openmc.Element

class openmc.Element[source]

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
Variables:name (str) – Chemical symbol of the element, e.g. Pu
expand(percent, percent_type, enrichment=None, cross_sections=None)[source]

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 – Naturally-occurring isotopes of the element. Each item of the list is a tuple consisting of a nuclide string, the atom/weight percent, and the string ‘ao’ or ‘wo’.
Return type:

list

Notes

When the enrichment argument is specified, a correlation from ORNL/CSD/TM-244 is used to calculate the weight fractions of U234, U235, U236, and U238. Namely, the weight fraction of U234 and U236 are taken to be 0.89% and 0.46%, respectively, of the U235 weight fraction. The remainder of the isotopic weight is assigned to U238.