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This discussion relates to Technology Review's article TR10: Traveling-Wave Reactor .

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  hsfrey
  

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  02/25/2009 02:15 AM

  What is the end product?

  What is the end product?
  How much will there be?
  How radioactive will it be?
  What is its effective half-life?
  How much shielding will it require?
  What is its potential for mischief?

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    JonPaul
    

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    02/25/2009 08:20 AM

    Re: What is the end product?

    These are exactly the questions I have, hsfrey.
    
    Also, what will be the volume of waste and what are the costs of dealing with the waste?

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    pronuke
    

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    03/07/2009 09:12 AM

    Re: What is the end product?

    Re: hsfrey questions
    
    What are the end product?
    The end products are residual (unburned) U-238, fission products, and transuranic elements (Np, Pu, Am, and Cm)
    
    How much will there be?
    The fuel in this reactor is Pu-239. The energy content in 1 lb of Pu-239 is equivalent to more than 2,000,000 lbs of coal, so nuclear power produces an enormous amount of energy and an extremely small amount of waste. 
    Currently we have 104 nuclear reactors in operation in the US, which generate about 20% of our electricity. The total amount of spent fuel discharged is about 2,000 tons per year. Of this, 95% is U-238 (which could be used as fuel in the Wave reactor), 4% is fission products (waste), 1% is transuranics (TRU). Of the 1% TRU, 90% is Pu, which can be recycled as fuel. The remaining 10% (0.1% of the total) is Np, Am, and Cm, which is considered waste, but can be recycled in a fast reactor like the Wave. The amount of fission products (waste) generated each year is 4% of 2,000 tons or 160,000 lbs. There are 300 million people in the US, so the average share of the nuclear waste is 160,000 lbs / 300 million = 0.0005 lbs, or 0.2 grams per person per year. If you received 100% of your electricity from nuclear power for your entire lifetime, all of the nuclear waste generated from your use would fit in a coffee cup. Compare this to the average person's carbon footprint of 20 tons of CO2 per year.
           
    How radioactive will it be?
    The radioactivity of the end products from the Wave reactor would be essentially the same as from the current generation of reactors.
    
    What is its effective half-life?
    The half-lives of the numerous fission products vary from a fraction of a second to many years. It takes about 500 years for the fission products to decay to same level of radioactivity as the natural uranium we started with.
    
    How much shielding will it require?
    Spent fuel is stored under water for at least 5 years to allow the fuel to cool (water is also an excellent shielding material). After that the fuel can be transferred to dry storage casks, which use steel and concrete for shielding. Six inches of concrete will stop more than 90% of the radiation from the spent fuel. A typical cask has about 3 inches of steel (for gamma shielding) and almost 3 feet of heavily reinforced concrete (for both gamma and neutron shielding).
    
    What is its potential for mischief?
    None. The combination of physical security, the huge mass of the storage systems, and self-protecting nature of radioactive materials make spent fuel extremely unattractive for mischief or misuse.

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      AMcA
      

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      03/08/2009 01:21 AM

      Re: What is the end product?

      Does this all sound too good to be true?
      
      The only by-product is a small fraction of what we get now?  And it's fail-safe?
      
      What shuts this down is my question.  I know we drop neutron absorbers into current reactors, and they end the chain reaction, and the reactor doesn't over-heat and destroy itself.  How do we accomplish stopping the chain reaction here?
      
      My impression -- and I'm pretty much Joe Average Citizen here -- is that once this thing is lit, you're not going to put it out.  And following that train of thought, if you can't put it out, and the cooling system hiccups, does it want to melt itself down?
      
      Do I have that right?

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        pronuke
        

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        03/08/2009 08:27 AM

        Re: What is the end product?

        The Wave reactor, like other reactors, would have a control system to shutdown the reactor. It would have to be shutdown for periodic inspections and maintenance (usually required once a year or once every two years). The control system could be control rods or a moveable neutron reflector (the reflector would surround the core and is necessary to maintain criticality. Move the reflector and neutrons escape, shutting down the reaction).
        
        Read about the Toshiba 4S reactor for more info on reflectors. The 4S has some similarities to the Wave, but the fuel is enriched U, not depleted, and the core is vertical, not horizontal. Both burn slowly from end to end. The design life of the 4S core is 30 years.  
        
        From Wikipedia:
        
        "The 4S is a fast neutron reactor. It uses neutron reflector panels around the perimeter to maintain neutron density. These reflector panels replace complicated control rods, yet keep the ability to shut down the nuclear reaction in case of an emergency."
        
        Also, although it may be theoretically possible to design a core that lasts 100 years, the first generation of Wave reactors would have cores with shorter lifetimes, say 5 or 10 years. Then the reactor vessel will be smaller, and more importantly, spent fuel can be replaced with new, improved fuel designs at each refueling. 

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        constantnormal
        

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        03/09/2009 12:09 PM

        Re: What is the end product?

        Even if if only takes 500 years for the waste products to decay to nominal levels of radioactivity, that's over twice the length of time that the US has been in existence, and almost five times as long as we have even known about radioactivity.
        
        Would it not be a good idea to encase the cooled-down dry wastes and bury them in a deep ocean subduction zone, where they can be "recycled" into the mantle over the longer view, with no human management required or even practical (except via robot sentries) at this point in our technological development?

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          pronuke
          

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          03/09/2009 01:18 PM

          Re: What is the end product?

          There are a number of possible disposal options, including deep seabed. Above ground was selected because it is accessible. Today's waste may be the fuel of the future.

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  rlindsl
  

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  02/25/2009 11:55 AM

  Technology will happen

  This technology will be developed and used by other countries that have stockpiles of spent fuel, experience with nuclear technology, and climates less hospitable to solar and wind.
  
  The containment and safety (coolant system failure means what?) are two issues that require some focus internationally. Is this reaction relatively controllable and can it be quenched easily and quickly?
  
  This process degrades spent fuel that may be reprocessed into weapons. Reprocessing is a security and environmental threat far in excess of this alternative.
  
  What are the potentially smallest configurations of this reactor style?

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    GaryB
    

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    03/27/2009 12:35 AM

    Re: Technology will happen

    The fact is: The scale of the energy problem is so large that we will need to employ all viable non-carbon sources to get off of carbon based fuels. 
    
    The traveling wave reactor has many possible advantages of less maintenance and lower proliferation potential than breeder or traditional reactors.  It should be a high priority for development IMHO. 

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  dnoonie
  

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  02/26/2009 11:16 PM

  Other good designs

  Other designs that have traction are the Fast Reactor type, http://www.nextgenerationnuclearplant.com/index.shtml
  http://nuclear.inl.gov/gen4/index.shtml
  How they burn without proliferation material!
  http://www.world-nuclear.org/info/inf98.html, check the US and Japanese designs as they are the ones that use non proliferation material.  Keep in mind that not all of these designs use non proliferation material but that is the goal of the new forth generation design.
  
  I think these designs address proliferation and waste much better than the design outlined here.
  
  They area also more inherently safe, since they have no critical fuel they can’t go super critical.
  

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