UO2-ZrO2固溶体の融点および熱伝導率の分子動力学解析 [Published online in advanced , by J-STAGE]

Journal of Computer Chemistry, Japan [No.2015-0007] Published online in advanced by J-STAGE
<Title:> UO2-ZrO2固溶体の融点および熱伝導率の分子動力学解析
<Author(s):> 有馬 立身
<Corresponding author E-Mill:> arima(at)nucl.kyushu-u.ac.jp<Abstract:> 原子炉過酷事故の事象進展には溶融燃料の熱的物性が大きく影響する.溶融燃料の主な物質であるUO2-ZrO2固溶体の融点を古典分子動力学法を用いて組 成をパラメータとして,また熱伝導率を組成・温度を変えて固体から液体状態まで評価した.融点に関しては固液2相共存法が単相で評価するよりも実 験値に近い値を与えた.これは結晶性固体の単相に対して温度を上げても融解の核が生成しにくく,過加熱状態に陥りやすいことを意味している.ま た,UO2とZrO2を互いに固溶させることにより融点は低下し,それが融解エンタルピーの減少と相関することを明らかにした.熱伝導率は平衡分 子動力学法によりグリーン-久保の関係式から,エネルギーと電荷の流れの相互効果を考慮し,固体から液体状態までの格子振動の寄与を評価した.固 体の熱伝導率には,ウムクラップ散乱による温度上昇に伴う低下,低温の固溶体で見られるフォノンの不純物散乱による低下が確認できた.一方,超高 温の液体状態の熱伝導率は低く,温度および組成の依存性は小さいことが分かった.
<Keywords:> Molecular dynamics, Thermal conductivity, Melting point, UO2, ZrO2
<URL:> https://www.jstage.jst.go.jp/article/jccj/advpub/0/advpub_2015-0007/_article/-char/ja/

 

Molecular Dynamics Simulation of the Behavior of Beryllium Diffusion in Corundum [Published online in advanced , by J-STAGE]

Journal of Computer Chemistry, Japan [No.2015-0016] Published online in advanced by J-STAGE
<Title:> Molecular Dynamics Simulation of the Behavior of Beryllium Diffusion in Corundum
<Author(s):> Jun Kawano, Muneyuki Okuyama, Takeshi Miyata<Abstract:> Molecular dynamics (MD) simulations are highly useful for analyzing atomic behavior during diffusion, especially in systems that are difficult to investigate experimentally. The focus of the present study was the diffusion behavior of Be in corundum, which was analyzed by MD calculations. First, we derived new potential parameter sets for O, Al, and Be. This parameter set was verified to well reproduce the structures and properties of corundum, bromellite, and chrysoberyl. Based on MD simulations of corundum containing Be as interstitial atoms, where the simulations were performed using the newly derived potential parameters, the diffusion coefficient was estimated to be approximately 10-7 cm2/s at around 2100 K. This is consistent with previously published experimental results, which confirms the validity of the MD simulation. The present calculations also reveal the detailed atomic movement, where Be atoms jump between Al sites and/or interstitial sites, and that the activation energy of this process is approximately 1.1 × 102 kJ/mol.
<Keywords:> Diffusion, Molecular dynamics simulation, Corundum, Beryllium, Gemology
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URL: https://www.jstage.jst.go.jp/article/jccj/advpub/0/advpub_2015-0016/_article/-char/ja/
Corresponding author E-Mill: j-kawano(at)mail.sci.hokudai.ac.jp

 

Interlayer Bonding Energy of Mg-Chlorite: A Density Functional Theory Study [Published online in advanced , by J-STAGE]

Journal of Computer Chemistry, Japan [No.2015-0008] Published online in advanced by J-STAGE
Title: Interlayer Bonding Energy of Mg-Chlorite: A Density Functional Theory Study
Author(s): Hiroshi SakumaAbstract: Interlayer bonding energy (ILBE) of Mg-chlorite was calculated based on the density functional theory with dispersion force correction (DFT-D2). The calculated ILBE of Mg-chlorite was smaller than brucite, phlogopite, gibbsite, and muscovite and was comparable to talc, kaolinite, pyrophyllite, and lizardite. The attractive interaction between layers would be generated by the weak hydrogen bond between layers. The ILBE of Mg-chlorite should be the minimum ILBE in natural chlorite group, since the natural chlorite shows the isomorphic substitution which induces high layer charge resulting in stronger attractive interaction between layers like phlogopite and muscovite.
Keywords: Separation energy, Friction, Clay mineral, Chlorite, DFT
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URL: https://www.jstage.jst.go.jp/article/jccj/advpub/0/advpub_2015-0008/_article/-char/ja/
Corresponding author E-Mill: SAKUMA.Hiroshi(at)nims.go.jp