ML19275A382

Forwards Request for Addl Info Re Guide Thimble Tube Wear in Westinghouse Fuel Assemblies

ML19275A382
Person / Time
Site:	McGuire, Mcguire
Issue date:	09/11/1979
From:	Baer R Office of Nuclear Reactor Regulation
To:	Parker W DUKE POWER CO.
References
NUDOCS 7910040222
Download: ML19275A382 (8)

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UNITED STATES 87

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NUCLEAR REGULATORY COMMISSION WASHING TO N, D. C. 20555 pl SEP 111979 Docket Nos. 50-369 and 50-370 Mr. William O. Parker, Jr.

Vice President, Steam Production Duke Power Company P. O. Box 2178 422 South Church Street Charlotte, North Carolina 28242

SUBJECT:

GUIDE THIMBLE TUBE WEAR IN WESTINGHOUSE FUEL ASSEMBLIES (McGuire Nuclear Station, Units 1 and 2)

Westingbouse has observed guide thimble tube wear on some of its fuel assemblies 7.nd have submitted information (see References 1, 3 and 5 of the Enclosure) to us on this matter.

Since this experience could potentially effect the McGuire fuel, we requqst that you provide us with additional information as described in the Enclosure.

Your response should incorporate at least by reference the submittals previcusly made to us by Westinghouse (References 1, 3 and 5).

We request that this information be provided to us no later than October 29, 1979.

Please contact us if you have any questions on this matter.

Sincerely, A

Dq Robert L. Bac", Chief Light Water Reactors Branch No. 2 Division of Project Management

Enclosure:

Request for Additional Information ecs w/ enclosure:

See next page 1099 029 g

05652N 7 D10 04 Q A21

Mr. William 0. Parker, Jr.

Vice President, Steam Production Duke Power Company P. O. Box 2178 422 South Church Street Charlotte, North Carolina 28242 cc: Mr. W. L. Porter Duk'e Power Canpany P. O. Box 2178 422 South Church Street Charlotte, North Carolina 28242 Mr. R. S. Howa rd Power Systems Division Westinghouse Electric Corporation P. O. Box 355 Pittsburgh, Pennsylvania 15230 Mr. E. J. Keith EDS Nuclear Incorporated 220 Montgomery Street San Francisco, California 94104 Mr. J. E. Houghtaling NUS Corporation 2536 Countryside Boulevard Clearwater, Florida 33515 Mr. Jesse L. Riley, President The Carolina Environmental Study Group 854 Henley Place Charlotte, North Carolina 28207 J. Michael McGarry, III, Esq.

Debevoise & Liberman 1200 Seventeenth Street, N. W.

Washington, D. C.

20036 Robert M. Lazo, Esq., Chairman Atomic Safety and Licensing Board U. S. Nuclear Regulatory Commission Washington,D. C.

20555 Dr. Emmeth A. Luebke Atomic Safety and Licensing Board U. S. Nuclear Regulatory Connission Washington, D. C.

20555 Dr. Cadet H. Hand, Jr., Director Bodega Marine Lab of California P. O. Box 247 Bodega Bay, California 94923 109o 030

Mr. William 0. Parker, Jr.

cc: Anthony Z. Roisman, Esq.

Natural Resources Defense Council 917 - 15th Street, N. W.

Washington, D. C.

20555 Richard P. Wilson, Esq.

Assistant Attorney General State of South Carolina 2600 Bull Street Columbia, South Carolina 29201 Office o Intergovernmental Relations 116 West ones Street /

Raleigh, N rth Carollia 27603 County Mana er o cklenburg County 720 East Fo r ff Street Cha rlotte,

rth Carolina 28202 U. S.

viron ental Protection Agency ATTN-EIS Co dinator Rep on IV Offi e 3 5 Courtland treet, N. W.

t1anta, Georgi a 30308

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ENCLOS.U_R_E, REQUES_T FOR _A_DDIT_I,0NAL _IJ1 FORMATIO.N GUIDE THlMBLE TUBE WEAR AU_ GUST 1979 1.

Please provide the basis and derivation of the guide thimble wear model described in Reference 1.

In particular, explain assumption 4 and the equations provided under assumption 7 Does the model predict maximum local wear er average circumferential wear?

2.

Using the guide thimble wear model, Westinghouse has predicted maximum stresses and stress intensity limits for worn guide thimble walls in two fuel assembly designs, which were subjected to a 69 handling load.

These calculated values are listed in Table 4.1 of Reference 1.

We note that the stress intensity limits increase as a function of time for both fuel assembly designs and that the limits always remain greater than the maximum stresses, which increase as the wall is war.n away.

From the supporting discussion preceeding Table 4.1, it is not clear if the stre s intensity limits are time dependent.

Such an assumption would explain the noted increase in stress limits but does not address the decreasing material toughness. associated with irradiation hardening.

If :uch credit is being used, it is contrary to the previous Westinghouse position in Reference 2 and item 4.0.5 of Reference 1.

Please clarify whether or not Westinghouse has taken credit for irradiation strengthening.

Show that the criteria adopted represents the more conservative approach.

3.

Guide thimble wear data, which were taken from Point Beach Units 1 and 2 spent fuel, are discussed, listed, and plotted in Section 2.3, Table 2.1, and Figure 5, respectively, of Reference 1.

Please confirm that the time units in Section 2.3 and Table 2.1 are in.rror and make corre'ctions as needed. Should not the units be days instead of hours?

