ML18086B343

X 17 Fuel Assembly Guide Thimble Tube Wear Exam Rept.

ML18086B343
Person / Time
Site:	Salem, North Anna, 05000000
Issue date:	01/31/1982
From:	Kunishi H, Schmidt G, Skaritka J WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
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ML18086B342	List: ML18086B341 ML18086B343
References
NUDOCS 8203050371
Download: ML18086B343 (19)

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ENCLOSURE SALEM UNIT I 17xl7 FUEL ASSEMBLY

• GUIDE THIMBLE TUBE WEAR EXAMINATION REPORT JANUARY 1982 Edited by: J. Skaritka Contributors: H. Kunishi, G. R. Schmidt WESTINGHOUSE ELECTRIC CORPORATION Nuclear Energy Systems P.O. Box 355 Pittsburgh, PA . 15230 r~S20-3oso371 020361- -

I PDR ADOCK 05000272 1, P PDR .-: ;

• TABLE OF CONTENTS Title 1.0 Introduction and Summary 1-1 2.0 Scope of Surveillance Program 2-1 2.1 Guide Thimble Tube Wear Examination 2-1 2.2 Fuel Assembly Location and Irradiation History 2-1 3.0 Examination Equipment and Techniques 3-1

3. 1 Equipment 3-1 3.2 Procedure 3-2 4.0 Results 4-1 5.0 Conclusions 5-1 6.0 References 6-1

-*---=- -.,------***-**-~ ----- *---~~*-** . .,_ .... ,_,, ____ ,... .... ,..-~.-...- .. -~... --.-*- ***-.-*** - -** .. -*--*---* --- *--*:-~******"'-****.**,.--;----; , .. *-**:*

1.0 INTRODUCTION

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SUMMARY

Background

Fuel assembly guide thimble tube wear has been observed during post irradiation examinations of irradiated fuel assemblies. from several operating reactors, most notably perforation of thimble walls in non-Westinghouse fuel assemblies which operated in the Millstone 2 reactor. Core coolant flow induces a vibrating motion in the fully withdrawn (parked) control rods~ Fretting wear of the Zircaloy-4 thimble wall occurs when the.end of the vibrating control rods (stain-less st.eel) contact the softer Zircaloy-4. Although some wear has been observed in Westinghouse designed fuel, no guide thimble tube wear perforations have ever been observed in Westinghouse fuel.

Westinghouse has analyzed wear data from irradiated fuel assemblies.

Based on conservative wear analyses of 14xl4, 15xl5 and 17xl7 fuel assemblies, Westinghouse concluded that the mechanical integrity of the guide thimble tube(s) is maintained during normal operation, accident conditions, and non-operational loading conditions for at least 225 weeks (>3 cycles) of fuel assembly operation in core locations containing,parked control rods. The NRC evaluated the Westinghouse wear analyses and concluded that*the analyses probably accounts for all the major variables in the wear process(l). However, to obtain additional confirmatory information of no thimble wear hole formation in 17xl7 fue 1, t,he NRC requested a non-destructive *survei 11 ance program from several near-term OL applicants. A cooperative program was established by Duke Power, PG&E, PSE&G, TVA, VEPCO and Westinghouse to obtain the necessary wear data from Salem Unit l. The NRC agreed with a surveil-lance program( 2) to examine for wear holes all guide thimble tubes in six fuel assemblies having parked control rods in either one or two cycles of operation. The examination was completed in September 1981.

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Summary This report summarizes the results of the Salem Unit 1 17xl7 fuel assem-bly guide thimble tube on-site examination program conducted during September 1981. The primary objective of this program was to aemon-strate no wear hole penetrations in guide thimble tubes of 17xl7 fuel assemblies which contained control rods. This objective was success-fully completed by observing no wear hole formation during the exam-ination of all guide thimble tubes in six fuel assemblies. This confirms the Westinghouse analytical predictions of no wear holes and demonstrates that 17xl7 fuel assemblies satisfy NRC acceptability criteria(l) for guide thimble tube structural integrity.

