The main factor of destruction of fuel rods in accidents with loss of coolant is associated with the vapor-zirconium reaction occurring between the fuel rod shell and the coolant (water). Improving the reliability of fuel cells can be obtained by modifying or replacing the fuel shell, materials that do not interact with the coolant during normal operation and in emergency situations. Increasing the reliability and economic characteristics of nuclear power plants is possible by replacing uranium dioxide with fissile compositions with a high content of fissile isotopes and with greater thermal conductivity. These two provisions form the concept of ATF (tolerant fuel). Variants of creation of tolerant fuel are considered., variants of modernization of shells and fissile compositions are studied for nuclear power plants with WWER reactors.

The main factor of destruction of fuel rods in accidents with loss of coolant is associated with the vapor-zirconium reaction occurring between the fuel rod shell and the coolant (water). Improving the reliability of fuel cells can be obtained by modifying or replacing the fuel shell, materials that do not interact with the coolant during normal operation and in emergencies. The loss of coolant accident is a design-basis accident in light water reactors. The postulated accident requires an analysis of the double guillotine break in a main primary coolant pipe, which allows the coolant to freely discharge out of the primary system into the containment of the building. In the present work, the heat stored in the active zone of the reactor, the heat capacity of the fuel and the shell temperatures are determined for ATF materials U-10Mo and U 3 Si 2 . The calculated values are compared with the usually used fuel UO 2 . The results showed beneficial effect of using ATF materials. The above quantities are decreased dramatically for ATF, promising to replace UO 2 with ATF fuels. This reduces the probabilities of accidents and oxidation in the nuclear reactors. The calculations are done for nuclear power plant, type VVER-1200.

The thermal conductivities for the traditional fuel UO 2 and for the Accident Tolerant Fuel (uranium Molybdenum alloy, U-10Mo and uranium silicide, U 3 Si 2 ) are calculated and compared. Then the temperature distributions on these core reactor, namely on the surface of the rod and in the center line of the rod were determined. The calculation is carried out using MATHCAD program. The calculations showed enhancement of thermal conductivity of the Accident Tolerant Fuel as they increased linearly with increasing temperature, and reduction of their center line temperatures of the rods. Beside, their steep thermal gradient, which may reduce the induced heat stresses in the core of the reactor.

The paper presents numerical investigation of the thermal resistance of the contact surface of heat exchange and melt of lead. Using a geometric model of the contact area, developed on the basis of image analysis of the contact surfaces of steel and lead, the calculation of the contact resistance between molten lead and the surface of steel EP-823. The results of the calculations are compared with experimental data on thermal resistance of contact of the lead with steels EP-823 and 312 steel.

Information about the change of thermal properties of the fuel elements needed for a successful and safe operation of the nuclear power plant. At present, the existing amount of information on the fuel thermal conductivity change and "fuel-shell" thermal resistance is insufficient. Also, there is no technique that would allow for the measurement of these properties on the non-destructive way of irradiated fuel elements. We propose a method of measuring the thermal conductivity of the fuel in the fuel element and the contact thermal resistance between the fuel and the shell without damaging the integrity of the fuel element, which is based on laser flash method. The description of the experimental setup, implementing methodology, experiments scheme. The results of test experiments on mock-ups of the fuel elements and their comparison with reference data, as well as the results of numerical modeling of thermal processes that occur during the measurement. Displaying harmonization of numerical calculation with the experimental thermograms layout shell portions of the fuel cell, confirming the correctness of the calculation model.

A design of the speckle-interferometric dilatometer intended for studying thermal expansion of solid bodies at temperatures of 20–100°C is described. The calibration results for the thermal coefficient of linear expansion of copper, Armco iron, and 12Kh18N10T steel samples are given.

A technique for measuring the thermal resistance of the liquid metal–structural steel interface is proposed. The results ofmeasurements of the thermal resistance of the interface between Pb-Mg-Zr alloys and EP-823 steel and the thermal conductivity of Pb-Mg-Zr alloys in the temperature range of 350–900 °C are presented.

The structure and thermophysical properties of materials formed in the system Dy2O3–HfO2 (molar ratio 1 : 3 to 3 : 1) as a result of isothermal firing of x-ray amorphous mixed hydroxides at temperature to 1600°C are investigated. It is shown that for ratios 1 : 3 to 1 : 1 the crystallization process results in the formation of single-phase solid solutions with the structure of defective fluorite and marked nonequivalence of the parameters of the local environment of the Dy and Hf atoms. It is determined that the ceramic based on dysprosium hafnate (Dy2O3: HfO2 = 1 : 1) possesses low, practically temperature independent (to 800°C), thermal conductivity about 1.4 W/(m · K).

In this paper, we present the results of the study of thermophysical properties of EP-823 steel (thermal diffusivity, thermal coefficient of linear expansion (TCLE), specific heat, thermal conductivity) in the temperature range of 200–900 ◦C. The presence of phase transitions affecting steel thermophysical properties is indicated.

В работе предложена методика определения теплопроводности жидкого свинца импульсным методом, в которой расчеты теплопроводности проводятся по начальному участку термограммы. Приведены результаты измерений теплопроводности жидкого свинца С1 в диапазоне температур 350–1000°С.

We propose a technique for the determination of the thermal conductivity of liquid lead by the flash method where the thermal conductivity is calculated on the basis of the initial section of the temperature-vs.-time profile. We present the results of measurements of thermal conductivity of the liquid C1 lead within the temperature range of 350–1000°C.

The results of the development of the techniques for determining the thermal resistance between a fuel and a fuel-element cladding and the fuel thermal conductivity, oriented to applications under conditions of a shielding box, are described. The schematic of the laboratory setup is presented, using which the operability of the techniques is shown on a fuel element prototype with dense fuel simulators.