What is the smallest possible nuclear reactor?

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Offline Roy P

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What is the smallest possible nuclear reactor?
« on: 10/08/2008 20:01:22 »
I'm wondering just how small a nuclear reactor can be? Is it possible that in the future we could power our laptops and other mobile devices with our own mini nuclear reactors? Maybe also our homes and cars?

Roy P
« Last Edit: 14/08/2008 15:39:58 by chris »
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lyner

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Re: What is the smallest possible nuclear reactor?
« Reply #1 on: 10/08/2008 20:34:17 »
Never mind about how big the reactor needs to be - what about the SCREENING?

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Offline Bored chemist

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Re: What is the smallest possible nuclear reactor?
« Reply #2 on: 10/08/2008 20:56:20 »
It depends what you mean by a nuclear reactor.
This doesn't fit the usual description but it's certainly portable.
http://www.pubmedcentral.nih.gov/pagerender.fcgi?artid=287459&pageindex=1

If you are on about a conventional fission reactor then there is a lower limit imposed by the requirement for a critical mass. I think the smallest reactors made are probably those in nuclear submarines.
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lyner

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Re: What is the smallest possible nuclear reactor?
« Reply #3 on: 11/08/2008 11:21:56 »
Yes, possibly, but it's not so much a reactor but a radioactive isotope where every atom is decaying, randomly, all on its own, not stimulated by neutrons flying through it, as in a conventional ('chain') reactor. Very safe, as long as it's mainly alpha and beta radiation but extremely low power.
'Small' is a relative word and even a Nuke Sub is a big beast and can carry quite a lot of weight compared with a land vehicle.

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Offline DonBrown

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Re: What is the smallest possible nuclear reactor?
« Reply #4 on: 14/08/2008 14:17:00 »
... there is a lower limit imposed by the requirement for a critical mass.
So I wonder what the smallest possible critical mass is?

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Offline Bored chemist

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What is the smallest possible nuclear reactor?
« Reply #5 on: 14/08/2008 19:17:34 »
I think it's about the size of a grapefruit. However, making a controlable reactor rather than a bomb is a different question. Getting a reactor that fitted in a car is, I guess, impossible. A railway locomotive might be possible.
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Offline Roy P

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What is the smallest possible nuclear reactor?
« Reply #6 on: 14/08/2008 19:47:33 »
Mmmm. So it's not practically possible as a power source for my iPod! Is it even theoretically possible?
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Offline ukmicky

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What is the smallest possible nuclear reactor?
« Reply #7 on: 14/08/2008 21:34:25 »
I dont really know any thing about nuclear power but doesn't the reaction produce heat and the heat is then converted into steam in order for us to to use it making a mini reactor impracticable. Could be wrong.

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Offline LeeE

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What is the smallest possible nuclear reactor?
« Reply #8 on: 15/08/2008 00:16:00 »
About grapefruit sized is right for a fissionable mass.  You'd need to add moderator and heat exchanger gubbins as well though, to make it usable.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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lyner

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What is the smallest possible nuclear reactor?
« Reply #9 on: 15/08/2008 17:38:31 »
About grapefruit sized is right for a fissionable mass.  You'd need to add moderator and heat exchanger gubbins as well though, to make it usable.

And what about all the necessary screening? You wouldn't sell many vehicles without protecting the occupants.

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Offline LeeE

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What is the smallest possible nuclear reactor?
« Reply #10 on: 16/08/2008 12:32:38 »
Yes, you'd need screening too, of course.  Just as big an issue would be making it crash-proof.
...And its claws are as big as cups, and for some reason it's got a tremendous fear of stamps! And Mrs Doyle was telling me it's got magnets on its tail, so if you're made out of metal it can attach itself to you! And instead of a mouth it's got four arses!

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Offline elephantwalker

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What is the smallest possible nuclear reactor?
« Reply #11 on: 30/09/2008 07:07:49 »
A nuclear reactor design is based upon three things:
1) the neutron crossection of the fuel
2) the density of the fuel
3) the method of heat removal

higher neutron crossection, and higher density gives more reactivity for the reactor per volume. This is why dense forms of u-235 such as UN or uranium nitride give the smallest size reactors. This type of reactor is in the megawatt range, and is the size of a small trash can.

This type of reactor has been tested for space travel (JIMO).

There has been speculation that small amounts of Am-241 could be used as a reactor, however, Am-241 has not been succesfully fabricated into fuel, and handling the 241m for would be particularly difficult. Also, Am-241 generates fast neutrons, which would require reflectors, and other complications of such a small reactor design.

The HEU UN reactor remains the smallest of any design tested.

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Offline rbagwell

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What is the smallest possible nuclear reactor?
« Reply #12 on: 13/10/2008 13:20:25 »
Many years ago nuclear power could be carried in a backpack.

http://en.wikipedia.org/wiki/Suitcase_bomb :  says

"The smallest nuclear warhead ever acknowledged to have been manufactured by the USA was the W54, which was used in both the Davy Crockett 120 mm recoilless rifle–launched warhead, and the backpack-carried version called the Mk-54 SADM (Special Atomic Demolition Munition). The bare warhead package took the form of an 11"x16" cylinder that weighed only 51 lbs (23 kg). It was, however, easily small enough to fit in a footlocker-sized container."

