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Radiation-resistant optics, which is necessary to transfer light from plasma to detectors in ITER, will be exposed to neutron fluxes at D-T stage. Achromatic lenses located in the interspace and in the port cell areas must have a sufficient optical radiation hardness to sustain a neutron irradiation without significant degradation of transmittance in as wide spectral range as possible. They will be made of two types of glass: KU1 fused silica and a flint glass. The radiation hardness of the candidate flint glasses under neutron irradiation to ITER-relevant doses has to be investigated.Six types of the commercial Ce-doped flint glasses have been irradiated in a nuclear reactor up to fluencies of the fast neutrons (E > 0.1 MeV) within the range of 1012 − 1016 n/cm2. F108 and TF200 types have demonstrated the most prominent results. F108 type has a high transmittance in the visible region and a sufficient radiation hardness to be recommended for use in the port cell. TF200 type has a limited spectral range, but it has shown the best radiation hardness at a fluence of 1016 n/cm2. It can be used in the interspace area if a low transmittance in the violet-blue region is not an issue. Keywords: Flint glass, Radiation hardness, Neutron irradiation, ITER

A discrepancy in the divertor radiated powers between EDGE2D-EIRENE simulations and JET-ILW experiments employing a set of NBI-heated L-mode discharges with step-wise density variation is investigated. The analysis shows the importance of the contributions from the deuterium fuel to the divertor radiated power, making these discharges ideal for this study. Molecular radiation losses from D2 molecules have been included for the first time and the present simulations allow the atomic and molecular electron power loss terms in EIRENE to be independently scaled in order to understand their importance in determining the simulated electron temperatures and distribution of radiated power. PSI-22 keywords: Divertor modelling, Divertor diagnostic, EDGE2D, JET, ILW

AbstractThe behavior of the dislocation loop of a self-interstitial atom (SIA) near an edge dislocation and its conservative climb process were modeled in body-centered cubic Fe by incorporating loop rotation. The stable position of the loop and its rotational angle due to the interaction with an edge dislocation were evaluated through molecular dynamics simulations and calculations of the isotropic elasticity. The results were used as input variables in kinetic Monte Carlo simulations to model the absorption of the loop by the dislocation via a conservative climb. Loop rotation was found to affect the velocity of the conservative climb only at short-distances because the gradient in the interaction energy between the dislocation and an atom at the edge of the loop, which is a driving force of the conservative climb, could not be precisely evaluated without loop rotation. Depending on the distance between the dislocation and the loop, allowing the loop rotation resulted in either an increase or decrease in the velocity of the conservative climb.

Beryllium will be used as a plasma-facing material for ITER and will retain radioactive tritium fuel under normal operating conditions; this poses a safety issue. Vacancies play one the key roles in the trapping of tritium. This paper presents a first-principles investigation dedicated to point defect in hcp beryllium. After showing the bulk properties calculated herein agree well with experimental data, we calculated the formation energy of a single-vacancy and henceforth propose an estimate of 0.72 eV. This value is discussed with regard to previous theoretical and experimental studies.

Positron annihilation spectroscopy was used to evaluate the defects in neutron irradiated tungsten exposed at five different irradiation conditions. The variables in neutron irradiation included temperature, displacements per atom (dpa), and neutron spectrum. A set of W, Re, WRe, and WReOs control samples were used in assessing the data. Positron annihilation lifetime spectroscopy and coincidence Doppler broadening measurements revealed that samples irradiated at 500 °C had more vacancy clusters than samples irradiated at higher temperatures. This trend was observed despite some higher temperature samples having a significantly higher dpa. Positron lifetimes indicate these are divided into large (>40) and small (<10) vacancy clusters, respectively. These combined results elucidate the competition between defect production and recovery in plasma facing components, where at the irradiation conditions herein, temperature has a much stronger effect on defect size than does dpa.

The first wall (FW) of a blanket or divertor faces high temperature plasma. Thus, the FW needs to withstand extremely high heat fluxes. Periodic plasma pulses bring some reliability challenges to FW structures. The FW is composed of tiles, heat sink and a bolt with different connection between the tile and the heat sink. In this study, the performances of two connection forms for the tile and the heat sink were investigated. The FLUENT software was used to evaluate the heat transfer performances for the two types structure. Elastic-plastic analysis was subsequently adopted to estimate the structural properties based on the thermal hydraulic results. At the same time, the thermal and structural results under a transient high thermal load (2 MW/m2) were also analyzed. Finally, structural fatigue analysis under a cyclic thermal load with 0.5 MW/m2 was also performed. The results indicated that there was a large discrepancy in the tile results for the two connections, while the differences in the heat sink result were not significant. The advantages and disadvantages of two connections also be discussed at last.

Mo has been applied to nuclear material, in which H and carbon impurities are unavoidable. In view of this, we have studied the effect of carbon on the H retention in Mo using first-principles simulations. In perfect Mo, there is always repulsion between H and carbon, and impurity carbon cannot capture H atoms. With the appearance of vacancy in Mo, vacancy and carbon-vacancy cluster trap seven and six H atoms, respectively. This means that impurity carbon has little effect on the H vacancy capturing. Finally, we explore the H diffusion by considering the presence of one Mo-carbon layer in Mo. Away from the Mo-carbon layer, H jumps along the optimal route with a diffusion barrier of 0.12 eV. As H moves close and passes through the Mo-carbon layer, the H diffusion barrier is increased to 0.73 eV. Therefore, the repulsive interaction between H and carbon can increase the H energy barrier in the vicinity of the Mo-carbon layer, which prevent the H diffusion and permeation in Mo. The current results can explain the promoting mechanism of bubble formation due to impurity carbon implantation and help us design future Mo-based nuclear material.