Takumi Chikada

Abstract:

Hydrogen isotopes are promising energy media in advanced energy systems. Chemical energy of hydrogen is extracted via fuel cells in hydrogen energy systems, and nuclear energy of hydrogen isotopes deuterium and tritium is harnessed in fusion reactors. One of issues in the usage of hydrogen is interactions with materials. Hydrogen can dissolve in most metals with forming metal hydrides, leading to a degradation of mechanical properties of metal structural materials, as it is called hydrogen embrittlement. Moreover, hydrogen can permeate through metals fastest of all elements at elevated temperature due to its smallest size, resulting in a crucial fuel loss and radiological hazard in the case of tritium. Another concern is corrosion and erosion of structural materials by high-temperature liquid fluids such as supercritial water and carbon dioxide, liquid metals, and molten salts. In the fusion reactors, radiation and thermal durability are also required. A promising solution to reduce degradation of structural materials and fuel efficiency without major change of plant design is to form a smart coating which satisfies required functions depending on the system. Our efforts have been dedicated to investigating hydrogen isotope permeation behaviors in tritium permeation barriers with high chemical stability using erbium oxide and yttrium oxide coatings for a decade. The hydrogen isotope permeation mechanism was elucidated, leading to the world's highest permeation reduction factor (100000) at elevated temperature. The development of coating process toward plant-scale fabrication has also progressed using liquid phase methods. A ceramic-metal multilayer structure has opened the possibility to allocate multiple functions to each layer. Moreover, recent achievements using accelerated heavy ions and a ƒ×-ray source revealed that the coating mitigated irradiation effects on hydrogen isotope permeation. In this presentation, potential and current challenges for the research and development of the smart coating are introduced.