diff --git a/docs/source/methods/cross_sections.rst b/docs/source/methods/cross_sections.rst index a4d0f7d248..b9043a944d 100644 --- a/docs/source/methods/cross_sections.rst +++ b/docs/source/methods/cross_sections.rst @@ -66,6 +66,8 @@ Other Methods A good survey of other energy grid techniques, including unionized energy grids, can be found in a paper by Leppanen_. +.. _windowed_multipole: + Windowed Multipole Representation --------------------------------- @@ -141,6 +143,40 @@ but not always the case. Future library versions may eliminate this issue. The data format used by OpenMC to represent windowed multipole data is specified in :ref:`io_data_wmp`. +.. _temperature_treatment: + +Temperature Treatment +--------------------- + +At the beginning of a simulation, OpenMC collects a list of all temperatures +that are present in a model. It then uses this list to determine what cross +sections to load. The data that is loaded depends on what temperature method has +been selected. There are three methods available: + +:Nearest: Cross sections are loaded only if they are within a specified + tolerance of the actual temperatures in the model. + +:Interpolation: Cross sections are loaded at temperatures that bound the actual + temperatures in the model. During transport, cross sections for + each material are calculated using statistical linear-linear + interpolation between bounding temperature. Suppose cross + sections are available at temperatures :math:`T_1, T_2, ..., + T_n` and a material is assigned a temperature :math:`T` where + :math:`T_i < T < T_{i+1}`. Statistical interpolation is applied + as follows: a uniformly-distributed random number of the unit + interval, :math:`\xi`, is sampled. If :math:`\xi < (T - + T_i)/(T_{i+1} - T_i)`, then cross sections at temperature + :math:`T_{i+1}` are used. Otherwise, cross sections at + :math:`T_i` are used. This procedure is applied for pointwise + cross sections in the resolved resonance range, unresolved + resonance probability tables, and :math:`S(\alpha,\beta)` + thermal scattering tables. + +:Multipole: Resolved resonance cross sections are calculated on-the-fly using + techniques/data described in :ref:`windowed_multipole`. Cross + section data is loaded for a single temperature and is used in the + unresolved resonance and fast energy ranges. + ---------------- Multi-Group Data ---------------- diff --git a/docs/source/usersguide/input.rst b/docs/source/usersguide/input.rst index b724d7f109..38e997e9cf 100644 --- a/docs/source/usersguide/input.rst +++ b/docs/source/usersguide/input.rst @@ -729,11 +729,12 @@ The ```` element has an accepted value of "nearest", "interpolation", or "multipole". A value of "nearest" indicates that for each cell, the nearest temperature at which cross sections are given is to be applied, within a given tolerance (see :ref:`temperature_tolerance`). A value of -"interpolation" indicates that cross sections are to be interpolated between -temperatures at which nuclear data are present. A value of "multipole" indicates -that the windowed multipole method should be used to evaluate -temperature-dependent cross sections in the resolved resonance range (a -:ref:`windowed multipole library ` must also be available). +"interpolation" indicates that cross sections are to be linear-linear +interpolated between temperatures at which nuclear data are present (see +:ref:`temperature_treatment`). A value of "multipole" indicates that the +windowed multipole method should be used to evaluate temperature-dependent cross +sections in the resolved resonance range (a :ref:`windowed multipole library +` must also be available). *Default*: "nearest"