====================
What's New in 0.13.0
====================

.. currentmodule:: openmc

-------
Summary
-------

This release of OpenMC includes several noteworthy and unique features. Most
importantly, mesh-based weight windows have been added and work with all
supported mesh types (regular, rectilinear, cylindrical, spherical, and
unstructured). Other additions include torus surfaces, an ability to place
CAD-based geometries in universes, a feature to export/import physical
properties, and a filter for particle time.

There is one breaking changing in the Python API. The
:class:`openmc.deplete.Operator` class used to accept :class:`~openmc.Geometry`
and :class:`~openmc.Settings` objects as its first two arguments; users now need
to pass a :class:`~openmc.model.Model` class instead.

The minimum supported Python version is now 3.6.

------------
New Features
------------

- Variance reduction using mesh-based weight windows is now possible with the
  :class:`~openmc.WeightWindows` class.
- Users can now model axis-aligned tori using the :class:`~openmc.XTorus`,
  :class:`~openmc.YTorus`, and :class:`~openmc.ZTorus` classes.
- DAGMC CAD-based geometries can now be placed in a universe using
  :class:`~openmc.DAGMCUniverse`, allowing users to combine CSG and CAD-based
  geometry in a single model.
- The C/C++ API has two new functions ``openmc_properties_export`` and
  ``openmc_properties_import`` with corresponding Python API bindings,
  :func:`~openmc.lib.export_properties` and
  :func:`~openmc.lib.import_properties`. These functions allow physical
  properties (temperatures, densities, material compositions) to be written to
  an HDF5 file and re-used for subsequent simulations.
- A new :class:`~openmc.stats.PowerLaw` univariate distribution
- The capabilities of the :class:`~openmc.Model` class have been substantially
  expanded (e.g., the :meth:`~openmc.model.Model.deplete`,
  :meth:`~openmc.model.Model.plot_geometry`, and
  :meth:`~openmc.model.Model.rotate_cells` methods).
- A new :class:`~openmc.TimeFilter` class that allows tallies to be filtered
  by the particle's time, which is now tracked.
- The :class:`~openmc.Source` class now allows you to specify a time
  distribution.
- The new :class:`~openmc.CylindricalMesh` and :class:`~openmc.SphericalMesh`
  can be used for mesh tallies over cylidrical and spherical meshes,
  respectively.
- Geometry plotting, which used to produce the files in the unusual .ppm format,
  now produces .png files by default.

---------
Bug Fixes
---------

- `Fix for shared fission bank memory errors <https://github.com/openmc-dev/openmc/pull/1856>`_
- `Make sure properties export only happens from root process <https://github.com/openmc-dev/openmc/pull/1864>`_
- `Fix pathlib use error in openmc-ace-to-hdf5 <https://github.com/openmc-dev/openmc/pull/1867>`_
- `Fix DAGMC and libMesh variable in CMake config <https://github.com/openmc-dev/openmc/pull/1870>`_
- `Fix bug associated with volume calc in MG mode <https://github.com/openmc-dev/openmc/pull/1889>`_
- `Add missing Settings.write_initial_source property <https://github.com/openmc-dev/openmc/pull/1895>`_
- `Bug fixes for specifying Materials.cross_sections <https://github.com/openmc-dev/openmc/pull/1898>`_
- `Removing Legendre filter in diffusion coefficient results <https://github.com/openmc-dev/openmc/pull/1909>`_
- `Ensure particles lost during event_calculate_xs are terminated <https://github.com/openmc-dev/openmc/pull/1911>`_
- `Fixed parsing of xsdir entries with a continuation line <https://github.com/openmc-dev/openmc/pull/1913>`_
- `openmc.RegularMesh attribute consistency <https://github.com/openmc-dev/openmc/pull/1922>`_
- `Ensure secondary particles below energy cutoff are not created <https://github.com/openmc-dev/openmc/pull/1924>`_
- `Allow compilation with g++ 11 <https://github.com/openmc-dev/openmc/pull/1938>`_
- `Depletion-related bug fixes <https://github.com/openmc-dev/openmc/pull/1946>`_
- `Miscellaneous bug fixes <https://github.com/openmc-dev/openmc/pull/1948>`_
- `Fixes for various bugs <https://github.com/openmc-dev/openmc/pull/1949>`_
- `Reset triggers in openmc_reset <https://github.com/openmc-dev/openmc/issues/1957>`_

------------
Contributors
------------

- `Hunter Belanger <https://github.com/HunterBelanger>`_
- `Helen Brooks <https://github.com/helen-brooks>`_
- `Andrew Davis <https://github.com/makeclean>`_
- `Valerio Giusti <https://github.com/valeriogiusti>`_
- `Jeff Hammond <https://github.com/jeffhammond>`_
- `Yuan Hu <https://github.com/YuanHu-PKU-KIT>`_
- `Andrew Johnson <https://github.com/drewejohnson>`_
- `Miriam Kreher <https://github.com/mkreher13>`_
- `Amanda Lund <https://github.com/amandalund>`_
- `Adam Nelson <https://github.com/nelsonag>`_
- `April Novak <https://github.com/aprilnovak>`_
- `Ariful Islam Pranto <https://github.com/AI-Pranto>`_
- `Gavin Ridley <https://github.com/gridley>`_
- `Paul Romano <https://github.com/paulromano>`_
- `Olaf Schumann <https://github.com/ojschumann>`_
- `Jonathan Shimwell <https://github.com/Shimwell>`_
- `Patrick Shriwise <https://github.com/pshriwise>`_
- `John Tramm <https://github.com/jtramm>`_