Body-centered cubic metals and alloys irradiated by energetic particles form highly mobile prismatic dislocation loops with a/2 {111} -type Burgers vectors. We show how to simulate thermal diffusion of prismatic loops using a discrete dislocation dynamics approach that explicitly includes the stochastic forces associated with ambient thermal fluctuations. We find that the interplay between stochastic thermal forces and internal degrees of freedom of loops, in particular the reorientation of the loop habit planes, strongly influences the observed loop dynamics. The loops exhibit three fundamental types of reactions: coalescence, repulsion, and confinement by elastic forces. The confinement reactions are highly sensitive to the internal degrees of freedom of the loops. Depending on the orientation of the loop habit planes, the barrier to enter an elastically confined bound state is lowered substantially, whereas the lifetime of the bound state increases by many orders of magnitude.