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NASA Power Space Hardware

New Small Fission Reactor For Deep-space Missions Demonstrated 122

Posted by samzenpus
from the in-space-nobody-can-hear-you-split-an-atom dept.
cylonlover writes "Exploring the regions of deep space beyond Mars means sending probes where solar power isn't practical. Since the 1960s, NASA has equipped its Apollo missions and unmanned explorers with Radioisotope Thermal Generators (RTGs). These have worked very well, but they run on plutonium 238, which is currently in short supply. Therefore, the Los Alamos National Laboratory is developing a new small nuclear reactor for spacecraft that uses uranium instead of plutonium to power Stirling engines and generate electricity. At the Nevada National Security Site's Device Assembly Facility near Las Vegas, engineers from Los Alamos, the NASA Glenn Research Center and National Security Technologies LLC conducted a Demonstration Using Flattop Fissions (DUFF) experiment that produced 24 watts of electricity using a pair of free-piston Stirling engines."
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New Small Fission Reactor For Deep-space Missions Demonstrated

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  • Re:Plutonium upgrade (Score:5, Informative)

    by cbhacking (979169) <been_out_cruisin ... nOSPam.yahoo.com> on Thursday November 29, 2012 @10:30PM (#42138323) Homepage Journal

    It's probably less the number of probes we're sending, and more the general decrease in amount of Plutonium. PU hasn't been manufactured much since the end of the cold war; everybody is busy stepping down their weapon programs instead. Now, some of that former-warhead material is great for RTGs, but the stuff degrades. It has a moderately short half-life (it has to, or it wouldn't be active enough to passively generate the heat needed for an RTG) and a lot of the stuff that was viable for spacecraft 30 years ago is pretty cold now (see the Voyager probes, for example, which are running on extremely low power).

    They can't just fix the problem by sending more, either; not only is it in short supply in general, but it's too heavy to send much on a spacecraft. Instead, they send enough to run the mission at full capacity for a few years, scaling back over time. That requires a supply of pretty fresh / pure Plutonium though, and that means making and separating more of it... except doing runs into a serious political problem. We *could* keep using RTGs (although they aren't perfect by any means, they get the job done) if we could convince people to let us manufacture their fuel source...

  • by Anonymous Coward on Thursday November 29, 2012 @10:33PM (#42138347)

    The usual plutonium bomb/reactor fuel is Pu 239, which is not exactly common (consider how hard Iran tries to get its hands on some). Pu 238 is much rarer than Pu 239, because of its short half life (87.7 years compared to 1000's of years). That higher radioactivity is also why it's usable in an RTG (thing that generates power by the heat of radioactive decay). With a fission reactor they could use Pu 239 which is (to nuclear countries like the US) plentiful, relative to small uses like this.

  • by Anonymous Coward on Thursday November 29, 2012 @10:35PM (#42138359)

    It is truly an irrational pursuit that only sees these materials as weapons. It is our most valuable resource. Actually that would be U-235. We could be using it a lot more efficiently in a new generation of molten salt type reactors.

  • by cbhacking (979169) <been_out_cruisin ... nOSPam.yahoo.com> on Thursday November 29, 2012 @10:39PM (#42138405) Homepage Journal

    Only critical if combined. If the rocket breaks apart or the engines explode, the core would fall apart; it lacks the explosives necessary to bring the Uranium to super-criticality. Worst likely case would be that the control rod gets jammed but the housing stays intact, but the cooling system is destroyed, leaving the core at critical and causing a meltdown. The odds of that seem extremely low, though.

    It'd be a very nasty "dirty bomb" if it blew up in the atmosphere, but no more than that, and a slug of Plutonium hot enough to run a spacecraft for a few years or even decades is a nasty thing to blow up in the atmosphere too. We've been launching those for decades, though.

