Diamonds turn nuclear waste into nuclear batteries

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Skipjack
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Joined: Sun Sep 28, 2008 2:29 pm

Re: Diamonds turn nuclear waste into nuclear batteries

Post by Skipjack »

Nickle has a density of 10 grams per cm3. Carbon 14 is 1 grams per cm3. So we get somewhere between 1 uW/g and 5uW/g power density.
Pretty awful...

Now, I have done some digging on my own and what I found to be a near perfect beta emitter in terms of half life (~29 years) and power density is Strontium 90.
Now that (by itself) emits about 1 kW of energy per gram in the form of beta particles. Or rather it decays into an Yttrium 90, which in turn beta decays into Zirconium 90 within 64 hours. The latter is where the meat is with electrons of ~1.14 MeV of energy released in the beta decay. The electron released by the Sr90 by itself is only about 0.27 MeV. But combined they have quite an "oomph". And this happens at a rate of 5.21 TBq/g.
Problem is of course that a betavoltaic device would not just be made of Sr90...
So anyway, I did the math and wondered. Why has no one done that? It sounds near perfect. And low an behold... someone did!
https://www.nature.com/articles/srep381 ... 8GsSW7I-CI

"A collection of such devices that generates 100 W would weigh less than 5 kg".
So we get 20 Watts/kg. Not great, but not bad at all. One could make a car battery from that. Of course with Sr90 come other problems... It is extremely dangerous when ingested since it gets integrated into bone. That in turn will likely cause bone cancer. So for consumer applications, it is no darn good.
Plus it will need some shielding too...
Also noteworthy is that Sr90 works better in an RTG where I calculated a power density of ~33 watts/kg (assuming the highest efficiency of 7%). Of course for space applications you will need cooling too then if you want your RTG to work...
Oh well, those nuclear batteries are still a dream that just does not want to come true, I am afraid.

GerardFianen
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Re: Diamonds turn nuclear waste into nuclear batteries

Post by GerardFianen »

"So we get 20 Watts/kg. Not great, but not bad at all. One could make a car battery from that."

Well, I have to disagree.

First that is way to low power. When driving a car easily needs 15-20 kW constant power and an EV like the Tesla Model-3 has 225 to 360 kW maximum Power. For that 225 kW power @ 20W/kg an 11.250 kg (!) battery would be needed. That car would be as heavy as a truck and have a very bad efficiency due to that weight.

Second, what matters for EV is now ' just' power, but energy density. As in kWh/kg and kWh/liter.
How big would a 250 kW / 50-100 kWh battery using that tech be ?

Third --> costs. As an EV needs a lot of power and energy -many kW's and kWh's-, the multiplication factor is big. One needs 200+ kW peak and 50-100 kWh energy. The price per kWh is a very critical specification and a make-or-break for the feasibility of use in an EV.

Next to that of course the availability and (as you already referred to) environmental friendlyness to get / mine al materials as well as pollution resulting from recylcing or (in case of a car fire) after an accident.

Skipjack
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Re: Diamonds turn nuclear waste into nuclear batteries

Post by Skipjack »

GerardFianen wrote:
Tue Sep 01, 2020 1:26 pm
First that is way to low power. When driving a car easily needs 15-20 kW constant power and an EV like the Tesla Model-3 has 225 to 360 kW maximum Power. For that 225 kW power @ 20W/kg an 11.250 kg (!) battery would be needed. That car would be as heavy as a truck and have a very bad efficiency due to that weight.
Not quite. A Tesla Model 3 long range has a 75 kWh battery and gets 290 miles on the Freeway out of it. That equals a constant drain of ~18kW. So a one tonne battery would be able to handle that. Still quite a bit heavier than the one in the Tesla, but almost doable. Yes, the battery could obviously not handle the maximum drain during fast acceleration and so on. But those only last a few seconds. For this, one would need an additional small battery or capacitor that would recharge between those bursts of high power demand. Some of it would probably recovered from regenerative braking. So the trickle charge from the Sr90 battery would not have to deliver all of that charge.
Again, not saying it would be working extremely well, but it is at least within the realm of possibility (from a pure math/physics POV), unlike that diamond battery, which is off by several orders of magnitude.
Second, what matters for EV is now ' just' power, but energy density. As in kWh/kg and kWh/liter.
How big would a 250 kW / 50-100 kWh battery using that tech be ?
Well, the 20kW engine would be 1 tonne in mass and it would deliver those 20kW for roughly a decade before the battery degrades below 80%. I can't say anything about the kW/liter. That is a very good question. That said Sr90 is relatively heavy (compared to Li and Si). So I would assume that it could be relatively dense and might actually be smaller than a Lithium Ion battery. Though one would need additional mass/volume for shielding, encasement, cooling, etc...
Next to that of course the availability and (as you already referred to) environmental friendlyness to get / mine al materials as well as pollution resulting from recylcing or (in case of a car fire) after an accident.
Well, the Sr90 would almost exclusively come from nuclear waste (it is a very common fission product). That is nice, because the cost of the raw material is probably negative. The rest of the arguments are still valid, though.
Again, let me emphasize that I was not saying that one should make a car battery from this, but that one could from a pure math/physics POV power a car with it.
It wouldn't be great, but one could kinda get it to work. The diamond battery though is a complete nonstarter unless there is some really weird magic happening somewhere.

Thinking of it, one application, where the Sr90 battery could be relatively practical is to power large ships. A 4,000 tonne battery could deliver enough to power a large container ship like the Emma Mærsk for a decade without refueling. For comparison, the Diesel engine of that ship alone has a mass of 2,300 tonnes and delivers 80 MW, when burning some 10 tonnes of fuel per hour. So those 4,000 tonnes would be the equivalent of 400 hours (16 days) worth of fuel.
And let's not forget that electric motors are much more efficient and thus much lighter than Diesel engines. So it is definitely doable.
Now Sr90 is not water soluble. So even in case of a major accident that would sink the ship, very little of it should get into the environment. And mind you, the same risk applies to "normal" nuclear reactors (as they will contain a good amount of Sr90 too) which we are using on ships all the time.
So, I think that would/could work. I believe it would need a lot more than just a forum threat to figure out if it would be practical in the end, though.
And thinking of it some more. These batteries would emit quite a bit of heat that could be harvested with Thermophotovoltaic cells or maybe a sterling engine to produce even more power.
Considering how much shipping contributes to global emissions, this could be interesting.

kunkmiester
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Re: Diamonds turn nuclear waste into nuclear batteries

Post by kunkmiester »

Unfortunately even without a reactor, you're probably still going to need at least one nuclear certified person on board, and probably all the paperwork related to having a reactor, aside from the greenie opposition.

And you need a source of strontium.
Evil is evil, no matter how small

Skipjack
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Joined: Sun Sep 28, 2008 2:29 pm

Re: Diamonds turn nuclear waste into nuclear batteries

Post by Skipjack »

kunkmiester wrote:
Wed Sep 02, 2020 3:50 pm
Unfortunately even without a reactor, you're probably still going to need at least one nuclear certified person on board, and probably all the paperwork related to having a reactor, aside from the greenie opposition.

And you need a source of strontium.
Agree about the nuclear certified person. As I mentioned Sr90 is a very common fission product and makes a large part of nuclear waste.

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