I'm sure everyone has decided what great idea these are, except those who
will have one by the river they live next to. ahem.
I'm assuming water cooling but you can use sodium and other stuff, makes for
a better explosion if hings go wrong. grin.
There are some small sodium-cooled reactors but AFAIK this technology
has not been considered for small modular reactors. That's not really
because of problems with the sodium-water reaction (although the
Russians managed to have one at one of their research reactors).
One historical problem with reactor designs, in my view, is that the
initial concepts are developed by nuclear physicists and materials
scientists, then it is up to engineers to make them work. A subtle
problem with "pool-type" sodium cooled reactors is that you get waves on
the surface of the sodium pool. Because of the highly effective heat
transfer, these waves give you very high cycles of temperature
fluctuations for the sodium container at the sodium / cover gas
boundary. This causes thermal stresses and ultimately fatigue. When you
talk to fast reactor chemists, the nasty aggressive fluid that causes
all sorts of problems with materials is, in fact, the water in the steam
For the UK gas cooled reactors, on-line refuelling turned out to be much
more difficult than originally expected because of the environment for
the mechanical equipment, and also because faults like stuck elements
present a challenging safety case. But engineering and safety cases tend
to come along after the basic design concepts have been frozen.
Declaration of interest, 50 years of working on nuclear engineering
might have given me some prejudices. And that is as a physicist turned