ML17264A155
| ML17264A155 | |
| Person / Time | |
|---|---|
| Site: | Ginna  |
| Issue date: | 09/11/1995 |
| From: | Marsh L NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML17264A154 | List: |
| References | |
| NUDOCS 9509140204 | |
| Download: ML17264A155 (6) | |
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UNITED STATES NUCLEAR REGULATORY COMIVIISSION WASHINGTON, D.C. 2055&4001 V
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RE VEST TO USE A TERNATIVE HAT IALS LOY 690 TYPE HELD H
A S I
TH FABRICATI AN INST LL TION OF PLAC MENT STEAM GE E
TO S
OC STER GAS AND ELECT IC CORPO T ON E.
G NNA NUC EAR P
WER PLANT 0 KET UMBER 50- 44 1.0 IHTTRO UCTi N
By letter dated December 5,
- 1994, Rochester Gas and Electric Corporation (RGSE or the licensee),
requested approval under the provisions of 10 CFR 50.55a(a)(3)(i) to use Section IX of American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code)
Code Cases 2142 and 2143 during the impending fabrication and installation of replacement steam generators (SGs) for the R.
E. Ginna Nuclear Power Plant.
These two ASME Code Cases introduce and classify new nickel base weld metals that closely match and are intended for welding Alloy 690..
ASME Code Case 2142 establishes welding classifications and other requirements for a bare wire filler metal.
ASHE Code Case 2143 establishes welding classifications and other requirements for a coated electrode.
The subject Code cases were adopted by the ASME on December 7,
- 1992, and were published in ASME Code Case Supplement 3 in April 1993.
Due to the fact that this is a Supplement to the 1992 Edition of the ASHE Code, these Code cases cannot be used by the licensees without prior NRC staff review.
The 1992 Edition of the ASHE Code has not been incorporated by reference into the regulations.
RGKE intends to use.Alloy 690 tubing and components in the fabrication and installation of replacement SGs for the Ginna Nuclear Power Plant.
ASME Code Case N-474-1 will allow the use of Alloy 690 for use as a construction material for the replacement SGs.
RG8E believes that use of the new weld metals will enhance the service life of the replacement SGs.
Industry studies indicate that these new weld metals are less susceptible to intergranular stress-corrosion cracking (IGSCC) than the other nickel base weld metals currently applied.
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0 Use of Code Cases 2142 and 2143 is advantageous to RGAE because it eliminates the burden of requiring qualification of separate welding procedures for each weld metal, as is the case for non-Code welding materials.
Thus, this relief request incorporates two issues:
1.
Use of Alloy 690 type weld metals in Code class I construction,
- and, 2.
The use of 2 ASIDE Code cases which group the new weld metals in the same welding categories as other commonly employed nickel base weld metals.
This allows the use of appropriate existing welding procedures and 'performance qualifications with the new weld metals.
2.0 ~UO Due to the extensive history of IGSCC problems in alloy 600, the industry has sought an alternative alloy.
Currently, alloy 690 is the industry material of choice.
This choice is the result of numerous laboratory studies which show-that alloy 690 has little or no susceptibility to IGSCC in environments that simulate pressurized-water reactor (PWR) and boiling-water reactor (BWR) plant conditions.
The NRC staff review of these laboratory test results has resulted in the NRC staff position that, based upon the available technical
- evidence, there is no technical reason to disallow the use of alloy 690 base material in nuclear plant construction.
Alloy 600 type weld metals (such as Inco 82 and 182) were widely used during the construction of nuclear power plants.
Operating experience showed that Inco 182 was also susceptible to IGSCC, although primarily in BWR environments.
Weld metals matching alloy 690 have also been tested in simulated PWR and BWR environments.
Commercial development of these weld metals lagged that of the alloy 690 base metal.
No matching weld metal has been commercially available until now.
Thus, the NRC staff evaluation of these weld metals has not been previously conducted.
Corrosion studies examining the susceptibility of weld metals to IGSCC in SG environments are scant compared to the voluminous base metal studies.
This is because the base metal performance is a strong indicator of the expected performance of a matching weld metal.
