nuclear "backpack" reactor

[kbyron]

My questions and ideas stem from sci-fi fantasy, specifically the Warhammer 40k Universe. In that universe there are genetically engineered super soldiers called "Space Marines". These soldiers are all clad in Powered Armor that is self contained/powered and capable of receiving enormous amounts of abuse without failing. The armor is constructed from a fictional substance called 'Ceramite'. After a little research into ceramic composites i happened upon the U.S. Military's mock up of a powered armor system they termed a "personal combat vehicle". After a little more research into exo-skeleton design it became apparent to me that the main problem with exo-skeleton/powered armor ideas to date has been the actual power issue. Most of these designs require a relatively large amount of power to operate fully and current battery technology can only provide a minimum amount of operational time.

 

My Solution to the power issue is a scaled down 10-20kW nuclear "backpack" reactor that can be fitted to the back of the exo-skeleton. Traditionally, control rods are used to manage the reaction taking place, with new technology control rods can be removed for a smaller more efficient control system using liquid Lithium-6. For actual power generation a gas turbine using the brayton cycle was what i was thinking, using Helium gas as the medium.

 

There is a substantial amount that i do not know regarding fabrication, cooling, unused/used fuel storage and i recognize that. The main reason for this post is to find out where best to direct my inquiries and to find new sources of information to further my idea. From my modest experience it is rather hard to just 'Google' specifics on reactor design and so here i am hoping someone might be able to point me in a better direction.

[insane_alien]

and you've just killed your supersoldier from radiation exposure...

 

there is a minimum size where nuclear reactors can operate. submarines are pretty close to it as it stands.

[Gilded]

What insane_alien said. Regarding batteries to power combat suits, that's certainly one technology that will benefit tremendously from improvements in nanotechnology and will most likely take giant leaps forwards in the next few decades. For example nanowire batteries look very promising.

[npts2020]

You might see me struggling to get out from underneath of one of those backpacks but I doubt you would see me ever carrying it around.

[DrP]

So in essence then, we can have nuclear powered submarines but not spacemarines....... yet, anyway.

[insane_alien]

yep, a fuelcell of some sort could make it possible though, you just need an efficient way to store hydrogen(or whatever fuel it uses)

[kbyron]

with regards to fuel cells, i've read that palladium can store upto 900x its volume in hydrogen. That would be an efficient way to store fuel, but then the powerplant would in essence be an ICE (internal combustion engine). It would require constant refueling and in the middle of a combat operation having to retreat to refuel could be deadly.

I've also read, but i'm not sure on the veracity of the information, that there has been a resurgence of interest in solid state(cold) fusion with palladium's ability to store such a large amount of hydrogen relative to its volume. Also since palladium is so closely related to platinum it can also be used as the catalyst for fusion. There was a successful experiment in japan where a scientist was able to "Using sample powders of zirconium oxide and palladium subjected to deuterium gas in a electrolysis cell, they were able to show generation of continuous heat along with helium. .... Arata used pressure to force deuterium gas into an evacuated cell that contained a palladium and zirconium oxide mix. By using powdered palladium, he increased the surface absorption area for deuterium. The excess heat generated by the fusion reaction kept the center of the cell warm for 50 hours." - http://world.std.com/~mica/cft.html

I had considered this as a possibility but due to the lack of current research and technology had dismissed it. Also i was unaware that fission reactors had a minimum size req. Is the minimum size due to the amount of fuel required to cause sufficient fission to sustain the temps required for power generation? If thats the case, could using weapons grade enriched uranium 85%+ u-235 as fuel make a difference?

[insane_alien]

fuel cells do not work like internal combustion engines. and yes, it would need refuelled every now and again but so would a nuclear reactor that small.

 

cold fusion is a bunch of crap, there have never been repeatable experiments performed.

 

fission reactors have a minimum size because:

 

1/ you need more than a critical mass of uranium, but in the right geometry

2/ you need thick shielding as these thins are as radioactive as hell if not more so

3/ cooling requirements are MASSIVE to keep it from melting down.

4/ if cooling water cannot be piped to it from a source like a river, your going to need a big ass radiator. and we're talking huge. not only will this make your super soldier easy to spot, but also easy to kill as you just need to put a few holes in the radiator.

 

its not so much that the reactor core needs to be huge, its just that all the supporting equipment and control systems take up a heck of a lot of space.

 

weapons grade uranium/plutonium would decrease the necessary size of the core, but not the overall reactor.

[kbyron]

fuel cells do not work like internal combustion engines. and yes, it would need refuelled every now and again but so would a nuclear reactor that small.

 

cold fusion is a bunch of crap, there have never been repeatable experiments performed.

