
Triso particles have safety features that may power a new generation of reactors - wscott
https://www.wired.com/story/nuclear-power-balls-triso-fuel/
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acidburnNSA
TRISO fuel has some very interesting capabilities as noted in the article. It
also has some challenges. Traditionally, the challenges are:

* Very low power density requiring absolutely massive reactor vessels for a certain power level

* Very expensive fuel fabrication ($10k/kg), hopefully can be brought down

* Difficult to reprocess (this is probably fine until nuclear produces like 50% of the world's energy, at which we will begin to challenge the fuel resources)

Also traditionally, these are high temperature gas-cooled reactors. A new
twist is the molten-salt cooled (basically just melted salt, not fluid fuel
like in full-on molten salt reactors) TRISO-fueled reactors. These are called
FHRs.

~~~
pfdietz
TRISO sounds like another example of solving the wrong problem. Nuclear's big
problem isn't safety, it's cost.

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

~~~
jessriedel
But the high cost of nuclear power is probably due to the extraordinary (and
perhaps very excessive) safety procedures, no? It's not like the raw material
or basic principles are very expensive. So I presume the idea is to hope that
having a more intrinsically safe fuel will allow those expensive safety
procedures to be relaxed (although, given the sclerotic nature of nuclear
regulation, probably not).

~~~
pfdietz
The safety procedures don't help the cost, but even the non-nuclear part of a
nuclear power plant is expensive. The "nuclear island" is just 1/3rd the cost
of a nuclear power plant. All externally heated thermal power plants have
become uncompetitive now. Not just nuclear, but also coal, geothermal, and
concentrating solar thermal.

So, TRISO is depending not just on the nuclear island being cheaper, but the
non-nuclear part somehow becoming less expensive. This probably involves very
high temperature, for example for nuclear air Brayton. But any time you go to
higher temperature material problems rapidly accumulate.

In any case, there will always be a cost premium to the nuclear part of a
nuclear power plant, if only because it has to be very reliable because it
can't be repaired if something serious breaks. In (say) a coal fired power
plant one can send workers into the guts of the shut down plant to fix or
replace things. In a reactor, I don't think that's possible, even if the fuel
has been removed. The residual radioactivity is too high.

~~~
jessriedel
Thanks.

> All externally heated thermal power plants have become uncompetitive now.
> Not just nuclear, but also coal, geothermal, and concentrating solar thermal

Are you saying that an externally heated power plant is unlikely to be cost
competitive even if the source of energy is _free_? If not, your overall
comment doesn't make sense to me. If so, that's an extraordinary that could
very well be true, but I haven't heard anyone argue it and I'd be _extremely_
interested in further reading/links/citations.

~~~
pfdietz
Yes, that is the direction things are going in. The remaining thermal power
technology that's still (for the moment) viable is combustion turbines, which
are internally heated (combined cycle does have an externally heated bottoming
cycle, but only 1/3 the power output goes through that, and it shares the
generator with the combustion turbine proper.) But even combustion turbine
sales are falling; that's what's gotten General Electric in such trouble
lately.

~~~
jessriedel
Much appreciated! Are there any forward-looking doc's you can recommend that
discuss this in more depth, especially any that try to get at the basic
physics or economics? It's truly startling to me, and to the extent it's true
it really changes the way people should think about future energy tech.

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pjscott
Because the article isn't clear: no, this isn't about pebble bed reactors.
This is about a type of fuel where a little bit of uranium has been encased in
a number of protective layers, such that the fuel will remain safely contained
in its tiny packaging even at very high temperatures. You take a bunch of
these poppy-seed-sized things and embed them in graphite rods or pellets,
which both keeps them in place and acts as a moderator for the reaction. These
can then be used in a variety of reactors, including (but not limited to)
pebble bed reactors.

~~~
oxymoron
The confusing part about the article was that it initially stated that they
were very small, and then went on to speak about billiard ball size. Does that
mean that the protective coating is very thick, or that there’s a range of
sizes for the actual uranium mass?

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.

~~~
pjscott
The TRISO fuel particles are very small -- about a millimeter or so in
diameter. The "billiard ball sized" fuel pebbles designed for the Xe-100
reactor are graphite balls with a bunch of TRISO fuel particles embedded in
them.

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VBprogrammer
I went through a phase of reading about nuclear power and in particular the
nuclear accidents. It feels like we kinda got to the Comet¹ stage of Nuclear
power and gave up. We still learn lessons from each accident, for example
Fukushima has resulted in Passive auto recombiners being installed which
convert hydrogen back to water. It also added provisions for using mobile
generation and cooling (fire trucks).

I certainly don't have the answer but to how we can make nuclear power fool
proof but I do feel like we should still be asking the question.

[1]
[https://en.m.wikipedia.org/wiki/De_Havilland_Comet](https://en.m.wikipedia.org/wiki/De_Havilland_Comet)

~~~
corty
Use of passive auto recombiners (PARs) started over 30 years ago on a large
scale and has been state of the art for more than two decades now:
[https://inis.iaea.org/collection/NCLCollectionStore/_Public/...](https://inis.iaea.org/collection/NCLCollectionStore/_Public/33/020/33020098.pdf)

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.

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Xcelerate
> Most nuclear reactors today operate well below 1,000 degrees Fahrenheit

I have a background in chemical engineering and still had no clue that nuclear
reactors operate at the temperature of a pizza oven. That's wild.

~~~
klodolph
What’s amazing to me is that the kind of graphite used in nuclear reactors
doesn’t burn until it’s white hot, somewhere around 1650°C.

~~~
corty
That is not a property of the graphite, its a property of the atmosphere (CO₂,
He) or lack thereof (H₂O, molten salts) around the graphite. The Chernobyl
core started burning as soon as external atmosphere hit the graphite after an
explosion.

