The most secure place to store Plutonium is inside an operating fission reactor 1

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  1. I don’t think I have seen a post here that I agree with more! The demonization of Pu is utterly insane and the idea that using it in reactors somehow is less safe from a proliferation stand-point is doubly so. We already incidentally use plutonium to make electricity in conventional reactors due to natural breeding of Pu out of the U-238 present in the fuel, so we might as well go all the way and intentionally use it! Let’s turn those swords into plows!

    As an aside, due to the larger cross section (750 barns vs the 585 barns of U-235) and the higher neutron production rate (about 1.17X more than U-235) opens up many options for smaller reactors as well. Plutonium-239 has a bare sphere critical mass ~1/5th that of U-235 so there may be interesting options for even smaller reactor cores or less over-all fissile inventory. The Pu/Th fuel cycle is also an interesting option that could be good for PHWRs or MSRs.

  2. I agree that the idea may be a good one domestically as a variant of used-fuel electro-processing, extended to decommissioned nuclear warheads. The main advantages are that it would give us a way to draw down Pu239 inventories and sharply limit the need for Uranium mining. Making it work domestically would require deep depoliticization of US energy policy, which in turn would require intensive reform of STEM education to feature nuclear physics basics (e.g., fission chain reactions and exponential decay of highly radioactive fission products) and debunking of baseless Linear-No-Threshold (LNT) arguments, but all of that seems doable and important for other reasons. However, I suspect that exporting SMR reactors preloaded with Pu239 based fuel could remain a nonstarter for the foreseeable future.

  3. The FFTF is not ashamed of its successful MOX fuel. Combining two expensive waste products into limitlous energy. Great idea.

  4. It seems like they’ve been using Plutonium for a long time as fuel with the MOX fuel. It seems logical that if you want to get rid of the stuff that burning it in a reactor is one of the best waste to energy projects around. This looks like an opportunity to use the old Feynman quote.

    “For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled.” – Richard Feynman

    The quote wasn’t a perfect fit, but close enough. Thanks for the article.

  5. All:
    Thanks Rod for the article and what turns out to be an ice-breaking discussion topic, and thanks everyone else for their comments. A few moments’ thought tells me that you are all right about sharing Pu239 openly with countries that are already using MOX and observing weapons test ban treaties. Hostile and rogue nations, not so much.

    About the role of STEM education. Personally I believe that it should be possible to both strongly support nuclear fission energy technology and strongly oppose that of nuclear weapons, even though both are based on the same science, specifically the physics of controlled nuclear fission chain reactions. The science is what it is, but the technologies are what you get based on your project objectives, what you do with control mechanisms, and the quality of work you do with the assistance and consent of your community. I think it is essential to keep in mind that science and technology are not one and the same, in order to keep discussions of energy in mainstream media open and science-based rather than letting them devolve into the emotional hot mess that they are today.

  6. Simply eye-opening…need a second and third read. I wouldn’t have passed the, “What you know about Pu-239 test.”
    Thank You.

  7. Yes, PU please. PU and Thorium have great possibilities!!!

    For years I have not been able to understand the strong connection made by the anti-proliferation crowd between PU in a reactor and PU in a weapon. They are so different that they CANNOT be used in the same context. Ultra pure PU needed for weapons cannot be used in a reactor – it is too reactive and cannot be controlled in a reasonable way for power production. At the same time the blended down percentages used for power production CANNOT be used in a weapon. It would fizzle and make a mess but not an explosion. If I am wrong about this all you all can correct me.

    The worst was going after pacemakers. Digging up bodies in cemeteries to recover the PU in a pacemaker is the ultimate confusion of categories. Seriously? You really think someone will use that pattern to create a weapon? To slowly gather the pacemakers of long dead people, gain a few grams of very impure PU, wash very well after the stinking job. Go on to the next one. Take several years to gather enough kg to have enough to stick into a high quality centrifuge and spend months trying to purify it. What a stupid lark. I cannot believe the actual target for this inanity was keeping weapons out of the hands of other nations or terrorists.

    I listened to a long discussion of anti-proliferation by one of the key figures on a podcast. The man promoted light water reactors to North Korea “knowing” that they are safe from being able to produce weapons. The USA provided these to NK. In the mean time, NK simply used a different method to make its weapons. It shows the utter futility in all the anti-proliferation efforts. With all due respect to the highly intelligent and skilled commenters here, Nuclear Power and Nuclear Physics are within the understanding of most fairly educated individuals. Making a weapon is always the decision of a nation state. It takes the physics, the support systems to maintain them, the delivery systems to put them in the right place. It is barely conceivable that a highly organized terrorist organization might make one weapon from PU and find a way to deliver it. But why bother? U234 is easier by far and very reliable. That is a terrible thought but not nuclear war. Terrorists are VERY unlikely to use PU. The process of creating pure PU is so complex it took NK digging caverns inside mountains to hide it. In the open, it can be detected quickly on the basis of what has been placed in a power reactor. At the same time the process of creating impure PU fuel is so simple that nearly all reactors do it!

