ML12339A723

Official Exhibit - NYS000378-00-BD01 - History of Westinghouse Model 44 Steam Generators (from NRC Website (Nov. 2, 2000))

ML12339A723
Person / Time
Site:	Indian Point
Issue date:	06/19/2012
From:	Office of Information Services
To:	Atomic Safety and Licensing Board Panel
SECY RAS
References
RAS 22624, 50-247-LR, 50-286-LR, ASLBP 07-858-03-LR-BD01
Download: ML12339A723 (2)

Text

United States Nuclear Regulatory Commission Official Hearing Exhibit Entergy Nuclear Operations, Inc.

In the Matter of:

(Indian Point Nuclear Generating Units 2 and 3) c:..\,.~p..R REGlI~;. ASLBP #: 07-858-03-LR-BD01 l~'~:

Docket #: 05000247 l 05000286

• 0 Exhibit #: NYS000378-00-BD01 Identified: 10/15/2012

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Admitted: 10/15/2012 Withdrawn: NYS000378

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0.... Rejected: Stricken: Submitted: June 19, 2012

• • • • il Other:

History of Westinghouse Model 44 Steam Generators ,. /

[ Indian Point 2 Event I Nuclear Reactors I NRC Home Page 1 Ginna 0711970 06/1996 Point Beach 1 12/1970 03/1983 H. B. Robinson 03i197i lOil984 Point Beach 2 10/1972 12/1996 Turkey Point 3 12/1972 0411982 Turkey Point 4 0911973 05/1983 Indian Point 2 0811974 N/A Indian Point 3 08i1976 06il989 Degradaiion lViechanisms in Westinghouse lViodei 44 Steam Generators Model 44 Steam Generators (SGs) use alloy 600 material for tubing. The tubes are supported vertically by the thick tube sheet at the bottom of the steam generator and laterally by drilled-hole tube support plates which are made of carbon steet Corrosive products (typically magnetite) tend to accumulate in the crevice beh'leen v.!be !!..!1d tube support plates because of the d..riHed-hole configuration and the susceptibility of the

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circumferentially oriented stress corrosion cracking in tubeS. Tl-Js degradation illecharJsm was the predominant reason for tube plugging in model 44 SGs.

The tubes in Model 44 SGs were mechanically rolled for only a few inches into the tubesheet starting at the primary (lower) face of the tubesheet. As a result, a crevice exists between the tube and the tubesheet for the portion of the tube within the tubesheet that is not expanded. Since the tube was mechanically roned into t.h.e. tubesheet; the expansion tra..l1sition is cormnonly referred to as a roll transition. Plants with sa tubes t.~at 2J'e cr..ly rell expanded for a SIr'~l distance 'Nithin t.l).e tubesheet ;are referred to as

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andior at the roll transition has led some plants to fe-roll the tubeS abOVe the original rolled region to provide a new pressure boundary free of any detectable defects. By so doing, the iicensees have been able to apply alternate repair criteria, such as the F-star criterion, in which tubes with degradation in a certain specified distance below the top of the tubesheet or the bottom of the roll transition (whichever is lower),

~ay remain in service. Tubes accepted for continued service on the basis of the F-star criterion have stnlctura! and 1ea..lcage integrity consistent with regulatory criteria.

In genera1~ plants 'with SGs that have orJy been pa..-tially expanded into the tube sheet have e~h.ibited verj little circumferentially oriented degradation either at the exparlsion transition or at the top of the tubesheet.

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}v1ost of these pla.'1ts have exhibited axially oriented primary water stress corrosion craddng at the roll transition, axially oriented outside diameter stress corrosion cracking in the tubesheet crevice region, andior intergranular attack in the tubesheet crevice region.

The small u-bend regions of the tubes have exhibited axial and circumferential cracking. The degradation is caused by excess ovality during tube fabrication process, residual stresses, and tube denting at the top tube support plate. However, some plants had preventively plugged the row of tubes with the smallest u-bends (innermost row).

There were wastage problems in early operation of mcdel44 SGs. (see tube rupture events below). With improved secondary side chemistry, the tube wastage problem was essentially elilTJnated.

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