Crippling diseconomies of scale.
Rooftop solar is an example of small scale decentralized energy production, maximum efficiency is not the only relevant metric.
> And you probably don't want dozens of "microreactors" scattered across cities
Why not? If they're considered safe and pass all inspections, what's the problem?
Rooftop solar does not have these issues.
Secondly although generating large amounts of power is more efficient in terms of generation, generating power close to the point of use is significantly more efficient in terms of power loss on the grid as I understand it.
They have diseconomies of scale. Some of the costs of a nuclear power plant scale sublinearly with power. Neutron economy is improved in a larger core. Larger turbines are more efficient than smaller turbines. It doesn't take 1000x as many operators to operate a NPP with 1000x the power output.
You'd also probably find similar issues with diesel generators, but small diesel generators do roaring trade and have great commercial applications.
Diesel generators have the advantage of being very cheap -- an order of magnitude cheaper than NPPs per unit power output -- and of having much of their total cost being fuel cost, so they can operate at lower capacity factor. But even so, we don't see large power plants composed of arrays of diesel microgenerators.
(The solution for current higher capacity factor diesel users, like say remote operation at mines, would be to supplement them with renewables and storage to reduce fuel costs. This is already happening.)
A significant problem with any small power plant is fixed costs. A 1 MW(e) plant (Antares is said to be between 100 kW(e) and 1 MW(e)) making power at 90% capacity factor and selling at $0.05/kWh will gross about $400K/year. A single full time employee, like a security guard, will cost a good chunk of that.
Oh sorry, I thought you were talking about efficiency. Ok, what is the cost is for these plants?
> A single full time employee, like a security guard, will cost a good chunk of that.
I dunno, a 1MW nuclear plant could end up being pretty small. It might easily be economic to install them places that already have security guards.
All of these reactors were built in the early 1960's and the last (MH-1A) was retired in 1978. All of them were operated in places that had lots of soldiers around (though McMurdo and Camp Century relied more on being really difficult to get to than actual sentries) And they were never replaced. Because even having guards already paid for didn't help the economics of the situation. Maybe things are different now. But I've yet to see any evidence for it.
They were all buried in shielded caskets, several feet deeper than normal.