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Paul Romano
GitHub
commit
9fa0ca2b06
81 changed files with 33696 additions and 442 deletions
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@ -1,8 +1,8 @@
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.. _io_nuclear_data:
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========================
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Nuclear Data File Format
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========================
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=========================
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Nuclear Data File Formats
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=========================
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|
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---------------------
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Incident Neutron Data
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|
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@ -10,7 +10,7 @@ Incident Neutron Data
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**/**
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:Attributes:
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:Attributes: - **filetype** (*char[]*) -- String indicating the type of file
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- **version** (*int[2]*) -- Major and minor version of the data
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**/<nuclide name>/**
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@ -22,7 +22,9 @@ Incident Neutron Data
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- **atomic_weight_ratio** (*double*) -- Mass in units of neutron masses
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- **n_reaction** (*int*) -- Number of reactions
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:Datasets: - **energy** (*double[]*) -- Energy points at which cross sections are tabulated
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:Datasets:
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- **energy** (*double[]*) -- Energies in [eV] at which cross sections
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are tabulated
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**/<nuclide name>/kTs/**
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@ -31,7 +33,7 @@ temperature-dependent data set. For example, the data set corresponding to
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300 Kelvin would be located at `300K`.
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:Datasets:
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- **<TTT>K** (*double*) -- kT values (in eV) for each temperature
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- **<TTT>K** (*double*) -- kT values in [eV] for each temperature
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TTT (in Kelvin)
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**/<nuclide name>/reactions/reaction_<mt>/**
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@ -113,6 +115,92 @@ temperature-dependent data set. For example, the data set corresponding to
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:ref:`tabulated <1d_tabulated>`) -- The recoverable fission Q-value
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(Q_prompt + delayed neutrons + delayed photons + betas)
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|
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--------------------
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Incident Photon Data
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--------------------
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**/**
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:Attributes: - **filetype** (*char[]*) -- String indicating the type of file
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- **version** (*int[2]*) -- Major and minor version of the data
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**/<element>/**
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:Attributes: - **Z** (*int*) -- Atomic number
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:Datasets:
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- **energy** (*double[]*) -- Energies in [eV] at which cross sections
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are tabulated
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**/<element>/bremsstrahlung/**
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:Datasets: - **electron_energy** (*double[]*) -- Incident electron energy in [eV]
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- **photon_energy** (*double[]*) -- Outgoing photon energy as
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fraction of incident electron energy
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- **dcs** (*double[][]*) -- Bremsstrahlung differential cross section
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at each incident energy in [mb/eV]
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**/<element>/coherent/**
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:Datasets: - **xs** (*double[]*) -- Coherent scattering cross section in [b]
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- **integrated_scattering_factor** (:ref:`tabulated <1d_tabulated>`)
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-- Integrated coherent scattering form factor
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- **anomalous_real** (:ref:`tabulated <1d_tabulated>`) -- Real part
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of the anomalous scattering factor
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- **anomalous_imag** (:ref:`tabulated <1d_tabulated>`) -- Imaginary
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part of the anomalous scattering factor
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**/<element>/compton_profiles/**
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:Datasets: - **binding_energy** (*double[]*) -- Binding energy for each subshell in [eV]
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- **num_electrons** (*double[]*) -- Number of electrons in each subshell
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- **pz** (*double[]*) -- Projection of the electron momentum on the
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scattering vector in units of :math:`me^2 / \hbar` where :math:`m`
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is the electron rest mass and :math:`e` is the electron charge
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- **J** (*double[][]*) -- Compton profile for each subshell in units
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of :math:`\hbar / (me^2)`
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**/<element>/incoherent/**
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:Datasets: - **xs** (*double[]*) -- Incoherent scattering cross section in [b]
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- **scattering_factor** (:ref:`tabulated <1d_tabulated>`) --
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**/<element>/pair_production_electron/**
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:Datasets: - **xs** (*double[]*) -- Pair production (electron field) cross section in [b]
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**/<element>/pair_production_nuclear/**
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:Datasets: - **xs** (*double[]*) -- Pair production (nuclear field) cross section in [b]
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**/<element>/photoelectric/**
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:Datasets: - **xs** (*double[]*) -- Total photoionization cross section in [b]
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**/<element>/stopping_powers/**
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:Datasets: - **I** (*double*) -- Mean excitation energy in [eV]
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- **energy** (*double[]*) -- Energies in [eV]
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- **s_collision** (*double[]*) -- Collision stopping power in [eV-cm\ :sup:`2`\ /g]
|
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- **s_radiative** (*double[]*) -- Radiative stopping power in [eV-cm\ :sup:`2`\ /g]
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**/<element>/subshells/**
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:Attributes: - **designators** (*char[][]*) -- Designator for each shell, e.g. 'M2'
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**/<element>/subshells/<designator>/**
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:Attributes: - **binding_energy** (*double*) -- Binding energy of the subshell in [eV]
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- **num_electrons** (*double*) -- Number of electrons in the subshell
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:Datasets: - **transitions** (*double[][]*) -- Atomic relaxation data
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- **xs** (*double[]*) -- Photoionization cross section for subshell
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in [b] tabulated against the main energy grid
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:Attributes:
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- **threshold_idx** (*int*) -- Index on the energy
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grid of the reaction threshold
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-------------------------------
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Thermal Neutron Scattering Data
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-------------------------------
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|
|
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@ -32,6 +32,19 @@ standard deviation.
