Deposition and distribution of Chernobyl fallout fission products and actinides in a Russian soil profile.

In this article the distribution of fission products and actinides in a soil profile from Novo Bobovicky in Russia, which was contaminated due to the Chernobyl nuclear power plant accident, is described. The ground deposition of long-lived fission products determined by gamma-spectrometry was (recalculated to 26 April 1986) 1600 kBq (137)Cs/m(2), 900 kBq (134)Cs/m(2) and 60 kBq (125)Sb/m(2). Of these radionuclides (137)Cs shows the dominating activity at the present time. After 6.5 years 90% of the Cs and Sb activity was contained in the upper 4 cm. A (239,240)Pu ground deposition of 77.4+/-8.0 Bq/m(2) was determined by alpha-spectrometry. The (238)Pu/(239,240)Pu activity ratio of 0.30+/-0.03 and (241)Pu/(239,240)Pu activity ratio of 115+/-14 (in 1986) measured in the soil profile, indicates that the analysed Pu originates mainly from the Chernobyl accident. The average (234)U/(238)U activity ratio of 1.06+/-0.29 indicates that the uranium in this soil is dominated by naturally occurring uranium. The alpha- and beta-autoradiography revealed that the activity is mainly present in particulate form. It could further be observed that the spots containing alpha- or beta-activity originated from different particles. A comparison of alpha-autoradiography with the bulk Pu and Am activity showed that 92% of the alpha-activity was present as clearly detectable alpha-spots. The beta-active particles, located by beta-autoradiography were correlated with gamma-spectrometric measurements and contained only (137)Cs. These hot spots ranged from 0.02 to 0.15 Bq.It could be concluded that the vertical transport of (137)Cs and fuel fragments occurs mainly by movement of particles through the soil. It could also be concluded that the fuel fragments found, in this soil were depleted in respect to Cs, Sb and Eu. Comparison of the analysed (238)Pu/(239,240)Pu, (241)Pu/(239,240)Pu and (241)Am/(239,240)Pu ratios with the ratios calculated with ORIGEN-S code gave an estimate of the average burn-up of the fuel particles to be in the range of 11-12 GWd/tU. The results presented in this article are valid for this single soil profile and should not be generalised unless validated in a more rigorous study of a larger number of soil profiles.

Ion chromatography inductively coupled plasma mass spectrometry (IC-ICP-MS) and radiometric techniques for the determination of actinides in aqueous leachate solutions from uranium oxide.

The choice of the analytical method for the determination of actinide isotopes in leachate solutions has to be made considering several parameters: detection limit for each isotope, sample preparation procedure in terms of duration and complexity, counting time and interferences. A leachate solution obtained by keeping a pellet of UO2 doped with 238Pu in contact with distilled water was investigated for the content of U and Pu isotopes by radiometric methods (alpha-, gamma-spectrometry and liquid scintillation counting). The results of the radiometric methods were compared with those obtained from the analysis performed by inductively coupled plasma mass spectrometry on-line to a system for chromatographic separation (IC-ICP-MS). The comparison confirmed that IC-ICP-MS is a powerful method for the detection of long-lived radionuclides. The radiometric methods have a detection limit two orders of magnitude lower than IC-ICP-MS in the case of short-lived radioisotopes mostly due to the low background in the detector. On the other hand, the sample preparation and the analysis duration are more time-consuming compared to IC-ICP-MS; moreover, not all isotopes can be determined by using only one radiometric technique.