ML20045F765
| ML20045F765 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 07/02/1993 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20045F762 | List: |
| References | |
| NUDOCS 9307080373 | |
| Download: ML20045F765 (3) | |
Text
{{#Wiki_filter:- i ENCLOSURE SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE USE OF LEAK-BEFORE BREAK TECHNOLOGY SOUTH CAROLINA ELECTRIC & GAS COMPANY VIRGIL C. SUMMER NUCLEAR STATION. UNIT NO I DOCKET NO. 50-395
1.0 INTRODUCTION
By letter dated March 26, 1993, South Carolina Electric & Gas Company, the licensee, requested approval under the provisions of 10 CFR 50.55a(a)(3)(1) to use American Society Mechanical Engineers Code (ASME Code) Section IX Code Cases 2142 and 2143 during the impending fabrication and installation of replacement steam generators (SGs) for the Virgil C. Summer Nuclear Station, Unit No. 1, (Summer Station). These two Code Cases introduce and classify new nickel base weld metals that closely match and are intended for welding Alloy 690. Code Case 2142 establishes welding classifications and other ~ requirements for a bare wire filler metal. Code Case 2143 establishes welding classifications and other requirements for a coated electrode. The subject Code Cases were i.dopted by the ASME on December 7, 1992, and were scheduled to be published in AME Code Case Supplement 3 in April 1993. Since this is a Supplement to the 1992 Edition of the ASME Code, these Code Cases cannot be used by the licensees without prior NRC staff review. The 1992 Edition of the ASME Code has not been incorporated by reference into the regulations. The licensee intends to use Alloy 690 tubing and components in the fabrication and installation of replacement steam generators for Summer Station. Industry studies indicate that use of the new weld metals for tube-to-tubesheet (non-structural) welds will increase the service life of the replacement SGs by reducing the welds' susceptibility to intergranular stress corrosion cracking (IGSCC). Use of Code Cases 2142 and 2143 would eliminate the burden of requiring qualification of separate welding procedures for each weld metal, as is the case for non-Code welding materials. This relief-c e nt, therefore, incorporates two issues: 1. Use of Alloy 690 type weld metals in Code class I construction, and 2. The use of 2 ASME Code cases that group the new weld metals in the same welding cat'egories 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. 93070B0373 930702 PDR ADOCK 05000395 P PDR' n - - -.
r ! 2.0 EVALUATION Use of Allov 690 Alloy 600 was used in the fabrication of many of the SGs in service in the industry today. Due to the many instances of IGSCC of Alloy 600 components occurring in these generators, the industry sought a new material from which to fabricate various SG components. The current base metal of choice is Alloy 690. This metal was chosen because laboratory tests indicate that it is resistant to both IGSCC and general corrosion in a simulated reactor environment. Use of Alloy 690 as a base metal has already been approved by the staff; the licensee is now seeking approval to use the new compatible weld metals. i Results of the principal corrosion study examining the susceptibility of weld metals to IGSCC are found in the Electric Power Research Institute (EPRI) report NP-5882M, " Stress Corrosion Cracking Resistance of Alloys 600 and 690 and Compatible Weld Metals in BWRs." Two Alloy 690 weld metals (designated as Inco 52 and Inco 152) 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 resistant to IGSCC as well as general corrosion in pure water environments; however, since these were laboratory simulations of a boiling water reactor (EWR) environment, the results are only an indicator of the weld metals' performance in a pressurized water reactor (PWR) environment. A series of tests conducted by the Inco Research and Development Center, the laboratory that developed both Alloy 600 and Alloy 690, showed that Alloy 690 weld metal was highly resistant to both general corrosion and IGSCC in a simulated SG environment. Additional testing also demonstrated a high resistance to stress corrosion cracking. The results of this study are documented in " Corrosion Testing of Inconel Alloy 690 for PWR Steam Generators," J. R. Crum and R. C. Scarberry, Journal of Materials for Energy Systems, Vol. 4, No. 3, Dec. 1982. 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 j performance of Alloy 690 suggests there would be minimal effect. After revie-vi u.e EPRI and Inco studies, the staff has concluded that the use of Alloy 690 matching weld metals in nuclear power plant construction is acceptable. The use of Alloy 690 as a weld metal in tube-to-tubesheet and other primary side welds will provide an acceptable level of quality and i safety; furthermore, it is likely to provide greater resistance to IGSCC and SCC than does the Alloy 600 matching weld metal. Since this would be a first use for these weld metals, however, the 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. r
.. Use of Code Cases 2142 and 2143 Code case 2142 lists the American Welding Society (AWS) specification (AWS-A5.14) and Unified Numbering System (UNS) designation (UNS N06052) for a filler metal conforming to Inco 52. It establishes the F-No. (a number describing the general welding characteristics) of this metal as F-No. 43. 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 allowing the licensee to use Code cases 2142 and 2143, the staff is affirming the Code Committee's designation of F-No. 43 for Inco 52 and Inco 152. Affirming this Code Committee designation would permit the employment of previously qualified welding procedures, and would eliminate the need to establish specific procedure and performance qualifications for welding with these metals. Since Inco 52 and Inco 152 are similar in their welding characteristics to many other Code nickel base weld metals, the staff has concluded that specific procedure and performance qualification for these materials is not necessary. Use of previously qualified procedure and performance standards for welding with these metals will provide an acceptable level of quality and safety. The use of Code cases 2142 and 2143 is, therefore, acceptable.
3.0 CONCLUSION
The staff has reviewed the licensee's request and, pursuant to 10 CFR 50.551a(a)(3)(i) has determined that the licensee's proposed use of the Alloy 690 weld metal and employment of Code cases 2142 and 2143 as an alternative may be authorized as requested. The alternative to the ASME Code requirements authorized herein provides an acceptable level of quality and safety and reasonable assurance that the structural integrity of the plant's systems, components, and supports will be maintained. i Principal Contributors: G. Hornseth G. Wunder Date: July 2,_1993 5 e =}}