Environmental Engineering Reference
In-Depth Information
they are generated, or buried in shallow trenches beneath about 3 feet
of soil. For decades, these storage areas have been described as temporary
sites, to be emptied and transported to a permanent site somewhere. At
these designated temporary shallow burial sites, the metal drums corrode
as the years roll on, and stress is placed on them by the continuous
radiation from the material in the drums. How long they will remain
coherent is unknown. Many drums at some sites have leaked radioactive
liquids into the soil and groundwater.
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Another disposal method for low-level waste, now banned, was to
cast it into concrete, encase it in steel drums, and dump it into the deep
ocean. Tens of thousands of tons of these drums were dumped prior to
1993 at an internationally agreed site in the Atlantic Ocean 1,300 miles
southwest of England, where they sank 15,000 feet to the ocean fl oor.
They are supposed to remain safe and undisturbed there for at least
hundreds of years. However, if the drums eventually leak, the concrete
in them, which is composed of calcium carbonate (limestone), will dis-
solve in the undersaturated ocean bottom water and release the drum's
contents. Those who favor the sub-sea method of disposal believe that
any leakage over time will be diluted into insignifi cance by the vast mass
of ocean water and dispersed harmlessly into the surroundings. The fl aw
in this scenario is that fi sh that swim near the leaking drums become
irradiated. When the smaller fi sh are eaten by larger carnivorous fi sh,
the irradiation is spread in an ever-widening area whose limit is unknown.
In other words, the barrel dumpers are conducting an experiment whose
outcome is unknown. Although deep-sea dumping no longer occurs,
radioactive waste is still pumped into nearshore waters off the coast of
England.
Recently an Israeli company developed a process for dealing with
low-level waste using plasma gasifi cation melting technology.
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First,
plasma torches break down the waste; carbon leftovers are gasifi ed and
inorganic components are converted to solid waste. The gas is purifi ed
and is used to operate turbines to generate electricity. The remaining
vitrifi ed material is inert and can be cast into molds to produce tiles,
blocks, or plates for the construction industry. The processing facility
can convert up to a ton of waste per hour and produces energy, 70
percent of which goes back to power the reactor with a 30 percent excess,
which can be sold. Processing costs $3,000 per ton and reduces the waste
to 1 percent of its original volume. Considering that 99 percent of radio-
active waste is low level, the plasma gasifi cation process holds great
promise.