Results of the principal study which included weld metals are found in the Electric Power Research Institute (EPRI) report NP-5882H, titled, "Stress Corrosion Cracking Resistance of Alloys 600 and 690 and Compatible Weld Metals in BWRs."
Two experimental alloy 690 weld metals were tested.
They were tested under the same conditions as the base metals; thus, allowing direct comparison of results.
Results showed that both of the alloy 690 weld metals are immune to IGSCC in pure water environments.
However, since these were laboratory simulations of a BWR environment, the results are only an indicator, and not a guarantee, of the weld metals performance in a PWR environment.
In this report the designations R-127 and R-135 were used for the experimental weld metals.
These were the Inco designations for the developmental weld'
metals that [+came Inco 52 and 152, respectively.
Inco 52 is the commercial filler metal (tig wire) described in ASHE Code Case 2142.
Inco I52 is the coated electrode described in Code Case 2143.
Another paper, "Inconel 690:
A New High Nickel Alloy for Corrosive Environments at Elevated Temperature,"
by A. J. Sedriks, et al, of the Inco Research and Development Center, included tests of a matching filler metal in a wide variety of environments.
The two most intere'sting tests were conducted in simulated SG environments:
deaer ated ammoniated and borated water at 316 degrees C.
Test results showed the welds and weld metal were highly resistant to general corrosion.
Stress-corrosion cracking susce'ptibility was tested by exposing welds to a variety of chloride environments.
The controls used in these tests were alloy 800 (not 600) and type 304 stainless steel.
Both of these alloys are known to crack in elevated temperature chloride environments.
In all cases, alloy 690 was tested for periods significantly longer than the time to crack alloy 800 (the more resistant of the two control alloys).
In no case did the, alloy 690 welds crack despite test durations 8 times longer than that of the:
control alloys.
Additional testing for IGSCC susceptibility in pure water environments was conducted.
Another group of alloy 690 welds plus control alloys were exposed to undeaerated water at elevated temperatures in the presence of a crevice.
Cracking was readily initiated within the controls.
None of the alloy 690 welds cracked despite testing durations 24 times longer than for alloy 600 and 12 times for alloy 800 and 304 stainless.
Not considered in either study is the effect, if any, of heat to heat variations in the weld metal compositions.
Such variations were found to play a substantial role in the IGSCC susceptibility of alloy 600.
The strong performance of alloy 690 suggests there would be minimal effect.
ASHE Code Case 2142 lists the American Welding Society (AWS) specification (AWS A5.14) and UNS designation (UNS N06052) for a filler metal conforming to Inco 52.
It establishes the F-No. of this weld metal as F-No.
43 for both procedure and performance qualification purposes.
Code Case 2143 lists appropriate AWS and UNS specifications for a coated electrode matching Inco 152 and establishes F-No.
43 for this material for welding purposes.
By this set of specifications and F-No. assignments, these materials are completely described for welding purposes as similar in their welding characteristics to many other Code nickel base weld metals.
These materials are similar in composition and mechanical/thermal properties to approved metals;
- thus, these two weld metals need not meet the requirements for specific procedure and performance qualifications for non-Code materials.
3.0 CQHCCOI The NRC staff concludes that based upon the available technical
The
metals have sufficiont material integrity to provide an acceptable level of weld integrity, quality and safety.
fhe licensee has determined that their use could enhance the safety of the replacement SGs.
Further, the NRC staff finds that the Code cases appropriately identify and classify these same two weld metals for welding purposes, thereby eliminating the burden that would be imposed by the requirement for special procedure and performance qualifications for non-Code materials.
Pursuant to 10 CFR 50.55a(a)(3)(i), relief is granted to employ the alternative welding materials of Code Cases 2142 and 2143 and the benefits of these Code cases for procedure and performance qualification purposes fo'r the SG replacement project at Ginna Nuclear Power Station, in that the proposed alternatives would provide an acceptable level of quality and safety.
Due to the fact this would be a "first use" for these weld metals, the NRC staff recommends that the licensee either use one heat of each type of weld metal or maintain detailed records of individual heat usage locations for this project.
3'i Principal Contributor:
G. Hornseth Date:
September 11, 1995