ML19257A266
| ML19257A266 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 12/18/1979 |
| From: | Parr O Office of Nuclear Reactor Regulation |
| To: | Proffitt W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| References | |
| NUDOCS 8001030397 | |
| Download: ML19257A266 (7) | |
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UNITED STATES E j ) *.c( ( %,
g NUCLEAR REGULATORY COMMISSION 5. \\
/,' C WASHINGTON. D. C. 20555 e
DEC i L"
Docket No.: 50-339 Sr. W. L. Proffitt Senior Vice President Power Operations Virginia Electric and Power Company P. J Box 26666 Richmond, Virginia 23261
Dear Mr. Proffitt:
SUBJECT:
DEGRADATION OF GUIDE THIMBLE TUBE WALLS Enclosed are the results of our review of the subject matter for North Anna, Unit 2.
We believe that the analysis accounts for the major variables that control the wear process on guide thimble tube walls. Nevertheless, due to the complexities and uncertainties in the wear process, it is necessary to establish a surveillance program for guide tube wear.
This issue is resolved for North Anna, Unit 2 for the first cycle of operation, if TVA agrees to perform a surveil. lance program that meets our minimum objective as described in the enclosure. A cooperative owner's group commitment would also be acceptable, provided a comitment is made prior to January 1, 1980.
If neither of these parties comit to tnis program, it may be required that each near term applicant commit to this program.
Sincerely,
!d lan
. Parr, % Chief Light Water Reactors, Branch No. 3 Division of Project Management
Enclosure:
As Stated cc: See Next Page 1667 031
3 Mr. W. L. Proffitt cc: Mr. Anthony Gambaradella C1arence T. Kipps, Jr., Esq.
Office of the Attorney General 1700 Pennsylvania Avenue, N.W.
11 South 12th Street - Room 308 Washington, D. C.
20C06 Richmond, Virginia 23219 Carroll J. Savage, Esq.
Richard M. Foster, Esq.
1700 Pennsylvania Avenue, N.W.
Musick, Williamson, Schwartz Washington, D. C.
20006 Leavenworth & Cope, P. C.
P. O. Box 4579 Mr. James C. Dunstan Boulder, Colorado 80306 State Corporation Comission Commonwealth of Virginia Michael W. Maupin, Esq.
Blandon Building Hunton, Williams, Gay & Gibson Richmond, Virginia 23209 P. O. Box 1535 Richmond, Virginia 23212 Alan S. Rosenthal, Esq.
Atomic Safety and Licensing Appeal Board Mrs. June Allen U.S. Nuclear Regulatory Comission 412 Owens Drive Washington, D. C.
20555 Huntsville, Alabama 35801 Michael C. Farrar, Esq.
Mrs. James Torson Atomic Safety and Licensing Appeal Board 501 Leroy U.S. Nuclear Regulatory Comission Socorro, New Mexico 87801 Washington, D. C.
20555 Mrs. Margaret Dietrich Dr. John H. Buck Route 2, Box 568 Atomic Safety and Licensing Appeal Board Gordonsville, Virginia 22942 U.S. Nuclear Regulatory Commission Washington, D. C.
20555 William H. Rodgers, Jr., Esq.
Georgetown University Law Center Atomic Safety and Licensing Board Panel 600 New Jersey Avenue, N. W.
U.S. Nuclear Regulatory Comission Washington, D. C.
20001 Washington, D. C.
20555 Mr. Peter S. Hepp Mr. Michael S. Kidd Executive Vice President U.S. Nuclear Regulatory Comission Sun Shipping & Dry Dock Company P. O. Box 128 P. O. Box 540 Spotsivania, Virginia 22553 Chester, Pennsylvania 19013 Dr. Paul W. Purdom Mr. R. B. Briggs Department of Civil Engineering Associate Director Drexel University 110 Evans Lane Philadelphia, Pennsylvania 19104 Oak Ridge, Tennessee 37830 1667 032
s Mr. W. L. Proffitt cc:
Dr. Lawrence R. Quarles lipartment No. 51 Kenda l-a t-Longwacd Kennett Square, Pennsylcania 193 4 Mr. Irwin B. Krcot Citizens Energy Forum P. O. Box 138 McLean, Virginia 2210 ;
James B. Dougherty, Esq.
Potomac Alliance 1416 S Street, N....
Washington, D. C.
