
Small Modular Nuclear Reactors Overcome Existing Barriers to Nuclear - Osiris30
http://blogs.scientificamerican.com/plugged-in/3-ways-small-modular-reactors-overcome-existing-barriers-to-nuclear/
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shaqbert
This is not really about micro reactors, but about making the monolith power
plant more like a microservice modular thing. So that you can potentially
prevent decomissioning after 40 to 60 years and keep it operating much longer.

The downside of nuclear power still remains though: \- still high upfront
costs (maybe lower that monolith plants, but still freaking high) \- poisonous
and radioactive fission products that are hard to deal with \- perverse
incentives between economic efficiency and safety (did I mention that a couple
of those babies [1] here would have prevented the fukushima disaster)

[1]: [http://us.areva.com/EN/home-1495/new-challenges-proven-
solut...](http://us.areva.com/EN/home-1495/new-challenges-proven-solutions-
mitigation-passive-autocatalytic-recombiner-par.html)

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Aelinsaar
To be fair, the byproducts are not something we're unaware of how to manage,
we're just socially and politically unwilling to do it. Likewise, we know how
to design and maintain much safer and more efficient reactors than anything we
currently have running, but we lack the social and political will to make the
change.

Besides, we like to pretend that burning coal isn't killing millions of us
around the world, decade in, decade out. Focusing on the real human cost of
when nuclear goes wrong, vs. when coal goes right makes it an easy choice.

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jon_richards
Per kilowatt, nuclear energy is by far the safest. People fall off wind and
solar installations all the time. Hydro fails _catastrophically_.

~~~
Aelinsaar
I don't know about Solar and wind being inherently less safe, in fact I'd
disagree with that. The issue though, is that we still can't rely on them to
power our entire grid. Hydro though, even without failure, seems to have a
pretty undesirable environmental impact. Nuclear has to go catastrophically
wrong for that to be the case.

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bewaretheirs
For residential installs, solar systems go up on roofs, a few kilowatts at a
time. The main risk is to the installers (they fall off). Little capacity per
roof, every roof different, every fall a potential hazard = higher risk per
kilowatt than you might think..

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mschuster91
> The main risk is to the installers (they fall off).

Huge NO. The biggest risk is for firefighters if any part of the PV panel or
the technology or the roof itself catch fire!

The DC side can easily pack in a couple hundred volts DC with double-digit
amperages. And you can't turn it off unless the sun goes dark... not to
mention that it's hard for firefighters to fight a fire if the whole roof is
PV-panel-filled and something in the roof is burning.

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Animats
This is strange. There is no "containment vessel". That's the reactor pressure
vessel. Usually, there's an outer containment vessel as well. Chernobyl didn't
have one at all, which is why that was such a disaster. Fukishima's reactors
had ones that were too small and didn't have enough expansion volume to
diffuse the pressure after loss of coolant. There's a design assumption here
that there will never be a meltdown.

~~~
ParrotyError
A containment vessel at Chernobyl would have been useless. The Chernobyl
disaster was a combination of poor reactor design leading to dangerous reactor
physics, poor safety systems, poorly-trained staff, and an dangerous and
unnecessary "experiment" being performed on the reactor (i.e. operating it in
a dangerous regime). No containment building could have been strong enough to
contain the explosion. The RBMK is a particularly bad design of reactor.

~~~
pdkl95
> dangerous and unnecessary "experiment"

We always hear about how they were running the reactor in a dangerous mode to
run the experiment, but the nature of that experiment is rarely mentioned. The
experiment itself is the craziest part!

The experiment was a test of a new cooling system feature. The RBMK's
_suicidally stupid_ design had a positive void coefficient of reactivity[1].
Coolant voids _increased_ reactor activity. The operators new this; they had
backup diesel pumps that would take over from the electric pumps if power
wasn't available. They also knew that it would take some time[2] for the
backup pumps to reach full speed, which was not fast enough.

So someone had the "clever" idea to modify the electric pumps so they would
continue to spin freely when they lost power, so their remaining kinetic
energy could continue pumping coolant at a rapidly falling rate. The hope was
that there would be sufficient kinetic energy to keep the reactors from
voiding. The experiment was basically a bad hack to work around several
serious design problems.

The experiment shouldn't have _existed_. Everything about the coolant
situation should have been a reason to decommission the reactor. The
experiment itself is evidence that _someone_ knew about the positive void
coefficient problem, or they wouldn't have tried such a crazy workaround. Yes,
a lot of the staff was poorly trained, but someone knowledgeable about
reactors decided they couldn't afford even a few seconds[2] without coolant.

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

[2] like 50 seconds? if I remember correctly?

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Aelinsaar
A positive void coefficient doesn't have to be suicidal or stupid, it just was
in that design. See: CANDU

