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GRAND GULF NUCLEAR STATION

UNIT 1

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NUMBER 1 LOW PRESSURE' TURBINE ROTOR ;

ULTRASONIC INSPECTION SUMMARY )i

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PREPARED BY

NUCLEAR PLANT ENGINEERING

F. W. TITUS, DIRECTOR

LB912110240.891201.;PDR.~ADOCK 05000416Q PDC

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:! NUMBER 1 LOW PRES $URE TURBINE ROTOR !I 't J ULTRA $0NIC INSPECTION SUMMARY

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TABLE OF CONTENTSi

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1. INTRODUCTION............................................................. 3.

2. DESCRIPTION OF INSPECTf0NS............................................... 4i

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02.1. Corner Reflection Technique (45 technique).................... 4 102,2. Grazing incidence (90 technique).. ........................... 4 i

02.3. Radial Incidence (0 technique)................................ 4'

3. INSPECTION SUMMARY....................................................... 4;

4. INSPECTION RESULTS..................................,.................... 5'

5. EVALUATION OF RESULTS.................................................... 6:

TABLE 1.................................................................. 5 1

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NUMBER 1 LOW PRESSURE TURBINE ROTOR lULTRASONIC INSPECTION SUMMARY i't

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1. INTRODUCTION

Grand Gulf Nuclear Station (GGNS), Operating License No. NPF 29, LicenseCondition 2.C.(26) requires an ultrasonic inspection (UT) of the bores andkeyways of the low pressure (LP) turbine disc for indications of cracking.The inspections are required before the turbine rotor exceeds 50,000 hoursof operation and are required to continue on a 50,000 hour interval.

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During GGNS's third refueling outage (RF03), the number 1 LP turbine wasdisassembled for maintenance and the rotor disc bore and keyways were UTinspected. The number 1 LP turbine rotor had accumulated approximately28,253 service hours since commercial operation. The RF03 inspections wereperformed by the turbine manufacturer, Kraftwerk Union (KWU),

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NUMBER 1 LOW PRESSURE TURBINE ROTORULTRASONIC INSPECTION SUMMARY !

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2. DESCRIPTION OF INSPECTIONS

For complete inspection of the disc bores and keyways several inspectiontechniques are required. The sensitivity of these inspection techniqueshave been verified by testing and by actual UT inspections of other LProtor shrunk-on discs.

02.1. 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 aradial depth of about 0.5-0.8 mm. The ultrasonic beam meets thebore at 450 (in a circumferential direction) and is onlyreflected to the receiving probe if there is a reflector withradial-axial orientation.

02.2. Grazing incidence (90 technique) -

This is a technique that also utilizes shear waves. The beammeets the bore at 900 in the tangential direction. Thistechnique is used for sizing indications in the undisturbed boresurface with depths greater than 2.5 mm. Furthermore, thistechnique is used to detect defects in the keyways with depthsgreater than 2.5 mm.

02.3. Radial Incidence (0 technique)

If reflectors greater than 2.0 mm EFH (equivalent flat bottom *hole) are detected with the grazing incidence technique, theradial incidence technique is used to size the radial depth ofthe reflector. Longitudinal waves of high frequencies are usedwhich meet the bore surface perpendicularly. This techniqueassumes branch cracking and that the defects have a radial depth,greater than 2.0 mm.

3. INSPECTION SUMMARYI

The shrink-fit area of the disc bore is subdivided into 15 to 22 inspectionzones depending on the width of the discs. These zones are inspected stepby step using the corner reflection technique. If indications areidentified, the same zone (s) is inspected by the grazing incidencetechnique. If the grazing incidence technique reveals indications greater,than 1.5 mm EFH, the area is inspected using the radial incidencetechnique. For each test step there is a written test instruction

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NUMBER 1 LOW PRESSURE TURBINE ROTORULTRASONIC INSPECTION SUMMARY

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that includes all values for the settings to perform the inspection of thezone correctly. The side zones of the bore are inspected using a tandemtechnique (pitch-catch technique with two probes). The sound emitting/ sound receiving probes are fixed to the disc surface by a manipulationsystem. 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 0to 360 in the circumferential clockwisedirection. The received signals are viewed on an oscilloscope andsimultaneously recorded on a graph and a magnetic tape data storage unit.

0Also, the 0 position corresponding to the 0 position which is stamped onthe face of the TS-coupling is recorded. With this information eachindication and reflector can be identified to a definite axial andcircumferential position in the shrink-fit area.

4. INSPECTION RESULTS

Using the corner reflection technique, several indications were identifiedin the bore of discs 1 TS, 2 GS and 5 GS. Table 1 provides informationspecific to each indication. Indication No. 1 in disc 5 GS is the largestreficctor with a maximum amplitude of 2.1 mm EFH and extended within oneinspection zone. Additional inspections using the grazing incidencetechnique did not record a radial depth for the indications detected by thecorner reflection technique. No indications were detected in the discskeyways,

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TABLE 1

Disc Refl. Insp. Zone Circumf. Corner Ref1. 45 |GrazingInc.90 Radial Insp. ONo. No. No. From/to Position Sonic Dist.

[FH |iSonic Dist. [FH Sonic Olst. Radial Remarks 5

m Degree m m m m Depth mm115 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 12 - 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- -

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Legend: Ts Turbine $1de, GS = Generator Side, NRI a No Recordable Indication, SM = Score Marknrcturb

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NUMBER 1 LOW PRES $URE TURBINE ROTORULTRASONIC INSPECTION SUMMARY j

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5. 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. Thisevaluation is confirmed by the grazing incidence technique since a radialdepth could not be detected for the indications identified by the corner 'reflection technique. Because the grazing incidence inspection did notrdetect a radial depth for the indications identified by the corner -

reflection technique, the radial scans were not required.P

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