I don't understand how the dump tank contributes to proliferation resistance. Dump U-238 into the fuel salt? Dump the fuel salt into a bed containing U-238?
Here's the text of an email I sent to the authors of the CISSM paper mentioned at the beginning of the thread. I hoping to get advocates of LFTR among the nonproliferation specialists. I had a long train ride back from DC, so I wrote this. I hope I didn't make too many errors.
Center for International and Security Studies at MarylandRe: Can Future Nuclear Power Be Made Proliferation Resistant?
I am interested in the world's energy, climate, and pollution future. Consequentially I have had to learn more about nuclear proliferation than I anticipated. I read your helpful paper at http://www.cissm.umd.edu/papers/display.php?id=353
. I have some comments that may be useful to you if you publish a follow-on document.Liquid Fluoride Thorium Reactor (LFTR)
I have become convinced that the liquid fluoride thorium reactor (a molten salt reactor) holds promise for inexpensive, nonpolluting, low waste nuclear power. My comments are mainly from the point of view of the potential of the LFTR.Atmospheric CO2 pollution
The LFTR holds the potential for producing electric power cheaper than from coal. Such power can undercut the economics of coal-fired power production, not just in the OECD countries, but in the developing nations such as India and China. Carbon taxes and/or cap-and-trade credits will not stop CO2 emissions. The United States did not sign Kyoto. Europe has spent $50 billion in such carbon credits, many of which flowed to the coffers of the worst polluters. CO2 emissions have risen in Europe. China and India will certainly never agree to such taxes that would withstrain their economic growth towards achieving an OECD lifestyle.
Power cheaper than from coal can overcome this problem, while creating a rising economic tide for all nations.Aim High
An introduction to the benefits and technologies of LFTR can be viewed starting at http://rethinkingnuclearpower.googlepages.com/aimhigh
Thorium has an availability advantage of 3:1 over uranium, and 100% would be used up in the LFTR, vs 0.7% in a standard LWR with a once-through fuel cycle. I do admit that uranium power would not be much more expensive than now even if ore depletion makes us resort to adsorbing uranium from seawater.LFTR fuel supply
In your Table 4.1 for a 1 GWe reactor the Thorium MSR initial core requirement of 17.5MT 20 % LEU seems excessive. Compared this to about 5MT in the Energy From Thorium at posts in http://energyfromthorium.com/forum
. Also, the LFTR can be started with spent LWR fuel instead of LEU or HEU.
In the table, Ongoing U(nat) requirements should be zero, not 50 MT/yr. The reactor would require about 1 T/yr of thorium. No enrichment SWUs would be required.
Total discharge of spent fuel will be the fission products, only, or about 1 T/yr, not 5-9 T. Total discharge of fissile material is not 25 kg/yr as stated in the table, but perhaps 30 g/yr. This amount is a subject of debate and research on the forum, where some engineers say "trace" or "virtually zero" or "none". TRUs are all consumed in the LFTR, except some TRUs leak into the fission product waste stream, depending on the chemical process to separate the FPs from the fuel salt. Eventually the tradeoff will be chemical processing cost vs tolerable fissile waste.
The similar table on page 36 is sized for a reactor half that size. You labeled it 500 GWe, but I think you mean 500 MWe.
A strong advantage of the LFTR will be the lack of need (or excuse) for states to build centrifuge enrichment plants.Pebble bed reactor
I have been an advocate of the pebble bed reactor, too. It has many of the same advantages of modular construction, intrinsic safety, high temperature and conversion efficiency, and on-line refueling -- as does the LFTR. One advantage of the PBR is that the waste fuel is encapsulated in layers of pyrolytic carbon and silicon carbide that virtually prevent reprocessing. It is also an advantage in that the fuel form is ready for direct geological storage. Many people are fearful of geological storage of such waste.
