ML20006E282
| ML20006E282 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 02/08/1990 |
| From: | Shelton D TOLEDO EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 1766, IEB-89-001, IEB-89-1, TAC-M75848, NUDOCS 9002220507 | |
| Download: ML20006E282 (4) | |
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I TOLEDO EDISON 1
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DONALD C. SHELTON -
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LDocket Number: 50-346 LicenseLNumberlNPF-3
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-February,8, 1990 United. States Nuclear Regulatory Commission
,NRC Document Control Desk
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Washington,- D. C. 20555l
Subject:
' Proposed Alternative to ASME Section III Requirements to Permit the-Use of Nickel' Base Alloy 690 Steam Generator Tube Plugs (TAC
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Number.M75848)-
Gentlemen:
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By letter dated November'7, 1989, Babcock and Vilcox (B&V) requested NRC p
approval of~the use of Nickel Base Alloy 690, ASTM specification SB-166-(UNS
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N06690) in-the fabrication-of steam generator tube plugs.
B&W also has requested approval ~from the American Society of Mechanical Engineers ~(ASME)
?for=the use.of Alloy 690 for ASME'Section III repairs. The ASME Boiler and L
Pressure Vessel (B&PV) Code Committee has assigned this request Code: Case 1
Number.N-474-1, an addendum to: Code Case N-474. 1The NRC, in its December 11,
.1989 response to the-B&W request, stated that pending ASME approval'and generic NRC endorsen:ent of the implementing Code Case for Alloy 690, licensees may request NRC approval of the use of Alloy 690 steam generator tube plugs as an alternative' to the requirements of 10CFR50.55a, " Code:: and Standards"'.
In accordance with 10CFR50.55a(a)(3), this letter requests NRC approval'of-the use of Alloy 690 steam generator tube plugs at the Davis-Besse Nuclear Power Station Unit 1 (DBNPS).
NRC Bulletin 89-01, " Failure of Vestinghouse Steam Generator Mechanical Tub'e i
Plugs," identified concerns regarding the potential for primary water stress corrosion-cracking (PUSCC) of steam generator tube plugs manufactured from Alloy 600 heat numbers 3279, 3513, 3962 and 4523. No steam generator tube 1
. plugs from-these' heats are installed at the DBNPS.
However, B&V has i
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identified additional heats of inconel 600 material that may be susceptible to PUSCC.. Toledo' Edison has reviewed this B&V information and has made plans to l
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.Page'2 replace 21 upper tube sheet rolled plugs with Alloy 690 plugs during'the sixth refueling outage, if Alloy 690 tis approved.
Otherwise, Toledo Edison plans only to inspect these 21 plugs and replace them with Alloy 600 plugs, as determined necessary.
The ASME B&PV Code includes Alloy.690, ASTM SB-163, for Section III (Code Cases ~N-20-3 and N-474), but Alloy 690, ASTM SB-166 is not currently included.
Toledo Edison proposes to use steam generator tube plugs fabricated from Alloy 690, ASTM SB-166. Regulatory Guide 1.85 lists Code Case N-20-1 as approved; however, this case applies only to ASTM SB-163 seamless tubing with 40 ksi minimum yield strength for condenser or heat exchanger applications.
Code Case N-20-1 has expired and has been renewed as Code Case N-20-3.
Code Case N-474 has been approved by the ASME Code Committee (which includes approval by NRC representative Mr. R. J. Bosnak) during its February 1989 meeting, and vill appear in the next ASME B&PV Code Case publication. Code Case N-474 applies only to ASTM SB-163, but allows the use of 35 ksi minimum yield strength material. As noted above the B&W request for ASME approval of the use of Alloy 690, ASTM SB-166, is being reviewed as an addendum to Code Case N-474 by the Code Committee.
.The current body of knowledge indicates that Alloy 690 possesses superior resistance to. stress corrosion cracking.
The increased chromium content of Alloy 690 produces a material ~that has beea demonstrated to be immune or resistant to degradation mechanisms that are active in Alloy 600. Reference (a) states on page 2-9 that all available data for Alloy 690 suggests this material (microstructure) is not susceptible to primary water stress corrosion j
cracking (PVSCC). Therefore, even though the other factors are present j
(stress and temperature), PWSCC has not been observed in this alloy." Page B-1 of Reference (b) concludes, " Alloy 690 was immune to SCC in pure water 6
under.all conditions evaluated" and " Ranking of the alloys in terms of their SCC resistance in the simulated resin intrusion environment indicated that
... Alloy 600...had intermediate resistance, and Alloy 690...had the highest
. resistance." Page y of reference (c) states, " Alloy 690 was much more i
resistant to stress corrosion than Alloy 600 and was immune to cracking in most.of the acidic sulfate solutions' examined." Also references (d) and (e) conclude that crack initiation times for Alloy 600 are. reduced as the room temperature yield strength and residual stresses are increased. The same relationship would be expected for Alloy 690 material.
The design values that will be used for ASME Code calculations for this application vill be based on those given in Code Case N-474, approved May 6,
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1989 for ASTM SB-163 material, and Code Main Committee Item 88-360, approved December 9, 1988 for all forms of Alloy 690.
g Toledo Edison believes that Alloy 690 is a superior alternative to Alloy 600 for steam generator tube plugs and will provide an acceptable level of quality and safety in this application.
NRC approval of the use of Alloy 690 steam generator tube plugs is requested by March 1, 1990 to allow replacement of the Alloy 600 plugs during the upcoming cycle 6 refueling outage currently scheduled to commence on February 1, 1990.
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- Dockat Nu: ber' 50-3461 License. Number NPF-3.
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!Page' 3-.
If you have= any. questions regarding this request',: please contact :
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-Mr. R'.sV. Schrauder, Managerg-Nuclear Licensing,-~at (419) 249-2366.
,, n (Very tru yours,:
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~PWS/ssg Attachment
' :ce's P.:M. Byron','DB-1.NRC Resident Inspector A. B. Davis,' Regional Administrator, NRC Region III r
.T.LV.:Vambach,.NRC/NRR DB-1 Senior Project Manager H. F. Conrad, NRC/NRR, Division of Engineering Technology
' State of Ohio I
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.". i # ' Docket Number 50-346
'Licznsa humbar NPF-3
' Serial Number 1766'
' - Attachment Page'l
. References (a) Steam Generator; Tube Plug Integrity Summary. Report, April 1989, Westinghouse Electric Corporation, VCAP-12244, Revision 1 (b) Stress Corrosion Cracking Resistance of Alloys 600 and 690 and Compatible
-Weld Metals in BVRs, July 1988, Electric Power Research Institute, NP-5882M Pinal Report (c) Stress Corrosion Cracking Resistance of Alloys 600 and 690 in Acidic Sulfate Solutions at Elevated Temperatures, October 1983, Electric Power Research Institute, NP-3043 Final Report (d) Intergranular Stress Corrosion Cracking in Steam Generator Tubing.
Testing of Alloy 690 and Alloy 600 Tubes, K. Norring, et al.,
Environmental Degradation of Materials in Nuclear Power Systems Vater Reactors, TMS, 1988 (e) A Comparsion of the Stress Corrosion Cracking Behavior of Alloys 600 and-690 in AVT Water, B. P. Migin and C. E. Shoemaker, Corrosion 86, NACE,
-March 1986 r
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