[en] The Russian technological program 'Proriv' and the consequent search for safety improvements and economic increases in nuclear power plants with fast neutron reactors have justified the use of mixed fuel of uranium and plutonium nitrate with high thermal conductivity with a closed fuel cycle for the BN-1200 and BREST reactors. This high thermal conductivity of these nitrates reduces the temperature of the fuel, resulting in a reduction in the thermal energy stored in the pellet and the mitigation of the negative effects caused by a loss of coolant from the core. This drop in temperature also mitigates thermal stresses and deformations in the coating, in addition to reducing the rate of corrosion processes. However, the thermomechanical interaction of these fuels with the clad and the need to guarantee effective heat flow between them and the steel of the linings are factors limiting the performance of these fuel elements with nitrate pellets. One of the solutions found was the use of a liquid metal heat-conducting sublayer with liquid metals (LMCS) between the nuclear fuel and the steel coating of the fuel element. In this way, the GAP (0.25 - 0.5mm) was filled with molten lead (Pb) or lead-sodium eutectic alloys (Pb-20at.% Na) and lead-bismuth (LBE- 20at.%Na). To determine the efficiency of this sublayer, a thermal characterization study was developed by MEPHI University, in the Department of Heat Physics, using the Laser Pulse Heating Method, thus determining values for thermal conductivity, thermal resistance and thermal resistances of contacts. This work presents the results of this study and the importance of the values found in the effectiveness of using this metallic sublayer through the drop in the core temperature of this mixed nitrate fuel. (author)

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[en] Results of experimental investigation of heat conduction coefficient and coefficient of linear thermal expansion and thermal shrinkages of the STEF-1 textolite-glass widely used in superconducting magnetic systems as electric insulating and structural material are presented. Samples of two types have been died: sample axisa is perpendicular to a plae of fiberglass layers ad sample axis is parallel to a plane of fiberglass layers. Heat conduction coefficient was decreased almost a five times with temperature decrease from 300 up to 5K and was slightly dependent on a sample type. Temperature variation of linear dimensions in a sample of the first type occurs in twice as fast as compared to the sample of the second type

[en] In an MR reactor performance tests of 16 fuel assemblies, with elements having essentially the same structure as standard VVER-100 fuel elements, were carried out. Tests of five more fuel assemblies are continuing. Of the 16 assemblies, 13 were studied in a hot laboratory. The test in the MR, carried out at high loads and with a large number of transition processes, as well as the postreactor studies, indicated the fuel elements of the specified design (with initial helium pressures of 1.96-2.45 MPa) have a high reliability. None of the elements of the fuel assemblies studied malfunctioned due to design defects or faults in their fabrication. During the tests the jackets were subject to a little oxidation and hydrogenation (zirconium-oxide film < μm thick, hydrogen content less than 0.008% by mass), and their plasticity remained high (the relative elongation at the working temperature remained at the 20% level)

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[en] A valuable information on high temperature superconductors (HTSC) may be received from both superconducting and nonsuperconducting states researches. Experimental investigations of HTSC properties showed a number of anomalies below room temperature, particularly in the temperature range of Tc-280 K. Sometimes the HTSC data scatter largely at these temperatures. Some of the properties - thermal conductivity, thermal expansion, acoustic constants, revealed a hysteresis behaviour related usually to structural transitions into the spinodal decomposition region of Y-Ba-Cu-O. Otherwise, it is known that experiments on thermal conductivity of solids may be useful and powerful tools for structure relaxation studies, because of their sensitivity to modifications in the micro- and macrostructure of materials. However, there was a little of information on the HTSC materials thermal conductivity till now. In the work presented we report the results of experimental studies on the temperature variation of the thermal conductivity coefficient for two Y-Ba-Cu-O superconducting ceramic samples. The results received show more significant hysteresis in the temperature range from 80 K to 300 K compared with data of Jezowski et al, but it was weaker than indicated recently by Terzijska et al. (orig.)

[en] The electric resistivity and linear thermal expansion coefficient ceramics YBa₂Cu₃O_7-x are measured in the temperature range of 80 to 100 K and 180-210 K. The experimental results suggest a structural transformation in the ceramics YBa₂Cu₃O_7-x not only in the superconducting region but also at 180-210 K

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