  • by jeffb (2.718) (1189693) on Thursday November 29, 2012 @10:56PM (#42138503)

    It seems like you're confusing Pu-239, which is used in weapons and has a half-life of 24000 years, with Pu-238, which is not used in weapons and has a half-life of around 90 years.

  • Re:Plutonium upgrade (Score:3, Informative)

    by Anonymous Coward on Thursday November 29, 2012 @11:02PM (#42138529)

    It is a common misconception that weapons grade plutonium can be repurposed for RTGs. However weapons grade plutonium is Pu-239, and has a long half life, 24000 years making it unsuitable for an RTG. The plutonium used in RTGs is Pu-238, with a half life of just 88 years, and is specially made for RTG purposes.

  • by Anonymous Coward on Friday November 30, 2012 @12:10AM (#42138825)

    No, the boron in the control rod stops the reaction when inserted. If the control rod comes out then you would have a critical mass. I assume that thermal expansion of the core gives this a negative coefficient reactivity which probably makes it safe. This still seems somehow more problematic than launching an RTG with a sub critical mass of Pu.

  • Re:Fission Reactor (Score:3, Informative)

    by esldude (1157749) on Friday November 30, 2012 @12:23AM (#42138877)
    You might want to read a bit about fission reactors. A controlled reaction producing heat to be used. That is what it is. It isn't a pile of hot isotopes. Those have been used in the past. As often the case, reading the article might have helped. Or maybe reading about fission reactors on Wikipedia. Good luck.
  • by cyn1c77 (928549) on Friday November 30, 2012 @01:30AM (#42139099)

    No, the boron in the control rod stops the reaction when inserted. If the control rod comes out then you would have a critical mass. I assume that thermal expansion of the core gives this a negative coefficient reactivity which probably makes it safe. This still seems somehow more problematic than launching an RTG with a sub critical mass of Pu.

    Removing the control rod starts the reaction, but it is a sub-critical mass so there is no explosion.

    Just because it is enriched Uranium doesn't mean that it is enriched to weapons grade.

  • by Bomazi (1875554) on Friday November 30, 2012 @01:43AM (#42139131)

    Pu-238 is not used in nuclear explosives proper but some nuclear weapons use a Pu-238 fueled RTG as a power source (see RCED-97-52 [fas.org], section "ELECTRICAL POWER SOURCES").

    Historically most Pu-238 was produced for security applications. The space program was a minor user. The end of the cold war caused a dramatic reduction in the number of weapons. Thus the existing stockpile plus the Pu-238 recovered from dismantled weapons constituted a more than adequate reserve that rendered continued production unnecessary.

    Today they are comparatively few weapons and most have migrated to different power sources. Hence the space program can no longer count on the nuclear weapons program to "subsidize" production. If it wants more Pu-238 it will have to cover a large portion of the cost of restarting production. We can thus expect RTGs to be used less often than in the past.

  • It's small (Score:4, Informative)

    by Animats (122034) on Friday November 30, 2012 @03:26AM (#42139431) Homepage

    Nuclear reactors have been used in space since the 1960s, by both the US and USSR. They've generally powered thermocouple-type electrical generators, which are inefficient but very reliable. The one US reactor launched massed 290Kg and produced 500 watts. Soviet reactors were bigger and produced more power.

    The innovation here is a small unit around 65Kg that produces only 24 watts. Electronics has become so low-power that a 24 watt power plant is useful.

    Note that all these reactors are unshielded.

  • Re:Plutonium upgrade (Score:4, Informative)

    by necro81 (917438) on Friday November 30, 2012 @07:56AM (#42140539) Journal

    a lot of the stuff that was viable for spacecraft 30 years ago is pretty cold now (see the Voyager probes, for example, which are running on extremely low power).

    The halflife of Pu-238 is 88 years. The Voyagers' Pu is only about a half-of-a-halflife old. The falloff in power for a Pu RTG is due largely to material degradation in the thermocouples that generate electricity, not due to a drastic falloff in heat.

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