Effects of U-Mo irradiation creep coefficient on the mesoscale mechanical behavior in U-Mo/Al monolithic fuel plates

Abstract

The fuel foils in U-Mo/Al monolithic fuel plates will evolve into porous media owing to the formed gas bubbles. Three-dimensional finite element simulations are implemented for the thermo-mechanical behavior in U-Mo/Al monolithic fuel plates with different U-Mo irradiation creep coefficients, and the results of mesoscale normal stress, bubble volume fraction and bubble pressure in the fuel foil are obtained. In the simulations, the mechanistic fission gas swelling model is adopted, considering the dependence of external hydrostatic pressure. The mesoscale normal stress refers to the effective normal stress in the skeleton of porous fuel foil, which relates to the fuel fracture. The numerical results indicate that an irradiation creep coefficient of 2000 × 10−31 m3/MPa can be identified for the current U-10Mo fuel foil, because the calculated fuel-foil thickness increments match well with the experimental data. The influences of U-Mo irradiation creep coefficient on its bubble volume fraction and pore pressure are significant in the vicinity of fuel foil edges and corners. The dangerous regions locate near the fuel foil corners, surrounding the points with maximum mesoscale normal stresses. The enlarged irradiation creep coefficient will result in stress relaxation on the whole, but the through-thickness creep strain components can be heavily magnified. When the irradiation creep coefficient increases from 10 × 10−31 m3/MPa to 1000 × 10−31 m3/MPa, the maximum mesoscale normal stresses will decrease from 58.04 MPa to 28.04 MPa, with a reduction of ∼52%; while the corresponding through-thickness creep strain components increase by ∼5%. With an increase of irradiation creep coefficient from 1000 × 10−31 m3/MPa to 2000 × 10−31 m3/MPa, the maximum mesoscale normal stresses increase by ∼9%, and the corresponding through-thickness creep strain components increase by ∼219%. The irradiation creep performance should be optimized and an extreme large creep coefficient is not a good choice, because the creep-induced damage might degrade the mesoscale strength of the fuel foil. Keywords: Bubble volume fraction, Bubble pressure, Irradiation creep coefficient, Porous media, Mesoscale normal stress, Creep damage