Nuclear batteries

  1. jcsd
  2. Morbius

    Morbius 1,160
    Science Advisor

    Mark1,

    We have already had nuclear batteries for decades. They are used primarily
    on NASA's deep space probes - the ones that go to the outer reaches of the
    solar system. Solar cells aren't particularly useful that far from the Sun.

    These "nuclear batteries" are usually called RTGs.

    There are two basic classes of RTGs - the thermoelectric and thermionic
    types. The "betavoltaics" described in the link appears to be a new
    improved type of thermionic RTG.

    The concept of the nuclear battery has been around for decades - the
    article you reference is just another new design or implementation of
    the nuclear battery concept.

    Dr. Gregory Greenman
    Physicist
     
    Last edited: May 16, 2005
  3. Thermal battaries are very smart, but I highly doubt they will ever make it onto the shelfs for public use. Can you immagine haveing two AA size nuclear battaries? You drop your CD player and the country goes up in smoke!
     
  4. Beta batteries - a long-overdue good idea

    If you dropped your CD player, you might contaminate the local area. There would be no explosion.

    The linked article was talking about tritium-powered batteries, which are different from traditional plutonium-powered batteries. It doesn't operate from the heat of decay, so it would not be a thermal battery. If it was a thermal battery, you might not want it in your CD player since thermal batteries are only ~5% efficient and therefore can get quite hot.

    I have been following tritium battery development for awhile and I see a major difficulty in retaining enough tritium to have a useful energy density. Typical 10-year tritium exit signs only hold 1 milligram of tritium in the entire sign, which produces ~1 milliwatt of energy before conversion losses. If you want a battery that can put out a more-useful 1-watt or 10-watts of electrical power, you are going to have to find a package that can hold seriously compressed tritium gas without risk of breakage. I have seen a suggestion that hollow, thick-walled glass spheres the sizes of marbles might be usable. The trick would be to figure out how to manufacture these economically with high-pressure tritium gas captured inside.

    Anyway, I think part of the big picture is that the American military would be very interested in a battery that never needs replacing. (Supposedly, the field service life of the current lithium-ion batteries in deployment is measured in months. The heat in Iraq and Afghanistan is probably one culprit, as well as a poor battery-maintenance culture. Of course, since a tritium battery never needs servicing or charging, it would be ideal for addressing the latter problem. Heat can sometimes affect transistor performance, though, so I think the former problem might possibly mean larger tritium batteries would be needed for deployment in high-ambient-temperature environments such as the Middle East.)
     
  5. Greetings all

    I am a science fiction writer not by any means a scientist. None the less tritium Ion batteries (beta-voltaics in general) have fascinated me for a while. I have postulated a power cell that uses Tritium gas surrounded by a spherical collector array. Now knowing that energy density may be low in packages small enough to be considered portable my cells actually use the fairly low current high voltage output to charge more traditional integrated battery cells. Thus we have a self recharging battery....

    Anybody want to comment on the possible reality or inherent problems herein.

    P.S. My assumptions about beta-voltaics are based on a paper (which I barely understood) that I found on line.
     
    Last edited: Sep 10, 2009
  6. russ_watters

    Staff: Mentor

    Why bother attaching it to a battery? Why not just use the electricity directly?
     
  7. Astronuc

    Staff: Mentor

    The gist of a beta emitter is to have a collector that collects the electrons (beta particles) and passes them through the load before they recombine with the material from whence they originated.

    The problem with nuclear batteries is that they are always on, i.e. the radionuclide decays whether or not there is a load associated with.

    We already have radioisotopic thermal generators (RTGs) which use the thermal energy by converting with to electrical energy via thermoelectrics.

    http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator

    http://www2.jpl.nasa.gov/galileo/messenger/oldmess/RTGs.html

    http://www.osti.gov/accomplishments/rtg.html

    http://www.ne.doe.gov/pdfFiles/MMRTG.pdf

    http://saturn.jpl.nasa.gov/spacecraft/safety/power.pdf

    http://voyager.jpl.nasa.gov/spacecraft/instruments_rtg.html
     
  8. Re: Beta batteries - a long-overdue good idea

    Why is it necessary to make a beta-voltaic using high-pressure tritium gas? Wouldn't it make more sense to use another beta emitter like Sr-90? Or are those betas too high energy to effectively capture?
     
  9. Astronuc

    Staff: Mentor

    Please note that hitssquad last posted May19-05.
     
  10. Well that means his tritium battery would still be producing ~75% of its initial power by this point, which should be enough to manage a reply :)
     
  11. If I understand (if I actually do) the issue is low power output for small sized packages. Thus if you wanted a portable beta-voltaic power source the current potential at any given moment is low but the voltage can be (relatively) hi. Thus you have the perfect instrument for charging a capacitive circuit like a battery. A battery can store the charge over time allowing comparatively hi currents in a comparatively compact package. Take for instance the analogy of the car battery and an associated commercially available (reasonably priced) charger.

    Both the charger and battery have about the same outside dimensions and the battery is only a few pounds heavier (especially if you use modern led mesh types). The average charger delivers around 15 amps at 14.5 volts continuous. The battery on the other hand can deliver up to 50 to 60 amps continuous at 12.5 volts (+or-) for short periods of time and over 300 amps in brief surges. In this example the portable beta-voltaic/beta source device is the charger and could not produce enough current (power, watts, Volt-amps) to do the work that needs doing. We therefore use the continuously provided low power voltage to charge a high output battery so when we need high power we can tap it from the batteries.

    This system is not unlike the original hybrid automobile designs (many published in the 70's in popular science magazine). This is also analogous to other systems like the diesel- electric locomotive which uses a diesel engine to run a generator that powers electric motors that drive the wheels.

    Oh and why a beta source and not a thermal or alpha source... On word "Shielding." Beta particles (as I understand them and don't forget Im not a scientist) are very easy to stop and often lack the energy to even penetrate human skin. With this in mind the system has some inherent safety over other types of "nuclear batteries."
     
    Last edited: Sep 11, 2009
  12. Sr-90 is actually an excellent source for an RTG.

    http://en.wikipedia.org/wiki/Strontium-90

    Sr-90 is a natural fission product, so if we were using breeder reactors or Thorium for our electricity we would produce large amounts of Sr-90. For a 1GW thorium reactor, you would be talking about 140 pounds a year and even a breeder reactor could produce over 100 pounds a year. Those are back of the envelope numbers.

    I wouldn't suggest it for home use, since it is pretty nasty if it is ingested, but for military and remote equipment applications it could be quite useful. The alternative is to store it for a few hundred years and harvest the decay products, which you can still do anyway when you recycle the RTG.

    The efficiency of a RTG is pretty pathetic. There is work being done on using a Stirling engine instead.

    http://translate.dc.gov/ma/enwiki/en/Stirling_radioisotope_generator
     
  13. Astronuc

    Staff: Mentor

    Alpha particles are stopped in the skin or by a sheet of paper. Beta particles are more penetrating, and gamma rays are much more penetrating of tissue.
     
  14. Oops.... See that's why I ask a scientist...
    Just out of curiosity are the beta particles produced by decaying tritium particularly energetic.
    Would a thin aluminum housing do the trick or do I need a block of lead.
    (Wish I could find the original source that gave me this idea)
     
  15. Astronuc

    Staff: Mentor

Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook

Have something to add?