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if A Humanoid Was Powered By Nuclear Reactions


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Scenario: An android is capable of eating human food but it simply converts it into electricity for it to use instead of digesting it the way we do. Nonetheless the android must still 'liquid' and do number 2 to get rid of waste from eating and must sleep like a normal human.

Alternately the android can use it's own nuclear reactor (a small one that fits inside it's humanoid body) for electricity.

 

When using the reactor the android does not have to sleep or eat, as the reactor provides all it's energy needs.

The only risk it runs is overheating because a NUCLEAR REACTOR is running inside them. So they must be in cold environments to compensate or else they would die from heat exhaustion. And also avoid humans for fear of radiating them.

 

Main question: Provided the android has the same energy needs as a human and was living in some frigid icy location... like Antartica,.... would a nuclear reactor small enough to fit inside the human body provide enough energy for him to to do what humans do.... or will hw behave and have only the energy level of ninety year old?

Why do I have the amusing feeling that the energy a small nuckear reactor like that would put out may not be enough to match daily human energy needs.

What I mean is enough energy to perform like a twenty year old.

Coukd nuclear do that or not?

Edited by Spacescifi
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Human energy needs vary widely depending on whether they have a male or female physiology, how old they are, how big they are, how active they are etc. etc.

For the sake of argument lets assume an energy requirement of 2,500 dietary calories per day. One dietary calorie is approximately 4.2 KJ, so 2,500 dietary calories is approximately 10.5 MJ.  

That energy will be expended over the course of a day, or 86,400 seconds, giving an average power output of 122 W or 0.12 KW

I couldn't find a nuclear power source that's both small enough to fit into a humanoid android and capable of putting out 100+ watts of power, but feel free to have a look yourself.

 

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33 minutes ago, KSK said:

I couldn't find a nuclear power source that's both small enough to fit into a humanoid android and capable of putting out 100+ watts of power, but feel free to have a look yourself.

RTG.

And energetic milk from RTG cow.

Edited by kerbiloid
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I did wonder about RTG's but they all seemed to be a bit big. Happy to be proven wrong though! I also looked at non-thermal atomic batteries (including a very interesting Russian design) but the power densities all seemed too low for the application at hand.

 

Edited by KSK
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30 minutes ago, StrandedonEarth said:

Voyager-class RTG produced about 157W initially, halving every 87 years. So just replace the Pu-238 slug every forty years or so...

https://en.wikipedia.org/wiki/MHW-RTG

 

The cooler part is that RTG's are not hazardous to humans nearby unless you literally take them apart, grind up, and inhale the fuel pellets. Which no sane person would do.

So the android could work around humans without issue.

Humans would have to be suited for cold weather though, since I am not sure what temperature the android would need not to overheat from the RTG, but I reckon refigerator cold levels are in order..... since the android will overheat at the same temperature that a human would.

Edited by Spacescifi
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MHW-RTG looks a bit big to me, judging from the pictures on this site. Considering that they were also putting put 2.4 kW of thermal power... well I like the smell of roasting android as much as the next non-synth.

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3 minutes ago, KSK said:

MHW-RTG looks a bit big to me, judging from the pictures on this site. Considering that they were also putting put 2.4 kW of thermal power... well I like the smell of roasting android as much as the next non-synth.

Perhaps future RTG's can be made smaller?

Although I am also aware that some things do not scale well down and others do not scale up well

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Sure.  RTGs are limited by the efficiency with which they can convert heat to electricity. The MHW-RTG is about 5% efficient.  If you can figure out a way of upping that percentage you can either get more electrical power from the same size RTG or the same amount of electrical power from a smaller RTG.

No idea how you'd do that in practice but in fiction - why not. 

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They are developing "radioactive batteries" based on Selenium for pace-makers, essentially a micro-RTG suitable for wetware. Size and thickness of a penny and producing 16 nW at 0.9 V. My SI Standards book didn't list a conversion ratio for pennies to human body, but according to some googling a penny is about 0.35mL. Assuming the battery doesn't have a bass-relief and scientists tend to round favourable when talking to journalists, let's say 40 nW out of a mL, or 40 uW out of a liter, or around 3-4 mW out of an acceptable proportioned human body. That doesn't bode well... And that's assuming the entire body is made up out of these batteries.

Let's forget the "must not sterilize every human in a 10 km radius" requirement for a moment...

"The spacecraft [Cassini] also carried 82 strategically placed radioisotope heater units (RHUs), which provided focused warmth in the form of one watt of thermal power each using a pencil eraser-sized pellet of plutonium dioxide."

Hmm, no mention in my SI units book about pencil erasers either, but it sure sounds more promising. I'd say a pencil eraser is around the same volume as a penny, since we already established there are around 3000 of those in a liter, at a 5% conversion to electrical that's 150W for a 'heart' of 1 liter. Not bad. Of course then you need the lead shielding, and a way to get rid of almost 3kW of waste heat. And I'm not sure how far you could push that stuff before you reach critical mass...

Of course this is an RTG, not a 'nuclear reactor', however I'm pretty sure reactors don't come in a size anywhere near small enough to fit into a human body volume. The mentioned 150W should be enough though, in theory, after all biology got it done :) I would add to that that a LOT of our energy goes to keeping warm (which you won't need to worry about with 2.85 kW of waste heat) and to our digestive system which we could also scrap. So a beer can sized plutonium dioxide pellet might very well be enough just to drive the CPU, sensor package and actuators.

I really need to get a new edition of this SI Standards book, no beer can volume in there either...

I think all in all the problem is not so much to fit enough nuclear material to generate the needed energy, but handling all the side effects like heat and radiation. A rechargeable chemical energy source might be more efficient in the end (again, it's what biology came up with :) ) but of course makes the android vulnerable to simply running out of juice - just like its human templates.

 

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