR) plants, several design modifications were implemented to eliminate the thermal cycling that led to crack initiation. BWR Plants witn these design changes have successfully operated for over ten years without any recurrence of g cracking. To provide further assurance of this, the U.S. Nuclear Regulatory Commission (NRC) issued NUREG-0619. This document established periodic ultrasonic testing (UT) and liquid penetrant testing (PT) requirements. While these inspections are useful in confirming structural integrity, they are time consuming and can lead to significant radiation exposure to plant personnel.

g' In particular, the PT requirement poses problems because it is difficult to perform the inspections with the feedwater sparger in place, and it leads to additional personnel exposure. Clearly an inspection program that eliminates the PT examination and still verifies the absence of surface cracking would be extremely

,J valuable in limiting costs and radiation exposure. This report describes the application of advanced UT techniques to assure integrity of BWR feedwater nozzles.

O The inspection methods include: 1) scanning with optimized UT techniques from the outside vessel wall for inspection of the nozzle inner radius regions, and 2) scanning from the rnzzic forging outside-diameter for inspection of the nozzle bore regions.

Methods of analyzing the data using 3-D graphics displays were 9 developed to accurately display crack locations and depth sizes.

These techniques have been developed to the point where they are now a reliable alternative to the PT requirements of NUREG-0619.

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) GE-NE-508-023-0193 D

TABLE OF CONTENTS D 1. INTRODUCTION 1 !

i

11. ULTRASONIC INSPECTION TECHNIQUE 3 A. GENERAL ELECTRIC REMOTE INSPECTION l i

SYSTEM (GERIG) 5 D B. EXAMINATION TECHNIQUES . 7 ;

C. ULTRASONIC SUBSYSTEM 8 D. DATA ANALYSIS . . 8 E. FLAW SIZING 9 3 111. ULTRASONIC TECHNIQUE QUALIFICATION PLAN . 10 A. QUALIFICATION NOZZLE MOCKUPS 11 B. QUALIFICATION TEST RESULTS ... 12 IV. REFERENCES . . 14 D

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J- GE-NE-508-023-0193 -

.UST OF FIGURES 3

Fiaure Description Pace 1 Feedwater Nozzle Examination Zones . . ... . 3

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2 Nozzle-Mounted Scanner .. . . .. 5 3 Safe-End-Mounted Scanner . . . . . . . .. 6

) 4 GERIS A-scan Display . ... .. ..... 9 D

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O GE-NE-508-023-0193 O LV M 4 1

As a result of extensive feedwater nozzle cracking experienced by I several boiling water reactor (BWR) plants in the mid-to-late 1970's, the Nuclear Regulatory Commission (NRC) issued O NUREG-0619 (Reference 1). This NUREG discussed design modifications and established guidelines for periodic ultrasonic (UT) and liquid penetrant (PT) testing. Included in the design modifications were removing the cladding from the inner-radius and bore and installing a new therrnal sleeve design. There has O been no cracking reported since these modifications were incorporated. The purpose of using autumated UT examinations is to provide a technical basis for supplanting the PT exams required by NUREG-0619. Automated UT also has the potential to reduce the frequency of UT examinations in the future.

O 1 The original designs of feedwater nozzles were potentially subject )

to cracking initiated by thermal fatigue and propagated by suosequent operational temperature and pressure cycling. The crack initiation was the result of rapid temperature cycling O associated with the turbulent mixing of cooled feedwater with hot reactor water (caused by leakage around the thermal-sleeve),

coupled with the presence of stainless steel cladding on the inner surface of the low-alloy steel (LAS) nozzles. As a result of extensive evaluation, General Electric (GE) developed new thermal-sleeve designs with reduced leakage and recommended O that the cladding be removed from the nozzle inner-radius and bore, thereby reducing the high-cycle fatigue susceptibility and improving ultrasonic inspectability. In addition, changes in sparger design, specific system modifications and changes in operational procedures have been implemented to further mitigate crack O nitiation and growth. These system modifications have been implemented at most BWRs. The NRC has indicated in NUREG-0619 that these changes are responsive to the issue and provide an acceptable approach to nozzle crack mitigation. To account for unexpected crack initiation, or the presence of previous O indications, NUREG-0619 also requires a crack growth evaluation and periodic volumetric and surface examinations. A hypothetical flaw sizu assumption of 0.250" depth into the base metal is used for all NUREG-0619 evaluations (Reference 2).

