  Background: Neutron stars are astronomical systems with nucleons submitted to
extreme conditions. Due to the long range coulomb repulsion between protons,
the system has structural inhomogeneities. These structural inhomogeneities
arise also in expanding systems, where the fragment distribution is highly
dependent on the thermodynamic conditions (temperature, proton fraction, ...)
and the expansion velocity.
  Purpose: We aim to find the different regimes of fragment distribution, and
the existence of infinite clusters.
  Method: We study the dynamics of the nucleons with a semiclassical molecular
dynamics model. Starting with an equilibrium configuration, we expand the
system homogeneously until we arrive to an asymptotic configuration (i. e. very
low final densities). We study the fragment distribution throughout this
expansion.
  Results: We found the typical regimes of the asymptotic fragment distribution
of an expansion: u-shaped, power law and exponential. Another key feature in
our calculations is that, since the interaction between protons is long range
repulsive, we do not have always an infinite fragment. We found that, as
expected, the faster the expansion velocity is, the quicker the infinite
fragment disappears.
  Conclusions: We have developed a novel graph-based tool for the
identification of infinite fragments, and found a transition from U-shaped to
exponential fragment mass distribution with increasing expansion rate.
