Kloosterman on TMSR/LFTR Technology

Jan Leen Kloosterman is an Associate Professor at Delft Technical University in the Faculty of Applied Science. Professor Kloosterman specializes in the Physics of Nuclear Reactors, and Thorium Fuel Cycle MSRs are among his professional interests. He has prepared a list of the technological advantages of the LFTR/TMSR. Here is his list:

The MSR in combination with the thorium fuel cycle has many advantages:

1. Fluoride inorganic salts are used as a carrier for the fuel and as a coolant. They are among the most stable of chemical compounds and have proven stable under reactor operating conditions. They have a high solubility for actinides, very low vapor pressure, and good heat transfer properties. Furthermore, they do not react with air or water, and are inert to some commonly used structural materials.

2. Soluble fission products can be removed on-line in a chemical processing plant, while non-soluble fission products and the noble metals can be extracted from the salt by helium bubbling. This enhances the neutron economy. Together with the large number of neutrons liberated in U-233 fission events, new fissile material can be bred from abundantly available thorium.

3. There are no mechanical valves in the salt circuit. Flow is blocked by plugs of frozen salt cooled by electrical fans. If the salt heats up to levels above design values or if the power supply fails, the plugs will melt and the salt will be drained into storage drums cooled by natural convection (see the Figure).

4. A fast excursion of the fuel temperature will lead to salt expansion providing instantaneous negative reactivity feedback, which will slow down or completely stop the fission process. Although heating of the graphite moderator will generally introduce positive reactivity, this process is much slower and can easily be controlled. Furthermore, a fuel salt temperature too high will always lead to drainage of the fuel into passively cooled storage tanks.

5. The primary and secondary circuits are operated under ambient pressure, which is considered a very important safety feature.

6. The thorium fuel cycle produces much less long-lived nuclear waste. Compared with the standard once-through fuel cycle in a Light Water Reactor (LWR), a thorium fueled MSR produces 4,000 times less neptunium, plutonium, americium and curium. Plutonium production is reduced even with a factor of 10,000.

7. Among all nuclear reactors, the MSR is most suited to utilize the thorium cycle. Neutron capture by Th-232 produces Pa-233, which decays with a half life of 27 days to U-233. To avoid Pa-233 capturing an extra neutron, which would produce the non-fissile U-234, part of it can easily be stored in a hold-up tank to let it decay to U-233. This enhances the breeding process, which makes the MSR, in combination with its excellent neutron economy, the most attractive reactor for using thorium.