ML19094A557

Letter Documentation of Discussions with Staff on Inspection Program, Response to Questions Raised About Criteria for Inspection Program & for Future Inspections

ML19094A557
Person / Time
Site:	Surry
Issue date:	10/07/1977
From:	Stallings C Virginia Electric & Power Co (VEPCO)
To:	Case E, Reid R Office of Nuclear Reactor Regulation
References
Download: ML19094A557 (4)

Text

Mr. Edson G. Case Acting Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington,.D. C.

20555 Attn:

Mr. Robert.W. Reid, Chief Operating Reactors Branch 4

Dear Mr. Case:

Serial No. 326B/072077 PO&M/TAP: das Docket No. 50-281 License No. DPR-37 This letter is to document the results of the discussions with your staff in reference to our recently completed Surry Unit No. 2 Steam Generator inspec-tion program.

The following items were discussed:

1)

Questions were raised about the criteria for the inspection program and the criteria for future inspections.

Response

It was agreed to discuss the future inspection programs prior to their implementation.

2)

The plugging criteria needed clarification.

Response

In reference to our letter of September 30, 1977, the following are revisions to the plugging criteria.

Criteria b (in addition to existing criteria)

Restricted tubes in the extreme corners of the tube lane (columns 2-4, 92-94) are evaluated individually since the rates of growth of contours in the area are lower than the general rate of. growth of the contours in the corner areas.

Review of the growth of the contours in the extreme corners and the location of two tubes in Steam Generator B restricted to 0.540 inch (i.e. R4-C3 and R4 C92) indicates that plugging 3 Rows beyond these tubes is sufficient.

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VIRGINIA ELECTRIC AND POWER COMPANY TO Mr. Edson.G. Case Page.:t-10. 2

• *criteria d The.tubes in any column for which plugging under criteria a, b or c above is implementedwi11 also.be plugged in the lower.row numbered tubes back to the.tube lane, if not already plugged; un-less the :required p~ugging would connect two apparently *unrelated areas~

3)

In the.wedge.region of 2C steam generator, it appears the plugging cri-

.teria was not followed.

• Response The tubes located at diagonals f.romtubes located at R37 C74, R35 C74 R34,C76 which did not pass a O. 540 probe were. not plugged as criteria (g-3) stated.

The following tubes should have b_een.plugged: R38 C73, R34 C73, R33 C75, and R33 *077.

However; as all of these tubes passed a 0.610 probe and the last two passed a. 0.650 probe. and as the projected rates of strain growth in this area will, at the end of six months~ still.result in less than the is% strain at which tube leakage has occurred in the past, the tubes will not be plugged this. outage.

4)

Tubes were inspected per Reg. Guide 1. 83 and some were plugged.

What is the_ thinning rate and.why will it not.be a problem?

• Response The number of tubes which have exceeded the 40% tubewa.11 criteria*are:

May 1975

. May 1976

• Sept,1977 2A 35

20.

6 2B 29 35 13 2C 68 20 2

As is.readily apparent, the occurrence of tubes with:greater than 40%

of thinn~ng is markedly.decreasing.

A comparison of the tubes plugged this last outage versus.their condition in May 1976 and the rate of thinning shows*that.the:ratevariesbetween 0.375%.and.2%.per month (attachment 1).

The nominal.average increase is* 1% p.er month~

However, the majority of tubes which.we inspected do not show thi~ thinning rate.

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VIRGINIA ELECTRIC AND POWER COMPANY TO Mr. Edson G. Case Page No. 3 Attachment Therefore, no substantial tube degradation from the previously exper-ienced corrosion mechanisms is expected to occur in the six month opera-ting period requested in our letter of September 30, 1977.

Very truly yours,

~' 21);?. ~u~r C. M. Stallings Vice President-Power Supply and Production Operations cc:

Mr. James P. O'Reilly

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C REG. GUIDE RESULTS EDDY CURRENT

~

S/G I

ROW COLUMN

. MAY r76 SEPTEMBER 177

. PERCENT PERCENT 2A 15 47

?< 20

/

48 13 36 36 50 17 41 39 41 23 41

.e 20 41 20 33 36 46 22 41 26 42 2B 12 34 No defect shown 41 16 34 36

. ~,. '.

48

~*

19 37 34 47 15 38 20 53 20 38 38 5[,

19

. 38 3.3 54 20 39 34 48 20 40 32 41 20 41 39 48 16 43 35 41 21 54 28 45 15 56

< 20 47 35 47 Not Run 57 2C 20 53 36 45 19 59 29 42