3 ms·

So ignoring the safety issues, would there be enough radioactive isotopes on Earth for every house to have it's own RTG? Imagine unlimited energy, and heat you

So ignoring the safety issues, would there be enough radioactive isotopes on Earth for every house to have it's own RTG? Imagine unlimited energy, and heat your home with the waste heat?

jlgreco 14y ago
Plutonium 238 would be your best bet for such devices, if only because it's halflife is 87.7 years. Strontium 90 might also work, with a halflife of 28.8 years. However plutonium would not be easy to put in every house since you have to make it in nuclear reactors. You get about half a kilowatt per kilogram of it, I don't think production of it could scale that high. Strontium is naturally occurring and relatively common. Sr 90 is a trace isotope though. Off the top of my head I would suspect you would be facing similar challenges that separation of Uranium isotopes face.
- adestefan 14y ago
  Sr-90 is not naturally occurring because of its short half-life. Any Sr-90 found today is either from weapons testing or made in a reactor.
InclinedPlane 14y ago
Probably not. The problem with isotopes needed for things like this is that they tend to have short half-lives (short half-lives = high decay rate = lots of heat generated), which means they pretty much don't exist naturally at all. So they will need to be produced artificially as fission fragments or through neutron irradiation of other isotopes. It's easy enough to produce large quantities of "hot" isotopes in a fission reactor which could be used for RTGs (ignoring safety) but the problem there is that if you're operating a nuclear reactor anyway why not use the heat production from the isotopes to produce energy there instead of going the roundabout, and unsafe, route of packaging things up in RTGs?
- outworlder 14y ago
  There's also the thermocouples, which also wear out and are made of pretty expensive materials themselves. However, it is likely that a "home" device could be made simpler/less expensive.
  - jimktrains2 14y ago
    Couldn't they use a sterling engine as well? That would be a bit more maintainable I would think?
rmc 14y ago
You're also ignoring the political/emotive aspect. People don't like things called 'nuclear'.
- jlgreco 14y ago
  There are certainly some places that would probably be more accepting of it than average. http://en.wikipedia.org/wiki/File:Soviet_RTG.jpg http://en.wikipedia.org/wiki/File:Soviet_RTG.jpg ;) Those are 10 watt Sr90 RTGs, sitting around. The used to use them for lighthouses.
- InclinedPlane 14y ago
  Well... as much as I like RTGs and even fission reactors there is a little bit of justification there. Of necessity an RTG pretty much needs to contain hazardous radioisotopes. Putting that into the hands of every joe blow is probably not the best idea at present.
Cushman 14y ago
Just cribbing from Wiki, the generator contains 11 pounds of Pu-238 and produces ~150W of electricity from ~2000W of heat. It's hard to put an exact price on it, but it's definitely in the $millions per kg. It's theoretically feasible, but the cost would be, ah, prohibitive.
uvdiv 14y ago
What's wrong with the economies of scale of larger nuclear plants? I'm asking curiously, I don't understand the fascination with home energy sources. Radioactive decay is a small energy source compared to fission. Look at the binding energies [1]: the energy accessible by fissioning heavy elements is about 200 MeV -- 1 MeV per nucleon. Radioactive decays are two orders of magnitude less, or smaller. Pu-238 is one of the nicest ones because it is "clean" -- emitting only alpha radiation, which is easy to shield. You can transmute on the order of 1 atom of it per 100 fission events [2]. A fission event is 200 MeV; a Pu-238 decay is 5.6 MeV. So at steady state, you can support less than 1/3,000th as much Pu-238 power as you can fission power. If you have a Pu-238 source, you also have a vastly larger nuclear fission power source, so why not just use that? More broadly, it's not a likely idea on physics, even if you accept all radioisotopes (difficult-to-shield gamma emitters) and not just "nice" ones. The high-Z radioactive decay chains end quickly at the element lead [3], so only release a fraction of the energy that is accessible by fission. (Look back to the binding energy curve [1]). And many of these decays are unusably, geologically slow. The naturally-occurring radioisotopes have half lives of >10^8 years (otherwise they wouldn't exist anymore -- they were created in ancient history in supernovae). And trying to transmute them doesn't improve much -- i.e. in a fission reactor, the most common [4] high-Z product is Pu-239 (half life >10^4 years), whose next decay is to U-235 (half life >10^8 years). Others are similar. So I don't see any way forwards. [1] http://en.wikipedia.org/wiki/File:Binding_energy_curve_-_common_isotopes.svg http://en.wikipedia.org/wiki/File:Binding_energy_curve_-_com... [2] Through the several processes which create Np-237 from uranium -- a relatively rare process [4]. Np-237 can be isolated and transmuted to Pu-238 separately through neutron irradiation [3] http://en.wikipedia.org/wiki/File:Radioactive_decay_chains_diagram.svg http://en.wikipedia.org/wiki/File:Radioactive_decay_chains_d... [4] Small table here: http://en.wikipedia.org/wiki/Minor_actinide http://en.wikipedia.org/wiki/Minor_actinide