 

fission reactors have a minimum size because:

 

1/ you need more than a critical mass of uranium, but in the right geometry

2/ you need thick shielding as these thins are as radioactive as hell if not more so

3/ cooling requirements are MASSIVE to keep it from melting down.

4/ if cooling water cannot be piped to it from a source like a river, your going to need a big ass radiator. and we're talking huge. not only will this make your super soldier easy to spot, but also easy to kill as you just need to put a few holes in the radiator.

 

its not so much that the reactor core needs to be huge, its just that all the supporting equipment and control systems take up a heck of a lot of space.

 

weapons grade uranium/plutonium would decrease the necessary size of the core, but not the overall reactor.

 

couple things, i was equating the fuel cell to a gas tank, the cell holds the hydrogen which is syphoned off and used to power a generator, like how they propose to power cars with hydrogen.

 

second, not worried about melt downs. current technology for the most part uses fuels with negative thermal coefficients of reactivity. so if the coolant is shut off the reaction actually slows. i'm not sure if thats the case with HEU.

 

with regards to shielding, i concede the point at the moment because i'm not sure the amount required for the scale of reactor i'm thinking about.

 

as for cooling, yes for large reactors because of the amount of heat generated the cooling requirements are immense. i suspect however, although i'm not positive that it will scale with the reactors size, dramatically reducing the cooling needed for the scale i'm proposing.

[insane_alien]

fuel cells are not gas tanks, they ARE the generator, you still need a tank for the fuel.

 

yeah, see you are assuming scaling down means you can use the same technology as you can in larger reactors with no penalties. in practice, this doesn't work. making this assumption usually results in one of two things, the device fails to work at all or you get catastrophic failure. the fact that you proposed weapons grade fuels leans it over to the catastrophic failure side.

 

with regards to shielding, i concede the point at the moment because i'm not sure the amount required for the scale of reactor i'm thinking about.

 

its going to be a lot, even for some sort of exo skeleton to carry.

 

as for cooling, yes for large reactors because of the amount of heat generated the cooling requirements are immense. i suspect however, although i'm not positive that it will scale with the reactors size, dramatically reducing the cooling needed for the scale i'm proposing.

 

yes, it does scale with reactor size. i accounted for that. 20kW is a fair amount of heat to disperse if all you've got to disperse it in is air. and the reactor would likely need to be more than 20kW due to the size of the equipment needed to move it.

 

you do realise you would be better off with a giant nuclear tank don't you? and i haven't even started on the cost of this thing. miniturisation is a costly thing.

[kbyron]

fuel cells are not gas tanks, they ARE the generator, you still need a tank for the fuel.

 

didnt know that, brings up a couple of new ideas to ponder.

 

its going to be a lot, even for some sort of exo skeleton to carry.

 

yea, i was guessing about 2000 pounds for the weight of the reactor including cooling and fuel. The exo skeleton that i was looking at currently has a load capacity of 8000 pounds, but it uses servos. darpa is currently funding a myomer research project that could greatly increase the load capacity without increasing weight significantly. i do not know however how far that project is or the specs of the myomers in question.

 

 

you do realise you would be better off with a giant nuclear tank don't you? and i haven't even started on the cost of this thing. miniturisation is a costly thing.

 

cost is irrelevant to me at the moment. planning and research on my own time is free. yea a tank might be a better idea with current technology, but i don't want current i want to push the envelope of whats possible. i agree that miniaturization is costly, not just monetarily but with regards to time as well. new production methods would be required and that necessitates knowledge resources i do not possess, but its benefits are too great to not at least give it some serious thought.

[insane_alien]

1/ i think you have severely underestimated the minimum weight and size of this. you really are looking at the equivalent of carrying a fully loaded medium size lorry(both in mass and volume) MINIMUM.

 

2/ you are not factoring in issues that arise with scaling, from what you have said it is more like you are unaware of them than purposefully ignoring them. in this case they are very very significant in that power will always drop off faster than size.

 

i really would advise looking at other power sources, especially for individual use.

 

EDIT: another thing i should mention, in addition to the weight of the reactor, you would also have to consider the weight and complexity of armour for the reactor. because they aren't going to do you any good if your cooling, or god forbid, core is full of bullet holes.

Edited October 21, 2008 by insane_alien

[big314mp]

What if hydraulic pistons were used to power the exoskeleton, except the pistons worked like an ICE engine?

 

Sort of like there is a piston in a cylinder, with a spark plug/valves on each side of the piston. Which ever way the piston needs to move, the correct cylinder can be fired.

 

I need to draw this, since this explanation is failing miserably.

 

And my picasa install isnt converting to jpeg, so no pic will be forthcoming

 

The best way I can describe it is like a steam engine piston.

[insane_alien]

so basically, you want explosively powered actuators.

 

well, these are good at providing shock load but not sustained load. hydraulics can provide both greater force and sustained load.

