ML17340A094
| ML17340A094 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 07/07/1980 |
| From: | Varga S Office of Nuclear Reactor Regulation |
| To: | Robert E. Uhrig FLORIDA POWER & LIGHT CO. |
| References | |
| NUDOCS 8008130609 | |
| Download: ML17340A094 (6) | |
Text
1
.r KPIJMTI<J% MP:I h I: MPE Docket Nos. 50-250 and 50-251 Based on our revfew, we have concluded. that this issue
'fs resolved for the 15 x 15 fuel assemblies designed by Mestfnghouse for the Turkey Point Plant.
Sincerely, pz anginal signed,bgf S ~ ri ~
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T. Novak Dr. Robert E. Uhrfg, Vfce Presfdent S.
Varga Advanced Systems and Technology E. Conner Florfda Power and Light Company ti.. Grotenhuis Post Offfce Box 529100 Miami, FIorfda 33152 J.
Heltemes C. Parrish
Dear Dr. Uhrfg:
I8IE (3)
Attorney OELD The NRC staff has been revfewfng the subject of control rod guide thimble wear fn pressurfzed water reactors.
The enclosure to this letter des-crfbes our review and makes an assessment of this problem fn facilities wfth fuel assemblies designed by l(estfnghouse.
Enclosure:
Evaluation of Control Rod Guide Thimble )lear cc:
w/enclosure See next page Steven A. Varga, Chief Operating Reactors Branch 01 Division of Licensing 800818,0$ +
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 July 7, 1980 Docket Nos.
50-250 and 50-251 Dr. Robert E. Uhrig, Vice President Advanced Systems and Technology Florida Power and Light Company Post Office Box 529100 Miami, Florida
. 33152
Dear Dr. Uhrig:
The NRC staff has been reviewing the subject of control rod guide thimble wear in pressurized water reactors.
The enclosure to this letter des-cribes 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 15 x 15 fuel assemblies designed by Westinghouse for the Turkey Point Plant.
Sincerely,
Enclosure:
Eval uation of Contr ol Rod Guide Thimble Wear Obt n A.> arga, ie Operating Reactors Bra 81 Division of Licensing cc:
w/enclosure See next page
Robert E. Uhrig Florida Power and Light Company CC Mr. Robert Lowenstein, Esquire Lowenstein,
- Newman, Reis and Axelrad 1025 Connecticut Avenue, N.W.
Suite 1214 Environmental and Urban Affairs Library Florida International University Miami, Florida 33199':,
Mr. Norman A. Coll, Esquire
- Steel, Hector and Davis 1400 Southeast First National Bank Building Miami, Florida 33131 Mr. Henry Yaeger, Plant Manager Turkey Point Plant Florida Power and Light Company P. 0.
Box 013100 Miami, Florida 33101 Mr. Jack Shreve Office of the Publ ic Counsel Room 4, Holland Building Tallahassee, Florida 32304 Administrator Department of Environmental Regulation Power Plant Siting Section State of Florida 2600 Blair Stone Road Tallahassee, Florida 32301 Resident Inspector Turkey Point Nuclear Generating Station U. S. Nuclear Regulatory Coomission Post Office Box 971277 guai1 Heights Station Miami, Florida 33197
Enclosure EVALUATION OF CONTROL 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 assemblies taken from several operating pressurized water reactors.
Subsequently, it has been determined that coolant flow up 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" )
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 wear has been
,ound to be confined o the relatively soft Zircaloy-4 guide tubes because the control rod claddings--stainless steel for Westinghouse-NSSS designs--provide a relatively hard wear surface.*
The extent of the observed wear is both time and NSSS-design depen-dent and has, in some non-Westinghouse
- cases, been observed to extend completely through the guide 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 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 and condition 1-4 events;
- and, (2) hinder scramability.
In response to the staff's attempt to assess the susceptibility and impact of guide thimble wear in 'Westinghouse
- plants, two meetings were held with,Westinghouse and infor-mation was submitted (References 1 and 2) on their experience and understanding of the issue This information consisted, of guide thimble wear measurements taken on irradiated fuel assemblies from Point Beach, Uni,ts 1 and 2.(two-loop plants using 14 x 14 fuel assemblies).
Also described was a mechanistic wear model
('eveloped from the Point, Beach 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-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 assembly of the upper core structure..
Such construction provides the housing and guide path for the,rod cluster control assemblies (RCCAs) above the core and thus restricts control 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 fulfilltheir.design functions.
The staff concluded 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) determining contact forces, (b) surface-to-surface wear rates, (c) forcing functions, and (d) extrapolations of these variables to the new 17 x 17 fuel assembly design, the staff required several near-term OL applicants to submit to a survaillance p~ogram.
For acceptability, the minimum objective of such program was to
. demonstrate that there is no occurrence of hole formation in rodded guide thimbles.
'"Plants using Westinghouse HIPAR fuel assembly designs (stainless steel guide thimble tubes) are not considered susceptible to significant wear.
Enclosure To satisfy this request for confirmation of the Westinghouse analytical predications, a
cooperative owners group was established which is 'now sponsoring a program to obtain post-irradiation examination (PIE) data from the Salem, Unit No.
1 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 minimal.
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 l.
Letter from L. M. Mills, Tennessee Valley Authority, to L. S. RubensMin,
- 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.