Request: Allow `UnshapedComponent`s to thermally-expand

Right now we have the UnshapedComponent which allows a user to just enter the volume/area fraction of a component without having to worry explicitly what shape the component is: https://github.com/terrapower/armi/blob/6dcedacdea505a508cf85119b4eb22953a1763e0/armi/reactor/components/__init__.py#L116-L121

This is nice, but right now these components are not allowed to thermally-expand: https://github.com/terrapower/armi/blob/6dcedacdea505a508cf85119b4eb22953a1763e0/armi/reactor/components/__init__.py#L150-L159

(Note that the method signature and docstring imply that thermal expansion is possible, but the actual implementation contradicts this)

It would be nice to allow such components to thermally-expand. Though we don’t know specific parameters of the shape like radius, pitch, or side-length, we could still get the thermally-expanded area of the component just by using the thermal expansion coefficient directly. Since the areal thermal expansion is just twice the linear thermal expansion, and all material classes will have the linear expansion coefficient, it seems like we should have all that is needed to calculate the thermally-expanded area of UnshapedComponents.

This would allow for modeling thermal expansion effects in models when only the volume fractions are known (common in fast reactor benchmark specifications).

[jakehader]

@keckler can this be closed now?

[keckler]

I do not believe that warning is referring to what we’re talking about here. It is warning the user to make Tinput=Thot for the Rectangle component so that the assembly doesn’t change pitch. Because that warning doesn’t describe the error that would occur if Tinput != Thot in the UnshapedComponents (i.e. you’d lose mass).