The Fusion-Fission Hybrid Reactor

There is little debate that the US needs a way to increase its base load power capacity to keep up the expected increase in power demands.  Currently, alternative energy sources are not capable of supplying base load power; the two sources that can are coal and nuclear. If we are to reduce green house gas emissions, then coal is not the answer without great advances in sequestration technology.   This means that chances are that we must proceed with increased dependence on nuclear power.

One of the primary, if not the chief, concern of nuclear power is the high level nuclear waste.  However, a group of scientists, at UT no less, are working on a solution.  The solution of the waste problem may in lie with the design of a system that could eliminate up to 99% of the waste from nuclear reactors.

The UT-Austin design is called a compact Fusion-Fission Hybrid reactor, which is capable of destroying nuclear waste from fission reactions using nuclear fusion processes.  While this is in no way a new idea, the concept of using fission to as a the transmutation process to destroy high level nuclear waste, it is good to know that processes to solve part of the energy problems are continually being developed and researched.

It works like this…

Any nuclear reactor today generates its power by the fissioning of atoms; the resultant products contain extremely long-lived transuranics and other radionuclides.  What to do with this long-lived nuclides is a problem that the US, or rest of the world, has not been able to solve.  Utilizing transmutation is has been hypothesized for decades as a method of changing the long-lived isotopes of nuclear waste into more manageable isotopes (shorter half-lives).  This can be done by fuel reprocessing, but there are many issues with fuel reprocessing including cost and non-proliferation.  The fusion-fission hybrid, however, could utilize the high energy and neutron flux output of the nuclear fusion process to cause fission in the waste products of LWR’s to generate electricity and transmutate high-level waste.

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Schematic of Compact Fusion-Fission Hybrid http://www.utexas.edu/news/2009/01/27/nuclear_hybrid/

The fission-fusion hybrid design basically surrounds a deuterium-tritium (DT) fission core with fissile fission waste.  The fission waste comes from the LWR’s currently being used in the US.  The fusion process would provide a large neutron source, which would initiate the fission process in the waste material.   By now burning the waste from LWR’s, there will be a decrease of several orders of magnitude in the amount of nuclear waste that needs to be disposed.  Further, the heat generated from the fissioing of the waste can be used to generate electricity, which would decrease them amount of new fuel to be mined and created.

The problem with the fission-fusion hybrid reactor concepts has historically been the high temperatures and neutron flux of a confined fusion reactor.  Physicists at UT have been able to circumvent this dilemma with the advent of what is being referred to as the Super X Divertor.  This Super X Divertor is a “new magnetic configuration that allows the system to safely exhaust large heat and particle fluxes peculiar to CFNS‐like devices”

If this design could lead to the transmutation of high-level waste (this proposed design could augment the waste of 10-15 LWR’s for every hybrid reactor built), and consequently lead to the solution to one of the biggest problems in nuclear energy, then it certainly deserves full attention.

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1 Comment

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One response to “The Fusion-Fission Hybrid Reactor

  1. curv0e0clock

    I’m so happy to see someone writing on this topic! I’ve known about UT’s research on the fission-fusion hybrid for about a year now, and think it is a great idea. As an aspiring nuclear engineer, I am a proponent for the expansion of nuclear power in the United States. The only things holding nuclear power back are huge capital costs and large volumes of hazardous waste that no one in the United States knows what to do with. In order for nuclear power to truly expand in this nation, something needs to be done about the spent nuclear fuel. At the same time, fusion is the holy grail of alternative energy. It can produce tremendous amounts of heat and the only waste product from the fusion process is helium. The major problem with fusion, as you said, is the tremendous heat and radiation it produces is too great for any structure to contain. With the fission-fusion hybrid, spent nuclear fuel can be used to shield the intense radiation and break down the spent fuel at the same time. It is killing two birds with one stone! Any excess neutrons and heat can be removed with the Super X Divertor.

    The only thing I have against this plan is that the Super X Divertor, the revolutionary aspect of the design, only exists on paper. The concept works fine in theory [1]. Yet when operating in the real world, things are sure to go wrong. The perfection of a working Super X Divertor will take some more time and a considerable amount of more money. In due time, the Super X Divertor will become a real work of engineering.

    The next issue is that there is no economic incentive to build the fission-fusion hybrid reactor. Right now, nuclear fuel is cheap, about $41.50/lb of uranium [2]. So there is no need to recycle spent nuclear fuel to get more energy. The only incentive in recycling spent nuclear fuel is to reduce its volume. However, it is so much cheaper to simply leave spent fuel in on-site storage today. If a transmutation option were to be used to reduce the volume of spent fuel, it would not be the fission-fusion hybrid reactor. Much cheaper reactor designs exist for the burning of spent fuel that do not involve the complexities of fusion or wait upon the perfection of the Super X Divertor. The burner reactor design has been around for decades and can more easily be implemented in waste transmutation than the fission-fusion hybrid reactor [3]. The fission-fusion hybrid reactor is a great design, but it will not catch on for quite some time.

    References:
    1. http://iopscience.iop.org/0029-5515/50/3/035003/pdf/0029-5515_50_3_035003.pdf
    2. http://www.uxc.com/review/uxc_Prices.aspx
    3. http://worldwidescience.org/topicpages/a/Actinide+Burner+Reactors.html

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