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*Default*: false
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-------------------------------------
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``<create_fission_neutrons>`` Element
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-------------------------------------
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The ``<create_fission_neutrons>`` element indicates whether fission neutrons
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should be created or not. If this element is set to "true", fission neutrons
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will be created; otherwise the fission is treated as capture and no fission
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neutron will be created. Note that this option is only applied to fixed source
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calculation. For eigenvalue calculation, fission will always be treated as real
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fission.
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*Default*: true
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--------------------
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``<cutoff>`` Element
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--------------------
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@ -55,31 +68,35 @@ you care. This element has the following attributes/sub-elements:
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*Default*: 1.0
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:energy:
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The energy under which particles will be killed.
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:energy_neutron:
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The energy under which neutrons will be killed.
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*Default*: 0.0
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-------------------------
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``<energy_grid>`` Element
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-------------------------
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:energy_photon:
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The energy under which photons will be killed.
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The ``<energy_grid>`` element determines the treatment of the energy grid during
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a simulation. The valid options are "nuclide", "logarithm", and
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"material-union". Setting this element to "nuclide" will cause OpenMC to use a
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nuclide's energy grid when determining what points to interpolate between for
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determining cross sections (i.e. non-unionized energy grid). Setting this
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element to "logarithm" causes OpenMC to use a logarithmic mapping technique
|
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described in LA-UR-14-24530_. Setting this element to "material-union" will
|
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cause OpenMC to create energy grids that are unionized material-by-material and
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use these grids when determining the energy-cross section pairs to interpolate
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cross section values between.
|
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*Default*: 1000.0
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*Default*: logarithm
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:energy_electron:
|
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The energy under which electrons will be killed.
|
||||
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.. note:: This element is not used in the multi-group :ref:`energy_mode`.
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*Default*: 0.0
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.. _LA-UR-14-24530: https://laws.lanl.gov/vhosts/mcnp.lanl.gov/pdf_files/la-ur-14-24530.pdf
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:energy_positron:
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The energy under which positrons will be killed.
|
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|
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*Default*: 0.0
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||||
|
||||
--------------------------------
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``<electron_treatment>`` Element
|
||||
--------------------------------
|
||||
|
||||
When photon transport is enabled, the ``<electron_treatment>`` element tells
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||||
OpenMC whether to deposit all energy from electrons locally (``led``) or create
|
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secondary bremsstrahlung photons (``ttb``).
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||||
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*Default*: ttb
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.. _energy_mode:
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|
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@ -153,8 +170,7 @@ the estimated eigenvalue. It has the following attributes/sub-elements:
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|||
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*Default*: None
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||||
.. note:: See section on the :ref:`trigger` for more information.
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.. note:: See section on the :ref:`trigger` for more information.
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||||
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||||
---------------------------
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``<log_grid_bins>`` Element
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@ -169,6 +185,8 @@ based on the recommended value in LA-UR-14-24530_.
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.. note:: This element is not used in the multi-group :ref:`energy_mode`.
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.. _LA-UR-14-24530: https://laws.lanl.gov/vhosts/mcnp.lanl.gov/pdf_files/la-ur-14-24530.pdf
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|
||||
---------------------------
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||||
``<max_order>`` Element
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||||
---------------------------
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|
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@ -259,11 +277,21 @@ out the file and "false" will not.
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|||
-----------------------
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||||
|
||||
This element indicates the number of neutrons to simulate per fission source
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iteration when a k-eigenvalue calculation is performed or the number of neutrons
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per batch for a fixed source simulation.
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iteration when a k-eigenvalue calculation is performed or the number of
|
||||
particles per batch for a fixed source simulation.
|
||||
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*Default*: None
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||||
|
||||
------------------------------
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||||
``<photon_transport>`` Element
|
||||
------------------------------
|
||||
|
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The ``<photon_transport>`` element determines whether photon transport is
|
||||
enabled. This element has no attributes or sub-elements and can be set to
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either "false" or "true".
|
||||
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*Default*: false
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||||
|
||||
---------------------
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``<ptables>`` Element
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||||
---------------------
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|
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@ -379,6 +407,11 @@ attributes/sub-elements:
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|||
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*Default*: 1.0
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:particle:
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The source particle type, either ``neutron`` or ``photon``.
