ML20098D634
| ML20098D634 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 05/19/1992 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML20098D632 | List: |
| References | |
| NUDOCS 9205290201 | |
| Download: ML20098D634 (8) | |
Text
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- SURVEILLANCE REQUIREMENTS (Continued) 4.4.5.4 Acceptance Criteria a.
As used in this specification:
1)
Imperfection means c exception to the dimensions, fini.sh or contour of a tube or siseve from that required by fabrication l
drawings or specific tions.
Edd3 current testing indications below 20% of the nominal tube or sleeve wall thickness, if l
detectable, may be considered as imperfections;-
2)
Degradation means a service-induced cracking, wastage, wear or l
general corrosion occurring on eitner inside or outside of a j
tube or sleeve; I
l 3)
Degraded Tube means a tube or sleeve containing imperfections greater than or ? qual to 20% of the nominal tube or sleeve wall thickness caused by degradation; 4)
% Degradation means the percentage of the tube or sleeve wall i
thicKaess affected or removed by degradation; 5)
Defect means an imperfection of such severity that it exceeds the repair iimit.
A tube or sleeve containing a defect is
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defective; 6)
Repair Limit means the imperfection depth at or beyond which the.
tube shall be removed from service by plugging or repaired by sleeving.
It &lso means the imperfection depth at or beyond which a sleeved tube shall be plugged.
The repair limit is equal to 40% of the nominal tube or sleeve wall tnickness.
For Unit 1, this definition does not apply to the region of the tube subject to the alte,rnate tube plugging criteria.
If a tube is sleeved due to Jegradation in the F* distance, then i
any defects found in the tube below the sleeve will not necessi-i tate plugging.
l The.Bab cox process described in Topical Report BAL-2045(P -A will b sed for sleeving.
i hev. l 7)
Unserv ceable d ibes the condition of a tube if it leaks or contains4 large enough to affect its structural integ-rity in the event of an Operating Basis Earthquake, a loss-of-coolant accident, or a steam line or feedwater line break as specified in 4.4.5.3c., above; 8)
Tube Insoection means an inspection of the steam generator tube from the point of entry (hot leg side) completa1y around the U-bend to the top support of.the cold leg; CATAWBA - UNIT 3 1 & 2 3/4 4-15
- mcodment N. M (Unit 1)
'O 9205290201 920579 PDR ADOCK 05000413 P
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REACTOR COOLANT SYST!M i
BASES STEAM GENERATORS (Continued) generator tubes is based on a modification of Regulatory Guide 1.83, Revision 1.
Inservice inspection of stear generator tubing is essential in order to main-tain surveillance of the conditions of the tubes in the event that there is evidence of trechanical damage or progressive degradation due to design, manu-facturing errors, or inservice conditions that lead to corrosion.
Inservice inspection of steam generator tubing also provides a means of characterizing the nature and cause of any tube degradation so that corrective measuras can be taken.
The B&W process (or method equivalent) to the inspection method described in 045(P).A will_be used.
Inservice inspection of steam gen-
)g, l To ical Report BAW-:
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urator sleeves is also reosi ed to ensure RCS intcgrity.
Beecuse the sleeves introduce changes in the wail thickness ara di,tLter, they reduce the sensit'vity i
of eddy current testing, therefore, special inspection methods must be used.
A l
hg. f method is described in Topical Report BAW-204521-A;with supporting validmcn I
/~ data that demonstrates the inspectability of the sleeve and underlying tuW. As required by NRC for licensees authorized to use this repair process, Catawba com-mits to validate the adequacy of any system that is used for periodic inservice f
inspections of the sleeves, and will evaluate and, as deemed appropriate by Ouke Power Company, implement testing methocs as better methods are developed and l
validated for commercial use.
The plant is expected to be operated in a manner such that the secondary coolant will be maintained within' tnose chemistry limits found to result in negligible corrosion of the steam generator tubes.
If the secondary coolant chemistry is not maintained within these limits, localized corrosien tray likelj result in stress corrosion cracking. The extent of cracking during plant opera-tion woulo be limited by the limitation of steam generator tube leakage between the Reactor Coolant System and the Secondary Coolant System (reactor-to-seccndary leakage = 500 gallons per day per steam generator). Cracks having a reactor-to-secondary leakage less than this limit during operaticn will have an adequate margin of safety to withstand the loads imposed during normal operation and by m tulated accidents. Operating plants have demonstrated that reactor-to-l reprindary leakage of 500 gallons per day per steam generator can readily be detected by radiation monitors of steam generator blowdown. Leakage in excess a tnis limit will recuire plant shutdool-and an unscheduled inspection, during which the leaking tubes will be locateo and repaired.
Wastage-type defects are unlikely with preper chemistry treatment of the secondary coalant. However, even if a defect shculd develop in service, it will be founo ouring scheduled inservice steam generator tube examinations.
Repair will be required for all tubes with imperfections exceeding the repair limit cf 40% of the tube nominal wall thickness.
