IRIX and Software

Reactor simulation

I have seen them around but nothing that truly looks like it deserves to be called a simulator.
What I am talking about is a PWR (or equivalent) nuclear reactor simulator. the school has one for some reason in the science lab and it's just too damn cool to stop playing. I keep hearing of graphical open-source/freeware reactor simulators for linux (and hopefully something that can be worked for irix) but so far I have found nothing. Does anyone else know what I am talking about and where this software is available?
Remember, I am only looking for the stuff that is okay to freely distribute.
Image Image
^^Examples if you are still lost. yes, they are for windows but you still get the point. :)
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