Effects of irradiation hardening and creep on the thermo-mechanical behaviors in inert matrix fuel elements

• A new three-dimensional finite-strain constitutive relation is developed.
• The relative numerical simulation method is constructed and validated.
• The effects of irradiation creep are investigated.
• Irradiation creep will remarkably influence evolution of the mechanical behaviors.

An inert matrix fuel element consists of metal cladding and a composite fuel meat with the nuclear fuel particles embedded into the metal inert matrix. In order to precisely predict its in-pile thermo-mechanical coupling behaviors, the three-dimensional finite-strain constitutive relation is developed featuring consideration of the irradiation hardening plasticity and irradiation creep for the metal matrix and cladding; accordingly, several ABAQUS subroutines are built and validated to simulate irradiation swelling of the fuel particles and the above irradiation damage effects in the metal materials. Computation of the in-pile thermo-mechanical behaviors evolution is implemented. Compared to the calculation results considering only the irradiation hardening plasticity, the obtained results demonstrate that with the irradiation creep effect further included: (1) the mechanical interaction between the fuel particles and the matrix is weakened; (2) the maximum Mises stress and principal stress in the cladding tend to be very low; (3) similarly, the interfacial tensile stresses at the interface between the fuel meat and cladding also appear to be relatively smaller at higher burnup, and the interfacial shear stresses are close to zero; (4) the thickness increment of the fuel plate becomes comparably larger.