ML20151Y923
| ML20151Y923 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 04/25/1988 |
| From: | Esposito J PUBLIC SERVICE CO. OF NEW HAMPSHIRE, WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML20151Y818 | List: |
| References | |
| OL-1, NUDOCS 8805050146 | |
| Download: ML20151Y923 (8) | |
Text
P e
Cated April 25, 196d UNITED STATES CF APIRICA NUCLEAR REGULATCRY CCPMISSICN before the ATCHIC SAFETY AND LICENSING BOARD In the Matter of:
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PUBLIC SERVICE COMPANY OF
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Cocket Nos. 50 443-OL NEW HAMPSHIRE, et al.
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Eccket Nos. 50-444-OL
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Seabrook Station, Units
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On-site Ehergency Planning 1 and 2)
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and Safety Issues AFFIDAVIT OF JOHN N. ESPOSITO ON THE GINNA TUBE RUPTURE EVENT AND THE CESIGN OF AND EXPERIENCE WITH C0MESTIC MOCEL F STEAM GENERATORS I, John N. Esposito, being duly sworn, depose and state:
1.
I am employed by Westinghouse Electric Corporation as Manager of Technology Develognent in the Service Technology Division of the Power Systems Business Unit.
2.
My professional qualifications are attached hereto and marked "A".
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 A7T water chemistry controls which act to minimize tube degradation; and gMBle BM!if G
i (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 following 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 foreign 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 foreign 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 ensure that foreign objects are not left in the steam generators.
5.
The Fbdel F steam generator was designed in the mid-seventies.
The four Seabrook Unit 1 steam generators were shipped in December 1930. The Model F incorporates a nunber of design features which, together with the use of AVT water chemistry controls, reduce the potential for tube degradation. The major
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features of the Model F steam generators and their benefits are:
(a) Thermal treatment of Alloy 600 tube material -
Years of research into the performance of Alloy 600 tube material in various steam generator operating environments led to the development of a special thermal treatment process to improve its corrosion resistance. The thermal treatment produces a microstructure that is more resistant to the various forms of stress corrosion cracking (SCC) and improves corrosion resistance by as much as a factor of 10.
EPRI has sponsored a number of pNgrams which confirm this performance and has recccnended the use of thermally treated Alloy 600 for steam generator tubing.
(b) Full depth hydraulically expanded tubesheet joint -
The Model F tubesheet joint is formed by a full depth expansion process. After the tube is inserted into the tubesheet hole, it is expanded hydraulically in a single step. This process closes the crevice between the tube and the tubesheet hole (which is a region where dryout could otherwice produce chemical concentration if the crevice remains 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.
'4 hen 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 clearances between the support platas and the tubes producing forces sufficient to cause local tube deromation and producing high stresses which increase the potential for stress corrosion cracking of the tubes. The Model F tube support material is type 405 stainless steel. This material has improved 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 between the tube and the support plate to four narrow lands, 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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Following is a list of the Model F type steam generators operating in the United States:
Plant SG Model Loops Total Tubes Operation Date 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 Turkey Point 4 44F 3
9,642
- 4/83 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 Vogtle 1 F
4 22,504 3/87 7.
Rese plants account for 33 Model F-type steam generators with nearly 150,000 tubes. This represents more than 1,000 Effective Full Power Months of SG operation in 122 equivalent SG calendar years since initial plant startup. Bis operatir4 experience is sufficient to confirm the reliable operating characteristics of the Model F steam generators.
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Of the nearly 150,000 Model F tubes in service in the United States, 31 tubes have been plugged. The reasons associated with this plugging are as follows:
(a) Foreign Object Interactions -
Control of foreign objects is accompliched through careful inventory of materials introduced to the steam generator during maintenance and through periodic inspections in the tubesheet region. We presence of foreign objects has led to tube plugging in
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't peripheral ~ tubes at two Model F-type plants - Surry 2 (one tube) and Turkey Point 3 (three tubes).. Both of these plants began operation prior to implementation of programs to control foreign objects.
(b) Surface Artifacts - Eddy current indications in the free length of the tubing, thought to be caused by conductive deposits on the OD surface have been observed at Surry Unit 1.
Seven tubes with this type of indication were plugged at Surry. One of these was pulled and subjected to laboratory examination. Tests confirtned the absence of degradation where eddy current testing had suggested a indication of degradation. A similar condition is believed responsible for the plugging of four tubes at Turkey Point 3 and two tubes in Callaway 1.
l (c) AVB Wear - Tube wall degradation at anti-vibration bar (AVB) intersections has been observed in the past, most prominently in the 51 Series steam generators bu'. also in other models. AVB wear has been observed to occur at a rate of 5-155 per year. This mode of degradation is essentially mechanical in nature, and has been addressed in some plants with 51 Series steam generators by installation of new AVBs of a different design. AVB related wear has led to the pluggira of ten tubes at Callaway Unit 1 and two tubes at Millstone i
Unit 3.
1 (d) Other - Two additional tubes were plugged. One of these was at Surry 1 and was attributed to an internal tube i
restriction htlich prevented an eddy current inspection. The
m other was plugged at Callaway 1 for a variation in tube diameter not associated with the tube support plate region.
9.
Experience has shown that Model F steam generators operating with modern AVT water chemistry controls are extremely unlikely to experience tube corrosion wtiich could lead to steam generator tube rupture, particularly in the first few years of operation.
Further affiant sayeth not
'ff, Jofa N. F,sposito SUBSCsIBED AND SWORN to before me this <._ day of //. - (
, 1988.
AluA N.
M
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NOTARY PUBLIC
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testalet E. MPLICA. NOTAsf PURIC motsotvitti 8000. ALLientsY coust?
et cessission tumets otC.14. Isot meneer. Posersonais Asseuseos of estenes l
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'. er.n N'.
Espesti:
My na:e is.'Or.. N. Ispesi:. My tusiness address is P.O. Sex 3H, Fitts:.:. gr.,
ra.,
W,0.
I e oc/. y ) ty 'a'estic.ghause tectris 0 r;crati:. n 5 age,
Te:r..ci:gy Deve::;rer.:, Servi:e Te:*.n:legy O*.visi:n.
gradua:e: frc. Y: r.gs'.ewr. L*niversity, Y.ingstev., &ie V.tr. e !.S.
egree t.
Cr.esistry in 196C.
- n '966, I received a P'... in 2.enistry fr:= Case
.ns::.u.e e t N!.r.,1. y. 0;.. 16.4, cats. : aise opent : p:r'. ier. r f ' 9 A ' a d 1962 in service wi:r. the L'nited States Amy.
- n late '965, after een;;etion of all :he requireraents for ths grantir.g of.he Ph.0. degree, I began ex;leyr.or.: with the 'destinghouse Coctr' Cer;cratien at the Cer.:ra'. Pesearen ' aborat: ries ir. P1 :sturgn, PA. I was centi.ually es;1cyed at those '.aberatories until Novat:er cf 19*6.
At that time I transferred into the cecercial nuclear power division.
5'y ir.itial positi:P was W nager, Chemistry Te:.n: logy. The resperJitilities of this positier.
included investigation of cerrosier. and other roms of degrada icn f:r
'a'estinghouse steam generators. I have been involved V. n steam generator related activities to tne preser.: time. My present sanageria'. du.ies ir.:'.uae a::ivities re!.ated t: evaluatien Of stea*. generater ir.spection data, stea.
ge..trater caterials, an: Or.ecistry teen.: logy studies re* ated to steam ger. orators.
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