Radioactive nuclides cleaning

The selective extraction of a radioactive nuclide as a nonpolar compound or complex from an aqueous solution by an immiscible organic solvent Is frequently the most satisfactory method for making a fast radiochemical separation In either macro or trace concentrations. Separations by solvent extraction are simple, convenient, clean, and rapid. They usually require apparatus as uncomplicated as a separatory funnel and may readily be adapted to remote handling procedures. 

However, the protective properties of such screens deteriorate with time, and the screens themselves accumulate considerable amount of radioactive nuclides. Application of electrokinetic technology is very efficient for restoring the protective properties of such screens. Its application can help not only raise the sorption properties of a protective screen but also clean it from accumulated radioactive nuclides without extracting the polluted ground. 

Figures 5.3 and 5.4 show the results of determining electrokinetic migration of Sr and Cs in different forms in the sand-gel ground in free, dissolved, and sorbed forms. These graphs show that both free (dissolved) and sorbed (bound) radioactive nuclides in the sand ground strengthened with oxalic silica-alumina gel become involved in electrokinetic migration. Hence, electrokinetic treatment helps clean the screens and restore their protective ability.

ELECTROKINETIC CLEANING OF GROUND FROM RADIOACTIVE NUCLIDES... 

Cleaning of ground, including soils, from radioactive nuclide pollutants is another relevant problem. The electrokinetic method is the most efficient of the available methods of removing radioactive nuclides from the ground its application has two options—with and without flushing. 

We examined in our experiments the factors that influence electrokinetic cleaning of different clay grounds (from sandy loam to clay) from radioactive nuclides containing isotopes of °Sr, Sr, Cs, Cs, and so on. Of them, isotopes of °Sr and Cs are the most biologically harmful, having half-value periods of 28 and 30 years, respectively. These and other radioactive isotopes are present in both free (dissolved) and sorbed forms on particle surfaces (Cornell, 1993). 

Electrokinetic technologies can be successfully applied for localization of radioactive pollution foci, cleaning polluted ground from radioactive nuclides, and restoring protective functions of sorption screens on the way of radioactive nucUde migration. Electromigration is fully assessed for the determination of the migration parameters of different radionuclides in soils. 

Liquid waste is generated in numerous places with activities <0.1 GBq/ m. Such waste is classified as low level. Some of these liquids may be clean enough to be released directly into the environment. Others are cleaned by flocculation, ion exchange, sorption, and similar processes. The general philosophy for liquid wastes is to concentrate all radioactivity to the next higher level because the waste volumes decrease in the order LLLW > MLLW > HLLW. Thus, in principle, the three kinds of wastes are reduced to two (HLLW and MLLW) and cleaned aqueous effluent. The MLLW and residues from LLLW cleaning are treated as the wastes of the nuclear power stations, i.e. concentrated and put into a disposal matrix such as concrete or bitumen (see 20.4.3). At some coastal sites it has been the practice to release the LLLW to the sea, with official permission. The nuclides of main concern are H, °Sr, Cs, Ru, and the actinides. 

Labeling also applies to the workstation it is important to label all storage containers, clearly indicating nuclide, compound, specific activity, total activity, date, and name of user. Where other containers or apparatus are used to hold or manipulate radioactivity during experiments, use appropriate clear means to warn others that these tubes, etc., are potentially contaminated, or clean to decontaminate them before leaving the workstation. 

Along with many other authors, LeRoy and Koksoy have drawn-attention to a common source of error in the studies of the mineral content of lichens. It is difficult to avoid the contamination of the samples by the substratum, because of the close contact of the species with it and even the decaying of the lower parts of the thallus. Other sources of error that they mentioned are the composition of surface and near-surface water, age of the thalli, the contamination from the atmosphere, and soil that was not removed from the thalli during cleaning for the experiments. Radioactive fallout, also mentioned as a possibility, is of secondary importance with respect to inactive nuclides, because the absolute mass of a certain radionuclide representing a rather high radiation effect is usually vanishingly small compared with the inactive mass of that element. 

---