Sciencemadness Discussion Board

Plutonium pill as laptop battery ?

metalresearcher - 14-7-2015 at 10:26

The New Horizons approached Pluto today, due to its remoteness, solar panels won't work (flux = 1W/m2 while 1000W/m2 on Earth), so an RTG with PuO2 fuel is used.

Why not a small verston of such a power source as a laptop power supply ?
This can be not larger than a medication pill.

Bert - 14-7-2015 at 10:51

How much Plutonium do you want leaking into ground water from discarded electronics at your local land fill?

Loptr - 14-7-2015 at 10:51

There might be an issue with the possession of plutonium, which as far as I know, is pretty much illegal wherever you happen to reside.

Fulmen - 14-7-2015 at 11:09

What is the average power consumption of a laptop? Pu238 radiates a whopping 540W/kg, but once you factor in the 5% efficiency of an RTG you're down to 27W/kg Pu.

unionised - 14-7-2015 at 12:08

No off switch.

froot - 14-7-2015 at 12:10

The RTG on Curiosity delivers 800watts for 10 years and that will dwarf a laptop. You also need to maintain a decent thermal gradient between the isotope and the exterior for it to work properly.

phlogiston - 14-7-2015 at 12:31

It is undesirable to give the public access to macroscopic amounts of such extremely radioactive substances.

However, Pu238 based RTGs have been used in pacemakers. Excellent applications, since it is not easily accessible for extraction, pacemakers need only very little power and replacing the battery is very invasive, so you want a power source that lasts for a long time.

Another terrestrial application has been to power lighthouses along the north coast of Russia, but they have been raided for their metal content by thieves that seems to be largely unaware of the extreme danger of stripping the shielding of a large block of extremely radioactive material. It landed several people in hospitals.

[Edited on 14-7-2015 by phlogiston]

Fulmen - 14-7-2015 at 14:34

RTGs are fascinating, and while they will never power laptops they do have real life applications like pacemakers.

Personally I'd kill for an ounce or two of Pu238. It would make for the coolest candle ever, a chunk of Pu contained in glass glowing read from it's own decay heat.



[Edited on 14-7-15 by Fulmen]

Oscilllator - 14-7-2015 at 18:24

Everybody else here is making comments about how such a device would never exist, which I think is silly. Here are some numbers that I came up with relatively quickly:

One the laptop I am writing this on the battery is rated for 10.5V/3.8A, or 39.9 watts. Because I don't use this laptop at maximum capacity all the time, let's drop that down to 20 watts and have a small battery to act as a buffer for peak usage (remember that the RTG can charge 24/7).
Now looking at the wikipedia page for RTG's is seems the best one available is the GPHS-RTG(used on the new horizons probe :)) that delivers 5.4 watts/kg. Based on this, the RTG would have to weigh 3.7kg, or 3.5 times the total weight of my laptop. Not very practical.

But plutonium actually produces 564 watts/kg of heat energy. Suppose were able to make a generator that operated at 50% efficiency, because we live in an atmosphere or something. That means that 35g of plutonium would be needed. Taking into account the actual mass of the generator, I think that should be rounded up to 100g. That seems like a reasonable weight to me, but it ultimately is a pie in the sky number.

Fulmen - 14-7-2015 at 22:33

The RTGs deliver 5.4W/kg at 5-10% efficiency, so at 50% it would still be only 50-100W/kg (assuming it scales linearly). Both assumptions are improbable at best.

metalresearcher - 15-7-2015 at 07:49

But an RTG to charge only a laptop ?

Praxichys - 15-7-2015 at 10:27

The risk of someone building a "dirty bomb" will disallow consumer applications of RTGs, unfortunately.

There would also be a huge supply issue. At peak production, all of our breeder reactors could only make a few kg per year.

CRUSTY - 29-9-2017 at 09:13

Using plutonium in any sort of domestic application that can be opened, broken, etc. is incredibly impractical for the obvious reason of "misuse" of the radioisotope, but if we're talking theory here, I think a thermophotovoltaic cell would do better for this application. According to Wikipedia, around 20% efficiency has been achieved fairly consistency, but some 30+% cells have been theorized.

Melgar - 9-10-2017 at 01:02

Strontium 90 would be a better isotope for a consumer RTG than plutonium 238 would be. It decays quite a bit faster, with a half-life of 20-some years, but that's a lot better than the average useful life of a typical battery, and it would never need charging. It's also a really common isotope found in waste from nuclear reactors, so there's more of it available than there's use for, unlike plutonium 238, which we seem to have run out of. It's also used in a few civilian applications, and was used extensively by the USSR for powering remote weather stations and things like that.

unionised - 9-10-2017 at 02:10

Quote: Originally posted by Melgar  
Strontium 90 would be a better isotope for a consumer RTG than plutonium 238 would be. It decays quite a bit faster, with a half-life of 20-some years, but that's a lot better than the average useful life of a typical battery, and it would never need charging. It's also a really common isotope found in waste from nuclear reactors, so there's more of it available than there's use for, unlike plutonium 238, which we seem to have run out of. It's also used in a few civilian applications, and was used extensively by the USSR for powering remote weather stations and things like that.

And it is exceptionally dangerous, so it's the last thing we should distribute into the environment.

Melgar - 9-10-2017 at 18:05

Quote: Originally posted by unionised  

And it is exceptionally dangerous, so it's the last thing we should distribute into the environment.

