I disagree with your assertion. It's simply time value of money. As an investor, you don't want to wait decades for a higher risk low return that may never materialize, or the bond defaults entirely because your nuclear plant is shuttered for safety or political reasons. Could government insure the bond? Yes! But then they're subsidizing nuclear when that money could go into renewables and storage.

You didn’t disagree, you just affirmed it. The debt markets treat it as high risk precisely because so many parties can easily stop it.

Nobody refuses to invest in nuclear because of the negligible meltdown risk.