ML19260B474
| ML19260B474 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 11/23/1979 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Roe L TOLEDO EDISON CO. |
| References | |
| NUDOCS 7912100237 | |
| Download: ML19260B474 (6) | |
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UNITED STATES 5 73 s-t, i NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555
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November 23, 1979 Docket No. 50-346 Mr. Lowell E. Roe Vice President, Facilities Development Toledo Edison Company Edison Plaza 300 Madison Avenue Toledo, Ohio 43652
Dear Mr. Roe:
Significant wear of the Zircaloy control rod guide tubes has been observed in -
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facilities designed by Combustion Engineering (CE).
Similar wear has also been reported in those facilities designed by Westinghouse (W).
In our letter of June 13,1978, we requested information from Babcock and Wilcox (B&W) on the susceptability of the facilit'es designed by B&W to guide tube wear.
The infomation provided by B&W by letter dated January 12,1979 '..as insufficient for us to conclude that guide tube wear was not a significant problen in the facilities designed by B&W. This was documented in our letter to B&W dated 4
August 22, 1979.
Because significant guide tube wear could inpede the control rod scram capability, and also effect the required coolable geonetry of the reactor core, we consider this wear phenomenon a potential safety concern.
Therefore, we are requesting that you provide detailed infomation on the wear character-istics of the control rods on the guide tubes in fuel assemblies in Davis-Besse, Unit No. 1.
The enclosed NRC concerns are provided to assist you in planning your control rod and guide tube surveillance program. When you have completed your surveil-lance program plan, we request that this program be submitted for NRC review before implementation.
Although this data-gathering progran may be perfomed on available irradiated assemblies in spent fuel pools, we find that this issue should be resolved for each facility before startup from your next scheduled refueling outage commencing after January 1,1980.
To excedite our review of your progran, a meeting at NRC headquarters in Bethesda, !'aryland, has been scheduled for December 20, 1979, at 9:30 a.m.
This meeting will provide you the opportunity to clarify and discuss the enci: sed MC concerns and the details of your proposed progran.
Your agenca of the neeting should be provided by Decenber 17, 1979.
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.c Should you have any questions on the type of infomation we need or scheduling requirements, please contact our Operating Reactors Branch #4 Project Manager assigned to your facility.
Si ncerely, O
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kbbert W. Reid, Chief Operating Reactors Branch #4 Division of Operating Reactors Enclosure cc: w/ enclosure See next page a
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Toledo Edisen Company cc w/ enclosure (s):
Mr. Donald.H. Hauser, Esq.
Mr. Ted Myers The Cleveland Electric Licensing Engineer Illuminating Comps.y Toledo Edison Company P. O. Box 5000 Edison Plaza Cleveland, Ohio 44101 300 Madison Avenue Toledo, Ohio 43652 Gerald Charnoff, Esq.
Shaw, Pittman, Potts &
Mr. Rick Jagger Trowbridge Industrial Commission 1800 M St., NH State of Ohio Washington, DC 20036 2323 West 5th Avenue Toledo, Oh.io 43216 Leslie Henry, Esq.
Fuller, Seney, Henry & Hodge.
300 Madison Avenue Toledo, Ohio 43604 Mr. Robert B...
en Babcock & Wilcox Nuclear Power Generation Division Suite 420, 7735 Old Georgetown Road Bethesda, Maryland 20014 Ida Rupp Public Library 3
310 Madison Street Port Clinton, Ohio 43452 e
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Enclosure NRC CONCERNS ON CONTROL R0D GUIDE TUBE WEAR IN FACILITIES DESIGNED BY B&W The B&W surveillance experience on worn control rod guide tubes, as described in their January 12, 1979 letter, consists of (a) air testing of sixteen guide tubes from an Oconee-1 15x15 fuel assembly that had experienced one cycle of operation under a control rod assembly and (b) clam-shell sectioning of two guide tubes from a 17x17 fuel assembly that had undergone a 1000-hour flow test under a control rod assembly. As documented in our letter of August 22, 1979, we find that this experience is not sufficient to support the B&W con-clusion that there is strong evidence for the absence of wear in B&W-designed plants.
In fact, to the contrary, worn guide tubes have been observed in Crystal River, Unit 3 spent fuel (see BAW-1490 Rev. 1, July 1978).
Our position is further ' ~
based on observations made by other NSSS vendors who have found a " plant-specific" and " core-position" dependence in the. observed wear. Furthermore, out-of pile flow tests have demonstrated that the wear rate is a function of several design and operating variables.
1.
Propose a post-irradiation examination (P E) program with a schedule for its implementation and a commitment to execute the orogram for NRC review.
This data-gathering program should be completed expeditiously considering i
the availability of irradiated assemblies in all B&W-designed plants.
Details of the sur/eillance plan should include the following:
a.
Methods c# examination (e.g., destructive, ed:;. :;rrert crobe, boroscope, mechanical gage) accompanied by oualification of those methods.
b.
Characterization of the examined guide tu:es, ircludir.; their in-core locations, EFDHs. flow rates, fluence, aac wear tire under rods (control, instrument, axial-pcv.er Shacing, burnav e poison, startuo source, and orifice).
c.
Examination of those rods (centrel, instra er, axial-:cwer snacing, burnable coison, startue source, aed : " ice; ccetained within the guide tubes to identi#y #a-i se, s 'e55 cccsicr 3Mb 1521 221
cracking, wear, denting, or anj other conditions that can degrade their design function, reduce their design lifetime, or impede their movement.
d.
Analysis of results including quantification of guide tube wall wear depth and distribution. This DIE progran may be satisfied in part of totality by reference to data taken from another B&W designed plant (s) that uses the sane type of fuel assemblies.
In such case, justification must be given that wear in the referenced plant adequately represents that of the plant design in cuestion.
Provide all correlations supported by your tests and discuss how these correlarions are used to predict guide tube wear during reactor operations over the fuel lifetime.
2.
Provide an evaluation on the predicted guide tube wear on the stress analyses contained in the FSATs. The evaluation snould
.j address loadings associated with Condition-1 through -4 events including fuel handling accidents, control roc scrams, and seismic and LOCA transients. The discussion should describe the state of stress in the worn guide tubes and how the wear affects the loadbearing characteristics of the worn tubes.
(Note that nonuniform wear results in a shift of the neutral tube axis which then induces not only direct stresses but also bending stresses.) Show that the loadbearing capacity of the worn guide tubes satisfies the acceptance criteria for these loading events.
3.
Provide or reference all material property correlations that are used in the guide tube stress analyses. These correla:icns shoulo accomnodate the effects of hydrogen absoroa cn and the procensity for ydrogen uptake in the Zircaloy guide tubes as a function of accumulative wear.
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. 4.
Address the consequences of hole formation in worn guide tubes.
Consider the extent and distribution of wear to see if hole formation is possible.
If the potential for hole formation can-not be discounted, evaluate the impact of such holes on the guide tube integrity, control rod motior and local thermal-hydraulic performance. This evaluation should account for flow-induced vibration resulting in crack propagation and possible fatigue frac-ture in locally thinned areas of the tube wall. This discussion should also address the entire core residence time, both during periods of wear (under rods; i.e., control, instrument, axial-power shaping, burnable poison, startup source, and orifice) and when the tubes are not rodded.
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