Radionuclide characteristics of the fuel component of the Chernobyl radioactive depositions

The distributions of activity ratios of "non-volatile" radionuclides of the Chernobyl depositions have a definite dispersion. It is the result of both errors in activity measurements and in heterogeneity of the fuel burnup in preaccidental reactor. The activity ratio for 137Cs and 134Cs nuclides is the most sensitive indicator of fuel assemblies burnup. Comparison of the values of this ratio, obtained by measurements of individual particles, with calculated values permitted to define the distribution of fuel particles in depositions basing on the burnup. The mean depth of burnup in dispersed fuel appeared to be approximately 20% lower than in preaccidental reactor. It was shown, that the variety of radionuclide characteristics in the fuel component of depositions is determined, at a considerable extent, by heterogeneity of reactor fuel. Thus, preaccidental history of the reactor is reflected in depositions and radionuclide patterns of fuel particles make it possible to attribute them to different groups of fuel elements in preaccidental reactor.