Can Ionizing Radiation Be Directly Converted to Electricity?

[snorkack]

Is there any way to convert ionizing radiation to electric energy without converting it to heat in the meantime?
I don´t mean avoiding losses as heat - these are unavoidable - but direct conversion of some energy to electricity, by a mechanism that does not depend on buildup of heat.
For example, batteries convert chemical energy to electricity, and photoelements convert visible light to electricity. Anything for ionizing radiation?

 

[berkeman]

Is there any way to convert ionizing radiation to electric energy without converting it to heat in the meantime?
I don´t mean avoiding losses as heat - these are unavoidable - but direct conversion of some energy to electricity, by a mechanism that does not depend on buildup of heat.
For example, batteries convert chemical energy to electricity, and photoelements convert visible light to electricity. Anything for ionizing radiation?

https://en.wikipedia.org/wiki/Magnetohydrodynamic_generator

 

[Astronuc]

Is there any way to convert ionizing radiation to electric energy without converting it to heat in the meantime?
I don´t mean avoiding losses as heat - these are unavoidable - but direct conversion of some energy to electricity, by a mechanism that does not depend on buildup of heat.
For example, batteries convert chemical energy to electricity, and photoelements convert visible light to electricity. Anything for ionizing radiation?

Basically, one is describing charge separation, i.e., can one expel electrons from a mass (emitter) and collect the electrons on another mass (collector) at some constant rate (ideal) such that one maintains a constant voltage/current, which is the idea behind beta-voltaics.

https://en.wikipedia.org/wiki/Betavoltaic_device
http://large.stanford.edu/courses/2013/ph241/harrison2/
https://www.technologyreview.com/s/416312/a-25-year-battery/
https://www.energy.gov/sites/prod/files/2015/08/f26/Cabauy Tritium Focus Group Presentation.pdf

berkeman cited MHD, in which the working fluid/gas in a strong magnetic field would be ionized by radiation resulting in charge separation, but recombination is a problem if the separation of emitter and collector are large compared to the range of the radiation.

 

[snorkack]

Is there any semiconducting device capable of converting kinetic energy of fission fragments into electricity?

 

[Astronuc]

Is there any semiconducting device capable of converting kinetic energy of fission fragments into electricity?

Fission fragments have very short range in solids. Fission spikes are generally less than about 7 microns, or effectively less than a typical nominal UO₂ grain diameter. Converting fission fragments in a thermo-electric semiconductor would be problematic from that standpoint of accumulating a variety of chemical species in the semi-conducting material, in addition to the neutron activation and radiation effects due to neutron and gamma radiation. Most thermoelectric concepts I've seen involve liquid metals removing heat from the core and passing it though an ex-core heat exchanger. I've also seen in-core thermionic concepts, which have similar issues regarding activation/transmutation and radiation effects.

 

[snorkack]

Fission fragments have very short range in solids. Fission spikes are generally less than about 7 microns,

How does this compare with alpha particle range? Alpha particles have lower mass, but also lower energy...

 

[anorlunda]

Is there any semiconducting device capable of converting kinetic energy of fission fragments into electricity?

Did you ignore the beta voltaic device that @Astronuc linked in #3?

BTW: @Astronuc 's very impressive knowledge of nuclear tech seems to be encyclopedic.

 

[snorkack]

Did you ignore the beta voltaic device that @Astronuc linked in #3?

Beta radiation is not kinetic energy of fission fragments.

 

[etudiant]

If memory serves, some of the more advanced fusion reactions yield entirely charged particles whose energy could in theory be harvested by suitable electrostatic fields. There were some studies of a possible demonstration using the fragments of collisions in an accelerator, but nothing was ever reduced to actual practice that I know of.
Conceptually, this idea of direct electrical energy harvesting is a lot more appealing than splitting atoms to boil water, but there are technical obstacles.

 

[Astronuc]

How does this compare with alpha particle range? Alpha particles have lower mass, but also lower energy...

It's been a few decades since I've done calculations, but looking around I found some data at NIST.

http://physics.nist.gov/PhysRefData/Star/Text/ASTAR.html (on can enter iron (Fe)), select No graph, and submit. One obtains a table of alpha particle range by energy.

The range in g/cm² can be divided by density in g/cm³ to get range in cm. It looks like the range of an alpha particle of energy 1 MeV is about 0.18 mm in iron/steel, and for a 4 MeV energy, the range is about 0.72 mm. I plotted range as a function of energy on a log-log plot, and there are two linear portions with a transition in between. So the range of alpha particles is considerable longer than fission products.

I haven't verified the numbers, so consider the ranges preliminary.