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. 4 Submitted Westinghouse infomation does not explain why the guide thimble wear model, which was developed from measurements taken on two 2-loop plants with 14x14 fuel assemblies, is applicable to wear predictions on plants of other designs. Other NSSS-vendor-designed plants have exper-ienced a " plant-specific" and " core-position" depend?nce in the observed wear. Therefore, please explain how the model accounts for wear differ-ences and provide suoporting data for all Westinghouse design variations.

If the analytical treatment of design variations are justified, the sup-porting data can be provided in a confimatory manner after NRC approval of the model.

Please provide details of your data-gathering proposal, a schedule for its implementation, and state your commitment to carry out this confimetory program. This data-gathering program should be completed expeJitiously corsidering the availability of irradiated assemblies in all Westinghouse plants.

5.

In Reference 3. Westinghouse stated thut the effect of hydrogen content on the, mechanical properties of Zircaley is discussed in WCAP-9179 (Reference 4).

We have reviewed that topical report and found no infoma-tion.on this issue.

Please provide your evaluation of how this considera-tion affects the safety analysis.

Include in this evaluation a description of the propensity for hydrogen uptake of the Zircalor as a function of the accumulative wear.

6.

When eddy current testing was conducted on worn guide thinble tubes from the Point Beach Units, did the presence of zirconium hydrides affect the e

resdits' How sensitive is the interpretation of eddy current signals to hydride presence? How is this effect taken into account?

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3 7

References 1, 3, and 5 do not address the consequences of hole formation in worn guide thimble tubes. Moreover, it is not clear from the submitted information if Westinghouse (1) has observed holes daring inspection of the 49 quide thimbles tubes that were examined in tie Point Beach spent fuel, or (2) has predicted bith the gJide thimble wear model) hole formation to occur during projected fuel lifetime.

Please clari fy. Al so, i f ho e s have been observed or are anticipated, provide a discussion on the imoact of such holes or guide thimble tube integrity, control rod motion, and thernal-hydraulic performance.

This discussion should also account for flow-induced vibration resulting in crack propagation and possibly fatigue fracture in locally thinned areas of the thimble wall. This dis-cussion should address the integrity of the thimble tubes curing the entire core residence tire; both during periods of wear (under RCCA) and when the fuel assemblies are not under RCCAs.

8.

During the review of WCAP-9179 (Reference 6), the staff questioned the Westinghouse value for the ultimate tensile strength of Zircaloy components.

The subsequent Westinghouse response (Reference 2) stated that the ultimate tensile strength of Zircaloy was not used in the design analyses of present fuel assembly designs. However, the analysis contained in Reference 1 uses the ultimate strength as a limiting variable. Therefore, please submit for review the Westinghouse correlation for the ultimate tensile strength of Zircaloy.

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i 4-9.

Section 4.1 of Reference i states that the stress intensity factors are plotted as a function of time for 14x14 and 17x17 fuel assemblies in Figure 5.

This is not true. Please provide such a figure or amend Figure 5 as necessary.

10.

Per item 4, Section 4.0 of Reference 1, your analyses are based on uniform wear in all thimble tubes. Address the margin of conservatism for this -

assumption. Con are your results with an analysis that considers non-uniform wear resulting in a shift of the neutral axis. Note that lch shifts will result in both direct stress and bending stresses.

11.

For Condition-1 and -2 load analyses of Reference 1, a skew factor is mentioned that accounts for the uneven axial load distribution. Clari fy how the skew factor is.'c.i.ted to both geometric changes (resulting from uneven wear) and assembly misalignment. How does the skew factor impact the load analyses?

12. The equation for the wear volume in Reference 1 appears linear with time.

However, in Figures 5 and 6, wear depth is plotted versus time, and the resulting currelation appears to be non-linear. Please pmvide information on how these parameters are related.

13.

For Condition-3 and 4 load analyses described in Reference 1, it is stated that the stresses in a worn guide thimble tube are based on generic stress calculations. Please reference where these generic stress calcula-tions can be fo'snd.

It is also stated that the stresses in trie unworn j

guide thimble tubes are increased to account for the reduction of the tube cross section due to the wear scar. This would indicate credit for a load 10~99 035

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redistribution to the unworn guide thinble tubes.

Is a skew factor ernployed in the Condition-3 and -4 load analyses? Describe the state of stress in the worn guide tubes and how the uneven wear affects the load-bcaring char-acteristics of the worn tubes.

References 1

T. M. Anderson (W' letter (N5-TMA-2102) to D. G. Eisenhut (USNRC),

dated June 27, 1779.

T. M. Anderson (W) letter (NS-TMA-1985) to J. F. Stolz (USNRC),

2.

dated Nover.ber l'f,1975.

(W'. letter (N5-TMA-1936) to D. G. Eisenhut (USNRC),

3.

T. M. Anders y dated Septe-ber T2, ic7E.

4 P. J. Kuchirka, " Properties of Fuel and Core Component Materials,"

Westing 5:ase Eie w n C; ;;r:t's.. " arc-t, WCAP-9179. Rev.1, da ted July 197E.

5.

T. M. Anderson ('.

letter (NS-TMA-1992) to D. G. Eisenhut (USNRC),

dated December 15, 1975.

6.

P. J. Kuchirka, " Properties of fuel and Core Component Materials "

Westinghouse Electric Corporation Report, WCAP-9179, dated October 25, 1977.

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