# Greetings,First Post. How small a nuclear reactor? **URL:** \ **Category:** Factual Questions\ **Created:** [April 12, 2007, 8:18am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771 "2007-04-12T08:18:38Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Shamozzle](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)\ **Post date:** [April 12, 2007, 8:18am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/1 "2007-04-12T08:18:38Z")
Hello All, I’ve recently discovered these forums and I’ve been devouring their content ever since. I would just like to say that there is some serious “brain power per square footage” on these forums and I’m excited to participate. Thanks in advance to all. Ok, here’s my question(s): What would be the first technical barrier encountered in an attempt to dramatically scale down the size of nuclear reactors to, say, something that would fit on your kitchen counter? In your pocket? What’s the smallest nuclear reactor around? For simplicity sake let’s ignore cost and safety issues. Thanks ---
**Author:** ![aldiboronti](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)\ **Post date:** [April 12, 2007, 8:41am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/2 "2007-04-12T08:41:52Z")
Welcome to the board, **Shamozzle**! Until someone who knows what they’re talking about comes along, here’s what I found on the net. (Not really kosher to google up answers for General Questions, I know, but the question interested me and I just thought I’d share this nugget of info.) It’s a summary from the [American Nuclear Society site](http://www.ans.org/pubs/journals/nse/va-153-1-90-92) and the full article is available only by subscription, but this is the nitty-gritty: > [@](#): > > It was found that the smallest reactor is a spherically shaped solution of 242mAm(NO3)3 in water. The weight of such a reactor is 4.95 kg with 0.7 kg of 242mAm nuclear fuel. The radius of the reactor in this case is 9.6 cm ---
**Author:** ![Shamozzle](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)\ **Post date:** [April 12, 2007, 8:50am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/3 "2007-04-12T08:50:57Z")
[QUOTE=aldiboronti] Welcome to the board, **Shamozzle**! Until someone who knows what they’re talking about comes along, here’s what I found on the net. (Not really kosher to google up answers for General Questions, I know, but the question interested me and I just thought I’d share this nugget of info.) It’s a summary from the [American Nuclear Society site](http://www.ans.org/pubs/journals/nse/va-153-1-90-92) and the full article is available only by subscription, but this is the nitty-gritty: [/QUOTE] Thanks for the reply Wow! That is amazing. I had no idea a reactor could be that small. Perhaps in 2013 we will see the iReactor from Apple… (Ok, maybe 2063) ---
**Author:** ![glee](https://avatars.discourse-cdn.com/v4/letter/g/b5a626/32.png) [@glee](https://boards.straightdope.com/u/glee)\ **Post date:** [April 12, 2007, 9:54am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/4 "2007-04-12T09:54:26Z")
Shamozzle, welcome to the boards! 🙂 I like your first question - although you’ve set a high standard for yourself in future. :eek: Sadly I’m not a nuclear physicist. However I can see some difficulty in placing nuclear reactors in the hands of the general public. Remember these are the sort of people who: - **microwave cats** An investigation is under way after the body of a cat was found in a microwave oven. [http://www.manchestereveningnews.co.uk/news/c/192774\_cat\_killed\_in\_microwave.html](http://www.manchestereveningnews.co.uk/news/c/192774_cat_killed_in_microwave.html) - **try to avoid paying bills by tampering with meters** A fire which left about 25 Greater Manchester residents homeless may have been caused by someone tampering with an electricity meter. [http://www.fire.org.uk/BBC\_News/News2002/January/bbc210102i.htm](http://www.fire.org.uk/BBC_News/News2002/January/bbc210102i.htm) - **have home accidents** More people die in the home every week than in road accidents, according to a government report. In the UK, 76 people are killed in domestic accidents each week. > **[BBC News | HEALTH | Home hazards 'kill more than cars'](http://news.bbc.co.uk/2/hi/health/1230176.stm)** > > More people die in the home every week than in road accidents, according to a government report. ---
