LFTRs Are Worthless for Making Nuclear Weapons

No nuclear weapon has Ever been made using U-233, because of inevitable U-232 contamination. [Correction: one tiny experimental bomb, see comments.] (Separating out U-232 is even more complex than U-235 enrichment or plutonium breeding.)

Thorium absorbs a neutron, then decays to Protactinium-233, which sends out bright gamma cascade, before it decays to Uranium-233 that would be used in the reactor. Pa-233 has a one month half life, so for about 3 months that fuel is gamma hot.

Gamma rays from Pa-233 and U-232 destroy electronics needed for any bomb, harm technicians, and are easily detected on land or by satellite, impossible to disguise.

“The uranium-233 produced from thorium-232 is necessarily accompanied by uranium-232,… [which] has a relatively short half-life of 73.6 years, burning itself out by producing decay products that include strong emitters of high-energy gamma radiation. The gamma emissions are easily detectable and highly destructive to ordnance components, circuitry and especially personnel. Uranium-232 is chemically identical to and essentially inseparable from uranium-233.” Hargraves, American Scientist Vol 98, July 2010

“Only a determined, well-funded effort on the scale of a national program could overcome the obstacles to illicit use of uranium-232/233 produced in a LFTR reactor. Such an effort would certainly find that it was less problematic to pursue the enrichment of natural uranium or the generation of plutonium. In a world where widespread adoption of LFTR technology undermines the entire, hugely expensive enterprise of uranium enrichment — the necessary first step on the way to plutonium production — bad actors could find their choices narrowing down to unusable uranium and unobtainable plutonium.” Hargraves, American Scientist Vol 98, July 2010

“In the context of proliferation resistance, … The local fuel processing of the breeder and burner configurations eliminates the possibility of diversion during transport. The fission-product-saturated fuel salt of the minimal fuel processing converter reactor is highly self-guarding during transportation. Further, the transport casks are massive because of the required amounts of shielding. In general, diversion of molten salt materials is difficult. The reactor operates as a sealed system with an integrated salt processing system that is technically difficult to modify once contaminated. The hot salt freezes at relatively high temperatures (450-500°C), so it requires heated removal systems. FS-MSRs operate with very low excess reactivity. Loss of a significant amount of fuel salt would change the core reactivity, which could be measured by a well-instrumented reactivity monitoring system. During operation (with the exception of deliberate fissile material removal for a breeder or addition for waste burner), the fissile materials always remain in the hot, radioactive salt. However, FS-MSRs, with integrated fuel separation, may be unsuitable for deployment in nonfuel-cycle states to minimize dispersal of separation technologies.” Fast Spectrum Molten Salt Reactor Options, Oak Ridge National Laboratory, July 2011

Less Uranium Shipped

Terrorists steal uranium, virtually always, during shipment.

With LWRs uranium is shipped several times after mining: for enriching, making into pellets and rods, delivery to the reactor, and long-term storage.

A 1GW LWR needs 35 tons of Uranium per year. Lifespan 30-50 years, 1050-1750 tons shipped.

With LFTRs, Uranium is only used to start the reaction (Uranium is produced within the reactor from Thorium). MSRs generally have online processing, any transuranic elements generated in the reactor get circulated back to the reactor core to be fissioned. A 1 GW LFTR would use 1/4 ton mined Uranium in 50 years (and about 50 tons of thorium).

Break even operation [make as much uranium as consume] only requires approximately 800 kg of thorium per GW(e) year added simply as ThF4. Start-up fissile requirements can be as low as 200 kg/GW(e) D. LeBlanc / Nuclear Engineering and Design 240 (2010) 1644-1656

(A waste-burning FS-MSR would likely be located at the LWR waste storage facility, no shipping uranium. A thorium-burning LFTR would require shipping thorium, which is barely radioactive, and is common world-wide.)

Exportable Technology

“The no-heavy-metal separation converter cycle FS-MSR reactor presents a distinctive capability for a highly proliferation-resistant resource-sustaining fast-spectrum reactor. The potential lack of fissile material separation technology within a converter cycle FS-MSR has the potential to enable a fast-spectrum reactor that is exportable to nonfuel-cycle states without requiring a fuel return. Because of the ability of a fast-spectrum reactor to tolerate the accumulation of significant amounts of fission products, the only fuel processing that appears necessary for many years of FS-MSR converter cycle operation is capture of the fission gases (possibly extracted via helium sparging) and mechanical filtering of the noble metal fission products particles as they accumulate in the fuel salt.” Fast Spectrum Molten Salt Reactor Options, Oak Ridge National Laboratory

Don’t waste resources pushing for greater protection for nuclear reactors as sources of nuclear weapons material. They are easy to protect (internet-enabled sensors of many types, surveillance, etc.) and have chemicals that are extremely difficult for terrorists to work with. Those resources would be better used detecting the easy methods of making nuclear weapons materials!

