Equivalent Nature And Rod Components Of The Dispersion Fuel Irradiation Mechanical Behavior

Compared with the traditional nuclear fuel rods, the metal matrix dispersion nuclear fuel rods have higher burnup and higher thermal conductivity, so they have been extensively usd in the research reactors, and they have good prospects in the nuclear waste disposal and nuclear power vessels.The metal matrix dispersion fuel rod consists of the metal cladding and the dispersion nuclear fuel meat. The meat is distinguished by having the nuclear fuel particles dispersed through the metal matrix. Inside the demanding environment of the nuclear reactors, the fuel particles generate heat by nuclear fissions, the fission product accumulation results in irradiation-induced swelling of particles; the metal matrix creeps with time and becomes brittle. In order to use the fuel rod safely, the integrity of the matrix and cladding must be guaranteed and the stability of the rod should be kept. Thus . the relative researches are necessary to the safety and optimal design of the fuel rod.In the present work, the effective thermal properties and the effective mechanical properties of the dispersion nuclear fuel are investigated firstly. The effective thermal conductivity coefficient, the effective thermal expansion coefficient and the effective elastic coefficient are studied by the finite element method using the micromechanics. The study indicates that the numerical results of the effective thermal conductivity coefficient are in good agreement with the law of Maxwell and Brailsford; the numerical results of the effective thermal expansion coefficient are in good agreement with the law of mixtures; and the numerical results of the effective elastic coefficient are in good agreement with the law of Mori-Tanaka and self-consistent.A simplified model is developed to simulate the fuel rod and the temperature field is calculated by FEM. The stress field and strain field at lower burnup and higher burnup are investigated also. The effect of burnup and microstructure on the stress field and strain field are studied.The results of the temperature field indicate that increment of the heat generation rate or the volume fraction of the fuel particles will induce higher temperature in the rod; the convection coefficient can not be lower than 0.005 W/mm~2K; the effect of the size of the fuel particles on the temperature field is little.At lower burnup level, the thermal stress is the principal factor affecting the safety of the rod. The increment of the heat generation rate or the volume fraction of the fuel particles will increase the stress level and plastic level in the rod, and the effect of the size of the fuel particles on the temperature field is little.At higher burnup level, the irradiation-induced swelling induces the volume expansion of the fuel particles. A virtual temperature increment is applied to the particles to simulate the irradiation-induced swelling. The stress level is much higher than that at the lower burnup level and the plastic strain increase quickly. At 15% FIMA burnup level, the stress and plastic strain level in the matrix is very high. Especially, 10 FIMA burnup may induce the damage of the matrix while the volume fraction of the fuel particles is 30%. The first principal stress in the matrix will be very large if the radius of the fuel particles is 150μm, the material may be damaged by the higher tensile stress.This study could supply the simulation methods for the mechanical behavior analysis of the dispersion nuclear fuel rods, and it could provide numerical reference basis for the actual operation and optimization of the fuel rod.