T.A. Burtseva1, A.E. Gorodetsky2, A.P. Zakharov2, A.V. Markin2, N.N. Shipkov3
1 D.V. Efremov Institute of Electrophysical Apparatus,
189 631 Metallostroy, St. Petersburg, Russia
2 Institute of Physical Chemistry, Russian Academy of Sciences, Leninsky pr. 31, 117915 Moscow, Russia
3 NII "Graphite", Electrodnaya St. 2, 111524 Moscow, Russia
Tritium trapping by carbon-based compositions remains one of the critical issues limiting the use of these materials for cladding of the first wall and divertor plates for the thermonuclear reactor ITER. The tentative analysis of the results carried out by the authors allows for the assumption that it is possible to reduce hydrogen isotope permeability and sorption capacity in graphite by introducing titanium dopants (up to 2 at%), thus increasing the materials density to 2.25 g/cm2 and rising its crystallization degree, and by small (to 1 at%) amounts of boron in the solid substitution solution in the crystal lattice.
Based on the results of this work, a method was found for the introduction of boron into the initial charge of recrystallized graphite RG-Ti-B making it possible to increase the concentration of boron dissolved in the graphite lattice. Samples of this graphite grade with the same total content of boron and different boron contents in the substitution solution were produced. This method will help in unambiguously assessing the effect of the boron state on the value of hydrogen isotope absorption in graphite.
To estimate the hydrogen isotope inventory by recrystallized graphites in comparison to other more widely studied grades of graphite, sets of sorption experiments were performed. It is shown that RG-Ti-91 and USB graphites, when annealed in hydrogen atmosphere in the pressure range of 1-102 Pa and temperatures of 1200-1500K, are impermeable to molecular hydrogen as opposed to POCO-AXF-5Q and SEP N112, that are readily permeable. The sorption capacity of RG-Ti-91 and USB graphite is 10-4 atomic percent. Defects like unsaturated carbon bonds, when introduced in the above materials under ion irradiation and graphite gasification, increase the sorption layer capacity of materials to 1-3x10-2 atomic percent. Permeability of the graphite defect layer is simultaneously increased with respect to molecular hydrogen. Graphite modification with boron retards the growth of the sorption capacity under surface-condition-disruption influence.