For Unit 1, defective tubes which fail under the alternate tube plugging criteria do not have to be repaired. -Defec-tive steam generator tubes can be repaired by the installation of sleeves which span the area of degradation, and serve as a replacement pressure boundary for the degraded portion of the tube, allowing the tube tc remain in service.
Steam i
L generator tube inspections of operating plants have demonstrated the capability to reliably detect wastage type degradation that has penetrated 20". of the original tube wall thickness.
1 I
emenement u.y ? R l}
Sendment No.
C TAWBA - UNITS 1 & 2 8 3/4 4-3 m :;
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TECIINICAL SPECIFICATION CIIANGE This proposed amendment to the Technical Specifications (TS) will allow the use of the B&W sleeving process as described in BAW-2045P, Rev 1. This revision to the topical allows sleeving to be used in the tube support plate region, as well as in the tube sheet region which is currently allowed per TS 4.4.5.4.a.6.
DISCUSSION AND TECIINICAL JUSTIFICATION The ability to repair steam generator tubes by tube support plate sleeving will be important in the future due to the increasing number of secondary side stress corrosion cracking indications located in the tube support regions of the hot leg. At the end of Unit 1 Cycle 4,15 tubes were detected containing indications of intergranular attack (IGA / SCC) on the tube outer diameter. At the end of Cycle 5, the nuraber of indications had increased to 159. Origir.al analysis predicted that Catawba Unit I would be expected to reach 1% of tubes repaired at about 5 effective full power years. In reality, Catawba Unit I has reached this level in a little more than 4 effective full power years.
l If the steam generator tubes cannot be sleeved, all defects greater than 40% through-wall will be plugged. The rapid rate at which indications are increasing suggests that without the ability to use sleeving in the support plate region in the near future, a large numb of -
tubes may have to be plugged.
The purpose of sleeving is to repair a degraded tubc m a manner that maintains the function and integrity of the tube. A degraded tube means a tube or sleeve containing imperfections greater than 20% of the r,minal tube or sleeve wall thickness caused by degradation. A sleeve, consisting of an 11" or a 17.5" length of tubing. is placed inside the existing steam generator tube to span a tube support plate or tube sheet defect or indication. The risk of a tube leak or rupture is reduced. Sleeving also helps to maintain plant margin for safety analysis. Twenty sleeves can be installed with the same primary flow reduction as with one plugged tube. The use of sleeves rather than plugs leaves a greater heat transfer crea available in the steam generator. Forty-eight tube sheet, or sixty-five tube support plate sleeves, causes the same reduction in heat transfer as plugging one tube.
The sleeving process requires cleaning the area to be sleeved, inserting and kinetically welding the sleeve, and stress relieving the welds Robotic maniptdators commonly used in other. steam generator work perform the majority of these processes.
Cleaning is performed by a flexible hone system. The sleeve is inserted and positioned. For the tube
- support plate sleeves, both joints are simultaneously kinetically welcled.
Following welding, a temperature controlled heaur is inserted into the sleeve te 4ress relieve both freespan joints simultaneously for a support plate sleeve. Only the upper joint is stress relieved in the tube sheet sleeve. The details of these processes are presented in Topical Report BAW-2045P, Rev.1.
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Eddy current testing is used to verify positioning and expansions, as well as tube and sleeve
- integrity. A bobbin coil inspects the tube outside the sleeve area. In the sleeved area, a rotating pancake coil supplements the bobbin coil analysis.
M. S. Tuckman's letter, dated December 19, 1990, sebmitted a proposed revision to the Catawba Technical Specifications to allow the option of using the B&W Kinetic Sleeving Process for 3/4" OD Tube Repair described in Topical Report BAW-2045(P)-A. This proposed amendment was approved as Amendment 84/78 to the Catawba Technica:
Specifications on March 4,1991. At the time this amendment was issued, the staff concluded tnat there was reasonable assurance that operation in accordance with the proposed amendment would not endanger the health and safety of the public.
This proposed amendment will allow steam generator tube sleeving t.
be done in accordance with BAW-2045P, Rev.1. This topical allows the use of sleeving in the tube support plate region using kinetic welds at bc.h the upper and lowerjoints, which was not included in Rev. O of the topical. The topical a!so provides additional corrosion test data information from the 7/8" tube sleeve qualification program, and information on the redesign of the 3/4" tube sheet sleeve using a kinetic weld at both the upper and lower joints, where in the previous design the lower joint had been rolled.
The tube support plate sleeves are qualified to meet appli_able portions of the 1986 ASME Code Sections citeria for steam generator design and operation. Verificarian included analysis, and determinations of critical fatigue loading conditions. Leak testing, pressure cycling, and axial :oad fatigue testing verified the mechanical integrity of the support plate sleeves. The installed structural integrity of both the tube sheet and tube support plate kin ^.tically welded joints was proven by sOjecting the sleeve / tube weld samples to a series of tests representing design service conditio:v The samples were leak tested, fatigue l
tested, and leak tested again, to qualify the joint by experimental stress analysis.
