Solidified waste forms

Cocke, D. L. Molla, M. Y. A. 1993. The chemistry and leaching mechanisms of hazardous substances in cementitious solidification/stabilization systems. In Spence, R. D. (ed) Chemistry and Microstructure of Solidified Waste Forms. Lewis, Boca Raton, 187-242. 

Spence, R. D. (ed) 1993. Chemistry and Microstructure of Solidified Waste Forms. Lewis Publishers, Boca Raton. 

Poon CS, Lio KW (1997) The limitation of the toxicity characteristic leaching procedure for evaluating, cement-based stabilized/solidified waste forms. Waste Manage 17 ... 

The processes being developed at PNL convert the commercial high-level wastes to glasses or related ceramic forms. These materials offer the best practicable immobilization of radioisotopes, in a highly concentrated form, available today the AEG is also sponsoring continuing research on potentially more advanced solidified waste forms which may become available at a later date and offer added increments of safety or processing economy. 

Microwave solidification is an ex situ mixed-waste treatment process. The process is applicable for homogeneous, wet or dry, inorganic solids. The process dries the waste, mixes it with a matrix modifier, transfers it to a processing container, and subjects the mixture to microwave energy to melt the materials. The processed waste form then cools and solidifies to form crystalline mineral analogs. 

No chemical reaction occurs to solidify final waste form. 

IAEA 1985. Chemical Durability and Related Properties of Solidified High Level Waste Forms. Technical Reports Series No. 257. IAEA, Vienna. 

The use of inorganic ion exchangers to solidify liquid radioactive waste followed by pressure sintering to produce a ceramic waste form appears to be a viable alternative to calcina-tion/vitrification processes. Both the process and waste form are relatively insensitive to changes in the composition of the waste feed. The stability of the ceramic waste form has been shown to be superior to vitrified wastes in leaching studies at elevated temperatures. Further studies on the effects of radiation and associated transmutation and the influence of temperature regimes associated with potential geologic repositories are needed for a more definitive comparison of crystalline and amorphous waste forms. 

Second, solidified forms of high-level waste intended for permanent disposal are subject to LDRs for hazardous waste (EPA, 1986b 1990b) discussed in the previous section (see also Section 4.2.2). LDRs specify that vitrified high-level waste is an acceptable waste form under RCRA, but there are as yet no such provisions for other forms of high-level waste that might be intended for disposal. 

It is also known that small quantities of some compound could significantly reduce strengths and deteriorate the properties of cement solidified waste. That could be in the form of setting reduction, which could lead to the material disintegration and leaching. Examples of some waste components, which could give opposite effect to the cement stabilization, are given in Table 2. 

Solidification refers to techniques that encapsulate the waste, forming a solid material, and does not necessarily involve a chemical interaction between the contaminants and the solidifying additives. The product of solidification, often known as the waste form, may be a monolithic block, a clay-like material, a granular particulate, or some other physical form commonly considered solid. Solidification as applied to fine waste particles, typically 2 mm or less, is termed microencapsulation and that which applies to a large block or container of wastes is termed macroencapsulation [29]. 

Cheng KY, Bishop P (1992) Metals distribution in solidified/stabilized waste forms after leaching. Hazard Waste Hazard Mater 9 163-171... 

Mechanical stability. When a block of solidified waste is crushed by mechanical impact, fragments of various size will be formed. Two consequences are to be considered (1) The fraction of radioactivity leached in a certain period of time will be increased in proportion to the increase in surface area (2) the formation of very small particles in the order of 100 jum and less may enable radioactive material to be spread by air. Even larger particles may be carried by water. 

The volume of natural UaOg equal to the volume of solidified waste from reprocessing 1 MT of heavy metal. This volume is assumed to be 80 liters as an average. For unreprocessed fuel 120 liters have been used. UgOg has been chosen as the standard uranium species because this is the radioactive concentrate in a uranium ore just as solidified waste is the radioactive concentrate in a waste repository. Moreover, it is a sufficiently generalized uranium species. This reference leads to a dependence of the significant period on the waste oxide concentration in the waste form. 

Tl. Tymochowicz, S. A Collection of Results and Methods on the Leachability of Solidified High-Level Radioactive Waste Forms, Report HMI-B 241, 1977. 

Because the residual waste is in solidified form inside of steel containers in the elevator pit, and the combustion of hydrogen in the pit will not affect the solidified waste, the waste inventory is in a form which is not readily available for release (DOE 1994d). Thus, there is no credible source term of any significant magnitude. 

According to the plans of the Bundesamt fur Strahlenschutz (BfS), solid and solidified radioactive waste forms, but in particular those with marked decay heat generation shall be disposed of in a final repository in a salt dome formation 191. Heat-generating waste includes spent HTR fuel elements which are not to be reprocessed. 

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