If asked a question during the interview process about a time you had great difficulty completing a task and what you did to try to complete it--this would be a good topic.
First, discuss the entrance requirements, the A/school and NPS dedication and hard work you put in beyond the 8-hour school days it took to pass, the extra hours you put in trying to make it through prototype. Be honest, you are NOT expected to be perfect. Tell them that you just fell short and the nature of the work is that the standards cannot be compromised. So, you learned that when it comes to safety concerns, there is an attempt to correct, but never an attempt to compromise. You didn't do anything unsafe; however, each person must demonstrate a given level of knowledge and the program's safety record is partly founded on this aspect. Tell them I can appreciate and respect this knowing what I know what it takes to make a nuclear reactor run.
So, the turn around--POSITIVE--is that "I (you) was disheartened at first, to work so hard but fall short of my goal. So, I had to set new challenging, more realistic goals. I kept a positive attitude. I did not become a disciplinary problem or quit doing my best. Instead, I used the tools and strategies I learned from the nuclear power pipeline and applied them to my new goals. I believe I was more successful than I would have been had I not had the experience to learn from my failure. I learned that from failure comes an opportunity to try something different."
Just my two cents. I find it difficult to believe you became an STG. A/school gave you a rating: MM, EM, or the cream of the crop. Why did you get switched instead of going conventional? If this was a "reward" for your efforts, this would be a selling point because most people stick with what they earned their crow for in A/school. Or, were you an E-3 at the time?
Need input....