O Removal of the cladding has the additional benefit of enhanciy the ultrasonic inspectability of the nozzle inner-radius and bore.

1 0

O GE-N E-508-023-0193 Automated-UT scanners and data-acquisition techniques now provide the means of acquiring ultrasonic data in large quantities ver a relatively short period of time. These methods have been O-developed and tested on full-size mockups of nozzles welded to sections of the reactor pressure vessel (RPV) with the goal of determining, by test, which combination of the parameters is best suited for crack detection and sizing. There are numerous pa ameters to be considered, separately and in combination, so O the development and qualification program is based on extensive testing using full-scale mockups, and supported by computer modeling of the nozzle geometry. The improved methodology has resulted in accurate measurements of crack location and size.

P O The methods used for these examinations include scanning with optimized techniques from the vessel wall, the nozzle-to-vessel- l blend radius and the nozzle-forging outside-diameter (OD).

Methods of analyzing the data using three dimensional (3-D) ,

graphics displays were developed to determine the crack location ,

O and maximum depth of penetration into the inner surface of the nozzle. The program objectives to achieve accurate results within with existing field constraints while satisfying personnel radiation-exposure-reduction objectives (ALARA) were met. These techniques have been developed to the point that they are now a reliable alternative to the PT requirements of NUREG-0619.

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3 G E-N E-500-023-0193

11. ULTRASONIC INSPECTION TECHNIQUE -

l D Early in-service inspections (ISI) of nuclear plants using UT l methods utilized manual scanning and data-recording techniques normally performed in high-radiation zones where scan time was necessarily kept to a minimum. Nozzle inner surfaces were clad and the inspection entailed complex geometries with long metal 3 paths. These conditions, combined with the problems associated with precise positioning, resulted in a quantity and accuracy of data typically less than desired, which reduced the confidence in the examination rEsults. These and other factors, prompted the periodic internal PT inspection of feedwater nozzles, specified in NUR EG-0619.

3 GE has developed a program using the GE Reactor inspection System (GERIS) that has significantly improved flaw detection and characterization. The UT techniques were developed and tested on full-size Reactor Pressure Vessel (RPV) and nozzle mockups 3 of various sizes and designs. Notches and crack implants in these mockups, located in various zones along the nozzle inner-radius and bore, range in depth from 0.114" to 0.760" Figure 1 shows the various inspection zones of the nozzle inside surfaces.

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9 Figure 1 Feedwater Nozzle Examination Zones Technique development h'c been based on extensive mock-up

1. testing to determine which combination of parameters is test suited for flaw detection (i.e., the ability to resolve small flaw April 29,1993 3 9

O - GE-NE-508-023-0193 signals from noise signals). These parameters include, but are not limited to location of the UT beam entry surface, beam and O rotation angles, ultrasonic beam mode and the angle at which the beam intersects the flaw.

The data analysis software includes a 3-D graphics package that superimposes peak UT data points on a nozzle image. The software allows viewing data from various orientations and g

magnifications. Access to digitized A-scan data is available for viewing any selected data point, which greatly aids in the classification and evaluation of UT data. The signal amplitude is affected by the relative orientation of the ultrasonic beam direction

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• O The locations of the various flaws are indicated on the plan view of the nozzles, and the relative amplitude of the returns are color-coded for ease of interpretation.

