A molten salt reactor (MSR) has considerably attracted attention due to its several advantages for the safety and efficiency over the light water reactors. Because the structural material in MSR is contacted with high-temperature liquid fuel during long-term, the excellent material for corrosion resistance is required to be applied in MSR. In this study, we evaluated the corrosion resistance for alloy 600 and 617, which are the nickel-based materials, in KCl molten salt at 800ºC for 100 h under Ar atmosphere containing less than 1 ppm of moisture and oxygen. After the corrosion experiments of alloy 600 and 617, the amount of the weight loss for them caused by the KCl molten salt were determined. In addition, the variation in the crystal structure, surface morphology, and elemental distribution was examined using X-ray diffraction and scanning electron microscopy equipped with energy dispersive X-ray spectroscopy.

Alloy 617, Ni-22Cr-12Co-9Mo base oxide dispersion strengthened alloy was fabricated by using mechanical alloying, hot isostatic pressing and hot rolling. Uniaxial tensile tests were performed at room temperature and at . Compared with the conventional Alloy 617, ODS alloy showed much higher yield strength and tensile strength, but lower elongation. Fracture surfaces of the tensile tested specimens were investigated in order to find out the mechanism of fracture mode at each test temperature. Grain adjustment during tensile deformation was analyzed by electron backscattered diffraction mapping, inverse pole figures and TEM observation.

The very high temperature gas reactor (VHTR) is one of the next generation nuclear reactors for its safety, long-term stability, and proliferation-resistance. The high operating temperature of over 800˚C enables various applications with high energy efficiency. Heat is transferred from the primary helium loop to the secondary helium loop through the intermediate heat exchanger (IHX). The IHX material requires creep resistance, oxidation resistance, and corrosion resistance in a helium environment at high operating temperatures. A Ni-based superalloy such as Alloy 617 is considered as a primary candidate material for the intermediate heat exchanger. In this study, the microstructures of Alloy 617 crept in pure helium and air environments at 950˚C were observed. The rupture time in helium was shorter than that in air under small applied stresses. As the exposure time increased, the thickness of outer oxide layer of the specimens clearly increased but delaminated after a long creep time. The depth of the carbide-depleted zone was rather high in the specimens under high applied stress. The reason was elucidated by the comparison between the ruptured region and grip region of the samples. It is considered that decarburization caused by minor gas impurities in a helium environment caused the reduction in creep rupture time.