The suicide issue is a no brainer when it comes to OPs. Like it was said we don't need any more head cases. The HP end of it might be a problem in some situations as far as surveys but I have seen some rather large techs sitting control points. They MMPI at the first plant may be a problem but after that, as long as you keep working at plants within a year, you shouldn't have to take the thing again. Some plants require you to take it no matter what so be prepared. As far as disclosure, will that could be a touchy point. Disclose what is required and don't add to the fire. Its knd of like being a witness in a trial, answer what you are asked and nothing more. The more your mouth runs the deeper the hole can become. If the brig issue was considered criminal you will have to disclose it no matter what and regardless of the discharge status. Do not lie!!!! If your chem background is strong I would recommend the chemistry side of things. It may fit your situation better than the HP/OPs side. HP on the DOE side is easy and doesn't have many of the issues of working in PPs. The conditions there are not as difficult, in most cases, as you will find working in the plants but the work environment can be a lot more difficult (i.e, weather, travel, location, etc.)
The only part of this I disagree with is the "no-brainer" part. There is no such thing.
Getting a job as an operator and getting unescorted access art two different things. Dude, you did a few things wrong. That doesn't mean that you are a threat to anybody's reactor. Your biggest obstacle isn't your service record, your medical record, or the MMPI. It is your level of maturity.
You are still a very young guy, and by your account you react to stress in a relatively immature way. But we have all been there at some point or another. The trick is to get over it. You need to spend a little time taking care of yourself before you worry about a career. Get your head clear, and your body too. You know as well as anyone that the two are interlocked.
When you are ready to put up with the bullshit that we call "working for a living" come on out and try. There won't be a lot of pressure to keep your weight down - though you should do it for your own physical and mental health. There will always be aggravations, but out here there are far fewer mind games, and people don't feel that they have the right to evaluate your worth as a human being every half-hour. Your supervisor won't be someone who got promoted based on signing a contract to work two more years; he/she will be a person who has earned the position, and will not continually tell you that you are worthless because you don't fit into his or her paradigm of the perfect operator.
Having said that, I will warn you that there are a lot of judgmental a$$h01es out here with major "god" complexes.
I can tell you this much about the nuclear industry that I have learned over the years.
1. There are a lot of (mostly ex-navy) people who believe that the job they are doing is so crucial to the future of the world and so difficult that only someone as perfect as they are could possibly do it.
2. If they are perfect, and you are not exactly like them, then you cannot be perfect.
3. If you are not perfect, you cannot do the job that they do; therefore if you are not exactly like them you cannot possibly work at the same job.
4. They are delusional. The delusion that one is perfect is a mental defect. Therefore, anyone who believes that he is perfect simply cannot be right.
5. Since no two people are alike, the standard of perfection is as variable as they are. So, if you DO impress one person as being perfect in his eyes, there will be 5,999,999,998 people who will not agree.
5. Finally, those who operate nuclear reactors fall into one of two categories - a.) those who are flawed and human and b.) those who refuse to admit that there is actually only one category.
Dude, stop judging yourself on what you have done - for whatever reason - in the past. Set a goal, a realistic goal, and live up to it. Good luck.