ML19262A676
| ML19262A676 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 11/23/1979 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Stewart W FLORIDA POWER CORP. |
| References | |
| NUDOCS 7912100222 | |
| Download: ML19262A676 (6) | |
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c UNITED STATES
[ h,. c (,j NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555
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November 23, 1979 Docket No. 50-302 Mr. W. P. Stewart Manager, Nuclear Operations Florida Power Corporation P. 0. Box 14042, Mail Stop C-4 St. Petersburg, Florida 33733
Dear Mr. Stewart:
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 facilities designed by B&W to guide tube wear.
The information provided by B&W by letter dated January 12, 1979 was insufficient for us to conclude that guide tube wear was not a significan; aroblem in the 1"
facilities designed by B&W. This was documented in our letter to B&W dated August 22, 1979.
Because significant guide tube wear could impede the control rod scram capability, and also effect the required coolable gecretry 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 t,rystal River, Un1t No. 3.
The enclosed NRC concerns are provided to assist you it. planning your control rod and guide tube surveillance program. When you have completed your surveil-lance program plan, we request that this progran be submitted for NRC review before implementation.
Although this data-gathering program ray be performed 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 expedite our review of your program, a meeting at NRC headcuarters in Bethesda, Maryland, has been scheduled for Decerber 20, 1979, at 9:30 a.m.
This neeting will provide you the opportunity to clarify anc discuss the enclosed NRC concerns and the details of your procosec crograr.
Your agenca of the neeting shoild be provided by Decemer l',1979.
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s Should you have any questions on the type of infomation we need or scheduling requirements, pleaea contact our Operating Reacters Branch #4 Project Manager assigned t,,our facility.
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Sincerely, Q
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, g -fet O. x J Robert W. Reid, Chief Operating Reactors Branch #4 Division of Operatv.g Reactors Enclosure cc: w/ encl osure See next page 4
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1:-i:a :: ee Corporation cc:
- r. 5. A. Brandimore
ics 3resicent and General i
Cour.sel P. 2. Eox 14042 5. :etersburg, Florica 33733 Mr. Robert B. Borsum Babcock & Wilcox
!;uclear Power Generation Division Suite 420, 7735 Old Georgetown Road Bethesda, Maryland 20014 Crystal River Public Library Crystal.' River, Florida 32629 Mr. Jack Shreve Office of the Public Counsel Room 4, Holland Building Tallahassee, Florida 32304 1,
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t Enclosure NRC CONCERNS ON CONTROL R00 GUIDE TUBE WEAR IN FACILITIES DESIGNED BY B&W The B&W surveillance experience on worn control rod guide tuoes, 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 17xl7 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 (PIE) program with a schedule fer its implementation and a commitment to execute the program 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 surveillance plan should include the following:
a.
Methods of examination (e.g., destructive, eddy current erobe, boroscope, mechanical gage) accompanied by aualification of those methods, b.
Characterization of the examined guide tubes, including their in-core locations, EFPHs. flow rates, fluence, and uear tire under rods (control, instrument, axial-power shaping, burnable ooison, startup source, and crifice).
c.
Exa-ination of those rods (control, instru ent, axial-cower snacing, burnabis coison, startuo source, and orifice) contairec iw thin the guide tubes to identify #atigue, stress corrosien 1527 1 0
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-2 cracking, wear, denting, or any other conditions that can degrade the.f r 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 PIE program may be satisfied in part of totality by reference to data taken from another B&W designed plant (s) that uses the same type of fuel assemblies.
In such case, justification must be given that wear in the refere.nced plant adequately represents'that of the plant design in question.
L Provide all correlations supported by your tests and discuss how these correlarions are used to predict guide tube wear during reactor oport.tions over the fuel lifetime.
2.
Provide an evaluation on the predicted gu.de tube wear on the stress analyses contained in the FSAR. The evaluation should address loadings associated with Condition-1 through -4 events including fuel handling accidents, control rod scrams, and seismic and LOCA transients. The discussion shguld 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 correlations should accommodate the effects of hydrogen absorption and the propensity for hydrogen 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 resiuence time, both during periods of wear (under rods; i.e., control, instrument, axial-power shaping, burnable poison, startup source, and orifice) and when the tube: are not rodded.
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