Extensive mockup testing has shown that this nozzle inspection O method is more effective than previous techniques, because: ]

The system design provides improved signal-to-noise ratio responses and improvements in flaw detection capability; O Enhanced data acquisition, storage and retrieval capabilities, as well as A , B- and C-scan displays, provide for a larger data base and a more reliable baseline for comparison with the results from future fr.spections.

As a result of these improved techniques, GE has demonstrated O increased examination accuracy and reliability on full-size nozzle mock-ups. The integrity of the feedwater nozzles can now be more throughly assessed by automatic ultrasonic inspections.

lO O

O i

April 29,1993 4 O

O GE-NE-508-023-0193 A. GENERAL ELECTRIC REMOTE INSPECTION SYSTEM (GERIS)

Automated scanners controlled by GERIS move UT transducers radia'ly and circumferentially around the outside surface of a lO nozzle or the adjacent surface of the RPV. The UT data are j collected and stored in a digital format. When data of particular l interest are found, the complete A-scan is digitized and recorded l on optical disks. Later during data analysis, the UT data stored on the optical disks are analyzed by qualified analysis personnel. l 0

l Nozzle-Mounted Scanner For scanning Zone 1 and 2A as shown in Figure 1, a nozzle-

O mounted scanner, mounted on a channel track clamped around l

I the nozzle OD cylindrical surface, provides the means of ,

performing a remote ultrasonic examination (Figure 2). The nozzle l device includes the nozzle tractor, scanner arm and transducer  !

package.

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Figure 2 Nozzle Scanner O

The nozzle 'ractor consists of a main body with two motor-driven spril 29,1993 5 O

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GE-NE-508-023-0193 magnetic wheels and two hinged-end sections, each with one motor-driven magnetic wheel assembly. The reciprocating scanner O arm is attached to the nozzle tractor and extends perpendicular to the nozzle trac'K for scanning the nozzle-to-vessel welds and l

nozzle inner-radius.

The transducer package consists of a combination of various iO transducer wedges individually mounted in a frame. The wedges -

l produce beam angles as required by the examination technique.

1 Safe-End Mounted Scanner (Zone 2 3 Scanner).

O The safe-end mounted scanner (Figure 3) is mounted on a l channel track clamped around the nozzle safe-end and provides l the means of performing a remote ultrasonic examination of the nozzle inner bore surface. The safe-end mounted scanner is designed for scanning Zones 2A,28 and 3 as shown in Figure 1.

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The safe-end mounted tractor consists of a main body with two motor-driven magnetic wheels and two hinged-end sections, each with motor-driven magnetic wheel assemblies. A pendulum and O resolver are mounted on the main body to give the angular position of the tractor. The reciprocating scanner arm is attached April 29,1993 6 01

GE-NE-508-023-0193  :

O-I to the tractor and extends perpendicular to the safe-end track for scanning the nozzle-bore region.

O r B. EXAMINATION TECHNIQUES ,

Zone 1 Examination -

g.

The nozzle inner-radius is examined from the vessel plate with

• refracted shear waves that pass through the nozzle-to-vessel weld. This scan is performed with the nozzle scanner (see Figure ,

2). The sound beam is designed to intersect the inner-radius at a l O favorable impingement angle. Sound beam and rotation angles i are dependant on the individual nozzle design.

in addition, methods for examining the nozzle inner-radius with refrac'ed shear wsves from the nczzle OD blend radius have been O developed and qualified. As is the case for the Zone 1 examination from the vessel plate, the sound beam and rotation angles are dependant on nozzle design. .,

O Zone 2A Examination The Zono 2A area of the nozzle bore is examined with refracted shear waves from the surface where the nozzle OD t' lend radius merges with the cylindrical surface of the RPV, This scan 'is performed with the nozzle scanner (see Figure 2).

g Scanning from the nozzle OD blend radius affords favorable conditions for flaw detection in areas where detection was once difficult. Typically, coverage extends from the Zone 1 region into i the Zone 2B area.