    1. David

      Your sentiments are spot on, but I’d like to offer a few corrections on technical details.

      1. It’s technically possible to design and build power producing reactors that use relatively pure fissile Pu as the fuel source. But even in those reactors, the Pu fuel material is surrounded by corrosion resistant cladding or layers of something like SiC and/or graphite. The structures and poison materials inside a reactor prevent the creation of an explosive chain reaction. Once operated for any significant period of time in a reactor, the material becomes extremely difficult to use in a weapon, even if the cladding is removed and separated.

      2. Pacemakers were fueled with Pu-238, an isotope of plutonium that is not fissile. As a general rule of physics, fissile isotopes need an odd atomic number. Pu-238 decays with an energetic alpha particle and generated relatively intense heat with an 87 year half life. It’s an incredible tool for applications that need modest, long lived power.

      3. It might have been a typo in your comment, but the naturally occurring fissile isotope of Uranium are U-235.That is what can be concentrated using centrifuges or other enrichment technologies.

      Finally, though the US and South Korea had an agreement with N. Korea to supply light water reactors, they never came close to completing the reactors. Lots of money was spent and (and earned), but no power was ever supplied.

      1. Thanks for the corrections Rod. Yes, U234 was a typo. Yes, the PU in the pacemakers was U238. Which made the program doubly insane! I did not know that fairly pure PU would work in a power reactor. I guess that’s the same as pure U.

        I was amazed listening to the story of what happened in N. Korea. Here was a man, convinced to this day that he was protecting the world by opposing proliferation. He was deeply deceived by the difference between the possible and the likely.

  8. Excellent piece, Rod.

    A few comments:

    1. Catchy title, though technically a bit questionable; there’s no way a reactor could be safer than, say WIPP or Holtec’s Hi Store UMAX.
    2. Point 1 is a bit pedantic, perhaps: has anyone ever been injured or killed by plutonium in reactors? Chernobyl was the only accident that released significant quantities of plutonium to warrant health concerns, but it appears there is no evidence for any injury or deaths from the plutonium even there. Plutonium oxide is not mobile, it’s basically a rock.
    3. Plutonium is an ideal startup fuel for thorium reactors. Much more reactive than HALEU, and unlike HALEU, has a large stockpile inventory for use. And unlike uranium fueled reactors, it makes almost no new plutonium in the process. It is an ideal “destroyer” of plutonium. Not that I am advocating for campaigns against entire elements, mind you – that is for the chicken littles that call themselves environmentalists or anti-proliferationists, who by the way, seem to know very little about environmental science and seem to proliferate very little common sense or perspective on matters of nuclear energy.

    1. @Cyril R

      The title says “most secure” place, not the safest place.

      It is a statement about the virtual impossibility of obtaining material from an operating reactor. Not only is material inside a reactor protected by guards and layers of locked/welded steel & concrete, but it is also protected by an intense field of radiation.

      WIPP and Hi Store UMAX are certainly secure, but I’d say they aren’t quite as well protected as the inside of an operating reactor.

  9. Use whatever extra Pu is on the shelf for whatever special applications of HALEU it could be substituted easily, assuming that satisfactory TRISO, oxide, carbide analogs may be directly substituted in fuel products…. oxides of all grades of Pu have been used in conventional fuel rods for LWR, SFR.

    but suggesting we should have a plutonium economy seems a lot like insisting we should FORCE a market… What is the problem anyhow? Is it climate? Is it poverty? Is it politics? What problem is the inventory of Pu causing?

    The uranium supply is not choked. A Pu market would be forced; sort of like the federal/state EV mandates.
    Pragmatically speaking, what Pu is safely stored inside spent fuel rods, safely stored in pools and casks, should remain where it is until the day it is actually needed, which may be never considering the amount of uranium available.

    If the uranium supply does ever become choked, the thorium/uranium cycle is better suited for stretching the fuel supply for the big thermal spectrum power reactors that currently deliver an astounding 17Mlb/hr of 65 bar steam 700 days on end (many windmill equivalents).

    Why is the thorium/uranium cycle better suited for the big thermal spectrum power reactors? Because thorium/uranium MOX supports a significantly higher conversion ratio (fissile creation rate/fissile destruction rate) in such reactors compared to the uranium/plutonium cycle. Additionally, the fissile species in the thorium/uranium cycle may be separated using the condensation of 233UF6 upon conversion of the irradiated fuel to the fully fluoridated state (i.e. ThF4, UF6, FP(F)x), which seems a lot simpler than the aqueous PUREX/UREX methods used to recycle uranium/plutonium – there is a lot of infrastructure for handling fluorides of uranium and high kilotons of UF6 on hand in north America alone.

