ANS Nuclear Cafe Matinee: DUFF Space Nuclear Reactor Prototype

A joint Department of Energy and NASA team has demonstrated a simple, robust fission reactor prototype [note: see Comments for more accurate and complete description] intended for development for future space exploration missions. The DUFF (Demonstration Using Flattop Fissions) experiment represents the first demonstration in the United State—since 1965—of a space nuclear reactor system to produce electricity.

The uranium–powered reactor is the first use of a “heat pipe” to cool a small  nuclear reactor (measuring one foot!) and power a Stirling engine. The following short video from Los Alamos National Laboratory explains the hows and whys:

See this article from Los Alamos on the details of the DUFF experiment recently successfully conducted.  Also, see this CNN article for an excellent description.

Many future space missions will only be feasible with the use of reliable and safe nuclear energy, and this proof-of-concept is a steppingstone toward that future.


6 thoughts on “ANS Nuclear Cafe Matinee: DUFF Space Nuclear Reactor Prototype

  1. Denis Beller

    I really appreciate the ANS posting this exciting news for space nuclear power, I’m hoping it’s the first of many nuclear power and propulsion tests in Nevada.

    However, the description of this demonstration as a “fission reactor prototype” is a bit misleading and confusing. Flattop is one of four old, much used critical assemblies that were moved from the Criticality Experiments Facility (CEF) at LANL TA-18 to the Nevada National Security Site’s National Critical Experiments Research Center (NCERC) several years ago (at the time of the move it was NTS and CEF, both later renamed). These assemblies (others are Godiva 4, Comet, and Planet) are used for criticality benchmark experiments, cross section measurements, DOE/NNSA’s hands-on criticality safety training courses (I was a recent student), and a variety of other training and research projects. Flattop, which is a uranium-reflected highly enriched (233U, HEU, Pu, or other) sphere, is unique in that it can be operated super critical to produce an internal temperature of about 300 C (not quite what one would expect in a power reactor “prototype”). Flattop also has a hole through its center that permits insertion of experiments or other actinides, in this case a heat pipe that was built specifically for this test (I don’t believe it’s a space power prototype either, but someone from NASA or LANL might disagree). In addition, the purpose of the heat pipe is not to cool the reactor (LANL’s words, not this authors) although it does remove a tiny amount of the fission power, it is to transfer energy to the Sterling engine so it will produce electric power.

    Finally, the folks at NSTec, which operates the NNSS for NNSA, deserve some of the credit for this wonderful accomplishment. It might also be worth noting that several groups at LANL collaborated and that this was a really short and relatively low-cost project, reminiscent of the good old days.

    No, UNLV was not involved, but I sure wish we had been (we tried).


    PS: the first successful DUFF test was conducted on Sep 13 (about 10 weeks ago) and produced 24 We for 10 min.

  2. Bruce Behrhorst

    If memory serves me, Stirling engine power from HEU reactors for space based similar to old SNAP series. Stirling power transfer + reactor go back decades. The SNAP-10A produced max. 590 We. Ion engines to icy planet systems w/ payload + robo lander DUFF will need more than the tiny power output of 24We for 10 minutes.
    Didn’t NASA-DOE make noise about the NEP-JIMO mission back in 2004?
    As usual Gov’t pulled plug because it ran out of money and mission was top heavy with ‘pork contracts’ not to mention the thrust-to-weight ratio not too appealing for mission flight directors.

  3. Denis Beller

    @Bruce: your comment is exactly why I posted mine above. DUFF is not/was not a space power system, it was a low-budget technology demonstration using low-temperature nuclear heating from a small spherical assembly with a bare surface, which is why it produced just 24 We. The comparison to SNAP-10A is useless.

    In addition, SNAP-10A did not have heat pipes and Sterling engines, it used inefficient thermoelectric technology (590 We maximum out of 30,000 Wth), so again, there is simply no comparison between DUFF and SNAP.

    A space system would include optimized space nuclear power and heat transfer systems as well as multiple Sterling engines and generators, with 10 to 20 percent efficiency. All of the SNP and NTR development and testing of the 60s and 70s should make the transition from DUFF demo to launch-ready system straightforward, but not cheap. Fortunately, unless DOE has it there way, the massive facility for conducting the testing at the NNSS remains (it will cost about $40 M to demolish & dispose, or the same amount to refurbish for new missions).

  4. Bruce Behrhorst

    Fine, if you think DUFF is your cup of tea. Seeing is believing.
    My take it’s just another exercise in test-for-test sake. There are maybe 80 different scheme proposals I’ve read ranging the gamut from RTG-NEP-NTR. Only RTG variant type space nuclear technology has really ever flown for NASA.
    I seem to have interviewed LANL’s S.A.F.E system back in the day.
    In my personal opinion space nuclear anything is horribly politicized to the detriment of space commercial venture & exploration advancement.
    And this also applies to a U.S. nuclear industry who in general is restrained from innovation in (SMR) fission and fusion R&D funding.

  5. Denis Beller

    @Bruce: not sure exactly what “…if you think DUFF is your cup of tea” implies. I was simply clarifying the news piece, trying to keep the misinformation and confusion to a minimum. I’m not an advocate or opponent of this system, but I am an advocate of R&D and education for all things nuclear. The SAFE space reactor concept on which you interviewed Dave Poston is different from the upcoming (I hope) SAFE NTR test at the NNSS (Poston’s Safe Affordable Fission Engine vs Howe’s Subsurface Active Filtration of Exhaust).

  6. Bruce Behrhorst

    Of course, I’m also in favor & an advocate of R&D and education for all thinks nuclear. But I also know industry and Gov’t bureaucracy get in the way of funding commitments and completion. In this case the systems you just mentioned.
    In my opinion, it’s too cruel to ask national labs and the people they employ with the industry to test and build fissile or fertile fission system and not fly & deliver on surpassing technical and legal ‘show stoppers’ by not space flying (employ) a perfectly excellent system that has passed all required tests for SAFE.
    It is possible to fly more robust space nuclear systems when the agencies & industry are committed we need only see MSL Curiosity & its MMRTG to prove things nuclear can get employed in space.