Evaluation of Microstructural, Mechanical Properties and Corrosion Behavior of AISI Type 316LN Stainless Steel and Modif
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LIQUID sodium is used as coolant in liquid metal fast breeder reactors. High thermal conductivity, low vapor pressure, high boiling point, large heat capacity, and low cost makes sodium suitable for the purpose. Fast breeder reactors (FBRs) are designed with two sodium coolant circuits to contain radioactivity. In the primary circuit, sodium transports the heat generated in N. SIVAI BHARASI and K. THYAGARAJAN, Scientists, are with the Corrosion Science and Technology Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603 102, Tamil Nadu, India. Contact e-mails: [email protected]; [email protected] H. SHAIKH, formerly with Indira Gandhi Centre for Atomic Research, is now Dean (Research), with the Mohamed Sathak AJ College of Engineering, Egattur, Chennai 603 103, India. M. RADHIKA, Scientist, is with the Physical Metallurgy Division, Indira Gandhi Centre for Atomic Research. A.K. BALAMURUGAN, S. KALAVATHY, and A.K. TYAGI, Scientists, are with the Materials Science Group, Indira Gandhi Centre for Atomic Research. S. VENUGOPAL and A. MOITRA, Scientists, are with Materials Technology Division, Indira Gandhi Centre for Atomic Research. R.K. DAYAL, formerly with Indira Gandhi Centre for Atomic Research, is now Professor, with the Department of Mechanical Engineering, VIT University, Chennai Campus, Chennai 600 048, India. S. CHANDRAMOULI, Scientist, and K.K. RAJAN, Directorate, are with the Fast Reactor Technology Group, Indira Gandhi Centre for Atomic Research. Manuscript submitted January 28, 2011. Article published online September 21, 2011 METALLURGICAL AND MATERIALS TRANSACTIONS A
the core to the intermediate heat exchanger (IHX). The sodium from the IHX then transfers heat to the water in the steam generator. Austenitic stainless steels of different grades are used as structural materials in the primary circuit, intermediate heat exchanger, and piping in secondary loop because of their reasonable compatibility with high-temperature sodium and adequate hightemperature mechanical properties.[1] In the prototype fast breeder reactor (PFBR) at Kalpakkam, AISI type 316LN stainless steel has been selected as structural material in the primary circuit to circumvent the problem of sensitization and related aqueous corrosion issues during fabrication and storage. Modified 9Cr1Mo steel has been selected as the construction material for steam generators mainly because of its resistance to waterside corrosion, such as chloride and caustic stress corrosion cracking and adequate high-temperature mechanical properties. The compatibility of these materials with liquid sodium is of utmost importance for the safe operation of the reactor. Although localized electrochemical corrosion of structural materials is absent in sodium, liquid sodium can dissolve some of the constituents of stainless steel at high temperatures, which then are deposited at different regions.[2] This mass transfer is influenced by impurities such as oxygen because of formation of ternary oxides of sodium, primarily sodium chromite.[3–6] The
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