More accurately simulate the neutron flux profile

[OceanNuclear]

Description

Calculates the neutron flux profile in the first wall and blanket, using an extremely simplified diffusion-based model of an infinite slab sandwich.

Reason for choosing this model

It's better than not having a neutronics model.
It's also very simplified, so it can be calculated on the fly, without installing any deterministic neutron transport codes as dependency.

Checklist

I confirm that I have completed the following checks:

• My changes follow the PROCESS style guide
• I have justified any large differences in the regression tests caused by this pull request in the comments.
• I have added new tests where appropriate for the changes I have made.
• If I have had to change any existing unit or integration tests, I have justified this change in the pull request comments.
• If I have made documentation changes, I have checked they render correctly.
• I have added documentation for my change, if appropriate.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 58.64929% with 349 lines in your changes missing coverage. Please review.
✅ Project coverage is 50.23%. Comparing base (771e4d2) to head (7a08d64).
⚠️ Report is 286 commits behind head on main.

Files with missing lines	Patch %	Lines
process/models/neutronics/base.py	53.99%	219 Missing ⚠️
process/models/neutronics/data.py	64.28%	130 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3653      +/-   ##
==========================================
+ Coverage   47.81%   50.23%   +2.41%     
==========================================
  Files         143      154      +11     
  Lines       29993    30750     +757     
==========================================
+ Hits        14342    15447    +1105     
+ Misses      15651    15303     -348     

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[OceanNuclear]

The current state of this branch is:

• 1-group 2-layer model is written
• 1-group 2-layer model is fully tested (regression & unit tests)
• Multi-group model & >2-layer model is written
• Multi-group model & >2-layer model is tested
• incorporated real data
• Wrote function that accepts collapsed cross-section data (The downloading and collapsing of nuclear data has to be done by the user using a class that inherits from ENDFRecord.)
• Plotting is already available, example 1-group 2-layer model:

• Plotting is tested

[OceanNuclear]

@chris-ashe In the new folder structure, would you prefer the neutronics.py and neutronics_data.py to live in model/ or core/?

[je-cook]

I'm not sure descriptors is the right way to go. Most descriptor stuff I've written I have eventually rewritten without descriptors because I found a better way.

On the atomic data is there any reason we cant use something like periodictable which we use in elsewhere.

[OceanNuclear]

Happy to hear out examples of where descriptors were removed and see if I can implement anything similar. So far I'm unaware of any other ways of writing the code that wouldn't make it even more spaghetti: the @summarize_values decorator is doing a lot of heavy lifting and cutting the amount of code that I have to write down by half.

[je-cook]

Great, need to have a think but will let you know

[OceanNuclear]

periodictable sounds good, thanks for the suggestion, I'll likely replace the atomic_data.json with it, and possibly cutting down the size of the PR as a result.

I haven't figured out yet the right way of getting the abundance values in periodictable (in the same format as written at the top of the atomic_data.json), but I'm sure I'll find it eventually.

[OceanNuclear]

I'll add a bit of context for your consideration while thinking about refactoring away the descriptors:

Regarding the @summarize_values decorators, I think they can be improved upon as well, for the following reasons:

1. I observed redundancy. The NeutronFluxProfile class has the following list of ..._in_layer() methods:

• groupwise_neutron_flux_in_layer
• groupwise_neutron_current_in_layer
• groupwise_neutron_heating_in_layer
• groupwise_tritium_production_in_layer
  and it also has the following list of ..._in_layer() methods, which simply chooses the correct layer according to the x value:
• groupwise_neutron_flux_at
• groupwise_neutron_current_at
• groupwise_neutron_heating_at
• groupwise_tritium_production_at
  This suggest that there's definitely duplicated code that can be abstracted away.

2. I'm unhappy with the signature of the _in_layer methods:

• Current signature: (self, n: int, num_layer: int, x: float | npt.NDArray)
• Preferred signature: (self, num_layer: int, n: int, x: float | npt.NDArray), which aligns with the indexing order of the coefficients.

[OceanNuclear]

Listing all of the methods available under the NeutronProfile class (for my own use/sanity):

Continuous range of values per layer:

Quantity	methods (manually select layer)	methods (automatically select layer)	units
Neutron flux	(groupwise_)neutron_flux_in_layer	(groupwise_)neutron_flux_at	$m^{-2} s^{-1}$
Neutron current	(groupwise_)neutron_current_in_layer	(groupwise_)neutron_current_at	$m^{-2} s^{-1}$
Heating	(groupwise_)neutron_heating_in_layer	(groupwise_)neutron_heating_at	$W m^{-3} $
Tritium production	(groupwise_)tritium_production_in_layer	(groupwise_)tritium_production_at	mole $m^{-3}$

One value per layer:

Quantity	method(s)	unit
Neutron flux	(groupwise_)integrated_flux_in_layer	$m^{-2} s^{-1}$
Neutron current	(groupwise_)neutron_current_through_interface/(groupwise_)neutron_current_escaped	$m^{-2} s^{-1}$
Heating	(groupwise_)integrated_heating_in_layer	$W m^{-2}$
Tritium production	(groupwise_)integrated_tritium_production_in_layer	mole $m^{-2} s^{-1}$
linear heating density	groupwise_linear_heating_density_in_layer	$J m^{-1}$

This gives a total of 27 available methods.

[je-cook]

https://docs.python.org/3/library/collections.html#collections.defaultdict