Soviets did not want czechoslovakia to have nuclear power, soviets wanted to be only one enriching, so czechs designed their own - gas cooled one, which did not needed enriched fuel. Wikipedia says "with help of soviets" but wikipedia forgot to say that soviet "input" was reason said reactor had so many problems.
And after that they were forced to use water cooled ones from soviets. But they built every screw in those 5 power plants. 15-20 reactors.
Also currently working plants were progressively updated and electrical output increased by 30 %.
Czechs were last in europe to have uranium mines, some of mines were used as slave labor camps for dissidents / political prisoners (60 000 i think) under soviet occupation (pre1989). They were mining radioactive ore with bare hands and lived in buildings without heating. ( clergy was big part of political prisoner population, connection with clergy man Mendel )