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鈴木 康文; 荒井 康夫
日本原子力学会誌, 40(2), p.111 - 112, 1998/00
国際会議「アクチニド'97」の概要を紹介する。本会議には30ヶ国以上から350名以上の研究者が参加し、アクチニドの分析、配位化学、廃棄物管理、重元素研究、高圧物性、高温物性、磁性、熱力学等の分野で320件余の発表があった。
町田 昌彦; 中村 博樹
no journal, ,
Thorium has been considered as an alternative nuclear fuel element to uranium. Thorium is well-known to be more abundant in nature than uranium. Furthermore, it is widely spread that thorium dioxide is chemically more stable than uranium dioxide. From an economical and secure point of view, thorium fuel can be a candidate fuel in next-generation nuclear reactors. However, the data of thermal properties of thorium dioxide are insufficient, in particular, in the high-temperature region near its melting point. In order to supplement such thermal data of the materials, classical molecular dynamics have played an important role and been applied also to thorium compounds. However, the thermal properties obtained by classical molecular dynamics often depend on the empirical parameters giving the atomic potential. Especially, it is known that the Bredig transition (rapid growth of heat capacity slightly below melting point) strongly depends on the choice of parameters of the atomic potential in the case of molecular dynamics of uranium dioxide. Thus, classical molecular dynamics is not so reliable for high-temperature behaviours, such as the Bredig transition. Therefore, we adopt first-principles molecular dynamics to avoid this parameter sensitivity. In the present paper, we evaluate thermal properties of thorium dioxide at high temperature using first-principles molecular dynamics. The calculated enthalpy agrees well with the observed data. We find that the obtained Bredig transition temperature coincides with the experimental values and that this transition is caused by the high mobility of oxygen by visualizing the oxygen motions. Consequently, we reveal that the first-principles molecular dynamics can provide reliable data of thermal properties of nuclear fuels even at high temperature.