Back in the 1950's, as part of a study for putting ICBM bases in Greenland, the US Army built a 2MW reactor (PM-2A) and deployed it to the test base (Camp Century) in Greenland. It powered the camp for about three years, modulo a little problem where it was shut down for a while after a prototype (SL-1) killed two soldiers and a sailor in Idaho. In addition, the Navy operated another one (PM-3A, 1.75MW) for a decade in Antarctica at McMurdo Sound, until they cut it up and brought it back to the US. There was also the MH-1A (10MW- and the only one I've mentioned that used LEU instead of bomb-grade HEU) sitting on a freighter in Lake Gatun to power parts of the Panama Canal Zone.

All of these reactors were built in the early 1960's and the last (MH-1A) was retired in 1978. All of them were operated in places that had lots of soldiers around (though McMurdo and Camp Century relied more on being really difficult to get to than actual sentries) And they were never replaced. Because even having guards already paid for didn't help the economics of the situation. Maybe things are different now. But I've yet to see any evidence for it.