

2 billion-year-old African nuclear reactor - givan
http://www.extremetech.com/extreme/181620-2-billion-year-old-african-nuclear-reactor-proves-that-mother-nature-still-has-a-few-tricks-up-her-sleeve

======
yread
interesting topic, you'd perhaps do better reading the wikipedia article

[http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor](http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor)

they've found out about it because the uranium ore had smaller ratio of U235
than usual so they suspected that some of it might have been stolen for
weapons.

The reactor worked because U235 was more abundant naturally 2 billion years
ago, now it has decayed more, so it's no longer possible. The reactor was
periodically flooded with water which moderated the reaction. After 30 minutes
of reaction all water would boil away.

It is interesting for the study of nuclear waste disposal - this is 2 billion
years old nuclear waste still sitting exactly in the place where it was
created

~~~
ISL
To a modern physicist, perhaps the most interesting thing about the Oklo
reactor is that it gives us one of the biggest levers on the question "Have
the laws of physics changed over time?"

So far as anyone can tell, nuclear physics was the same back then as it is
today.

~~~
dragonwriter
> To a modern physicist, perhaps the most interesting thing about the Oklo
> reactor is that it gives us one of the biggest levers on the question "Have
> the laws of physics changed over time?"

I don't think it really does, because our interpretation of the causes that
produced the effects that we can see now as something which supports the
conclusion that the laws of physics were the same then itself rests on the
assumption that the laws of physics were the same then.

~~~
maaku
It provides one more data point that constrains just how different the laws of
physics could have been in the past -- no matter how different the laws of
physics were, it must have still enabled an event which created the isotopic
concentrations we see today.

Yes, that is a much looser constraint than the GP described, but it is still a
significant data point.

------
dalke
This topic has been making the rounds the last few weeks around the various
technical-oriented sites, with mentions on HN at
[https://news.ycombinator.com/item?id=7687948](https://news.ycombinator.com/item?id=7687948)
and
[https://news.ycombinator.com/item?id=7683888](https://news.ycombinator.com/item?id=7683888)
.

I don't believe the author of this Extreme Tech piece quite understands the
deep time involved. The article says:

> This boil-seep-boil system would have made the area extremely volatile —
> perhaps some remnant of that violence explains why the area features so
> heavily in local lore and has even grown to prominence in modern day
> religions such as Falun Gong.

It also points out that the natural reactor was 2 billion years ago.

That's long enough for a mountain chain to form and erode back down into a
flat surface. Any physical remnants from that era should be much less
interesting than innumerable more recent geological events.

~~~
simonh
I find it hard to believe ancient Falun Gong practitioners were operating
geological nuclear reactors in Gabon 2 billion years ago. I wouldn't put it
past a Pak Protector(1), but the timeline indicates the Tnuctipun(2) are more
likely suspects ;)

1)
[http://en.wikipedia.org/wiki/Pak_Protector](http://en.wikipedia.org/wiki/Pak_Protector)
2)
[http://en.wikipedia.org/wiki/Tnuctipun](http://en.wikipedia.org/wiki/Tnuctipun)

~~~
kabdib
Indeed. Spoilers here.

[http://www.larryniven.net/stories/downinflames.shtml](http://www.larryniven.net/stories/downinflames.shtml)

~~~
simonh
DIF is fun, but it changes too much established canon for my liking. I have my
own grand unified Known Space theory, originally in two forum posts which a
friend has compiled together:

[http://news.larryniven.net/concordance/content.asp?page=The%...](http://news.larryniven.net/concordance/content.asp?page=The%20Tnuctipun%20Plot)

~~~
pavel_lishin
Ooh, a fellow Niven fan!

I have a problem with your theory that the Outsiders built the ring as a
doomsday Protector breeding ground: why would they create copies of Known
Space worlds, and then seed them with the inhabitants of those worlds?

~~~
simonh
Cop out answer: The same reason anyone else would, i.e. that's not a
particular reason to exclude them as against anyone else.

