Hi Vaipan,

You may want to check 80,000 Hours' job board, selecting "nuclear security" as the area.

I'm aware that most of these jobs are government-issued and mostly kept private or sent by referrals

You're mostly right, but with some caveats. The jobs are publicly listed because they need applicants, but those who work in those industries tend not to (at least directly) label themselves online for security reasons. They'll have their job listed on their LinkedIn, but might be more cagey on forums etc. So they won't exactly be posting 'Come work with me at nuclear reactor xyz!'.
 

It may vary between industry and nation, but when I've worked in similar fields before most recruiting has been done by specialist recruiters, and by public posts on sites like Indeed. From memory 75% of the recruitment comes from those recruiters because the applicants tend to already have the right security clearances and vetting in place which significantly shortens the resources and time required to recruit them. The other 25% are fresh newbies like graduates who have to take the 'long road' but are preferred for more long-term hires. Many of these come from graduate schemes pitched to universities as well.

I imagine most qualified people for such roles will already have a network, and I should hope the clearances/vetting required, and so will be found by recruiters or be recommended roles anyway.
 

That said, there's nothing to stop a list of public posts being made and updated once a week or so - though geographical restrictions might impact that a bit. It might be helpful for people to get a sense of how many roles are around, what is required, and so on.