ML17331A439

Forwards Review & Assessment Re Control Rod Guide Thimble Wear in Pwrs.Issue Resolved for Unit 2.Unit 1 Review Is in Progress

ML17331A439
Person / Time
Site:	Cook
Issue date:	08/14/1980
From:	Varga S Office of Nuclear Reactor Regulation
To:	Dolan J INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
References
NUDOCS 8009170228
Download: ML17331A439 (8)

Text

>@0L@OW rpt,~p DISTRIBUTION Docket Fi1 es 50-.31/5/316

'UGusy NRC PDRs (2) 4 1880

'ocal PDR TERA NSIC NRR Reading ORBl Reading T. Novak Mr. John Dolan, Vfce President S.

VArga Indiana and Michigan Electric Company K.

Post Office Box 18 S. Miner Bowling Green Station C. Parrish New York, Hew York 10004 I&E 855 (3)

Attorney, OELD

Dear Mr. Dolan:

J.Olshinski J.Heltemes The NRC Staff has. been revfewfng the subject of control rod guide thfmble wear in pressurfzed water reactors.

The enclosure to this letter des-cribes our review and makes an assessment of this problem fn facilities with fuel assemblfes,desfgned by klestfnghouse.

Docket Ho. 50-315

'and 50-316 Based on our review, we have concluded that this issue fs resolved for the 17 x 17 fuel assemblies designed by Mestfnghouse for the D. C.

Cook Unit Ho. 2.

Me are continuing our review of this subject for facilities such as D. C.

Cook Unit No.

1 which uses fuel assemblies designed by Exxon.

Me Qfll advise you of any additional concerns that result from this review.

Sincerely, It fs not expected that the above conclusion will be alterad by the results of the surveillance program sponsored by a cooperative owners group to obtain post-irradiation examfnatfon data from Salem, Unit No. l.

>le will notify you of any addftfonal

concerns, when the results of this examination are evaluation.

Enclosure:

Evaluation of Control Rod Guide Thimble Wear cc:

w/enclosure See next page

,S.

'V

~77edb Steven A. Varga, Chief Operatfng Reactors. Branch 81 Division of Licensing O~~ICEP SURNAME DATEf DL:ORB1 SMiner.j 08/8 /80 D

SA ra 0

/80 NRC FORM 318 I9 76) NRCM 0240 AU.S. GOVERNMENT PRINTING OFFICE: 1979 289 369

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UNITE D S TAT F S NUCLEAR REGULATORY COMMISSION

'IVASHINGTON, O. C. 20555 Docket No.

50-316 and 60-316 August 14, 1980 Mr. John lblan, Vice President Indiana and Michigan Electric Company Post Office Box 1S Bowlino Green Station

<<ew York, Hew York 10004

Dear Mr. Dolan:

The NRC Sta,f nas been reviewino the subject of control rod guide thimble wear in pressurized water reactors.

The enclosure to this letter des-cribes our

. eview 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 17 x 17 uel assemblies designed by Westinghouse for the D.

C.

Cook Unit No.

2.

It is not expected that the above conclusion will be altered by the results o, the surveillance program sponsored by a cooperative owners group to obtain post-i I adiat ion examination data from Sa1 em, Unit No.

1 We wl 1 1 Aotify vou oi any additional concerns when the resul s of his examination are evaluation.

We ale coAtinuing our review of this suoj ect

=or facilities such as D.

C.

Cook Unit, No.

1 whicn uses fuel assemblies designed by.xxon.

WIe will

vise you of any additional concerns that result from this review.

Sjncereiy, r:,.~

d4..',(",.i"I~

Dlvl5ion of Lqcensino

=.". c I 0 s uI e

'va iua ion 0 Control Roc Guioe I <imbl 2 Weat cc:

w/enclosure See nex paoe

indiana and i!ichigan;lectric Co~any August 14, 1980 cc:

Hr. Robert ':l. Jurgensen Chief iluclear Engineer American Electric Power Service Corporation 2 Broadway llew York, Yew York 10004 Cerald Charnof=,

Esquire Shaw, Pittman, Potts and Trowbridge 1800 H Street, N.';.'.

Washington, D.

C.

20036 Citizens

=or a Better Environment 5

East

'/an Buren Street Chicago, Illinois 60605 laude Preston Palenske f'memorial L ibrary 500 iiarket Street St.

Joseph, Michigan 49085 Nr. 0. Shaller, Plant ilanager Donald C.

Cook i'tuc'lear P lani P. 0.

Box 458

Bridgman, michigan 49106 U. S. nuclear Reculatorv Comrission Resident Inspec.ors Office 770 Red Arrow '.-'.ighway S tevensvi l le,

. lichi gan 49127

'><'i 1. i am J Scanlon)

Esquir 2034 Pauline Boulevard Ann Arocr, Michigan 48103

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 wi thdrawn ("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 2ircaloy-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, Units 1 and 2 (two-loop'lants 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 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.

'he staff concluded that the Westinghouse analysis probably accounts for'll 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 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 West)ng ouse HIPAR fuel assembly designs (stainless steel guide thimble tubes) are not considered susceptible to significant wear.

r I

Encl osure 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 1.

Letter from L.

M. Mills, Tennessee Valley Authority, to L. S. Rubenstain,

NRC, Dockets 50-327 and 50-328, dated November 27, 1979.

2.

Letter from T.

M. Anderson, Westinghouse, to H.

R. Oenton, NRC, NS-TMA-2238~

dated April 29, 1980.

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