O' Zone 2B Examination O The Zone 2B area of the nozzle bore is examined from the nozzle -

OD cylindrical surface. This scan is performed with the safe end scanner (see Figure 2). Up to three separate (quarter, mid and three quarter point) refracted shear waves can be utilized to examine their respective areas on the nozzle bore (see Figure 1).  ;

d The terms quarter, mid and three-quarter point are designations for the three examination areas of the nozzle bore in Zone 2 (i.e.,

April 29,1993 7 j J

.O GE-NE-508-023-0193 quarter-point being 1/4 of the Zone 2 length from Zone 1).

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Zone 3 Examination The Zone 3 area of the nozzle bore is examined from the M cylindrical surface of the nozzle OD wnere the beam is directed l

perpendicular to the nozzle axis. The sound beam geometry is similar to that used in a circumferential piping examination.

O.

C. ULTRASONIC SUBSYSTEM l

The UT subsystem consists of a multi-channei, multiplexed, UT l flaw detection instrument. For each channel, digitized output can O

be obtained indicating the amplitude and sweep (time) positions of l

reflectors. The pulse sequence for each of the channels is controlled by the command computer. Each channel is equipped with adjustable gate length, position and amplitude controls to accommodate various types of angle-beam examination l O conditions. The system is equipped with special time-corrected-l-

gain (TCG) circuits with a multiple-slope capability to correct the i

distance-amplitude correction (DAC) curve to a nominal level of  !

amplitude. The A-scan display is used for instrument calibration of sweep, sensitivity, TCG and recording level. Data acquisition is-O automatic through the command computer.  !

D. DATA ANALYSIS O

The GERIS system utilizes a 3D color-graphics workstation to assist in evaluating and characterizing indications from service, fabrication and geometric related UT reflec* ors. The workstation displays peak-amplitude-UT data superimposed on a 3-D wire-O frame model of the nozzle or component being examined. Three-dimensional graphic tools include component viewing at any perspective or magnification. These capabilities assist in accurate UT data evaluation by analysis personnel. An on-line data base of scanner position, UT data and A-scan data can be accessed during data analysis.

O-The real-time A-scan is readily accessible and can be viewej for April 29,1993 8 O-

GE-NE-508-023-0193 data analysis. Figure 4 is an A-scan display of a 0.170" deep nozzle inner-radius EDM notch in GE's clad-removed feedwater

-O nozzle mockup. A-scan data can be viewed either statically or dynamically. Dynamic viewing enhances data evaluation by providing the echo-dynamic characteristics of recorded data. Tip-diffraction sizing techniques are incorporated utilizing the digitized -

A-scan. Tip-diffraction sizing affords the accuracy in flaw depth D. measurements that is needed to supplant the NUREG-0619 PT exams.

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Figure 4 GERIS A-Scan Display lo' E. FLAW SIZING l

The sizing method used is totally dependant on the so-called tip-

'O diffraction phenomenon - sound energy encountering the tip of a defect will be radially. scattered. This radially scattered sound retums to the transducer. Sound energy also reflects from the flaw comer and retoms to the transducer. Frem the relationship between the time of arrival of the reflected signal from the flaw

,0 comer, and the tip diffracted signal, and the angle of incidence of the sound energy on the flaw, the depth of the flaw can be derived.

The crack-tip signalis generally smallin amplitude in comparison to the comer reflection. Depending on the interaction of the sound -

O beam with the flaw und type of flaw, the crack-tip signal can be reduced by 20 decibels (dB) or more in amplitude from that'of the April 29,1993 9 0

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GE-NE-508-023-0193 corner reflection. 6 0-Ill. U LTRASO NIC TECH NIQ U E QUAU FICATION PLAN The ultrasonic qualification plan is based on testing full-scale O mockups (one with the clad removed). The plan incorporates a ,

data sample set developed using ASME Code Section XI, Appendix Vill as a guideline. Appendix Vill does not presently contain specific rules for qualification of inside radius examination methods for unciad nozzles, but it was used as a guide to evaluate data, define sizing methodology and devise field o inspection procedures.

