

How Seawater Can Power the World - martey
http://www.nytimes.com/2011/07/11/opinion/11Prager.html

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yaakov34
After actually looking at the numbers and the details regarding fusion
technology, I've come to the conclusion that the advantages over fission are
illusory.

I think people believe that fusion is somehow "way more powerful", because
they know that fusion bombs are way more powerful than mere atom bombs.
Actually, in many of the most powerful fusion bombs, the vast majority of the
energy is produced by fission, with fusion serving as only an intermediate
step to release neutrons and create more fission. A step you don't need in a
reactor, which can control the fission rate itself.

My guess is that a lot of people who haven't looked at the numbers think that
fusion is hundreds of times more powerful than fission. Well, let's look at
those numbers: the fission of a uranium-235 atom produces 202.5 MeV. The
fusion of D+T produces only 17.6 MeV. That's more energetic per unit mass of
fuel, since D and T are just hydrogen isotopes, but if you do the math, it's
only about 3.5 times more energetic even using this measure. And fuel mass is
a tiny portion of the mass of the whole powerplant. To make it worse, hydrogen
is far less dense than uranium (by a lot more than a factor than 3.5), so you
actually end up with a lot more fuel volume and containment volume. There are
other reactions than D+T, but none of them look as good as plain old fission.
That's before we even get into the fact that for most fusion reactions, a lot
of the energy goes into extremely dangerous neutrons.

The talk about "getting the fuel from seawater" is also misleading. It's
technically true, but the process is very expensive, and, if we are going to
talk about seawater, uranium can also be extracted from it.

Finally, the idea that the danger from proliferation would go away is also
false - anything producing a neutron flux as strong as a fusion reactor can be
used to produce isotopes suitable for a bomb. And even aneutronic fusion
(which is technically even more difficult) can be made to produce neutrons
with suitable additions to the fusion fuels.

EDIT: P.S. I am not an expert. I do think I can understand numbers and
technical arguments, and I would love to hear expert analysis. But one thing:
for every technology which you assume will help fusion (such as wonder-
containments for the neutrons), please analyze how fission reactors would
benefit from it, as well. Then let's see if we can make fusion come out
"better" than fission in some meaningful sense.

EDIT: I can't resist adding that the talk of "harnessing the reaction that
powers the Sun" is aimed at people who don't know the numbers, and is very
annoying. The Sun is not a good model; it has a huge mass (duh), and a tiny
surface-to-mass ratio, which is why the energy it produces makes it so bright.
But pound-for-pound, the Sun produces a lot less energy than _slightly warm
chicken soup_. Do the math yourself, and be surprised. We can not build a
reactor that works like the Sun.

~~~
lucasjung
I've never thought if the advantages of fusion power in terms of "more
powerful" than fission, but rather "less dangerous," "cleaner," and "more
sustainable."

The problem with fission is that the fuel is really nasty stuff that requires
all kinds of special precautions when you mine it, when you process it, and
when you dispose of or recycle it. Even when you shut down a fission reactor,
you still have a bunch of highly radioactive material sitting there that has
to be dealt with. Also, the world will eventually run out of uranium, just
like it will eventually run out of fossil fuels. I'm not going to try and
predict exactly when that will happen (I'm guessing probably not in my
lifetime), but it _will_ happen eventually.

Fusion, on the other hand, uses hydrogen as fuel and leaves you with helium as
waste. I don't know what kind of radioactive isotopes come out of fusion, but
I'm willing to bet that, unless you're deliberately trying to produce them,
you probably get way less than you do with a fission reactor. In short, waste
disposal for a fusion reactor is trivial compared to a fission reactor, and
when you shut down a fusion reactor the radiation hazard pretty much goes away
immediately. Hydrogen is also a lot more common than uranium, so long after
all of the uranium is gone we'll still have plenty of hydrogen around.

~~~
yaakov34
I understand that this is the promise, but it all starts to sour once you look
at the details. The most commonly proposed fusion reactors use D+T fusion,
which produces hugely energetic neutrons, the most dangerous kind of radiation
that you can think of. You need hugely thick walls to contain these neutrons
and be heated up by them, and some kind of system to extract the energy from
the walls. And yes, the walls and the extraction system end up radioactive,
and now you have this huge radioactive mass to take care of somehow, instead
of tiny pellets of spent fuel in their cladding. You have other problems for
other reactions. Again, the devil is in the details here, an individual fusion
reaction might look good, but by the time you include everything else you
need, not so much.

