A little of everything..., I think you missed a rotation (start checking again for hiring this fall), plus, those jobs are highly competitive due to the economic situation all over the country..., so the listings don't last long. Besides the standard ex navy nukes and college grads applying, you are competing with people that may have left nuclear for "greener" pastures only to find that things aren't so green anymore..., so they are trying to get back in. Look around this site, there are new "trying to get back in" posts every couple of weeks.
My best advice is to keep trying, make checking all of the utility jobs sites part of your daily routine, you might start seeing some things pop up towards the end of the summer. Rumor around here (Beaver Valley) is that they may be trying to fill an NLO class near the end of the year. A friend on FB recently posted that he thinks his company will be hiring a class this fall.
I know that wasn't very encouraging, but it is simply a matter of timing, economics and competitiveness.
Hopefully some folks from other utilities will give their perspective.
Good luck!