The economics of nuclear power versus coal-fired power generation is discussed with special account for scale effects. It is assumed that new plant capacity will be needed at the beginning of 1990s. The comparison of levelized power production costs indicates the apparent cost advantage of large 1000 MW nuclear units over coal-fire power plants, but the advantage is lost as the unit size is decreased to 500 MW. Further analyses show that the position of small nuclear units is not improved in the case of demand uncertainty. For nuclear alternatives the effect of scale economies largely outweighs the penalty of possible overcapacity.