Leaching mechanisms of solidified low-level waste. The literature survey
A literature survey on leaching mechanisms, available mathematical models and factors that affect leaching from solidified low-level radioactive waste (LLW) was compiled. Physicochemical mechanisms identified include diffusion, dissolution, ion exchange, corrosion and surface effects. Diffusion was generally considered to be the predominant mechanism in LLW leachability. However, this hierarchy of importance has been strongly questioned for waste forms containing soluble salts and has been shown to be invalid for waste forms incorporating sorbents which control the release of radionuclides by ion exchange. Leaching behavior was modeled both mathematically for curve fitting to leaching data and by consideration of physical and chemical interactions within and between solidification agents, waste materials and additives, if any. Physicochemical analyses of bitumen and polymer solidification agents have considered them to be inert encapsulants with limited water permeability. All of the mathematical models are derived from solutions to the diffusion equation. Other mechanistic processes are included as additional terms in the equation. No comprehensive evaluations of mathematical models for LLW based on curve fitting to data were found in the literature. Factors that affect leaching have been categorized as system factors, leachant factors and waste form factors. System factors include temperature, pressure, radiation, time and the ratio of waste form area to leachant volume. Leachant factors include pH, Eh, flow or replacement frequency and composition while waste form factors include composition, surface condition, porosity and surface area to volume ratio. Information from the literature is reported for each of these factors. 75 refs., 2 figs., 4 tabs.
- Research Organization:
- Brookhaven National Lab., Upton, NY (USA)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 5158484
- Report Number(s):
- BNL-51899; ON: DE86002088
- Country of Publication:
- United States
- Language:
- English
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