| ITER is an experimental fusion reactor based on magnetic confinement fusion, with the cooperation of seven countries including EU, China, Japan, et al. The fundamental purpose of TBM (Test Blanket Module) is to verify the feasibility and reliability of tritium self-sufficiency in fusion reactor. China has decided to develop and test the helium-cooled ceramic breeder (HCCB) test blanket module. The tritium in breeder materials will be extracted by0.1%H2/He, hydrogen is used to enhance the performance of isotope exchanging. There will be some amount of tritiated water in the purge gas. In order to evaluate the total amount of tritium and recovey tritium from tritiated water, tritiated water should be transfered to elemental tritium effectively.Hot metal bed is a convenient and reliable method to decompose tritiated water, the principle is reduction of water by metal/alloy to produce hydrogen. This method is simple, without mechanics, compact, cost-effective and safe. Hot metal bed has been designed to split HTO in HCCB-TBM TES both by EU and China, but nowadays the is still no corresponding research report, so it is necessary to carry out experimental research to provide project for water decomposition in TBM TES. The general research method for gas-solid reaction was used in this study, and the detailed work is as following:(1) Based on the demand of low tritium inventory in material, two kinds of commercial zirconium alloy was selected:one is ST909(ZrMnFe), another is ZrNi5. In addition, ultrafine ZrMnFe was synthesized by solution-combustion and calcium reduction method aimed to improving dynamics property. The hydrogen absorption properties was investigated in the temperature range673-773K and with hydrogen pressure below1000Pa, the hydrogen absorption mass ration is less than0.04%o for all the three alloys, they can meet the demand of low tritium inventory in TBM TES. The kinetics of reaction between the three alloy and water was studied, the results showed that the process of ST909could be described by Ginstrign-Brounshtoerin model with the activation energy118kJ· mol-1, the synthesized ZrMnFe could be described by Jander model with the activation energy47kJ· mol-1, and ZrNi5could be described by homogeneous reaction model with the activation energy55.8kJ· mol-1;the reaction are all one order for water.(2) To meet the demand of renewablity of material, the system of Fe/Fe3O4was selected. Nanometer Fe powder was synthesized by solution combustion-hydrogen reduction, and the reaction rate increased more than10times than micrometer Fe powder. The recyclability was promote by addition of zirconium and the optimal proportion is10at%; the addition of Rh significantly improve dynamics performance and the optimal proportion is lat%. Zr10%-Rhl%-Fe was selected as the optimal system, cycle experimental result showed that the dynamics performance didn’t drop even after20cycles, the kinetics experiment indicated that the reaction is first order for water and the process could be described by homogeneous reaction model with the activation energy30.8kJ· mol-1.(3) The water decomposition experiment in micro-fixed bed reactor was carried out for above four materials and the breakthrough performance was investigated at different conditions. One-dimensional isothermal plug-flow reactor model was established to predict the breakthrough curves. The outcomes of modeling agree well with the experimental results, it showed that the reaction model is correct and is suitable to describe the reaction process. The normalized mass transfer zone was calculated by the modified mass balance equation, the results showed that the length of the mass transfer zone of ST909is about ten times larger than the other three materials, so ST909is not suitable to be used as packing material in TBM-TES water handling. A method for predicting the breakthrough point was established based on the normalized mass transfer zone, the breakthrough time could be accurately predicted by this method.(4) The breakthrough performance with hydrogen added in the reactant gas was investigated; the result showed that hydrogen adding has no significant effect on the breakthrough curve of zirconium alloys; but hydrogen has significant negative effect on Fe, so Fe is not suitable for online water decomposition in TBM-TES purge gas. The breakthrough curve of D2O instead of H2O and He instead of Ar was also investigated with the same condition, the result showed that the difference in mass of water or purge gas didn’t affect the reaction rate.(5) In order to design the larger scale reactor, momentum transfer mass transfer and energy transfer process were investigated. Firstly, the pressure drop in fixed-bed reactor packed with three size of zirconia pebbles was studied at different temperature and flow rate, pressure drop was calculated by McDonald equation and Ergun equation, the result showed that McDonald equation can accurately describe the pressure drop; the powder of metal/alloy must be made into pellet, and the pellet with the diameter no less than2mm will be needed in TBM-TES HTO decomposition reactor. Secondly, the kinetics of pellet was investigated and the kinetic equation was described by the grain equation adding the diffusion equation of water into interval in particle; the length of the mass transfer zone of pellet is larger than powders. Thirdly, the axial dispersion coefficient was investigated, the mass transfer zone will prolong with the increasing axial dispersion coefficience and the utilization rate of mass transfer zone will decrease. Fourthly, hot point temperature in fixed-bed was investigated, the result showed that hot point temperature depends directly on water concentration in reactant gas but didn’t affected obviously by the flow rate. The water concentration in TBM-TES is ppm grade, the water decomposition reactor can be treated as an isothermal.(6) The experiment of practical tritiated water decomposition was carried out in glove-box closed system, the result indicated that tritiated water could be splited completely by the ZrNis bed; the conversion efficiencies of H2O and HTO were measured independently and were observed to be similar, so the isotope effect in the reaction needn’t be considered.(7) The water decomposition reactor for TBM-TES was designed based on the mass transfer zone theory. The programs were established for ZrNi5, ultrafine ZrMnFe and Zr10%-Rhl%-Fe, the parameters can be obtained in these programs, such as dimension of reactor、the loading mass of alloy or metal、the rate of utilization、et al. |
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