  Carbon-rich grains with isotopic anomalies compared to the Sun are found in
primitive meteorites. They were made by stars, and carry the original stellar
nucleosynthesis signature. Silicon carbide grains of Type X and C, and
low-density graphites condensed in the ejecta of core-collapse supernovae. We
present a new set of models for the explosive He shell and compare them with
the grains showing 12C/13C and 14N/15N ratios lower than solar. In the stellar
progenitor H was ingested into the He shell and not fully destroyed before the
explosion. Different explosion energies and H concentrations are considered. If
the SN shock hits the He-shell region with some H still present, the models can
reproduce the C and N isotopic signatures in C-rich grains. Hot-CNO cycle
isotopic signatures are obtained, including a large production of 13C and 15N.
The short-lived radionuclides 22Na and 26Al are increased by orders of
magnitude. The production of radiogenic 22Ne from the decay of 22Na in the He
shell might solve the puzzle of the Ne-E(L) component in low-density graphite
grains. This scenario is attractive for the SiC grains of type AB with 14N/15N
ratios lower than solar, and provides an alternative solution for SiC grains
originally classified as nova grains. Finally, this process may contribute to
the production of 14N and 15N in the Galaxy, helping to produce the 14N/15N
ratio in the solar system.