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2.0 SCOPE OF SURVEILLANCE PROGRAM

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2. l GUIDE THIMBLE TUBE WEAR EXAMINATION The purpose of the wear examination was to determine if any wear holes

(> 1/16 inch) occurred in guide thimble tubes with parked control rods during one or two cycles of operation in Salem Unit 1. The visual examination of the inside diameter of the guide thimble tubes was per-formed by a borescope for the top 20 inches of the thimbles. Figure 2-1 shows the axial location of a fully withdrawn (parked) control rod in a guide thimble ~ube. Parked control rods extend .approximately seven inches into the guide thimble tubes. The parked control rod position has the greatest potential for causing wear due to flow induced rod vibrations. The selected tubes were all the thimbles in the six fuel assemblies given in Table 2-1. Two of the assemblies had parked control rods for two cycles, and four assemblies had parked control rods only for the first cycle of operation. The six discharged Region l fuel assemblies were non-destructively examined with a Westinghouse designed borescope and a TV camera system which is described in Section 3.0. The system was designed to be capable of detecting ~ear holes of at least l /l 6 diameter *.

11 2.2 FUEL ASSEMBLY LOCATION AND IRRADIATION HISTORY The six fuel -assemblies were selected from each core quadrant to assess the effect, if any, of core locat1on on guide thimble tube wear. The assemblies experienced a representative range of coolant flow velocities in the control rod cluster guide column region above the core.

Figure 2-2 shows the Salem Unit l Cycle* l core locati~ns pf the six sur-veillance assemblies and the parked control rods used. Cycle l attained full power opera.tion in May 1977 and achieved a core average burnup of 15,400 MWD/MTU when shutdown for refueling in April 1979. The Cycle l full power operating conditions were 3338 MWt core power, 2250 psia core 2-1

pressure, approximately 378,600 gpm core flow and approximately 570°F core average coolant temperature. The shutdown and control rods for the six assemblies remained in the fully withdrawn {parked) ~osition at 228 steps throughout Cycle l except during scrams.or shutdowns.

Figure 2-3 shows the Salem Unit l Cycle 2 core locations of the six f_uel assemblies and the parked control rods in two of the fuel assemblies.

The Cycle 2 full power operating conditions were the same as that fo*r Cycle 1. Cycle 2 attained full power operation February 1980 and was shutdown for refueling in September 1980 with a Cycle 2 burnup of 8,300 MWD/MTU.

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TABLE 2-1 FUEL ASSEMBLIES EXAMINED FOR GUIDE THIMBLE TUBE WEAR Operating Time With Fuel* Core Location Control Rod Banks Parked Control Rods

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Assembly Cycle l Cycle 2 Cycle Cycle 2 (weeks}

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A37(a) PB KB c 160 Sc A18( a) KlO J6 NONE 120

-~:* SD A22(a) H2 H6 c 160

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A59(b) Dl2 GlO SA NONE 120 A61 (a) Cl B7 SB NONE 120 A30( a) L3 L4 A NONE 120

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(a) Assemblies not near pressure vessel coolant outlets.

(b) Assemblies located in same region of pressure vessel as coolant outlets.

• All 24 guide thimble tubes in each asse~bly examine~ for wear.

SA,SB,SC,SD - Shutdown Banks A,C - Control Banks 2-3

TOP NOZZLE ADAPTER PLATE STAINLESS STEEL SLEEVE ZIRCALOY GUIDE THIMBLE EXPANSION LOBE CONTROL ROD

- _7.0" NOH I MAL TOP GRID

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.+1--- TOP OF ROD TRAVEL (AT 228 STEPS)

Figure 2-1. Axial L~cation of Fully Withdrawn Control Rod in Fuel Assembly 2-4

~ ' r 15 14 13 12 11 10 8 8 7 6 5 4 3 2 1 R

D Sc ..... D p A2 A37 A6 OUTLE T c A Se Se A c N NOZZLE CS8 14.25 A58 A13 M9 C51 OUTLET SA B SA. N OZZLE

~ M A50 A17 14.36 A5 14.51 A So SA So A'llllJI L

MS 838 A64 A53 824 A30 D So~ c So D 14.8 A31 A18 A&O A41 A43 A38 Sa SA So Se 14.57 A27 A47 A15 A32 MO 5c B c D c B Sc""'llli H 14.34 14.12 A11 A29 A26 A52 A22 Sa SA Se G MS A20 A44 A3 A23 A42 D So c So D F 14.18 A7 14.55 14.35 14.10 14.1 AUi '

A SA So A E A54 827 14.56 Al3 B59 A33 OUTLET SA..... B SA NOZZLE D

OUTLET A59 M A21 M6 A14 NOZZLE I c A Sa Sa 'llllJI A c c C33 A65 D

A48 Sc A61 D

A28 C15

. B A39 A24 Al2 A

kxx~ RCC TY,E FUEL ASSEMBLY . SA, Se, Sc So

• SHUTDOWN BANK RCC A

• ABANKRCC B

• BBANK RCC C

• CBANK RCC FUEL ASSEMBLY SELECTED D

• DBANK RCC FOR THIMBLE EXAMINATIOi\I Figure 2-2 Salem Unit 1 Cycle 1 Fuel Assemblies in RCC Locations 2-5