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*Default*: neutron
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:file:
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If this attribute is given, it indicates that the source is to be read from
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a binary source file whose path is given by the value of this element. Note,
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||||
|
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@ -812,20 +845,6 @@ and 10. The verbosity levels are defined as follows:
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|||
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||||
*Default*: 7
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||||
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||||
-------------------------------------
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||||
``<create_fission_neutrons>`` Element
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||||
-------------------------------------
|
||||
|
||||
The ``<create_fission_neutrons>`` element indicates whether fission neutrons
|
||||
should be created or not. If this element is set to "true", fission neutrons
|
||||
will be created; otherwise the fission is treated as capture and no fission
|
||||
neutron will be created. Note that this option is only applied to fixed source
|
||||
calculation. For eigenvalue calculation, fission will always be treated as real
|
||||
fission.
|
||||
|
||||
*Default*: true
|
||||
|
||||
|
||||
-------------------------
|
||||
``<volume_calc>`` Element
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||||
-------------------------
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||||
|
|
|
|||
|
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@ -125,8 +125,8 @@ attributes/sub-elements:
|
|||
:type:
|
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The type of the filter. Accepted options are "cell", "cellfrom",
|
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"cellborn", "surface", "material", "universe", "energy", "energyout", "mu",
|
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"polar", "azimuthal", "mesh", "distribcell", "delayedgroup", and
|
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"energyfunction".
|
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"polar", "azimuthal", "mesh", "distribcell", "delayedgroup",
|
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"energyfunction", and "particle".
|
||||
|
||||
:bins:
|
||||
A description of the bins for each type of filter can be found in
|
||||
|
|
@ -299,6 +299,9 @@ should be set to:
|
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``energyfunction`` filters do not use the ``bins`` entry. Instead
|
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they use ``energy`` and ``y``.
|
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|
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:particle:
|
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A list of integers indicating the type of particles to tally ('neutron' = 1,
|
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'photon' = 2, 'electron' = 3, 'positron' = 4).
|
||||
|
||||
------------------
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``<mesh>`` Element
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|
|
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|
|
@ -12,7 +12,8 @@ Theory and Methodology
|
|||
geometry
|
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cross_sections
|
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random_numbers
|
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physics
|
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neutron_physics
|
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photon_physics
|
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tallies
|
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eigenvalue
|
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parallelization
|
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|
|
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|
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@ -1,8 +1,8 @@
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.. _methods_physics:
|
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.. _methods_neutron_physics:
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|
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=======
|
||||
Physics
|
||||
=======
|
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===============
|
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Neutron Physics
|
||||
===============
|
||||
|
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There are limited differences between physics treatments used in the
|
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continuous-energy and multi-group modes. If distinctions are necessary, each
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275
docs/source/methods/photon_physics.rst
Normal file
275
docs/source/methods/photon_physics.rst
Normal file
|
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@ -0,0 +1,275 @@
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.. _methods_photon_physics:
|
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|
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==============
|
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Photon Physics
|
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==============
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|
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Photons, being neutral particles, behave much in the same manner as neutrons,
|
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traveling in straight lines and experiencing occasional collisions which change
|
||||
their energy and direction. Photons undergo four basic interactions as they pass
|
||||
through matter: coherent (Rayleigh) scattering, incoherent (Compton) scattering,
|
||||
photoelectric effect, and pair/triplet production. Photons with energy in the
|
||||
MeV range may also undergo photonuclear reactions with an atomic nucleus. In
|
||||
addition to these primary interaction mechanisms, all processes other than
|
||||
coherent scattering can result in the excitation/ionization of atoms. The
|
||||
de-excitation of these atoms can result in the emission of electrons and
|
||||
photons. Electrons themselves also can produce photons by means of
|
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bremsstrahlung radiation.
|
||||
|
||||
-------------------
|
||||
Photon Interactions
|
||||
-------------------
|
||||
|
||||
Coherent (Rayleigh) Scattering
|
||||
------------------------------
|
||||
|
||||
The elastic scattering of a photon off a free charged particle is known as
|
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Thomson scattering. The differential cross section is independent of the energy
|
||||
of the incident photon. For scattering off a free electron, the differential
|
||||
cross section is
|
||||
|
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.. math::
|
||||
:label: thomson
|
||||
|
||||
\frac{d\sigma}{d\mu} = \pi r_e^2 ( 1 + \mu^2 )
|
||||
|
||||
where :math:`\mu` is the cosine of the scattering angle and :math:`r_e` is the
|
||||
classical electron radius. Thomson scattering can generally occur when the
|
||||
photon energy is much less than the rest mass energy of the particle.
|
||||
|
||||
In practice, most elastic scattering of photons off electrons happens not with
|
||||
free electrons but those bound in atoms. This process is known as Rayleigh
|
||||
scattering. The radiation scattered off of individual bound electrons combines
|
||||
coherently, and thus Rayleigh scattering is also known as coherent
|
||||
scattering. Even though conceptually we think of the photon interacting with a
|
||||
single electron, because the wave functions combine constructively it is really
|
||||
as though the photon is interacting with the entire atom.