**Author:** ![samclem](https://avatars.discourse-cdn.com/v4/letter/s/a9a28c/32.png) [@samclem](https://boards.straightdope.com/u/samclem)\ **Post date:** [April 12, 2007, 11:14pm UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/5 "2007-04-12T23:14:32Z")
Welcome. I edited the title to make it more descriptive. More people read your thread if you tell something about it. **samclem** GQ moderator ---
**Author:** ![The\_Scrivener](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@The\_Scrivener](https://boards.straightdope.com/u/The_Scrivener)\ **Post date:** [April 12, 2007, 11:51pm UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/6 "2007-04-12T23:51:47Z")
No thread on this subject can overlook the strange case of David Hahn, the 17-year-old Michigan Boy Scout who [built a functioning (if highly unsafe) breeder reactor in his mother’s backyard garden shed](http://www.amazon.com/Radioactive-Boy-Scout-Backyard-Nuclear/dp/product-description/037550351X) in 1995. I can’t believe no one’s made a farcical, black-tinged comedy out of this one yet. ---
**Author:** ![aldiboronti](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)\ **Post date:** [April 13, 2007, 9:01am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/7 "2007-04-13T09:01:46Z")
What a fascinating story! Thanks for that. Here’s a link to the original Ken Silverstein piece, [The Radioactive Boy Scout](http://www.wesjones.com/silverstein1.htm) which goes into more detail. ---
**Author:** ![Shamozzle](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)\ **Post date:** [April 13, 2007, 9:14am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/8 "2007-04-13T09:14:18Z")
:eek: Holy Smokes! :eek: Well, if anything, we can’t say the kid lacked vision… And thanks for the replies, everyone. ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [April 13, 2007, 10:17am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/9 "2007-04-13T10:17:13Z")
[QUOTE=aldiboronti] It’s a summary from the [American Nuclear Society site](http://www.ans.org/pubs/journals/nse/va-153-1-90-92) and the full article is available only by subscription, but this is the nitty-gritty: [/QUOTE] > [@](#): > > It was found that the smallest reactor is a spherically shaped solution of 242mAm(NO3)3 in water. The weight of such a reactor is 4.95 kg with 0.7 kg of 242mAm nuclear fuel. The radius of the reactor in this case is 9.6 cm Whats the power output? I am guessing it is pure thermal decay, thus the power output is low and basically constant. Assuming you are talking about something that generates power by fission, the lower limit is pretty large (at least 50kg fissile material to get a critical mass (probably more - 400kg of 20% uranium), more mass than that for moderating the neutrons, tonnes of radiation shielding and cooling) - the powerplants used by nuclear subs are probably the optimal limit - they have an excess of power generation and are fitted into a restricted space, so if they could be made smaller, they would be. I can’t find details of size. The Radioactive Boy Scout had a breeder reactor - he was not generating power, he was using fission to convert one element into another. No mean feat, and potentially lethal, but no huge power output. So - no fission nuclear powered cars. Certainly not on a kitchen bench. Si ---
**Author:** ![Shamozzle](https://avatars.discourse-cdn.com/v4/letter/s/9f8e36/32.png) [@Shamozzle](https://boards.straightdope.com/u/Shamozzle)\ **Post date:** [April 13, 2007, 10:27am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/10 "2007-04-13T10:27:26Z")
Yes, that would seem to be true, wouldn’t it: the reactors in US Navy submarines would approach minimal size limits with respect to their given output… But now this leads me to another question: What is the Watts/Kilo ratio for a cutting edge: jet engine? internal combustion engine (formula 1 car?)? fission reactor? ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [April 14, 2007, 11:12am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/11 "2007-04-14T11:12:51Z")
[QUOTE=si\_blakely] So - no fission nuclear powered cars. Certainly not on a kitchen bench. Si [/QUOTE] however nuclear powered aircraft were looked at, and a 1MW operating reactor flown in a B36 bomber > **[Nuclear-powered aircraft](https://en.wikipedia.org/wiki/Nuclear_aircraft)** > > A nuclear-powered aircraft is an aircraft whose power source is nuclear fission. Most designs use a nuclear reactor that heats compressed air inside a jet engine to provide thrust. Either a turbojet or a ramjet can be used, as with ordinary chemical propulsion. During the Cold War, the United States and Soviet Union researched nuclear-powered bomber aircraft, the greater endurance of which could enhance nuclear deterrence, but neither country created any such operational aircraft. The adven Nucle... ---
