
Thorium power has a protactinium problem - ArtWomb
https://thebulletin.org/2018/08/thorium-power-has-a-protactinium-problem/
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acidburnNSA
Quick summary for anyone in a hurry. Thorium-232 fertile material absorbs a
neutron in a reactor and quickly transfers through Protactinium-233 to
Uranium-233, a fissile fuel. Pa-233 is a strong neutron absorber so reactor
designers like to pull it out of the reactor chemically to let it decay to
U-233. Problem is, if you pull it out and let it decay and you're a bad guy,
you can get fairly pure weapons-grade U-233, which is like U-235 and
Plutonium-239.

Countermeasures are to make sure there's some U-238 around to blend it down
(but then it makes Plutonium and minor actinides), use faster neutrons (not as
affected by the Pa), or install safeguards around the reactor.

I'm a huge proponent of nuclear reactors but I have yet to see a design that
is truly proliferation-proof. All reactors require safeguards. It's still well
worth getting that low-footprint 24/7 clean energy, which nukes alone can
produce.

Thorium is great. It doesn't automatically solve all issues in nuclear. Here
are the highlights of modern common Thorium Misconceptions:
[https://whatisnuclear.com/thorium-
myths.html](https://whatisnuclear.com/thorium-myths.html)

~~~
mdorazio
Thanks for this summary. Personally, I think at some point we're going to have
to accept that non-proliferation is kind of a lost cause. We're rapidly
approaching a time when anyone with some spare time and internet access can
start CRISPRing a new plague or fly a drone spewing sarin above a crowd of
people. Going to great lengths to cripple power production to prevent the
production of some fissile material is like plugging a leak in your boat when
there are multiple torpedoes about to hit. If you can go from some U-233 to a
working weapon capable of threatening other nations, there are probably other
avenues available to you as well.

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acidburnNSA
Fully agreed. And it's usually much easier to just get some high-speed
centrifuges and enrich uranium and make a very simple gun-type nuclear bomb.
This requires no nuclear reactor whatsoever and will not go away if we ban
nuclear reactors.

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angry_octet
Well, it takes _lots_ of electricity and a cascade of hundreds of ultra high
speed (2kHz) centrifuges full of ultra corrosive, poisonous uranium
hexafluoride.

'Just getting' some of these is the story of modern proliferation, the theft
of the tech specs from Europe by AQ Khan, and his/Pakistan's subsequent
proliferation to Iran, Libra and North Korea. Because without good
centrifuges, the SWU (separation work) per electrical energy is very poor --
more than 100 times more energy.

~~~
acidburnNSA
That's why Silex technology (laser isotopic enrichment) is the only privately
held information that is classified by the US government [1]. It can bring
energy needs down by a lot, with a much smaller footprint.

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

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nickik
Yes, Thorium is not much better in terms of resistance to proliferation, but I
think the reality is that threat of commercial reactors being used for for
weapons making is pretty small. That's not how nations made their weapons
arsenals.

One point, that is often ignored, about Uranium 232 is that it is super easy
to find. Meaning its incredibly easy for the IAEA to say that something
containing Uranium 232 was used anywhere or to validate that it did not leave
the reactor site.

That said, a lesser known program after the Molten Salt Breeder Experiment at
Oak Ridge National Laboratory was the Denatured Molten Salt Reactor, that was
specifically designed to be more proliferation resistant (they hope
proliferation resistant research would keep their program alive, and it did
for a little bit).

This work actually lives on and the company furthers ahead in building a
Molten Salt Reactor (Uranium) is the Canada based Terrestrial Energy. They are
building the Integrated Molten Salt Reactor.

In both designs you avoid some of these problems you have if you do
separation, but rather you just switch to a burner design and burn it all in
one big reactor, no piping, no chemical plants and so on.

The problem is once you go to a burner, the primary reason why Thorium is an
interesting fuel cycle (>2 neutron fission rate) is lost in a burner. That
means the extra work to prove that Thorium is safe is just more work that you
have to prove safe to the regulator. Pretty much all Molten Salt companies,
even when they have met at a Thorium conference (as Terrestrial Energy did),
switch to Uranium because of this issue.

