Triso particles have safety features that may power a new generation of reactors

TRISO will also make dealing with spent fuel more difficult, as the dry casks are going to have to be much larger.

I remember reading in one of Feyman’s biographies about how he visited an early fuel plant, and was horrified to see them storing what amounted to a near a critical mass in barrels, in long rows. we’ve come some way since.

Seems we are on a global level not very much learning from incidents. These are common (mandatory?) in Germany and colloquially named “Töpfer-Kerze” after the minister who had them installed: https://de.m.wikipedia.org/wiki/Reaktorsicherheit#T%C3%B6pfe... Klaus Töpfer was responsible for nuclear security from 1987-1994. This would have been the time to learn.

However, many operators didn't want to spend the money, which is why Fukushima didn't have a PAR at the time of the accident. The problem with Fukushima is that I fear we do not learn from accidents. Otherwise, Fukushima wouldn't even have been in operation at the time of the accident as it is an old reactor model well past its design life. The location was, as we have known before the accident, poorly chosen. Safety measures, such as PARs, seawalls and properly redundant power supplies were skipped or badly implemented due to the cost involved. All this was known before the accident, however neither the operator nor the national oversight took any action before it was too late.

1000°F = 538°C

2000°F = 1093°C

Why can't nuclear reactors at least have the option to power themselves?

This was also the problem at three mile island.

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.

I think that reactor standardization really paid off there. They have few types, a wide operation experience, and apparently well thought-out procedures.

This, of course, is hard to achieve without a massive rollout planned ahead.

Sounds like you have read Charles Perrow's 1984 book Normal Accidents [1]. New fuel systems are actually key to safe design, IMHO. All the major nuclear power incidents, that I'm aware of, are due to one underlying problem: zirconium clad fuel rods produce large amounts of hydrogen during loss of coolant accidents (LOCA). Nuclear power plants weren't supposed to go BOOM but it turns out they do so readily with hydrogen explosions.

Even with zirconium clad fuel rods, the CANDU reactor design seems to have managed the complexity and tight-coupling issues surrounding nuclear power generation; the design, however, never managed to reduce the immense capital costs involved.

Price-per-Performance is all that matters and in an age of cheap natural gas. I'm not convinced that new nuclear reactor designs will find anything other than niche markets. There are many lessons to learn from Charles Perrow but complete distrust of engineering should not be one of them.

[1] https://en.wikipedia.org/wiki/Normal_Accidents

    The Xe-100 is a small pebble-bed reactor that is designed to produce just 75 megawatts of power.

I remember watching a documentary on nuclear power in the US and how the thorium reactor was the focus of a lot of research in the 70s, but I can't remember for sure.

And yes, triso is pretty cool tech. Like the article says, it can withstand exceptional temperatures without any fission products escaping.

If one wants to do some fancier recycling and reprocessing rather than once through, I understand this is relatively undeveloped.