ML20234C869

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Affidavit of Jn Esposito on Ginna Tube Rupture Event & Design of & Experience W/Domestic Model F Steam Generators.* Related Info Encl
ML20234C869
Person / Time
Site: Seabrook  NextEra Energy icon.png
Issue date: 11/20/1987
From: Esposito J
WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML20234C672 List:
References
OL-1, NUDOCS 8801060351
Download: ML20234C869 (8)


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ko Ihted November 20, 1987 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION before the ATOMIC SAFETY AND LICENSING BOARD In the Matter of: )

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PUBLIC SERVICE COMPANY OF ) Ibcket Nos. 50-443-OL NEW HAMPSHIRE, et al. ) Docket Nos. 50-444-OL

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Seabrook Station, Units ) On-site Bnergency Planning 1 and 2) ) and Safety Issues AFFIDAVIT OF JOHN N. ESPOSITO ON THE GINNA TUBE RUPTURE EVENT AND THE DESIGN OF AND EXPERIENCE WITH DOMESTIC MODEL F STEAM GENERATORS I, John N. Esposito, being duly sworn, depose and state:

1 1. I am employed by Westinghouse Electric Corporation as Manager )

of Technology Development in the Service Technology Division of the Power Systems Business Unit.

2. My professional qualifications are attached hereto and marked "A". l 3 The purpose of my affidavit is to provide discussions of; (a) the Ginna tube rupture event including the mechanism which led to the event and the corrective actions instituted to avoid similar events in the future; (b) the Model F steam generator design features and the AVT )

I water chemistry controls which act to minimize tube i degradation; and i

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(c) the operating history of Model F type steam generators in the United States which demonstrates their reliability.

4. On January 25, 1982, a tube ruptured in steam generator B at the Ginna nuclear power station. The fbilowing sequence of events was determined to have occurred:

(a) A metal object was inadvertently left in the steam generator during a field modification in 1975. This foreign object was later found on the tubesheet at the periphery of the tube bundle.

(b) During operation, flow forces caused the fbreign object to impact the peripheral tubes resulting in damage to both plugged and operational tubes. This process continued until tube R42C55, located two rows in from the periphery of the tube bundle, ruptured.

(c) Investigations showed that the fbreign object produced an axial wear scar and local wall thinning by which the ruptured tube experienced loss in tube wall thickness over a eight month period.

(d) As a result of this event, utilities now routinely perform visual searches of the steam generator tubesheet periphery to i ensure that foreign objects are not left in the steam generators.

5. The Model F steam generator was designed in the mid-seventies.

The four Seabrook Unit 1 steam generators were shipped in December 1980. The Model F incorporates a number of design features which, together with the use of AVT water chemistry controls, reduce the potential for tube degradation. The major l

., features of the Model F steam generators and their benefits are: m. 1 s (a) Thermal treatment of Alloy 600 tube material - 3

<t Years of research into the performance of Alloy 600 tube material in various steam generator operating environments led to the development of a opecial thermal treatment process to o>

improve its corrosion re51 stance. The thermal treatment

. produces- a microstructure that is more resistant to the various

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resistance by as much ak a factor of 10. EPRI has sponsored a number of programs which confirm this performance and has ,

recommended the use of thermally treated Alloy 600 for steam generator tubing.

.r (b) Full depth hydrq lically expanded tubesheet joint - ,

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The Model F tubesheet joint is formed by a full depth f expansion process. After the tube is inserted into the '

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, 3 tubesheet hole, it is cxpanded hydraulically in a single i ai step. This process closes the crevice between the tube and 0 the tubesheet hole (uden is a region where dryout could otherwise produce chemical concentration if the crevice remains N

open) while at the same time producing low residual stresses, which reduces the potential for stress corrosion cracking.

(c) Stainless steel tube support plate material - The steam generator tube support plate material of early model steam generators was carbon steel. Under most conditions, this material proved to be satisfactory. However, in the mid-70s corrosion of this material due to the presence of chemical

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impurities led to a tube degradation phenomenon called '

denting. When carbon steel corrodes, the oxide occupies a volume that is greater than that of the original material.

Under certain conditions formation of this oxide has been found to fill clearanced between the support plates and the tubes .

producing forces sufficient to cause local tube deformation and producing high stresses which increase the potential for stress L

I corrosion cracking of the tubes. The Model F tube support material is type h05 stainless steel. This material has improvM corrosion resistance and with modern, AVT water chemistry control, the volume of the oxide does not exceed the material loss thus eliminating the potential for denting.

(d) Quatrefoil tube support hole geometry - The Model F tube support plate holes are broached to produce a four-lobed hole

! which directs the flow through the tube support plate to cleanse the interface with the tube. This cleansing action limits the potential for local chemical concentration and subsequent tube corrosion. This design limits the contact s

between the tube and the support plate to four narrow lands, j which minimizes local dryout and chemical concentration. Tests  !

have confirmed that the quatrefoil design produces lower local

\ superheat at the interface with the tube than the conventional drilled tube hole. In tests which modeled sludge buildup in the crevice between the tube and tube support plate, the buildup was limited to the width of the lands, which provides lower potential for corrosion at the interface.

