Liquid-fluoride thorium reactors and their associated technologies will produce many valuable byproducts and secondary product streams.

Electrical Energy

Electrical energy generation is the primary product of LFTR operation. LFTRs are designed to convert thorium, a natural, inexpensive and abundant fuel, into uranium-233 which can then undergo nuclear fission. The fission of uranium-233 will release approximately a million times more energy per unit mass than the combustion of fossil fuels. This energy is released as heat into the fuel salt of the reactor and this heat energy is then transferred to a coolant salt in a primary heat exchanger. The coolant salt, in turn, transfers its heat to a gaseous working fluid that drives a closed-cycle gas turbine. The turbine is connected to an electrical generator that is synchronized to the electric grid, providing the power needed to drive our modern society.

A closed-cycle gas turbine using supercritical carbon dioxide (sCO2) appears to be the best power conversion system for the LFTR, enabling both high conversion efficiency (~45%) and compact turbomachinery. The LFTR will be responsive to changes in electrical demand due to its strongly negative temperature coefficients of reactivity. Unlike current reactors, the formation of xenon will not pose a challenge to load-following since xenon gas is continuously removed from the fluid fuel during normal operations.

Desalinated Water

Some LFTR installations will be near seawater, which may be used to cool the gas used in the closed-cycle gas turbine before it is pressurized and heated for further use. The heat from the working fluid of the gas turbine is rejected over a temperature range of approximately 70 Celsius to 30 Celsius, which is a sufficiently high temperature to use this rejected heat to produce desalinated water from seawater using simple modifications to existing desalination practices. Current-technology nuclear reactors that use steam turbines for power conversion cannot use their rejected waste heat directly to drive desalination processes. This is one of the key advantages of the high-temperature nature of the LFTR.

Medical Therapeutic Radioisotopes

The thorium fuel cycle, in the course of normal operation, produces an important cancer-fighting radioisotope with unique properties. Uranium-233, the fuel of the LFTR, has a slow decay rate that forms thorium-229, which can be chemically extracted from the fuel and set aside for medical use. Actinium-225 decays from thorium-229 and is harvested and sent to hospitals in a “generator”. Then oncologists can harvest bismuth-213 from the actinium-225 as it decays with a 10-day half-life. Bismuth-213 (Bi-213) decays through alpha emission, unlike most of the fission products that decay through beta emission. By binding Bi-213 to an antibody, it can be directed swiftly to a cancerous cell and attach to it. When the bismuth-213 decays, the alpha particle it emits has a high probability of killing the cancer cell.

decay-alpha

Thus one atom of bismuth-213 can kill a cancer cell made up of about 100 trillion atoms. That’s a remarkable leverage. Another advantage of fighting cancer this way is that it minimizes “collateral” damage to the patient, since an alpha particle can only kill the adjoining two or three cells from its point of emission. This avoids the unpleasant consequences of typical chemotherapy, like hair loss and nausea.

Unfortunately, the present world inventory of thorium-229 is far too low for targeted alpha therapy to be used to its potential, but the development of LFTR technology has the potential to change that. Every 1000 kg of uranium-233 in a LFTR generates about 5 grams of thorium-229 each year that can be harvested for medical purposes, and those 5 grams can treat hundreds of patients using targeted alpha therapy. As more and more LFTRs are built and operated, the world inventory of thorium-229 will continue to grow and more opportunities will exist to use targeted alpha therapy to fight not only cancer, but also other diseases such as antibiotic-resistant tuberculosis and staph.

Stable Fission Products

The fission of uranium-233 will produce approximately 35 different elements as fission products in varying quantities. These elements include xenon, neodymium, molybdenum, and zirconium. Xenon is easily removable during normal operation since it is a gas and has a low solubility in the fluoride fuel salt. The radioactive isotopes of xenon decay quite quickly leaving only the stable isotopes of xenon behind. Stable xenon is used by NASA as propellent for ion engines and also by a variety of other industries, and could prove to be valuable.

Neodymium also stabilizes quickly and is the primary constituent of high-performance magnets. Removing neodymium from the salt could be done in connection with a larger strategy to remove all lanthanides, some of which have high neutron-absorption cross sections.

Other valuable fission products that take longer to stabilize include rhodium, ruthenium, and palladium. Rhodium and ruthenium will stabilize completely about a decade after removal from the reactor and are very valuable. Palladium has a single long-lived radioisotope that might diminish its value somewhat but would probably still allow it to be used in catalysts.

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