Severe Nuclear Accident Program (SNAP) has been developed at the Norwegian Meteorological Institute (met.no) for
modelling dispersion of radioactive debris in case of nuclear accidents. The model has been tested based on the data available from
the Chernobyl accident as well as from the ETEX experiments. The main user of model results is the Norwegian Radiation
Protection Authority (NRPA) which is responsible for calculating doses in case of a real accident. The model is fully operational for
NRPA as well as for met.no. Following a request from NRPA, the SNAP model was modified in such a way that not only dispersion
from nuclear accidents can be simulated, but dispersion from nuclear explosions as well. The source term for the model run in case
of nuclear explosion has been developed based on cooperation among Scandinavian countries. The source term includes mainly
particles of different size and density, which are subject to dry and wet deposition during atmospheric transport. Description of the
model and examples of the simulations related to hypothetical nuclear explosions are presented and discussed
