Abstract. The main temperature characteristics of a pressurized water reactor are distinguished, supporting its safety and reliable operation. The special role of the uranium fuel effective temperature is emphasized and the accuracy of the analytical determination of the power effect is increased. The calculation of the temperature distribution along the radius of the fuel rod was carried out taking into account the temperature dependence of the thermal conductivity UO2. The design procedure was corrected for using the Finca-Ronchi dependence for the thermal conductivity of 95% density of the theoretical one.
Abstract. The main temperature characteristics of a pressurized water reactor are distinguished, supporting its safety and reliable operation. The special role of the uranium fuel effective temperature is emphasized and the accuracy of the analytical determination of the power effect is increased. The calculation of the temperature distribution along the radius of the fuel rod was carried out taking into account the temperature dependence of the thermal conductivity UO 2 . The design procedure was corrected for using the Finca-Ronchi dependence for the thermal conductivity of 95% density of the theoretical one. Primary temperature characteristics of reactorThese include the following integral and differential characteristics [1,2].The temperature effect of reactivity (TER), which is defined by the difference of reactivity, caused by the same temperature change from the cold to the hot state of all materials in reactor core (RC). The initial temperature of the cold reactor is set to 20-40 °C. Hot reactor temperature varies with a minimum controlled power level due to external heat sources. Fuel reactivity effect is responsible for forming the neutron spectrum and its leakage.The power reactivity effect (PRE) N U is determined by the mean or effective temperature of uranium fuel eff T and the actual presence an isotope 238 U in it. Due to the Doppler effect, there are resonance levels of the uranium isotope broadening with temperature rise, which increases the neutron absorption probability, thereby reducing reactivity. The higher the fuel temperature and the lower its concentration, the greater the effect. Also, magnitude N U is important for to assess the mode extension fuel campaign using the power effect reactivity. U reactivity coefficients determine self-regulation, self-protection, reliability and safety of the nuclear reactor. Both coefficients to provide these nuclear reactor properties must be negative: the first is near the operative point, the second is on the entire range of power transient.The fuel effective absolute temperature is determined by the exact integral formula
This research presents a computational investigation of the thermal convection of a heat-generating liquid having variable viscosity in a semi-cylindrical cavity. The analysis is carried out to obtain the time patterns of the average Nusselt number at the lower border of the chamber and understand the impact of the variable viscosity, the Prandtl number, and the Rayleigh number on this parameter. The natural convection in the cavity is defined by the set of non-dimensional equations based on the Boussinesq approach employing the non-primitive parameters such as vorticity and stream function. These governing equations are worked out numerically based on the finite difference technique. The time dependencies have been obtained at the Rayleigh number equal to 104, 105, and 106 and the Prandtl number taking values of 7.0, 70, and 700. The results obtained for variable and constant viscosity have been compared. Additionally, the paper represents maps of isotherms and streamlines for the mentioned values of the Rayleigh number. The influence of variable viscosity on the parameters of natural convection is poorly studied in closed systems; therefore, this research gives necessary data to understand the general time nature of the average Nusselt number at cooling surface of various parameters. Additionally in this research, the model for simulating the natural convection in non-primitive variables is presented in polar coordinates when the dynamic viscosity varies with temperature. The computational model designed could be used to simulate the free convection in systems with inner heat production such as chemical reactors, inductive metal melting facilities, or corium in-vessel retention to analyze the impact of various factors on the parameters of the natural convection in such systems.
The problem of finding an effective temperature is highly important. This characteristic provides calculation of the power effect reactivity (PER), which defines safe and stable operation of nuclear reactor. The numerical experiment, which is considered on average and maximum heat load conditions, is put to find out changing of the effective temperature in the high burnup fuel of WWER-1000. In the course of the experiment mathematical statement of the problem is made, numerical solution of which is found with using the finite differences approximation of both control equations and border conditions. Also, the method of simple iteration is used for calculating temperature distributions, according to determination of the effective temperature. The linear approximation was obtained basing on effective and maximum temperatures depending on the burnup.
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