|
||||
|
||||
The differential cross section for Rayleigh scattering is given by
|
||||
|
||||
.. math::
|
||||
:label: coherent-xs
|
||||
|
||||
\frac{d\sigma(E,E',\mu)}{d\mu} &= \pi r_e^2 ( 1 + \mu^2 )~\left| F(x,Z)
|
||||
+ F' + iF'' \right|^2 \\
|
||||
&= \pi r_e^2 ( 1 + \mu^2 ) \left [ ( F(x,Z)
|
||||
+ F'(E) )^2 + F''(E)^2 \right ]
|
||||
|
||||
where :math:`F(x,Z)` is a form factor as a function of the momentum transfer
|
||||
:math:`x` and the atomic number :math:`Z` and the term :math:`F' + iF''`
|
||||
accounts for `anomalous scattering`_ which can occur near absorption edges. In
|
||||
a Monte Carlo simulation, when coherent scattering occurs, we only need to
|
||||
sample the scattering angle using the differential cross section in
|
||||
:eq:`coherent-xs` since the energy of the photon does not change. In OpenMC,
|
||||
anomalous scattering is ignored such that the differential cross section
|
||||
becomes
|
||||
|
||||
.. math::
|
||||
:label: coherent-xs-openmc
|
||||
|
||||
\frac{d\sigma(E,E',\mu)}{d\mu} = \pi r_e^2 ( 1 + \mu^2 ) F(x, Z)^2
|
||||
|
||||
To construct a proper probability density, we need to normalize the
|
||||
differential cross section in :eq:`coherent-xs-openmc` by the integrated
|
||||
coherent scattering cross section:
|
||||
|
||||
.. math::
|
||||
:label: coherent-pdf-1
|
||||
|
||||
p(\mu) d\mu = \frac{\pi r_e^2}{\sigma(E)} ( 1 + \mu^2 ) F(x, Z)^2 d\mu.
|
||||
|
||||
Since the form factor is given in terms of the momentum transfer, it is more
|
||||
convenient to change variables of the probability density to :math:`x^2`. The
|
||||
momentum transfer is traditionally expressed as
|
||||
|
||||
.. math::
|
||||
:label: momentum-transfer
|
||||
|
||||
x = \kappa \alpha \sqrt{1 - \mu}
|
||||
|
||||
where :math:`\alpha` is the ratio of the photon energy to the electron rest
|
||||
mass, and the coefficient :math:`\kappa` can be shown to be
|
||||
|
||||
.. math::
|
||||
:label: kappa
|
||||
|
||||
\kappa = \frac{m_e c^2}{\sqrt{2}hc} \approx 29.14329,
|
||||
|
||||
where :math:`m_e` is the mass of the electron, :math:`c` is the speed of light
|
||||
in a vacuum, and :math:`h` is Planck's constant. Using :eq:`momentum-transfer`,
|
||||
we have :math:`\mu = 1 - [x/(\kappa\alpha)]^2` and :math:`d\mu/dx^2 =
|
||||
-1/(\kappa\alpha)^2`. The probability density in :math:`x^2` is
|
||||
|
||||
.. math::
|
||||
:label: coherent-pdf-x2
|
||||
|
||||
p(x^2) dx^2 = p(\mu) \left | \frac{d\mu}{dx^2} \right | dx^2 = \frac{2\pi
|
||||
r_e^2 A(\bar{x}^2,Z)}{(\kappa\alpha)^2 \sigma(E)} \left (
|
||||
\frac{1 + \mu^2}{2} \right ) \left ( \frac{F(x, Z)^2}{A(\bar{x}^2, Z)} \right ) dx^2
|
||||
|
||||
where :math:`\bar{x}` is the maximum value of :math:`x` that occurs for
|
||||
:math:`\mu=-1`,
|
||||
|
||||
.. math::
|
||||
:label: xmax
|
||||
|
||||
\bar{x} = \kappa \alpha \sqrt{2} = \frac{m_e c^2}{hc} \alpha,
|
||||
|
||||
and :math:`A(x^2, Z)` is the integral of the square of the form factor:
|
||||
|
||||
.. math::
|
||||
:label: coherent-int-ff
|
||||
|
||||
A(x^2, Z) = \int_0^{x^2} F(x,Z)^2 dx^2.
|
||||
|
||||
As you see, we have multiplied and divided the probability density by the
|
||||
integral of the squared form factor so that the density in :eq:`coherent-pdf-x2`
|
||||
is expressed as the product of two separate densities in parentheses. In OpenMC,
|
||||
a table of :math:`A(x^2, Z)` versus :math:`x^2` is pre-generated and used at
|
||||
run-time to do a table search on the cumulative distribution function:
|
||||
|
||||
.. math::
|
||||
:label: coherent-form-factor-cdf
|
||||
|
||||
\frac{\int_0^{x^2} F(x,Z)^2 dx^2}{\int_0^{\bar{x}^2} F(x,Z)^2 dx^2}
|
||||
|
||||
Once a trial :math:`x^2` value has been selected, we can calculate :math:`\mu`
|
||||
and perform rejection sampling using the Thomson scattering differential cross
|
||||
section. The complete algorithm is as follows:
|
||||
|
||||
1. Determine :math:`\bar{x}^2` using :eq:`xmax`.
|
||||
|
||||
2. Determine :math:`A_{max} = A(\bar{x}^2, Z)` using the pre-generated
|
||||
tabulated data.
