Liquid Fluoride Thorium Reactors (LFTR)

LFTR

Work done at Oak Ridge National Laboratories (ORNL) back in the 1950s and 60s demonstrated the feasibility of breeding U-233 from Thorium-232 as well as 'burning' U-233 in Molten Salts (ionic compounds). These molten salts  (lithium fluoride and beryllium fluoride) serve as a carrier fluid for both Thorium (Thorium tetraflouride) [Blanket] and Uranium (Uranium tetraflouride) [Core]. The resulting design has been coined the Liquid Fluoride Thorium Reactor or LFTR (See diagram above). Below is a simplified LFTR diagram. 

 

In a LFTR, fission takes place in a liquid core. Fission generates heat that ultimately finds use to do some useful work (e.g. drive a turbine to make electricity). Surrounding the core is a blanket of liquid carrying Thorium. Neutrons from fission pass from the core to the blanket for absorption by the Thorium. This transforms the Thorium to Uranium-233. After chemical removal of the Uranium-233 from the blanket, it goes into the core as new fuel. Next is the chemical removal of the fission products from the core. The process is self-sustaining, requiring only Thorium as input.

A LFTR was never built at ORNL. However, they did build and operate the Molten Salt Reactor Experiment (MRSE) for four years from 1965 through 1969. This reactor generated 7.5 Megawatts, allowing the scientists to determine the design parameters and work through system issues to arrive at a design that allows for the burning nuclear fuel in molten salts. The MSRE worked out nearly all key issues needed to build a LFTR.

The MSRE demonstrated:

1. The burning of both U-235 as well as U-233 in a carrier salt of LiF-BeF2-ZrF4-UF4
2. Operation at high temperature (650°C) at full power for more than one year
3. Operation at atmospheric pressure
4. That carrier salts were impervious to radiation damage
5. The carrier salt chemistry and metals metallurgy to eliminate corrosion
6. An efficient method of on-line refueling
7. Largely validated predictions

The MSRE did not:

1. Have a blanket to breed U-233 from Thorium (therefore, it was not a complete LFTR)
2. Have the size of a utility class power plant, (this was the next step before funding ceased)
3. Have a power conversion system to generate electricity

Conventional Nuclear Power suffers from two key issues: spent nuclear fuel or nuclear waste and costs of plant construction. Significant mitigation of both of these issues is accomplished with a LFTR.

LFTRs have some significant advantages compare to today’s nuclear power. The most significant of these stem from the liquid core running at atmospheric pressure.

These advantages are:

1. No water under pressure, therefore no pressure vessel, reducing cost
2. No large reinforced concrete containment building is required, reducing cost
3. Can be built in a factory, reducing costs
4. Because the core can be drained, LFTRs exhibit an enormous level of passive safety
5. Can be refueled without shut down
6. Exhibit 100% fuel burn up and generates almost no long lived radioactive waste
7. Configurations of LFTRs can consume the long lived radioactive elements in our present stockpiles of nuclear waste
8. Allow for the extraction of molybdenum-99 for medical purposes. Eliminating a supply shortage issue (ncbi.nlm.nih.gov/pubmed/21512666)
9. Allows for the extraction (in large quantities) of other radioactive isotopes for medical purposes
10. Can operate at high temperature, allowing the use of waste heat to desalinate seawater; higher temperatures can make for economical generation of synthetic fuels, (could use CO₂ from the atmosphere, thus making synthetic fuels carbon neutral)

(Energy From Thorium)