The results of investigations of the yttrium oxide distribution in the weld joints of dispersion-hardened steel cladding, manufactured by the powder metallurgy method, are presented. It is shown that when using the methods of fusing welding of thin-walled fuel-element cladding, the content and uniformity of the yttrium oxide distribution in the metal of a seam changes as compared with the cladding metal. The concentration and uniformity of the yttrium oxide distribution in the section of a weld joint obtained by pulsed laser welding is higher than that obtained with argon-arc welding.Dispersion-hardened ferrite-class steel is one of the promising structural materials used for manufacturing the parts of fast-reactor cores. The specially developed composition of this steel, the manufacturing technology (powder metallurgy method), and the dispersion hardening of the matrix by yttrium oxide give higher heat resistance, improved radiation resistance, and a long life span of fuel elements [1-3]. These features are largely achieved by the presence of uniformly distributed, finely dispersed, 10-20 nm yttrium oxide inclusions in the material [4].The methods of fusion welding for sealing fast-reactor fuel elements can affect the uniformity of the distribution of such inclusions in a weld joint [5]. This is largely due to the heat cycles of the welding methods used, the characteristics of weld-joint formation, the dynamical processes in the weld pool, and other factors. In addition, the use of 05Kh12N2M steel with no hardening oxides should affect the concentration and distribution of yttrium oxide in a weld joint.To evaluate the fusion welding methods used, the yttrium oxide distribution in weld joints was investigated and compared with that observed in the main metal of the cladding. Samples of the weld joints in cladding consisting of ferrite dispersion-hardened steal 6.9 mm in diameter with 0.4 mm thick walls were investigated. The weld joints were made using argon-arc welding by the method of melting the end face and by laser melting in the pulsed regime (Fig. 1). The ratio of the dispersion-hardened steel and the 05Kh12N2M steel, just as in a structural part, was 85:15 in the first case and 50:50 in the second case.The investigations were performed in an XL30 ESEM-TMP scanning electron microscope (the Netherlands), equipped with an INCA Wave 700 spectrometer (Great Britain). The yttrium was detected using the L series α line. Pure yttrium from a set of standard samples was used to tune the spectrometer.

The production of the artificial 51Cr neutrino source with activity > 3 MCi for the experiment BEST is presented. This procedure consisted of making a 50Cr target and irradiating it with thermal neutrons in a nuclear reactor SM-3. The production of a target in the form of disks with a thickness of 4 mm and a diameter of 84 and 88 mm included enrichment (to 96.5% in 50Cr) of natural chromium in the form of oxyfluoride by gas centrifugation, electrolytic reduction and refining of metallic chromium, as well as the formation of chromium disks by spark plasma sintering. Simulations of various source geometries, neutron flux and nuclear transmutation were carried out to validate the design of the source, the irradiation device and the transport container, the required chemical purity of the target and the irradiation schedule in the reactor. The calculated activity of the source after 75 effective days of irradiation was 3.55 MCi. The activity of the source was measured by the calorimetric method and amounted to 3.41 MCi at the time of its delivery to the Baksan Neutrino Observatory. This is the most intense chemically pure neutrino source ever produced.

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