I only said it would be better than plutonium, not that it would be problem-free. Plutonium 238 is even more dangerous, due to its heavy metal toxicity and long, complicated decay chain, but because there isn't really any of it left on Earth, there aren't all these alarmist articles on the web about how dangerous it is. Due to the fact that strontium 90 is quite common in nuclear waste, and some has escaped into the environment as a result of Chernobyl and Fukushima, there are plenty of alarmist articles about that particular radioisotope. It's really a matter of selection bias. But if the problems could be solved by engineering, it would be better to use an isotope that's currently a waste product, rather than one that we have essentially none of, no?

Cezium - 9-10-2017 at 22:50

Sr-90 is not as poisonous as Pu, it is similar to biogenous Ca so it has high affinity to bone metabolism, it used to be used as bone metastasis treatment, now is obsolete due to various side effects (mainly it messes with blood) and Sm-153 is in use instead. In long run it will accumulate in body and replace Ca with all the consequences, so not a good idea.
Electricity from radionuclides was viable option before advanced Lithium batteries in ICDs (in body defibrillator) where there is capacitor that can accumulate continuous mikroAmps from source. In laptop there will be needed hundreds of curies for tens watts produced. Such an activity is no go for public use. Only viable option will be use in remote areas (arctic, space) where you can trace source and collect it back at the end of the life for proper disposal. But where is sun there is solar panels preferred so nor this is way to go. Also this laptop will have several kilograms in additional weight due to cooling and stuff.
Activity is not for public use, every kid with hammer will dissect your pill no matter how good you think you secure it. The closest to the public that you can get with activity is to build a community reactors one for small town (up to 100000 inhabitants), approx size of shipping container buried deep in the ground running on may be thorium as an alternative to renewable energy.

[Edited on 10-10-2017 by Cezium]

Melgar - 10-10-2017 at 05:18

Sr-90 has the interesting property of being solely a beta emitter though, meaning it could potentially be used in a betavoltaic device, which is much more efficient than an RTG. I agree that we have a lot of better options available though, especially fuel cells and the like, which could be refilled like a butane lighter rather than plugging it in.

Why would the reactor have to be deep underground? Seems like that'd make it easier to contaminate the water, and harder to access if anything did go wrong. Not to mention the coolant issue. Personally, I like the idea of portable nuclear rectors, since it'd allow us to inhabit really cold places much more easily. Like Antarctica, or Mars, or the moons of Jupiter and Saturn.

Cezium - 10-10-2017 at 06:00

Deep underground is not needed necessarily but until mankind is stupid enough to make more wars and less love, burying underground will protect against blast. Ideally there will be concrete bed-nest with entrance which will allow access for regular maintenance and once in a decades replacing whole container.
Cooling wouldn't be an issue, mainly can heat/cool households through heat exchanger and with less excess heat dissipated with same principle as in ground source heat pump as this will be especially usefull in areas where isn't access to continuous water stream.
Not to mention if people coudn't see reactor they wouldn't afraid so much and also wouldn't try to break in.

Melgar - 10-10-2017 at 14:44

I know that a lot of the new designs for reactors are fail-safe, so that if the core becomes critical, it melts through a plug underneath it and empties into a shallow concrete pan. By spreading the fuel out like that, it's no longer at critical mass, and so it stops reacting. With molten salt reactors, the fuel is actually supposed to be in liquid form, and so it can just drain out of the reactor area to slow it down, then pumped back in when it's needed.

You really couldn't use a ground-source heat pump to cool a nuclear reactor though. Soil is too good of an insulator, and eventually the soil around the heat exchangers would get too hot to accept any more heat. IIRC, they're only really recommended for areas with a high water table, and even then, for just one house, they'll often cause problems with the neighbors having warm tap water.

[Edited on 10/10/17 by Melgar]

Cezium - 11-10-2017 at 02:02

I admit that ground-source heat pump wouldn’t be the best solution, but I mean it as kind of buffer, main cooling will be thru heat exchanger for households.
This is meant to be just free time theory, all kinds of improvements will be needed before real realization. I just thought that in the future it would be nice to have decentralized grid of small reactors (for various reasons).
Over all take home message was that radionuclides for general public usage is not a good idea.

Melgar - 11-10-2017 at 02:34

Quote: Originally posted by Cezium  
I admit that ground-source heat pump wouldn’t be the best solution, but I mean it as kind of buffer, main cooling will be thru heat exchanger for households.
This is meant to be just free time theory, all kinds of improvements will be needed before real realization. I just thought that in the future it would be nice to have decentralized grid of small reactors (for various reasons).
Over all take home message was that radionuclides for general public usage is not a good idea.

Strontium 90 has a few niche commercial uses already though. I agree that it wouldn't be a good idea to use it to power a laptop, but I think that now that we understand the dangers of radioactive isotopes much better, we should be researching potential new uses for them.

The radioisotopes that are in use now include the americium 241 in smoke detectors, and the strontium 90 that's used in devices that can test airplane wings for ice buildup and metal for internal fractures. These uses were all discovered before Chernobyl happened, which is about when the public suddenly changed their minds about how dangerous radioactivity was. I doubt there has been any significant research since then, aside from its use in medicine. But they never forced industry to stop using the radioisotopes that they'd already been safely using for years, and so a lot of them are actually still in widespread use.