In comp.sys.ibm.pc.hardware.chips Cydrome Leader wrote in part:
I find it unlikely they still don't know how nuclear weapons
work, especially considering they're mature technology and
they've been around for decades.

A two-stage thermonuclear warhead is a surprisingly complex
device -- look up Teller-Ulam. To work properly, the design has to
transfer enough light energy to ignite and burn the fusion secondary
before the fission primary shock waves disassemble the device.
There's _lots_ to simulate here in at least 2D over many timeslices.

Yes, we know how to make them go bang. Just follow the recipe.
But we don't always know the critical parts of that recipe, and
what parts we could change.

In general, the whole field of Finite-Element computation is
still short of cycles and can swallow everything available.
Multi-CPU clusters are still being built. Imagine being able
to simulate vehicle collisions -- designers would be able
to determine where metal could be added or other changes to
improve occupant survival.

-- Robert