Of course they could. Almost any country could.
Nonetheless, the cost to the constructor is such that without a military reason it doesn't make any sense to build one.
I expect North Korea will turn its attention to civilian nuclear power fairly soon now that the race to become a fully fledged nuclear power is complete. It would make economic sense to them given the industrial capacity, skills and resource base it has accumulated in the process of building the bomb.
One of the previous commenters above mentioned that China abandoned their own plans bought their design from Germany, so it's conceivable that if China had no military nuclear program they could have still built a reactor. (That's of course if the western world allowed it)