Moving Spent Fuel pool off Core and onto Reactor

[john-science]

What is the change?

I moved the Spent Fuel Pool (SFP) object was on the Core instead of the Reactor.

I wanted to make the shift more cleanly than I did, but when you call Core.removeAssembly(), it wants to put the assembly in the SFP. Which means the Core needs to at least know the SFP is on the Reactor. But fine.

For some reason the

Why is the change being made?

The SPF is, objectively, not inside the Core. This was just wrong. And more importantly, counterintuitive for the users.

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes (location doc/release/0.X.rst) are up-to-date with any important changes.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in setup.py.

[albeanth]

@john-science does this resolve and close #876 ?

[albeanth]

Should there be an else for the case when this conditional fails? I don't expect it to for standard analyses, but there might be some corner case where a user inits a standalone Core and does stuff with it. In that case, they'd be thinking they're adding assemblies to the sfp, but really wouldn't and there wouldn't be any way of knowing so.

[john-science]

Well, imagine we said:

if self.parent is not None and  hasattr(self.parent, "sfp"):

It turns out hasattr() covers our bases so we don't need the "is not None" statement.

My major concerns are:

1. This is Python, you can build a "Core" object in vaccuum with no "Reactor" object.
2. Maybe someone wants to build multiple cores for an analysis, that should be allowable with them having to build multiple reactors.
   a. People who complain about ARMI usually complain that everything is too complicated because they can't just do the one thing they want without: building a whole reactor or building an Operator/Plugin. So I take it people would prefer they were freed from having to do so.

[albeanth]

Totally. I wasn't necessarily concerned with an is not None getting checked. I was thinking more about what happens in the case when there isn't a parent Reactor but a user still tries to add an assembly to r.sfp. In this current implementation, the user would never know that the assembly wasn't getting added as the code wouldn't tell them. The conditional would just evaluate to false and move on. So I was thinking maybe something akin to:

if hasattr(self.parent, "sfp"):
    self.parent.sfp.add(a1)
else:
    runLog.warning(f"There is no parent Reactor object for {self}, so {a1} will not be added to the spent fuel pool")

I believe @keckler had a similar thought as well. #1336 (comment)

[albeanth]

Same comment here on else for failing conditional.

[keckler]

I don't see anything here that conflicts with my models which employ the SFP, so I'm good with these changes!