Nasa / Space

Geek Trivia: (Melt)down to Earth

Where is the world's only known naturally occurring nuclear reactor located -- a geological formation that induced and maintained a fission chain reaction without any human intervention?

On Nov. 29, 1955, Experimental Breeder Reactor #1 (EBR-1) outside Arco, ID became the first reactor on the planet to suffer a meltdown, thereby inaugurating the era of nuclear reactor accidents. Now, to be fair, the meltdown was only partial, was due to operator error, and occurred at a time when there were only a handful of reactors operating in the world. Still, the fact that meltdowns go back at least 50 years demonstrates just how fine the line is between sustainable energy source and an outtake from The China Syndrome.

For a quick review, all you need for a nuclear chain reaction is a starter stock of some enriched fissile isotope (say, Uranium-235 or Plutonium-239) and a few free neutrons to start the ball rolling. Hit a nucleus of U235 with a neutron, and it will split into two lesser elements and release a bunch of energy (about 180 million electronvolts) and three neutrons.

This trio of neutrons will go on to hit three more U235 nuclei lying around. Thus, the process will spiral upward in an exponential manner, releasing a lot of energy -- the kind that wipes cities off the map, if you have enough fissile material involved.

Of course, it's not that easy, because the neutrons released by U235 fission (or that of any fissile material) are often thrown off too fast to impact other nuclei. To slow down the neutrons, reactors employ neutron moderators -- usually deuterium or graphite -- which keep the particles moving at reaction-friendly speeds.

Fair warning: Once you've encouraged a chain reaction with a neutron moderator, you need a counterbalance to keep the nuclear reaction under control. That's where control rods made of cadmium, hafnium, or boron -- all of which absorb neutrons -- come into play, siphoning off the neutrons that keep the reaction going.

The trick to maintaining a healthy nuclear reactor is controlling the speed and production of your neutrons. Get either factor out of balance, and the reactor will either fizzle or meltdown.

If that sounds complicated, it is. That's why meltdowns -- and sustained fission chain reactions of any kind -- are virtually unheard of in nature. Virtually, but not completely unheard of, as there's at least one place where naturally occurring reactor-style nuclear fission is known to have taken place.

WHERE CAN ONE FIND THE WORLD'S ONLY KNOWN NATURALLY OCCURRING NUCLEAR REACTOR?

Get the answer.

About

Jay Garmon has a vast and terrifying knowledge of all things obscure, obtuse, and irrelevant. One day, he hopes to write science fiction, but for now he'll settle for something stranger -- amusing and abusing IT pros. Read his full profile. You can a...

15 comments
Dr_Zinj
Dr_Zinj

See "A Natural Fission Reactor," by George A. Cowan; Scientific American, July 1976].

Nicholas.Newman@Skynet.be
Nicholas.Newman@Skynet.be

Ah, I knew the answer to Jay Garmon's question, but I didn't know how or when I learned it. Now I know, unless it was from a French publication possibly about the same time.

catseverywhere
catseverywhere

I read scientific american cover to cover, every issue from 1973 to 2002. Around 1999 they got bought out and went way south. (a political agenda became obvious) I remembered this article, too. I knew the answer for once! Now my quibble: EVERYBODY knows the Earth is only 4,000 years old and men rode dinosaurs. So your whole BS about 1.5 billion years doesn't cut it. God made that vein with less than 0.72% U-235 to confuse the French. God knows they need it. Off to get me some freedom fries... =) (relax, it's the weekend...)

Snak
Snak

Is this a quibble? The mechanism that keeps the Earth's core molten and hot, is the nuclear reactions that are going on right now - and have (probably) been going on for four and a half billion years.

Justin James
Justin James

Maybe on this planet, but certainly not in nature. Stars are nuclear reactors. Fusion reactors, to be specific. J.Ja

jgaskell
jgaskell

...it did say the WORLD's only known natural reactor, which sort of counts out stars.

Justin James
Justin James

You are right, I missed that! I came so close! I will get an official quibble accepted one day. I promise. And then... I might get a TechRepublic mug. Or a mention in the newsletters! Oh... wait... I already have a TR mug... and I am in the newsletters all of the time. Hmm. Maybe I will get a plaque then. Yeah, that's the ticket. :) J.Ja

ben.h.loosli
ben.h.loosli

My father-in-law was one of the security guards on duty at the site that night. He was one of the first to get to the reactor building.

jeffarndt
jeffarndt

Good article, I haven't thought about this stuff since I left the nuclear power world about 10 years ago. Just a quibble about the moderators and control rods. This could be totally different in the commercial world. The most common neutron moderator is pure water. The hydrogen atoms in the water are about the same mass as the neutrons and do a good job slowing down neutrons. Plus it is cheap and abundant. Nice thing about using water as your moderator, if you lose pressure and there is no water, fission shuts down The graphite you mention as a moderator was used in early reactors to serve as a control rod (think Manhattan project) and was flammable at high temperatures (look up the Windscale fire). Hafnium it pretty commonly used as a control rod and we kept boron around as a last ditch control rod. Put some in the cooling water and the reactor will shut down, as long as you haven't created a bubble in the reactor core (TMI). Good luck trying to start it back up again.

seanferd
seanferd

the fantastic Sodium-cooled reactors. Yummy. The Windscale fire was exciting enough, along with events like TMI and Chernobyl, not to mention Detroit's (Enrico Fermi) reactor accident and whichever incident it was that included an operator getting pinned to the cieling of the reactor building with a control rod (experimental reactor, I believe, possibly military). Glad we haven't seen what happens when a large radioactive sodium leak makes contact with atmosphere. So, a "thanks" and a ton of respect for those souls who have fought reactor fires, breaches, excursions, etc.

RandyB1
RandyB1

A prototype reactor that was to be used for a power source in the antartic. A "depressed" operator lifted a central control rob by hand, causing criticality. A steam explosion ejected the control rod, and pinned the operator to the ceiling.

smetts
smetts

Jeff isn't it funny all the stuff you remember from NUC school that you just don't think about when your in the fleet. Good to see you have settled down. BTW how's the finger?

jeffarndt
jeffarndt

Man, it has been a long time. Doing pretty well, left the Navy after the L.Y. Spear decommed. Two kids and doing great. Finger is good...I have a pretty healthy respect for electricity (especially 450v).

smetts
smetts

Jeff, glad to hear you're doing well! My daughter is in college now and driving me crazy. Retired in 1996 that's when I left the Jville.