  Nanopores of nanometer-size holes are very promising devices for many
applications: DNA sequencing, sensory, biosensoring and molecular detectors,
catalysis and water desalination. These applications require accurate control
over nanopores size. We report computer simulation studies of regrowth and
healing of graphene nanopores of different sizes ranging from 30 to 5 {\AA}. We
study mechanism, speed of nanopores regrowth and structure of healed areas in
the wide range of temperatures. We report existence of at least two distinct
healing mechanisms, one so called edge attachment where carbons are attached to
the edges of graphene sheet and another mechanism that involves atom insertion
directly into a sheet of graphene even in the absence of the edges. These
findings point a significantly more complicated pathways for graphene
annealing. They also provide an important enabling step in development of
graphene based devices for numerous nanotechnology applications.
