Given that uranium is one of the most common heavy elements in the crust, I think that the dwarves should be able to collect and refine it. Since normal uranium is quite stable it wouldn't give much damage until after prolonged exposure, which is why heavy utility dresses made from cloth and metal (preferably lead) would be made by tailors. GIven the density and melting point of uranium it would require a magma furnace to melt into bars.
In the next step, given dwarves' skill at mechanical constructing, they should be able to make enrichment centrifuges to turn the low-grade uranium into plutonium. The centrifuge itself could be driven by pack animals and would require a number of high-grade mechanisms as well as much metal. This off course would also require a skilled alchemist with an adjoining laboratory. Since enriching uranium yields more intensely active isotopes handling them would require master-woven utility suits.
Enriched isotopes could then either be used in a reactor to produce enormous steam, heat and/or pressure, perhaps to create a steam catapult for sub-orbital bombardment of other kingdoms, fortresses or hostile strongholds, or as delivery systems for orbital deliveries, which would tie in with DF's space arc. The material be packed into metal containers with conventional explosives (produced by alchemists) for being terminally introduced under intense pressure to achieve critical mass enough to set of a thermo-nuclear reaction. The production of this encasing would require skilled weaponsmiths, alchemists and mechanics.
Dwarves are hardy, of excellent constitution. Even so, children born, especially those in close proximity to enrichment centrifuges, reactors or weapon storages, and perhaps even to a lesser extent, those close to uranium stockpiles, should increasingly exhibit mutations. To make this simulationally more interesting, rather than create a high proportion of severely handicapped or inviable offspring, we could reduce the nativity but make the survivors have interesting effects: extra arms and eyes (which on the one hand make them good fighters due to multiple redundancies, but on the other hand requires specialised armour), or even mental deficiencies (tree-fancying).
The risk of nuclear strikes also makes deeper fortresses preferable in that they alleviate mortal anxiety and reduce unhappy thoughts.
Finally, weapon stockpiles have a new function in that they now can affect diplomacy and negotiations.
[ April 24, 2008: Message edited by: Mikademus ]