In the '50's Ford conceived an atomic powered car.

http://en.wikipedia.org/wiki/Ford_Nucleon

Had we not "outlawed" atomic power for so many years most 18 wheelers , locomotives , ships, and even cars would be nuclear powered today.

Designs incorporating closed cycle gas turbines like discussed here :

http://www.atomicengines.com/engines.html

would make factory made nuclear energy devices common.


 

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Offline yor_on

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What is the smallest possible nuclear reactor?
« Reply #13 on: 12/11/2008 01:24:42 »
Screening is for wimps:)
Real men just 'tans'.
Smilingly...

Awh, that was my worst joke yet.
As long as we don't have any real long-term storage we shouldn't touch this.
fifty, a hundred, even a thousand years is only a tiny winy bit of it..
That's my view for now, we still have time to develop alternative energy sources.
But then 'energy/power' just might become decentralized?
And as we all know. Power is power:)
"BOMB DISPOSAL EXPERT. If you see me running, try to keep up."

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Offline Bored chemist

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What is the smallest possible nuclear reactor?
« Reply #14 on: 12/11/2008 20:00:19 »
Many years ago nuclear power could be carried in a backpack.

http://en.wikipedia.org/wiki/Suitcase_bomb :  says

"The smallest nuclear warhead ever acknowledged to have been manufactured by the USA was the W54, which was used in both the Davy Crockett 120 mm recoilless rifle–launched warhead, and the backpack-carried version called the Mk-54 SADM (Special Atomic Demolition Munition). The bare warhead package took the form of an 11"x16" cylinder that weighed only 51 lbs (23 kg). It was, however, easily small enough to fit in a footlocker-sized container."

In the '50's Ford conceived an atomic powered car.

http://en.wikipedia.org/wiki/Ford_Nucleon

Had we not "outlawed" atomic power for so many years most 18 wheelers , locomotives , ships, and even cars would be nuclear powered today.

Designs incorporating closed cycle gas turbines like discussed here :

http://www.atomicengines.com/engines.html

would make factory made nuclear energy devices common.

 
A bomb can be made that's only a little bigger than the critical mass.
However, if you want control, transfer of the heat produced and enough screening to stop it killing the user then the best you can do is roughly the sort of thing they put in nuclear submarines- lets face it, if they could make those reactors smaller, they would.

Just because you can make a small bomb is no reason to think that you would have a nulear powered truck or car these days if it weren't for legality. Plenty of places have invented their own reactors for power and, to be honest, to make material for bombs like the UK did. Nobody has a nuclear truck.
Anyway, the insurannce costs would be too high.
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Offline top_kat

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What is the smallest possible nuclear reactor?
« Reply #15 on: 25/11/2008 02:07:09 »
One of the smallest operational reactors was utilized by the naval submarine NR-1 which I think is on the order of tens of kilowatts output.

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Offline Gyro77

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What is the smallest possible nuclear reactor?
« Reply #16 on: 13/12/2009 15:58:19 »
Maybe we need to look at it from another angle. How big can a nuclear reactor be, can it power cars and lorries by powering the roads kind of like the scalelectric toy cars.
This would have other advantages like not having to steer the car until your ready to turn off the powered route.
Or you could use a nuclear reactor to fuel electric cars for instant.
I'm wondering just how small a nuclear reactor can be? Is it possible that in the future we could power our laptops and other mobile devices with our own mini nuclear reactors? Maybe also our homes and cars?

Roy P

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Offline Nizzle

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What is the smallest possible nuclear reactor?
« Reply #17 on: 15/12/2009 09:20:09 »
Roses are red,
Violets are blue.
Most poems rhyme,
but this one doesn't

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Offline Bored chemist

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What is the smallest possible nuclear reactor?
« Reply #18 on: 15/12/2009 20:31:35 »
Good question. What about it?
In particular, what about it has anything to do with the thread?
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Offline Nizzle

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What is the smallest possible nuclear reactor?
« Reply #19 on: 16/12/2009 09:34:14 »
It's a nucular battery ain't it?

I reference the topic title question: "What is the smallest possible nuclear reactor?"
Roses are red,
Violets are blue.
Most poems rhyme,
but this one doesn't

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Offline Bored chemist

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What is the smallest possible nuclear reactor?
« Reply #20 on: 16/12/2009 20:29:03 »
Mea Culpa.
Oops! it seems there's more than one type of sulphur battery.
http://en.wikipedia.org/wiki/Sodium-sulfur_battery
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Offline Colonelbauer

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What is the smallest possible nuclear reactor?
« Reply #21 on: 14/05/2011 00:20:39 »
Would it be possible to have a train run on a nuclear reactor?

