Unlike organic contaminants (and similar to metals),
radionuclides cannot be destroyed or degraded; therefore,
remediation technologies applicable to radionuclides involve
separation, concentration/volume reduction, and/or
immobilization. The most commonly used treatment technology for
radionuclides in soil, sediment, and sludge is
solidification/stabilization (S/S). This treatment technology is
described briefly below.
processes produce monolithic blocks of waste with high structural
integrity. The radionuclides do not necessarily interact
chemically with the solidification reagents (typically
cement/ash) but are mechanically locked within the solidified
methods usually involve the addition of chemical binders, such as
cement, silicates, or pozzolans, which limit the solubility or
mobility of waste constituents even though the physical handling
characteristics of the waste may not be changed or improved.
Solidification/stabilization of radionuclides can be conducted
either in situ or ex situ. In situ S/S techniques are now
considered innovative and are discussed in Section 4.
There are many innovations in the stabilization and
solidification technology. Most of the innovations are
modifications of proven processes and are directed to
encapsulation or immobilizing the harmful constituents and
involve processing of the waste or radionuclides. Some distinct
innovative processes include: radioactive waste solidification
and vitrification/molten glass.
In radioactive waste
solidification (Grouting/Other) treatment,
solidification additives are used to form a uniform and stable
matrix to encapsulate radioactive waste materials. Assemblies
include pumps for liquids or slurries, conveyors for sludges or
solids, storage silos, weigh feeders, piping, mixers and disposal
or molten glass, processes are solidification methods that employ
heat up to 1,200° C to melt and convert waste materials into
glass or other glass and crystalline products. The high
temperatures destroy any organic constituents with very few
byproducts. Materials, such as heavy metals and radionuclides,
are actually incorporated into the glass structure which is,
generally, a relatively strong, durable material that is
resistant to leaching. In addition to solids, the waste materials
can be liquids, wet or dry sludges, or combustible materials.
Borosilicate and soda-lime are the principal glass formers and
provide the basic matrix of the vitrified product.
Excavation, retrieval, and
off-site disposal of contaminated soil (with or
without stabilization) to a landfill have been performed
previously at many sites. Landfilling of radionuclides is
becoming increasingly difficult and expensive as a result of
growing regulatory control, and may be cost-prohibitive for sites
with large volumes, greater depths, or complex hydrogeologic
environments. Determining the feasibility of off-site disposal
requires knowledge of land disposal restrictions and other
regulations developed by state governments.