The issue is that you won't find an insurance company willing to insure a risk that they can't calculate. There's too little data to find a price here.
In the end, the government always bears the cost, because any catastrophic event will likely bankrupt the operator involved.
I think it's fair to count these catastrophic costs as subsidies, but they're not "untold gazillions". Estimates for the Fukushima disaster go up to about a trillion[1]. At the other side, the costs for Germany's "Energiewende" will run up over half a trillion[2], with relatively little to show for it[3].
In the end, the government always bears the cost, because any catastrophic event will likely bankrupt the operator involved.
I think it's fair to count these catastrophic costs as subsidies, but they're not "untold gazillions". Estimates for the Fukushima disaster go up to about a trillion[1]. At the other side, the costs for Germany's "Energiewende" will run up over half a trillion[2], with relatively little to show for it[3].
[1] https://www.cleanenergywire.org/factsheets/how-much-does-ger...
[2] https://cleantechnica.com/2019/04/16/fukushimas-final-costs-...
[3] https://www.cleanenergywire.org/news/energiewende-scores-mix...