The primary purpose of this demonstration was to qualify the UT equipment and techniques. Development of the full protocol for ,

an Appendix Vill qualif ation is an industry effort that is on-going O at the present time. Use of existing mock-ups with flaws placed in the various inspection zones was considered sufficient, in the ,

absence of protocol qualification. Automatic data recording and retrieval capability allowed for subsequent reviews of inspection .

data, as required to confirm the validity cf the detection and sizing O

results.

The qualification plan is focused on specific portions of Appendix Vill that are applicable to the feedwater nozzle inspection. Flaw 3 depths in the sample set, enconapassed the 0.250" basis in O NUREG-0619. The flaw sizing criteria provided by Appendix Vill was app!ied to the flaw samples to generate a measurement which can be compared to the actual notch depth. Since the data was automatically recorded, it is available for subsequent scrutiny and review for adequacy.

O Appendix Vill, Supplement 5, " Qualification Requirements for inside Radius Examinations" provides rules for extending a qualification for examination of the clad-base metal interface on the vessel (Supplement 4) to a no:tzte inside radius by using a m kup containing some additional notches. Supplement 5 states O that the specimens shall comply with Supplement 4, except that the flaws may be either cracks or notches. For the case of the nozzle inner-radius examination, notches are considered equally representative; however, to verify the capability of the UT techniques to detect and size actual fatigue flaws, two fatigue O cracks were implanted in the inner-radius of another nozzle mockup. The similarity between the fatigue cracks and EDM April 29,1993 10 0  ;

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lO GE-NE-508-023-0193 notches was demonstrated. Because this qualification plan is concerned with only the uncled nozzle inner-radius, the O requirements for the size and number of flaws have been adopted directly from Supplement 4 of Appendix Vill.

The minimum sample is seven flaws for detection qualification, and an additional three flaws to qualify the sizing technique (i.e., a

,0 total of ten are required). The GE qualification sample set contained more than the required 10 flaws. Supplement 4 allows flaws up to 0.750"in depth to be used in the sample set. Manual sizing techniques, which may be used to supplement the automated sizing data, were verified on notches with a maximum depth of 0.750". Some notches are slightly wider than nominally O

specified by Appendix Vill, but this is not considered detrimental to the qualification. Variations in notch width showed no significant difference in detection or sizing results. The notches  ;

were not filled; however, this was not expected to impact the i ultrasonic examination. The flaw configuration in the feedwater l O nozzle mock-up had flaws in all inspection zones for the qualification data set. Flaws were radially oriented as specified in Appendix Vill, which is also consistent with fracture mechanics predictions and field experience with nozzle cracking.

O Field service personnel who perform the on-site examinations have been trained and demonstrated their proficiency in the UT techniques using the samples in the clad removed feedwater nozzle mock-up. Those performing data analysis have received a practical examination using recorded data, similar to that used O under SNT-TC-1A qualification programs.

A. QUALIFICATION NOZZLE MOCKUPS O

CLAD REMOVED FEEDWATER MOCKUP (EDM NOTCHES)

The clad removed feedwater nozzle mock-up used in the qualification testing was fabricated by GE of components from a

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O The forging was machined to represent a barrel type feedwater nozzle which had the cladding removed. The scanning for Zone 2A was performed on the nozzle-to-vessel weld surrace. This surface was hand welded and ground and is typical of the nozzles O that had experienced nozzle-in.'er-radius cracking in the field.

This nozzle-to-vessel weld configuration was selected Decause April 29,1993 11

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GE-NE-508-023-0193 -

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l scanning from this hand-ground surface is the most difficult to perform.

O The EDM notches were distributed throughout the examination volume. A notch of each nominal depth was located in each I inspection zone to demonstrate the individua; testing technique for both detection and sizing. The notches are radially oriented as specified in Appendix Vill, which is also in accordance with fracture lO mechanics predictions and field experience with actual nozzle fatigue cracks.

