ML20136G115

Safety Evaluation Granting Request to Use Alternative Matl in Fabrication of SGs for License DPR-67

ML20136G115
Person / Time
Site:	Saint Lucie
Issue date:	02/28/1994
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20136C539	List: IR 05000335/1994009 IR 05000335/1996002 L-96-227, Forwards LER 96-S01 Re Tampering W/Key Switches on Hot Shutdown Control Panels ML20136D672 ML20136D791 ML20136D807 ML20136D826 ML20136E425 ML20136E584 ML20136E630 ML20136E877 ML20136F036 ML20136F141 ML20136F193 ML20136F245 ML20136F260 ML20136F319 ML20136F524 ML20136F542 ML20136F548 ML20136F555 ML20136F561 ML20136F567 ML20136F575 ML20136F583 ML20136F590 ML20136F595 ML20136F604 ML20136F608 ML20136F623 ML20136F647 ML20136G031 ML20136G074 ML20136G089 ML20136G115 ML20136G254 ML20136G294 ML20137D404 ML20137D421 ML20137D436 ML20137D457 ML20137D508 ML20137D737 ML20137D744 ML20137D777 ML20137D818 ML20137D837 ML20138D105 ML20138D113 ML20138D124 ... further results
References
FOIA-96-485 NUDOCS 9703170206
Download: ML20136G115 (4)

Text

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1 EAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REOUEST TO USE ALTERNATIVE MATERIAL IN THE FABRICATION OF STEAM GENERATORS FOR FLORIDA POWER AND LIGHT COMPANY RT. LUCIE UNIT NO.

1.

DOCKET NO. 50-335

1.0 INTRODUCTION

By letter dated November 29, 1993, Florida Power and Light Company, the licensee, requested approval under the provisions of 10 CFR SC.55a(a) (3) (1) to use ASME Section IX Code Case 2143 4

during the impending fabrication of replacement steam generators (SG's) for St. Lucie Unit no. 1.

This Code Case introduces and classifies a new nickel base weld metal that closely matches and is intended for welding Alloy 690.

Code Case 2143 establishes welding classifications and other requirements for a coated electrode.

The subject Code Case was adopted by the ASME on December 7, 1992, and was 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 ASME Code, this Code Case 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 of replacement steam generators for St. Lucie Unit no.

1.

The licensee believes that use of the new weld metal will enhance the service life of the replacement SG's.

Industry studies indicate that this new weld metal is less susceptible to intergranular stress corrosion cracking (IGSCC) than the other nickel base weld metals currently applied.

Use of code case 2143 is advantageous to the licensee because it eliminates the burden of requiring qualification of separate welding procedures for this weld metal, as is the case for non-Code welding materials.

Thus, this relief request incorporates two issues:

1.

Suitability of Alloy 690 matching weld metal in code class 1 construction, and, 9703170206 970301 PDR FOIA PDR BINDER 96-485

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4 2._.The appropriateness of the ASME Code case which groups the new weld metal in the same welding catagories as other conconly employed nickel base weld metals.

Such grouping allows the use of appropriate existing welding procedures and performance qualifications with the new weld metal.

i 2.0 DISCUSSION 2.1 Suitability of Material 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 significantly reduced susceptibility to IGSCC in environments that simulate PWR and BWR plant conditions. 'NRC staff review of these laboratory test results has resulted in the staff position i

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 i

experience showed that Inco'182 was also susceptible to IGSCC, although primarily in BWR environments.

Wald 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, staff evaluation of these weld metals has not been previously conducted.

Corrosion studies examining the susceptibility of weld metals to IGSCC in steam generator environments are scant compared to the voluminous base metal studies.

This is because the base metal performance is a strong inoicator of the expected performance of a matching weld metal.

Results of the principle study which included' weld metals are found'in the Electric Power Research Institute (EPRI) report NP-5882M, titled " Stress corrosion Cracking Resistance of Alloys 600 and 690 and Compatible Weld Metals in BWRs".

An experimental alloy 690 matching stick electrode was tested.

It was tested under the same conditions as the base metals, thus allowing direct comparison of results.

Results showed that alloy 690 matching stick electrode is highly resistant to IGSCC in pure water environments.

However, since j

these were laboratory simulations of a BWR environment, the results are only an indicator, and not a guarantee, of the weld metal performance in a PWR environment.

(Note: in this report the designation R-135 was used for the experimental weld metal that became Inco 152, 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,

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d ie a

l included tests of a matching filler metal in a wide variety of environments.

The two most interesting tests were conducted in simulated SG environments: deaerated ammoniated and borated water at 316 degrees C.

Test results showed the welds and weld metal were highly resistant to general-corrosion.

t i

SCC susceptibility was tested by exposing welds to a variety of j

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 j

significantly longer than the time to crack alloy 800 (the more l

7 resistant of the two control alloys).

In no case did,the alloy 690 welds crack despite test durations 8 times longer than that j

of the control alloys.

i Additional testing for IGSCC susceptibility in pure water j

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 1

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.

t Not considered in either study is the effect, if any, of heat to j

heat variations in the weld metal compositions.

Such variations j

were found to play a substantial role in the IGSCC susceptibility 4

of alloy 600.

The strong performance of alloy 690 suggests there would be minimal effect.

2.2 Appropriateness of the Code Case Classification l

The purpose of a weld metal Code case is the establishment of uniform chemical and material properties, and the classification of the weld metal with respect to its welding characteristics.

This welding characteristics classification is known as an "F-i No."

Wald metals with like characteristics are grouped together for welding and welder qualification purposes in order to 1

eliminate unnecessary duplication.

Code case 2143 lists American Welding Society (AWS) and Unified Numbering System (UNS) chemical and tensile specifications for a i

nictel-base alloy coated electrode, known as AWS/UNS W86152 fr.ummercial designation: Inco 152), that is a matching weld metal I

or Inconel 690.

Additionally it assigns F-No. 43, which is the s No. for similar nickel-base weld metals, to this material for v 1 ding purposes.

The staff finds the Code case to appropriately specify and classify the necessary weld metal parameters.

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\\- !.

fj T.

3.0 CONCLUSION

The staff concludes that based upon the available technical evidence, there is no reason to prohibit the use of the subject weld metal as a substitute for other weld metals where the licensee-has determined that its use could enhance the safety of I

the replacement steam generators.

Additionally, the staff finds i

that the Code case appropriately specifies and classifies this weld metal for welding purposes.

Consequently, the staff finds that imposition of additional procedure and performance qualifications would not result in any increase in quality or safety.

Pursuant to 10 CFR 50.55a(a) (3) (1), relief is granted to employ the alternative. welding material of code case 2143 and the benefits of this Code case for procedure and performance qualification purposes in the construction of the replacement steam generators for St. Lucie Unit no.

1.

Due to the fact this would be an early use of this weld metal, the staff recommends that the licensee either use one heat of weld metal, or, maintain detailed records of individual heat usage locations for this project.

Technical contact:

G. Hornseth, 504-2756 Dated February 28, 1994.

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