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15. 14 13 12 11 10

• 8 7 6 5 4 3 2 ,

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R D Sc D p C34 B36 C39 c A Sa Se A c N

OUT LE T AS BSD B15 B32 812 A1 OUTLET NOZZLE 8 NOZZLE SA 811 C8 A17 C42 SA B7 -----M A - ~

A B3D A2 B35 SA B62 So A38 B34 ---L D So .c~ So D cso C28 CS9 A31 C33 CS4 CS8 ----K Se B23 SA Bsa c

B18 B45 A~

So B52 B

Se B1D ----.1 Sc B D C'lllllil Sc H

B27 A.7 A47 C3 A22 A43 824 Sa 81 So 820

~ So 844 So 857 SA B9 Se B31 ----G D So c So D F

C43 C82 CS1 A16 C15 C21 C14 B6D A So A.19 SA 826 So B63 So A62 A

BA3

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E SA B SA OUTLE T D NOZZLE B17 C64 Ml C25 B53 OUTLET c A Se Se A c N OZZLE A31 864 B61 B13 B6 A4

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*- c D

C38 Sc 859 Al~ D C9 8

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A RCCTYPE FUEL ASSEMBLY SA,. Sa,. Sc. Sg

• SHUTDOWN BANK RCC A

• A BANK RCC B

• BBANK RCC C

• CBANK RCC

[j l"U!L .ASSEMBLY SELECTED FOR THIMBLE EXAMINATION D

• DBANK RCC Figure 2-3 Salem Unit 1 Cycle 2 Fuel Assemblies in RCC Locations 2-6

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I f, 3.0 EXAMINATION EQUIPMENT AND TECHNIQUES 3.l EQUIPMENT The Fuel Assembly Thimble Tube Examination System consists*of a borescope assembly, X-Y-Z position plate, 17xl7 guide block, lower support fixture assembly and console. A schematic of the system without the console is shown in Figure 3-1.

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The borescope assembly is shown in Figure 3-2. A lo*w light level TV....

camera is mounted in the support bracket. There are two different view-ing heads. One is a circumferential viewing head which essentially provides a 360° view of the guide thimble tube inner surface at each axial examination location. The forward oblique viewing ~ead provides a high magnification view of a specific area; it can be used to more closely examine any anomaly found.

As shown in Figure 3-1, the borescope assemb~y is attached to an X-Y-Z positioning plate. A position potentiometer on the plate provides ver-tical location to a digital display on a TV screen. A hand wheel on top of t~e plate is used for rotation of the borescope, and rotational posi-tion measured by a potentiometer is also digitally displayed on* the TV screen. The X-Y-Z' positioning plate is set on a tie plate of the lqwer support fixture assembly which hangs from the poolside curb wall. The fixture can be moved left or right to a position over the ~ew fuel elevator.

The fuel assembly is placed in the new fuel elevator for examination.

The elevator is raised so that the top of the fuel assembly is ten feet below the surface of the pool water duri_ng the examination. A guide block with chamfered holes at the fuel assembly guide thimble tube loca-tions seats on the top nozzle of the fuel assembly. The block acts to guide the borescope into the guide thimble tube and has a numbering system which identifies the guide thimble tube. A TV monitor in the

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I J control console provides the borescope field of view and digital dis-plays of assembly number, guide thimble tube number, _tube orientation, and vertical position of the borescope.

• ~ A defect standard with slots and holes of various sizes was used to qualify the system. Using this standard, the system checked-out before shipment of the equipment to the site and at the beginning of the guide thimble tube examination.

3. 2 PROCEDURE The complete inside surface of the top 20 inches of each guide thimble tube was visually examined and recorded on video tape. Four progressive passes with the borescope were used to examine each guide thimble tube~

Pass l was at a zero degree orientation with the borescope travelling at a slow rate. The borescope was then rotated 90° clockwise and with-drawn at the slow rate for pass 2; In the same manner as passes 1 and 2, the borescope examinations were made at 180° and 270° orienta-tions for passes 3 and 4. The field of view on the TV screen ranged from about 100° to 250° for each p~ss so that the entire inner sur-face of each guide *thimble tube was examined for the top 20 inches.