Perhaps the PBR could be a power generator of choice in the non-weapons states. I do not agree with your idea of a technology democracy where all state have equal rights to all nuclear technologies. I would hope the NPT to continue for another 50 years, or more. Most of the world population is in the weapons states (also the CO2 producing states) and could be first served by LFTRs, until a level of comfort with nonproliferation features of the LFTR is achieved and they could be exported worldwide.Guaranteed fuel supply
If uranium-powered reactors become the power source of choice, some international, strong, guarantees of nuclear fuel supply will be essential to prevent non-weapons states from resorting to building uranium enrichment factories. This is one of the goals of GNEP, to which about a dozen nations have subscribed. Your paper says the GNEP is "shaky".
If, instead, LFTR power plants are widespread, there is no need for such a guaranteed fuel supply. Thorium is widely available, with many alternative sources of supply and no need to control it.Other proliferation paths
Nowhere in this paper do you mention the CANDU or heavy-water technology, which allows countries like India to manufacture weapons-quality plutonium without access to enrichment. I believe the Russia RBMK reactors, like Chernobyl, also can do this, once started up.Latent proliferation
One way to prevent the spread of "latent proliferation" is not to incentivize development of nuclear engineering skills in every nation. If the US, or other technically advanced states, could export LFTR (or PBR) modules at competitive costs, with internationally guaranteed fuel supplies, there would be no need for universal, independent, national cadres of nuclear experts.
I think terrorism by theft of HEU from research reactors is being addressed, worldwide by converting them to operate on LEU.LFTR nonproliferation measures
The LFTR does convert Th-232 to U-233. A 1GWe LFTR might have 1 T of U-233 dissolved in the molten salt. An LFTR captured by a technically advanced non-weapons state might, conceivably, be modified to extract the U-233 to make many nuclear weapons. Several nonproliferation techniques can be designed into the LFTR to prevent this.
(1) The designs and controls of the LFTR can ensure a breeding ratio of 1.0, not higher. With no surplus, any removal of U-233 would shut down the LFTR, revealing a theft.
(2) The fuel salt containing U-233 can be diluted with U-238, so that HEU U-233 can not be extracted by chemical processes, only expensive enrichment technologies such as diffusion, centrifuge, or laser isotope selection.
(3) The fuel salt will certainly contain amounts of U-232, whose decay chain includes isotopes that emit high-energy gamma radiation hazardous to weapons builders, should the uranium be extracted.
(4) The LFTR could be designed for automatic injection of U-238 to dilute (denature) the U-233 to weapons-useless levels on indications of tampering, or by remote control from an international body.
(5) U-233 itself is more radioactive and hazardous to work with than U-235.
(6) U-233 removed from a LFTR will be contaminated with fission products hazardous to weapons builders.
(7) The LFTRs can be designed to operate without personnel, lowering operating costs, risks of experimentation, errors in operator training or execution, and exclusion of weapons-fabrication-intent technicians, engineers, or scientists from the LFTR. This operatorless mode also reduces the chance for "latent proliferation".
(8) Combinations of the above techniques can be employed. No single nonproliferation protection need be iron clad. The combination needs only to be sufficiently protective that creating a weapon from a LFTR would be an order of magnitude more difficult that building one in the least challenging ways. These time-tested ways are (1) centrifuge uranium enrichment for HEU to make a gun-type uranium bomb, (2) CANDU/RBMK production of PU-239 to make an implosion-type plutonium bomb.Terrorism
Regarding terrorist attacks on facilities the LFTR, like the PBR, is designed for passive air cooling in the event of permanent disruption of cooling.Submarines
Regarding the prohibition of HEU in naval reactors, I don't think you can persuade governments to give up nuclear submarines! Besides, submarines are nuclear weapons.International control
I don't see how we could put all uranium mining, milling, enrichment, fissile materials depots, etc under international control. Even embassies are sometime taken over in hostilities.Nuclear batteries
With respect to the hub-spoke nuclear batteries idea, both NuScale and Hyperion have recently announced attractive products.Reprocessing
Expansion of uranium nuclear power may lead to ore depletion and the need to change from a U-235 once-through cycle to reprocessing to make use of the 99.3% of U-238 available. Adopting the LFTR will avoid extensive build-out of plutonium-isolating reprocessing plants, if the thorium/uranium fuel cycle is adopted. In an LFTR no fissile material is ever isolated. None is transported out. None is transported in, except at startup.