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Merge pull request openmc-dev#256 from walshjon/res_scat
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Improved resonance scattering methods
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@paulromano
paulromano committed Sep 11, 2014
2 parents 49f600e + 15c7677 commit 55fb5a5
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4 changes: 4 additions & 0 deletions docs/source/publications.rst
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Expand Up @@ -4,6 +4,10 @@
Publications
============

- Jonathan A. Walsh, Benoit Forget, and Kord S. Smith, "Accelerated sampling
of the free gas resonance elastic scattering kernel," *Ann. Nucl. Energy*,
**69**, 116--124 (2014). `<http://dx.doi.org/10.1016/j.anucene.2014.01.017>`_

- Benoit Forget, Sheng Xu, and Kord Smith, "Direct Doppler broadening in Monte
Carlo simulations using the multipole representation," *Ann. Nucl. Energy*,
**64**, 78--85 (2014). `<http://dx.doi.org/10.1016/j.anucene.2013.09.043>`_
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59 changes: 59 additions & 0 deletions docs/source/usersguide/input.rst
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Expand Up @@ -260,6 +260,65 @@ or sub-elements and can be set to either "false" or "true".

*Default*: true

``<resonance_scattering>`` Element
----------------------

The ``resonance_scattering`` element can contain one or more of the following
attributes or sub-elements:

:scatterer:
An element with attributes/sub-elements called ``nuclide``, ``method``,
``xs_label``, ``xs_label_0K``, ``E_min``, and ``E_max``. The ``nuclide``
attribute is the name, as given by the ``name`` attribute within the
``nuclide`` sub-element of the ``material`` element in ``materials.xml``,
of the nuclide to which a resonance scattering treatment is to be applied.
The ``method`` attribute gives the type of resonance scattering treatment
that is to be applied to the ``nuclide``. Acceptable inputs - none of
which are case-sensitive - for the ``method`` attribute are ``ARES``,
``CXS``, ``WCM``, and ``DBRC``. Descriptions of each of these methods
are documented here_. The ``xs_label`` attribute gives the label for the
cross section data of the ``nuclide`` at a given temperature. The
``xs_label_0K`` gives the label for the 0 K cross section data for the
``nuclide``. The ``E_min`` attribute gives the minimum energy above
which the ``method`` is applied. The ``E_max`` attribute gives the
maximum energy below which the ``method`` is applied. One example would
be as follows:

.. _here: http://dx.doi.org/10.1016/j.anucene.2014.01.017

.. code-block:: xml
<resonance_scattering>
<scatterer>
<nuclide>U-238</nuclide>
<method>ARES</method>
<xs_label>92238.72c</xs_label>
<xs_label_0K>92238.00c</xs_label_0K>
<E_min>5.0e-6</E_min>
<E_max>40.0e-6</E_max>
</scatterer>
<scatterer>
<nuclide>Pu-239</nuclide>
<method>dbrc</method>
<xs_label>94239.72c</xs_label>
<xs_label_0K>94239.00c</xs_label_0K>
<E_min>0.01e-6</E_min>
<E_max>210.0e-6</E_max>
</scatterer>
</resonance_scattering>
.. note:: If the ``resonance_scattering`` element is not given, the free gas,
constant cross section (``cxs``) scattering model, which has
historically been used by Monte Carlo codes to sample target
velocities, is used to treat the target motion of all nuclides. If
``resonance_scattering`` is present, the ``cxs`` method is applied
below ``E_min`` and the target-at-rest (asymptotic) kernel is used
above ``E_max``. An arbitrary number of ``scatterer`` elements may
be specified, each corresponding to a single nuclide at a single
temperature.

*Defaults*: None (scatterer), ARES (method), 0.01 eV (E_min), 1.0 keV (E_max)

``<run_cmfd>`` Element
----------------------

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161 changes: 121 additions & 40 deletions src/ace.F90
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Expand Up @@ -36,6 +36,7 @@ subroutine read_xs()
integer :: i ! index in materials array
integer :: j ! index over nuclides in material
integer :: k ! index over S(a,b) tables in material
integer :: n ! index over resonant scatterers
integer :: i_listing ! index in xs_listings array
integer :: i_nuclide ! index in nuclides
integer :: i_sab ! index in sab_tables
Expand Down Expand Up @@ -80,6 +81,30 @@ subroutine read_xs()
! array
call read_ace_table(i_nuclide, i_listing)

