Severe Nuclear Accident Programme
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SNAP, the Severe Nuclear Accident Programme is a lagrangian type atmospheric dispersion model specialized on modelling dispersion of radioactive debris. A model description can be found at this link.

Meteorological input fields

SNAP needs meteorological driver data from NWP models in sigma or eta-hybrid model-levels, in the netcdf format. The minimum list of parameters are for the surface layer:

  • surface-air-pressure
  • precipitation (eventually split into convective and large-scale)
  • x- and y-wind-10m

And for the model layers:

  • x- and y-wind
  • air-temperature or potential-temperature
  • ap and b hybrid level values, or sigma level values

Parameter names can be specified in readfield_nc.f90.

And example on how to set up downloading of freely available meteorological data from the NOAA GFS model can be found under src/naccident/examples/gfs/


SNAP requires the following libraries and programs to be installed for compilation

  • fortran77/90 compiler, e.g. gfortran or ifort
  • NetCDF (netcdf > 4.1.1)
  • NetCDF-fortran
  • Python3 (optional)
  • git (optional)
  • fimex (optional)


Create a file in the src directory. Use e.g the file as a template. The most important parameters to modify are NCDIR and BINDIR, where the final files will be installed to. THE MIINC and MILIB should be uncommented.

In the src directory run then:

make install

This will install bsnap_naccident to BINDIR. Run SNAP using the command

bsnap_naccident snap.input

Examples of snap.input can be found in the directory src/naccident/examples/.


The master branch in git is used for development. Stable versions are tagged as 'vX.YY.ZZ'. Releases should also have a DOI for citation, see . For the user-interface snappy, we use tags like 'snappy-vX.YY.ZZ' with independent version numbers. Other tags are used internally.

The build system uses automatic versioning based on git tags and revision numbers and embeds this into the resulting program. If git or python3 is unavailable, this logic should be bypassed by setting the environment variable VERSION to some value, e.g.

env VERSION="some_version_number" make install


SNAP: Servere Nuclear Accident Programme
Copyright (C) 1992-2023  Norwegian Meteorological Institute

SNAP is free software: you can
redistribute it and/or modify it under the terms of the
GNU General Public License as published by the
Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program, i.e. see COPYING for more information.
If not, see <>.
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