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Update documentation to better describe temperature treatments

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Paul Romano 2016-09-15 09:20:58 +02:00
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36
docs/source/methods/cross_sections.rst
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@ -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
----------------

11
docs/source/usersguide/input.rst
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@ -729,11 +729,12 @@ The ``<temperature_method>`` 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 <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
<multipole_library>` must also be available).
*Default*: "nearest"