! 0K resonant scatterer information, if treating resonance scattering
if (treat_res_scat) then
do n = 1, n_res_scatterers_total
if (name == nuclides_0K(n) % name) then
nuclides(i_nuclide) % resonant = .true.
nuclides(i_nuclide) % name_0K = nuclides_0K(n) % name_0K
nuclides(i_nuclide) % name_0K = trim(nuclides(i_nuclide) % &
& name_0K)
nuclides(i_nuclide) % scheme = nuclides_0K(n) % scheme
nuclides(i_nuclide) % scheme = trim(nuclides(i_nuclide) % &
& scheme)
nuclides(i_nuclide) % E_min = nuclides_0K(n) % E_min
nuclides(i_nuclide) % E_max = nuclides_0K(n) % E_max
if (.not. already_read % contains(nuclides(i_nuclide) % &
& name_0K)) then
i_listing = xs_listing_dict % get_key(nuclides(i_nuclide) % &
& name_0K)
call read_ace_table(i_nuclide, i_listing)
end if
exit
end if
end do
end if

! Add name and alias to dictionary
call already_read % add(name)
call already_read % add(alias)
Expand Down Expand Up @@ -217,6 +242,7 @@ subroutine read_ace_table(i_table, i_listing)
real(8) :: awrs(16) ! list of atomic weight ratios (not used)
real(8) :: awr ! atomic weight ratio for table
logical :: file_exists ! does ACE library exist?
logical :: data_0K ! are we reading 0K data?
character(7) :: readable ! is ACE library readable?
character(10) :: name ! name of ACE table
character(10) :: date_ ! date ACE library was processed
Expand Down Expand Up @@ -320,19 +346,32 @@ subroutine read_ace_table(i_table, i_listing)

select case(listing % type)
case (ACE_NEUTRON)

! only read in a resonant scatterers info once
nuc => nuclides(i_table)
nuc % name = name
nuc % awr = awr
nuc % kT = kT
nuc % zaid = NXS(2)
data_0K = .false.
if (trim(adjustl(name)) == nuc % name_0K) then
data_0K = .true.
else
nuc % name = name
nuc % awr = awr
nuc % kT = kT
nuc % zaid = NXS(2)
end if

! read all blocks
call read_esz(nuc)
call read_nu_data(nuc)
call read_reactions(nuc)
call read_angular_dist(nuc)
call read_energy_dist(nuc)
call read_unr_res(nuc)
call read_esz(nuc, data_0K)

! don't read unnecessary 0K data for resonant scatterers
if (data_0K) then
continue
else
call read_nu_data(nuc)
call read_reactions(nuc)
call read_angular_dist(nuc)
call read_energy_dist(nuc)
call read_unr_res(nuc)
end if

! Currently subcritical fixed source calculations are not allowed. Thus,
! if any fissionable material is found in a fixed source calculation,
Expand All @@ -344,9 +383,12 @@ subroutine read_ace_table(i_table, i_listing)

! for fissionable nuclides, precalculate microscopic nu-fission cross
! sections so that we don't need to call the nu_total function during
! cross section lookups
! cross section lookups (except if we're dealing w/ 0K data for resonant
! scatterers)

if (nuc % fissionable) call generate_nu_fission(nuc)
if (nuc % fissionable .and. .not. data_0K) then
call generate_nu_fission(nuc)
end if

case (ACE_THERMAL)
sab => sab_tables(i_table)
Expand Down Expand Up @@ -377,43 +419,82 @@ end subroutine read_ace_table
! total xs, absorption xs, elastic scattering xs, and heating numbers.
!===============================================================================

subroutine read_esz(nuc)
subroutine read_esz(nuc, data_0K)

type(Nuclide), pointer :: nuc

logical :: data_0K ! are we reading 0K data?

integer :: NE ! number of energy points for total and elastic cross sections
integer :: i ! index in 0K elastic xs array for this nuclide

real(8) :: xs_cdf_sum = ZERO ! xs cdf value

! determine number of energy points
NE = NXS(3)
nuc % n_grid = NE

! allocate storage for energy grid and cross section arrays
allocate(nuc % energy(NE))
allocate(nuc % total(NE))
allocate(nuc % elastic(NE))
allocate(nuc % fission(NE))
allocate(nuc % nu_fission(NE))
allocate(nuc % absorption(NE))

! initialize cross sections
nuc % total = ZERO
nuc % elastic = ZERO
nuc % fission = ZERO
nuc % nu_fission = ZERO
nuc % absorption = ZERO

! Read data from XSS -- only the energy grid, elastic scattering and heating
! cross section values are actually read from here. The total and absorption
! cross sections are reconstructed from the partial reaction data.

