Dynamic Monte-Carlo modeling of hydrogen isotope reactive–diffusive transport in porous graphite

Abstract

Deuterium and tritium will be the fuel used in a fusion reactor in equal mixtures.It is important to study the recycling and mixing of these isotopes of hydrogen in graphite from several points of view: (i) impact on the ratio of deuterium to tritium in a reactor, (ii) continued use of graphite as a first wall and divertor material, (iii) reaction with carbon atoms and the transport of hydrocarbons will provide insight into chemical erosion. Dynamic Monte-Carlo techniques are used to study the reactivediffusive transport of hydrogen isotopes and interstitial carbon atoms in a 3-D porous graphite structure irradiated with hydrogen and deuterium and is compared with published experimental results for hydrogen re-emission and isotope exchange.

Modeling of hydrogen isotope exchange from porous graphite

“…In the absence of incoming energetic ions, the samples which are 'virgin' (having very less damage), molecules are indeed formed locally at the end of the ion range. Structural dependence of re-emission was also observed by the present authors in previous simulations [9].…”

“…A 3D multi-scale model has been developed to model the hydrogen isotope reactivediffusive transport in porous graphite [8,9]. The two-region model developed by Haasz et al [10] has been implemented distinguishing the atomic and molecular transport processes within the bulk and surface region on the graphite crystallites.…”

“…For samples having less internal porosity mixing is very low. Therefore the internal structure of graphite, which affects the diffusion coefficient [4][5][6][7] and consequently molecule formation and atomic re-emission [8,9], plays the most crucial role for the H,D mixing. A new mechanism based on the KMC and SDTrimSP simulation is proposed to explain the experimental data.…”

Hydrogen release and retention from porous graphite

“…The internal geometry plays a major role in retention and release, so we will first keep the internal structure the same in all the cases. The effect of void fraction and void size was studied [33], and we have also shown that even the orientation of the voids affects the hydrogen release (this is to be published). For a systematic study, we take a sample with cubic voids, neglecting here the further dependence on the voids.…”

Modelling of hydrogen isotope inventory in mixed materials including porous deposited layers in fusion devices

“…The input data used include diffusivity, trap sites, etc. and are shown in Table 1 and Table 2, where most of these were used in MD or KMC simulations [14,15,16,25] and gleaned from either experiments (E D , E HD or an educated guess was used (like ω o corresponds to typical phonon frequency [19]). The backscattering rate R is from [27].…”