Any job giving out $100,000 reenlistment bonuses should be a red flag. Why do they have to go to such extremes to keep employees?
Why do they need to give out $100k bonuses (which is for 6 years, so about $18k per year)? Because they're competing with companies that can pay a lot better for higher quality of life (depends on your point of view I suppose) and slightly lower benefits.
As an example, at my 20 year point, I was being paid about $70k per year (about $24k was tax free, so it would come out to about $90k if it was all taxed). When I started my civilian job last year, I started in 6 figures, with annual bonuses (mine was in 5 figures, or would have been if I had worked there all year), with comparable benefits (medical has a higher deductible than Tricare, but dental insurance was about the same price with better coverage). I didn't go into Operations, by the way, so quality of life is really good (M-F, 7-4, with occasional weekends that pay straight time, not 1.5x for overtime). I also know guys who were able to get out at their 10 year point, go into Ops at more than what I make.
Like someone else said, if your son enlists, support him and make sure he knows to work like he plans on staying in for 20+ years. If he decides to get out before then, he'll have set himself up for pretty much anything when he gets out. I've had guys go into maintenance/operations at power plants and other industrial jobs, work for Google/Yahoo data centers, become teachers, or use their GI Bill go to college to become doctors and lawyers. And, yes, nuclear plants are still hiring, even the old ones, since a lot of the senior operators are starting to retire now, and have been for a decade. I'd avoid the plants in CA, they're not fond of nuclear power.