Study On The Desorption Behavior Of Hydrogen Isotopes In Liquid Lithium Under The Influence Of Impurities

In the future fusion device,the plasma facing material in the fusion device needs to withstand higher heat flux,and the interaction between the boundary plasma and the material is one of the main problems faced by the fusion device.The flowing liquid lithium first wall which is self-healing can help to remove thermal deposition and provide clean wall conditions,thus improving the plasma performance parameters.It is an alternative scheme for plasma facing material.However,the strong chemical activity of lithium brings a problem of fuel particle retention,so it is necessary to develop technologies related to tritium recovery,and further researches are needed on the desorption behavior of hydrogen isotopes in liquid lithium.This paper designed an experimental system for thermal absorption/desorption of D2 in liquid lithium,conducted thermal analysis and quantitative calibration of the reaction system,studied the desorption behavior of different concentrations of deuterium gas(D2)in liquid lithium,and clarified that the presence of a small amount of impurities in liquid lithium can also affect the desorption temperature of D2.Experiments were conducted to investigate the influence of impurities on the absorption rate and the desorption behavior of D2 and the mechanism of action was explored.The impact of the results in this article on the technologies related to tritium recovery was also discussed.The specific results of this paper are as follows:First of all,,the absorption and desorption experiments of D2 in liquid lithium with different contents were carried out,and desorption characteristics of D2 in liquid lithium with different forms were analyzed.It was found that D dissolved in liquid lithium was desorbed at about 485℃,and the saturated D which existed in the form of LiD was first dissolved in liquid lithium and then released.When the content of D was low,there was a significant change in the position of the D2 desorption peak,and the desorption temperature of a very small amount of impurity gases such as N2 and H2O in the sample varied with the temperature of the D2 desorption peak.This indicated that the relative content of impurities to D in liquid lithium was a key factor affecting the D2 desorption temperature.The possible impurity components and their sources were verified by experiments.The absorption rates of lithium to the main components of the air such as N2,O2,H2O and H2 at different temperatures were compared.It was found that the gases above could react with lithium at room temperature,but the reaction rate was much higher at about 400℃.Secondly,the influence of N2,O2,H2O and air on the desorption behavior of D2 in liquid lithium was studied.It was found that N2 and H2O could increase the desorption temperature of D2,thus improving the thermal stability of D in liquid lithium.The same content of H2O had greater influence on the desorption behavior of D2 than N2.When N2/D2 was close to 50%or H2O/D2=15%,the products of preabsorbed N2 and H2O in liquid lithium could react with all of the D2.The experiment of pre-absorbed air showed that when these components existed at the same time,more complex interactions would occur.The change of D2 desorption temperature was related to the proportion of air components.Although the impurities changed the desorption temperature of D2,they had no obvious effect on the desorption amount of D2.Finally,the interaction mechanisms of pre-absorbed N2 and H2O with D2 in liquid lithium were discussed,and it was considered that LiNxDy and LiOxD1-x(x<<1)were formed,resulting in the change of desorption temperatures.The results of experiments were also verified by the impurity desorption phenomenon in the EAST liquid lithium experiment.The influence of the impurities in liquid lithium on the solubility of D2 was analyzed.And the influence of the experimental results on tritium recovery technologies was discussed.For example,the permeation window and electrochemical method,which were used to measure the concentration of dissolved tritium,ignored the content of other tritium compounds,which may lead to the smaller measurement results.The reabsorption of desorbed gases by vaporized lithium brought a problem to the thermal desorption method when tritium in liquid lithium need to be separated.According to the experimental results of the reactions between impurities and D2 in liquid lithium,a new method for removing impurities in liquid lithium was proposed.According to the research results,the desorption performance of D2 in liquid lithium have been thoroughly understood.The influence of impurities on the desorption temperature of D2 has been clarified.A key factor affecting D2 desorption temperature has been found to be the relative content of impurities to D in liquid lithium.The possible reaction mechanisms have been explored,which provides basis for the design of relevant technical schemes for tritium recovery in liquid lithium.