Radioactive leaching

Barn swallow, Hirundo rustics, Idaho, 1976-77, nesting near radioactive leaching ponds Whole adults ... 

Millard, J.B. and F.W. Whicker. 1990. Radionuclide uptake and growth of bam swallows nesting by radioactive leaching ponds. Health Phys. 58 429-439. 

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. 

Considering the C-radioactivity leached tfarou the lysimeter soil (9.98%),absoibed and translocated by rice plants for sox years after the pC]azimsuliuion treatment(4.01%), and renaming in soil in die 6th year(47.5%), most of the loss fiom the lysimeter would be due to mineralization to C02 in the 0-10 cm topsoil, mosdy by the miaobial and dienical degradation. 

Uranium Extraction from Ore Leach Liquors. Liquid—Hquid extraction is used as an alternative or as a sequel to ion exchange in the selective removal of uranium [7440-61-1] from ore leach Hquors (7,265,271). These Hquors differ from reprocessing feeds in that they are relatively dilute in uranium and only slightly radioactive, and contain sulfuric acid rather than nitric acid. 

Performance assessments are predictions of radioactivity releases, the rate of transfer of contaminants through various media, and the potential for hazard to the pubHc. These are based on a combination of experimental data obtained in the process called site characterization and detaded computations about radionuchdes and their effects. The progressive attack on the metal or ceramic waste container, the diffusion of water into the waste form, the leaching of the radioactive compounds, diffusion out, and washing away of radionuchdes are all considered. 

Thermosetting Reactive Polymers. Materials used as thermosetting polymers include reactive monomers such as urea—formaldehyde, phenoHcs, polyesters, epoxides, and vinyls, which form a polymerized material when mixed with a catalyst. The treated waste forms a sponge-like material which traps the soHd particles, but not the Hquid fraction the waste must usually be dried and placed in containers for disposal. Because the urea—formaldehyde catalysts are strongly acidic, urea-based materials are generally not suitable for metals that can leach in the untrapped Hquid fractions. Thermosetting processes have greater utiHty for radioactive materials and acid wastes. 

The fact that is not radioactive means that it can be used safely in experiments in the field, but it also means that much patient work is needed to obtain results. The approach is demanding in terms of time, equipment, and skilled manpower, but it has made a great contribution to the understanding of the nitrate problem. The results that are outlined here are from experiments made by staff at Rothamsted, but key contributions have also come from Scotland and France. " The majority of the Rothamsted experiments involved winter wheat, but oilseed rape, potatoes, beans, and sugar beet were also grown. The soil is a factor in nitrate leaching, and three types were used, the flinty, silty clay loam at Rothamsted, a sandy loam at Woburn in Bedfordshire and a heavy sandy clay at Saxmimdham in Suffolk. 

Ground radiation is from deposited radioactive particles. The deposition rate from a radioactive cloud without rain (dry deposition) is so low that the ground radiation dose is about the same as the inhalation dose. A heavy rain, however, may wash out enough particles from the plume to make ground radiation the dominant contributor to the total dose in a limited area. Rain will also attenuate radiation by leaching the radioactivity to be shielded by the soil and by moving it to streams for further removal. 

Note that the concentrations of additive oxides differ. No attempt has been made to scale this effect with additive concentration). This curious reduction effect is not easily understood but emphasizes the complex nature of the glasses including the possible cooperative involvement of the multiple components. Similarly complex phenomena might influence leaching behavior in the complex, multicomponent glasses of interest for radioactive waste storage. 

While it is expected that the source rocks for the radionuclides of interest in many environments were deposited more than a million years ago and that the isotopes of uranium would be in a state of radioactive equilibrium, physical fractionation of " U from U during water-rock interaction results in disequilibrium conditions in the fluid phase. This is a result of (1) preferential leaching of " U from damaged sites of the crystal lattice upon alpha decay of U, (2) oxidation of insoluble tetravalent " U to soluble hexavalent " U during alpha decay, and (3) alpha recoil of " Th (and its daughter " U) into the solute phase. If initial ( " U/ U).4 in the waters can be reasonably estimated a priori, the following relationship can be used to establish the time T since deposition,... 

Chemicals. Purified, P Cj-labelled alachlor (specific activity = 17 mCi/mM), butylate (specific activity = 2.54 mCi/mM) and metolachlor (specific activity = 4.5 mCi/mM) were used in the leaching, adsorption, and diffusion studies. The radiopurity of these compounds was greater than 95% as determined by thin-layer chromatography. All other studies were conducted using analytical grade, non-radioactive material (purity 5 95%). 

Soil Column Leaching. The distribution of radioactivity from [ 1 C]butylate applied at 4.5 KG/HA and [1 l C]alachlor and [1 C] — metolachlor applied at 2.25 KG/HA and leached with 15 cm of water in Felton sand, is shown in Figure 4. Although all three herbicides are mobile in this soil type, butylate showed less mobility, with 59.6% of the applied raidoactivity found in the upper 10 cm of the column, while 28.4% and 24.3% of the applied 1 C was found in the upper 10 cm of the alachlor and metolachlor columns, respectively. 

Merritt, W.F. "The Leaching of Radioactivity from Highly Radioactive Glass Blocks Buried Below the Water Table -Fifteen Years of Results" IAEA Vienna IAEA-SM-207/98, 1976... 

Apatite is being considered as a barrier that will prevent the leakage of radioactive nuclei from the radioactive waste storage. Because of the similarity in the chemical and spectral features REE have been chosen as a model of the fission products of the actinides. For this reason it is of importance to recognize whether the elements are incorporated in the bulk of the barrier, or adsorbed on the surface where they can be subjected to leaching out (Martin et al. 1996 Martin et al. 1999a Martin et al. 1999b). 

T0040 Andco Environmental Processes, Inc., Electrochemical Iron Generation T0151 Ceramic Immobilization of Radioactive Wastes—General T0155 CFX Corporation, CFX MiniFix T0510 Metals Recovery, Inc., Metals Leaching... 

The ISV process uses electricity to heat and melt soil and other earthen materials contaminated with organic, inorganic, and radioactive compounds. Organic compounds undergo pyrolysis (thermal decomposition in the absence of oxygen). The pyrolyzed compounds then migrate to the surface zone, where they are collected and oxidized in a collection hood. Inorganic and radioactive components are incorporated as oxides into a leach-resistant vitrified product. 

The ChemChar process is a patented, ex situ method for the treatment of hazardous and mixed wastes using reverse-burn gasification. Organic components of the treated waste are converted to a combustible gas and a dry, inert solid. The solid can be mixed with cement to prevent leaching of radioactive or heavy-metal constituents retained in the char residue after gasification, or the solid can be further reduced by forward-bum gasification. 

---