~~~
klodolph
Actually, it is a property of graphite. You may be surprised.

[http://nucleargreen.blogspot.com/2011/03/does-nuclear-
grade-...](http://nucleargreen.blogspot.com/2011/03/does-nuclear-grade-
graphite-burn.html)

------
pdonis
The article is conflating two very different kinds of "meltdown". A meltdown
during actual reactor operation is the kind the article is talking about in
the first paragraph, and the kind that the type of reactor discussed in the
article is designed to make impossible, according to the rest of the article.

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.

~~~
joncrane
So apparently Fukishima's power failed and the generators were damaged by the
tsumami.

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

~~~
jabl
Normally they do, but when you shut it down you need something to get rid of
the decay heat. That's why nuclear power plants have these emergency
generators. Those failed at Fukushima, leading to the meltdown.

Some newer designs opt for passive decay heat removal, eg through convection.

~~~
hansthehorse
In American PWR designs decay heat removal post loss of power is accomplished
by natural circulation. Height and temperature differences between the steam
generators and the reactor vessel produce flow of primary liquid between the
two. Heat is rejected via the secondary system. The limiting factor becomes
make up water to the secondary side of the steam generators.

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nordsieck
One thing that' slightly worrying:

> But during the INL tests, Demkowicz demonstrated that triso could withstand
> reactor temperatures over 3,200 degrees Fahrenheit.

> ...

> Sell says. “It is physically impossible—as in, against the laws of
> physics—for triso to melt in a reactor,”

3200 F = 1760 C

> The first phase lasted only several seconds, with temperatures locally
> exceeding 2,600 °C, when a zirconium-uranium-oxide melt formed from no more
> than 30% of the core.[1]

It seems like it's yet to be demonstrated that Triso fuel can withstand the
highest recorded temperature inside a nuclear reactor. I get that the
physically impossible quote is probably partially puffery, but IMO puffery is
not appropriate when it comes to nuclear reactors.

___

1\.
[https://en.wikipedia.org/wiki/Corium_(nuclear_reactor)#Chern...](https://en.wikipedia.org/wiki/Corium_\(nuclear_reactor\)#Chernobyl_accident)

------
LatteLazy
All the major incidents with nuclear power are despite dozens of safety
systems, redundancies, clever designs etc.

This is because nuclear power is tightly coupled and complex. Humans have
never mastered such systems. We have them and we accept they fail sometimes
(eg fires at conventional power plants: 200 plus years of engineering and they
still happen). But with nuclear that isn't an option.

This is why people are unconvinced by clever new fuels or "it's totally
guaranteed this time" engineering. You can't fix a systems/human nature
problem with new fuel cells.

~~~
nine_k
France is choke-full of nuclear power plants. Can you remember a major nuclear
power incident in last, say, 30 years?

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.

~~~
VBprogrammer
One thing I like to remember is that there are still 10 RMBK reactors in
operation. Fundamentally the same design as the reactor 4 at Chernobyl. In
fact, one thing a lot of people don't realise, the 3 other reactors at
Chernobyl were restarted and ran until 2000 (actually, reactor 2 shut down
earlier because of a non-nuclear accident with its generator) when the EU paid
to have them shutdown.

~~~
LatteLazy
The Chernobyl reactors were all perfectly safe. It was almost impossible for
them to suffer a meltdown. That's the problem here: greed and incompetence and
pride can't be fixed with better cooling systems. Today's perfect reactor is
just as dangerous as the perfect reactor at Chernobyl once someone wants a
bonus or needs to improve efficiency or doesn't want to admit he is confused
and turn the thing off...

~~~
VBprogrammer
Perfectly safe is a long stretch. As originally installed they had numerous
design faults, the control rods operated too slowly, the carbon tips of the
control rods could locally increase reactivity when they were being inserted,
the reactor was too large and consequently hard to control, they lacked the
secondary containment structures which were common place in western reactors
of the era.

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sparker72678
Is this the same thing as “pebble bed” reactors I read about many years ago?

~~~
tersers
I also believe it's true of liquid fluoride thorium reactors:
[https://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reacto...](https://en.wikipedia.org/wiki/Liquid_fluoride_thorium_reactor#Safety)

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.

~~~
pjscott
To clarify: molten fueled reactors (like LFTRs) trivially can't have their
fuel accidentally melt, because their fuel is already molten. (And there are
some nice options for dumping their fuel into a subcritical passively-cooled
configuration in case of an emergency.) This is different from TRISO fuel,
which isn't supposed to be molten in normal operation but which structurally
limits the spread of fuel and fission products at high temperatures.

~~~
acidburnNSA
They can melt. They all do during fuel synthesis. They're pre-melted.

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peachy_no_pie
Can anyone speak to the implications for this type of Triso fuel and
radioactive waste? Is there less radioactive waste once it is spent or how
similar is it to other types of nuclear fuel in that regard?

~~~
jabl
It ought to be safer since the fission products are encased in the protective
and non-corroding triso structure. That being said, used LWR fuel rods are
also enclosed in protective cylinders (see eg the designs for the Finnish
Onkalo storage site). Both safe enough per current best knowledge.

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

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dukoid
What are the exact differences between this "new generation" of reactors and
the failed AVR(1) and THTR-300(2)

1)
[https://en.wikipedia.org/wiki/AVR_reactor](https://en.wikipedia.org/wiki/AVR_reactor)

2)
[https://en.wikipedia.org/wiki/THTR-300](https://en.wikipedia.org/wiki/THTR-300)

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IXxXI
What ever happened to thorium based nuclear energy?

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empath75
Capitalism being what it is, it doesn’t matter how much this improves safety,
newer plants will keep pushing for tighter and tighter safety tolerances
chasing after efficiencies until this is just as risky as the current fuel.

