Персона: Огородникова, Ольга Вячеславовна
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Positron annihilation spectroscopy study of radiation-induced defects in W and Fe irradiated with neutrons with different spectra
© 2020, The Author(s).The paper presents new knowledge on primary defect formation in tungsten (W) and iron (Fe) irradiated by fission and high-energy neutrons at near-room temperature. Using a well-established method of positron-annihilation lifetime-spectroscopy (PALS), it was found that irradiation of W in the fission reactor and by high-energy neutrons from the p(35 MeV)-Be generator leads to the formation of small radiation-induced vacancy clusters with comparable mean size. In the case of Fe, smaller mean size of primary radiation-induced vacancy clusters was measured after irradiation with fission neutrons compared to irradiation with high-energy neutrons from the p(35 MeV)-Be generator. It was found that one of the reasons of the formation of the larger size of the defects with lower density in Fe is lower flux in the case of irradiation with high-energy neutrons from the p(35 MeV)-Be source. The second reason is enhanced defect agglomeration and recombination within the energetic displacement cascade at high energy primary knock-on-atoms (PKAs). This is consistent with the concept of the athermal recombination corrected (arc-dpa) model, although the measured dpa cross-section of both fission neutrons and wide-spectrum high-energy neutrons in W is between the conventional Norgett–Robinson–Torrens (NRT-dpa) and arc-dpa predictions. This means that the physics of the primary radiation effects in materials is still not fully known and requires further study through a combination of modeling and experimental efforts. The present data serve as a basis for the development of an improved concept of the displacement process.
Migration, trapping and release of deuterium from tungsten in the presence of high density of defects: theory and experiment
The most common experimental methods to study hydrogen (H) in a metal are nuclear reaction method (NRA) for depth profile measurements, thermal desorption spectroscopy (TDS) and permeation experiments. Rate equations are used to model experimental data. The diffusivity, solubility, reflection coefficient, surface barrier, binding energies of H with different types of defects and density of defects are input parameters for rate equation model. These parameters can be derived from the first-principle (DFT) calculations, effectivemedium theory (EMT), molecular dynamics (MD) and TRIM calculations. Incorporation of binding energies of deuterium (D) with a vacancy and a dislocation recently calculated by DFT [1,2] and penetration probability and ion range calculated by MD and TRIM [3] in the rate equation model allows us to validate different predictions against experimental data, for the first time. A comparison of the first-principle calculations and calculations by other theoretical models with experimental values can clarify the physics underling the hydrogenmetal interaction and can provide an answer on several important questions, namely, (i) which type of trap corresponds to certain D binding energy, (ii) which is a range of validity of MD and TRIM models and (iii) which process is rate-limited in respect to the D uptake and release in a material.
DEUTERIUM RE-EMISSION AND THERMAL DESORPTION FROM IRON AND EUROFER
Reduced-activation ferritic-marthensitic (RAFM) steels, such as Eurofer, are considered as candidates for structural materials in fusion reactors due to the high thermal conductivity, the low thermal expansion coefficient and good resistance to radiation swelling. There are also some concepts of fusion reactors, where RAFM steels also considered as material for plasma-facing components. In this regard, the key aspects of hydrogen (H) isotopes interaction with RAFM steels, such as tritium (T) retention and migration in these materials are particularly important as a point of safety concern.
DEUTERIUM AND HELIUM RETENTION AND CORRESPONDING MODIFICATIONS OF W-BASED MATERIALS UNDER STATIONARY OPERATION REGIME AND TRANSIENTS
Tungsten and dense nano-structured tungsten (W) coatings are used as plasma-facing materials in current tokamaks and suggested to be used for future fusion devices. In this regard, a study of accumulation of deuterium (D) and helium (He) in W materials and corresponding material modifications under normal operation conditions and transient events appears necessary for assessment of safety of fusion reactor due to the radioactivity of tritium and material performance and for the plasma fuel balance. Therefore, sequential and simultaneous (with 10% of He seeding) D/He plasma exposure of W-based samples (polycrystalline W, nano-structured W coating and W with He-induced W ‘fuzz’) in quasi-stationary high-current plasma gun QSPA-T below and above the melting threshold with a pulse duration of 1 ms and number of pulses from one to thirty was performed and compared with stationary plasma loads. Material modification was investigated using an electron microscope equipped with a focused ion beam for in-situ cross sectioning and an x-ray diffractometer.
