Although I don't work in the field I can tell you from living around it and reading the job requirements as to why there are no new juniors coming up, here are my observations.
1. Look at the outage schedule. You think its rough on seniors, how about people just starting out? Most of these people don't have 2 income families or a nest egg. You expect people to be able to work 1 maybe 2 jobs in the fall and the same in the spring and want to get into this business? Why would they want to train for a job that they have little hope of making a living at?
2. The majority of junior jobs require you to have 6 months+ experience, where are you going to get it? If you get to work 4 outages a year at about 8 weeks per outage that’s 32 weeks a year. You do the math...
3. In my humble opinion we began loosing our juniors when we stopped the practice of hiring wives and other family members to fill in the vacant slots. Remember the days when companies hired family members of techs to fill spaces for clerks, control point/junior and even decon jobs.
You took care of your seniors by giving them an extra income and you built up a pool of future workers. I myself worked several outages years ago but gave it up to stay in one spot and raise children. Heck even my mother back in the late seventies did courier work and delivered film badges.
Finally when you treat juniors with the same respect that you treat senior techs and this rules not only applies to fellow techs, but the utilities and the companies then maybe just maybe you'll get a few more juniors. Offer the same per diem, offer extra training, tell them the truth up front, offer some guidance, be a mentor; after all the junior by your side today just may save your ass one day