I'm currently doing a PhD in a STEM field, partly sponsored by a start-up company. I am potentially interested in continuing a research career either in the UK or the US, and have noticed that some of the labs that carry out this research are twinned with government bodies (e.g. US DoE). The nature of the research is not a case of top-level national security (e.g. nuclear weapons) although it is an area that is gaining a lot of traction due to global importance and scientific advancement (nuclear fusion). As far as I am aware, you only really need some form of security clearance for nuclear jobs if you are working with nuclear fission, due to the radioactive waste it produces. Nuclear fusion is much cleaner, as it doesn't produce any undesirable radioactive products.
I am aware that some nuclear jobs require some form of background check before starting - for example, a Baseline Personnel Security Standard (BPSS) check. This amounts to not much more than a criminal record check and address check, which I have successfully completed without any issues. However, I am conscious of the fact that some jobs require a higher level security clearance, which can probe into different aspects of your life.
I went through a dreadful mental health crisis just over a year ago, and obviously I am keen to avoid going through any sort of relapse or anything that might bring up upsetting thoughts or events relating to my episode. Even though I don't live some sort of double life as an axe-wielding homicidal maniac, naturally I am nervous about the prospect of bring probed on things that are not directly related to the job for which I am applying.
What level of clearance would I need if I was to work for a national/government laboratory, in the UK or in the US (for example, one twined with the DoE)? And would having mental health difficulties and being neurodivergent (autism/ADHD) be considered a red flag when it comes to completing any background checks? (just to be clear, I don't mean in terms of disability discrimination, but whether knowing that I have these disabilities and mental health issues could be interpreted as being more error-prone or more likely to divulge classified information without realising?)