Search

We examine the effect of neutron irradiation on the release of deuterium from tungsten at 573 K to understand the efficiency of tritium removal by baking out at moderate temperatures. Tungsten samples, undamaged and neutron-irradiated to a damage level of approximately 0.016 displacements per atom, are exposed to low-energy (108 eV), high-flux (3.0 × 1021 to 9.4 × 1021 m−2 s−1) deuterium plasma at temperatures ranging from 573 to 773 K to an ion fluence of 1.1 × 1025 m−2. At each exposure temperature, two undamaged and two neutron-irradiated tungsten samples are exposed to plasma. The deuterium content in the tungsten samples is measured by thermal desorption spectrometry soon after the plasma exposure and after post-plasma annealing at 573 K for 30 h. It is found that: (i) the deuterium retention in the neutron-irradiated tungsten samples is significantly higher than that in the undamaged tungsten samples; (ii) annealing at 573 K of undamaged tungsten samples pre-exposed to deuterium plasma at 573–773 K leads to an almost complete (60%–99%) release of deuterium from the samples; (iii) annealing at 573 K of neutron-irradiated tungsten samples pre-exposed to deuterium plasma at 573–773 K leads to a significant (8%–20%) release of deuterium from the samples. [ABSTRACT FROM AUTHOR]

Eight samples of F82H ferritic/martensitic steel were irradiated at 300 K with 20 MeV W ions to the damage level of 0.54 displacements per atom at the damage peak. Three samples were afterwards annealed in vacuum at 423 K for 72 h and then at 373 K for 106 h. Three other samples were annealed in H 2 atmosphere at 100 kPa at the same annealing temperatures and durations. All samples were exposed at room temperature to D 2 O vapor at the partial pressures in the range from 3 to 6 kPa for 365 to 1181 days. After termination of the D 2 O vapor exposure, the surfaces of the samples were partly covered by small (≤1 mm in diameter) drops of D 2 O water. Thus, the damaged samples were exposed to a mixture of D 2 O vapor and water. Trapping of deuterium at the ion-induced defects in the damage zone was examined by the D( 3 He, p) 4 He nuclear reaction. It has been found that the W-ion-induced defects generated in the F82H samples are decorated by deuterium diffusing from the surface. [ABSTRACT FROM AUTHOR]

Modelling tritium retention in radiation-damaged pure-tungsten samples, the concentration of deuterium retained in the tungsten-ion-induced damage zone decreases with increasing exposure temperature; whereas for a similarly treated tungsten–rhenium alloy, it can drop significantly faster than in pure tungsten, given sufficiently high temperatures. In contrast, similar changes in retention behaviour were not observed in undamaged samples. Based on these findings, as well as on corresponding previous TEM results, it is concluded that the concentration of high-energy radiation-induced defects responsible for trapping of deuterium is lower in the alloy than in pure tungsten. Therefore, a small amount of transmutation rhenium in damaged tungsten should be able to keep tritium retention to a low level in ITER. [ABSTRACT FROM AUTHOR]

Abstract: First wall protection tiles manufactured from recrystallized graphite doped by Ti (RGTi) were extracted from the first wall of the Globus-M spherical tokamak after being used as plasma-facing components (PFCs) during more than 8000 pulses (more than 800s). The analysis of chemical composition and structure of the irradiated tiles was performed by different methods. It was found that most of the tiles were covered with mixed layers. In the deposits the amount of absorbed deuterium was measured and minimum D concentration was found in the region of maximum power loads. Only a small amount of deuterium has been detected in the bulk of RGTi tiles exposed to plasma. [Copyright &y& Elsevier]

Abstract: The differential D(3He,p)4He reaction cross-section was determined at a laboratory angle of 135° for 3He energies between 0.5 and 6MeV. Deuterium depth profiles are determined from the measurement of the proton yield as a function of incident 3He energy with following deconvolution of the obtained yield function. This allows deuterium depth profiling to very large depths. Deuterium depth profiling to a depth of 7μm in W and 50μm in B4C is demonstrated. The accuracy of the method is discussed. [Copyright &y& Elsevier]

Abstract: Samples of polycrystalline ITER-grade W and recrystallized W were irradiated at room temperature with 20MeV W ions to displacement damage up to 0.5dpa. The damaged W samples were then exposed to (i) D neutrals at 403–573K and (ii) D2 gas at 673–1073K and pressures of 1.2 and 100kPa. Trapping of deuterium in the damage zone was examined by the D(3He, p)4He nuclear reaction with 3He energies between 0.69 and 4.0MeV allowing determination of the D concentration up to a depth of 6μm. It has been found that generation of the W-ion-induced displacement damage leads to accumulation of deuterium in the damage zone up to concentration depending on the exposure temperature and, at temperatures ⩾673K, on the D2 gas pressure. Thermal desorption spectra allowed a conclusion that deuterium is mainly accumulated in the form of D atoms bound to inner walls of vacancy clusters. [Copyright &y& Elsevier]