[cyberax]

> The last design plans I saw one could fit within a single city block, buried under ground with only 1 story exposed.

This is a completely unrealistic plan, designed to lure investors.

An SMR meltdown will produce enough radioactive contamination to make a small city unlivable, at least for a while. So you'll need a full containment building. You'll need emergency generators, coolant pumps, etc.

Then you have a question of security, an easily accessible reactor will provide a great target for terrorism. So you'll need a perimeter around it with armed guards.

Then there's a question of control. A working reactor requires at least two trained nuclear engineers on duty at all times. So each reactor will likely need around 15 highly specialized engineers. That will have to live within a commuting distance.

Sounds bad already. But that's not all. There's also a question of inspections, something like the NRC can be reasonably expected to regulate several hundred reactors. They are not prepared to inspect many thousands of reactors. And the last thing I personally want is a "self-regulating" nuclear industry.

Any _realistic_ SMR power plant will look just like a regular large nuclear plant, except that it'll have multiple reactor units instead of just one large reactor.

[kwhitefoot]

There are designs for modular reactors that are inherently safe. Using subcritical reactors and a particle beam. See Aker Solutions: https://www.neimagazine.com/features/featureaker-s-ads-uses-...

Haven't seen any news from them recently though.

[cyberax]

They are not "inherently safe". Reactors that produce power (in large quantities) are dangerous because fission products are radioactive, and they produce energy even after the chain reaction stops. So once cooling is lost, these fission products can melt through the reactor vessel and escape the confinement.

Also, accelerator-driven reactors are just bonkers. They make no freaking sense for power generation. They are being investigated because they can produce very energetic neutrons, in quantities that are large enough to transmute some long-lived nuclear waste.

[kwhitefoot]

Are you implying that they do not produce more energy than they consume? Conventional commercial reactors release only a tiny fraction of the energy available in the fuel. Accelerator driven reactors make it possible to release more of it. They can also make effective use of thorium.

[cyberax]

No. I'm implying that they are completely impractical.

You need to have a system with cryogenic superconducting magnets and high vacuum within centimeters from a reactor producing at least hundreds of megawatts of power (if not gigawatts) within a volume of several cubic meters. You're basically constructing a fusion reactor at this point.

Oh, and parts of your accelerator close to the reactor will become activated, so you won't be able to do maintenance. ITER (the fusion reactor project) is planning to solve this problem using robots.

Fission reactors solve this by using VERY THICK pipes made of special steel, with careful inspection of every single weld. So once the vessel and its connections are placed, they stay inside the shielded area until it's time to decommission the reactor.