UNCLAD FEEDWATER NOZZLE MOCKUP (FATIGUE CRACK IMPLANTS)

.O To confirm that the GE procedures will detect and size fatigue cracking, fatigue crack implants were welded into an unclad feedwater nozzle forging. The unciad feedwater nozzle mockup used for implanting these fatigue cracks was from another cancelled BWR.

The fatigue cracks were generated in material specimens tne same g as the nozzle forging.

O B. QUALIFICATION TEST RESULTS DETECTION As discussed earlier and shown in Figure 1, the inner-radius and bore O are divided into different inspection zones. To effectively examine these zones, specially developed techniques are used where -

examinations are performed from the vessel plate, OD blend radius and nozzle OD. All the techniques that are presently used by GE were included in this qualification testing. Individua' nozzle geometries will determine which of the above techniques will be O )

applied. )

A comparison of the EDM notch data and fatigue crack detection data showed that the amplitude responses of fatigue cracks and EDM n t hos of comparable depths were similar.

O In summary, the fatigue cracks were equally detectable as the EDM notches. This coupled with the extensive qualification with the EDM notches provides confirmation of the effectiveness of the UT system and techniques to detect fatigue cracking in the field.

April 29,1993 12 0

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- GE-NE-508-023-0193

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scanning from this hand-ground surface is the most difficult to perform.

O The EDM notches were distributed throughout the examination I volume. A notch of each nominal depth was located in each l

inspection zone to demonstrate the individual testing technique for both detection and sizing. The lotches are radially oriented as l specified in Appendix Vill, which is also in accordance with fracture O mechanics predictions and field experience with actual nozzle fatigue l cracks.

UNCLAD FEEDWATER NOZZLE MOCKUP (FATIGUE CRACK IMPLANTS)

O To confirm that the GE procedures will detect and size fatigue cracking, fatigue crack implants were welded into an unclad l feedwater nozzle forging. The unciad feedwater nozzle mockup used for implanting these fatigue cracks was from another cancelled BWR. 1 The fatigue cracks were generated in material specimens the sam 6 O as the nozzle forging.

O B. QUALIFICATION TEST RESULTS DETECTION As discussed earlier and shown in Figure 1, the inner-radius and bore O are divided into different inspection zones. To effectively examine these zones, specially developed techniques are used where examinations are performed from the vessel plate, OD blend radius and nozzle OD. All the techniques that are presently used by GE were included in this qualification testing. Individual nozzle O geometries will determine which of the above techniques will be applied.

A comparison of the EDM notch data and fatigue crack detection data showed that the amplitude responses of fatigue cracks and EDM notches of comparable depths were similar.

g In summary, the fatigue cracks were equally detectable as the EDM notches. This coupled with the extensive qualification with tne EDM notches provides confirmation of the effectiveness of the UT system and techniques to detect fatigue cracking in the field.

April 29,1993 12 0

O GE-NE-508-023-0193 SIZING O

Sizing capabilities were qualified both with automated and manual techniques. Manual techniques may be used to supplement the automated data, if necessary, during a field examination. For this qualification program, the EDM notches and the fatigue crack O implants were sized with both manual and automated data from both directions. The sizing of flaws from both directions increases the i qualification data base for number of samples by a factor of two and better assesses the technique's sizing capabilities. The sizing '

acceptance criteria as outlined by Appendix Vill was demonstrated.

lO in summary, the EDM notches and fatigue crack implants were successfully sized. The sizing results are acceptable to Appendix Vill acceptance criteria. The UT techniques are fully validated for crack sizing in the field.

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O GE-NE-508-023-0193 lO IV. REFERENCES i

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1) NUREG-0619, "BWR Feedwater Nozzle and Control Rod Drive 3 l

lO Return Line Nozzle Cracking", November 1980.

2) NRC Generic letter 81-11 to all Power Reactor Licensees from Darrell Eisenhut, February 28,1981.

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