Define the characteristics of a canonical geometry

[gonuke]

Brainstorm the set of characteristics that a canonical geometry should contain, including:

• multiple volumes
• overlaps
• details to be removed
• non-solid volumes to be filled

[gonuke]

This will be complete when there is a new document (probably GH markdown) in this repo that defines the characteristics of a canonical geometry.

[gonuke]

Some things to think about:

• use of this geometry for MELCOR models, esp. flows that split and recombine