 

it still isn't going to get around the fact that you have basically turned a small nimble soldier into a lumbering hulk more akin to a tank than a soldier.

[big314mp]

I figured there must be a reason that actuators like that aren't built. It would make a pretty awesome jackhammer though...

 

The point you bring up is an interesting one, as an exoskeleton appears to trade mobility for protection/firepower. So perhaps the idea of an exoskeleton can be dispensed with, since it is trying to fit one device into two roles: the role of tanks/bombers and the role of the soldier working in close proximity to the enemy (i.e. Iraq type situations). Since the roles are contradictory, it may be better to keep them apart.

[insane_alien]

actuators like that ARE built. they are only useful in certain circumstances though, typically fail safes or for scientific experiments where something like a valve needs to be shut as quickly as possible.

[kbyron]

actually, armor is where my idea originated. before i switched to looking into a power source since its the main downfall of exo skeleton armor at the moment i had wanted to look into composite ceramic and composite plastic armors for exo skeletons already being worked on. what i was thinking for armoring the reactor was light weight advanced plastic/carbon fiber base with a composite ceramic armor on the outer shell with a .5-1" steel or titanium allow sandwiched in between for added strength and durability.

 

i'm sure there is a way to scale a reactor for my purposes without reducing output significantly, its just beyond us at the moment. I do not want to discard the idea out of hand because it seems impossible or impractical. i want to prove its merits are not worthwhile first (read: i'm stubborn and have to prove to myself my idea is idiotic before i'll listen to others who say it is so)

 

i recognize my knowledge is sub-par for a project like this, so if you can think of any reading materials that might shed more light on this for me it would be greatly appreciated. especially anything about the scaling and cooling issues.

[npts2020]

First learn about reactors and reactor configuration, that will give you an idea of minimum size and weight requirements to sustain a fission reaction. Afterwards you can work on miniaturization of other components. It was quite an engineering feat to make a usable one small enough for a submarine. I am not one to often call things impossible but in order to achieve anything close to what you are talking about, it will require overcoming technical hurdles that have confounded others for decades. BTW submarines already use HEU so you will not gain much from further refining.

[insane_alien]

not only are there technological limits(which can usually be over come given enough time, funding, brainpower and caffeine.) but there are also physical limits and these can't really be overcome even if you have all the coffee in the universe.

[Mr Skeptic]

So, there is a threefold problem posed by trying to shrink a fission reactor.

1) The fissile core. To have a self-sustaining fission reactor, you need your core to capture one neutron per fission. Shrinking the reactor reduces the fissile mass and increases the relative surface area, so more neutrons escape. Atomic bombs can reduce their fissile mass requirements by using high explosives to increase the density to compensate, but for a reactor there really isn't a way to reduce the mass of the fissile core.

2) Radiation. Fission produces both gamma rays and neutrons, which are among the hardest types of radiation to block. Blocking that kind of radiation would be bulky and heavy.

3) Heat dissipation. Since you have a minimum size reactor core producing a minimum amount of heat, you are going to need a large radiator. Nuclear reactors have huge cooling towers, and ships and subs can use the ocean to cool them. If you want to use evaporative cooling instead of a cooling tower, then you need to constantly refill that with water. In any case, you will be bright on an infravision, and be a nice target for homing missiles, which will make short work of your armor.

 

I should note that the government of the US studied the possibility of nuclear powered airplanes and nuclear powered ground vehicles, and decided that it was too bulky and risky. I don't see how it would suddenly be a good idea to use on individual suits.

 

Your biggest problem is #1 that I mentioned. It is possible to make a smaller reactor, but only if you don't want a self-sustaining reaction. Google for "nuclear boyscout" for a description However, the self-sustaining reaction is what gives nuclear its impressive power.

 

Also, consider the alternative. If you were to replace the reactor and associated shielding and radiator with fuel tanks, how much fuel could you carry?

[insane_alien]

several hundred tonnes for the same volume. seriously, to do this you are NOT looking at a suit, your looking at a personal tank(ignoring the further complications that arise if you want to go giant japanese cartoon fighting robot style).

 

fuelcells would be the way to go now, in the future, we may find a way to make small scale fusion produce more power than it consumes and then we could build nuclear powered exoskeletons but thats doubtful.

[Mr Skeptic]

Fusion would also generate lots of gamma rays, neutrons, and heat. But at least it is theoretically scalable, and the plasma could be used for plasma weapons and possibly propulsion.

[npts2020]

* Boron impregnated plastics have been used as neutron shields, so overcoming shielding weight, imo, would be less of an achievement than significantly scaling down the cooling system for a reactor enough and still be able to perform useful work with it. It would certainly require a radical departure from any current reactor design and probably fuels.

 

insane_alien you just described Tetsuo the Iron Man perfectly.