Easy conversion process of titanium surface covered with passive film into functional surface

Surface functionalization of titanium metal is of great interest, especially as the conversion of the surface passive film into objective functional film can be widely used in bio- and environmental applications. However, since the surface passive film is very stable, the functionalization (such as conversion into photocatalytic anatase-TiO₂) has been performed using relatively complicated processes, for example, hydrothermal reaction and anodic oxidation. This is because direct oxidation of titanium metal only leads to thermodynamic formation of octahedral-rutile-TiO₂ in the entire temperature region, while chemical synthesis using precursors can easily produce tetrahedral-anatase-TiO₂ at 600°C or less. Here, we report a simple process for the direct formation of photocatalytic anatase-TiO₂ on titanium by simple oxidation. In the first step in our process, titanium is treated with a reducing agent to create a surface titaniumhydride layer. After that, the treated titanium covered with titaniumhydride is immerged in aqueous silica; subsequent calcination at 900°C (specific temperature) in air effectively generates the surface anatase-TiO₂ layer. This is because the covered tetrahedral-silica stabilizes the anatase structure that is formed. The covered silica is easily removed by quenching in water to reveal the photocatalytic surface layer composed of anatase-TiO₂.     

Development of passive safety systems for Next Generation PWR in Japan

Our country’s energy demand is expected to increase steadily into the future. When the situation of our country, which is not rich in energy resources, is taken into account, it seems that the importance of nuclear power generation will be heightened. Based on such a background, the basic policy for nuclear power generation is ‘from light water reactors to fast breeder reactors’. However, considering that light water reactors have become common, the recent outlook for the supply and demand for uranium resources, development trends of fast breeder reactor technology, etc., the light water reactor is expected to remain dominant in our country until at least the second half of the 21st century. Therefore, five PWR utilities in Japan (Hokkaido, Kansai, Shikoku, Kyushu, and Japan Atomic Power), Mitsubishi Heavy Industries Ltd and Westinghouse Electric Corporation have jointly started researching the Next Generation PWR (N.G.P) which is expected to be the leading nuclear power plant, taking place of APWR [T. Magari, Development of Next Generation PWR in Japan, Proceedings of the 10th Pacific Basin Nuclear Conference, 1996; K. Fujimura, et al., Proceedings of the Second International Symposium on Global Environment and Nuclear Energy Systems, 1996]. In this program, construction is targeted to start from 2010 based on expected future environmental conditions. Now, the capacity of more than 1500 MWe class PWR concept is investigated and a plant concept which has innovative features of a hybrid safety systems, i.e. an optimum combination of active and passive safety systems, and horizontal steam generators for core cooling at the accidents is developed as a promising candidate. The plant concept and the results of the investigation are presented in this paper.     

Morphological changes and their thermal conductivities of MgO crystals containing various impurities (B,Ca, Si)

MgO is industrially produced from seawater or dolomite as the raw material. MgO synthesized from seawater has a relatively low impurity concentration. However, these impurities strongly affect the fine structure and physical properties (especially the thermal conductivity) of MgO. In this research, the influence of impurity concentration on the MgO grain growth and its thermal conductivity was investigated. The processing conditions for MgO powder synthesis were optimized by a polymer complex method using magnesium nitrate hydrate, citric acid, ethylene diamine, and chemical compounds containing B, Ca, or Si, which are the main impurities of MgO produced from seawater. The morphology and phase composition of the MgO powders were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). The morphological changes and differences in the thermal conductivity of MgO crystalline systems containing impurities (B, Ca, and/or Si) were clarified, and the relationship between the fine structure of MgO crystals containing impurities and their thermal conductivities was described in detail.     

The history and the prospects of japanese nuclear power development program

FBRs are regarded as the most probable option among non-fossil energy resources which will underpin the future energy demand in Japan, considering the effective uranium utilization and the need to lower the burden on the natural environment. However, it will take a long time to utilize FBRs due to a number of pending technical issues and improvements of cost efficiency. For the time being, therefore, light water reactors will continue to play a dominant role in power generation: thus, it is urgently necessary to establish the quasi-domestic nuclear fuel cycle for them, especially in the field of enrichment and spent fuel reprocessing — a goal of the Japanese nuclear policy since the dawn. Furthermore, public acceptance is significant factor which must be considered. This can best be achieved by more safety performance of light water reactors and through publication of extensive information, including decisions by the industry and government.