| Popis: |
After accident at the Fukushima Daiichi nuclear power plant, some undesirable performance characteristics of standard fuel system were highlighted. Developing accident tolerant fuel systems is one of the solutions to improve the safety of LWR. The improvement in accident tolerance fuel includes many aspects, and looking for a new alloy or materials as cladding material is one of them. A new multi-metallic layered composite (MMLC) was proposed as one of the candidates of cladding materials. The layers of the new proposed MMLC are designed to perform specific functions unattainable by single alloys. It consists a stainless steel overlaid onto a zircaloy base. In addition, diffusion barrier layers of Cr and Nb will be used in between zircaloy base and iron based alloy. In which both Zircaloy 4 and stainless steel 304 are candidates of cladding materials and they will also be layers in this new propsed MMLC material. Due to the lack of information on the high temperature and high-pressure corrosion and stress corrosion cracking study, this research will focus on the corrosion behaviors of zircaloy 4 and stainless steel 304 in simulated primary water condition. An autoclave was fabricated to provide a simulated environment, which is 300 degree C and 2000 psi. EIS (electrochemical impedance spectroscopy) and polarization curve was measured and analyzed to determine the oxidation activity on the surface and the corrosion resistance of two alloys. Furthermore, a critical thinking in stress corrosion cracking (SCC) is given and a set of SCC test equipment was introduced. A binary phase diagram can show the equilibrium phases expected to be formed between two metals. This phase diagram can help to design the processing schedule for multiple layered materials. Recently, a new phase field crystal model was developed and it constructed the binary phase diagram between an imaginary FCC (face-centered cubic) and BCC (body centered cubic) alloy via microstructures. This research will also applied this phase field crystal model into real situation and simulated Fe-Zr and Fe-Nb binary system. |
