Homogenized Viscoplastic  Material Model for a Dual Cooled Lead Lithium Blanket

A non-linear multiphysics component scale finite element blanket model and homogenized viscoplastic material model were developed for modeling creep and void evolution in the dual cooled lead lithium (DCLL) blanket.The constitutive behavior of a material and the evolution of the voids within are highly coupled processes, which are governed by dissipative potential.The potential could be matched using homogenization approach and simplified representative volume to accurately capture the constitutive behavior of the blanket material system.The viscoplastic model is implemented within MOOSE and it is formulated based on the Gurson-Tvergaard-Needleman method that is widely used for modeling damage evolution in ductile materials.A separate model that correlates changes in neutron damage and operational temperature to void swelling of F82H steel at fusion relevant temperatures is implemented to supply the volume fraction of the voids.The results of the homogenized strain and the stress-induced evolution of the cavities in the first wall and back wall are presented.The result of the creep analysis which is consistent with previous work showed that the maximum creep strain at the first wall is about 0.45% at 3,000hrs with rupture time of about 42,000hrs.The robust creep model capturing radiation and stress-induced voids evolution produced shorter time to onset of tertiary creep and rupture showing that the traditional creep model could be very conservative.The stress of 173MPa at the first wall would lead to larger stress-induced voids evolution compared to those induced by radiation.