Thermal Numerical Calculation Of A Core Fuel Rod In The Pressurized Water Reactor

With the rapid development of nuclear power industry,thermal-hydraulics optimization design advanced pressurized water reactor core has become a research hotspot in the field of nuclear power.Safety performance is the first element in the thermal design of the reactor and it is necessary to ensure the safe operation of the reactor in any situation.In this thesis,the unsteady heat conduction equation is discretized from the fully implicit finite volume method.The heat transfer temperature and exergy loss distribution of a fuel rod is numerically calculated and analyzed by Fortran90/95,as well as thermal safety characteristics under different operating conditions.Firstly,the calculation and analysis on the steady state heat transfer condition of the single channel model is carried out.The analytical solution for the temperature field distribution of the inner/outer cladding surface,the surface and center of the fuel pellet,are obtained by the theoretical derivation and agree well with the numerical solution for two kinds of temperature,which contain constant thermal conductivity and the thermal conductivity changes with temperature.The analysis shows that a high temperature zone appears in the center of the core and the temperature gradually declines at the two ends.There is a large temperature drop in the air gap and core area,and the temperature drop rate is the most significant in the air gap region.Meanwhile,the temperature of the outer surface of the cladding is evenly distributed,and the maximum temperature appears between the center of the heat channel and the outlet.Secondly,three common accident conditions of temperature distribution of a fuel rod based on the two phase of the project of Qinshan PWR prototype are discussed.When the reactivity is introduced into the core,temperature feedback effect can make the sharp rise of temperature gradually stabilized and ensure the safe operation of the reactor,especially the negative temperature coefficient.At the same time,the change of the boundary condition of the upper and lower wall of the fuel rod has little influence on the temperature field.When the fuel pellet is eccentric,the overall temperature of the fuel rod has declined and the high temperature zone is offset to the fuel pellet in the opposite direction.The drift rate increases with the increase of eccentricity.Meanwhile,the temperature distribution on the outer surface of the cladding is no longer uniform and the maximum temperature is higher.When there is a loss of flow accident(LOFA),the change of the convective heat transfer coefficient along the thermal channel is small.The temperature of core and cladding rises as the heat transfer coefficient decreases,especially in less than 20 kW/(m2·?).At this point,the position of the highest temperature on the outer wall of the cladding is close to the center point of the fuel rod.However,the change of heat flux density is very small.Finally,according to the combination of the first law of thermodynamics and the second law of thermodynamics,exergy loss is numerically calculated to discuss the process of the energy conversion and heat transfer of the reactor.The research results show that the lower temperature of the nuclear fuel and lower heat transfer temperature difference make less energy loss.But the two restrict each other.IF the total exergy is constant,the change in the distribution of internal heat sources has small influence on total exergy loss,which only changes the exergy loss distribution of the fuel rod.This method provides a useful reference for optimization of reactor thermal design and reliability evaluation.