 

[snorkack]

Note that a never run reactor would have a background of alpha decays.

 

[Astronuc]

Note that a never run reactor would have a background of alpha decays.

Yes, but the activity is very low. When fuel assemblies are manufactured, there is very little heat generated, and the fuel is stored without shielding in open air. There is no cooling necessary. The half-lives of U-235 and U-238 are very long, 704 million and 4.468 billion years, respectively. In processing uranium ore, the decay products are removed.

 

[snorkack]

Yes, but the activity is very low. When fuel assemblies are manufactured, there is very little heat generated, and the fuel is stored without shielding in open air. There is no cooling necessary. The half-lives of U-235 and U-238 are very long, 704 million and 4.468 billion years, respectively. In processing uranium ore, the decay products are removed.

...except uranium 234, because it is uranium.
In natural uranium, the composition is approximately:
140 parts of U 238 to 1 part of U 235
18 000 parts of U 238 to 1 part of U 234 (because U 234 is a daughter of U 238 and that´ts the ratio of half-lives)
therefore 130 parts of U 235 to 1 part of U 234.
But in terms of alpha decay rates, it is approximately:
22 decays of U 238 to 1 decay of U 235
1 decay of U 238 to 1 decay of U 234 (because U 234 is daughter)
therefore 22 decays of U 234 to 1 decay of U 235.
Now, while full uranium series is 8 alpha and 6 beta decays, U 234 is long-lived (240 000 years). Until such time as U 234 shall build up, the decay of U 238 to U 234 contains just 1 alpha and 2 beta decays.
U 234 decay series is 7 alpha and 4 beta decays, but ionium is long lived (75 000 years). Until such time as Th 230 shall build up, the decay of U 234 to Th 230 contains just 1 alpha decay.
Full actinium series contains 7 alpha and 4 beta decays, but no daughter is U and Pa 231 is long lived (32 000 years). Until such time as Pa 231 shall build up, the decay of U 235 to Pa 231 contains 1 alpha and 1 beta decay.

What happens when U is enriched?
When U 235 is separated from U 238, U 234 is even lighter than U 235!
For example, if the ratio of U 235 to U 238 is increased 8 times, from 1:140 to 1:17,5, what happens to the ratio of U-234 to U-235?
Does it remain the same, at 1:130? Or increase 2 times (cubic root of 8), becoming 1:65?
Remember, the activity ratio of U 234 to U 235 begins at 22:1. Does enrichment cause further increase of U 234 activity relative to U 235?

 

[mheslep]

https://www.physicsforums.com/threads/nuclear-direct-electricity-conversion.841629/#post-5292588

 

[rootone]

Interesting thread,
I go with better technology for collecting solar power,

 

[Astronuc]

...except uranium 234, because it is uranium.
In natural uranium, the composition is approximately:
140 parts of U 238 to 1 part of U 235
18 000 parts of U 238 to 1 part of U 234 (because U 234 is a daughter of U 238 and that´ts the ratio of half-lives)
therefore 130 parts of U 235 to 1 part of U 234.

Natural U is approximately 0.0054% U-234, 0.72% U-235 and the balance (~99.27%) U-238.

I looked at some of my notes on enriched U for commercial fuel. I have assays giving U-234, U-235 and U-238. I did a quick fit of the data, which yielded U-234 (%) = 0.0006 * (U-235 (%))² + 0.007 * (U-235 (%)), so the fraction of U-234 increases with a slightly parabolic trend with enrichment (% of U-235). At maximum commercial limit of 5% U-235, the maximum expected U-234 proportion would be ~0.05%, and U-238 is about 94.95%.

The fraction of U-234 is not significant with respect to alpha activity. The half-life is ~245500 years, all the decay products have been chemically removed, and the decay of U-234 from mine to conversion and enrichment is not significant.

 

[snorkack]

The fraction of U-234 is not significant with respect to alpha activity. The half-life is ~245500 years, all the decay products have been chemically removed

To the contrary, it is highly significant. After all, even before enrichment, U-234 has as much activity in terms of alpha decay count as U-238 (although U-238 has 2 additional beta decays that U-234 does not have) and 22 times as much as U-235. Enrichment removes U-238, so the activity of U-234 becomes the most significant activity present.

 

[Astronuc]

To the contrary, it is highly significant. After all, even before enrichment, U-234 has as much activity in terms of alpha decay count as U-238 (although U-238 has 2 additional beta decays that U-234 does not have) and 22 times as much as U-235. Enrichment removes U-238, so the activity of U-234 becomes the most significant activity present.

