ML20004F600

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Responds to IE Bulletin 79-26,Revision 1,Item 4, Boron Loss from BWR Control Blades. Destructive Exam of Highly Exposed Control Blade Completed.Results Listed
ML20004F600
Person / Time
Site: Monticello Xcel Energy icon.png
Issue date: 05/22/1981
From: Gilberts D
NORTHERN STATES POWER CO.
To: James Keppler
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
References
IEB-79-26, NUDOCS 8106190190
Download: ML20004F600 (2)


Text

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Northem States Power Company 9

J 414 Nicollet Man D.E. Gilberts l Minneapoks. Minnesota 55401 s.n or vie. Pr ie.m  !

Telephone (612) 330-6071 Power supply 1 May 22, 1981 7 9 0  %

9> f dl 4 Mr. James G. Keppler c' N

nCULb((*d t L Director, Region III h. ..,13 IO3I h 'I Office of Inspection and Enforcement U. S. Nuclear Regulatory Ccamission g u.s. re,, g 799 Roosevelt Road i fj\,

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f Glen Ellyn, IL 60137

Dear Mr. Keppler:

MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Responge to IE Bulletin No. 79-26, Rev. 1 The destructive examination of Monticello's most highly exposed control blade 'nas been completed, with the following results, in response to IE Bulletin No. 79-26, Revisien 1, Item 4.

A. The tubes examined were tubes numbers 1, 2, 3, 4, 5, 7, 10, 12, 20 and 21 from wing 1 of control blade MT77R. (Tube 1 is the outermost tube).

B. All of the tubes were visually examined, and the tcp approximately one-half of each tube was also eddy-current tested. Through-wall defects were found in tube 1 at the following approximate dis:.ances from the tube top: 4, 4 , 5 , 9k,11,11 3/4,13k,16, 20, 26, 29 3/4, and 30 inches. No through-wall defects were found in any other tube.

C. The calculated B-10 depletion (percent) for each tube examined versus elevation is:

Tub e Upper 3' Upper Mid 3' Lower Mid 3' Lower 3' 1 47 37 33 7 2 45 35 32 6 3 43 34 30 6 4 41 32 29 6 5 39 30 27 5 7 36 28 25 5

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10 33 26 23 5

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12 32 25 22 4 20 25 20 18 3 i

21 24 19 17 3  !

810 a 10o 80 0
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Mr. James G. Keppler Page 2 May 22,1981 l D. The only significant loss of B gC was found to be in tube 1. The loss front extended from the top end plug down about 33 inches.

E. The =mv4=um local depletion for tubes having no cracks was found to be 6* .98 percent B-10 depletion, near the top of tube 3.

. F. The maximum local depletion for tubes having no loss o' boron was found to be 67.98 percent B-10 depletion, near the top of e <te 3. (This is the same as item I because the only tube with a crac 2 also showed a loss of boron.)

If additional information is required, please communicate directly with plant management.

Yours truly, D. E. Gilberts Senior Vice President Power Supply cc: '[r. C. H. Brown Mr. G. Charnoff Director, Office of Inspection and Enforcement Division of Reacter Operations Inspection U. S. Nuclear Regulatory Commission Washington, D. C. 20555 DEG:nk i

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