Part 1 of 2 Parts
I have written about molten salt reactors (MSRs) in the past. In a molten salt reactor, the fuel is mixed with a molten salt. The mixture not only acts as the fuel but also acts as the coolant. There are supporters of this technology who point out that tit will be much safer because MSRs cannot possibly melt down. They can be refueled without shutting down. Fuel is just dumped into the vat to melt into the mix and there is no needed for creating fuel rods and all the machinery they require. MSRs can run at higher temperatures which should make them more efficient. However, they do have problems and challenges which help explain why they have not been adopted for commercial power production even though they have been researched since 1964.
The main problem with MSRs is that the radioactive fission products in the fuel can easily escape. The fuel is not in tubes covered with cladding but is just sitting in a big vat mixed with a molten salt. The vat can be enclosed in multiple layers of containment but it is still difficult to track and trap all the radioactive materials. In addition to the radioactive fission products and actinides in the vat, there are also chemicals which can corrode the containment vessel.
1. Material degradation – The molten salt fuel in the vat contains about half the elements in the periodic table. That means that all of these elements are in contact with the containment vessel and this raises serious concerns about corrosion. Noble metals include rhenium, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold. They will naturally plate out on cold metal. In a nuclear power reactor, a heat exchanger will be the coldest metal available. This means that the heat transfer surfaces will need periodic replacement. Inside the Molten-Salt Reactor Experiment at the Idaho National Laboratory, tellurium caused the Hastelloy-N material to crack. This was solved by chemically treating the fuel, but the same type of problem could plague commercial reactors with long life-spans.
2. Tritium production – If lithium is one of the ingredients for the fuel, tritium will be produced. Tritium is the radioactive isotope of hydrogen. It is extremely mobile and can easily move thru metals. At the Oak Ridge National Laboratory, they used a special sodium fluoroborate intermediate salt to capture most of the tritium produced but a great deal still escaped into the environment.
3. Complex Chemical plant – It will be fairly easy to remove some of the fission products from the fuel. However, more serious fission product (or actinides) separation will require complex processes such as the liquid bismuth reduction process, volatilization or electroplating. These have been exhaustively researched but they are complex enough to be a challenge.
4. Remote Maintenance – The chemical plants associated with MSRs will need periodic maintenance but all of the equipment at the MSR will be highly radioactive. Remote maintenance is necessary and will be expensive. If a graphite moderator is used, it will be expensive to replace it with remote manipulation equipment.
Please read Part 2 next