  This paper reports the development of TOUCANS, a new Monte Carlo neutron
transport code fully written using the Geant4 toolkit. It aims at modeling
complex systems easily and rapidly, thanks to a simple key-value input file.
While its main focus is the transport of low energy neutrons -- below 20 MeV --
using evaluated cross-section libraries, it also takes advantage of the
state-of-the-art capabilities offered by Geant4 regarding the modeled
cross-sections for practically all particles at all energies. Hence it gives
access to non-specialists to a wide variety of applications involving different
particles, such as for instance the simulation of compact accelerator based
neutron sources (CANS) which initially motivated its development. It leverages
on recent implementations performed within Geant4 to provide both shielding
calculation capabilities (using Adaptive Multilevel Splitting, which is a fully
automated variance reduction technique) and criticality calculation
capabilities (to estimate the keff of a multiplicative system). It also
benefits from a tight coupling with CADMesh to readily import CAD models, with
NCrystal to extend the support of thermal neutron transport to crystals, with
FIFRELIN to increase compound nucleus de-excitation accuracy, and with FUNZ to
provide to the user parametric simulation capabilities (such as multi-objective
algorithms, calculation of Pareto sets, etc). Thanks to recent improvements of
the neutron physics within the Geant4 Neutron-HP package, the TOUCANS code can
be considered on-par with industrial neutron transport codes such as Tripoli-4
or MCNP in term of neutron physics accuracy. Its sources should be released
soon amongst Geant4 advanced examples.
