  Radiation controls the dynamics and energetics of many astrophysical
environments. To capture the coupling between the radiation and matter,
however, is often a physically complex and computationally expensive endeavour.
We develop a numerical tool to perform radiation-hydrodynamics simulations in
various configurations at an affordable cost. We build upon the finite volume
code MPI-AMRVAC to solve the equations of hydrodynamics on multi-dimensional
adaptive meshes and introduce a new module to handle the coupling with
radiation. A non-equilibrium, flux-limiting diffusion approximation is used to
close the radiation momentum and energy equations. The time-dependent radiation
energy equation is then solved within a flexible framework, accounting fully
for radiation forces and work terms and further allowing the user to adopt a
variety of descriptions for the radiation-matter interaction terms (the
'opacities'). We validate the radiation module on a set of standard testcases
for which different terms of the radiative energy equation predominate. As a
preliminary application to a scientific case, we calculate spherically
symmetric models of the radiation-driven and optically thick supersonic
outflows from massive Wolf-Rayet stars. This also demonstrates our code's
flexibility, as the illustrated simulation combines opacities typically used in
static stellar structure models with a parametrised form for the enhanced
line-opacity expected in supersonic flows. This new module provides a
convenient and versatile tool to perform multi-dimensional and high resolution
radiative-hydrodynamics simulations in optically thick environments with the
MPI-AMRVAC code. The code is ready to be used for a variety of astrophysical
applications, where a first target for us will be multi-dimensional simulations
of stellar outflows from Wolf-Rayet stars.
