You should expect some knowledge/experience questions, especially if you were an intern or co-op anywhere. As an interviewer, I would expect you to be somewhat knowledgeable about the plant and it's current performance as rated by the NRC (see the most NRC inspection report on the NRC website). If your background is not nuclear, I would expect you to have at least a basic understanding of how that particular plant works (BWR vs PWR). Be open about what you know and don't know, as nothing turns off an interviewer like someone spouting BS instead of just saying that's not an area they're familiar with. Be able to articulate a good reason why they should hire you, rather than one of the others in the interview pool (work ethic, experience, obvious desire to work at this particular plant, ties to the area, etc.).