This argument causes some of the problems this argument tries to avoid.
> I'm opposed to the construction of new nuclear plants
The technology involved in nuclear plants has evolved tremendously, both in terms of efficiency and in terms of safety, but the technology of the new generation is fundamentally different.
> The biggest drawbacks of nuclear power (expensive and slow plant construction) are off the table with existing plants!
Old plants use outdated designs. Nobody would tolerate the 1972 Internet infrastructure nowadays, and yet Chernobyl was created that year, and is still in use.
The main reason old plants stick around instead of being replaced is that Greenpeace and Green parties influence each other into lobbying against building correct reactors.
Take Superphénix: a French Gen IV reactor started construction twelve years before the Chernobyl accident. Its design is still considered next-gen and highly favorable today.
Activists literally fired rocket-propelled grenades at it while it was being built. It got so bad that they had to shut it down.
They tried building a similar Gen IV reactor recently, ASTRID, that improved tremendously even compared to the advanced Superphénix, and it got cancelled six months ago because of lobbies.
So all that remains are old plants… designs that were essentially initial drafts meant to be replaced by better technology, but that never gets shut down because every replacement gets lobbied against.
Those old designs have awful properties, so yeah, we get Chernobyl and Fukushima. We would have had neither if people had let replace the oldest generation. But because of Greenpeace, people died, and fear rose, when all this was unnecessary.