Microsoft vs Micro-Kernel OSes

I am in a somewhat heated discussion with a colleague. Right now it's a matter of who is right and who is not, and I'm willing to admit being wrong, but I'd like some input from persons working in the relevant sectors.

My argument is that Microsoft Windows and even OSX are not used in mission-critical scenarios where mistakes mean the loss of life. My statements are that micro-kernel OSes like QNX are used at the core, and Windows is used for auxiliary tasks. Places I mentioned are in nuclear power plants, air traffic control, oil rigs, etc.

His argument is that Windows is used in all the places I've mentioned and more, and is at the heart of the operations in all those industries and others.

Having spoken with someone who works at a nuclear power plant I am certain this is not so, but I would love the feedback of others on this forum to see if I am right or wrong.

In reality - is Windows used at the core of these mission-critical applications where mistakes mean death? Is it a case where some companies use Windows at the core and others don't? And specifically to rebut a statement he made - are there any nuclear power plants anywhere in the world that have Microsoft Windows running at the core and managing the reactors?

Thank you all for your time and input.