Provide explicit __all__ lists for files in openmc/deplete
containing classes that should be brought into the "primary"
API. This prevents cluttering the openmc.deplete namespace
caused by the wildcard imports
```
from .nuclide import *
...
```
The abc, cram, and helpers modules are imported simply as
```
from . import abc
from . import cram
from . import helpers
```
Slight reformatting of the depletion documentation. The "Primary API"
is presented at the top, including integrators and the Operator.
This section is followed by a "Minimal Example" that demonstrates
how one might instantiate an Operator, and use it for depletion.
The comm communicator is moved into the "Internal Classes and Functions"
section, as the end-user is less likely to interact with this directly.
Lastly, a section on "Abstract Base Classes" is provided and expanded,
documenting the purpose of specific ABCs.
* __call__ methods for Operator documented
* CRAM16 and CRAM48 are closer to the top of the page
* Document deplete and timed_deplete functions
* Abstract integrators documented as part of abc submodule
* Abstract operator helpers documented as part of abc submodule
If the system energy is found to be zero, then
Operator.__call__ will exit the simulation using
comm.Abort / sys.exit if no mpi4py. Without this, the
reaction rates will be scaled by power / 0, causing errors
downstream in setting material compositions.
Depending on settings.photon_transport, obtain the total
system energy from the 301 [heating] or 901 [heating-local]
scores. The former is used in coupled neutron-photon transport,
as this does not include any energy from neutrons or
photons, assuming these particles deposit their energy along
their life. MT901 is used for neutron transport and is the default,
e.g. if scores is None. This score includes energy from
prompt and delayed photons taken from MT458 data.
Related PR: #1344 - Ability to generate KERMAs assuming local
photon energy deposition
In using lists of containing integer reactions as
the scores, e.g.
```
t = openmc.lib.Tally()
t.scores = [901]
```
The setter would fail as the integers do not have an
encode method. This converts all incoming scores
to strings prior to passing values to the shared library.
Introduce a new subclass of EnergyHelper, EnergyScoreHelper,
that computes the system energy using the energy-deposition score.
This energy is fed back to the Operator to normalize reaction rates.
The energy from the tally is only stored on the helper on the
MPI process 0 as to avoid scaling the system energy by the number
of processes. During the Operator unpacking, the energy reported
by each process is reduced, as the previous implementations took
fission reaction rates from the "local materials", e.g. the
materials each process is responsible for depleting.
The tally results are shared across all processes and only
contains a single quantity, the tallied energy deposition across
all materials.
This mode is controlled by passing the "energy_mode" argument passed
to the Operator. The two options are "fission-q" [default and previous
behavior] and "energy-deposition" [new features]. If energy_mode indicates using
the energy deposition score, the user-supplied fission-q dictionary is not used.
(cherry picked from commit d566f3080f)
