Inherit XS Settings when creating a new XS ID

[mgjarrett]

What is the change?

When the cross section group manager creates a new XS ID that is based on a previous XS ID within CrossSectionGroupManager._getModifiedReprBlocks(), the new settings will now be inherited from the settings for the original XS group.

Why is the change being made?

Previously, a new XS ID would just be initialized with default cross section settings. Typically, when a user is creating a modified representative block with a new XS ID, they would want to keep the cross section settings from the original XS group.

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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.
• If any requirements were affected, mention it in the release notes.
• The dependencies are still up-to-date in pyproject.toml.

[jakehader]

Hi @mgjarrett - I might be misremembering but I think that we need to handle the case where the original XS settings are a link to an external cross section file or files. In that case we might need to default to 0D. Maybe I am misrememberinf why I implemented it this way.

[mgjarrett]

Hi @mgjarrett - I might be misremembering but I think that we need to handle the case where the original XS settings are a link to an external cross section file or files. In that case we might need to default to 0D. Maybe I am misrememberinf why I implemented it this way.

We shouldn't be trying to make a modified representative block based on a XS group that uses pregenerated cross sections. There is a warning logged in that situation:

armi/armi/physics/neutronics/crossSectionGroupManager.py

Lines 1255 to 1261 in 6163e94

	if self.xsTypeIsPregenerated(origXSID):
	runLog.warning(
	"A modified representative block for XS ID `{}` cannot be created because it is "
	"mapped to a pre-generated cross section set. Please ensure that this "
	"approximation is valid for the analysis.".format(origXSID),
	single=True,
	)

No error is thrown, and you could even end up not getting the warning, depending on the arguments passed into _getModifiedReprBlocks. Maybe we need stronger controls around this. I can't tell if the intention is actually to prevent the user from passing in pregenerated XS to this method, or just to warn and allow it anyway.