Question about “percent_type” argument of the new method “add_elements_from_formula()” introduced in version 0.12

New Ideas
1

Hi, developpers of OpenMC,

The “percent_type” argument of “add_element_from_formula” confuses me a little, since it seems that it should not be “wo”. Thus, it may be better to remove this argument and force “percent_type” as “ao”?

Another choice is adding “percent” argument for this method and adding the following modification:

  • If “percent_type” is “ao”, the atom percent of each element in formula is “percent” arg multiplied by atom number of this element in formula.
    (e.g. call add_element(percent = percent * atom_number, percent_type = “ao”, …) in the last part of the implementation of “add_element_from_formula()”))
  • If “percent_type” is “wo”, each element’s weight percent is “percent” arg multiplied by weight percent of this element in the chemical formula.
    (e.g. call add_element(percent = percent * element_weight_percent, percent_type = “wo”, …) in the last part of the implementation of “add_element_from_formula()”)

Then users can easily define a material composed of several compounds with different weight or molecule percent. For example, UO2-Gd2O3 fuel with a density a of 10.3g/cm3 can be defined as below:

fuel.add_elements_from_formula(“UO2”,percent=0.92,percent_type=”wo”,enrichment=3.2,percent_type=’wo’)

fuel.add_elements_from_formula(“Gd2O3”,percent=0.08,percent_type=”wo”,percent_type=’wo’)

fuel.set_density(10.3)

This modification can also make the arguments of this method similar to “add_element” and enables users to call both “add_element_from_formula” and “add_element” for the same openmc.Material object. Just my litte recommendation.

PS: why can’t I log in with my “staged” account?
cut

Best regards,
Yue

2

Nice idea. I agree that by itself, using add_elements_from_formula along with a weight percent doesn’t seem to make much sense. You are always welcome to make a pull request proposing a change to this function, which can be found in openmc/material.py.

Regarding this login issue, I have merged your previous staged account with the one you created, so all your prior posts should now be attributed to your new account.

3

Thanks, Paul

I have another question. Can users add the same nuclide multiple times into a material? If so, will this lead to longer time in simulation?

For example, does
fuel.add_nuclide("U235", "ao"=1)
fuel.add_nuclide("U235", "ao"=3)
have the same effect as
fuel.add_nuclide("U235", "ao"=4)?

I tried a simple example. If I add U235 to a material twice, the result seems still correct. However, if I add H1 twice to a moderator with “c_H_in_H2O”, openmc will raise the error below during simulation:
terminate called after throwing an instance of 'std::runtime_error'
what(): Did not sample any nuclide during collision.

4

If it works, it is by accident because materials were not really designed to have duplicate nuclides in them. I’ve had similar discussions with others about this and it is probably something we should fix. I can see two possible resolutions: 1) check for this at the time add_nuclide is called and combine the densities or 2) check for this at the time the material is exported to XML.