ML18086B343

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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 R, SKARITKA J
WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
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ML18086B342 List:
References
NUDOCS 8203050371
Download: ML18086B343 (19)
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Text

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020361--I PDR ADOCK 05000272 1, P PDR * *

  • 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 1.0 2.0 3.0 4.0 5.0 6.0 *

  • TABLE OF CONTENTS Title Introduction and Summary 1-1 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 Examination Equipment and Techniques
3. 1 Equipment 3.2 Procedure Results Conclusions References 3-1 3-1 3-2 4-1 5-1 6-1 -*---=-

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1.0 INTRODUCTION

AND

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 Core coolant flow induces a vibrating motion in the fully withdrawn (parked) control Fretting wear of the Zircaloy-4 thimble wall occurs when the.end of the vibrating control rods less st.eel) contact the softer Zircaloy-4.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 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. 1-1

. . . ' ** Summary This report summarizes the results of the Salem Unit 1 17xl7 fuel bly guide thimble tube on-site examination program conducted during September 1981. The primary objective of this program was to strate no wear hole penetrations in guide thimble tubes of 17xl7 fuel assemblies which contained control rods. This objective was fully completed by observing no wear hole formation during the 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.

1-2

  • , ;; ':. -------------\ 2.0 SCOPE OF SURVEILLANCE PROGRAM / 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 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 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 holes of at least l /l 6 11 diameter *. 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 pf the six 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) 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. 2-2

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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 Assembly Cycle l Cycle 2 Cycle Cycle 2 (weeks} A37(a) PB KB Sc c 160 A 18( a) KlO J6 SD NONE 120 A22(a) H2 H6 Sc c 160 A59(b) Dl2 GlO SA NONE 120 A61 (a) Cl B7 SB NONE 120 A30( a) L3 L4 A NONE 120 (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 for wear. SA,SB,SC,SD

-Shutdown Banks A,C -Control Banks 2-3

-,:; }: EXPANSION LOBE -_7.0" NOH I MAL TOP NOZZLE ADAPTER PLATE STAINLESS STEEL SLEEVE ZIRCALOY GUIDE THIMBLE CONTROL ROD TOP GRID .+1---TOP OF ROD TRAVEL (AT 228 STEPS) Figure 2-1. Axial of Fully Withdrawn Control Rod in Fuel Assembly 2-4 ..

.. ' r 15 14 13 12 11 10 8 T OUTLE NOZZLE OUTLET NOZZL E I D 14.8 5c 14.34 D 14.18 c CS8 A MS Sa 14.57 Sa MS A A54 c C33 D A2 A 14.25 SA A50 A17 So 838 A31 A18 SA A27 B c 14.12 A11 A20 So A7 14.55 827 SA ..... A59 M A A65 D A39 RCC TY,E FUEL ASSEMBLY FUEL ASSEMBLY SELECTED FOR THIMBLE EXAMINATIOi\I Se A58 A64 A47 A44 SA 14.56 Sa A48 8 Sc ..... A37 B 14.36 c A&O D A29 c 14.35 B A21 Sc A24 7 6 5 D A6 Se A A13 M9 A5 SA So A53 824 So A41 So A15 A32 c A26 SA A3 A23 So 14.10 So Al3 B59 M6 Sa 'llllJI A A61 A28 D Al2 4 3 c C51 SA. 14.51 A'llllJI A30 A43 Se MO B A52 Se A42 14.1 A A33 SA A14 c C15 2 D A38 Sc""'llli A22 D AUi 1 ' OUTLET OZZLE N OUTLET NOZZLE . SA, Se, Sc So

