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Evaluation of Material Compatibility in High Temperature

Supercritical-CO2 Environment


The supercritical-carbon dioxide (S-CO2) Brayton cycle has been considered one of the promising alternatives to the conventional steam Rankine cycle for the sodium-cooled fast reactor (SFR) and other energy conversion applications. By applying the S-CO2 cycle to the SFR, thermal efficiency and inherent safety of the system could be improved. Meanwhile, from the structural material point of view, the compatibility of candidate materials in the S-CO2 environment should be evaluated to assure the long-term integrity of the components in the power conversion system, including the compact-type intermediate heat exchanger (IHX). High temperature corrosion of IHX materials is one of the important factors to be properly assessed because excessive corrosion may threaten the structural integrity and deteriorate the heat transfer capability of the IHX.


Research Key Words and Materials



Material compatibility

High temperature corrosion


Ni-based alloys

Fe-based austenitic alloy

Diffusion bonding

Post bond heat treatment




Related Project


Project Title:

Compatibility Study of the Structural Materials for Supercritical-CO2 Cycle for iSFR


Project Period:

2013.03.01 - 2016.02.29


Project Purpose:

1) Evaluation of corrosion behavior of structural materials in S-CO2 environment

- Assessment of long-term corrosion behavior of candidate structural materials in SFR S-CO2, with pressure and impurity effects on corrosion behavior.

2) Evaluation of long-term integrity of structural materials in S-CO2 environment

- Assessment of microstructure (carburization) and tensile property changes after exposure to S-CO2 environment.

- Assessment of creep properties in S-CO2 environment.

3) Evaluation of corrosion behavior and integrity of diffusion-bonded printed-circuit heat exchanger (PCHE)

- Development of diffusion-bonding and post-bond heat treatment conditions for PCHE candidate materials.

- Assessment of tensile property changes after exposure of diffusion-bonded alloys in S-CO2 environment

Selection of optimal structural material for SFR S-CO2 environment through evaluations on corrosion resistance and long-term integrity


Brief Description:

For the high temperature and pressure corrosion test in S-CO2 environment, corrosion test equipment was developed. Nine candidate structural materials such as Ni-based and Fe-based austenitic alloys have been selected and tested in the SFR-relevant S-CO2 environment (550-650 oC and 20 MPa) up to 3000 h. First, corrosion and carburization behavior were evaluated by various analysis tools. In addition, changes in tensile property using mini-size tensile specimen after exposure to S- CO2 were assessed to assure long-term integrity. On the other hand, for the application of printed circuit heat exchanger (PCHE)-typed IHX, diffusion bonding process including post bond heat treatment (PBHT) were conducted for candidate materials. Tensile property of those diffusion bonded specimen was assessed as compared to each base material.  



TEM mapping images and line scanning of oxide layer formed on Alloy 800HT in S-CO2 environment (up)

and SIMS depth profile (bottom left) and changes in tensile property after exposure to S-CO2 (bottom right)



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