This is a good example of Am-242 isotope app. to smaller space Battery,
but I don't expect much success in Dr. Ronen to sell the system since
NASA is not interested in things nuclear as a power source in space yet.

NASA follows the Bush doctrine which is, "A U.S. space program is only as relevant to its public as its last space mission." which in reality is not very relevant. Currently dust storms on the surface of Mars is an indication of what can happen to a solar photo-voltaic system under stress.

Any pics of this passive Am-242 isotope battery???

I presume that we are talking about Am242 M isomer Americium?

http://ie.lbl.gov/toi/nuclide.asp?iZA=950542

How do you make that and not make the other isotopes of Americium?

In this talk Prof. Ronen will present a simplified 242Am-fueled nuclear battery concept design, featuring direct fission products energy conversion and passive heat ejection. Optimization of the battery operating characteristics and dimensions will be presented.
RTG's use any high heat source. Passive heat sources have usually been radioisotope fuels like 210Po,238Pu,90Sr,242Cm and they normally fall in the watt range for electrical power unless thermopiles are subjected to very high heat in excess of 1700K that usually comes from coolant derived from a fast reactor like NaK (SNAP 10A). Still this system index is of kW(e). The other option is the Thermionic Generator in-pile favored by the Russian TOPAZ liquid metal as coolant. These are fast reactor driven.
The only other passive systems are the AMTEC conversion (alkali metal to electric converter) heat source Pu238. Or the use of an updated 'Isomite Battery'.

All these are examples of watt power electric how does this 242Am system
provide MW power? 

-- Edited by NUKE ROCKY44 at 06:13, 2007-07-23

Americium isotopes are capable of neutron chain reactions--so criticality issues would need to be addressed. Although the critical amount depends upon the geometry and many environmental factors (whether it is encased in something that acts as a neutron reflector) I would say, knowing nothing else, that americium is roughly just about as critical as plutonium isotopes are, so in the 10 kilogram range for mostly 'pure' isotopes...

Even plutonium-238 is capable of chain reaction--it's just that it is fairly undersirable for it to do so in the context of an RTG.

I guess it's a fast reactor using 242Am as fuel to heat whatever ?? (thermopile, thermionic or AMTEC). This is in the KW range. It would be Ok
to use for a Lunar power source project if it can be shown to be a straight black box plug in-for-power setup without much complication to setup on lunar site. And of course 242 Am fuel mitigated for launch mishap contingencies.
Then by all means the good doctor should pitch the system.

As you know nuke 'batteries' (bad term) do have terrestrial applications too...  
  

Andrew wrote:

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RTG's rely on the passive decay of radioactive material, and do not go under any reaction (unless you count radioactive decay as a reaction), so literally its not a reactor.

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Yes, but Dr. Ronen's concept is NOT an RTG.

That goes because it is a fission reactor, and because it doesn't use the thermoelectric effect.

Fission products carry a multiple electric charge when first emitted, in a vacuum.
Achieving direct energy conversion with such particles, which come to a dead stop on hitting the first solid object they encounter, converting their kinetic energy to heat in the process, is not an easy proposition.

No doubt the scheme is analogous to the very tiny electric current generated by alpha particles emitted by Am-241 in domestic smoke detectors.

But doing this on a scale of kilowatts or even megawatts seems well-nigh impossible.

First of all, the Am-242m fuel must be in the form of extremely fine (nano-scale) fibers, to avoid self-heating by the emitted fission products.

Secondly, besides having a near-perfect vacuum, the anodes & cathodes must be closely interspersed, but not making contact (short-circuit).

So while the principle seems simple enough, the fabrication sounds like pure magic.

And, incidentally, the reason this fission battery requires Am-242m for operation, is because the reactor core is mostly empty space (vacuum).
Only Am-242m has a high-enough fission x-section to achieve criticality in such a border-line configuration.
(The thermal neutron fission x-section of Am-242m is about seven times higher than other fissile nuclides, like U-235, Pu-239 and U-233).

-- Edited by 10kBq Jaro at 01:16, 2007-07-24

NUKE ROCKY44 wrote:

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If you say Am242m isomer fuel is in the form of nano sized fibers how do you prevent clumping of fuel and fission products and avoid excess heating, how do you achieve efficient distribution?

