It's immune to meltdown.
The first important safety feature is the fact that it simply doesn't melt. The fissile material is contained in a ball of graphite (which is theorized to sublimate directly to carbon vapor somewhere north of 7000F) and silicon carbide. (decomposes to silicon and carbon somewhere north of 5000F) They tested the fuel at 3200F and none of it failed. The zirconium cladding on the fuel at Chernobyl, Three Mile Island, Fukushima, etc all failed somewhere in the ballpark of 2000F.
The second thing is called Doppler broadening; once the uranium fissile material gets that hot, it ceases to be able to sustain a nuclear reaction. The uranium nuclei are zipping around too quickly for thermal neutrons to effectively induce fission. Normal zirconium cladding fails before this effect can become significant.
The net result of these two effects is that you don't need coolant. As the temperature increases, the rate of decay decreases to the point where the device will passively cool itself without coolant. This equilibrium point is really stinkin' hot, but the entire facility will have been designed around this fact.
The reactor design itself is fairly interesting in its uninterestingness: the only interesting dial an operator has is the coolant pump. If you pump more coolant in, you get more power out; that's it. Turning the reactor "off" just means turning the coolant pumps off, which in most other types of reactors is the thing that causes the disaster. There aren't control rods, I don't think it even has a SCRAM facility.
Why can't nuclear reactors at least have the option to power themselves?
Some newer designs opt for passive decay heat removal, eg through convection.
Some Fukushima reactors did have some self-powered safety features, like a little steam turbine that comes from the boiling coolant and is hooked to a coolant pump. These features are at least a little related to why some reactors failed at different times than others in Fukushima.
But seriously, there is enough decay heat to do more of this so it's a pretty good point.
https://en.wikipedia.org/wiki/Fort_St._Vrain_Generating_Stat...
Running some kind of heat engine off decay heat should be possible, but it would be very different from the primary turbines, (You probably couldn't use it during normal operating temperatures, but it'd still have to be connected to the coolant circuit) have to be nuclear rated, (expensive!) and only be used in an accident scenario where you lose external power and the diesel generators are then destroyed, or run out of fuel.
Also, reactors containing graphite (as many pebble-bed reactors will) do need a oxygen-free atmosphere, otherwise the graphite will ignite. So only convection of the proper uncontaminated protective atmosphere will work.
This was also the problem at three mile island.
That's the singular safety selling point of Gen IV reactors that have passive cooling features.
It was demonstrated in April, 1986 at EBR-II in Idaho, weeks before Chernobyl. Very few people have heard of this awesome capability.
https://en.wikipedia.org/wiki/Experimental_Breeder_Reactor_I...
But the meltdown at Fukushima was caused by lack of decay heat removal after shutdown, which is different from what could or could not happen during actual reactor operation. So there are two kinds of "prevent meltdown" that are required, not one. The article does not talk at all about how, or whether, the type of reactor it discusses would prevent a meltdown of the second kind, the kind that happened at Fukushima.