Nuclear Homes

lavalamp

Recently I got a whole new central heating system. Apparently it's all very efficient (over 90%). The boiler is used to produce hot water that's piped round the house to radiators, and also to provide instantaneous hot water for the taps.

However, since it is gas fired, it throws out rather a lot of CO2, which depending on your point of view is either bad or irrelevant. For the sake of this thread, lets assume that it's bad.

So I was thinking, a boiler doesn't have to be particularly powerful, I believe mine has a peak power output of 28 KW, so what would be the feesability of using a small amount of radioactive material to heat the water, rather than requiring a constant supply of gas?

I understand that such a device would require shielding, however since only a small amount of power is required, only a small amount of fuel would be required, therefore hopefully the shielding wouldn't need to be excessive. There are questions that I don't have answers to though, such as what's the smallest amount of fuel that could be used? If there's too little it simply won't chain react, if there's too much it would be wasteful and possibly dangerous.

What the fuel might be is another question, I gather that Plutonium trumps Uranium when it comes to chain reactions, however the government might get a bit antsy about handing out Plutonium. Thallium springs to mind as it is abundant in the crust and fairly useless as a nuclear bomb, though of course any radioactive fuel could find an application as a dirty bomb.

Just to be clear I was thinking that such a device would provide energy only in the form of heat, which would simplify it over a whole electrical power plant design. Similar in design to perhaps a nuclear powered aircraft which would in theory just heat the air for thrust as a sort of ramjet without combustion.

Also, about the fuel, would it be possible to include enough fuel for the device to run until way past when it is obsolete and needs to be replaced? This would side-step the issue of having the home owner getting their hands dirty/irradiated. If we assume an average power output of 1KW, then that's 3.16 TJ of energy over 100 years (far more than should be needed to ensure it never needs to be refueled).

But I'm not done yet, when I get thinking I tend to think in several directions at once, so I also thought, what if it did include an electrical generator? How small could a nuclear powered generator be made? If it's not possible to make a home generator small enough, perhaps it would be possible to build neighbourhood generators which would generate electricity and steam to be delivered to homes. The steam would be mixed with cold water to provide the hot water for central heating and the taps.

It seems that huge power plants throw away most of their energy as heat, whereas a home or neighbourhood plant could put this "wasted" energy to good use.

I'm curious as to what anyone has to say in terms of problems associated with such systems (other than public opinion) and ways in which they might be solved. For example, nuclear power plants are monitored by engineers with lots of letters after their names, but could a mini reactor be monitored by software to a sufficient extent that it could run autonomously with only routine maintenance?

russ_watters

Nuclear fuels are some of the more poisonous and expensive substances on the face of the earth, so no, you're not getting your hands on any.

As for waste heat, a lot of power plants these days are cogen plants, producing both electricity and hot water or steam.

lavalamp

Would a small amount of some nuclear fuel be more expensive than years and years worth of gas though? And yes, I understand that nuclear fuels can be dangerous, but so many things are, bleach for instance, at least this would be in a sealed unit.

Poop-Loops

Wouldn't be worth it. Nuclear plants can do it because of the scale at which they work. They only need 1 massive reactor (or system of reactors, however it works), a bulk load of the material, and enough people to run the thing safely.

For home use, you'd need everybody to have their own reactor, which would automatically drive the cost way up, buy the material in small quantities, which would cost a lot more than buying in bulk, and also need to have someone install this for you, because letting a non-specialist do it is like releasing a pedophile in a kindergarden. Yes, it would be just as horrific.

Moreover, turning a nuclear reactor on and off isn't as simple as cutting off gas flow in the heater. So it's much easier to let the big reactor just keep producing it and then let you tap in whenever you want some juice, like we do it now.

vanesch

Nuclear stuff is EXTREMELY dangerous. We know also how to handle it, and if one does it right, one can master the dangerousity while getting the benefits. But that has a price: draconian safety rules, inspections, authorisations etc... which can only become cost-effective and effective all together when used on large scale. The safety problems would become unmanageable if everyone had his mini-reactor in his basement!

Because apart from the direct radiation (which is the least of the problems) and the sealing, the main problem is the heat management: what do you do when you can't get rid of the heat ? There's no plug to pull, or valve to close to stop the heat production: you have to have a good heat evacuation in all kinds of disaster scenario's which is BTW, the main challenge in the design of a good reactor.

sas3

I do not know how reliable this story is but take a look here.

http://www.engadget.com/2007/12/19/t...r-your-garage/

Astronuc

The story is correct in these details, but this is not a system for one's home, unless one has many millions of dollars. A 20 ft by 6 ft is just the reactor - the containment and generator building is much larger.

The smaller the core, the greater the enrichment required, particular if the core is not to be refueled. Generation of nuclear energy by fission produces fission products, which themselves produce high levels of radioactivity, hence the need for shielding. For these reasons, small nuclear systems are very expensive - mainly due to high capital and backend costs.

vanesch

Well, two things make we wary: first of all, Toshiba doesn't seem to know it itself (do a search on their press releases of their nuclear activities, you'll find lots of stuff, but no "micro nuclear reactor").

Next, a Wiki article on this subject was recently deleted, and the reason given is that it is a hoax.


That said, low power nuclear reactors do exist of course. But usually they have special purposes (such as research).

Astronuc

It is certainly doubtful that a 200 kWe (~600-800 kWt) reactor would be feasible, but the Endgadget story seems to be based on the Toshiba 4S modular reactor, which was originally envisioned in the 10 MWe range.

The small modular reactor was proposed for Gelana, Alaksa.
http://www.iser.uaa.alaska.edu/Publi..._15Dec2004.pdf

http://www.roe.com/pdfs/technical/Ga...er%20Rev02.pdf

http://www.atomicinsights.com/AI_03-20-05.html

Toshiba has looked at smaller compact designs from the technical side, but economically it a whole different matter.

daveb

The problem with using radionuclides for home heating (or any other type of energy use) is that in order to do so, you need large activities (i.e., far exceeding the exempt from licensing quantity), meaning you are now regulated by either the NRC or an Agreement State. If you're going to possess special or source material for a reactor, it's the NRC. In this case, the annual fee for your license is going to be prohibitively expensive unless you are a power company. Plus, in any case, you'll need shielding, proper training, etc., making it prohbitively expensive, again, unless you're a power company. Even using regular radionuclides instead of nuclear fuel wouldn't work. Remember, 1 Curie of activity at 1MeV/disintegration only produces about 6 milliwatts power - not a lot. the reason reactors can produce so much power is that 200 MeV per usion is released, and there are in excess of 10^12 neutrons for fission per cubic centimeter.

Emfuser

Building a reactor for a home heating device is definitely a Rube-Goldberg sort of adventure. It's fun to talk about, but is wholly impractical and definitely dangerous. You'd be better off just piping your current heater exhaust into a CO2 scrubber.

russ_watters

Duh, I forgot about that - while a big furnace and a little furnace are fundamentally the same (a little natural gas and a lot of natural gas act the same), reactors aren't as scaleable.