  • SHUTDOWN BANK RCC A
  • ABANKRCC B
  • DBANK RCC Figure 2-2 Salem Unit 1 Cycle 1 Fuel Assemblies in RCC Locations 2-5 R p N M L H G F E D c .. B A I
15. 14 13 12 11 10 T OUT LE NOZZL OUTLE NOZZL E T E [j D C34 c A AS BSD SA 811 C8 A B3D A2 D So cso C28 CS9 Se SA B23 Bsa Sc B c B27 A.7 A47 Sa So 81 820 D So C43 C82 CS1 A So B6D A.19 SA B17 C64 c A A31 864 D C38 RCCTYPE FUEL ASSEMBLY l"U!L .ASSEMBLY SELECTED FOR THIMBLE EXAMINATION
  • 8 Sc B36 Sa B15 8 A17 B35 A31 B18 D C3 So 844 c A16 SA 826 B Ml Se B61 Sc 859 7 Se B32 SA B62 B45 So 857 So B63 Se B13 6 5 4 D C39 A 812 SA C42 B7 -So A38 So C33 CS4 So B52 C'lllllil B A22 A43 SA B9 So C15 C21 So A62 SA C25 B53 A B6 D C9 3 2 c A1 A B34 D CS8 Se B1D Sc 824 Se B31 D C14 A BA3 c A4 , -----R p N OUTLET NOZZLE -----M ---L ----K ----.1 H ----G F ----E D OUTLET OZZLE N ----*-c 8 ----A SA,. Sa,. Sc. Sg
  • SHUTDOWN BANK RCC A
  • DBANK RCC Figure 2-3 Salem Unit 1 Cycle 2 Fuel Assemblies in RCC Locations

' 2-6 r,'. :*-,. * ... j'! t; 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. 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 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 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 is attached to an X-Y-Z positioning plate. A position potentiometer on the plate provides tical location to a digital display on a TV screen. A hand wheel on top of plate is used for rotation of the borescope, and rotational 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 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 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 \ . 3-1 I J **. ;), control console provides the borescope field of view and digital 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 Pass l was at a zero degree orientation with the borescope travelling at a slow rate. The borescope was then rotated 90° clockwise and 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 so that the entire inner sur-face of each guide *thimble tube was examined for the top 20 inches. 3-2

.. :. '* :-. .; . . . . ,_;: } j KEY: A -ROLLERS B -BRAKE C -GUIDE PINS D-TVCAMERA H E -X-Y POSITIONER F -TV CABLE TO RECORDER X-Y-Z POSITIONING

'AND MONITORS 0 1 PLATE G. -BORESCOPE H -ROTATIONAL ORIENTATION POTENTIOMETER F BORESCOPE ASSEMBLY DECK

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

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) . I . -. 43" OBJECTIVE SECTION

  • BRACKET T.V. CAMERA .. C .. MOUNT FOCUSING RING ELECTRICAL CONNECTION GAS VALVE 72" EXTENDER '"* Cl RCUMFERENTIAL VIEWING HEAD Figure 3-2 Borescope Assembly . 3-4
  • BORESCOPE OBJECTIVES

' , *.fr *.* *. ,; -r --:* I 1 !" * 4.0 RESULTS All 24 guide thimble tubes in each of the six fuel assemblies 1 were examined by the procedures in Section 3.0 to determine if any-wear holes were present. The examinations 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-ble tubes. The interior wall of each guide thimble tube had a gray non-lustrous surface over the entire 20 inches examined.

A typical ance of the interior wall of a guide thimble tube is shown in Figure 4-2. Minor longitudinal scratch were occasionally observed.

Figure 4-3 shows the most pronounced 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 Figure 4-4. The area was located about 7.5 inches below the top of the guide thimble tube at about 90° location.*

The area was estimated to be about o.*5 inches long (tube axial direction) and 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. -l I

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

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END OF THIMBLE TUBE STRUCTURAL SUPPORT Figure 4-2 Typical Appearance of Top End of Guide Thimble Tube from Guide Thimble No. 12 of Assemb l y A22 4-2 ..... -... ' .... _.,. .. -* .,

  • ' t LIGHT STRUCTURAL SUPPORT GAP THIMBLE WALL SCRATCH MARKS BORESCOPE HEAD Figure 4-3 Longitudinal Scratch Marks Seen on Inner Surface of Thimble Tube No. 14 of Assembly A 18 Figure 4-4 LIGHT STRUCTURAL SUPPORT BORESCOPE HEAD BLACK SPOT THIMBLE WALL Irregular Shaped Black Area Seen on Inner Surface of Thimble Tube No. 12 of Assembly A22 4-3

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5.0 CONCLUSION

S Based on the examination of 144 guide thimble tubes in Salem Unit 1-fuel assemblies operating for orie or two cycles of irradiation with parked control rods, it is concluded that Westinghouse 17xl7 fuel blies will not develop wear holes in the guide thimble tubes when ating with Westinghouse designed 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. 5-1 .. _:, :._ ..

I I l" "* 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. 6-1

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