A new method to simulate the micro-thermo-mechanical behaviors evolution in dispersion nuclear fuel elements

• The three-dimensional stress update algorithms for materials under irradiation are formulated.
• The corresponding consistent tangent stiffness moduli are also developed.
• The user subroutines to define the special constitutive relations are formed and validated.
• An efficient method is built for modeling the in-pile behaviors in dispersion fuel elements.

The large-deformation constitutive relations and stress update algorithms in a co-rotational framework are formulated respectively for the fuel particles, the matrix and cladding in dispersion nuclear fuel elements undergoing irradiation, with the main irradiation-induced effects within them considered. Their specific consistent tangent stiffness moduli are also developed. Correspondingly, the user subroutines UMAT have been programmed for definition of their mechanical constitutive relations. Besides, the user subroutines UMATHT have been written to define their thermal constitutive relations, in which degradation of the thermal conductivity of fuel particles are involved. An efficient method is established for modeling the irradiation-induced micro-thermo-mechanical behaviors evolution in dispersion nuclear fuel elements. The developed methodology is validated with the simulation results of the thermo-mechanical behaviors in fuel elements under an assumed irradiation condition. This study lays a foundation for optimal design of dispersion fuel elements.