ML19327A573
| ML19327A573 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 07/21/1980 |
| From: | Clark R Office of Nuclear Reactor Regulation |
| To: | Mayer L NORTHERN STATES POWER CO. |
| References | |
| NUDOCS 8008060402 | |
| Download: ML19327A573 (4) | |
Text
'
j.,Y UNITED STATES g
9,,
NUCLEAR REGULATORY COMMISSION y
g 3
E WASHINGTON, D. C. 20555 e
\\[.....f July 21, 1980 Docket No. 50-2S2 306 Mr. L. O. Mayer, Manager Nuclear Support Services Northern States Power Company 414 Nicollet Mall, 8th Floor Minneapolis, Minnesota 55401
Dear Mr. -Mayer:
The NRC staff has been reviewing 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 14xl4 fuel assemblies designed by Westinghouse.for the Prairie Island plant.
We are continuing our review of this subject for facilities using fuel assemblies designed by Exxon. We will advise you of any additional concerns that result from this review.
Sincerely, o-Robert A. Clark, Chief Operating Reactors Branch 43 Division of Licensing
Enclosure:
Evaluation of Control Rod Guide Thimble Wear cc w/ enclosure:
See next page 8008060
Mr. L. O. Mayer Northern States Power Company cc: Gerald Charnoff, Esquire Mr. John C. Davidson, Chairman Shaw, Pittman, Potts and Trowbridge Goodhue County Board of Commissioners 1800 M Street, N.W.
321 West Third Street Washington, D. C.
20036 Red Wing, Minnesota 55066 Ms. Terry Hoffman Bernard M. Cranum Executive Director Bureau of Indian Affairs, DOI Minnesota Pollution Control Agency 831 Second Avenue Scuth 1935 W. County Road 82 Minneapolis, Minnesota 55402 Roseville, Minnesota 55113 Chairman, Public Service Commission The Environmental Conservation Library of Wisconsin Minneapolis Public Library Hill Farms State Office Building 300 Nicollet Mall Madison, Wisconsin 53702 Minneapolis, Minnesota 55401 Director, Technical Assessment Division Mr., F. P. Tierney, Plant ~ Manager Office of Radiation Programs (AW-459)
Prairie Island Nuclear Generating Plant U. S. Environmental Protection Agency Northern States Pcwer Company Crystal Mall #2 Route 2 Arlington, Virginia 20460 Welch, Minnesota 55089 J. S. Environmental Protection Agency Joclyn F. Olson, Esquire tederal Activities Branch Special Assistant Attorney General negion V Office Minnesota Pollution Control Agency ATTN: EIS COORDINATOR 1935 W. County Road B2 230 South Dearborn Street Roseville, Minnesota 55113 Chicago, Illinois 60604 Robert L. Nybo, J r., Chai rman Minnesota-Wisconsin Boundary Area Commissior.
619 Second Street Hudson, Wisconsin 54016 Clarence D. Feierabend Resident Inspector Prairie Island Nuclear Generating Plant U. S. Nuclear Regulatory Commission P. O. Box 374 -
Red Wing, Minnesota 55066 I
Enclosure EVALUATION OF CONTR'0L-ROD GUIDE THIMBLE-
' WEAR IN FACILITIES DESIGNED BY WESTINGHOUSE A degradation of control rod guide thimble / tube walls has been observed during post-irradiation examinations of irradiated fuel asserblies taken from several operating Subsequently, it has been determinec' that coolant flow up pressurized water reactors.
i through the guide tubes and turbulent cross flow above the fuel assemblies have been responsible for inducing vibratory motion in the normally fully withdrawn (" parked")
When these vibrating rods are in contact with the inner surface control rods position.
of the guide tube wall, a fretting wear of the wall occurs. Significant wear has been found to be confined to the relatively soft Zircaloy-4 guide tubes because the control rod claddings--stainless stell for Westinghouse-NSSS designs--provide 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 completely through
- he guide tube walls, thus resulting in the formation of holes.
Guide thimble / tubes function principally as the main structural members of the fuel asse-bly and as channels to guide and decelerate control rod motion. Significant loss of mechanical integrity due to wear or hole formation could:
(1) result in the inability of the guide thimble to withstand their anticipated loadings for~ fuel handling accidents t
and condition 1-4 events; and, (2) hinder scramability.
In response to the staff's attempt to assess the susceptibility and impact of guide d
- nimble 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 assemblies from Point Beach, Units 1 and 2 (two-loop plants using 14 x 14 fuel assemblies).. Also descr.ibed was a mechanistic wear model (developed from the Point Seach data) and the impact of the model's wear predictions on the safety analyses of plant designs.
Westinghouse believes that their fuel designs will experience less wear than that repor-i ted in some other NSSS designs because the Westinghouse designs use thinner, more flexi-ble, control rods that have a relatively more lateral support in the guide thimble Such construction provides the housing and guide assembly of the-upper core structure.
patn for the rod cluster control assemblies (RCCAs) above the core and thus restricts con rol rod vibration due to lateral exit flow. Also, Westinghouse believes that their wear model conservatively predicts guide thimble wear and that even with the worst anti-cipated wear conditions (both in the degree of wear and the location of wear) their guide thimbles will be able to fulfill tneir design functions.
t
.The staff concluded that the Westinghouse analysis probably. accounts for all of the major variables that control this wear process. However, because of the complexit' n and uncertainties in (a) dotermining contact forces, (b) surface-to-surface wear ra: s, (c) forcing functicns, and (d) extrapolations of these variables to the new 17 x 17 l
fuel' assembly design, the staff' required several near-term OL applicants to submit to a survaillance program.
For acceptability, the minimum objective of such program was ta 1
+
demonstrate' that-there is no occurrence of hole formation in rodded guide thimbles.
- Plants using Westingnouse HIPAR fuel assembly designs (stainless steel guide thimole tubes) are not consicered susceptible to significant' wear.-
--...-,--w r
em,--
r-,
.e-
.w
- E :losure
-To satisfy this r<. guest for confirmatien of the Westinghouse analytical predications, a cooperative owne.s grouo was established which is now sponsoring a program to fatain post-irradiation examination (PIE) data from the Salem, Unit Nc. I facility. This PIE program will examine all guide thimbles in six rodded fuel assemblies having either one or two cycles of burnup.
It is our expectation that the program will confirm Westing-house predictions, and therefore this issue should be considered resolved for all Westing-house plants using the newer 17 x 17 fuel assembly 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 minical. And certainly the extrapolation of wear prediction is less than 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 provided is sufficient to resolve the issue of guide thimble / tube wear in plants fueled with 14 x 14 and 15 x 15 fuel assemblies.
References 1.
Letter from L. M. Mills, Tennessee Valley Authority, to L. S. Rubenstuin, 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.
l
- - -