A late April Fools day Joke: Nuclear batteries that last for years

Use this board for general non-cycling-related chat, or to introduce yourself to the forum.
mercalia
Posts: 14005
Joined: 22 Sep 2013, 10:03pm
Location: london South

A late April Fools day Joke: Nuclear batteries that last for years

Postby mercalia » 31 Aug 2020, 9:12am

They use the nuclear waste from power stations so a win-win ?

Would revolutionise ebikes and cars? ( but read the update and be disappointed)


https://newatlas.com/energy/nano-diamond-self-charging-batteries-ndb/

Just be careful not to store a critical mass of bartteries in one place.

User avatar
[XAP]Bob
Posts: 17680
Joined: 26 Sep 2008, 4:12pm

Re: A late April Fools day Joke: Nuclear batteries that last for years

Postby [XAP]Bob » 31 Aug 2020, 12:00pm

Doesn’t read like a joke at all... but my instinct says that the constant power delivery density won’t supply an electric car... an e bike that’s used only relatively small frequently could be an option.

Just be careful not to store a critical mass of bartteries in one place.

They're using the C14 from the control rods, so there is no critical mass. That's one of the reasons this is such a neat idea.

Anyway... let's run the numbers:

1 C14 beta decay yields 156 keV or about 2.5E-14J
Half life of 5730 years is 1.8E11 seconds
1kg of C14 contains ~ 4.3E25 atoms

So we would expect 1/2 of 4.3E25 to decay releasing 2.5E-14J each over 1.8E11 seconds or about 3 watts average, so that's starting at ~4W/kg (assuming 100% efficiency).

That supports my gut feel that it's ideal for low powered devices, but not so much for transport which takes significantly more power. What about the current cutting edge of supercapcitors...
Blimey - 200+kWh/kg and 32kW/kg... That's insane, and means that duty cycle is the important thing...


An electric bike needs 250W output capacity
That's 23 minutes of peak power per kg per day (assuming no losses - and supercaps themselves already have >99% round trip efficiency).

For an electric car this might work - you can afford to carry a lot more battery... It wouldn't be an infinite range vehicle for single long journeys, but it could effectively negate home charging, instead you'd plug in overnight to power the home.
200kg of battery would be 800W: ~19kWh/day, which is between 60 and 80 miles range a day - every day.

The Tesla 85kWh battery pack is 540kg... so 200-250 of diamond is probably quite possible.

Looks like my gut was completely wrong - although it was mostly wrong because of the insane density of next gen super capacitors.

Currently available supercaps are closer to 6kW/kg power delivery and 6Wh/kg. And it's this last which is the killer for transport... you really do need to have several KW stored, which would take several tons of capacitor.

You could of course have a Li-ion pack with one of these tacked on the back, but the next gen super capacitors seem like the best bet to partner them - some interesting carbon nano fabrication is going on which could change that around completely.
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.

hamster
Posts: 3573
Joined: 2 Feb 2007, 12:42pm

Re: A late April Fools day Joke: Nuclear batteries that last for years

Postby hamster » 3 Sep 2020, 6:03pm

The real one is the RTG in spacecraft...the Voyager probes are ticking away on it, although the power available is depleting.
https://en.wikipedia.org/wiki/Radioisot ... _generator

User avatar
simonineaston
Posts: 3418
Joined: 9 May 2007, 1:06pm
Location: Live & work in Briz'l

Re: A late April Fools day Joke: Nuclear batteries that last for years

Postby simonineaston » 3 Sep 2020, 9:14pm

Soviets made shed-loads...
The Soviet Union constructed many uncrewed lighthouses and navigation beacons powered by RTGs using strontium-90 (90Sr). They are very reliable and provide a steady source of power. Most have no protection, not even fences or warning signs, and the locations of some of these facilities are no longer known due to poor record keeping. In one instance, the radioactive compartments were opened by a thief.[5] In another case, three woodsmen in Tsalendzhikha Region, Georgia found two ceramic RTG heat sources that had been stripped of their shielding; two of them were later hospitalized with severe radiation burns after carrying the sources on their backs. The units were eventually recovered and isolated.[28] There are approximately 1,000 such RTGs in Russia, all of which have long since exceeded their design operational lives of ten years. Most of these RTGs likely no longer function, and may need to be dismantled. Some of their metal casings have been stripped by metal hunters, despite the risk of radioactive contamination.[29]
I bet one would power both the motor and the lights on my 'leccy Brompton...
ttfn, Simon in Easton
(currently enjoying a Moulton TSR & a nano Brompton...)

User avatar
[XAP]Bob
Posts: 17680
Joined: 26 Sep 2008, 4:12pm

Re: A late April Fools day Joke: Nuclear batteries that last for years

Postby [XAP]Bob » 4 Sep 2020, 8:45am

These are not classic RTGs - those rely on plutonium, these are *carbon* based, and with a half life measured in millennia their power output won't appreciable deteriorate over the course of a human lifetime (or several).

Each of the three RTGs on each Voyager spacecraft weighed in at a little shy of 40kg, contained nearly 5kg of P238 as an oxide (i.e. 86% of 4.5kg =~ 3.9kG of plutonium itself).
They generated about 157w (electrical) initially, and that halves every 90 years. Note however that this was because they are r*t*gs, they use the decay to generate heat, then use thermocouples to convert that to electricity - fundamentally different from harnessing the energetic electrons directly.

These batteries are carbon based, and promise about the same power density, but with a much longer life, and are massively safer (in terms of not distributing weapons grade nuclear waste around the world).

Having just run that power density calculation I think we can guess where these will first be used - NASA has a very limited supply of plutonium, and these would be awesome for probes to the outer solar system, or to the surfaces of celestial bodies - dealing with low solar radiation due to either night or weather...


Same calculation for P238:
- Decay energy 5.6MeV = 9E-13 J
- Half life 87.7 years = 2.8E9 s
- Nuclei per kg PO2 = Av/276 = 2.2E22
- 1/2*2.2E22 * 9E-13 / 2.8E9 = 3.53W/kg
But that ignores the EM decay products... the total decay heat is actually 560W/kg


Let's go for the total energy released as per the most famous equation in all of science:
Theoretical total energy output of C14 -> N14 = 14.003241 -> 14.003074 + .000549 = 3.82E-4 u
P238 -> U234 = 238.049553 u -> 235.043930 + 4.001506 = 9.96E-1 u
That's a scale factor of 3000 in terms of energy release per decay.
1/2*nuclei/kg/half life => C14 1.2E14 decays/s/kg
P238 => 3.9E12 decays/s/kg

So the C14 recovers a factor of 30 through density/half life considerations... so P238 releases ~100 times more power/kg than C14.

That's actually not terrible - and given that the efficiency of the RTGs is so poor (~6%), and they therefore require spacecraft to carry radiators and cooling systems as well... potentially saving even more mass.

Total power output for C14 ~ 5-6W/kg. We make much lower power electronics now than we did in the early 70s as well, so this could well end up on space probes (though they like to prove things for a while on earth first)...
A shortcut has to be a challenge, otherwise it would just be the way. No situation is so dire that panic cannot make it worse.
There are two kinds of people in this world: those can extrapolate from incomplete data.