Creep Rupture Characteristics of Cladding Tubes of FC92B and FC92N: Candidate Alloys of SFR Fuel Cladding Tube Materials

To develop South Korea’s own SFR nuclear fuel cladding tube that has excellent high temperature creep characteristics, candidate alloys for a new cladding material that has better performance than the conventional Gr.92 (9Cr–2W–Nb–V) steel were selected by conducting a high temperature tensile test and creep test for the candidate alloys fabricated by adequately combining precipitation and strengthening of alloy elements (C, Ta, Nb, V, N) with solid solution treatment and hardening of alloy elements (Cr, Mo, W, B). Among the candidate alloys, two types—FC92B and FC92N—that had excellent creep characteristics were used to fabricate the cladding tubes. In the results of the creep test, when a cladding tube was fabricated by using FC92N, which showed excellent creep performance in the air atmosphere, the creep performance declined. After the creep tests of FC92B and FC92N cladding tubes, this study examined the microstructures of specimens and analyzed the relationship between microstructure and creep rupture life. When the creep test was performed in the air and argon gas atmosphere, FC92N showed a larger increase in the thickness of an oxide layer than FC92B. It was determined that the FC92B alloy, in which 130 ppm of B was added, showed excellent creep performance in both the air and argon gas atmospheres because its oxidation resistance was relatively excellent compared to that of FC92N.