|
||||
|
||||
3. Sample the cumulative density by calculating :math:`A' = \xi_1 A_{max}` where
|
||||
:math:`\xi_1` is a uniformly distributed random number.
|
||||
|
||||
4. Perform a binary search to determine the value of :math:`x^2` which satisfies
|
||||
:math:`A(x^2, Z) = A'`.
|
||||
|
||||
5. By combining :eq:`momentum-transfer` and :eq:`xmax`, calculate :math:`\mu =
|
||||
1 - 2x^2/\bar{x}^2`.
|
||||
|
||||
6. If :math:`\xi_2 < (1 + \mu^2)/2`, accept :math:`\mu`. Otherwise, repeat the
|
||||
sampling at step 3.
|
||||
|
||||
Incoherent (Compton) Scattering
|
||||
-------------------------------
|
||||
|
||||
Before we noted that the Thomson cross section gives the behavior for photons
|
||||
scattering off of free electrons valid at low energies. The formula for photon
|
||||
scattering off of free electrons that is valid for all energies can be found
|
||||
using quantum electrodynamics and is known as the Klein-Nishina_ formula after
|
||||
the two authors who discovered it:
|
||||
|
||||
.. math::
|
||||
:label: klein-nishina
|
||||
|
||||
\frac{d\sigma_{KN}}{d\mu} = \pi r_e^2 \left ( \frac{\alpha'}{\alpha} \right
|
||||
)^2 \left [ \frac{\alpha'}{\alpha} + \frac{\alpha}{\alpha'} + \mu^2 - 1
|
||||
\right ]
|
||||
|
||||
where :math:`\alpha` and :math:`\alpha'` are the ratios of the incoming and
|
||||
exiting photon energies to the electron rest mass energy equivalent (0.511 MeV),
|
||||
respectively. Although it appears that the outgoing energy and angle are
|
||||
separate, there is actually a one-to-one relationship between them such that
|
||||
only one needs to be sampled:
|
||||
|
||||
.. math::
|
||||
:label: compton-energy-angle
|
||||
|
||||
\alpha' = \frac{\alpha}{1 + \alpha(1 - \mu)}.
|
||||
|
||||
Note that when :math:`\alpha'/\alpha` goes to one, i.e., scattering is elastic,
|
||||
the Klein-Nishina cross section becomes identical to the Thomson cross
|
||||
section. In general though, the scattering is inelastic and is known as Compton
|
||||
scattering. When a photon interacts with a bound electron in an atom, the
|
||||
Klein-Nishina formula must be modified to account for the binding effects. As in
|
||||
the case of coherent scattering, this is done by means of a form factor. The
|
||||
differential cross section for incoherent scattering is given by
|
||||
|
||||
.. math::
|
||||
:label: incoherent-xs
|
||||
|
||||
\frac{d\sigma}{d\mu} = \frac{d\sigma_{KN}}{d\mu} S(x,Z) = \pi r_e^2 \left (
|
||||
\frac{\alpha'}{\alpha} \right )^2 \left [ \frac{\alpha'}{\alpha} +
|
||||
\frac{\alpha}{\alpha'} + \mu^2 - 1 \right ] S(x,Z)
|
||||
|
||||
where :math:`S(x,Z)` is the form factor. The approach in OpenMC is to first
|
||||
sample the Klein-Nishina cross section and then perform rejection sampling on
|
||||
the form factor. As in other codes, `Kahn's rejection method`_ is used for
|
||||
:math:`\alpha < 3` and a direct method by Koblinger_ is used for :math:`\alpha
|
||||
\ge 3`. The complete algorithm is as follows:
|
||||
|
||||
1. If :math:`\alpha < 3`, sample :math:`\mu` from the Klein-Nishina cross
|
||||
section using Kahn's rejection method. Otherwise, use Koblinger's direct
|
||||
method.
|
||||
|
||||
2. Calculate :math:`x` and :math:`\bar{x}` using :eq:`momentum-transfer` and
|
||||
:eq:`xmax`, respectively.
|
||||
|
||||
3. If :math:`\xi < S(x, Z)/S(\bar{x}, Z)`, accept :math:`\mu`. Otherwise repeat
|
||||
from step 1.
|
||||
|
||||
Doppler Energy Broadening
|
||||
+++++++++++++++++++++++++
|
||||
|
||||
LA-UR-04-0487_ and LA-UR-04-0488_
|
||||
|
||||
Compton Electrons
|
||||
+++++++++++++++++
|
||||
|
||||
|
||||
Photoelectric Effect
|
||||
--------------------
|
||||
|
||||
|
||||
Pair Production
|
||||
---------------
|
||||
|
||||
|
||||
-------------------
|
||||
Secondary Processes
|
||||
-------------------
|
||||
|
||||
New photons may be produced in secondary processes related to the main photon
|
||||
interactions discussed above. A Compton-scattered photon transfers a portion of
|
||||
its energy to the kinetic energy of the recoil electron, which in turn may lose
|
||||
the energy as bremsstrahlung radiation. The vacancy left in the shell by the
|
||||
ejected electron is filled through atomic relaxation, creating a shower of
|
||||
electrons and fluorescence photons. Similarly, the vacancy left by the electron
|
||||
emitted in the photoelectric effect is filled through atomic relaxation. Pair
|
||||
production generates an electron and a positron, both of which can emit
|
||||
bremsstrahlung radiation before the positron eventually collides with an
|
||||
electron, resulting in annihilation of the pair and the creation of two
|
||||
additional photons.
