Papers by Keyword: Rate Theory

Abstract: The average size and density evolution of dislocation loops in AL-6XN austenitic stainless steel, a candidate fuel cladding material for supercritical water-cooled reactor, under proton irradiation were simulated through a rate theory model. The simulation results exhibit relatively good agreement with the experimental results at 563 K. The size and density of defect clusters are calculated under irradiation temperature between 550 K and 900 K and irradiation doses up to 15 dpa which satisfies the working condition in supercritical water-cooled reactor. The fast nucleation between self-interstitials happens at the initial stage of irradiation. The average size of dislocation loops increases while the average density of these loops reduces with the increasing temperature, and the average density approaches to a constant when irradiated at higher irradiation doses. The mechanism is discussed based on the variation of rate constants of defect reactions and the variation of the diffusion coefficients of interstitials and dislocation loops with dose and temperature.

Abstract: The Cluster Dynamics method is assessed for the investigation of fission gas behaviour in a krypton-implanted and annealed UO₂ sample. The simulation results are then compared to Thermal Desorption Spectroscopy (TDS) data. A release mechanism is proposed: the initial burst is related to krypton migration via an interstitial mechanism, while the second stage of the release process can be accounted for by the diffusion of krypton in a substitutional position. This latter mechanism is compatible with a diffusion coefficient of 4.10^-21 m²/s.

Abstract: The surface concentrations of organic compounds in a three-component (isopropanol-diethylphthalate-octanol) system were in situ measured using a quartz crystal microbalance. Additionally, the surface concentrations were calculated on the basis of the rate theory, to show that the surface concentration of organic compound was influenced by the other organic compounds. The net situation of airborne organic contamination may change, even when the total amount of organic compounds adsorbed on silicon surface seems to be in a steady state.

Abstract: - and -SiC powder mixtures with 0.3 mass% of AlB2 were sintered at 2200oC. Porous materials having 43-45% porosity were obtained. Grains in the powder mixtures grew into plate-shaped grains of 6-8 m size, and -SiC transformed into -SiC. Free energy due to the polytype transformation enhanced material transport very much. The new rate theory proposed here explained very well the behavior of the grain growth.

Abstract: The aim of this paper is to give a short review on cluster dynamics modeling in the field of atoms and point defects clustering in materials. It is shown that this method, due to its low computer cost, can handle long term evolution that cannot, in many cases, be obtained by Lattice Kinetic Monte Carlo methods. Indeed, such a possibility is achieved thanks to an important drawback that is the loss of space correlations of the elements of the microstructures. Some examples, in the field of precipitation and irradiation of metallic materials are given. The limitations and difficulties of this method are also discussed. Unsurprisingly, it is shown that it goes in a very satisfactory way when the objects are distributed homogeneously. Conversely, the source term describing the primary damage under irradiation, by nature heterogeneous in space and time, is tricky to introduce especially when displacement cascades are produced.