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Offline CliffordK

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What is the smallest possible nuclear reactor?
« Reply #22 on: 14/05/2011 02:06:47 »
Most of the satellites sent to the outer planets have used some kind of an RTG generator.

http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

The smallest one was about 2 kg and put out about 2 watts.

I don't think anybody would allow cars and trains to use portable nuclear reactors due to the "fear factor".

There are a few Nuclear Ice Breakers.  Some plans for experimental Nuclear container ships.  But, the current construction cost for a nuclear powerplant is very high. 

The list of nuclear ships around the world is very short.
http://www.radiationworks.com/nuclearships.htm

The USA owns all but one of the Nuclear Aircraft Carriers (France has the other one).

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Offline CliffordK

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What is the smallest possible nuclear reactor?
« Reply #23 on: 14/05/2011 05:17:14 »
Oh...
Also, many colleges and universities around the country have small nuclear reactors on the order of 200 KW in size.

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Offline Bassasasin

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What is the smallest possible nuclear reactor?
« Reply #24 on: 26/08/2011 16:36:11 »
There are heat transfer chips that when heated the opposite side gets cooled and produces voltage and current.
I wonder if these chips could be used to cool a reaction and produce current.
Then things could all be made smaller.

Ah!  The Seebeck effect..
Already been done!
Radioisotope thermoelectric generator. 
Trouble is long after these have produced hundreds of watts for years they quit and there's a disposal environmental problem.  Effectively the cost of disposal vrs. kWh used doesn't make it cost effective.
Lighthouses above the Arctic circle use them (Russian) and the Cassini probe used them.

Bass.
« Last Edit: 26/08/2011 16:45:12 by Bassasasin »

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Offline SeanB

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What is the smallest possible nuclear reactor?
« Reply #25 on: 26/08/2011 21:48:18 »
Mars rovers use a few small nuclear heaters ( around 1W AFAIK) to keep essential parts warm, and of course the longest running probes use them as well, Voyager is still working, though power levels are rather much lower than when it was launched over 30 years ago. Pioneer is probably still running, though the signals are too weak to be received back on earth.

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Offline CliffordK

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What is the smallest possible nuclear reactor?
« Reply #26 on: 28/08/2011 08:43:23 »
An RTG is a "valid" nuclear reactor in that it performs work.  And, while it may not have a fission reaction, all nuclear reactors are generating and harnessing heat.

However.

What about a Tritium Exit sign?
Radium Watch Dial?

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Offline sophktt

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Re: What is the smallest possible nuclear reactor?
« Reply #27 on: 13/12/2013 09:28:39 »
I'm wondering just how small a nuclear reactor can be? Is it possible that in the future we could power our laptops and other mobile devices with our own mini nuclear reactors? Maybe also our homes and cars?

Roy P

Bilibino Nuclear power plant in the Chukotka Autonomous Okrug, Russia, houses the world's smallest commercial nuclear reactor. This is also featured in an energy industry site. Here is the link

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Offline RD

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Re: What is the smallest possible nuclear reactor?
« Reply #28 on: 13/12/2013 13:22:33 »

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Offline wolfekeeper

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Re: What is the smallest possible nuclear reactor?
« Reply #29 on: 23/12/2013 18:47:35 »
I think to be a reactor it has to be critical mass (RTGs are not reactors) and not blow itself to pieces (nukes are not nuclear reactors).

Minimum critical mass that Wikipedia knows about is Californium 252, at just 7 cm across, 2.7 kg, and that's without a tamper; a tamper can reduce the size.

https://en.wikipedia.org/wiki/Critical_mass
« Last Edit: 23/12/2013 18:49:06 by wolfekeeper »

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Offline SeanB

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Re: What is the smallest possible nuclear reactor?
« Reply #30 on: 24/12/2013 17:23:18 »
The Mars rovers ( all of them) use small 1W, 5W thermoelectric heaters to keep parts warm. those are basically small apple sized units with a thick corrosion resistant housing, which provides both shielding and protection. All in all they each have as much nuclear material in them as a ton of coal.

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Offline alancalverd

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Re: What is the smallest possible nuclear reactor?
« Reply #31 on: 25/12/2013 00:41:00 »
A "bare reactor" http://en.wikipedia.org/wiki/Godiva_device is about the size of a football but of little use as a controllable source of heat. There is market interest for dustbin-size reactors of a few megawatts: anything smaller would not meet the criteria of criticality and controllability.

Shielding need not be a problem if the beast can be located some way from human occupancy. There have been proposals for remote-controlled nuclear submarine tugs towing cargo barges but the engineering complexity of such a system makes it uneconomic compared with a conventional on-board reactor since weight is not a limiting factor in sea transport. A bare-reactor powered aircraft is feasible but presents problems of ground handling. It is difficult to incorporate a reactor with adequate shielding in a standard width road vehicle but several designs have been proposed for a nuke in a shipping container: fine for use as a mobile power source but not as a prime mover for road transport itself as it could only tow one more container on normal roads. The "nuke in a box" could however be an excellent replacement for steam and diesel locomotives, which require much less investment in track infrastructure than electric trains.
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