20009 l
l 1667 033
ENCLEURE GUIDE TUBE THIf3LE WALL WEAR An unexpected degradation of guide thimble tube walls has been marved during post-irradiation examinations of irradiated fuel assemblics taicn from several operating pressurized water reactors.
Subsequently i; has been determined that coolant flow up through the guide thimble tubes and turbulent cross flow above the fuel assemolics have been responsible for inducing vibratory motion in the normally fully withdrawn ("parkeJ")
control rods. When these vibrating rods are in contact with the innar surface of the thimble wall, a fretting wear of the thimble wall cccurs.
Significant wear has been found to be confined to the relatively sof t Zircaloy-4 thimble tubes because the coatrol rod claddings -- stai:less steel for Westinghouse-NSSS designs -- provirie a relatively hard wear surface. The extent of the observed wear is both time and NSSS-design dependent and has, in some cases, been observed tc extend completely through the guide thimble tube walls, thus resulting in the formation of holes.
Guide thimble tubes function principally as the main structural members of the fuel assembly and as channels to guide and decelerate control rod mo tion.
Significant loss of mechanical integrity due to wear or hoic fornation could (1) result in the inability of the guide thimble tubes to withstand their anticipated loadings for fuel handling accidents anc condition 1-4 events and (2) hinder scramability.
In response to the staff's attempt to assess the susceptibility and impact of guide thimble tube v. ear in Westinghouse plants, Ncstinghouse and'the applicant have submitted information (Referenccs 1-4) on their experience and understanding of the issue. This information consisted of guide thimble tube wear measurements taken on irradiated fuci assemblies from Point Beach Units 1 and 2 (two-loop plants using 14x14 fuel asse-blies).
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-2 Also described was a mechanistic wear nodel (developed from the Point Beach data) and the impact of the mod'l's wear predictions on the safety analyses of. plant designs such as those utilizing 17x17 fuel assenblies.
Westinghouse believes that their fuel designs will experience less wear than that reported in other USSS designs because the Westinghouse desicns use thinner, more flexible, control rods that have relatively more lateral support in the guide tube assembly of the upper core structure.
Such construction provides the housing and guide path for the RCCA's above the core and thus restricts control rod vibration due to latcral exit flow. Also, Westinghouse believes that their wear model conservatively predicts guide thimble tube wear and that even with the worst anticipated v. car conditions (both in the degree of wear and the location of wear) their guide thimble tubes will be able to fulfill their design functions.
The staff concludes that the Westinghouse analysis probably accounts for all of the major variables that control this wear process.
- However, because of the complexities and uncertainties in (a) determininn contact forces, (b) surface-to-surface wear rates, (c) forcing functions, and (d) extrapolations of these variables to other fuel designs (such as the 17xl7 design used in Sequoyah), we believe that it is prudent for the applicant to make a conmitment, before issuance of the OL, to submit for review a surveillance plan and schedule for the examination of guide thimble tube wear.
The specifics of such a surveillance program have not yet been determined, but since the wear phenomenon is a time-dependent process the details of such an inspection program do not need to be specified prior to the first Sequoyah refueling outage. Furthermore, such inspection may not have to be conducted at Sequoyah. For example, the applicant cmuld join in a cooperative owner's group and thereby submit applicable infomation derived from a sirrilar type of plant using 17x17 fuel assemblies.
For acceptability, the minimum objective of such program should be to de.~oa-strate that there is no occurrence of hole formation in rodded guide thimble tubes.
p g 3 mJh} lI 1667 035
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Provided that the applicant agrees to ':ommit to the performance of the surveillance described above, this is'ue is adequately resolved for the first cycle of operation. This issue will be resolved for later cycles of oneration provided that surveillance results confirm the predictions of the analysis described above.
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REFERENCES 1.
Letter from T. M. Anderson, Westinghouse, to D. G. Eisenhut, NRC, NS-TMA-1936, dated September 12, 1978.
2.
Letter from T. M. Anderson, Westinghouse, to D. G. Eisenhut, NRC, NS-TMA-1992, dated December 15, 1978.
3.
Letter from T. M. Anderson, Westinghouse, to D. G. Eisenhut, t.RC, flS-TMA-2102, dated June 27, 1979.
4.
Letter from L. M. Mills, Tennessee Valley Authority, to L. S. Rubenstein, NRC, Dockets 50-327 and 50-328, dated November 27, 1979.
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