Dynamical Damage Processes of Neutron-Irradiated Meterials

点击翻译按钮获取中文摘要

In materials which are irradiated with neutrons, primary knock-on atoms of high energy are generated. Subsequently displacement damage cascades are formed. Damage structure in materials evolves with cascade damage overlapping, structural relaxation due to thermal vibration at high temperature, formation of voids and bubbles due to gas atoms generated by transmutation nuclear reactions and precipitates formation in alloys. In the present work of this year, atomistics of void formation are studied which are the most important and serious defect in breeder and fusion reactors.1.Utilizing eam many body potential of pure copper and pure nickel, atomistics of void formation was examined by molecular dynamics computer-simulation. These two materials have low stacking fault energy for pure copper and high stacking fault energy for pure nickel. These reflect the formation of relaxed (collapsed) stacking fault tetrahydra in copper and dislocation loops in nickel. When hydrogen atoms are trapped … More in small vacancy clusters, hydrogen atoms move around surface of voids and prevent the collapsing of vacancy clusters. This leads to the formation of voids in irradiated metals. Helium atoms could not move so fast in void embryo. Therefore, helium atoms are questionable to be effective gas atom on the formation of voids.2. To test reliability of the results of computer-simulation, copper and nickel were irradiated in fusion reactor to heavy high fluence at FFTF breeder reactor in Pacific Northwest Laboratory in the united state. Specimens are two kinds. One is as-received from the manufacture. Another is out-gassed by melting in ultra-high vacuum in order to remove the residual gas dissolved in as-received specimens. Only one capsule was success-fully irradiated. We could observe the remarkable difference of void number density in irradiated specimens. Out-gassed specimen shows low density of voids, while we observed high density of void in as-received specimens. Many other capsules show either sodium leakage or gas-leakage. In these cases, difference of void density could not be observed.3. It is widely believed that helium atoms contribute more seriously on the formation of voids. We examined its by computer MD simulations. Less