Am242m as RTG isotope

  • Thread starter smartalek86
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  • #1
smartalek86
I am wondering if anyone has considered this could be used in RTG's? To make Am242m one needs spent fuel that's been sitting around for a while, this has let the Pu241 decay to Am241. The question is, once you separate Am-241, can you run the reactor to favor Am242m production? Am242m is the only isotope that doesn't emit hard gamma rays and has a positive energy curve over its half life. It decays to Curium 242 and Pu238 which give 12Mev energy(double Pu238). Another problem is Curium has a SFx10 of Pu238.
 

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  • #2
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How much 242m1Am do you get? The poorly known half life suggests that extracting a large amount of that is very difficult.

Let's have a look at the decay chain:
50 keV for the gamma decay
- 17%: EC to long-living isotope (atom is lost)
- 83%: 670 keV for the quick beta decay, 6.3 MeV for the Cm alpha decay (6 months). 5.6 MeV for the subsequent decay to uranium with 88 years half life.

At 140 year half-life, we get an initial power of 360 W/kg after curium accumulated. A bit lower than 238Pu (540 W/kg), but thanks to the plutonium alpha decays the power does not decrease much - 99% after 50 years and 91% after 80 years.
A longer-living version of 238Pu, but I don't think you can get large samples of the required initial state.

Edit: typo
 
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smartalek86
How much 242m do you get? That is one of the questions i'm wondering if its worth investigating
So considering the design proposed here https://www.nasa.gov/pdf/636900main_Howe_Presentation.pdf It could also be used with Am241(if it where extracted...)

As you said, the yield is only 10% in a LWR for Am242m, but the "waste," decays, relativity quickly to Pu238. There should be large amounts of Am-241 accumulated in nuclear waste by now.
Another problem is Cm242 has a SF 6.33×10−6% while Pu238 is 1.9×10−7% so it will have 33 times the radioactivity? I'm not sure where the cut off for SF would be? My main attraction to this is, as you noticed is, it has a positive power curve(initially, then remains stable) as you pointed out).
Also as Am 242 reaches transient equilibrium with plutonium 238 power should be about 600w/kg?
You wrote w/g when i think you want to write w/kg for pu238, and Curium is Cm, not Cu :kiss:?
Thank you for you input
 
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I meant W/kg, sure.
Ah, no copper...

Some Considerations on 242mAm Production in Thermal Reactors
They conclude that the production of even 100 g of 242mAm would be a major effort. In particular:
This implies the handling of thousands of curies of the most radiotoxic nuclides. Moreover, the need of irradiating very thin samples, supposing 10 mg / cm 2 at the most, implies that the sample to be irradiated has a surface of 10 m 2 at least.
100 g is 36 W thermal, just a few W electric.

I wouldn't expect the SF probability to be a big issue. Other decay modes and gamma emission should be more problematic.

Also as Am 242 reaches transient equilibrium with plutonium 238 power should be about 600w/kg?
A quick simulation shows that the power never goes notably above the initial power. The peak is ~2.5% above the initial value after ~20 years. You can add plutonium to get a higher initial power, but then the power will go down.
 
  • #5
smartalek86
Thanks for the fast reply.
When you simulated this did you include Pu238 emitting 6Mev alpha ? Anyway, since those italian scientists ruled out any practicality of production I suppose I should find smth else do dwell upon?
 
  • #7
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When you simulated this did you include Pu238 emitting 6Mev alpha ?
Sure, otherwise the power wouldn't increase at all (I assumed we start with equilibrium of the first three isotopes).

10 tonnes of Am-241? At $1500/g, that would be 15 billion dollars of americium - if the world market would be that large.
Scaling it by a factor 100, we would get 1 kg after 2.5 years. That is probably not so bad, if there is enough americium around.
 
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I heard that 242mAm has high fission cross section
  • most 242mAm produced in a nuclear reactor would have been destroyed (undergo fission) before they can be extracted
  • you can use them to build portable miniature fission reactor thus you won't need an RTG if you have the same amount of them
 
  • #9
Astronuc
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I am wondering if anyone has considered this could be used in RTG's? To make Am242m one needs spent fuel that's been sitting around for a while, this has let the Pu241 decay to Am241. The question is, once you separate Am-241, can you run the reactor to favor Am242m production? Am242m is the only isotope that doesn't emit hard gamma rays and has a positive energy curve over its half life. It decays to Curium 242 and Pu238 which give 12Mev energy(double Pu238). Another problem is Curium has a SFx10 of Pu238.
Production of TU isotopes, such as Am242,242m, have been considered. In general, it is impractical to produce individual isotopes, because they do not occur in isolation.

In spent fuel, there are isotopes of Pu, which decay by beta emission to Am, to Cm. It is impractical to separate Am242, from Am241, Am243, and others. In general, TU elements are kept together as mixed oxides.
 

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