[en] The MABEL-2D code has been used to study the effect of different mechanical restraint conditions on the ballooning response of fuel rods in the MT-3 experiment. Changing the restraint conditions from those considered appropriate to MT-3, where the rods pushed apart before flattening, to those appropriate to a large, uniformly ballooning array, was predicted to lead to increases in the axial extent of ballooning, in rupture times and in rupture strains, for a given pellet eccentricity within the cladding. At an eccentricity of 0.35, corresponding to a constant minimum to maximum pellet/clad gap ratio of about 1:2, the time to rupture was increased from 180 s to 185 s and the rupture strain from 43% to 45%. The increases in rupture strain and time were generally the same or smaller than differences, calculated in earlier work, resulting from the movement of rods relative to each other during ballooning. Pellet stack asymmetry within the cladding remains the dominant source of azimuthal temperature gradients. The results are discussed. (author)