**Author:** ![coffeecat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/coffeecat/32/3405_2.png) [@coffeecat](https://boards.straightdope.com/u/coffeecat)\ **Post date:** [April 14, 2007, 12:04pm UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/12 "2007-04-14T12:04:59Z")
[QUOTE=si\_blakely] Whats the power output? I am guessing it is pure thermal decay, thus the power output is low and basically constant. Assuming you are talking about something that generates power by fission, the lower limit is pretty large (at least 50kg fissile material to get a critical mass (probably more - 400kg of 20% uranium), more mass than that for moderating the neutrons, tonnes of radiation shielding and cooling . . . [/QUOTE] If you don’t require fission, there’s practically no lower limit. A pacemaker battery converts nuclear energy to useful work. So does an arbitrarily small dot of radioactive paint on a watch dial. Neither is what most people would call a nuclear reactor, though. Just what _are_ Y. Ronen, E. Fridman, and E. Shwageraus talking about in their article, anyway? :smack: Where’s a nuclear engineer when you need one? ---
**Author:** ![coffeecat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/coffeecat/32/3405_2.png) [@coffeecat](https://boards.straightdope.com/u/coffeecat)\ **Post date:** [April 14, 2007, 12:25pm UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/13 "2007-04-14T12:25:45Z")
P.S. [QUOTE=Shamozzle] Thanks for the reply Wow! That is amazing. I had no idea a reactor could be that small. Perhaps in 2013 we will see the iReactor from Apple… (Ok, maybe 2063) [/QUOTE] I can see it now: “Get ready for the coming apocalypse! Grow weed for all your friends, without those embarrassing questions about your electric bill!” ::Silhouettes of dancing hippies and survivalists:: ---
**Author:** ![Sequent](https://avatars.discourse-cdn.com/v4/letter/s/dbc845/32.png) [@Sequent](https://boards.straightdope.com/u/Sequent)\ **Post date:** [April 14, 2007, 5:27pm UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/14 "2007-04-14T17:27:51Z")
This is why I love the SMDB…where else am I going to hear the story of the Radioactive Boy Scout? Although, I’ve gotta say, I found the following to be the most horrifying detail in that article: > [@](#): > > Radium was used in paint that rendered luminescent the faces of clocks and automobile and airplane instrument panels until the late 1960s, when it was discovered that many clock painters, who routinely licked their brushes to make a fine point, died of cancer. :eek: It really makes me wonder how many people today, right now, going about their seemingly innocuous lives are really canaries in the coal mine of our modern age… ---
**Author:** ![The\_Scrivener](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@The\_Scrivener](https://boards.straightdope.com/u/The_Scrivener)\ **Post date:** [April 15, 2007, 3:01am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/15 "2007-04-15T03:01:25Z")
On that note, there was a segment on one of the network news broadcasts about the asbestos problem in the U.S. Capitol Building, in the subterranean areas at least. It’s a real problem for the janitors, maintenance workers, etc. And yellow glass _used_ to be made with uranium as the tinting agent. (One such manufacturer: the storied Sandwich Glass factory in Massachusetts.) In theory, if you carried a Geiger counter with you to garage sales and flea markets, you’d occasionally find a yellow glass ashtray or candlestick holder or whatnot that’d raise a bit of a buzz… :eek: ---
**Author:** ![aldiboronti](https://avatars.discourse-cdn.com/v4/letter/a/9fc348/32.png) [@aldiboronti](https://boards.straightdope.com/u/aldiboronti)\ **Post date:** [April 15, 2007, 10:12am UTC](https://boards.straightdope.com/t/greetings-first-post-how-small-a-nuclear-reactor/399771/16 "2007-04-15T10:12:04Z")
[QUOTE=coffeecat] If you don’t require fission, there’s practically no lower limit. A pacemaker battery converts nuclear energy to useful work. So does an arbitrarily small dot of radioactive paint on a watch dial. Neither is what most people would call a nuclear reactor, though. Just what _are_ Y. Ronen, E. Fridman, and E. Shwageraus talking about in their article, anyway? :smack: Where’s a nuclear engineer when you need one? [/QUOTE] I’m not a subscriber either, so unfortunately I can’t get access to the full article. ☹