from collections import OrderedDict
import re
import os
from six import string_types
from xml.etree import ElementTree as ET
import openmc
import openmc.checkvalue as cv
from openmc.data import NATURAL_ABUNDANCE, atomic_mass
[docs]class Element(object):
"""A natural element that auto-expands to add the isotopes of an element to
a material in their natural abundance. Internally, the OpenMC Python API
expands the natural element into isotopes only when the materials.xml file
is created.
Parameters
----------
name : str
Chemical symbol of the element, e.g. Pu
Attributes
----------
name : str
Chemical symbol of the element, e.g. Pu
scattering : {'data', 'iso-in-lab', None}
The type of angular scattering distribution to use
"""
def __init__(self, name=''):
# Initialize class attributes
self._name = ''
self._scattering = None
# Set class attributes
self.name = name
def __eq__(self, other):
if isinstance(other, Element):
if self.name != other.name:
return False
else:
return True
elif isinstance(other, string_types) and other == self.name:
return True
else:
return False
def __ne__(self, other):
return not self == other
def __gt__(self, other):
return repr(self) > repr(other)
def __lt__(self, other):
return not self > other
def __hash__(self):
return hash(repr(self))
def __repr__(self):
string = 'Element - {0}\n'.format(self._name)
if self.scattering is not None:
string += '{0: <16}{1}{2}\n'.format('\tscattering', '=\t',
self.scattering)
return string
@property
def name(self):
return self._name
@property
def scattering(self):
return self._scattering
@name.setter
def name(self, name):
cv.check_type('element name', name, string_types)
cv.check_length('element name', name, 1, 2)
self._name = name
@scattering.setter
def scattering(self, scattering):
if not scattering in ['data', 'iso-in-lab', None]:
msg = 'Unable to set scattering for Element to {0} which ' \
'is not "data", "iso-in-lab", or None'.format(scattering)
raise ValueError(msg)
self._scattering = scattering
[docs] def expand(self, percent, percent_type, enrichment=None,
cross_sections=None):
"""Expand natural element into its naturally-occurring isotopes.
An optional cross_sections argument or the OPENMC_CROSS_SECTIONS
environment variable is used to specify a cross_sections.xml file.
If the cross_sections.xml file is found, the element is expanded only
into the isotopes/nuclides present in cross_sections.xml. If no
cross_sections.xml file is found, the element is expanded based on its
naturally occurring isotopes.
Parameters
----------
percent : float
Atom or weight percent
percent_type : {'ao', 'wo'}
'ao' for atom percent and 'wo' for weight percent
enrichment : float, optional
Enrichment for U235 in weight percent. For example, input 4.95 for
4.95 weight percent enriched U. Default is None
(natural composition).
cross_sections : str, optional
Location of cross_sections.xml file. Default is None.
Returns
-------
isotopes : list
Naturally-occurring isotopes of the element. Each item of the list
is a tuple consisting of an openmc.Nuclide instance and the natural
abundance of the isotope.
"""
# Get the nuclides present in nature
natural_nuclides = set()
for nuclide in sorted(NATURAL_ABUNDANCE.keys()):
if re.match(r'{}\d+'.format(self.name), nuclide):
natural_nuclides.add(nuclide)
# Create dict to store the expanded nuclides and abundances
abundances = OrderedDict()
# If cross_sections is None, get the cross sections from the
# OPENMC_CROSS_SECTIONS environment variable
if cross_sections is None:
cross_sections = os.environ.get('OPENMC_CROSS_SECTIONS')
# If a cross_sections library is present, check natural nuclides
# against the nuclides in the library
if cross_sections is not None:
library_nuclides = set()
tree = ET.parse(cross_sections)
root = tree.getroot()
for child in root:
nuclide = child.attrib['materials']
if re.match(r'{}\d+'.format(self.name), nuclide) and \
'_m' not in nuclide:
library_nuclides.add(nuclide)