|
||||
|
||||
Atomic Relaxation
|
||||
-----------------
|
||||
|
||||
|
||||
Electron-Positron Annihilation
|
||||
------------------------------
|
||||
|
||||
|
||||
Bremsstrahlung
|
||||
--------------
|
||||
|
||||
.. _ttb:
|
||||
|
||||
Thick-Target Bremsstrahlung Approximation
|
||||
+++++++++++++++++++++++++++++++++++++++++
|
||||
|
||||
|
||||
.. _Koblinger: https://doi.org/10.13182/NSE75-A26663
|
||||
|
||||
.. _anomalous scattering: http://pd.chem.ucl.ac.uk/pdnn/diff1/anomscat.htm
|
||||
|
||||
.. _Kahn's rejection method: https://laws.lanl.gov/vhosts/mcnp.lanl.gov/pdf_files/aecu-3259_kahn.pdf
|
||||
|
||||
.. _Klein-Nishina: https://en.wikipedia.org/wiki/Klein%E2%80%93Nishina_formula
|
||||
|
||||
.. _LA-UR-04-0487: https://laws.lanl.gov/vhosts/mcnp.lanl.gov/pdf_files/la-ur-04-0487.pdf
|
||||
|
||||
.. _LA-UR-04-0488: https://laws.lanl.gov/vhosts/mcnp.lanl.gov/pdf_files/la-ur-04-0488.pdf
|
||||
|
|
@ -122,6 +122,7 @@ Constructing Tallies
|
|||
openmc.SpatialLegendreFilter
|
||||
openmc.SphericalHarmonicsFilter
|
||||
openmc.ZernikeFilter
|
||||
openmc.ParticleFilter
|
||||
openmc.Mesh
|
||||
openmc.Trigger
|
||||
openmc.TallyDerivative
|
||||
|
|
|
|||
|
|
@ -19,6 +19,9 @@ Core Classes
|
|||
openmc.data.CoherentElastic
|
||||
openmc.data.FissionEnergyRelease
|
||||
openmc.data.DataLibrary
|
||||
openmc.data.IncidentPhoton
|
||||
openmc.data.PhotonReaction
|
||||
openmc.data.AtomicRelaxation
|
||||
openmc.data.Decay
|
||||
openmc.data.FissionProductYields
|
||||
openmc.data.WindowedMultipole
|
||||
|
|
|
|||
|
|
@ -8,19 +8,19 @@ A Beginner's Guide to OpenMC
|
|||
What does OpenMC do?
|
||||
--------------------
|
||||
|
||||
In a nutshell, OpenMC simulates neutral particles (presently only neutrons)
|
||||
moving stochastically through an arbitrarily defined model that represents an
|
||||
real-world experimental setup. The experiment could be as simple as a sphere of
|
||||
metal or as complicated as a full-scale `nuclear reactor`_. This is what's known
|
||||
as `Monte Carlo`_ simulation. In the case of a nuclear reactor model, neutrons
|
||||
are especially important because they are the particles that induce `fission`_
|
||||
in isotopes of uranium and other elements. Knowing the behavior of neutrons
|
||||
allows one to determine how often and where fission occurs. The amount of energy
|
||||
released is then directly proportional to the fission reaction rate since most
|
||||
heat is produced by fission. By simulating many neutrons (millions or billions),
|
||||
it is possible to determine the average behavior of these neutrons (or the
|
||||
behavior of the energy produced, or any other quantity one is interested in)
|
||||
very accurately.
|
||||
In a nutshell, OpenMC simulates neutral particles (presently neutrons and
|
||||
photons) moving stochastically through an arbitrarily defined model that
|
||||
represents an real-world experimental setup. The experiment could be as simple
|
||||
as a sphere of metal or as complicated as a full-scale `nuclear reactor`_. This
|
||||
is what's known as `Monte Carlo`_ simulation. In the case of a nuclear reactor
|
||||
model, neutrons are especially important because they are the particles that
|
||||
induce `fission`_ in isotopes of uranium and other elements. Knowing the
|
||||
behavior of neutrons allows one to determine how often and where fission
|
||||
occurs. The amount of energy released is then directly proportional to the
|
||||
fission reaction rate since most heat is produced by fission. By simulating
|
||||
many neutrons (millions or billions), it is possible to determine the average
|
||||
behavior of these neutrons (or the behavior of the energy produced, or any
|
||||
other quantity one is interested in) very accurately.
