A: US Government enrichment facilities built to support nuclear weapons programs. https://www.world-nuclear.org/information-library/country-pr...
One could argue that the mines were subsidized by the federal government (so they could enrich and breed nuclear-grade materials), but that is a far cry from GP's claim that "Once the direct subsidy of nuclear via the military's nuclear weapons buildout went away, new plant construction... went way", which is incomparable to the degree of subsidization as the USSR and their dual-use for RBMK reactors (why else design a reactor with a positive void coefficient).
EDIT: I'm not sure whether you're really concerned about the buildout of nuclear powerplants or the evolution of the USA's policy with regards to the nuclear fuel cycle, but I hope I addressed both.
EDIT2: Also: The "big 3" enrichment locations that the military used would also sell to civilian nuclear powerplants. But that's a far cry reason to "subsidize" the construction of nuclear powerplants. This "fuel subsidization" goes on today (MOX fuels) and the American monopoly of uranium enrichment has been broken since 1970 with the formation of Urenco, so the commercial civilian powerplants have always had other places to purchase from (if a regulatory hassle). There's really not a lot of strong evidence that the mining and enrichment of uranium for nuclear weapons somehow subsidized the construction of civilian nuclear powerplants.
This is easily false. When you look at historical nuclear powerplant construction via the NRC, you see a flatline of new reactors starting 1979: Three Mile Island accident year.
In fact, Ford and Carter (a nuclear engineer himself) banned reprocessing of spent nuclear fuels even before that! Due to nonproliferation concerns (NPT had been around since 1970).
The USA kept building nuclear weapons through the 80's, so where were those "subsidies" for civilian powerplants?
The answer is the strong anti-nuclear movement in the 80's society that was the culmination of several different political, disaster, and cultural events. Not because we stopped building nukes in the 80's (we didn't stop).
Edit: One of the defining features of the US's civilian power fleet of reactors is exactly because of its adherence to non-proliferation, independence of military, and economic viability of "standing on its own two legs". Contrast the PWR designs with the power+breeder designs of the RBMK, the Soviet design to accidentally produce power while also producing weapons grade materials. This is why, in contrast, in the USA the reactors at national labs and military sites are so secure and secretive, and why the fuel used in US civilian powerplants are very tame in comparison: only the military is subsidizing it's own reactors for its own weapons grade fuel.