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} j KEY:

A - ROLLERS H B - BRAKE C - GUIDE PINS D-TVCAMERA E - X-Y POSITIONER F - TV CABLE TO RECORDER I~::~~~~~~-;;:>- X-Y-Z POSITIONING

'AND MONITORS 01 PLATE

-~, G. - BORESCOPE H - ROTATIONAL ORIENTATION POTENTIOMETER F

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BORESCOPE ASSEMBLY

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DECK CURB WALL EW FUEL ELEVATOR Figure. 3-1 Schematic of Fuel Assembly Thimble Tube Examination System 3-3

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) .I BRACKET T.V. CAMERA .. C.. MOUNT FOCUSING RING ELECTRICAL CONNECTION GAS VALVE 72" EXTENDER '"*

Cl RCUMFERENTIAL VIEWING HEAD

• 43" OBJECTIVE BORESCOPE SECTION OBJECTIVES Figure 3-2 Borescope Assembly

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,~ 4.0 RESULTS All 24 guide thimble tubes in each of the six fuel assemblies 1were examined by the procedures in Section 3.0 to determine if any-wear holes were present. The examinations ~evealed no evidence of a wear hole or unusual wear of the inner wall of the guide thimble tubes. Typical results of the borescope examinations are discussed below.

Figure 4-1 shows a typical appearance of the top end of the guide thim-

• .fr ble tubes. The interior wall of each guide thimble tube had a gray non-lustrous surface over the entire 20 inches examined. A typical appear-ance of the interior wall of a guide thimble tube is shown in Figure 4-2.

Minor longitudinal scratch m~rks were occasionally observed. Figure 4-3 shows the most pronounced scratches~ which had a width less than 1/32 inches and extended axially from 3.0 to 8.0 inches below the top of the guide thimble tube. These scratch marks had no appreciable depth. They may have been caused by the borescope head scraping the guide thimble tube wall during the examination. An irregular shaped black area was J

,; observed on a guide thimble tube of fuel assembly A22, as shown in

-r Figure 4-4. The area was located about 7.5 inches below the top of the guide thimble tube at about 90° circumferenti~l location.* The area was estimated to be about o.*5 inches long (tube axial direction) and - l less than 1/16 inches wide. This area appeared to have no appreciable I

depth. The examinations revealed no evidence of a wear hole or* unusual wear of the inner wall of the guide thimble tubes. *

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INSIDE SURFACE OF THIMBLE TUBE GAP SCRATCH MARK LIGHT STRUCTURAL SUPPORT Figure 4-1 Typical of Inner Surface of Guide Thimble Tube from Thimble Tube No. 12 of Assembly A22

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.,--~-TOP OF END THIMBLE

~- ~* TUBE STRUCTURAL SUPPORT Figure 4-2 Typical Appearance of Top End of Guide Thimble Tube from Guide Thimble No. 12 of Assemb ly A22 4-2

STRUCTURAL SUPPORT GAP THIMBLE WALL SCRATCH MARKS BORESCOPE HEAD LIGHT Figure 4-3 Longitudinal Scratch Marks Seen on Inner Surface of Thimble Tube No. 14 of Assembly A 18 STRUCTURAL SUPPORT BLACK SPOT LIGHT THIMBLE WALL BORESCOPE HEAD Irregular Shaped Black Area Seen on Inner Surface of Thimble Tube No. 12 Figure 4-4 of Assembly A22 4-3 t

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5.0 CONCLUSION

S Based on the examination of 144 guide thimble tubes in s~x Salem Unit 1-fuel assemblies operating for orie or two cycles of irradiation with parked control rods, it is concluded that Westinghouse 17xl7 fuel assem-blies will not develop wear holes in the guide thimble tubes when oper:-

ating with Westinghouse designed ~ontrol rods. There was no evidence of.

excessive wear on the thimble tube wall.

The results of this surveillance program satisfy the NRC's request(l) to confirm Westinghouse's wear analytical results by demonstrating no guide thimble tube wear holes. The wear analyses, previously reviewed by the NRC(l), showed that the mechanical integrity of the guide thimble tubes is maintained under normal operation, accident conditions and non-operational conditions for at least 225 weeks of fuel assembly operation with control rods in the parked position. This represents more than three cycles of operation under the conservative assumption of continued insertion of control *rods for each fuel cycle.

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6.0 REFERENCE

1. R. Riggs, "Control Rod Guide Tube Wear in Operating Reactors,"

NUREG-0641, April 1980.

2. NRC memorandum from R. 0. Meyer to K. Kneil;

Subject:

Westinghouse Proposal for 17xl7 Guide Thimble Surveillance; FeQruary 29, 1980.

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