    Sure, Pu belongs in reactors. It’s not very high on anybody’s list of concerns – except those government employees tasked with it and other special interest agitators.

    1. “What problem is the inventory of Pu causing?”
      The current ROD (pardon the pun) sends excess Pu to geologic storage in glass. No consideration for MOX or metal fission energy production.
      “Supplemental EIS, DOE/NNSA analyzed the potential environmental impacts of alternatives for the disposition of 13.1 metric tons (MT) (14.4 tons) of surplus plutonium for which a disposition path is not assigned… Preferred Alternative is to prepare 6 MT of surplus non-pit plutonium for disposal at the Waste Isolation Pilot Plant (WIPP) near Carlsbad, New Mexico, a geologic repository for disposal of transuranic (TRU) waste generated by atomic energy defense activities.

      1. 13 tons of fissile material is like 7 LWR reloads worth of fissile material, or a little bit more fissile material than Illinois uses in a year.

        I don’t really see a large scale crisis glassing 13 tons of fissile material, although I believe it should be kept on the shelf in oxide, waiting for the day somebody comes up with a cool use for it.

  10. Excellent post.

    I would add that a combination of thorium and plutonium is pretty useless as a weapon.
    In ThorCon’s case, we found that even if you pulled the fuel out at the ideal point when the plutonium was 94% Pu-239, as long as the fuel contained 10 times as much thorium as Pu-239, it would not go critical. no matter how much Pu you had. Thorium soaks up neutrons. To make a weapon from this stuff , you would need a Thorex plant which is even more difficult than a Purex plant.

    The tragedy is with no HALEU, designs like ThorCon cannot spike the fuel with thorium and we lose this safeguard.

    1. It is hard to argue that fissile material of any mixture or purity is “pretty useless as a weapon”. Truth or not.

      Now, a significant quantity of 238U in thorium/uranium fuel will certainly hinder bomb making, considering the fissile vector in the discharged fuel would be dominated by 238U.

      Plutonium appears to have a hexavalent state (per Wiki), which means you could separate Pu/U from irradiated fuel mixture containing thorium/uranium/plutonium upon conversion to the fully fluoridated state (Th4, PuF6, UF6). Seems to me easy to get the Pu out of the Th.

      1. This will be news to the people that worked on this at the national labs in the 1950’s and 1960’s. Purex is tough, but Thorex was tougher. Like Purex, Thorex was a solvent extraction process, but due to teh insolubility of thorium required hydrogen fluoride, and long dissolution times. Efforts were abandoned int he 70’s. AFAIK, the only people working on this are the Indians but they are not trying to produce thorium free plutonium.

        AFAIK, the fluoride volatility route has never been tried. Guessing it’s because it’s difficult to get Pu all the way up to PuF6, and the compound is very unstable,
        producing HF when it decomposes.

        There are far easier ways to make a bomb than to try and separate plutonium from a whole bunch of thorium. It’s a lot easier to separate U from Pu by fluoride volatility
        precisely because making UF6 is much easier that PuF6.

        1. Well, the comment was based on a wiki article stating that PuF6 was similar to UF6. I’m not going to die on that hill. The fact remains that uranium (at least) may be separated from thorium by the physical process of condensation, upon full fluoridation. Regarding chemical stability, hypostoichiometric (under-fluoridated, like UF4) salts to be used in MSRs are demonstrably less stable than oxide, as demonstrated by the problems storing the MSRE fuel at ORNL (F2 and UF6 in the gas space of canisters).

          The proliferation argument only shuts down a concept if it involves process handling of the irradiated material, which is a basic feature of the thermal MSRs.

          The fast MSR guys think they can get away from online handling of the fuel so I guess they’ll just linearly build a source term for 20, 40, 60 years /s /s /s.

          I guess it is all academic because whatever the inventory of Pu, it’s not going to power the US fleet for 20 years like Megatons to Megawatts.

  11. Lightbridge alloy of WG plutonium-in-zirconium would denature quicker than any plutonium-in-uranium fuel. In the neutron budget of fission+absorption+escape, it is the plutonium itself that absorbs a neutron instead of the uranium. Consequently the Pu240 fraction increases quickly, removing the fuel from weapon grade status.

    The fission products and the absorption product (Pu240) are produced in proportion to their neutron cross sections of 747 b and 272 b. If the burn continues until (Lightbridge’s) 21% burn up, the ratio of Pu240 to the remaining Pu239 will be 0.107, that is, 10.7%, so the plutonium is no longer weapons grade.

    -> The plutonium becomes denatured in a single pass through the reactor. No reprocessing necessary.


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