XSS_index = 1
nuc % energy = get_real(NE)

! Skip total and absorption
XSS_index = XSS_index + 2*NE

! Continue reading elastic scattering and heating
nuc % elastic = get_real(NE)

! read in 0K data if we've already read in non-0K data
if (data_0K) then
nuc % n_grid_0K = NE
allocate(nuc % energy_0K(NE))
allocate(nuc % elastic_0K(NE))
allocate(nuc % xs_cdf(NE))
nuc % elastic_0K = ZERO
nuc % xs_cdf = ZERO
XSS_index = 1
nuc % energy_0K = get_real(NE)

! Skip total and absorption
XSS_index = XSS_index + 2*NE

! Continue reading elastic scattering and heating
nuc % elastic_0K = get_real(NE)

do i = 1, nuc % n_grid_0K - 1

! Negative cross sections result in a CDF that is not monotonically
! increasing. Set all negative xs values to ZERO.
if (nuc % elastic_0K(i) < ZERO) nuc % elastic_0K(i) = ZERO

! build xs cdf
xs_cdf_sum = xs_cdf_sum + (sqrt(nuc % energy_0K(i)) * nuc % elastic_0K(i) &
& + sqrt(nuc % energy_0K(i+1)) * nuc % elastic_0K(i+1)) / TWO &
& * (nuc % energy_0K(i+1) - nuc % energy_0K(i))
nuc % xs_cdf(i) = xs_cdf_sum
end do

else ! read in non-0K data
nuc % n_grid = NE
allocate(nuc % energy(NE))
allocate(nuc % total(NE))
allocate(nuc % elastic(NE))
allocate(nuc % fission(NE))
allocate(nuc % nu_fission(NE))
allocate(nuc % absorption(NE))

! initialize cross sections
nuc % total = ZERO
nuc % elastic = ZERO
nuc % fission = ZERO
nuc % nu_fission = ZERO
nuc % absorption = ZERO

! Read data from XSS -- only the energy grid, elastic scattering and heating
! cross section values are actually read from here. The total and absorption
! cross sections are reconstructed from the partial reaction data.

XSS_index = 1
nuc % energy = get_real(NE)

! Skip total and absorption
XSS_index = XSS_index + 2*NE

! Continue reading elastic scattering and heating
nuc % elastic = get_real(NE)

end if

end subroutine read_esz

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45 changes: 42 additions & 3 deletions src/ace_header.F90
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Expand Up @@ -112,6 +112,17 @@ module ace_header
real(8), allocatable :: absorption(:) ! absorption (MT > 100)
real(8), allocatable :: heating(:) ! heating

! Resonance scattering info
logical :: resonant = .false. ! resonant scatterer?
character(10) :: name_0K ! name of 0K nuclide, e.g. 92235.00c
character(16) :: scheme ! target velocity sampling scheme
integer :: n_grid_0K ! number of 0K energy grid points
real(8), allocatable :: energy_0K(:) ! energy grid for 0K xs
real(8), allocatable :: elastic_0K(:) ! Microscopic elastic cross section
real(8), allocatable :: xs_cdf(:) ! CDF of v_rel times cross section
real(8) :: E_min ! lower cutoff energy for res scattering
real(8) :: E_max ! upper cutoff energy for res scattering

! Fission information
logical :: fissionable ! nuclide is fissionable?
logical :: has_partial_fission ! nuclide has partial fission reactions?
Expand Down Expand Up @@ -147,6 +158,22 @@ module ace_header
procedure :: clear => nuclide_clear ! Deallocates Nuclide
end type Nuclide

!===============================================================================
! NUCLIDE0K temporarily contains all 0K cross section data and other parameters
! needed to treat resonance scattering before transferring them to NUCLIDE
!===============================================================================

type Nuclide0K

character(10) :: nuclide ! name of nuclide, e.g. U-238
character(16) :: scheme = 'ares' ! target velocity sampling scheme
character(10) :: name ! name of nuclide, e.g. 92235.03c
character(10) :: name_0K ! name of 0K nuclide, e.g. 92235.00c
real(8) :: E_min = 0.01e-6 ! lower cutoff energy for res scattering
real(8) :: E_max = 1000.0e-6 ! upper cutoff energy for res scattering

end type Nuclide0K

!===============================================================================
! DISTENERGYSAB contains the secondary energy/angle distributions for inelastic
! thermal scattering collisions which utilize a continuous secondary energy
Expand Down Expand Up @@ -342,12 +369,24 @@ subroutine nuclide_clear(this)

integer :: i ! Loop counter

if (allocated(this % grid_index)) deallocate(this % grid_index)
if (allocated(this % grid_index)) &
deallocate(this % grid_index)

if (allocated(this % energy)) &
deallocate(this % energy, this % total, this % elastic, &
this % fission, this % nu_fission, this % absorption)
if (allocated(this % heating)) deallocate(this % heating)
& this % fission, this % nu_fission, this % absorption)

if (allocated(this % energy_0K)) &
deallocate(this % energy_0K)

if (allocated(this % elastic_0K)) &
deallocate(this % elastic_0K)

if (allocated(this % xs_cdf)) &
deallocate(this % xs_cdf)

if (allocated(this % heating)) &
deallocate(this % heating)

if (allocated(this % index_fission)) deallocate(this % index_fission)

Expand Down
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