Why do radioactive wastes 
   have to be treated properly?

    Nuclear power enables a large amount of 
    energy to be produced from a very small 
    amount of fuel, therefore only a small
    amount of waste is produced. However,
    in September 1987, an accident ocurred at
    Goiana in Brazil. A strongly radioactive 
    caesium-137 source, the radioactive waste
    from a telegraphy machine in an  abandoned 
    clinic, toke away 4 people's lives and 
    generated about 3500 cubic metres of 
    radioactively contaminated waste when 
    it was improperly removed from  its protective 
    housing. This accident indicated that nuclear 
    waste could be a potential hazard if it is 
    not properly handled, despite their small 
    size. The general objective of radioactive 
    waste disposal is that the waste should be 
    treated without causing harm to both 
    human and the environment as well as to 
    minimise the burden placed on future 
    generations. Generally, this purpose is 
    achieved by converting any waste which is not 
    in a stable solid form into such a form, encase with a corrosion resistant canister, which is
    generally surrounded by a virtually impermeable backfill like plastic clay, and stored in a 
    repository in low permeability rock. (either in a near surface one or an underground one, 
    depends on characteristics of the waste) This "multi-barrier approach" helps to keep 
    radioactive wastes away from people until they become barely distinguishable from 
    naturally occurring materials.

     It should be noted that there is a great difference between radioactive waste and non-
     radioactive waste like chemicals used in industries, the potential hazard of the former declines 
     over time due to radioactive decay, while that of the latter will stay the same forever.

     How are those wastes treated?
     As different kinds of radioactive waste have different of radioactivity, different management are
     required. Different types of radioactive wastes could be classified according to their half-lives 
     (which determines how long they have to be handled), their concentrations (high, intermediate 
     or low level) and whether they are heat generating or not. (the last two factors determine how 
     the waste should be handle and whether shielding is necessary) All three factors together 
     determine how the waste is to be handled.


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