Decontamination of Radio-Isotopes Polluted Soils
Development of Scientific Basis for Decontamination of Soils, Contaminated as a Result of Chernobyl Accident
Tech Area / Field
- ENV-RED/Remediation and Decontamination/Environment
3 Approved without Funding
All-Russian Scientific Research Institute of Non-Organic Materials named after A. Bochvar, Russia, Moscow
- Institute of Radioecological Problems, Belarus, Minsk
Project summaryThe Chernobyl Accident has caused a wide scale contamination of Belorussian rural and urban lands with radionuclides. The large territories are out of agricultural use or used insufficiently. Population is still receiving overpermisable doses of radiation. The analysis carried out has shown that the soil is a prime source of the population external and internal exposure.
The rehabilitation problem arises a row of questions, which needs a complex approach to be solved. The decontamination and especially the soil decontamination questions seem to be the most important and the most complicated among them.
VNIINM and IREP has been working active on the soil decontamination problem since 1986. Accumulated experience of the investigation was shown that the soil decontamination technology can be developed only on the basis of a deep scientific investigation of radionuclides state in the soil and the soil solution, - sorption-desorption behavior of the Cs and Sr radionuclides with respect to different types of soil, influence of the soil composition on physico-chemical behavior of radionuclides. A lot of work in this direction has been carried out in our laboratory during 1986 - 1997 period. It was shown that Cs radionuclides exist mainly in the ionic form in the soil and the soil solutions (the samples of the soil were collected at 6, 40, 90, 150 and 260 km from the reactor in autumn of 1986).
The study carried out shows that the Cs radionuclides had concentrated in the fine silty fraction of soil in 5 - 6 years after the accident. The extraction this fraction of soil components permit to cleanup to 95% of the processing soils from radionuclides. This fact has been use in VNIINM for development of a soil decontamination method based on the hydroseparation processes. It was tested on territories Belarus, Russia and Ukraine during 90 - 97 period. The method allowed to cleanup of contaminated soil to reach the content of the Cs radionuclides not more than 1 Bk/ g.
Addition cleanup fine silty fraction of soil with chemical should increase later on the effectiveness of the decontamination processes. So, a combination of the two methods, mechanical (fractionation) and chemical (fine fraction treatment) can be a base for the effective decontamination technology development. It proposed that for development of a hydroseparated technology needs to investigation:
- the Cs radionuclides distribution between the soil fractions; - effectiveness of the soil fraction separation and its dependence on organic and mineral contents;
- the effectiveness of the different soil silty fraction extraction methods (hydroclassification, coagulation, enrichment);
- a technological scheme and equipment for the extraction of the soil silty fraction
For the development chemical method we suppose to investigate kinetics of Cs radionuclides sorption-desorption behavior. We have already carried out a lot of experiments on the sorption-desorption of Cs and Sr with soils and solutions of different compositions. A solution composition (NH4Cl, CsCl, pH=3) which extracts 97 - 99 % of Cs radionuclides from the silty fraction of soil has been found as a result of these experiments. However the kinetic of the desorption was very slow. It took 30 - 40 days to achieve equilibrium. Hence, the main task of the project is to investigate kinetic regularities of the Cs sorption-desorption behavior with respect to the soils of different compositions. The purpose of these investigations is to accelerate the exchange of the stable Cs atoms in the solution for radioactive Cs atoms in the silty soil fraction.
The obtained results of the project investigation would allow to define the peculiarities and the mechanisms of the contamination a soils with radionuclides and to develop this basis of a modern highly efficient safety decontamination technology for remediation of areas contaminated with radioactive substances as a result a severe accidents and decommissioning nuclear facilities.
At the movement three foreign institutes have shown an interest and support to this project:
- RISO National Laboratory, DK-4000 Roskilde Denmark, Dr.J.Roed.
- Sandia National Laboratory, Albugnergue NM 87185 USA, Dr.H.Westrich.
- Centre D'Etude Sur L'Evaluation De La Protection Dans Le Domaine Nucleare, F-92263 Fontenay-aux-Roses, France, Director J.Lochard.
We think that RISO National Laboratory will participate in the investigation on the Cs radionuclides distribution on the soil profile and desorbtion of Cs from soil with chemical solution.
Sandia National Laboratory will participate in planning of the work, the discussion of the obtained results of the Cs sorbtion-desorbtion investigation on soil mineral surfaces.
Centre D'Etude Sur L'Evaluation De La Protection Dans Le Domaine Nucleare will participate in the discution of the obtained results, in the working meeting and field tests.