Some thing I fear is, that if we have those extremely powerful weapons they will overshadow the cars and how the (probably lunatic) drivers handle them, which to my understanding should be the most extreme and impressive thing. It would turn into impressive technology instead of impressive drivers and how thy use whatever they have for the races.
And for the campaign I'd really like to see a diverse group of drivers like aliens, cybernetically enhanced humans (or aliens
), an AI or even a human brain in a jar put into a car.
The smallest nuclear explosion with a proper critical mass explosion (not dirty nuklear bombs) would about equal with 10-20 tons of TNT.
The GBU-43/B also known as "mother of all bombs" has about 11 tons. Its aftermath can be seen here.
With this we still ignore nuclear fallout.