Best answer I can come up with: they are laboratories for experimenting with
known space sentient species. After all these are species that evolved from
programmed good yeast, so the outsiders may want to figure out how that works
and if there are any nasty surprises hidden in their genomes.

Which is an interesting idea I think and I wouldn't have though of it if you
hadn't asked, so thanks!

------
pablobaz
> A huge, naked pile of nuclear waste has sat beneath Oklo for billions of
> years; why not put a bit more under the Nevada desert, in shielded canisters
> no less?

I think this is a bad case of survivorship bias.

~~~
chc
I think you can't reasonably claim that without any evidence.

------
Patrick_Devine
Regarding the comment toward the end of the article questioning why the west
doesn't sell CANDU reactors to Iran; I would guess that's probably to do with
the political situation in Canada with the ruling Conservative Party. Some
parts of the party tend to be quite jingoistic, and I'm sure would never
support building in Iran, despite there being CANDU reactors in India,
Pakistan and China. Also, despite heavy water reactors not being a good source
of enriched uranium, they still do produce tritium which can be used to do
nasty things.

~~~
jloughry
Could someone more knowledgeable about nuclear physics than I am comment on
the safety aspects of the positive void coefficient of the CANDU design? If
the water boils, the reaction could run away.

That said, the fact that a CANDU runs on unenriched natural uranium and the
way it can be refuelled without shutting down power generation are seriously
cool features. And they claim that the long time constant makes avoiding a
Chernobyl-style excursion unlikely if the operators are awake. But I still
worry about a design that isn't statically safe.

~~~
maaku
Chernobyl would have been safe if the operators were "awake" and doing their
job.

------
akiselev
> A huge, naked pile of nuclear waste has sat beneath Oklo for billions of
> years; why not put a bit more under the Nevada desert, in shielded canisters
> no less?

Most of our nuclear waste is _nothing_ like the nuclear "waste" in Oklo [1].
The primary danger comes not from the reactor but from the enrichment process
and uranium hexaflouride (UF6). During enrichment, fissile uranium atoms are
extracted to make "enriched" uranium while the rest (over 90%!) of the UF6,
which is very toxic and reacts with air and water to form extremely corrosive
compounds, is stored in gas cylinders as "depleted" uranium.

Think about that again: we use metal gas canisters to store toxic waste, waste
that reacts with some of the most abundant molecules to form more chemicals
that slowly destroy the canister. Depending on how these containers are stored
and maintained, the UF6 leaks into the air or, even worse, into our ground
water reservoirs, taking the non-fissile but still radioactive uranium with
it.

Injecting our nuclear waste into the Earth like we do carbon sequestration
would be great, but we just don't have the millions of years to wait for the
uranium to pass through the ground water system or the technology to figure
how and where our reservoirs interconnect (or even how big most of them are).
Until we do, storing waste like Oklo is just a step shy of giving everyone
some old Fiesta Ware.

[1] [http://web.ead.anl.gov/uranium/](http://web.ead.anl.gov/uranium/)

~~~
Turing_Machine
[http://web.ead.anl.gov/uranium/faq/storage/faq22.cfm](http://web.ead.anl.gov/uranium/faq/storage/faq22.cfm)

It says they're busy converting the UF6 to uranium oxides as we speak. Uranium
oxides are the primary uranium ore. So, what you're getting out is the same
stuff that came in from the mine, but considerably _less_ radioactive (since
the U235 and all the fission products (radium, etc.) have been removed).

"but we just don't have the millions of years to wait for the uranium to pass
through the ground water system"

Those uranium oxides sat in the ore bodies for billions of years without
causing trouble.

