Feature: Read process and process graph files only once #167
Description
Background and motivation
SaltProc currently reads the process and process graph files after every depletion step.
Description of idea
We should make changes in the algorithm in the app.py file to make it so that these only need to be read once at the start of runtime.
Implementation details
We'll need to modify the parameters to the reprocess_materials() and refill_materials() functions.
Potential snags
None