[en] The CYGRO-4 computer program is an advanced version of the CYGRO program for the analysis of axisymmetric deformations of the cross-section of an oxide fueled rod-type fuel element. CYGRO-4, which replaces the CYGRO-3 program, incorporates improved numerical methods, improved time step control, a new fuel-clad and rod-support interaction model, a new thermal conductivity model for the fuel-clad gap, and a new fuel cracking, crack deformation and crack healing model