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6. Following is a list of the Model F type steam generators operating in the United States:

Plant SG Model Loops Total Tubes Operation Ihte Surry 2 51F 3 10,026 9/80 Surry.1 51F 3 10,026 7/81 Turkey Point 3 44F 3 9,642 4/82  !

i Turkey Point 4 44F 3 9,642 4/83 i

Point Beach 1 44F 2 6,428 4/84 Callaway 1 F 4 22,424 10/84 Robinson 2 44F 3 9,642 1/85 Wolf Creek F 4 22,424 5/85 Millstone 3 F 4 22,504 1/86 l Vogtle 1 F 4 22,504 3/87

7. These plants account for 33 Model F-type steam generators with nearly 150,000 tubes and represent a total of 119 equivalent SG l operating years. This operating experience is sufficient to confirm the reliable operating characteristics of the Model F steam generators.
8. Of the nearly 150,000 mdel F tubes in service in the United States, 29 tubes have been plugged. The reasons associated with this plugging are as follows:

(a) Foreign Object Interactions - Control of foreign objects is accomplished through careful inventory of materials introduced to the steam generator during maintenance and through periodic inspections in the tubesheet region. 'Ihe presence of foreign objects has led to tube plugging in peripheral tubes at two Model F-type plants - Surry 2 (one

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( tube) and Turkey Point 3 (three tubes). Both of these plants ,

ci- 1 began operation prior to implementation of programs to contro]

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foreign obj9 cts. I l

. (b) Surface Artifacts - Eddy cui' rent indications.in.the free I length of the tubing, thought to be caused by conduct.i.ve {

deposite on the OD surface have been observed at Surry. Unit 1.

Seven tubes with this' type of indication were plugged at Surry. One of theci was pulled aM subjected t,o laboratory examination. Teste: ccnfirmed tbn acaence e,f . degradation where l

edCy current testing had suggested a indication of t degradation. A similar condition is believed responsible for the plugging of four tubes at Turkey Point 3 and two tubes in Callaway 1.

(c) AVB Wear - Tube wall degradation at anti-vibration bar  ;

3. s j (AVB) intersections has been observed in the past,.moEt prominently in the 51 Series steam generators but also in other

, models. AVB u%r has been observed to occur at a rate of '5- 15%

f per year. This mode of degradation is essentially c

mechanical in nature, and has been addressed in some plants [

with 51 Series steam generators by installation of new AVBa of a different design. AVB relatel wear has led to the plugging of ten tubes at Callaway Unit 1. l (d) Other - Two additional tubes were plugged. One of these was at Surry 1 and was attributed to an internal tube restriction which prevented an eddy current inspection. The other was plugged at Callaway 1 for a variation in tube diameter not associated with the tube support plate region.

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.., 9 Experience has shown that Model F steam generators operating with modern AVT water chemistry controls are extremely unlikely to experience tube corrosion which could lead to steam generator tube rupture, particularly in the first few years of operation.

Further affiant sayeth not

. 'l 4 Joh,ri N.' Espito to before me SUBSCRIBED this of f day of AND SpW/puw.6a/,1987. y t

(7$nwedbotax-NOTARY'PUBLIC P.,. _' ' u'i n rJ:'.te

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I John N. Especito My nar.e is .'ohn N. Esposito. My business address is P.O. Box 355, Pittsburgh,

n. . , ! 52 M . I c. ea,aluyed by Westinghouse Elcotrio Corporation as >>nagea, Technc10gy Eeve'.cpment, Service Techno1cgy Mvision.

graduated from Youngstown University, Youngster., Ohio with a B.S. Degree i, Chemistry in 1960. In *.966, I received a Ph.0. in Chemistry from Case

.tnst n uce of Techavtusy, 01 ,.=14.4, Ohis. I aise opent : p rtion cf 19M i,*/

1962 in service with the United States Amy.

In late 1965, after comp".etion of all the requirements for the granting of the Ph.D. degree, I began exploymer.t with the Westinghouse Electric Corporation at the Centrai ?.esearch Laboratories in Pittsburgh, PA. .I was continually employed at those laboratories until November cf 1976. At that time I transferred into the comercial nuc'. ear power division. My initial posit 10n l was Manager, Chemistry Technology. The responsibilities cf this positier included investigation of corrosion and other roms of degradation for Westinghouse steam generators. I have been involved with steam generator related activities to the present time. My present canagerial duties include activities re'.ated to evaluatien of stea:t generater inspection data, steam generator materials, and chemistry techtclogy studies related to steam generators.

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