Ohio has had power generation that has been over 60% coal power for decades. It was 80% coal power.
Nuclear power has been generating 14% or more of the electricity in Ohio. Until recently it is clear that if Ohio did not have nuclear energy then that power would have come from coal power.
15–17 TWh of clean electricity every year instead of coal. Ohio nuclear plants started operation in 1978 and 1987.
Even in 2015 the estimated air pollution costs were $18 billion per year and was costing 2200 lives per year. The air in Ohio would have been 25% worse without the nuclear plants.
The two Ohio nuclear reactor have each been saving around $2 billion per year in avoided air pollution damage and improving health and saving lives (40 years for the older plants and 32 years for the younger plant). A total of over 12000 lives saved from reduced air pollution in Ohio and $120 billion in cumulative reduced air pollution.
Overall nuclear energy global and historically has offset coal power. It is avoiding coal use in China, Germany and Japan and the US. Only in the last 10–15 years is it avoiding a mix of coal and a significant amount of natural gas. This historically over the last 40+ years is over 2 million lives saved from avoided air pollution damage.