New Metallic Nuclear Fuel Can Burn 21% of Uranium or Plutonium

Lightbridge plutonium disposition fuel variant consumes 5.5 times more plutonium per fuel rod than mixed-oxide (MOX) fuel. Lightbridge’s proprietary next-generation nuclear fuel technology features metallic fuel rods with a helical multi-lobe design that can be used to fuel small modular reactors as well as existing light water reactors and pressurised heavy water reactors. The high burnup of metallic fuel makes it particularly useful for consuming plutonium and reducing the proliferation risk from any residual plutonium: according to a 2018 study published in the peer-reviewed journal Nuclear Engineering and Design, any residual plutonium in the used fuel is “useless” for weapons purposes

Nuclear Technology Journal -‘Improved Disposition of Surplus Weapons-Grade Plutonium Using a Metallic Pu-Zr Fuel Design’ co-authored by Braden Goddard, of the Department of Mechanical and Nuclear Engineering at Virginia Commonwealth University, and Aaron Totemeier, senior nuclear fuel consultant to Lightbridge.

Lightbridge Corporation has several thermal reactor fuel designs that offer very high burnups, in the range of 21 at. % or approximately 190 900 MWd/tonne of heavy metal, which make them well suited for consuming excess weapons-grade plutonium. MCNP6.2 computer simulations were performed to quantify the mass of plutonium consumed in a Lightbridge-designed fuel rod compared to traditional mixed-oxide (MOX) fuel, as well as the attractiveness of the plutonium in the used fuel for weapons purposes. The results of these simulations show that the Lightbridge plutonium disposition fuel variant consumes approximately 5.5 times more plutonium per fuel rod than MOX fuel and that the material attractiveness of the Lightbridge-used plutonium is noticeably less than that of MOX fuel.

Burnup is a way to measure how much uranium is burned in the reactor. It is the amount of energy produced by the uranium. Burnup is expressed in gigawatt-days per metric ton of uranium (GWd/MTU). Average burnup, around 35 GWd/MTU two decades ago, is over 45 GWd/MTU today. Utilities now are able to get more power out of their fuel before replacing it. This means they can operate longer between refueling outages. It also means they use less fuel.

190 GWd/tonne is over four times the average fuel burnup.

11 thoughts on “New Metallic Nuclear Fuel Can Burn 21% of Uranium or Plutonium”

  1. Zr fuel has a lot more hydrogen generation potential in a SA. Wouldn’t that be problematic re containment pressure?

    • The metallic fuel doesn’t have temperature gradients like we see in oxide pellets w/zirc cladding so stored energy is lower resulting in lower peak temperature prior to LOCA reflood.

      If ECCS doesn’t show up, there is a lot more metal to burn with Lightbridge. Good point.

      • Exactly. Better for accidents with cooling, worse for accidents with no or delayed injection. Since regulators typically require containment analyzed for 100% Zr water reaction, wouldn’t that make Lightbridge fuel basically unlicensable for just about all existing reactors? Compact containments like NuScale would be especially troublesome.

  2. @combinatorics

    Haven’t seen an analysis of a fuel cycle using HALEU that shows a benefit mostly because the only commercial unit in operation using HALEU is the HTRPM. At some point, China might actually report on the economics. I think the PBMRs are pretty silly for a number of reasons.

    We throw away 9 tons of depleted uranium to produce 1 ton of 5% enriched. That would be close to 40 tons of depleted uranium to produce 1 ton of 20% enriched. I stopped short of getting a PhD in this, but I’m pretty sure that is very wasteful. I probably wouldn’t fit in at the DOE where they are upbeat about such things.

  3. Abstract of the paper says they’re analyzing to 190GWD/T fuel rod burnup which is 4 times the average discharge of my station (49GWD/T) using oxide fuel in clad tubes licensed to 62GWD/T. So there is 400% of the 550% improvement; the the remaining is likely just a favorable set of assumptions or could be related to reduced moderation (harder spectrum) if that is the case.

