Radioactive waste encapsulation

Increasing thermal conductivity (W/m K) Iron oxide 0.8 0.54 Radioactive waste encapsulation... 

Possible applications of AAS cements include precast concrete, concrete for corrosive environments, heat-resistant concrete, wood composites, radioactive waste encapsulation, and grouting. 

Engineered barriers generally include a waste form (spent nuclear fuel or glass containing radioactive wastes) encapsulated within a metallic container (e.g., steel and copper), which may be surrounded by a low-permeability, clay-rich buffer and backfiU. Natural barriers include the repository host rock and a volume of rock between the repository and biosphere. The engineered barriers and immediately adjacent host rock are referred to as the near field [1]. 

Cyclopentadiene oligomers have been formed by vapor deposition of CPD on kaolin to afford a sorbant for removal of oil from water (71). They are also employed as coatings for controlling release rates of fertilizers (72). Thermal addition of sulfur to a mixture of DCPD and CPD oligomers has led to a number of beneficial appHcations such as waste water oil adsorbant powdery foams (73), plasticized backing for carpets and artificial turfs (74), and in modified sulfur cements for encapsulating low-level radioactive wastes (75). 

Plasma gasification is a generic-type process that can accommodate virtually any input waste material in as-received condition, including liquids, gases, and solids in any form or combination. Also, moisture content is not a problem. Liquids, gases, and small particle-size waste materials are very easily and efficiently processed. Bulky items, such as household appliances, tires, and bedsprings, can also be readily accommodated without loss of destruction efficiency. The reactor vessel and waste feed mechanism are designed for the physical characteristics of the input waste stream. Even waste materials such as low-level radioactive waste can be processed to reduce the bulk and encapsulate the radioactive constituents to reduce leachability. 

In medical installations, the use of radioactive isotopes for diagnosis and therapy has significantly increased in the past years. Nonencapsulated radioactive elements are used for different purposes such as in diagnosis by tracers, treatment of thyroid or blood disorder, and in medical research. These activities produce some solid radioactive wastes like cotton, rubber gloves, syringes, etc., as well as liquid wastes, mainly scintillation liquids. Another type of waste is the encapsulated sources that are used for cancer treatment these elements must be changed when their activity decays below a certain level. 

Polymer encapsulation is an ex situ S/S technique involving the application of thermoplastic resins such as bitumen, polyethylene and other polyelfins, paraffins, waxes, and sulfur-based cements, as opposed to cements and pozzolans. Polymer encapsulation has been used primarily to immobilize low-level radioactive wastes and those waste types that are difficult to immobilize in cement, such as Cl- and SO4-based salts. Bitumen (asphalt) is the least expensive and (hence) used most often. Thermoplastic encapsulation heats and mixes the contaminated soil with the resin at 130 to 230°C in an extrusion machine. Organic pollutants and water boil off during the extrusion and are collected for treatment or disposal. The final product, a stiff yet plastic resin, is then discharged into a drum or other container and land-filled (U.S. EPA, 1997). 

The reaction between hard-burned MgO, water, and potassium dihydrogen phosphate produces a quick setting cementitious mass, KMgP04-6H20. This cement system was originally developed at Argonne National Laboratory for the stabilization and encapsulation of hazardous and radioactive wastes (Wagh et al., 1998). 

Vitrification is particularly useful for remediation of soils contaminated with radioactive heavy metals. The radioactive heavy metals are encapsulated in a highly inert, nonporous matrix, which can be stored permanently in underground secured radioactive waste storage facilities currently under development in some Asian countries. Vitrification can also be used for sediments and slndge pollnted by heavy metals. 

Nuclear energy, which is obtained when nucleons (protons and neutrons) are allowed to adopt lower energy arrangements and to release the excess energy as heat, does not contribute to the carbon dioxide load of the atmosphere, but it does present pollution problems of a different land radioactive waste. Optimists presume that this waste can be contained, in contrast to the burden of carbon dioxide, which spreads globally. Pessimists doubt that the waste can be contained—for thousands of years. Nuclear power depends directly on the discipline of chemistry in so far as chemical processes are used to extract and prepare the uranium fuel, to process spent fuel, and to encapsulate waste material in stable glass blocks prior to burial. Nuclear fusion, in contrast to nuclear fission, does not present such serious disposal-related problems, but it has not yet been carried out in an economic, controlled manner. 

The engineered barriers are composed of vitrified waste encapsulated in a canister, metal overpack and buffer material in a geological disposal system of high-level radioactive waste (HLW) adopted by INC (2000). Highly compacted bentonite is considered as the candidate buffer material for the system. Figure I shows the schematic view of the geological disposal system and expected processes after emplacement of the engineered barriers. 

Inorganic binders may be used to immobilize toxic or radioactive waste, with the aim of encapsulating it and converting it into an integral form of waste that can be conveniently and safely disposed. In this process, toxic and/or radioactive liquids, sludges, or dust are combined with the binder (and water) and converted into a solid form in the course of setting and hardening. 

Radioactive waste can be encapsulated in Pb0/Fe203/P205 glasses which are very resistant to leaching, and are stable to radiation [24-27]. Phosphate glasses are used in radiation dosimetry and they have other biomedical uses [28]. 

The solid waste treatment and storage system provides treatment, encapsulation and storage for the solid radioactive waste produced during, plant normal operation and maintenance. 

Intermediate Eevel Waste (ILWL which will comprise mainly adsorption and filter media from gaseous and liquid radwaste treatment. Following appropriate pre-treatment, the ILW will be encapsulated in cement (to immobilise radionuclides) and stored on site (prior to future consignment to an off-site repository facility). A BAT assessment for management of ILW is presented in a Radioactive Waste Management Case Evidenee Report (Reference 14.21). All lEW solid waste streams will be handled in internal areas and not exposed to the external environment. 

Sulfur polymer cement shows promise as an encapsulation and stabilization agent for use with low level radioactive and mixed wastes. Use of SPC allows accommodation of larger percentages of waste than PCC. As of this writing (1997), SPC-treated waste forms have met requirements of both the Nuclear Regulatory Commission (NRC) and the Environmental Protection Agency (EPA). 

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