ML19353B128
| ML19353B128 | |
| Person / Time | |
|---|---|
| Site: | Grand Gulf  |
| Issue date: | 12/01/1989 |
| From: | Titus F SYSTEM ENERGY RESOURCES, INC. |
| To: | |
| Shared Package | |
| ML19353B126 | List: |
| References | |
| NUDOCS 8912110240 | |
| Download: ML19353B128 (6) | |
Text
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GRAND GULF NUCLEAR STATION UNIT 1 i
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NUMBER 1 LOW PRESSURE' TURBINE ROTOR ULTRASONIC INSPECTION
SUMMARY
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PREPARED BY NUCLEAR PLANT ENGINEERING F. W. TITUS, DIRECTOR LB912110240.891201
.;PDR.~ADOCK 05000416 Q
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NUMBER 1 LOW PRES $URE TURBINE ROTOR I
't J
ULTRA $0NIC INSPECTION
SUMMARY
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Page 2 of 6 1
i TABLE OF CONTENTS i
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1.
INTRODUCTION.............................................................
3 2.
DESCRIPTION OF INSPECTf0NS............................................... 4 i
0 2.1.
Corner Reflection Technique (45 technique)....................
4 0
2,2.
Grazing incidence (90 technique)............................. 4 i
0 2.3.
Radial Incidence (0 technique)................................
4 3.
INSPECTION
SUMMARY
4 4.
INSPECTION RESULTS..................................,....................
5 5.
EVALUATION OF RESULTS....................................................
6 TABLE 1..................................................................
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F, NUMBER 1 LOW PRESSURE TURBINE ROTOR l
ULTRASONIC INSPECTION
SUMMARY
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1.
INTRODUCTION Grand Gulf Nuclear Station (GGNS), Operating License No. NPF 29, License Condition 2.C.(26) requires an ultrasonic inspection (UT) of the bores and keyways of the low pressure (LP) turbine disc for indications of cracking.
The inspections are required before the turbine rotor exceeds 50,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of operation and are required to continue on a 50,000 hour0 days <br />0 hours <br />0 weeks <br />0 months <br /> interval.
i During GGNS's third refueling outage (RF03), the number 1 LP turbine was disassembled for maintenance and the rotor disc bore and keyways were UT inspected.
The number 1 LP turbine rotor had accumulated approximately 28,253 service hours since commercial operation.
The RF03 inspections were performed by the turbine manufacturer, Kraftwerk Union (KWU),
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NUMBER 1 LOW PRESSURE TURBINE ROTOR ULTRASONIC INSPECTION
SUMMARY
Page 4 of 6 i
2.
DESCRIPTION OF INSPECTIONS For complete inspection of the disc bores and keyways several inspection techniques are required.
The sensitivity of these inspection techniques have been verified by testing and by actual UT inspections of other LP rotor shrunk-on discs.
0 2.1.
Corner Reflection Technique (45 technique)
This is a very sensitive technique that uses shear waves to detect small indications, e.g.
score marks in the disc bore.
Experience has shown that these indications typically have a radial depth of about 0.5-0.8 mm.
The ultrasonic beam meets the bore at 450 (in a circumferential direction) and is only reflected to the receiving probe if there is a reflector with radial-axial orientation.
0 2.2.
Grazing incidence (90 technique)
This is a technique that also utilizes shear waves.
The beam meets the bore at 900 in the tangential direction.
This technique is used for sizing indications in the undisturbed bore surface with depths greater than 2.5 mm.
Furthermore, this technique is used to detect defects in the keyways with depths greater than 2.5 mm.
0 2.3.
Radial Incidence (0 technique)
If reflectors greater than 2.0 mm EFH (equivalent flat bottom hole) are detected with the grazing incidence technique, the radial incidence technique is used to size the radial depth of the reflector.
Longitudinal waves of high frequencies are used which meet the bore surface perpendicularly.
This technique assumes branch cracking and that the defects have a radial depth greater than 2.0 mm.
3.
INSPECTION
SUMMARY
I The shrink-fit area of the disc bore is subdivided into 15 to 22 inspection zones depending on the width of the discs.
These zones are inspected step by step using the corner reflection technique.
If indications are identified, the same zone (s) is inspected by the grazing incidence technique.
If the grazing incidence technique reveals indications greater than 1.5 mm EFH, the area is inspected using the radial incidence technique.
For each test step there is a written test instruction nrcturb i
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NUMBER 1 LOW PRESSURE TURBINE ROTOR ULTRASONIC INSPECTION
SUMMARY
Page 5 of 6 that includes all values for the settings to perform the inspection of the zone correctly.
The side zones of the bore are inspected using a tandem technique (pitch-catch technique with two probes).
The sound emitting
/ sound receiving probes are fixed to the disc surface by a manipulation system.
While turning the rotor with a constant speed of about 0.5 rpm, the probes are coupled to the disc surface by a layer of water.
Each zone is inspected from 00 0
to 360 in the circumferential clockwise direction.
The received signals are viewed on an oscilloscope and simultaneously recorded on a graph and a magnetic tape data storage unit.
0 Also, the 0 position corresponding to the 0 position which is stamped on the face of the TS-coupling is recorded.
With this information each indication and reflector can be identified to a definite axial and circumferential position in the shrink-fit area.
4.
INSPECTION RESULTS Using the corner reflection technique, several indications were identified in the bore of discs 1 TS, 2 GS and 5 GS.
Table 1 provides information specific to each indication.
Indication No. 1 in disc 5 GS is the largest reficctor with a maximum amplitude of 2.1 mm EFH and extended within one inspection zone.
Additional inspections using the grazing incidence technique did not record a radial depth for the indications detected by the corner reflection technique.
No indications were detected in the discs
- keyways, TABLE 1 Disc Refl.
Insp. Zone Circumf.
Corner Ref1. 45 lGrazingInc.90 Radial Insp. O No.
No.
No.
From/to Position Sonic Dist.
[FH li Sonic Dist.
[FH Sonic Olst.
Radial Remarks 5
m Degree m
m m
m Depth m m
115 1
15 356/386 327 239 1.4 500 hRI SM 2
15 356/386 338 239 1.3 500 NRI SM 3
15 356/386 347 239 1.1 500 NRI SM 2GS 1
9 169/202 166 324 0.8 SM 1
11 235/272 164 307 1.5 557 NR1 SM 1
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272/305 166 325 1.1
$55 NRI SM SGS 1
16 157/491 157 270 2.1 502 NRI SM 2
16 157/491 291 270 2.0 502 NR1 SM Legend: Ts Turbine $1de, GS = Generator Side, NRI a No Recordable Indication, SM = Score Mark nrcturb
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I NUMBER 1 LOW PRES $URE TURBINE ROTOR ULTRASONIC INSPECTION
SUMMARY
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EVALUATION 0F RESULTS j
The ultrasonic inspection of the shrunk on discs of the number 1 LP rotor revealed several indications indicative of fabrication or score marks that I
occur when the discs are pressed onto the shaft with a shrink-fit.
This evaluation is confirmed by the grazing incidence technique since a radial depth could not be detected for the indications identified by the corner reflection technique.
Because the grazing incidence inspection did not r
detect a radial depth for the indications identified by the corner reflection technique, the radial scans were not required.
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