Small and passively safe Nuclear reactors for NASA and military missions

This month NASA will start testing a tiny 1 kilowatt uranium fission reactor Stirling engines for use in possible future missions to Mars.

The low power means very little of the uranium is burned up. Therefore, the fuel does not swell and releases very little gas.

The kilopower reactor running for 15 years would have 0.12% swelling. This is less than 10% of swelling from the heat generated.

Radiation damage is also so little it can be ignored.

Generating heat at 1200K can be used to efficiently convert the heat to electricity with a Stirling engine. The core power would be limited to 4 kWt.

Beryllium Oxide surround the core to reflect the neutrons back so that the system is only critical within the reflectors for safety and to keep the core smaller. 300 kilograms of low enriched uranium (7%) is enough to make the reactor work.

Using more highly enriched uranium (19%) allows a 35 ton nuclear reactor that could generate 500 KWe to 2 MWe.

Los Alamos National Research lab is helping to design small compact fast reactors like KiloPower and Megapower. They are designed to maximize mechanisms so the reactors are totally self-regulating. The Los Alamos objective is to design-in self-regulation as the front-line feature in order to minimize technical and programmatic risk and to demonstrate via testing that self-regulation is both reliable and repeatable.

A scaled up 2 megawatt system would be expected to weigh about 35 metric tons. It would transportable by air and highway.

These are clever and novel designs based upon well-established physics that simultaneously simplifies the reactor controls necessary to operate the plant and have inherent safety features that guard against consequences of launch accidents and operational transients.

The design objectives are different from the conventional large nuclear fission reactors where the objectives were 500MW to 1.4 gigawatts of utility scale power at the lowest price per kw.

11 thoughts on “Small and passively safe Nuclear reactors for NASA and military missions”

  1. The small Nuclear Power Plants are not highly radioactive until turned on and run for a short time. And highly radioactive RTG’s have had an accident on launch… The RTG was recovered and launched on another mission. The Space Nuclear Power can be used at a commercial Lunar Base at the Lunar South Pole for NASA and others to Live Off the Land on the Moon and Mars ! Also small NTR have been designed by NASA to fly to the Moon in 24 Hours and operate in the deep gravity wells of the Earth, the Moon and Mars. Also Nuclear Power Plants can power the VASIMR engines for fast trip time to Mars and Beyond. Back to the Moon to Stay and onto Mars and Beyond-Ad Astra… tjl

    • A scaled up 2 megawatt system would be expected to weigh about 35 metric tons. It would transportable by air and highway.

      The 35-ton version is not meant for space bro. The 1400 W version with a stirling engine is meant for space.

      • @Scaryjello 12:34, November 18, 2017

        Looking at the original articles [1], I see that you are actually correct. The 2 MWe is intended for disaster relief and forward operating bases. But the blame must be on Brian Wang, for not writing this explicitly and describing even the 35-ton version as being designed as “designed for launch incidents”. Transportability does not by itself imply earth applications.


  2. So, “going nuclear” for 2 MW of electric power is a good idea? Why? There were gasoline engines developed in the WW2 period that made nearly 2 MW of shaft power, and they didn’t weigh 35 tons (dry weight of PW R-2800 was about a ton). That is not to mention that any base or camp probably makes enough trash to power a 6 MW boiler to make 2 MW of electric power. Sorry guys, a 2 MW nuclear reactor is never going to be worth the trouble (here on Earth). Diesel engines and gas turbines got that shit locked up.

    Hmmm… (0.004MW*15y*365d/y)/0.3T = 73 MW-d/T

    PWR accumulate that burnup in 2 days; BWR accumulate that burnup in 3 days, so yeah, there wouldn’t be any swelling because the fuel will still be new after 15 years. 1200 K or 1700 deg-F is a reasonable temperature; ceramic fuel pellet centerline temperatures are higher. Heat pipes are interesting; would like to see them used here on earth for decay heat removal; kinda lame for the main heat transfer mechanism though.

    clever and novel designs based upon well-established physics

    Hmmm. Nothing really works well until volume production and operational experience illuminate the weaknesses. More likely to keep it “on the shelf” (the box of paper, that is) and say that it works than to really refine a solution looking for a problem.

    • So you aren’t bright enough to think the 35 ton version has a space application? You think an R-2800 can be anything like quiet? You think it can work underwater?

      There are already generators on trailers. These people are not reinventing a wheel, but square.

      Pro tip: It’s helpful if your comments are both true AND relevant.

      • Perk, don’t question my brightness. Stop being such a fanboi. Get on board with practicality; it will give you an enlightened existance.

      • And somehow the opinion of a PE who designs reactor cores for a living doesn’t hold up to perk and Combi. I’m getting real bored on this site. Y’all are just a bunch of fanbois.

    • 1. Of the 35 tons most of the weight is radiation shielding. In space you would just need a shadow shield. On the moon you would just bury it.
      2. They are using LEU. Switching to HEU would lower weight.
      3. WWII aircraft engines did not run continuously for years. Apples and Oranges until you include the fuel and oxidizer for the years of operation of the WWII engine.
      4. It is a good approach, something that NASA keeps playing around with. Decades ago they had their 200kw nuclear suitcase, more recently a 40kw lunar power plant.

      • 1. Not talking about space reactors.
        2. You are making assumptions about the characteristics of a device not detailed here. Taking the enrichment from 7% to 19% does not scale a 4KW machine to a 6MW machine at a reduced weight. PWR makes average 18MW out of a 0.455 ton assembly at 5%. The 4KW machine is essentially zero power density compared.
        3. Ok, so the radial engine is a bad example; a common diesel is a better example. They can run for months and cheap enough to buy 3 keeping 1 in maintenance and 1 in standby.
        4. You think it is “a good approach” because you are a fanboi. It is not practical for terrestrial use. Less so for space.

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