ML19318A070

Forwards Util Response to NRC Position Re Control Rod Guide Tube Support Pins.Although Not Required,Util Will Replace Existing Guide Tube Support Pins Mfg w/2,000 F Solution Heat Treatment Temp

ML19318A070
Person / Time
Site:	Farley
Issue date:	06/11/1980
From:	Clayton F ALABAMA POWER CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
NUDOCS 8006180415
Download: ML19318A070 (3)

Text

Alabama Power Company

. 600 North 18th Street

• Post Office Box 2641 Birmmgham. Alabama 35291 Telephone 205 323-5341 h k c

's, boy"f,1%n, Alabama Power the southem electrc system June 11, 1980 Docket No.50-36h Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Attention: Mr. A. Schwencer JOSEPH M. FARLEY NUCLEAR PLANT - UNIT NO. 2 CONTROL ROD GUIDE TUBE SUPPORT PINS Gentle::.en:

A telephone conference was held on June 5, 1980, with NRC staff personnel concerning the subject issue. The NRC position on this issue for Farley - Unit 2 along with our response to that position is provided in the enclosure.

Should you have any further questions regarding this =atter, please advise.

Yours very truly, o ,r nn g /l ,f 'uwx ()-

F. L. Clayton,pIr.

i RWS/rt Enclosure cc: Mr. R. A. Thomas Mr. G. F. Trowbridge Sool 5

ih 800618o415

ENCLOSURE CONTROL ROD CUIDE TUBE SUPPORT PINS NRC Position:

It is recommended that support pins in control rod guide tubes be replacad with pins that have been given a heat treatment which produces high resist-ance to stress corrosion.

Response

For non-UHI plants, such as J. M. Farley-Unit 2, our safety evaluation has confirmed that control rod operation will not be jeopardized due to guide tube misalignment in the event of breakage of a guide tube support pin.

This is true because the lower portion of the pin is captive in the lower guide tube flange and upper core plate, and the control rod drive line alignment feature is maintained.

In the unlikely event of a broken pin, some very small potential exists for interference of control rod movement due to a loose part. If a pin were completely broken at the shank to shoulder junction, the loose part would be too large to enter any clearance space or adversely affect control rod operation. Adverse effect on control rod operation could only occur as-a result of the combination of several unlikely events:

(1) breakage of the pin at a specific location (pin leaf breaking off),

(2) transport of the broken pin leaf to the upper part of the guide tube, and (3) preferential location, orientation, and lodging of the broken leaf on the control rod guide plate so as to interfere with control rod motion.

Although such an occurrence cannot be precluded, the probability for this combination of events is considered remote. Furthermore, the accident analysis bases assume that the most reactive control rod is not inserted from its fully withdrawn position, and thus the effect of a single inoperable rod is part of the current licensing basis. It is, therefore, inappropriate to require replacement of the support pins prior to plant operation for reasons of safety significance.

The same basic design of the guide tube support pin has been used in Westinghouse plants, starting with Rochester Gas and Electric's Ginna plant, for over 160 reactor years. No broken support pins have ever been found in Westinghouse built plants. This includes results of television inspection of the upper internals made during more than 20 in-service inspections which showed that all visible support pins were intact. These

Control Rod Guide Tube Support Pins Page 2 inspections include some of the earliest Westinghouse plants to go into operation and which are known to include guide tube pins manufactured at the 1625 F solution heat treatment temperature.

Based on the above, it is our position that, replacement of the existing Faricy guide tube support pins with new pins that hava been manufactured with a solution heat treatment temperature of 2000 F is not required at this time. However, in order to preclude the need for possible future pin inspection or replacement, which would require significant personnel exposure using current technology and inspection techniques, Alabama Power Company has elected to replace these pins prior to initial fuel load.

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