ML17250A450
| ML17250A450 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 07/10/1980 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | White L ROCHESTER GAS & ELECTRIC CORP. |
| References | |
| NUDOCS 8007280135 | |
| Download: ML17250A450 (7) | |
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Docket No. 50-244 I
JULY 10 1980 Mr. Leon D-White, Jr.
Vice President Electric and Steam Production Rochester Gas 8 Electric Corporation 89 East Avenue Rochester, New York 14649
Dear Nr. White:
DISTRIBUTION:
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SUBJECT:
CONTROL ROD GUIDE THIMBLE WEAR ISSUE (B-14)-
R. E. GINNA NUCLEAR POMER PLANT 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 14x14 fuel assemblies designed by Westinghouse for the R. E. Ginna Nuclear Power Plant, Sincerely, Original signed by Dennis M. Crutchf ielcf Dennis M. Crutchfield, Chief Operating Reactors Branch 85 Division of Licensing Encl osure:
Evaluation of Control Rod Guide Thimble Wear cc w/enclosure:
See next page
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t UNITED STATES e
NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 July 10, 1980 Docket No. 50-244 Mr. Leon D. White, Jr.
Vice President Electric and Steam Production Rochester Gas 5 Electric Corporation 89 East Avenue Rochester, New York 14649
Dear Mr. White:
SUBJECT:
CONTROL ROD GUIDE THIMBLE WEAR ISSUE (B-14)-
R.
E.
GINNA NUCLEAR POWER PLANT 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 14x14 fuel assemblies designed by Westinghouse for the R. E..Ginna Nuclear Power Plant.
Sin
- rely,
Enclosure:
Evaluation of Control Rod Guide Thimble Wear nni s M. Crutchf >
d, hi Operating Reactors Branch Division of Licensing cc w/enclosure:
See next page
Mr-. Leon D. White, Jr.
2 July 10, 1980 cc w/enclosure:
Harry H. Voigt, Esquire LeBoeuf, Lamb, Leiby 8 MacRae 1757 N Street, N.
W.
Washington, D. C.
20036 Mr. Michael Slade 12 Trailwood Circle Rochester, New York 14618 Rochester Coomittee for Scientific Information Robert E. Lee, Ph.D.
P- 0. Box 5236 River Campus Station Rochester, New York 14627 J effrey Cohen New York State Energy Office Swan Stre'et Building Core 1, Second Floor Empire State Plaza
- Albany, New York 12223 Director, Technical Development Programs State of New York Energy Office Agency Building 2 Empire State Plaza
- Albany, New York 12223 Rochester Public Library 115 South Avenue Rochester, New York 14604 Supervisor of the Town of Ontario 107 Ridge Road West
- Ontario, New York 14519 Director, Technical Assessment Division Office of Radiation Programs (AW-459)
U. S. Environmental Protection Agency Crystal Mall 82 Arlington, Virginia 20460 U. S. Environmental Protection Agency Region II Office ATTN:
E IS COORDINATOR 26 Federal Plaza New York, New York 10007 Herbert Grossman, Esq., 'Chairman Atomic Safety and Licensing Board U. S. Nuclear Regulatory Coomission Washington, D. C.
20555 Dr. Richard F. Cole Atomic Safety and Licensing Board U. S. Nuclear Regulatory Coamission Washington, D. C.
20555 Dr.
Emneth A. Luebke Atomic Safety and Licensing Board U. S. Nuclear Regulatory Comnission Washington, D. C.
20555 Mr. Thomas B. Cochran Natural Resources-Defense Council, Inc.
1725 I Street, N.
W.
Suite 600 Washington, D. C.
20006 t
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EVALUATION OF CONTROL ROD GUIDE THIMBLE Enclosure MEAR IN FACILITIES DESIGNED BY MESTINGHOUSE 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 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 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 o
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 Mestinghouse 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, Units 1 and 2 (two-loop plants using 14 x 14 fuel assemblies).
Also described was a mechanistic wear model (developed from the Point Beach data) and the impact of the model's wear predictions on the safety analyses of p'iant 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 var iabIes to the new 17 x 17 fuel assembly design, the staff required severa'l near-term OL applicants to submit, to a survaillance program.
For acceptability, the minimum objective of such program was to demonstrate that there is no occurrence of hole formation in rodded guide thimbles.
P ants 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 ')4 x 14 and 15 x 15 fuel assemblies.
References 1.
Letter from L. H. Hills, Tennessee Valley Authority, to L. S. Rubensttin,
- NRC, Dockets 50-327 and 50-328, dated November 27, 1979.
2.
Letter from T. N. Anderson, Westinghouse, to H.
R. Denton, NRC, NS-TN-2238~
dated April 29, 1980.