ML20004F600

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
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

.

g Northem States Power Company 9

J 414 Nicollet Man D.E. Gilberts 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

c' nCULb((*d t Mr. James G. Keppler N

L Director, Region III h.

..,13 IO3I h 'Ig Office of Inspection and Enforcement g u.s.

re,,

U. S. Nuclear Regulatory Ccamission i fj\\,

Og 799 Roosevelt Road

/

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

\\/ %$

10 33 26 23 5

~

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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+

)

e.

Mr. James G. Keppler Page 2 May 22,1981 D.

The only significant loss of B C was found to be in tube 1.

The loss g

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.

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