So ignoring the safety issues, would there be enough radioactive isotopes on Earth for every house to have it's own RTG? Imagine unlimited energy, and heat your home with the waste heat?

jlgreco 14y ago

Plutonium 238 would be your best bet for such devices, if only because it's halflife is 87.7 years. Strontium 90 might also work, with a halflife of 28.8 years. However plutonium would not be easy to put in every house since you have to make it in nuclear reactors. You get about half a kilowatt per kilogram of it, I don't think production of it could scale that high. Strontium is naturally occurring and relatively common. Sr 90 is a trace isotope though. Off the top of my head I would suspect you would be facing similar challenges that separation of Uranium isotopes face.

adestefan 14y ago
Sr-90 is not naturally occurring because of its short half-life. Any Sr-90 found today is either from weapons testing or made in a reactor.

InclinedPlane 14y ago

Probably not. The problem with isotopes needed for things like this is that they tend to have short half-lives (short half-lives = high decay rate = lots of heat generated), which means they pretty much don't exist naturally at all. So they will need to be produced artificially as fission fragments or through neutron irradiation of other isotopes. It's easy enough to produce large quantities of "hot" isotopes in a fission reactor which could be used for RTGs (ignoring safety) but the problem there is that if you're operating a nuclear reactor anyway why not use the heat production from the isotopes to produce energy there instead of going the roundabout, and unsafe, route of packaging things up in RTGs?

outworlder 14y ago
There's also the thermocouples, which also wear out and are made of pretty expensive materials themselves. However, it is likely that a "home" device could be made simpler/less expensive.
- jimktrains2 14y ago
  Couldn't they use a sterling engine as well? That would be a bit more maintainable I would think?

rmc 14y ago

You're also ignoring the political/emotive aspect. People don't like things called 'nuclear'.

jlgreco 14y ago
There are certainly some places that would probably be more accepting of it than average. http://en.wikipedia.org/wiki/File:Soviet_RTG.jpg http://en.wikipedia.org/wiki/File:Soviet_RTG.jpg ;) Those are 10 watt Sr90 RTGs, sitting around. The used to use them for lighthouses.
InclinedPlane 14y ago
Well... as much as I like RTGs and even fission reactors there is a little bit of justification there. Of necessity an RTG pretty much needs to contain hazardous radioisotopes. Putting that into the hands of every joe blow is probably not the best idea at present.

Cushman 14y ago

Just cribbing from Wiki, the generator contains 11 pounds of Pu-238 and produces ~150W of electricity from ~2000W of heat. It's hard to put an exact price on it, but it's definitely in the $millions per kg. It's theoretically feasible, but the cost would be, ah, prohibitive.

uvdiv 14y ago

What's wrong with the economies of scale of larger nuclear plants? I'm asking curiously, I don't understand the fascination with home energy sources. Radioactive decay is a small energy source compared to fission. Look at the binding energies [1]: the energy accessible by fissioning heavy elements is about 200 MeV -- 1 MeV per nucleon. Radioactive decays are two orders of magnitude less, or smaller. Pu-238 is one of the nicest ones because it is "clean" -- emitting only alpha radiation, which is easy to shield. You can transmute on the order of 1 atom of it per 100 fission events [2]. A fission event is 200 MeV; a Pu-238 decay is 5.6 MeV. So at steady state, you can support less than 1/3,000th as much Pu-238 power as you can fission power. If you have a Pu-238 source, you also have a vastly larger nuclear fission power source, so why not just use that? More broadly, it's not a likely idea on physics, even if you accept all radioisotopes (difficult-to-shield gamma emitters) and not just "nice" ones. The high-Z radioactive decay chains end quickly at the element lead [3], so only release a fraction of the energy that is accessible by fission. (Look back to the binding energy curve [1]). And many of these decays are unusably, geologically slow. The naturally-occurring radioisotopes have half lives of >10^8 years (otherwise they wouldn't exist anymore -- they were created in ancient history in supernovae). And trying to transmute them doesn't improve much -- i.e. in a fission reactor, the most common [4] high-Z product is Pu-239 (half life >10^4 years), whose next decay is to U-235 (half life >10^8 years). Others are similar. So I don't see any way forwards. [1] http://en.wikipedia.org/wiki/File:Binding_energy_curve_-_common_isotopes.svg http://en.wikipedia.org/wiki/File:Binding_energy_curve_-_com... [2] Through the several processes which create Np-237 from uranium -- a relatively rare process [4]. Np-237 can be isolated and transmuted to Pu-238 separately through neutron irradiation [3] http://en.wikipedia.org/wiki/File:Radioactive_decay_chains_diagram.svg http://en.wikipedia.org/wiki/File:Radioactive_decay_chains_d... [4] Small table here: http://en.wikipedia.org/wiki/Minor_actinide http://en.wikipedia.org/wiki/Minor_actinide