Radioactive wastes characteristics

U.S. Department of Energy. (1996) Integrated Data Base Report 1995 U.S. Spent Nuclear Fuel and Radioactive Waste Inventories, Projections and Characteristics, DOE/RW-0006, Revision 12. Washington, DC Author. 

DOE. 1999. Inventory and characteristics of spent nuclear fuel high level radioactive waste and other... 

Waste characteristics, which may limit the effectiveness or feasibility of the remedial technologies quantity/concentration, chemical composition, acute toxicity, persistence, biodegradability, radioactivity, ignitability, reactivity/corrosivity, infectiousness, solubility, volatility, density, partition coefficient, compatibility with chemicals, and treatability... 

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. 

The discrepancy in numbers between natural and synthetic varieties is an expression of the usefulness of zeolitic materials in industry, a reflection of their unique physicochemical properties. The crystal chemistry of these aluminosilicates provides selective absorbtion and exchange of a remarkably wide range of molecules. Some zeolites have been called molecular sieves. This property is exploited in the purification and separation of various chemicals, such as in obtaining gasoline from crude petroleum, pollution control, or radioactive waste disposal (Mumpton, 1978). The synthesis of zeolites with a particular crystal structure, and thus specific absorbtion characteristics, has become very competitive (Fox, 1985). Small, often barely detectable, changes in composition and structure are now covered by patents. A brief review of the crystal chemistry of this mineral group illustrates their potential and introduces those that occur as fibers. 

The beneficial use of radiation is one of the best examples of how careful characterization of the hazard is essential for its safe use. A radioactive substance can be safely stored or transported if appropriately contained. Depending on the characteristics of the radioactive material, it can be safely handled by using appropriate shielding and safety precautions. Laboratory workers usually wear special badges that quantify radiation exposure to ensure that predetermined levels of exposure, which are considered safe, are not exceeded. Unfortunately, after more than 50 years, society has not yet been able to design and implement a safe way to dispose of radioactive waste. The hazardous properties of radiation are explored further in a subsequent chapter. 

According to the vendor, a key advantage of the SpinTek system is that the membranes are less likely to foul compared to static membrane systems. This feature results in less downtime for the system. The system also allows continuous operation during changes in influent waste stream characteristics, eliminating downtime for flux recovery. In addition, SpinTek requires a relatively small area for operations. The vendor states that the system is ideal for operation in hostile environments, including high temperature, pH, radioactive waste, chemical solutions, and solvent solutions. 

The preparation, composition, structure and leaching characteristics of a crystalline, ceramic radioactive waste form have been discussed, and where applicable, compared with vitrified waste forms. The inorganic ion exchange materials used such as sodium titanate were prepared from the corresponding metal alkoxide. The alkoxides were reacted in methanol with a base containing the desired exchangeable cation and the final powder form was produced by hydrolysis in an acetone-water mixture followed by vacuum drying the precipitate at ambient temperature. 

Table 1.2—Summary of characteristics of radioactive wastes and disposal options in waste classification system... 

Characteristics of the system for classification and disposal of fuel-cycle waste. The current classification system for radioactive waste that arises from operations of the nuclear fuel cycle in the United States and the current requirements for disposal of waste in the different classes have the important characteristics discussed below. 

It is highly desirable that a waste classification system be expressed in quantitative terms. More specifically, the intrinsic waste characteristics that define the boundaries between waste classes should be stated numerically. Qualitative definitions of waste classes, such as the definition of high-level radioactive waste discussed in Section 4.1.2.3.1, simply defer the issue of waste classification to a subsequent definition of the qualitative terms or to case-by-case determinations that typically occur after waste is generated. 

The geochemical behavior of disposed radioactive wastes is controlled by a number of different physical and chemical phenomena. Some changes are caused by thermal processes which influence chemistry of both the stored material and its host. These thermal effects can also influence the physical characteristics of the stored material. Laboratory and field studies are underway in many scientific and engineering facilities to understand these effects. 

Inorganic contaminants are immobilized by washing the waste with soluble phosphates. This treatment uses a very small amount of phosphate, does not change other characteristics of the waste such as its granular nature or volume, and is relatively inexpensive. If the waste contains radioactive contaminants, phosphate washing is not sufficient because the dispersibility of the radioactive contaminant powders needs to be reduced, and hence, the waste needs to be solidified. Solidification requires generating phosphate ceramics of the waste in the form of a CBPC. In the case of radioactive waste, both stabilization and solidification are needed because they not only immobilize the contaminants, but also solidify the entire waste. As we will see in this and the next chapter, whether phosphate treatment is used only for stabilization or for both stabilization and solidification, it is very effective for a wide range of waste streams. 

For the treatment of conventional, nonradioactive liquid waste the predicted lifetime of membranes is 4—5 years. The effective lifetime depends on the conditions in which the membrane is used the characteristics of solutions treated, pressure, and temperature. While selecting the membrane for radioactive waste processing, one has to remember about its resistance and... 

In relation to future trends of the membrane treatments described in this chapter, they are expected to be applied for medical and research wastes of low-medium activity contaminated with Cs, or other radioisotopes with similar characteristics. Furthermore, membrane treatment has been proved as an efficient and quick treatment in an incident that generates low-medium radioactive wastes. 

Origins. Most of the radioactive waste at SRP originates in the two separations plants, although some waste is produced in the reactor areas, laboratories, and peripheral installations. The principal processes used in the separations plants have been the Purex and the HM processes, but others have been used to process a variety of fuel and target elements. The Purex process recovers and purifies uranium and plutonium from neutron-irradiated natural uranium. The HM process recovers enriched uranium from uranium—aluminum alloys used as fuel in SRP reactors. Other processes that have been used include recovery of and thorium (from neutron-irradiated thorium), recovery of Np and Pu, separation of higher actinide elements from irradiated plutonium, and recovery of enriched uranium from stainless-steel-clad fuel elements from power reactors. Each of these processes produces a characteristic waste. 

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