No abstract

No abstract

The envisaged service conditions of thermonuclear reactors (TNR) call for a number of stringent specifications on the structural materials (in particular, on the materials of the first wall of the reactors). Besides experiencing the action of intense neutron fluxes and electromagnetic radiation, these materials are subjected to powerful ion bombardment (deuterium, tritium, and helium), During neutron irradiation, a large quantity of hydrogen and helium forms in them due to the occurrence of the corresponding threshold nuclear reactions. Interaction of the introduced isotopes of hydrogen and helium with the radiational defects leads to the accumulation and redistribution of these gases in the structural materials and, finally, changes the physicomechanical characteristics of the structure (unit). In view of this, at the present time, a study of the behavior of hydrogen and helium in metals and alloys under the conditions simulating their service conditions in a TNR is extremely important from a practical standpoint.In order of conduct comprehensive investigations on the accumulation process and the behavior of hydrogen in the structural materials subjected to irradiation, we designed an experimental mass-spectrometric installation that makes it possible to study the kinetics of hydrogen penetration through metallic membranes during ion bombardment at different temperatures (Fig. i). The principle of its operation is based on mass-spectrometric determination of the quantity of hydrogen passing through an irradiated specimen of the structural material at a given temperature. The main structural elements of the installation include a doublebeam ion accelerator (VITA) that was developed by the I. V. Kurchatov IA~ for carrying out model implantation experiments concerning the interaction of plasma with the first wall of TNR [i] and a gas analysis chamber (containing the specimen of the experimental material) attached to it. Under a high vacuum (i0 -~ Pa), beams of hydrogen and helium ions having an energy up to 20 and 50 keV, respectively (with separation with respect to mass), can be obtained in the accelerator at an ion current density up to 4.10 -s A/m 2.The gas analysis chamber (Fig. 2) was made from stainless steel using copper seals. In order to monitor and measure the incident ion flux at the specimen surface, the mounting (fastening) unit of the specimen was isolated from the frame of the chamber using a ceramic insulator, Hermetic mounting (sealing) of the experimental specimen was carried out using a tooth-plane sealing system and copper or armco-iron packing pieces. A heating element made from tungsten wire was used for heating the specimen up to a temperature of ~1300aK. The temperature of the specimen (at its center and periphery) was controlled using elastically contacting platinum-rhodium-platinum thermocouples. Just before the experimental specimen, we placed a diaphragm and a shield which intercepts the ion beam and isolates the experimental specimen during the period of setting the accelerator accordi...

No abstract

No abstract