The physics of nuclear reactors push you towards making them big, and that means that there are correspondingly few of them, and they are all big civil engineering projects that are a little bit different from each other. This is a recipe for expensive and slow construction. The whole reason people are trying to make SMRs a thing is to try and get around this but it's not obvious there's an intersection between what the physics is happy to make efficient enough and a scale where you can actually get some learning rates and economies of 'scale' (which is more economies of unit volume than just in total how big something is).
The physics of nuclear reactors push you towards making them big, and that means that there are correspondingly few of them, and they are all big civil engineering projects that are a little bit different from each other. This is a recipe for expensive and slow construction. The whole reason people are trying to make SMRs a thing is to try and get around this but it's not obvious there's an intersection between what the physics is happy to make efficient enough and a scale where you can actually get some learning rates and economies of 'scale' (which is more economies of unit volume than just in total how big something is).