From the article, they're planning on the reactors being unmanned (but monitored). So, no employees watching it.
I get that we store actual nuclear bombs in unmanned remote sites (missile silos), but those are operated by the literal military and secure underground. These would realistically be operated by private companies, and are just shipping containers sitting on the surface.
> It uses TRISO fuel, which are fissionable materials enclosed in a carbon and ceramic shell that's extremely tough and can handle far higher temperatures than are present in a reactor without melting.
Each grain of fuel is about the size of a poppy seed, with the majority of the seed being the ceramic shell. It's not a dense fuel. This stops issues of radioactive material leaching into groundwater, and also makes it quite difficult to use the fuel for nefarious purposes (like a dirty bomb). Someone would need to separate the fuel from the shell, not a trivial thing to do. All this to say that it's not super attractive for terrorist types.
Also, remember that whilst they talk about using them in remote areas, it's mostly about being "remote to other infrastructure", not "remote from all people". These things will be installed in small regional towns / mine sites etc. Places where a town sized number of people will be. So it's not like it will be hours away from any first responder.
Finally, these can be secured pretty well physically. They won't be easy to move, or cut into, or siphon out the material, at least not in a smash-and-grab type scenario.
https://www.energy.gov/ne/articles/triso-particles-most-robu...
edit: I wouldn't say they are risk free, just not as big a risk as it first sounds locating a nuclear reactor out in the middle of nowhere :-)
edit2: I'm by no means an expert, but I really liked this video on the topic on the benefits of Small Modular Reactors (SMRs). I really love the concept, especially their mass produced, regularly rotated/retired nature:
> In 2009, this improved TRISO fuel set an international record by achieving a 19% maximum burnup during a three-year test at Idaho National Laboratory (INL). This is nearly double the previous mark set by the Germans in the 1980s and is three times the burnup that current light-water fuels can achieve—demonstrating its long-life capability.
That makes the entire industry seem like a bunch of liars and grifters.
Tripling the burnup when you're increasing the amount of U235 6x isn't an improvement, it's a step backwards. It uses 2x the uranium and almost 3x the enrichment.
Just present the fuel honestly on its actual merits rather than telling five lies and half-truths and one real advantage.
An analogue would be advertising a new car that gets 150mpg, but not mentioning the fuel it uses is a special exotic fuel not made in many existing refineries that requires 6x as much oil and you need 9 gallons of non-fuel to run through the engine for every gallon rather than 0.2.
Every single statistic nuclear proponents cite that can be easily checked in a few minutes is either technically true but designed to mislead like this one, or an outright lie. It makes it very hard to believe the things that cannot be easily checked.
In all likelihood one or more of the SMR concepts around is safe and economically viable enough to fill an important niche, but when all information they mention turns out to be lies it's kinda hard to trust.
Plus noone really know how you might make TRISO pellets not cost $40-600/MWh (or rather it costs well over $600/MWh and they think it might come down maybe) or cost $20/MWh to handle and store at the back end of the cycle (although this one might be solvable by burying the whole reactor I guess?), so it doesn't really matter how cheap the reactor is if it uses that fuel.
Those grains are fine as-they-are for a dirty bomb. Sure, one of the safest, cleanest dirty bombs you could have the pleasure to meet, but still a dirty bomb. Maybe not attractive to someone looking to deny territory through contamination, but great for someone looking to incite fear.
But I will say that if you spread this fuel over a large area with a bomb, it will ve orders of magnitude easoer to clean up, and result in far less long te issues. It wont leach into groundwater. If you swallowed/inhaled it, whilst it wpuldnt be gpod, it wont be absorbed ibto your tissue. Same with lifestock/crops. The cleanup problem goes from almost impossible, to pretty involved.
Again, I'm no expert, so take whatever with a grain of radioactive salt :-)
Prompt criticality is when a nuclear reactor is critical on prompt neutrons alone. This is to be avoided (in most cases) at all costs, as the doubling time of neutrons becomes very fast, a small fraction of a second. In a normally operating reactor, the core is subcritical on prompt neutrons, but critical on prompt + delayed neutrons. Delayed neutrons are emitted after the beta decay of certain fission products, and this slows the doubling of the neutron population enough that feedback control can keep the reactor's power steady.
Prompt criticality is what happened at Chernobyl.