ML19320D223
| ML19320D223 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 07/01/1980 |
| From: | Clark R Office of Nuclear Reactor Regulation |
| To: | Goodwin C PORTLAND GENERAL ELECTRIC CO. |
| References | |
| TAC-10144, NUDOCS 8007210123 | |
| Download: ML19320D223 (5) | |
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DISTRIBUTION:
Docket File ACRS,16 NRR Rdg IE, 3 ORB #3 Rdg JHeltemes DEisenhut Gray File Docket No. 50-344 RPurple J01shinski RTedesco Glainas Mr. Charles Goodwin, Jr.
TNovak Assistant Vice President RAClark Portland General Electric Company 123 S.W. Salmon Stm.t PWagner Portland Oregon 97204 CTramel1
Dear Mr. Goodwin:
The NRC staff has been ruviewing the subject of control rod guide thimble wear in pressurized water reactors. The enclosure to this letter describes our review and makes an assessment of this problem in facilities with fuel assemblies designed by Westinghouse.
Based on our review, we have concluded that this issue is resolved for the 17x17 fuel asserlies designed by Westinghouse for the Trojan Nuclear Plant.
It is not expected taat the above conclusion will be alt > red by the results of the surveillance program sponsored by a cooperative owners group to obtain post-irradiation examination data from Salem Unit No. 1.
We will notify you of any additional concems when the results of this examination ars evaluated.
Sincerely, Original Signed 3Z Rote-t A. Clark R. A. Clark, Chief Operating Reactoes Branch f 3 Division of Licensing
Enclosure:
Evaluation of Control Rod Guide Thimble Wear cc w/ enclosure:
See next page
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Mr. _ Charles Goodwin, Jr.
Portland General Electric Company cc: Mr. J. W. Ourhan4 Esquire Donald W. Godard, Supervisor Vice President and Corporate Counsel Siting and Reg 21ation Portland General Electric Company Oregon Department of inergy 121 S.W. Salmon Street Labor and Industries Building Portland, Oregon 97204 Room 111 Saleng Oregon 97310 Columbia County Courthouse Law Library, Circuit Court Room St. Helens, Oregon 97501 Michael Malmros, Resident Inspector U. S. Nuclear Regulatory Commission Trojan Nuclear Plant P. O. Box 0 Rainter, Oregon 97048 Robert M. Hunt Chairman Board of County Commissioners Colunbia County St. Helens, Oregon 97051 Director, Technical Assessment Division Office of Radiation Programs (AW-459)
U. S. Environmental Protection Agency Crystal Mall #2 Arling;cn, Virginia 20460 U. S. Environmental Protection Agency Region X Office ATTN: EIS COORDINATOR 1200 6th Avenue Seattle, Washington 98101 i
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Enclosure i
EVALUATION OF CONTROL ROD GUIDE THIMBLE WEAR IN FACILITIES DESIGNED BY WESTINGHOUSE A degradation of control rod guide thiele/ tube walls has. been observed during post-irradiation examinations of irradiated fuel assemblies taken from several operating Subsequently, it has been determined that coolant flow up pressurized' water reactors.
through the guide tubes and turbulen' cross flow above the fuel assemblies have been responsible for inducing vibratory mcaion in the normally fully withdrawn (" parked")
control rods position. When these vibrating rods are in contact with the inner surface of the guide tube wall, a fretting wear of the wall occurs. Significant w rod claddings--stainless stell for Westinghouse-NSSS designs--previde a relatively The extent of the observed wear is both time and NSSS-design depen-hard wear surface.*
dent, and has, in some non-Westinghouse cases, been observed to extend ccepletely through the guide tube walls, thus resulting in the formation of holes.
Guide thimble /tubcs function principally as the main' structural maders of the fuel Significant loss assedly and as channels to guide and decelerate control rod motion.(1) result in the inability of mechanical integrity due to wear or hole for:.ation could:
of the guide thimble to withstand their anticipated loadings forTuel handling accidrnts and condition 1-4 events; and, (2) hinder scramability.
fn response to the staff's a'ttempt to. assess the susceptibility and irrpact of guide thimble wear in Westinghouse plants, two meetings were held with Westinghouse an.d infor mation was submitted (References 1 and 2) on their experience and understanding of the This information consisted of guide thimble wear measurements taken on irradiated issue.
fuel assedlies from Point Beach, Units 1 and 2 (two-loop plants using 14 x 14 fuel Also described was a mechanistic wear model (developed from the Point assemblies).
Beach data) and the impact of the model's wear predictions on the safety analyses of plant designs.
Eestinghouse believes that their fuel designs will experience less wear than that repor-ted in seme other NSSS designs because the Westinghouse designs use thinner, ::cre flexi-ble, control rods that have a relatively more lateral support in the guide thimbie assembly of the upper core structure. - Such construction provides the housing and guide path for the rod cluster control assedlies (RCCAs) above the core and thus restrictsAlso, control rod vibration due-to lateral exit flow.
tear model conse'rvatively predicts guide thimble wear and that even with the worst anti-cipated wear conditiens (both in the degree of wear and the location of wear) their guide thimbles will be able to fulfill their design functions.
The staff concluded that the Westinghouse analysis protely accounts for all of the Mcwever, becat.se of the complexities major variables that control this wear process.
and uncertainties in (a) deter::ining contact forces, (b) surface-to-surface wear rates, (c) forcing functions, and (d) extrapolations of these variables to the new 17 x 17 fuel assemoly design, the staff required several near-tenn OL applicants to submic to a For acceptability. the minimum objective of such pecgram was to survaillance program.
' demonstrate that there is no occurrence of hole formation in redded guide thimbles.
"?lancs using Wescingneuse HIPAR fuel assedly designs (stainless stael guide thimble tubes) are not considered susceptible to significant wear.
, Enclosure n
-u To satisfy this request for confirmation of the Westinghouse analytical predications, a cooperative owners gr6u6 was established which is now sponsoring a program to obtain i
post-irradiation examination (PIE) data frcm the Salem, Unit No.1 facility. This PIE program will examine'all guide thimbles in six redded fuel assemblies having either one It is our expectation that the program will confirm Westing-or two cycles of burnup.
house predictions, anc therefore this issue should be considered resolved for all Westing-house plants using the newer 17 x 17 fuel assemb.ly design.
The relevant primary system design differences in plants fueled with the 15 x 15 fuel assemblies as compared with those of plants fueled with 14 x 14 fuel assemblies are minimal. And certainly the extrapolation of wear prediction is less then that associated with the extrapolation to the newer plants using 17 x 17 fuel assemblies. Thus it is reasonable to conclude that the wear in 15 x 15 fuel assemblies should be equivalent to-that experienced and measured in 14 x 14 fuel assemblies, and therefore these designs are not likely to experience significant wear to the degree that the design capabilities will be impaired. Therefore, we conclude that the information that has been orovided is sufficient to resolve the issue of guide thimble / tube wear in plants fueled h 14 x 14 7
and 15 x 15 fuel assemblies.
References 1.
Letter-from L. M. Mills, Tennessee Valley Authority, to L. 5. Rubenst2in, NRC, Dockets 50-327 and 50-328, dated November 27, 1979.
2.
Letter from T. M. Anderson, Westinghouse, to H. R. Denton, NRC, NS-TMA-2238,'
dated April 29, 1980.
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