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Comment by nomel | Hacker News Reader

> Larger reactors are needed.

Genuine question: Why? Why not many smaller reactors? Small modular reactors seem pretty neat.

Is there an efficiency loss/total cost difference with smaller reactors?

Like most industrial sites, large reactors are much more economical than small ones. This is why nobody has built SMRs since the 1950s.

The basic premise of "have a factory that produces reactors small enough to ship" always made sense to my uneducated mind. Is there a flaw in the idea? It seems like it should be much cheaper than if every reactor were bespoke

With smaller reactors, one needs more of everything: reactor vessels, containment structures, cooling systems, generators, etc. This is why industrial facilities are usually built as large as reasonably possible, and why SMRs fell out of fashion as soon as GW-class reactors became feasible in the 1960s.

SMRs have their use. Depending on the model and design you can build them or even bring them [0] to a remote place where you want to build industry but the infrastructure and access to electrical grid is lacking. I'd argue nowadays they are even more important with the huge rise in electricity demand.

0 - https://en.wikipedia.org/wiki/Akademik_Lomonosov

Is that actual cost or projected cost because right now large reactors look prohibitively expensive meanwhile as you say we haven't really tried building SMR's on a production line.

Meanwhile Sweden is putting its money where its mouth is:

https://www.rolls-royce.com/media/press-releases/2026/15-06-...

It's less about money and more about timeline risks. Canada's BWRX will cost per MW by plan more than French flamanville with all delays. But unlike Flamanville it has chances to be put on the grid faster

Technically yes, but in the case of nuclear, regulatory cost is what matters more. If the paperwork needed for construction of one large scale reactor is much more expensive than that needed for construction of a hundred smaller identical reactors, then the SMRs will win.

because opex is cheaper. Modularity can be achieved in large units too

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