  An accurate description of interactions between thermal neutrons (below 4 eV)
and materials is key to simulate the transport of neutrons in a wide range of
applications such as criticality-safety, reactor physics, compact
accelerator-driven neutron sources, radiological shielding or nuclear
instrumentation, just to name a few. While the Monte Carlo transport code
Geant4 was initially developed to simulate particle physics experiments, %-with
a large emphasis given on modeled cross-sections for all known particles at all
conceivable energies-, its use has spread to neutronics applications, requiring
evaluated cross-sections for neutrons and gammas between $0$ and $20$ MeV (the
so-called neutron High Precision -HP- package), as well as a proper offline or
on-the-flight treatment of these cross-sections. In this paper we will point
out limitations affecting Geant4 (version 10.07.p01) thermal neutron treatment
and associated nuclear data libraries, by using comparisons with the reference
Monte Carlo neutron transport code \tripoli, version 11, and we will present
the results of various modifications of the Geant4 neutron-HP package, required
to overcome these limitations. Also, in order to broaden the support of nuclear
data libraries compatible with Geant4, a nuclear processing tool has been
developed and validated allowing the use of the code together with ENDF-BVIII.0
and JEFF-3.3 libraries for example. These changes should be taken into account
in an upcoming Geant4 release.