Subsequent examination showed that the structural integrity of the sleeves and kinetic weld were maintained after testing. Thermally treated alloy 690 was selected for the sleeve material due to enhanced corrosion resistance. A battery vicorrosion testing showed h!!oy 690 was superior in nearly all steam generator environments when compared with alloy 600. Detailt of the sleeve qualification are found in BAW-2045P, Rev.1.
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I ATTACHAIENT III 4
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NO SIGNIFICANT IIAZARDS ANALYSIS 10 CFR 50.92 states that a proposed amendment involves no signi6 cant hazards consideration if operation in accordance.with the proposed amendment would not:
1)
Involve 'a sign ficant increase in the probability 'or corsquences of an accident i
previously evaluated; or 2)
Create the possibility of a new or different kind of accident from any accident previously evaluated; or 3)
Involve a signi6 cant reduction in the margin of safety.
Operation of Catawba in accordance with the proposed amendment would not involve a significant increase in the probability or consequences of an accident previously evaluated.
Considering the function of the sleeve, the principal accident associated with this amendment is the steam generator tube rupture accident. The steam generator sleeve has been analyzed and tested to the operating and design conditions of the original tube as documented in Topical Report BAW-2045P, Rev.1. The Topical Report contaias the design verincation results from the analysis and confirmatory testing performed on the sleeve. The probability or consequences of this previously evaluated accident does not involve a significant increase since the sleeve meets the original tube design conditions and the structural integrity of the tube is maintained by the sleeving process. The sleeve is less susceptible to the identified stress corrosion failure mechanisms of the original tube because of the B&W specified installation process and the use of improved material (Inconel alloy l
690); therefore, the potential for primary to secondary leakage is also reduced by the addition of a steam generator tube sleeve. The continued integrity of the sleeve will be verified by TS inspection requirements, and the sleeve will be plugged in accordance with TSs, if necessary.
Operation of Catawba in accordance with the proposed amendment would not create the L-possibility of a new or different kird of accident from any accident previously evaluated.
The purpose of the sleeve is to repair a defective steam generator tube to maintain the function and integrity of the tube as opposed to plugging and removing the tube from service. The sleeve functions'in essentially the same manner as the original tube, and has been analyzed and tested for steam generator design conditions. The sleeve is less susceptible to the identified stress corrosion failure mechanisms of the original tube because of the B&W specified installation process and the use ofimproved material (Alloy Inconel i-690); therefore, the potential for primary to secondary leakage is also reduced by the addition of a steam generator tube sleeve. The continued integrity of the sleeve will be verified by TS inspection requirements and the sleeve will be plugged in accordance with TSs, if necessary. Repairing a steam generator tube to a serviceable condition utilizing the propmed sleeve process does not create the possibility of a new or different type of-accident since the sleeving is a passive component with postulated failures that are similar I
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to the original tube.
Operation of Catawba... accordance with the proposed amendment would not involve a
. signincant reduction in a margin of safety.
The structural integrity of the tube is maintained by_ the installation of the sleeve and the sleeve / tube weld. The potential for primary to secondary leakage is reduced by the addition of the steam generator tube sleeve.
Kinetic sleeving has proven to be attractive from an ALARA point of view.
The Catawba LOCA analysis in Chapter 15 of the FSAR takes into account the effect of plugged tubes on primary coolant flow. The LOCA analysis assumes a worst case where 10% of the tubes are plugged. The effects of sleeve installation (versus tube plugging) on steam generator performance, heat transfer, flo's restriction, and steam generation capacity were analyzed and described in the B&W Topical Report. Twenty sleeves can be installed with the same primary flow reduction as with one plugged tube. Forty-eight tube sheet, or sixty-6ve tube support plate sleeves, causes the same reduction in heat transfer as plugging one tube.
ENVIRONMFETAL IMPACT ANALYSIS One of the major design objectives of the B&W steam pnerator tube sleeving process was to minimize personnel exposure. The results of a personnel exposure study are presented in Section 7.3 of the Topical Report BAW-2045P, Rev.1. The conclusion is that tube sleeving provides a radiological economic attemative to plugging and removing tubes from service.
The sleeving process does result in radioactive caste which is considered disposable and cannot be reused. The solid volume produced during the installation of 50 sleeves is approximately 0.75 cubic feet. This waste consists of r:q'on tubing, stress relief heaters, roll expanders, cleaning hones, and water. The cleaning hones (less than one percent of the waste) are expected to have the highest contamination dose rate. This contact will result in an expected hone radiation reading of approximately 1-2 R/hr after the usable life of the hone. The remainder of the waste is coasidered to be extremely low level waste.
l The cleaning water will be retrieved and piped to the station radioactive waste water treatment system. Approximately one gallon pu each tube will be required. Additional wastes will be prodneed consisting of protective clothing, tape, plastic bags, and other materials normally used in a radioactive area.
The proposed amendment does not involve a significant hazards consideration, nor significantly increase the types and amounts of effluents or waste that may be released offsite, nor increase individual or cumulative occupational radiation exposures. Therefore, the proposed TS amendment meets the criteria given in 10 CFR 51.22(c)(9) for categorical exclusion from the requirement for an Environmental Impact Statement.
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