|
||||
|
||||
Using Monte Carlo methods to determine the average behavior of various physical
|
||||
quantities in a system is quite different from other means of solving the same
|
||||
|
|
|
|||
|
|
@ -258,6 +258,49 @@ method using :attr:`Settings.resonance_scattering`.
|
|||
running the :meth:`IncidentNeutron.add_elastic_0K_from_endf` method
|
||||
may take several minutes to complete.
|
||||
|
||||
Photon Cross Sections
|
||||
---------------------
|
||||
|
||||
Photon interaction data is needed to run OpenMC with photon transport enabled.
|
||||
Some of this data, namely bremsstrahlung cross sections from `Seltzer and
|
||||
Berger`_, stopping powers from the `NIST ESTAR database`_, and Compton profiles
|
||||
calculated by `Biggs et al.`_ and available in the Geant4 G4EMLOW data file, is
|
||||
distributed with OpenMC. The rest is available from the NNDC, which provides
|
||||
ENDF data from the photo-atomic and atomic relaxation sublibraries of the
|
||||
ENDF/B-VII.1 library. By default, the :ref:`scripts_nndc` script will download
|
||||
the ENDF data in addition to the neutron and thermal scattering data, extract
|
||||
it, combine it with the data from other sources, and convert it to an HDF5
|
||||
library. Alternatively, the :ref:`scripts_photon` script can be used to
|
||||
download the photon data on its own and create the HDF5 library:
|
||||
|
||||
.. code-block:: sh
|
||||
|
||||
openmc-get-photon-data
|
||||
|
||||
As with neutrons and thermal scattering, it is possible to use the Python API
|
||||
directly to convert photon interaction data from an ENDF or ACE file to an HDF5
|
||||
file. The :class:`openmc.data.IncidentPhoton` class contains an
|
||||
:meth:`IncidentPhoton.from_ace` method that will generate photon data from an
|
||||
ACE table and an :meth:`IncidentPhoton.export_to_hdf5` method that writes the
|
||||
data to an HDF5 file:
|
||||
|
||||
::
|
||||
|
||||
u = openmc.data.IncidentPhoton.from_ace('92000.12p')
|
||||
u.export_to_hdf5('U.h5')
|
||||
|
||||
Similarly, the :meth:`IncidentPhoton.from_endf` method can be used to read
|
||||
photon data from an ENDF file. In the case, both the photo-atomic and atomic
|
||||
relaxation sublibrary files are required:
|
||||
|
||||
::
|
||||
|
||||
u = openmc.data.IncidentPhoton.from_endf('photoat-092_U_000.endf',
|
||||
'atom-092_U_000.endf')
|
||||
|
||||
Once the HDF5 files have been generated, a library can be created using the
|
||||
:class:`DataLibrary` class as described in :ref:`create_xs_library`.
|
||||
|
||||
-----------------------
|
||||
Windowed Multipole Data
|
||||
-----------------------
|
||||
|
|
@ -291,3 +334,6 @@ For an example of how to create a multi-group library, see
|
|||
.. _MCNP: http://mcnp.lanl.gov
|
||||
.. _Serpent: http://montecarlo.vtt.fi
|
||||
.. _TENDL: https://tendl.web.psi.ch/tendl_2015/tendl2015.html
|
||||
.. _Seltzer and Berger: https://www.sciencedirect.com/science/article/pii/0092640X86900148?via%3Dihub
|
||||
.. _NIST ESTAR database: https://physics.nist.gov/PhysRefData/Star/Text/ESTAR.html
|
||||
.. _Biggs et al.: https://www.sciencedirect.com/science/article/pii/0092640X75900303
|
||||
|
|
|
|||
|
|
@ -166,12 +166,57 @@ ENDF/B-VII.1. It has the following optional arguments:
|
|||
``openmc-get-nndc-data``
|
||||
------------------------
|
||||
|
||||
This script downloads `ENDF/B-VII.1 ACE data
|
||||
<http://www.nndc.bnl.gov/endf/b7.1/acefiles.html>`_ from NNDC and converts it to
|
||||
an HDF5 library for use with OpenMC. This script has the following optional
|
||||
arguments:
|
||||
This script downloads `ENDF/B-VII.1
|
||||
<http://www.nndc.bnl.gov/endf/b7.1/acefiles.html>`_ incident neutron ACE data
|
||||
and incident photon ENDF data from NNDC and converts it to an HDF5 library for
|
||||
use with OpenMC. This script has the following optional arguments:
|
||||
|
||||
-b, --batch Suppress standard in
|
||||
-b, --batch
|
||||
Suppress standard in
|
||||
|
||||
-n, --neutron_only
|
||||
Whether to exclude photon interaction/atomic data
|
||||
|
||||
.. _scripts_photon:
|
||||
|
||||
--------------------------
|
||||
``openmc-get-photon-data``
|
||||
--------------------------
|
||||
|
||||
This script downloads `ENDF data <http://www.nndc.bnl.gov/endf/b7.1/zips/>`_
|
||||
from NNDC for photo-atomic and atomic relaxation sublibraries and converts it
|
||||
to an HDF5 library for use with photon transport in OpenMC. This script has the
|
||||
following optional arguments:
|
||||
|
||||
-b, --batch
|
||||
Suppress standard in
|
||||
|
||||
-c, --cross-sections
|
||||
cross_sections.xml file to append libraries to
|
||||
|
||||
.. _scripts_compton:
|
||||
|
||||
-----------------------
|
||||
``openmc-make-compton``
|
||||
-----------------------
|
||||
|
||||
This script generates an HDF5 file called ``compton_profiles.h5`` that contains
|
||||
Compton profile data using an existing data library from `Geant4
|
||||
<http://geant4.cern.ch/>`_. Note that OpenMC includes this data file by default
|
||||
so it should not be necessary in practice to generate it yourself.
