Project goal: determination of the parameters of the hydrogen isotopes interaction with lithium with different surface states during the reactor irradiation, and an assessment of the potential use of lithium evaporation and condensation processes as a tool for control of tritium content.
Current State in Research Area. The use of lithium in the elements (divertor, limiter) of the fusion facilities exposed to high thermal loads makes us pay more attention to the processes of evaporation and condensation of lithium. These processes can be carried out under various conditions that pertain to the form of the existence of a condensed phase (liquid film, droplets); to the presence or absence of impurities on the surface of the liquid phase and in the presence of an uncondensable medium. In turn, the evaporation coefficient is strongly dependent on the presence of impurities on the surface of liquid lithium (films of chemical compounds, etc.). All surface impurities can reduce the rate of evaporation by orders of magnitude, which is related both to a change in the character of evaporation from molecular to viscous at relatively high temperatures and an increase in the vapor pressure of lithium above the surface, and with a change in the quality of the lithium surface. As a consequence the control of the impurities content of Lithium, and especially Tritium, is a topic of key importance for its use for fusion applications.
At the present time, there is a certain amount of work devoted to the study of the hydrogen isotopes interaction with liquid lithium. Most of them contain information on the solubility and diffusion of hydrogen isotopes in lithium, in particular, hydrogen and deuterium. There are practically no results with tritium. Also, the recent conferences in the field of thermonuclear fusion and the use of liquid metals in thermonuclear reactors (SOFT-2016, ISLA-2017) have shown that there is no sufficient data on research of the effect of impurity content on the interaction of lithium with hydrogen isotopes. Since the presence of impurities in lithium is the most important element, which determines the technology for lithium handling, there is the problem of determining the influence of the amount and types of impurities on the processes of lithium interaction with hydrogen isotopes. Also the studies of the effects of neutron irradiation (which will certainly be present in a thermonuclear reactor) on these processes are of the great interest.
Impact of the proposed project on the progress in this area. Successful implementation of the project will allow to improve the techniques based on lithization of fusion reactor’s chambers.
It will promote new technological solutions while designing and creating of new fusion facilities with lithium as plasma-facing material. Which in turn will promote development of the most prospective direction of electricity production – fusion power industry.
Expected Results and Their Application. Within the framework of the project it is planned to receive a number of important scientific results:- a methodology will be developed for study of hydrogen isotopes interaction with lithium with surface various states;
- the results of experiments will be obtained on the sorption and thermal desorption of hydrogen isotopes by different nature lithium films (for different states of the lithium surface);
- analytical studies will be carried out and characteristics such as the temperature dependence of the rate of sorption (desorption) of hydrogen isotopes by lithium will be determined for different states of the lithium surface;
- the parameters of chemical reactions on lithium surfaces will be determined, the processes of evaporation and condensation of a metal at various states of its surface will be described;
- a methodology will be worked out for carrying out in-pile studies of hydrogen isotopes interaction with lithium with different surface conditions;
- the results of neutron-physical and thermo-physical calculations for determining the parameters of reactor experiments will be obtained;
- reactor ampoules will be developed, manufactured and tested to study the hydrogen isotopes interaction with lithium under neutron irradiation conditions;
- sorption/ desorption dependences of the gas phase changes in the volume with lithium will be obtained for different lithium temperatures under neutron irradiation conditions at different neutron flux densities;
- an analytical study will be conducted, the results of which will determine the effect of reactor irradiation on the parameters of hydrogen isotopes interaction with lithium with different surface states;
- an assessment will be made of the potential use of lithium evaporation and condensation processes as a tool to control tritium content.
Thus, the project will include activities on development of the methods for conducting out-of-pile and in-pile tests of lithium, obtaining the experimental data on the parameters of hydrogen isotopes interaction with lithium with different surface conditions under neutron irradiation and without it.
Based on the results of the work done, a conclusion will be made about the prevailing mechanisms of hydrogen isotopes interaction with lithium and on the effect of neutron radiation on the processes of such interaction. The results of the project will undoubtedly be in demand in the international fusion community, fusion facilities operators and designers, research groups engaged in solving material science issues of fusion facilities.
