Again, there is a lot of opportunity in nuclear science, and it doesn't appear that it'll be going the way of the Victorian Age's Phrenology. That being said, more and more people are going into this field; more and more people means more and more competition.
If you're serious and it intrigues and excites you, again, getting the right education (and most likely, lots of it) will serve you well. And just like working in almost any industry, complacency in your job will not help your case when someone younger wants to take your place…at half the salary. In other words, this is a job where you'll constantly be learning, discovering, and re-educating yourself; just keep moving forward and you'll do fine.