There are almost certainly gigantic uranium ore deposits underneath the ocean.
No one is worrying about them.

~~~
akiselev
That deconversion process will take another 15-20 years [1] _if_ the Paducah
and Portsmouth plants are at the planned utilization, which AFAIK hasn't been
true since at least the 2013 budget sequestration. Our UF6 isn't going away
for another few decades.

> Those uranium oxides sat in the ore bodies for billions of years without
> causing trouble.

We've found ground water that is contaminated not only by uranium from coal
plant ash ponds [2], uranium mines [3], ore processing [4], and flooding [5]
but from the untouched ores lining natural underground aquifers as well [6].

> There are almost certainly gigantic uranium ore deposits underneath the
> ocean. No one is worrying about them.

Any ore deposit is compressed for eons under pressure that is hundreds, or
thousands, of times greater than anything we experience on a day to day basis,
or even at the extremes of our technology. There's a huge difference between
nature's long term storage and our temporary tin cans.

[1] [http://www.nrc.gov/materials/fuel-cycle-fac/ur-
deconversion....](http://www.nrc.gov/materials/fuel-cycle-fac/ur-
deconversion.html)

[2]
[http://en.wikipedia.org/wiki/Uranium_poisoning_in_Punjab](http://en.wikipedia.org/wiki/Uranium_poisoning_in_Punjab)

[3]
[http://www.denverpost.com/ci_14894696](http://www.denverpost.com/ci_14894696)

[4]
[http://www.epa.gov/radiation/docs/tenorm/402-r-08-005-voli/4...](http://www.epa.gov/radiation/docs/tenorm/402-r-08-005-voli/402-r-08-005-v1-ch4.pdf)

[5] [http://energy.gov/lm/articles/doe-releases-data-summary-
repo...](http://energy.gov/lm/articles/doe-releases-data-summary-report-
groundwater-and-soil-tests-conducted)

[6]
[http://www.sciencedirect.com/science/article/pii/08832927949...](http://www.sciencedirect.com/science/article/pii/088329279490037X)

~~~
Turing_Machine
"Any ore deposit is compressed for eons under pressure that is hundreds, or
thousands, of times greater than anything we experience on a day to day basis"

Sorry, that's simply not true. Ore can be in any form from hard rock to sand.
In fact a significant amount of uranium ore occurs as placer deposits.

Are you disputing that there are almost certainly very large uranium ore
deposits on the sea floor, exposed directly to (uber corrosive!) saltwater?
Why aren't you worried about those?

"There's a huge difference between nature's long term storage and our
temporary tin cans."

Oh, please.

~~~
Turing_Machine
1) There are about 4.5 _billion tons_ of uranium already in the ocean.

[http://spectrum.ieee.org/energy/nuclear/nuclear-fuel-from-
th...](http://spectrum.ieee.org/energy/nuclear/nuclear-fuel-from-the-sea)

2\. This 4.5 _billion tons_ represents a concentration of 3.3 parts per
billion.

3\. The U.S. has 470,000 tons of uranium (combined into 700,000 tons of UF6).

[http://web.ead.anl.gov/uranium/faq/storage/faq16.cfm](http://web.ead.anl.gov/uranium/faq/storage/faq16.cfm)

4\. As an exercise for the reader, figure out how much the ocean's
concentration of uranium in ppb would change if we just dumped all 470,000
tons directly into the sea (i.e., the worst case scenario to end all worst
case scenarios).

It's a non-issue, dude.

------
crb002
Would make for an interesting scify novel. What if humanity came on the scene
hundreds of millions of years earlier and U235 was at 1%.

~~~
iwwr
Hundreds of millions? It depends precisely what number. Terrestrial
macroscopic life is barely 500mil years old and 100mil years earlier the
atmosphere would have been too low in oxygen to breathe. Land animals with
larger brains are rather recent too, just 250mil years or so. But that still
leaves a large margin for sentient life to develop.

------
Eric_WVGG
Steven Baxter wrote about this in his sci-fi novel Manifold:Origin. Terrific
trilogy, I highly recommend them. And he’s ex-NASA, so the sci (of which
there’s plenty) is above-par.