Remember the way we made plutonium for the first bomb… the first production reactor that made plutonium-239 was the X-10 Graphite Reactor, the main one the Hanford B Reactor, both specialized for weapons-grade plutonium production. A “graphite pile reactor” is very simple design, un-enriched uranium and graphite — that’s what we should actually be watching for, in some cave near a uranium deposit. They’ll die building it, but that might be okay for them.

Wikipedia Plutonium-239 says “reactor-bred plutonium will invariably contain a certain amount of Pu-240 due to the tendency of Pu-239 to absorb an additional neutron during production. Pu-240 has a high rate of spontaneous fission events (415,000 fission/s-kg), making it an undesirable contaminant. As a result, plutonium containing a significant fraction of Pu-240 is not well-suited to use in nuclear weapons; it emits neutron radiation, making handling more difficult, and its presence can lead to a “fizzle” in which a small explosion occurs, destroying the weapon but not causing fission of a significant fraction of the fuel… Moreover, Pu-239 and Pu-240 cannot be chemically distinguished, so expensive and difficult isotope separation would be necessary to separate them. Weapons-grade plutonium is defined as containing no more than 7% Pu-240; this is achieved by only exposing U-238 to neutron sources for short periods of time to minimize the Pu-240 produced.” [That “fizzle” is normally called “pre-detonation”, goes off by itself, oops you just blew up your building. Separating U-235 from U-238 (3 weights apart) is difficult; Pu-239 from Pu240 (1 weight apart) is much harder.]

Both LWR and MSR are much more difficult sources of material for making a nuclear bomb or dirty bomb than just starting with natural (unenriched) uranium.

7 thoughts on “LFTRs Are Worthless for Making Nuclear Weapons”

  1. We, as Thorium advocates, should try to put out the most accurate information we know concerning U-233 and its potential usefulness for making weapons.

    I would like to offer some additional evidence that bears on the overall premise of this page that Thorium/U-233 “is useless for weapons”.

    You may or may not be aware that in 1998 India fielded a multiple device near simultaneous nuclear test called Pokhran-II. One device that was tested called Shakti-V which was a successful but very tiny pure U-233 explosive device with a yield of only 0.2 kilotons.

    When we consider the weaponizability of U-233 and whether this material is “useless for weapons”, it is well to consider the opinion of actual weapons designers and consider what exits in the unclassified domain to indicate their professional opinion of the usefulness of U-233.

    One report that is available in the literature is the following
    W.K. Woods, Report DUN-677 “LLNL interest in U-233″

    In this report prepared by W. K. Woods of Hanford Site regarding a meeting that he held with the most Senior LLNL weapons designers at Livermore.

    1. Good point. Pure U-233 could make a bomb. It would have to be so pure as to not have enough U-232, which emits gamma rays, to destroy the electronics of the bomb, or kill the people making the bomb.

      But LFTRs can’t make pure U-233.

      Every scientific report I’ve seen says that in a LFTR, “pure U-233″ can not be produced. A LFTR would lack the equipment to produce U-233 without any U-232. As the equipment to produce pure U-233 would be expensive, and eliminate a desired benefit (“can’t make bombs from a LFTR”), no LFTR designer would include it.

      In a single-fluid MSR, separating protactinium, is important, to prevent much of it absorbing an additional neutron and not becoming uranium, and people get worried that means people could make a bomb. But that separation would not be done to the strict standards needed to produce essentially zero gamma-ray producing U-232 (just good enough to produce enough uranium to keep the reactor running, and a little U-232 works almost as well for that, just has to absorb another neutron to become fissile U-233). The Molten Salt Reactor Experiment produced U-232.

      In a 2-fluid MSR, such as a LFTR, there is no need to separate protactinium before it decays to U-233. The blanket salt, containing thorium, is already outside the strong neutron flux of the reactor core, so most of the protactinium would decay to uranium.

