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Molten Salt Reactors and Thorium Energy

By: , Posted on: July 11, 2017

molten salt reactors and thorium energy

Most people want to reduce fossil fuel consumption to save the climate and our lungs. Solar and wind energy are excellent, but intermittent. Nuclear power is reliable, safe and affordable, but many people are afraid of accidents and radioactive waste, so we need better nuclear reactors to avoid these hazards.

Chapter Download: Thermal hydraulics of liquid-fueled MSRs

Present Nuclear Reactors

Most nuclear reactors are cooled by water, which is cheap and carries heat well, but it has several disadvantages, including:

  • High pressure requires thick, expensive pressure vessels and pipes to prevent leaks
  • High core afterheat after shutdown, which may cause fuel melting (Three Mile Island, Fukushima)
  • Evaporation can allow fuel rods to overheat and melt, releasing radioactive materials (Three Mile Island, Fukushima)
  • Steam can cause a powerful explosion (Chernobyl)
  • Hydrogen can be generated, causing explosions (Fukushima)

We need to use coolants that can operate at high temperatures and low pressures, without boiling, causing chemical reactions, or generating hydrogen.

Molten Salt Reactors (MSR)

If we heat up table salt (NaCl) to high temperatures it becomes a liquid, which can operate at high temperature and low pressure. Similar molten salts could cool metal fuel rods more safely than water. Alternatively, the fuel itself could be dissolved in the molten salt, which would avoid the need for fuel rod manufacture.

Fuel melt would not be a problem, since it is already molten. If the fuel overheated, a drain plug would melt, and it would flow down into drain tanks and gradually solidify, trapping radioactive materials.

A chemical processing system could add thorium, remove fission products, and recycle bred U-233 fuel. It should be able to operate reliably at high temperature in a highly radioactive environment. Some of the technology was developed for the Molten Salt Reactor Experiment (MSRE), which operated successfully at Oak Ridge National Laboratory from 1965-1969, but more chemical processing development is needed.

Figure 1 shows a simplified liquid fuel MSR:

Figure 1. Simplified view of a liquid fuel MSR power plant. HX=heat exchangers. The fuel salt (yellow) could be LiF-BeF2 containing UF4 and ThF4. The fissile materials in the fuel salt would sustain the chain reaction, and the extra neutrons emitted could breed 233U from the 232Th. The fuel processing plant (lavender) could separate U, Pu, Th, and Pa; adjust fuel salt composition to maintain reactivity; and remove fission products to reduce core radioactivity.

Modular molten salt reactors could

  • be manufactured inexpensively and shipped to the power plant site
  • cost less than water-cooled reactors
  • produce electricity, hydrogen, and desalinized water
  • be much safer than water-cooled reactors (no fuel melt accidents, steam explosions, or hydrogen explosions)
  • incinerate actinides, reducing the need for long-term radwaste storage
  • utilize thorium fuel.

The Shanghai Institute of Applied Physics has over 400 people working on MSR development.

Thorium Energy

Only 0.72% of uranium is U-235, which can be burned in nuclear reactors, and the rest is U-238. Some of the U-238 can be bred into plutonium to produce more energy, but the low breeding ratio requires many years to generate enough plutonium to start up more reactors, and most of the uranium is wasted.

Thorium can be converted into U-233 by neutron absorption and used as fuel. Over 90% of the thorium can be used, and it is four times as abundant as uranium in the earth’s crust. Thorium is an inexpensive byproduct of rare earth mining (needed for electronics), and many tons of it are in storage. Waste products from thorium are less hazardous than those from uranium fuels.

Summary

Nuclear energy can provide reliable power when solar and wind are not operating, but the present light water reactors are hindered by public fears of accidents and long-lived radioactive wastes. Molten salt reactors can prevent serious accidents and can incinerate their own long-lived products. We envision a world where most countries have affordable molten salt reactors burning thorium, uranium, and spent fuel actinides, producing electricity, hydrogen, and desalinized water with no serious accidents. This new book describes the great research and development efforts that are underway worldwide to develop these reactors.

Want to read more?

molten salt reactors and thorium energy

Molten Salt Reactors and Thorium Energy

  • Written in cooperation with the International Thorium Molten-Salt Forum
  • Covers MSR-specific issues, various reactor designs, and discusses issues such as the environmental impact, non-proliferation, and licensing
  • Includes case studies and examples from experts across the globe

For a limited time you can read Chapter 6: Thermal hydraulics of liquid-fueled MSRs on Science Direct

You can view the book on ScienceDirect. Need it in print? Enter STC317 at the checkout and save up to 30%

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