[en] Mechanical properties and swelling are studied in vanadium and V-Ti (10-35 at.%), V-Ti-Cr (20 at.% Ti, 10 at.% Cr) system alloys irradiated in BOR-60 reactor up to overall fluence of 1x10²³ neutr./cm² within the temperature range of 350-830 deg C. Alloy specimens are irradiated in lithium filled sealed ampoules. The swelling of vanadium and alloys after irradiation does not exceed 0.2%. The alloying with titanium (10-35 at.%) suppresses low-temperature radiation hardening and has the greatest effect at titanium content of 35 at.%. Contrary to the alloy with 10 at.% Ti, the alloy V-35 at.% Ti exhibits high-temperature radiation hardening. The combination of 20 at.% Ti and 10 at.% Cr in a vanadium base alloy results in low-temperature radiation hardening. The character of variations in mechanical properties of alloys under neutron irradiation is analyzed with accounting for phase diagrams. Limiting contents of Ti and Cr in vanadium base alloys are determined

[en] The article presents the results of the investigation of fission products release from microparticles with UO₂ core and five-layer HII PyC- and SiC base protection layers of TRICO type as well as from spherical fuel elements based thereon. It is shown that relative release of short-lived xenon and crypton from microparticles does not exceed (2-3) 10^-7. The release of gaseous fission products from fuel elements containing no damaged coated microparticles, is primarily determined by the contamination of matrix graphite with fuel. An analytical dependence is derived, the dependence described the relation between structural parameters of coated microparticles, irradiation conditions and fuel burnup at which depressurization of coated microparticles starts

[en] Experimental investigation results of fission product release from TRISO HTI coated particles with UO₂-kerncl and fuel elements on their base are presented. It's found that fractional leakage rate of short-living Xe and Kr nuclides from coated particles is less than (2-3). 10^-7. Gas fission product release from fuel elements with intact coated particles is due to matrix graphite fuel contamination. The mathematical model, connecting coated particles construction parameters, irradiation conditions and burnup value at which coated particles failure begins, is received. (author)

[en] The effect of irradiation with the stationary and pulsed hydrogen plasma fluxes on changes in mechanical properties (microhardness) of vanadium and some alloys on the basis thereof (V-10.6Ti, V-5Ti-5Cr, V-10Ti-6Cr-0.1Si-0.05Zr, V-3Ga-0.05Ce, V-15Ti-10Cr-0.05Y) is studied. It is established, that the irradiated materials are strengthened by the vanadium and its alloys interaction with the hydrogen plasma both in the stationary mode and in the modes, imitating the plasma break-away in the tokamak reactor. The microhardness of materials, treated with plasma, increases more than by four times near the surface and by two times by the samples whole thickness

[en] Main types of in-pile tests for specimen tightness control at the initial step, research of fuel particle radiation stability and also study of fission product release from fuel elements during irradiation are described in this paper. Schemes and main characteristics of devices used for these tests are also given. Principal results of fission gas product release measurements satisfying HTGR demands are illustrated on the example of fuel elements, manufactured by powder metallurgy methods and having TRISO fuel particles on high temperature pyrocarbon and silicon carbide base. (author)

[en] Facilities and methods for studying radiation stability of coated fuel particles and spherical elements are described. The design of irradiation devices, the conditions and main results of in-pile fission product release measurements, as well as the principal methods of postirradiation examination are reviewed. Brief descriptions are given of the techniques used for fuel elements deconsolidation, particle permeability control, and analysis of fission products distribution in coated particles and in fuel elements. The main results of investigations carried out on the pressed fuel elements with TRISO-coated UO₂ particles are given. (author)

[en] Main results of testing HTGR coated particles and spheric fuel elements developed in Scientific and Industrial Association ''Lutch'' under conditions of higher level of energy release and temperature than those designed are given in the report. The summarized data on tightness and characteristic defects change, on gas and solid fission products release under model accident conditions before, during and after radiation are presented. (author). 6 refs, 9 figs, 1 tab

[en] The post-irradiation methods for investigation of distributions of solid fission products and uranium in structural elements of the HTGR fuel elements are considered. Fission product migration in coated fuel microparticle, fuel element and surrounding details of an irradiation device is analyzed. It is shown that solid fission product relase from the fuel elements at irradiation temperature of 1000-1400 deg C and fuel burnup up to 20% depends mainly of the portion of coated fuel microparticles with failed coatings, as well as on the level of matrix graphite technological contamination with uranium

[en] The main results of testing the HTGR coated fuel microparticles and spherical fuel elements from the point of view of their behaviour under conditions of power release and temperature forcing in respect to nominal ones are considered. The data characterizing changes in thickness, typical defect developments, gaseous and some solid fission product release when modelling accidents before, in the process of and after fuel element scheduled irradiation are given