For those interested, here are some of the presentations about the current
companies working on Molten Salt Reactors:

\- Stable Molten Salt Reactor
([https://youtu.be/TvXcoSdXYlk?t=2m40s](https://youtu.be/TvXcoSdXYlk?t=2m40s))

\- Integrated Molten Salt Reactor
([https://www.youtube.com/watch?v=OgTgV3Kq49U](https://www.youtube.com/watch?v=OgTgV3Kq49U))

\- Longer term Liquid fluoride thorium reactor
([https://www.youtube.com/watch?v=R3lcIvS7cO0](https://www.youtube.com/watch?v=R3lcIvS7cO0))

~~~
acidburnNSA
The DMSR was a pivot to avoid the U233 problem but it worked by adding U238 to
the mix, which inevitably produces plutonium when irradiated. So it was trying
to balance low-quality fissile uranium with low-quantity plutonium. A
difficult balance. Still it's too bad the program didn't continue, they were
doing great work.

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ohazi
I thought the real problem with Thorium is that salt eventually corrodes just
about everything, which makes building a reactor that uses molten radioactive
salt a bit of a sketchy long-term proposition.

~~~
nickik
The primary problem for a Breeder is actually that it corrodes the graphite.
We have the metals that are corrosion resistant for long enough.

The primary problem with the metal is actually just qualifying that it is
actually the case. The material they used in the original Molten Salt
Experiment was great at resistance but re-qualifying this (or anything) to
modern standards is incredibly difficult.

The 'Stable Salt Reactor' for Moltex actually have a solution where they use a
slightly different salt that they can put some metal into and the chemistry
works out that it will corrode that metal first and the piping is fine.

I however primary believe that for the last 40 years, regulatory approve and
path to market were the primary issues. In the molten salt reactor experiment
they solved many of these problems in relatively short time with a tiny team
of people.

Because of regulations you basically can not develop a test reactor, and all
of the nuclear companies basically design directly to production because it
would be way to expensive to build a test reactor. Building a tiny research
reactor would be an option, but those are limited to sizes that are to small
to actually validate your design.

~~~
danmaz74
> The material they used in the original Molten Salt Experiment was great at
> resistance but re-qualifying this (or anything) to modern standards is
> incredibly difficult.

Care to elaborate? Looks like a very interesting problem.

~~~
nickik
I am not very knowledge about nuclear material qualification, I can just tell
you what I have heard.

The material they developed for the MSR was called Hastelloy N and showed a
lot of promise.

Sadly, because its primary benefit was working with salts, it was not further
developed and the use it saw does not qualify it for use in a modern nuclear
reactor.

Therefore you have to do a complete re-qualification of the material under
advanced neutron flux. Nuclear regulations are so incredibly strict that doing
that alone would probably blow most development timelines.

[1] [https://en.wikipedia.org/wiki/Molten-
Salt_Reactor_Experiment...](https://en.wikipedia.org/wiki/Molten-
Salt_Reactor_Experiment#Structural_alloy_Hastelloy-N)

~~~
j9461701
The original experimental reactor didn't go all the way and test the reactor
design in a "closed loop". As in you shovel in thorium and get out power
indefinitely. Instead it relied on temporary uranium fuel as a test of the
concept, with plans to step up to a full cycle test afterward (which never
happened as the navy lost interest in the project).

So not just regulations are at issue. We'd need a 2nd test reactor to really
iron out the kinks and fully vet the whole process in real life, and then we
can start getting approval for commercial plants. As I've said elsewhere,
thorium reactors are very exciting and we should be funding experiments on
them. _But_ we are still at the 'funding experiments' phase of this endeavor,
and so even at peak funding we're still a ways out from viable thorium grid
power.

~~~
nickik
The problem is that you can't say that 'the regulations are not the issue'
because its regulation that prevent all research in that direction.

The way the regulation works at the moment makes building a test reactor
basically impossible for a company to do that's why pretty much every single
nuclear company produces directly to a production model.

Thorium breeding was proven, but not in the MSR. So that does not necessarily
need validation.

The 2-fluid reactor design would need a test reactor, but there are other
reactor designs, like the IMSR that really would not need much further
research.

However, if you don't go to a fuel breeder with online refueling thorium does
not buy you much. Uranium is fine and does everything you want and that's why
most MSR companies use Uranium.

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ComputerGuru
Excellent article but in 2018 it really isn’t technical so much as political
and economical safeguards that prevent the development and spread of nuclear
weapons.

The world does not need an excuse to stop research into nuclear power for
another fifty years.

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andlier
Protactinium

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jwfxpr
Typo in HN title: it's 'protactinium', not 'proactinium'

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sctb
Updated. Thanks!

