Abstract
The Pebble Bed Modular Reactor (PBMR) is a small atomic power reactor which can be used in areas where the electric power transmission network is not well developed. It generates electricity by gas-turbines that used He-gas as a coolant. Ni-based superalloys are the primary materials used in gas-turbines. However if conventional Ni-base superalloys are to be used for PBMR, turbine maintenances will be difficult due to Co, as it can produce 60Co a recitative material that possesses a long half-life. Therefore, Co-free Ni-base superalloys are required for PBMR. In this paper, a Co-free single-crystal (SC) superalloy, TMS-82+(-Co), was developed; it was the same chemical composition as the 2nd generation SC superalloy, TMS-82+, except that it is Co-free creep tests were performed on the developed alloy, TMS-82+, under three conditions; 900°C/392 MPa, 1000°C/245 MPa, and 1100°C/137 MPa; CMSX-4, a popular SC alloy, was used as comparison. TMS-82+(-Co) displayed superior creep-rupture life in all creep tests; however, detrimental TCP were observed in the microstructure of the sample that underwent creep testing at 1100°C/137 MPa. This, the developed Co-free SC alloy should be further modified for long-term microstructural stability. Elimination of phase formation will allow the alloy to be utilized in the PBMR.
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