Terrific application for highly enriched uranium fuel – tiny NASA reactors
How many times have you heard politicians tell you that the only reason a nation with abundant oil and gas might want to enrich uranium is to build nuclear weapons.
The United States has always been one of the top two or three oil and gas producers in the world, but we also have scientists and engineers that have consistently recognized that U-235 is a special nuclear material with unique physical properties. Those properties can be put to nefarious purposes, but they can also provide incredible capabilities – like small, exceedingly long lived, reliable power sources for deep space and undersea applications.
Those applications sound pretty specialized until you realize that any power source that can work reliably in those airless environments can also work reliably in our normal environment without producing any obnoxious gaseous waste products that have to be constantly dumped.
I want one of NASA’s tiny reactors in my home. If you think such a device would be impossibly expensive for individuals, think about the fact I am old enough to remember when only deep space missions could afford to use microprocessors.
I’m old enough to remember when some pacemakers ran on Pu power. Never mind your home, these reactors were buried in peoples chests.
I don’t know about RTGs in widespread domestic use though, we would have to breed and handle LOT of U-235 and that might be problematic. Having said that I agree the technology is underused.
Did I write breed? I meant produce by enrichment.
Rod
A convergence of increased uranium supply and lazer isotope separation could make this design affordable. This is exactly the type of simple design that gives me hope and excitement. But for a home the shielding would need to be what?
The US has ~300 tons of HEU it needs to dispose of, and the number will only grow larger as more weapons are decomissioned.
Heck, even if I can’t get a reactor I am more than willing to take the Cs and Sr separated off from a reprocessing scheme and store that in my basement. The fact that they are pure beta emitters even makes the shielding requirements minimal. All the hot water I need on demand at no cost. I could live with that.
Bury it under the driveway. That way, when it needs replacing, you don’t have to close the house, the way you might if it were under the foundation. And it might help keep the driveway ice-free… One month every thirty years, park in the street.
It’s not an RTG. This is a fission reactor. I thought this was interesting and started a thread on Kirk Sorenson’s site. He knows these guys, and the inside story seems a lot less impressive than the press release.
Fission reactor with small stirling cycle engines.
“any power source that can work reliably in those airless environments can also work reliably in our normal environment without producing any obnoxious gaseous waste products that have to be constantly dumped.”
Nuclear fission does produce gaseous fission products that can be of concern if released into the environment. Probably the most significant from the standpoint of radiotoxicity is Kr-85 (other gaseous fission products include various isotopes of Xenon that decay to radioactive Cesium are also released).
Gaseous fission products can accumulate in sealed fuel assemblies or fuel pins. The buildup of gaseous fission products can, in part, determine how long cladded fuel assemblies or pins can stay in a reactor which in turn influences fuel burn up. Krypton-85 did build up mildly in the atmosphere during the 1960s era of atmospheric nuclear testing and from early fuel reprocessing activities.
http://www.ead.anl.gov/pub/doc/krypton.pdf
There is a practical nuclear technology that generates net energy while producing environmentally benign non-radioactive helium-4 as its nuclear waste and could fully power the planet for billions of years.
http://goo.gl/1DZhq
These are beyond awesome. This, from my understanding is like the SNAP-10A ( http://etec.energy.gov/Operations/Major_Operations/SNAP_Overview.html ) which was tested in orbit and even crash tested back when we were serious about space and the future.
Why not use Americium 242 instead? A 10kw reactor with 20gms of Am-242:
http://thefutureofthings.com/articles/26/americium-power-source.html
@Robert
Again, I warn you about being tiresome.
Toxicity of a noble (inert) gas? Give me a break. Kr-85 is only an external dose source and a rather minor one at that.
I am aware of long lived fuel designs that are able to keep all of the gaseous fission products inside the fuel elements for the entire life of a submarine – 33 years.
NOT an issue.
50 pounds of HEU but only half a kilowatt of power? Scale that to 100 megawatts as in power station reactor and it would require 4 and half thousand tonnes of HEU! Perhaps in striving for simplicity and reliability they have sacrificed too much efficiency? Or is a lot of this the simple scaling factor of small reactors, being less efficient at creating electricity.
As compelling as the idea is, the widespread use of this sort of power supply in civil applications is just not going to happen. While I am the last person to invoke security as a reason to inhibit the development of nuclear power, the specter of so much HEU distributed in so many packages gives me pause. This is particularly true, as we have already seen how lax attitudes with medical sources can lead to significant problems. Were these reactors in widespread use, there would be loss of containment events that would occur and that is unacceptable.
Jeremy:
Have you ever heard of the term “critical mass”? The concept helps to explain the answer to your question.
In order to create a self sustaining chain reaction, you need a certain amount of material or a certain purity arranged in a certain configuration. Computing the specific numbers can get pretty complicated because they depend on a lot of factors like neutron reproduction factor, thermal leakage, fast leakage, thermal utilization factor, resonance escape probability, and fast fission factor.
http://en.wikipedia.org/wiki/Six_factor_formula
Bottom line – you cannot ratio the quantity of uranium required from a very tiny power source up to a very large power source.
By the way, Happy Anniversary. Today, December 2, 2012 is the 70th anniversary of the very first test of the ability to control the nuclear fission chain reaction.
Fermi and his team stacked up a pile of graphite bricks and natural uranium (in both metal and oxide forms) and used wooden rods wrapped with cadmium to absorb neutrons and allow fine control of the process, bringing it critical adjusting power and shutting it down as predicted by working the equations and performing the precritical tests.
http://www.ne.anl.gov/cp1-anniversary/
Yes, I hadn’t considered how critical mass makes for a lower limit to the amount fuel possible to sustain a chain reaction.
Happy Anniversary.
If I remember that reactor produced enough to power a light bulb!
There’s obviously no limit to how inefficient you can extract power from a reactor.
The constraints of reliable unattended operation and light weight force the designers here to accept a low conversion efficiency. Its a trade off sure.
Just surprising that that same amount of fuel might power a submarine, ie produce megawatts but here it produces less than a kilowatt.
Part of the low conversion efficiency for any space thermal power source is the heat sink challenge.
Here on earth, we have several wonderful fluids that work well to remove heat from the cold end of a thermodynamic process using convection, but in space you have to depend on large radiators.
50 pounds of U-235 could be arranged in a core that could provide sufficient heat energy for a power plant big enough for a submarine; the design would need to include a sufficient quantity of material with low propensity for absorbing neutrons. Transferring fission heat power needs sufficient heat transfer surface area.