Also, any system of safety and containment that will make this look good, will
make fission look even better.

~~~
demallien
yaakov, you are fighting strawmen. When we look at nuclear fission reactors,
we note 4 major types of problem.

1) Meltdown. Chernobyl, Fukushima, TMI. This type of problem can't happen with
fusion reactors, as the reaction stops as soon as reactant stops being fed in.
This is not the case for fission, because of the need to attain near-critical
mass before the chain reaction can occur.

2) Waste disposal. As fissile material is consumed by a fission reactor, the
resulting waste products are still highly radioactive. This waste has to be
stored safely (the famous cooling pools from Fukushima were the first step in
this process), for very long periods of time, generally measured in decades
and centuries.

3) Fuel availability - there are not huge quantities of fuel-quality fissile
material available on Earth. This limits it's usefulness going into the future

4) Theft of fuel - although reactor fuel is not generally very useful for
bombs, sometimes the waste is. Some reactors, eg breeder reactors were in fact
designed to generate bomb material, more so than to generate electricity.

Have a look at that list, and think about how it applies to nuclear fusion.
Meltdown is impossible, waste disposal is far easier (it's just the reactor's
shield that gets radiated, which is a much more contained problem than that of
radioactive reaction by-products. The amount of fuel for a fusion reactor on
this planet is just huge, and you can't make bombs out of the material coming
in or out of a fusion reactor.

These are the reasons that fusion reactors are highly interesting, not because
of the possibility to generate more power.

~~~
yaakov34
I am arguing with the sort of vision of fusion power that's presented in
popular articles, like the NYT one that started this thread. "Clean power that
powers the Sun" - yup, he said that. A senior scientist who knows the numbers.
See below in the thread how relevant this is. "Relies only on seawater as
fuel" - check. "Offers no chance of a catastrophic accident" - oh come on,
even a coal powerplant offers that.

Articles like this _are_ a strawman, and Stewart C. Prager, director of the
Princeton Plasma Physics Laboratory, knows better and should be ashamed of
himself. To take up just the matter of catastrophic accidents: it is said
correctly that a fission powerplant can never explode like a fission bomb -
the atoms of fuel are in the wrong arrangement for that. But any continuous
system for producing fusion power is theoretically capable of "running away" -
it is a self-reinforcing process, after all - and producing an actual nuclear
explosion. They will design it to make this spectacularly unlikely? OK, sure
they will, but let's not talk about this being danger-free.

Or the "fuel from seawater" thing. Seawater contains 3.3 ppb of uranium, and
it would be commercially feasible to extract it if the prices were higher.
It's actually easier to do this than to design fusion reactors. And you can
use more advanced fission cycles, especially the thorium ones, to extend the
energy you get out of fission fuels.

EDIT: let me clarify the actual quote from Dr. Prager that I am complaining
about:

 _Harnessing nuclear fusion, the energy that powers the sun and the stars, has
been a goal of physicists worldwide since the 1950s. It is essentially
inexhaustible and it can be created using hydrogen isotopes — chemical cousins
of hydrogen, like deuterium — that can readily be extracted from seawater._

This is so incredibly misleading in many ways, without containing an actual
false statement. This kind of manipulation of popular opinion makes me angry.
Does anyone want to defend this, even as a popularization?

~~~
uvdiv
_Or the "fuel from seawater" thing. Seawater contains 3.3 ppb of uranium, and
it would be commercially feasible to extract it if the prices were higher. ...
And you can use more advanced fission cycles, especially the thorium ones, to
extend the energy you get out of fission fuels._

Indeed. There's about a factor of 100,000x right there -- 500x for increased
uranium supply (5e9 tons in oceans, vs. 1e7 tons in "conventional" <$130
kg/ton reserves (IAEA est.)), and 200x for increased fuel efficiency.

 _But any continuous system for producing fusion power is theoretically
capable of "running away" - it is a self-reinforcing process, after all - and
producing an actual nuclear explosion._

Don't think this is true. Fusion plasmas need active confinement -- a hotter
plasma is no longer confined, and will no longer fuse.

 _This is so incredibly misleading in many ways, without containing an actual
false statement._

For example, the limited resource is not deuterium but tritium (a
misdirection). The plan to create this is by fissioning lithium, which is
actually a rather scarce element (comparable with uranium, ironically). To get
more interesting sustainability you need to switch to something like D+D
fusion, which is much harder to achieve.

<http://en.wikipedia.org/wiki/Tritium#Lithium>

~~~
yaakov34
Thanks for the correction about runaway fusion reactions. Does this only
prevent it from doing a "Ivy Mike" on us, or can they actually make it
passively self-regulating to the point that it can't breach the containment?

