rename private exchng member for sim ctx for clarity and consistency
rename private exchng member for sim ctx for clarity and consistency

Baaaaam/cyclus,Baaaaam/cyclus,gidden/cyclus,gidden/cyclus,hodger/cyclus,gidden/cyclus,hodger/cyclus,rwcarlsen/cyclus,mbmcgarry/cyclus,mbmcgarry/cyclus,gidden/cyclus,hodger/cyclus,rwcarlsen/cyclus,rwcarlsen/cyclus,mbmcgarry/cyclus,rwcarlsen/cyclus,mbmcgarry/cyclus,hodger/cyclus,Baaaaam/cyclus,hodger/cyclus