|
||||
|
||||
.. _scripts_stopping:
|
||||
|
||||
-------------------------------
|
||||
``openmc-make-stopping-powers``
|
||||
-------------------------------
|
||||
|
||||
This script generates an HDF5 file called ``stopping_power.h5`` that contains
|
||||
radiative and collision stopping powers and mean excitation energy pulled from
|
||||
the `NIST ESTAR database
|
||||
<https://physics.nist.gov/PhysRefData/Star/Text/ESTAR.html>`_. Note that OpenMC
|
||||
includes this data file by default so it should not be necessary in practice to
|
||||
generate it yourself.
|
||||
|
||||
.. _scripts_plot:
|
||||
|
||||
|
|
|
|||
|
|
@ -151,10 +151,19 @@ time and another that should be sampled 30% of the time::
|
|||
|
||||
settings.source = [src1, src2]
|
||||
|
||||
Finally, the :attr:`Source.particle` attribute can be used to indicate the
|
||||
source should be composed of particles other than neutrons. For example, the
|
||||
following would generate a photon source::
|
||||
|
||||
source = openmc.Source()
|
||||
source.particle = 'photon'
|
||||
...
|
||||
|
||||
settings.source = source
|
||||
|
||||
For a full list of all classes related to statistical distributions, see
|
||||
:ref:`pythonapi_stats`.
|
||||
|
||||
|
||||
---------------
|
||||
Shannon Entropy
|
||||
---------------
|
||||
|
|
@ -190,6 +199,52 @@ property::
|
|||
|
||||
settings.entropy_mesh = m
|
||||
|
||||
----------------
|
||||
Photon Transport
|
||||
----------------
|
||||
|
||||
In addition to neutrons, OpenMC is also capable of simulating the passage of
|
||||
photons through matter. This allows the modeling of photon production from
|
||||
neutrons as well as pure photon calculations. The
|
||||
:attr:`Settings.photon_transport` attribute can be used to enable photon
|
||||
transport::
|
||||
|
||||
settings.photon_transport = True
|
||||
|
||||
The way in which OpenMC handles secondary charged particles can be specified
|
||||
with the :attr:`Settings.electron_treatment` attribute. By default, the
|
||||
:ref:`thick-target bremsstrahlung <ttb>` (TTB) approximation is used to generate
|
||||
bremsstrahlung radiation emitted by electrons and positrons created in photon
|
||||
interactions. To neglect secondary bremsstrahlung photons and instead deposit
|
||||
all energy from electrons locally, the local energy deposition option can be
|
||||
selected::
|
||||
|
||||
settings.electron_treatment = 'led'
|
||||
|
||||
.. warning::
|
||||
Currently, collision stopping powers used in the TTB approximation come from
|
||||
the `NIST ESTAR database`_, which provides data for each element calculated
|
||||
using by default the material density at standard temperature and pressure.
|
||||
In OpenMC, stopping powers for compounds are calculated from this elemental
|
||||
data using Bragg's additivity rule. However, this is not a good
|
||||
approximation --- the collision stopping power is a function of certain
|
||||
quantities, such as the mean excitation energy and particularly the density
|
||||
effect correction, that depend on material properties. Data for constituent
|
||||
elements in a compound cannot simply be summed together, but rather these
|
||||
quantities should be calculated for the material. This treatment will be
|
||||
especially poor when the density of a material is different from the
|
||||
densities used in the NIST data.
|
||||
|
||||
.. note::
|
||||
Some features related to photon transport are not currently implemented,
|
||||
including:
|
||||
|
||||
* Tallying photon energy deposition.
|
||||
* Properly accounting for energy deposition in coupled n-p calculations.
|
||||
* Generating a photon source from a neutron calculation that can be used
|
||||
for a later fixed source photon calculation.
|
||||
* Photoneutron reactions.
|
||||
|
||||
--------------------------
|
||||
Generation of Output Files
|
||||
--------------------------
|
||||
|
|
@ -224,3 +279,5 @@ As an example, to write a statepoint file every five batches::
|
|||
|
||||
settings.batches = n
|
||||
settings.statepoint = {'batches': range(5, n + 5, 5)}
|
||||
|
||||
.. _NIST ESTAR database: https://physics.nist.gov/PhysRefData/Star/Text/ESTAR.html
|
||||
|
|
|
|||
Loading…
Add table
Add a link
Reference in a new issue