I still think he is being disingenuous when he says that there is no danger of
accident with fusion reactors. Proposed designs have huge irradiated masses
and very large neutron fluxes. There is going to be a ton of active safety
systems needed, any way you imagine it.

~~~
uvdiv
There's also the fact that the plasma has extremely low density, so there is
very little fuel in the core at a time:

"Less than 1g of fusion fuel is present in the Vacuum Vessel at any one
moment."

<http://www.iter.org/mach/fuelcycle>

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rbanffy
I wonder why so many people insist that there has to be a "winning"
technology. So someday all of the world must commit to generate energy from
nuclear fusion (despeite the horrendous cost and quite modest results
scientists have to offer for the money spent) rather than harnessing the
cheapest easiest energy sources around. Big Fusion (ITER style) looks more
like a government program to employ physicists than anything really practical,
something like "we already spent so much on this it would be foolish to stop
now".

Not to mention the writer forgets there are countries without seashores. How
are they supposed to generate their energy in this fusion-driven utopia?

~~~
demallien
What would you suggest as an alternative base load technology?

~~~
rbanffy
I would go for thorium fission. As it seems, it's orders of magnitude easier
to implement than deuterium fusion. Fusion is safer, I agree, and we should
not abandon the research, but developing a thorium cycle for now instead of
betting money on an uncertain approach to energy generation is, IMHO, smarter.
As a civilization we need more energy (and, if climate changes faster, we'll
need more) and we need on a predictable schedule.

Fusion has been about the same number of decades (two) away since I was a
young boy. I don't think it deserves the faith we are depositing in it. Much
like space colonization and jetpacks, it is a broken promise.

I'd also not forget other alternatives like molten-salt solar, hydro, wind and
even photovoltaics that can offset some of the needs for power generation.

------
Zak
Fusion power has been 20 years away for the past 50 or 60 years according to
the top scientists in the field at the time. I suspect there's a good chance
that in 20 years, it will still be 20 years away.

~~~
maeon3
I hear the statement: "Technology T is Y years away", all the time, it is
usually is just speculation and wishful thinking.

I would rather people replace that overused line with the statement:
"Technology T has barriers B, C and D preventing its successful implementation
and mass production". Leave feel-good speculation out of it and focus on
overcoming the obstacles.

~~~
SoftwareMaven
I would imagine talking to lay-people in terms of road-blocks instead of
hypothetical times would cause a net reduction in funding, and these kinds of
articles are all about funding.

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trebor
I keep hearing "fusion" and keep wondering if we shouldn't go for the thorium
route first. It's safer than fission w/uranium and can even be taught to third
world countries without fear of giving them nuclear bombs.

~~~
iwwr
Less proliferation risk, but not zero. It's still possible to build a bomb
from U233 (obtained from the thorium cycle).

~~~
ams6110
At this point in time, how much additional risk does it add though? Any
nation-state that is bound and determined to develop nuclear weapons pretty
much just does it (e.g. Iran, North Korea) and the supposed anti-proliferation
watchdogs (UN, IAEA) pretty much just stand on the outskirts and say "please
stop," which has about as much effect as you'd expect.

~~~
iwwr
The thorium cycle is a higher technological level and more expensive to
develop, so a state capable of developing one is more than capable of a
conventional uranium bomb program.

~~~
trebor
But the way I understand it is that Thorium-based fission is more costly to
weaponize than uranium, or plutonium based fission.

Might be more technical, but it should be able to be operated without such a
high technological level. So you could sell a system to a third world country
without a great deal of concern over their nuclear capabilities.

------
ern
If Asian countries are enthusiastically funding the research, why couldn't the
US just license the technology after it is developed?

~~~
uvdiv
How would the director of the Princeton Plasma Physics Laboratory benefit from
that?

~~~
jrockway
Version 2.0.

------
bluedanieru
>A rough estimate is that it would take $30 billion and 20 years to go from
the current state of research to the first working fusion reactor. But put in
perspective, that sum is equal to about a week of domestic energy consumption,
or about 2 percent of the annual energy expenditure of $1.5 trillion.

Millions of years from now after the human race fails and alien archeologists
are picking apart the carcass of its long-dead civilization, they are going to
find an _enormous_ number of exactly these circumstances. From education to
space travel and power generation this kind of folly is so ubiquitous that it
is more newsworthy when it _doesn't_ happen. There must be some aspect of
human and group psychology that ensures it. As such it's hard to have much
hope for the future.

Just kidding about the aliens though. It's unlikely any would ever discover
our ruins.

~~~
iwwr
Large infrastructure projects are wasteful no matter how you cut it, so at
least they should have precise objectives (much shorter than 20 years) and
per-objective pricing (rather than cost-plus).

~~~
bluedanieru
How are they wasteful 'no matter how you cut it'? What if the cut is more
efficient energy production, or access to plentiful resources, or freeing the
fate of humanity from the fate of its home planet (everyone here should
appreciate separation of concerns). And why twenty years? Why rule out a
concrete multi-generational goal (assuming humanity can ever achieve that
level of social organization first) which has a large payoff and reasonable
chance of success?

~~~
iwwr
_Why rule out a concrete multi-generational goal?_

The project would be doomed to failure without intermediary objectives. Long
term planning is difficult as it is and politics adds to the implausibility.

