Materials Design Division
Nuclear Materials Engineering
Materials research for extreme environment in nuclear power systems
Ever-increasing global energy demand and also the social demand for the secure operation of nuclear power plants request further breakthrough of nuclear materials. Our mission is to advance materials science and technology for extremely severe environments in future fusion reactors and nuclear power reactors of the next generation. The extreme environment in nuclear power systems, such as irradiation with high-energy neutrons, high temperatures, and corrosive environment, degrades seriously mechanical properties of the materials. We evaluate the changes in microstructure and mechanical properties in steels and zirconium alloys under such environment. Another target is understanding and modeling of radiation damage processes of materials and of properties of various lattice defects induced by irradiation.
radiation damage, nuclear materials, fusion reactors
Effect of crystallographic mismatch on the obstacle strength of precipitates in dispersion strengthening: Nb precipitates in Zr fuel cladding. When the crystal structure of precipitates is bcc (stable configuration), the slip plane inside the particles is not parallel with that in the Zr matrix; they are Orowan-type strong obstacles against gliding dislocations. When precipitates are nano sized (in the early stage of precipitation), their crystal structure is hcp as well as the matrix; they are weak obstacles, as they are free from crystal mismatch. The experimentally-determined obstacle strength was 0.8~1 for the former and 0.1~0.5 for the latter
TEM-EDS maps of the surface oxide layer of Zr-Nb fuel cladding subjected to water corrosion. Nb precipitates have been believed to get dissolved into the Zr matrix upon corrosion; however, we demonstrated that they are actually not dissolved. Nb precipitates are invisible in STEM-DF images and Nb maps but visible in Mo maps due to a synergistic effect combining structural and compositional changes of precipitates and EDS artifacts.