Python LEAPR interface

[gridley]

Description

This provides a simple object-oriented interface to LEAPR that has type and enum checking and better documentation of the parameters. Like other NJOY stuff, it is painful to write inputs by hand. It isn't necessarily something that I think we should merge, but want to get others' opinions on if this is desirable. I may just put it into its own standalone repo.

Here is an example of generating an S(a, b) table for water. As you can see, much easier to understand than a plain old NJOY input.

lr = openmc.data.njoy.LeaprRun()
lr.title = 'water from GROMACS MD run'

lr.material_number = 1
lr.delta_rho = 1e-3
lr.n_rho = 501
lr.zaid = 1001
lr.free_atom_xs = 20.478
lr.awr = .99917 
lr.n_scattering_atoms = 1

# Amelia found these to be good alpha/beta grids.
lr.alphas = [1.0023e-05, ... 1.5810e+03]
lr.betas  = [0.0000e+00, ... 3.9526e+02]

# These are the output from GROMACS. Note that the translational component is subtracted out,
# hence having the first value as zero.
rho_293 = [0.0000e+00, ... 5.3943e-02]
rho_400 = [0.0000e+00,... 7.7357e-02]
rho_500 = [0.0000e+00,..., 9.7432e-02]

lr.add_temperature_point(293, rho_293,
                         twt=1.0014e-02, c=3.1640e+00)
lr.add_temperature_point(400, rho_400,
                         twt=2.0212e-02, c=7.4306e+00)
lr.add_temperature_point(500, rho_500,
                         twt=2.8092e-02, c=1.2537e+01)
lr.run()

Checklist

• I have performed a self-review of my own code
• I have run clang-format on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[paulromano]

@gridley Thanks for bringing this up. I can definitely empathize with you on the pain of writing NJOY inputs. I do worry a little bit about scope creep in OpenMC and personally feel this particular use case would be better suited as a standalone repo.

[gridley]

Thanks Paul! Yeah I agree, will just put it on my account, then. 😃