~~~
witty_username
CANDU has a very small positive void coefficient.

~~~
Aelinsaar
I didn't say anything about a _large_ void coefficient, and I pointed to CANDU
as an example of a reasonable beta, responsibly managed.

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cowardlydragon
LFTR should be implemented like this: modules that can be decommissioned on a
scheduled basis so that the transmuted parts of the container can be
recycled/extracted.

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tremon
The article doesn't seem to mention what type of reactor this is. Are these
still gen-III boiling water reactors, or is this a gen-IV type reactor?

~~~
shaqbert
Nobody designs new boiling water reactors these days. Reactors efficiency
increase with temperature, that is why pressurized water is the name of the
game - as it can have a much higher boiling point.

The higher temperature = better reasoning is also the reason why there is such
a hype train going for reactor designs based on molten salts.

Needless to say a higher temperature also puts more strain on any material and
makes safe operation generally harder.

~~~
wolfram74
One of the things that I don't get is that there a lot of cool fission designs
that are arguably only hampered by the state of the art in molten-salt
plumbing, but the only fusion design with mainstream support requires molten
lithium plumbing for breeding tritium and heat exchange, along with a few
other things that are still a touch experimental. Hash out the molten salt
plumbing for the fission reactors since it appears strictly a subset of the
fusion problems.

~~~
shaqbert
No, its not a subset of fusion problems. Very different problems:

Molten salt fission problem = dealing with vast quantities of a highly
chemically active salt touching our plumbing directly over 40 to 60 years.

Fusion problem = containment of a small quantity by a magnetic field.

~~~
Symmetry
Fusion also has the "dealing with vast quantities of a highly chemically
active salt touching our plumbing directly over 40 to 60 years." Nobody talks
about it because the magnetic containment problem is harder.

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monocasa
You can't use water like most fission designs?

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Gibbon1
Some fusion designs in theory would burn deuterium-tritium. Typical way to
produce tritium is from lithium. When lithium absorbs a neutron it fissions
into tritium + helium. Potential designs for fusion reactors then have a way
of exposing lithium to the neutron flux from the reactor.

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unique_parrot2
That's great. You know how expensive it is to get rid of radiactive material.
It this comes true the big power plants can just dump the waste into the river
and say "It wasn't me".

I would not want to live next to such a thing.

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marak830
Maybe someone here can inform me, howuch does the waste weigh? Would it be
viable to launch it into space then send it on a course to the sun?

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wiredfool
It's easier/less deltaV to send things out of the solar system than it is to
hit the sun.

(Basically, to hit the sun, you have to scrub out all/most of the velocity
from the Earth's orbit, or what you've done is put your waste in an orbit
around the Sun that may intersect the Earth's at some point in the future)

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mrfusion
Why not do an elliptical orbit that takes you close enough to the sun to burn
up? That seems like less energy than dropping to zero no?

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kazagistar
Bring it up does not change the fact that there is now radioactive material on
an orbit which still potential overlaps the earth. Out of the solar system is
a much better solution.

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Symmetry
On the other hand it's not like the Sun isn't spewing out way more radioactive
material continuously than we're talking about adding here.

EDIT: To give some orders of magnitude, the back of the envelope tells me that
the sun inflicts about 700 TBq of carbon-14 on us every year. For comparison,
countries like the USSR and UK have dumped 85,000 TBq of radioactive waste
into the ocean (and Fukushima added another 15,000). I don't know how to judge
how much of the vaporized waste would end up back on Earth so it's quite
possible I'm wrong in the above.

