[graphene]

I don't know if this is what you're referring to, but a common application for government-owned supercomputers is simulating the degredation of nuclear warheads. The degradation of the fissile material as well as its surroundings is highly critical to a nation's security, and also very hard to model well.

Of course in an ideal world those cycles would be used to help cure cancer, but given that these warheads exist, it's probably a good idea to invest resources into getting an idea of what shape they're in.

[twoodfin]

The old way to do that was to blow one of them up every so often. The Nuclear Test Ban Treaty put a stop to that.