Is this Am242m mini reactor core containment glass or metal?

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Like I said earlier, I will try to get some slides of Ronen's presentation later.

For now, I'm just reciting what I read years ago in his paper in Nuclear Science & Engineering journal, in which he briefly discussed a similar concept -- one for direct fission product propulsion.
Like the nuke battery he's presenting now, that old concept had a very loose matrix of Am-242m fuel, to allow the fission products to get out the aft end, while being just dense enough to achieve criticality.

10kBq Jaro wrote:

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GoogleNaut wrote:

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I would say, knowing nothing else, that americium is roughly just about as critical as plutonium isotopes are, so in the 10 kilogram range for mostly 'pure' isotopes...

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According to Dr. Ronen's slides, which I obtained today, the critical mass (thermal neutrons) is from 9.9 to 20 grams (ie. 0.0099 to 0.020 kg).

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Really!

Could you make a trigger for a mini-fusion device using this?

It would overcome a lot (though admittadly not all) of the fall out issues associated with near-earth Orion operations!

Now I understand better why Dr. Ronen's is referred to as a nuclear battery...20 grams. That is a phenomenally small nuclear reactor fuel load. I can imagine taking that fuel load and impregnating something almost like a Coleman Lantern Mantle with nuclear material and then passing a gas through the glowing ceramic mesh...

Because the individual fibers in a mesh have such a small size, substantial heat transfer could be accomplished with such a scheme. This could allow a tiny Brayton cycle conversion system to do the job--however, Brayton loses a lot of its appeal at small scales--the complexity of the turbo machinery becomes oppresively inefficient at small scales...

A 'lantern mantle' scheme maybe better used as a thermionic source, or maybe as something like a vapor core reactor concept....


The direct electrostatic fission fragment conversion is interesting...it is most like thermionic in that the energy of the reactor is used to transport charged particles across a vacuum gap. However, when the charge carriers are the fission fragments themselves then a lot more charge can be carried in one package...

I wonder about secondary x-ray emmisions from electrons recombining with the fission fragments at the inner electrode---being still fairly high-Z materials on their own, the first shells of electrons should emit a pretty heavy X-ray spectrum...could be enough to think about cooling the surrounding radiation shield....

10kBq Jaro wrote:

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Dusty wrote:

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Could you make a trigger for a mini-fusion device using this?

It would overcome a lot (though admittadly not all) of the fall out issues associated with near-earth Orion operations!

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NO!
That would require a fast neutron spectrum, not thermal.
In the latter, there is lots of moderator, like water.
So while the fissile mass (Am242m) is very small, the overall critical assembly, including water solvent & beryllium reflector comes to several kilograms.

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Aw Too bad!

OTOH a world where you could make nuclear explosive pits using sugar cube sized lumps of fissile material would likley be rather an "Interesting" place!

I'm guessing that you'd have to be talking about calfornium-251 with a half-life of about 900 years...

This stuff is pretty hot, and there are isotopes of californium that are very strong neutron emitters (like Cf-252 with a half-life of 2.5 years)--which would really make predetonation tough if present in even minute quantities...

I don't know if a fast-fission chain reaction is even possible with californium--only that it is probably so...

Neutron regeneration factors for U-235 are pretty close to 2.4 and for plutonium-239 are about 2.6-2.8 as I recall...

So if Cf-252 had something like that and a really big fast-fission cross section too, then a really small critical mass ought to be possible...

However, the difficulty of creating the conditions of supercriticality necessary for a detonation are substantial--and the smaller the physical size of the 'pit' the more quickly things must happen. And it is a fairly challenging technological choregraphy that must occur before an atomic explosion can happen...

Thanks Jaro--as always you have excellent supportive data. So if the neutron regeneration factors are also comparable to plutonium, then I would expect a similar pit mass (10 kg or so, depending of course on a similar density--a higher density would actually lower the total pit mass...)

So I would expect that a californium-251 bomb technically is possible--but I rather suspect that it would be more difficult, technically more challenging (probably active cooling for the pit since the half life is 30 times shorter than Pu-239) and far more expensive than plutonium-239...and ultimately only as destructive as its plutonium cousin...

So I would see little or nor advantage to going that route for a weapon or explosive device...