# Get a set of the mutual and absent nuclides. Convert to lists
# and sort to avoid different ordering between Python 2 and 3.
mutual_nuclides = natural_nuclides.intersection(library_nuclides)
absent_nuclides = natural_nuclides.difference(mutual_nuclides)
mutual_nuclides = sorted(list(mutual_nuclides))
absent_nuclides = sorted(list(absent_nuclides))
# If all natural nuclides are present in the library, expand element
# using all natural nuclides
if len(absent_nuclides) == 0:
for nuclide in mutual_nuclides:
abundances[nuclide] = NATURAL_ABUNDANCE[nuclide]
# If no natural elements are present in the library, check if the
# 0 nuclide is present. If so, set the abundance to 1 for this
# nuclide. Else, raise an error.
elif len(mutual_nuclides) == 0:
nuclide_0 = self.name + '0'
if nuclide_0 in library_nuclides:
abundances[nuclide_0] = 1.0
else:
msg = 'Unable to expand element {0} because the cross '\
'section library provided does not contain any of '\
'the natural isotopes for that element.'\
.format(self.name)
raise ValueError(msg)
# If some, but not all, natural nuclides are in the library, add
# the mutual nuclides. For the absent nuclides, add them based on
# our knowledge of the common cross section libraries
# (ENDF, JEFF, and JENDL)
else:
# Add the mutual isotopes
for nuclide in mutual_nuclides:
abundances[nuclide] = NATURAL_ABUNDANCE[nuclide]
# Adjust the abundances for the absent nuclides
for nuclide in absent_nuclides:
if nuclide in ['O17', 'O18'] and 'O16' in mutual_nuclides:
abundances['O16'] += NATURAL_ABUNDANCE[nuclide]
elif nuclide == 'Ta180' and 'Ta181' in mutual_nuclides:
abundances['Ta181'] += NATURAL_ABUNDANCE[nuclide]
elif nuclide == 'W180' and 'W182' in mutual_nuclides:
abundances['W182'] += NATURAL_ABUNDANCE[nuclide]
else:
msg = 'Unsure how to partition natural abundance of ' \
'isotope {0} into other natural isotopes of ' \
'this element that are present in the cross ' \
'section library provided. Consider adding ' \
'the isotopes of this element individually.'
raise ValueError(msg)
# If a cross_section library is not present, expand the element into
# its natural nuclides
else:
for nuclide in natural_nuclides:
abundances[nuclide] = NATURAL_ABUNDANCE[nuclide]
# Modify mole fractions if enrichment provided
if enrichment is not None:
# Calculate the mass fractions of isotopes
abundances['U234'] = 0.008 * enrichment
abundances['U235'] = enrichment
abundances['U238'] = 100.0 - 1.008 * enrichment
# Convert the mass fractions to mole fractions
for nuclide in abundances.keys():
abundances[nuclide] /= atomic_mass(nuclide)
# Normalize the mole fractions to one
sum_abundances = sum(abundances.values())
for nuclide in abundances.keys():
abundances[nuclide] /= sum_abundances
# Compute the ratio of the nuclide atomic masses to the element
# atomic mass
if percent_type == 'wo':
# Compute the element atomic mass
element_am = 0.
for nuclide in abundances.keys():
element_am += atomic_mass(nuclide) * abundances[nuclide]
# Convert the molar fractions to mass fractions
for nuclide in abundances.keys():
abundances[nuclide] *= atomic_mass(nuclide) / element_am
# Normalize the mass fractions to one
sum_abundances = sum(abundances.values())
for nuclide in abundances.keys():
abundances[nuclide] /= sum_abundances
# Create a list of the isotopes in this element
isotopes = []
for nuclide, abundance in abundances.items():
nuc = openmc.Nuclide(nuclide)
nuc.scattering = self.scattering
isotopes.append((nuc, percent * abundance, percent_type))
return isotopes