Most utilities will not accept a POSS result from another utility.
Sorry to necro bump this, but I feel this is misinformation, and may potentially mislead persons in the wrong way.
The following companies have accepted my POSS C score transfer from Entergy over the past couple years :
DTE Energy
Exelon
NextEra Energy
Florida Power And Light
Duke Energy
American Electric Power
Pacific Gas and Electric
Xcel Energy
NRG energy
I do appreciate this is a fairly incomplete list, compared to ALL the energy companies that exist; but I've applied to many places, and I've only had ONE company refuse a test score transfer (Consumers Energy). My list does include the lions share of nuclear plants in this country though. Some companies were easier than others (Florida Power and Light was a pleasure... Exelon was not...) and you may need to be a squeaky wheel to get the scores transferred in time, but its possible. Moral of the story is ASK THEM.