Ah but they do! As we discover those unique problems and how to solve them and how long it takes and the cost, our a priori cost estimate improves. The total numbers are so small it is really hard to say what the reliablity is. Newer plants tend to have more commonality and few parts, but we are still to discover all the many fantastic failure mechanisms. There are only 7 active Gen III reactors in the world, so it will be some time before we gain statistical confidence -- well after future designs are finalised.
> Ah but they do! As we discover those unique problems and how to solve them and how long it takes and the cost, our a priori cost estimate improves.
But it's not just our cost estimate that improves. Gen III reactors were designed with more data on how Gen I reactors were decommissioned than was available when Gen II reactors were being designed, and so on.
Finding a new decommissioning snag affects how you design the next reactor you build, but it doesn't really affect its predicted decommissioning cost because by that point you're aware of the issue and take steps to prevent it from occurring for the generation now being constructed.