HYDROGEN AND HELIUM RETENTION IN TUNGSTEN UNDER ION IRRADIATION
Interaction of helium and hydrogen ions with tungsten is intensively investigated during last decades in relation to construction of fusion reactor. Tungsten has the high melting temperature and the energy threshold for sputtering and, therefore, is considered as plasma facing material (PFM) in fusion devices in the area of largest heat loads and small energies of ions (divertor area). In particular, tungsten will be used in the international experimental reactor ITER, which is now under construction.
МОДЕЛИРОВАНИЕ РАДИАЦИОННЫХ ПОВРЕЖДЕНИЙ В СПЛАВАХ ВОЛЬФРАМА С ИСПОЛЬЗОВАНИЕМ ИОННОГО ОБЛУЧЕНИЯ
In this work, a comprehensive study of a W-6Re and W-10Cr alloys after accelerated irradiation with ions to a damage dose of 10 displacements per atom at temperatures of 300 and 500 °C was carried out. A detailed chemical analysis of radiation induced defects acquired by means of transmission electron microscopy and atom probe tomography. It is shown that, as a result of irradiation, nanosclae clusters enriched in rhenium and chromium are formed. In addition, a high density (of the order of 1024 m-3) of clusters of point defects was found in the area of material damage.
МОДИФИКАЦИЯ ПОВЕРХНОСТИ ВОЛЬФРАМА ПОД ВОЗДЕЙСТВИЕМ ГЕЛИЕВОЙ ПЛАЗМЫ С ПРИМЕСЬЮ ИНЕРТНЫХ ГАЗОВ
Одним из приоритетных направлений в области термоядерных исследований является контроль уровня плазменно-тепловой нагрузки на внутрикамерные элементы установок магнитного удержания горячей плазмы. Постепенное развитие технологии напуска примеси инертного газа (He, Ne, Ar) в процессе плазменного разряда в установках типа токамак и стелларатор [1, 2] как средства радиационного охлаждения периферии плазмы, предъявляют новые требования по контролю состояния поверхности обращённых к плазме элементов.
CORRELATION OF DEUTERIUM RETENTION WITH CRYSTALLINE STRUCTURE IN DENSE AND DISORDERED TUNGSTEN COATINGS
Dense nano-structured tungsten (W) coatings are used as plasma-facing materials in current tokamaks and thick coatings are suggested to be used also for the future fusion devices, ITER and DEMO. In this study, deuterium (D) retention in various W coatings was investigated to understand dependences of the D retention on the crystalline structure of each W coating and on the substrate material.
SURFACE MODIFICATIONS OF W-BASED MATERIALS UNDER HELIUM AND DEUTERIUM ION IMPLANTATION
In a thermonuclear reactor, materials will be irradiated with hydrogen isotopes and helium (He), neutrons, and heat fluxes. Tungsten (W) and dense nano-structured tungsten (CMSII) coatings are used as plasma-facing materials in current tokamaks and suggested to be used for future fusion devices. In this regard, the study of the accumulation of He and deuterium (D) in W based materials and corresponding surface modifications under normal operation conditions and transient events appears necessary for assessment of safety of fusion reactor due to the radioactivity of tritium and material performance and for the plasma fuel balance. Therefore, in this work, irradiation of W-based materials with D and He ions in stationary regime and in quasi-stationary high-current plasma gun QSPA-T below and above the melting threshold has been performed. In QSPA-T, a pulse duration was 1 ms and number of pulses was varied from one to thirty. In stationary plasma loads, ion energy was varied from 20 to 3 keV, temperature 300-1200 K and flux/fluence 1017-1021 at/m2s/1020-1025 at/m2.
МОДЕЛИРОВАНИЕ НАКОПЛЕНИЯ ДЕЙТЕРИЯ ПРИ ИМПУЛЬСНЫХ ПЛАЗМЕННЫХ НАГРУЗКАХ ХАРАКТЕРНЫХ ДЛЯ ИТЭР
В Международном термоядерном реакторе ИТЭР в качестве обращенного к плазме материала будет использоваться вольфрам (W), из которого будет изготовлено защитное покрытие диверторных пластин. Тепловые нагрузки на пластины дивертора в токамаке масштаба ИТЭР в стационарной стадии DT-разряда будут достигать ~10 МВт/м2, приводя к повышению температуры пластин в среднем до 1400 К; в срывах и ЭЛМах импульсные кратковременные нагрузки (~ 1 мс) на диверторные пластины будут достигать величины 0,6 – 3,5 ГВт/м2, что будет вызывать периодическое повышение температуры, сопоставимой с температурой плавления материала [1].