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208 lines
8.4 KiB
Python
208 lines
8.4 KiB
Python
from collections import OrderedDict
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import re
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import os
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from xml.etree import ElementTree as ET
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import openmc
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import openmc.checkvalue as cv
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from openmc.data import NATURAL_ABUNDANCE, atomic_mass
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class Element(str):
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"""A natural element that auto-expands to add the isotopes of an element to
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a material in their natural abundance. Internally, the OpenMC Python API
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expands the natural element into isotopes only when the materials.xml file
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is created.
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Parameters
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----------
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name : str
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Chemical symbol of the element, e.g. Pu
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Attributes
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----------
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name : str
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Chemical symbol of the element, e.g. Pu
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"""
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def __new__(cls, name):
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cv.check_type('element name', name, str)
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cv.check_length('element name', name, 1, 2)
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return super().__new__(cls, name)
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@property
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def name(self):
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return self
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def expand(self, percent, percent_type, enrichment=None,
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cross_sections=None):
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"""Expand natural element into its naturally-occurring isotopes.
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An optional cross_sections argument or the OPENMC_CROSS_SECTIONS
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environment variable is used to specify a cross_sections.xml file.
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If the cross_sections.xml file is found, the element is expanded only
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into the isotopes/nuclides present in cross_sections.xml. If no
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cross_sections.xml file is found, the element is expanded based on its
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naturally occurring isotopes.
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Parameters
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----------
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percent : float
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Atom or weight percent
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percent_type : {'ao', 'wo'}
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'ao' for atom percent and 'wo' for weight percent
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enrichment : float, optional
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Enrichment for U235 in weight percent. For example, input 4.95 for
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4.95 weight percent enriched U. Default is None
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(natural composition).
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cross_sections : str, optional
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Location of cross_sections.xml file. Default is None.
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Returns
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-------
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isotopes : list
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Naturally-occurring isotopes of the element. Each item of the list
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is a tuple consisting of a nuclide string, the atom/weight percent,
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and the string 'ao' or 'wo'.
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Notes
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-----
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When the `enrichment` argument is specified, a correlation from
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`ORNL/CSD/TM-244 <https://doi.org/10.2172/5561567>`_ is used to
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calculate the weight fractions of U234, U235, U236, and U238. Namely,
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the weight fraction of U234 and U236 are taken to be 0.89% and 0.46%,
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respectively, of the U235 weight fraction. The remainder of the isotopic
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weight is assigned to U238.
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"""
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# Get the nuclides present in nature
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natural_nuclides = set()
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for nuclide in sorted(NATURAL_ABUNDANCE.keys()):
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if re.match(r'{}\d+'.format(self), nuclide):
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natural_nuclides.add(nuclide)
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# Create dict to store the expanded nuclides and abundances
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abundances = OrderedDict()
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# If cross_sections is None, get the cross sections from the
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# OPENMC_CROSS_SECTIONS environment variable
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if cross_sections is None:
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cross_sections = os.environ.get('OPENMC_CROSS_SECTIONS')
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# If a cross_sections library is present, check natural nuclides
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# against the nuclides in the library
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if cross_sections is not None:
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library_nuclides = set()
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tree = ET.parse(cross_sections)
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root = tree.getroot()
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for child in root:
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nuclide = child.attrib['materials']
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if re.match(r'{}\d+'.format(self), nuclide) and \
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'_m' not in nuclide:
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library_nuclides.add(nuclide)
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# Get a set of the mutual and absent nuclides. Convert to lists
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# and sort to avoid different ordering between Python 2 and 3.
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mutual_nuclides = natural_nuclides.intersection(library_nuclides)
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absent_nuclides = natural_nuclides.difference(mutual_nuclides)
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mutual_nuclides = sorted(list(mutual_nuclides))
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absent_nuclides = sorted(list(absent_nuclides))
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# If all natural nuclides are present in the library, expand element
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# using all natural nuclides
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if len(absent_nuclides) == 0:
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for nuclide in mutual_nuclides:
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abundances[nuclide] = NATURAL_ABUNDANCE[nuclide]
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# If no natural elements are present in the library, check if the
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# 0 nuclide is present. If so, set the abundance to 1 for this
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# nuclide. Else, raise an error.
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elif len(mutual_nuclides) == 0:
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nuclide_0 = self + '0'
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if nuclide_0 in library_nuclides:
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abundances[nuclide_0] = 1.0
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else:
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msg = 'Unable to expand element {0} because the cross '\
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'section library provided does not contain any of '\
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'the natural isotopes for that element.'\
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.format(self)
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raise ValueError(msg)
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# If some, but not all, natural nuclides are in the library, add
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# the mutual nuclides. For the absent nuclides, add them based on
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# our knowledge of the common cross section libraries
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# (ENDF, JEFF, and JENDL)
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else:
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# Add the mutual isotopes
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for nuclide in mutual_nuclides:
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abundances[nuclide] = NATURAL_ABUNDANCE[nuclide]
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# Adjust the abundances for the absent nuclides
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for nuclide in absent_nuclides:
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if nuclide in ['O17', 'O18'] and 'O16' in mutual_nuclides:
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abundances['O16'] += NATURAL_ABUNDANCE[nuclide]
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elif nuclide == 'Ta180' and 'Ta181' in mutual_nuclides:
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abundances['Ta181'] += NATURAL_ABUNDANCE[nuclide]
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elif nuclide == 'W180' and 'W182' in mutual_nuclides:
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abundances['W182'] += NATURAL_ABUNDANCE[nuclide]
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else:
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msg = 'Unsure how to partition natural abundance of ' \
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'isotope {0} into other natural isotopes of ' \
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'this element that are present in the cross ' \
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'section library provided. Consider adding ' \
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'the isotopes of this element individually.'
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raise ValueError(msg)
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# If a cross_section library is not present, expand the element into
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# its natural nuclides
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else:
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for nuclide in natural_nuclides:
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abundances[nuclide] = NATURAL_ABUNDANCE[nuclide]
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# Modify mole fractions if enrichment provided
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if enrichment is not None:
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# Calculate the mass fractions of isotopes
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abundances['U234'] = 0.0089 * enrichment
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abundances['U235'] = enrichment
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abundances['U236'] = 0.0046 * enrichment
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abundances['U238'] = 100.0 - 1.0135 * enrichment
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# Convert the mass fractions to mole fractions
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for nuclide in abundances.keys():
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abundances[nuclide] /= atomic_mass(nuclide)
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# Normalize the mole fractions to one
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sum_abundances = sum(abundances.values())
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for nuclide in abundances.keys():
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abundances[nuclide] /= sum_abundances
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# Compute the ratio of the nuclide atomic masses to the element
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# atomic mass
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if percent_type == 'wo':
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# Compute the element atomic mass
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element_am = 0.
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for nuclide in abundances.keys():
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element_am += atomic_mass(nuclide) * abundances[nuclide]
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# Convert the molar fractions to mass fractions
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for nuclide in abundances.keys():
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abundances[nuclide] *= atomic_mass(nuclide) / element_am
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# Normalize the mass fractions to one
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sum_abundances = sum(abundances.values())
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for nuclide in abundances.keys():
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abundances[nuclide] /= sum_abundances
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# Create a list of the isotopes in this element
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isotopes = []
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for nuclide, abundance in abundances.items():
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isotopes.append((nuclide, percent * abundance, percent_type))
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return isotopes
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