I've handled enriched pellets, and they are cold to the touch, as in room temperature. There is no significant thermal energy available. I've stood next to barrels containing 500 kg of enriched UO₂, and they have no significant temperature.

 

[snorkack]

Sure.
The squash court pile was something like 5,4 t metallic U - unenriched - and 45 t "uranium oxide". Which one? UO₂ or U₃O₈?

 

[Astronuc]

Sure.
The squash court pile was something like 5,4 t metallic U - unenriched - and 45 t "uranium oxide". Which one? UO₂ or U₃O₈?

I would expect it was UO₂, which has a higher density of uranium. I'll have to dig into available technical documents.

From a brief description from U of Chicago: "Chicago Pile Number One, or CP-1 for short, consisted of 40,000 graphite blocks that enclosed 19,000 pieces of uranium metal and uranium oxide fuel." So uranium oxide is not very specific.

 

[snorkack]

So, a total of about 43...45 t natural U.
The thermal power of U-238 is quoted as 8,5 mW/t. Not sure what´s included - are Th-234 and Pa-234 decays in? Is U-234 included?
All told, the radiation of 43...45 t natural U should be somewhere under 1000 mW.
Well, CP-1 was operated up to 200 W - but that was judged to be a radiation hazard. Which is why subsequent experiments were limited to 500 mW... same order of magnitude as the background decay. Though a different spectrum, of course.

 

[snorkack]

Both metallic U and UO₂ are reactive towards air. U₃O₈ is the species that is stable to air.
How was Fermi pile protected against oxidation by air?

 

[mheslep]

Both metallic U and UO₂ are reactive towards air. U₃O₈ is the species that is stable to air.
How was Fermi pile protected against oxidation by air?

As are most (all?) metals, forming a surface coat of oxide. I doubt some surface oxygen has much effect on reactivity.

 

[snorkack]

As are most (all?) metals, forming a surface coat of oxide. I doubt some surface oxygen has much effect on reactivity.

Not directly.
A lot of metals don't form a surface coat of oxide because for various reasons the oxide cracks and crumbles, exposing the underlying metal to further oxidation.
And a reactor changing its geometry due to spontaneous chemical reactions has potential to interfere with its operations.
In the absence of air to react with:
U melts at 1132 Celsius (but undergoes an allotropic change from ortorhombic to tetragonal at 668 Celsius)
UO₂ melts at 2865 Celsius
U₃O₈ melts at 1150 Celsius
UO₃ decays at around 700 Celsius.

 

[mheslep]

http://www.ltbridge.com/fueltechnology/metallicfueltechnology

 

[Astronuc]

As are most (all?) metals, forming a surface coat of oxide. I doubt some surface oxygen has much effect on reactivity.

Metals do form oxide layers, and in many cases, e.g., with stainless steels, the layer is protective. However, some metals form friable oxides, which do not offer much protection, and instead, the oxidation process is unstable. In some cases, in the presence of water or steam, the underlying metal absorbs hydrogen and that enhances the oxidation. Uranium metal was usually clad in aluminum or zirconium alloys.

Update: Looking in my 1964 text, there is a sentence containing "uranium oxide (U₃O₈)", so it would appear that oxide refers to the higher oxide rather than UO₂. I was at a seminar recently, and some of the discussion was about a particular calciner, which produced uranium oxide (U₃O₈), which I found surprising. In order to produce UO₂, one needs to maintain a reducing environment in the reaction system/calciner.

 

[snorkack]

Also: uranium dioxide happens to be a semiconductor.
Has been proposed for solar cells, including Schottky diodes.
How could a diode including uranium dioxide as a semiconductor convert into electricity sunlight?
Alpha particles?
Fission fragments?
Prompt gammas?
Delayed, fission product betas?

 

[snorkack]

GPHS-RTG produces 4400 W thermal - all the time, from 7800 g Pu-238.
Spontaneous alpha radiation whether or not you need it. Nasty stuff when you plan to disperse and eat your reactor.
What's hotter - 8 kg of Pu-238 or 30 kg U-235?
Remember - if what you disperse and eat is a never run reactor, then it is just U-235 (and U-234) - no fission products as yet.
Shouldn't a small fission reactor be much safer than a radioisotope generator?

 

[mheslep]

Neutrons

 

[dgjxqz]

by a mechanism that does not depend on buildup of heat.

How about collecting hydrogen from radiolysis in an AHR and feed them into a fuel cell?

 

[Rive]

... diode including uranium dioxide ...

Whatever the method, the basic problem is that the starting point (radiation) is chaotic. This limits the efficiency.

Just a passing thought. Is there any paper somewhere what discusses alpha/beta decay as matter of (laser-like) induced emission?