Most interviews I have been associated with in Commercial nukes in the last 5 years have been about 4 on 1. You might have a training manager or designee, a union steward or president, a superintendent or equivalent in OPS, and a Human Resources rep.
They have a standard script which they only deviate slightly based on your answers. Each will ask a question, but all can follow up. Questions are open-ended so you should be able to blow your own horn. Some of the questions are tough, such as, "Give us an example of a time when you didn't think far enough in advance and found yourself in unexpected circumstances. What did you do to rectify the situation?"
As you can imagine, you want to be responsive but don't nail yourself to the wall.
Have a realistic expectation of the interview. Example: if scheduled for 30 minutes (you can find out from HR) then only 5 minutes are reserved for your questions at the end.
You need to write out more questions than you will ask, and then only ask the ones not previously addressed by the information they have volunteered. Some people try to ask questions that make you look better than other candidates. (Are there many problems with aging workforce at this site, what are most people who were hired in this position doing ten years later, what lateral moves would be available from Shift Manager for your later years with the utility.)
It is not the time to discuss money or benefits unless they bring it up. For example, if they ask about certain credits / degree, you might inquire about their tuition assistance program.
Good luck.