I'm sure someone else on the forum can explain the difference between AO,AUO, RO,SRO
I am sure I have done that before, but I guess it is time again.
AUO (Aux or Assistant Unit Operator) = NLO (Non-licensed Operator); these positions are the field operators. Not licensed by the NRC. Well-paid competent professionals making about the same as journeymen in the crafts. Good ones are worth their weight in gold.
RO (Reactor Operator) = RCO (Reactor Controls Operator) = Licensed operator; these positions are control room operators. Licensed by the NRC. Very well-paid professionals making more than the rest of the bargaining members on site.
SRO (Senior Reactor Operator) = US (Unit Supervisor) = Senior Licensed Operator; these positions are non-bargaining most places (and all TVA). Supervise the unit or the Work Control Center (WCC). May not be compensated for OT, but paid well.
SM (Shift Manager) is another SRO. He is serving in place of plant management on the back shift. Paid 10-25% more than SRO.
These terms are the standard. Other plants use various terms, but have the same positions. For example, TVA usually calls the RO a UO (Unit Operator) and FP&L calls the SM a NPS (Nuclear Plant Supervisor) and Beaver Valley calls (or at least did call) the US the ANUS (Assistant Nuclear Unit Supervisor).
Hope this helps.