Both Slovakia and Czechia are bit more "richer" than Poland (if you look at GDP (PPP) per capita), however Poland is much bigger economy - 5x size of Slovakia.
My guess is that because so far they had so much coal (largest reserves in Europe [4]), it was no brainer for them. However they are now in the process of commissioning nuclear power plant and plan to generate power from nuclear by 2033 [4]
[1] https://cs.wikipedia.org/wiki/Energetika_v_Česku#Výroba_elek... (second row - Jadro - is nuclear)
[2] https://en.wikipedia.org/wiki/Nuclear_energy_in_Slovakia
[3] https://www.seas.sk/mochovce-3-4-npp
[4] https://www.world-nuclear.org/information-library/country-pr...
I find that kind of hard to believe.
The smart way would be to commission half a dozen state of the art designs (the 2nd is cheaper easier than the first and so on) over a decade, the French did 15 reactors in about a decade and economies of scale and expertise make each successor simpler.
We desperately need more baseload supply to supplement on the ongoing renewables switch, the grid is is operating on the slimmest safety factor I can recall.
Though I guess Poland is still heated by NG, even if it’s coming from Russia. Heating with electricity is pretty inefficient.
But yeah, finding clean sources of electricity in winter is a challenge for a place like Poland. Poor hydroelectric resource. Only modest geothermal potential. Modest solar (not good for winter load). But wind potential isn't too bad in the north of the country and in the Baltic Sea. Nuclear power should be considered, however, as it is in Finland.
Nuclear has super high capital costs that usually must be subsidized by the state (and insurance definitely needs to be subsidized). Not to mention corruption has to be low enough that a disaster doesn’t occur. I can see less developed countries not being able to take this route.