Investigation of radionuclide contamination of materials stored in solid radwaste repository of the Chornobyl NPP

Abstract

The composition and features of radionuclide contamination of solid radioactive waste (SRW) stored in the western “light” compartment of SRW repository (RSRW) of the SSE “Chornobyl Nuclear Power Plant” (ChNPP) were studied. Representative samples of SRW taken from the top layer of materials at 1-m depth were split into four streams, and according to their physical state, they were classified into two categories: combustible (one stream) and non-combustible (three streams) ones. After relevant sample preparation was carried out, the SRW samples were investigated in the ChNPP Laboratory for water-radiochemical measurement in order to identify the radionuclides, which are subject to compulsory certification according to SRW acceptance criteria valid in the Exclusion Zone. It was stated that SRW radioactivity levels in the upper layer of western “light” compartment of SWR are, mainly, determined by radionuclide contents of 137Cs, 60Co, 90Sr, 94Nb, 235U, 238U, 241Am, 3 H and 14C. The parameters of regression dependencies and correlation coefficients between the specific activity of radionuclides in stream- and integrated (for non-combustible SRW) data samples compiled of measurement results (above the minimally detectable activity) were estimated. It was stated that the features of radionuclide contamination spectrum of the SRW in western and eastern compartments are largely similar ones, that, apparently reflects the typical properties of the ChNPP operational wastes produced in period from 1978 to 1986, and which had been stored in mothballed state in the RSRW before the accident at the ChNPP Unit 4 occurred. However, for such radionuclides as 60Co, 94Nb and 90Sr, observable levels of SRW contamination in the western compartment are significantly higher, than in the eastern one. At the same time, the specific activity of uranium isotopes 235, 238U is several times lower. It was concluded that the experimental and analytical results obtained in this work can be used as the source data for the next stage of studies — calculation of scaling factors and determination of radionuclide vectors needed to certify the difficult-to-measure radionuclides in the ChNPP SRW packages being transported to their burial.