      (Terrorists wouldn’t make a LFTR, plus protactinium-extraction equipment, to make a bomb, there are much simpler ways to get bomb-quality U or Pu, such as the X-10 Graphite Reactor)

  2. Although I am a proponent of LFTR, I have a question. I understand the argument about LFTR U-233 being impractical for military purposes. Its U-232 impurity emission of hazardous gamma rays precludes bombs based on it being safely manufactured and handled, and U-232 cannot be easily seperated. However, I have not read why the U-233 as part of the LFTR cycle should be safer. Given the quantity and strength of the gamma rays emitted from a LFTR, how much shielding is needed for such reactors? What would it cost? In my reading, I have not yet found a thorough discussion of this issue. Small LFTRs in homes or even autos are predicted by some enthusiasts – sounds impractical if gamma-ray shielding should be a problem. Could you point me to an appropriate source? Thanks!

    1. Few inches of lead stops gamma radiation, more thickness needed for less dense material. We won’t have LFTR-powered cars; we can have MSR provide heat to make gasoline from water + CO2.

  3. I would like to point out that while it doesn’t produce any fissile materials for a nuclear *bomb*, it can still be used to make materials for a ‘dirty bomb’, broadcasting radioactive dust all over an area with conventional explosives.

    As a military weapon, a dirty bomb is ineffective. As a weapon of terror, however, it is quite effective at causing a panic, mostly because people don’t seem to understand how radiation works.

    So even though it can’t be used to make the correct isotopes necessary to produce a nuclear explosive device, it is still not something you want floating around third world nations with fractious and dangerous fringe elements.

    Which is a shame, because they’re the ones who need a good supply of power the most, so they can get access to the internet and decent education, which will ultimately undercut said fractious and dangerous fringe elements by eliminating their ability to recruit from a largely ignorant population. Sadly those fringe elements are too ignorant to realize they can’t make nuclear bombs from an FS-MSR, and will break it in the attempt.

    1. The fuel is low radioactivity. The fission products are all higher radioactivity (said another way, the fission products have both shorter half life and higher energy radiation).

      The gasses would always be removed and stored (they simply bubble out of the molten salt), so the amount on-site could be very low (if moved off-site), but even if stored on-site gasses are harder to work with for a dirty-bomb. The dirty-bomb now needs to be not just made while radioactive, but also made “air-tight” (krypton gas wouldn’t leak out).

      There’s reasons terrorists haven’t exploded dirty bombs, though the “cause terror” factor is clearly high. Maybe the security around LWR fuel rods has been adequate? Important we check, and I’m hearing more about car bombs than spent-nuclear-fuel bombs.

      MSRs can be constructed completely underground, inside multiple layers of “keep out” cement, with multiple types of electronic surveillance. All fission product storage containers can have electronic tracking.

      Idiots stole a radioactive medical device in Mexico in 2013, not knowing what it was, probably for the scrap metal. They were located even before the radiation sickness stopped them. If you don’t know what you’re doing handling highly radioactive material, you’ll probably not be able to make your bomb.

      If you do know what you’re doing handling radioactive material, there are plenty of chemical hazardous materials to make a bomb with that are easier to handle.

      What happens to a country that drops either a nuclear dirty-bomb or a fission-bomb on a city? We started wars with Iraq and Afghanistan on the pretext (known then and now to be a lie) of weapons of mass destruction. Wouldn’t we and other countries do worse to anyone stupid enough to actually explode a nuclear dirty bomb? Even the most zealous groups wouldn’t bring that destruction on their own people. The Cold War somehow did not end in World War III.

      Let’s get rid of the hysteria, so we can put effective security around the actual hazards. For example, the anti-nuclear people forced many plant changes at Fukushima but largely ignored the sea wall being much too low — now that’s scary. USA LWR plants not passing basic fire safety codes (like for any apartment building or office building) is scary. Just as scary as coal plants not passing basic safety codes.

      Are all the oil trains exploding from terrorists? Or corporate negligence? Oil pipeline leaks? Coal ash ponds leaking, or sliding into the river? Pesticide plants exploding? Natural gas pipelines exploding? Compared to these, MSRs look quite safe to me.

      And, let’s make sure every MSR built would be even safer than LWR, under normal conditions and in natural disasters and in terrorist attacks. MSR is inherently safe in areas where LWR is engineered safe, and we can install security and monitoring.

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