High-temperature Softening of ASTM Gr.92 Steel for a SFR Fuel Cladding

Ferritic/martensitic (F/M) steels are widely used as structural materials in various types of nuclear reactor facilities. The main advantages of the steels are their high resistance to void swelling, low irradiation creep rates, and relatively low radioactivation after neutron irradiation. The steels have higher thermal conductivities and lower expansion coefficients than austenite stainless steels. Nowadays, the F/M steels are currently being considered as candidate materials for cladding and duct applications in a Gen-IV SFR fuel. Since the operation condition in the design of Gen-IV SFR would be envisioned to be harsh from the viewpoints of temperature (>600 .deg. C) and irradiation dose (≥200 dpa), the primary emphasis is on the fuel cladding materials, i.e. high-Cr F/M steels. However, the well-known disadvantages of the F/M steels are their low long-term creep strength at high temperatures and their inclination to low-temperature irradiation embrittlement. A softening behavior of the steels is also observed during tensile tests and it is characterized by low maximal homogeneous elongation compared to the fracture elongation. The softening behaviors of ASTM Gr.92 steel during the uniaxial tension has been study in this study. Tensile tests have been carried out at 650 .deg. C, a typical operating temperature of cladding for the Gen-IV SFR fuel, in order to analyze the influence of the softening behaviors of the ASTM Gr.92