The metalfuel version of the FPIN2 fuel element mechanics model has been incorporated into the SASSYS/SAS4A code system. In this implementation, SASSYS/SAS4A provides the fuel and cladding temperatures, and FPIN2 performs the analysis of fuel and cladding deformation. The FPIN2 results aid in the understanding of accident progression by providing the estimates of the axial expansion of fuel, time and location of cladding failure, and the condition of the fuel at the time of failure. The validation of the integrated SASSYS/SAS4A-FPIN2 model has been performed using the data from in-reactor TREAT tests for the prototypic binary and ternary fuels of the Integral Fast Reactor concept. The integrated model calculations are compared with available experimental data for the six fuel elements in these tests, and good agreement is obtained for the key parameters related to transient behavior of the metallic fast reactor fuel elements.