That seemed to be Carlo Rubbia's thinking. He invented the underground accelerator-linked lead-cooled fast reactor. The accelerator provides some of the neutrons necessary to achieve criticality. That makes it easy to stop the reaction - you just turn off the accelerator and the reaction has to stop because there are no longer enough neutrons to sustain it (the accelerator, of course, cannnot accelerate neutrons since they have neutral charge - it generates neutrons indirectly by firing protons at the lead which then, in turn, undergoes spalatial fission, releasing neutrons).
Here are diagram 1
and diagram 2
of the Rubbia Energy Amplifier.
Rubbia's idea was that the reactor had almost no way of melting down (a common scenario for a meltdown involves coolant pump failure and in Rubbia's design there are no pumps - the lead coolant relies instead on natural heat-driven circulation), so his reactor actually might not be a good example of one that is built underground to protect against the hazards of a meltown. But his reactor might still be a good example of building underground to avoid
a meltdown. Being underground, it is difficult for the coolant to escape. It would also seem to present a more challenging target for human-guided missile-airplanes.
On a side note, Richard Garwin thought of a variation on the Rubbia reactor where the accelerator is left out and the resulting neutron deficit is made up with either decommissioned weapons plutonium or uranium-233 bred from thorium-232. See Megawatts and Megatons
for details (Amazon lets you read about fifty scanned pages for free with their Search Inside this Book
feature - search for the keyword rubbia
. Also, Know Nukes
is a good place to ask nuke questions.