    What I know about LightBridge:
    1. IPO November 2000 @ $2250/share, been $5/share. Lost 98% of market value by 2016.
    2. Semi-annual press release announcing joint venture or MOU or test program. Lightbridge had to pay $4M to Framatome to terminate the ENFISSION joint venture in 2021 (outstanding invoices).
    3. Proven fuel style with Russian Ice Breaker pedigree. The fuel works, but it needs 13% enrichment to load the same spatial density of 235U or 239PU to be equivalent to the heavier 5% enriched oxide fuel element. Currently the CFR doesn’t allow commercial operations to use greater than 5% enriched although that is likely to change soon to take advantage of higher burnups possible, with neutron penalty, from ATF cladding (FeCrAl or chrome sputtered cladding).

    • I just realized that the 190GWD/T divided by 13/5 (enrichment ratio between LB/oxide) is equivalent to 73 GWD/T as far as neutron fluence. Normal BWR fuel rods are licensed to a peak rod segment burnup of 72 GWD/T with current cladding. So, LB is suggesting they can take the whole assembly to 73GWD/T, which is 13/5*190GWD/T. Ok, I buy that.

      Still, there is no lead test rod or assembly anywhere on the planet in a commercial LWR. There are currently many test assemblies with different cladding and pellet and fuel compositions all over the world including USA, but no such program in a COMMERCIAL reactor for LB.

        • So actually, this is a fine way to use weapons material. Judging by how the SRS MOX plant debacle went, don’t see how it will happen in the USA….

          It’s actually the original idea: metallic fuel rods with bonded zirc on the waterside. Just like every NAVY reactor since SW1. There is a cute self-supporting aspect to the helix useful in other ways too.

          Imagine 23 years they’ve been trying to introduce this product that was used in ice breakers decades ago. They keep insisting that the lower uranium (or plutonium) density (needing to alloy the uranium with zirc) is a benefit even though it requires effective enrichment of 13% to carry the energy of a 5% enriched oxide assembly. In this case, the benefit is some construct of burning more plutonium upon adopting the fuel cycle modeled. In the case of plutonium in excess of wartime needs, maybe this is fine, until you burn through that excess – then you find yourself in a plutonium economy, which is fine, but requires breeders to feed the lighbridge burners. Now we’re in fantasy land.

          • Yes Plutonium economy is fantasyland. However they want to hop on the HALEU train so maybe when excess bomb Plutonium is gone they would switch to HALEU train track.

            What are your thoughts on their projected economic savings? Lets be honest that is what really matters when it comes to adopting their fuel.

      • What’s the percentage of U235 left in the oxide fuel after it’s taken out of the reactor ? Any difference between BWR and PWR ? Presumably the LB fuel would get more of a bonus from burning generated plutonium, since it’s in the reactor longer, even though there’s much less U238 to transmute.

        • You can use avogadro’s number and 190MeV/fission with an average atomic number of 237 to calculate 10GWD/T per 1% atoms fissioned. Average discharge burnup at a big PWR is about 49GWD/T, corresponding to ~5% atom burnup for an assembly initially enriched to 4.5% 235U. There are ‘enrichment cutback zone’ top/bottom 6-inch of our assemblies and we tend to split a load of 80 feed assemblies with half at 4.4% and half at 4.8% for a core average of about 4.5% considering the ‘cutback’ blanket.

          So, there might be 0.5% 235U left in the assemblies at discharge, another 0.8% in plutonium and STILL you split 5% of the heavy atoms.

          BWR on 24 month cycle might average 45 GWD/T. The large batch loaded to go 23 months might negate some of the better conversion ratio of BWR (voided, faster neutrons, make more Pu per textbook).

          However this fuel cycle study worked out with lightbridge, you can be sure they picked their assumptions to amplify whatever point they wanted to make. It’s likely all a wash. Nobody’s licence currently allows enrichment over 5%, and nobody uses MOX in North America.

          LB is unfortunately a nonstarter for many reasons. Solution looking for a problem. It’s navy fuel: expensive, yet could be ramped quickly without damage in load following operation.

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