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Dr. James Hansen, Columbia U. and NASA scientist, wrote this excellent 4-part series of “letters to Obama”. Barry Brook has republished these on Brave New Climate. Hansen’s Pt III on fast nuclear reactors should be compelling to anyone concerned about GHG concentrations. Hansen begins with an overview leading up to a discussion of Gen IV reactors such as the Integral Fast Reactor (IFR) and the Liquid-Fluoride Thorium Reactor (LFTR) :

Nuclear Power. Some discussion about nuclear power is needed. Fourth generation nuclear power has the potential to provide safe base-load electric power with negligible CO2 emissions.

There is about a million times more energy available in the nucleus, compared with the chemical energy of molecules exploited in fossil fuel burning. In today’s nuclear (fission) reactors neutrons cause a nucleus to fission, releasing energy as well as additional neutrons that sustain the reaction. The additional neutrons are ‘born’ with a great deal of energy and are called ‘fast’ neutrons. Further reactions are more likely if these neutrons are slowed by collisions with non-absorbing materials, thus becoming ‘thermal’ or slow neutrons.

All nuclear plants in the United States today are Light Water Reactors (LWRs), using ordinary water (as opposed to ‘heavy water’) to slow the neutrons and cool the reactor. Uranium is the fuel in all of these power plants. One basic problem with this approach is that more than 99% of the uranium fuel ends up ‘unburned’ (not fissioned). In addition to ‘throwing away’ most of the potential energy, the long-lived nuclear wastes (plutonium, americium, curium, etc.) require geologic isolation in repositories such as Yucca Mountain.

There are two compelling alternatives to address these issues, both of which will be needed in the future. The first is to build reactors that keep the neutrons ‘fast’ during the fission reactions. These fast reactors can completely burn the uranium. Moreover, they can burn existing long-lived nuclear waste, producing a small volume of waste with half-life of only sever decades, thus largely solving the nuclear waste problem. The other compelling alternative is to use thorium as the fuel in thermal reactors. Thorium can be used in ways that practically eliminate buildup of long-lived nuclear waste.

The United States chose the LWR development path in the 1950s for civilian nuclear power because research and development had already been done by the Navy, and it thus presented the shortest time-to-market of reactor concepts then under consideration. Little emphasis was given to the issues of nuclear waste. The situation today is very different. If nuclear energy is to be used widely to replace coal, in the United States and/or the developing world, issues of waste, safety, and proliferation become paramount.

Nuclear power plants being built today, or in advanced stages of planning, in the United States, Europe, China and other places, are just improved LWRs. They have simplified operations and added safety features, but they are still fundamentally the same type, produce copious nuclear waste, and continue to be costly. It seems likely that they will only permit nuclear power to continue to play a role comparable to that which it plays now.

Both fast and thorium reactors were discussed at our 3 November workshop. The Integral Fast Reactor (IFR) concept was developed at the Argonne National Laboratory and it has been built and tested at the Idaho National Laboratory. IFR keeps neutrons “fast” by using liquid sodium metal as a coolant instead of water. It also makes fuel processing easier by using a metallic solid fuel form. IFR can burn existing nuclear waste, making electrical power in the process. All fuel reprocessing is done within the reactor facility (hence the name “integral”) and many enhanced safety features are included and have been tested, such as the ability to shutdown safely under even severe accident scenarios.

The Liquid-Fluoride Thorium Reactor (LFTR) is a thorium reactor concept that uses a chemically-stable fluoride salt for the medium in which nuclear reactions take place. This fuel form yields flexibility of operation and eliminates the need to fabricate fuel elements. This feature solves most concerns that have prevented thorium from being used in solid fueled reactors. The fluid fuel in LFTR is also easy to process and to separate useful fission products, both stable and radioactive. LFTR also has the potential to destroy existing nuclear waste, albeit with less efficiency than in a fast reactor such as IFR.

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