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.

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 LFTR would likely be located at the 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

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3 thoughts on “LFTRs Are Worthless for Making Nuclear Weapons

  1. Robert Steinhaus

    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.
    http://en.wikipedia.org/wiki/Pokhran-II

    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″
    http://1.usa.gov/g5XVno

    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.

    Reply
    1. glerner Post author

      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)

      Reply

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