Результати верифікації радіонуклідного вектора для характеризації твердих радіоактивних відходів ЧАЕС, що спрямовуються на захоронення

Abstract

The first radionuclide vector (RV) for characterization of operational solid radioactive wastes (SRW) of Chornobyl Nuclear Power Plant (ChNPP) according to the IAEA methodology was established in 2018 and consisted of a set of scaling factors (SF), which have never been refined and updated, as it is recommended to be done from time to time. In this work, verification algorithm of previously established SF values, provided for by RV setting technique, was tested, and their values were updated with taking into account the implementation of a new approach for sorting ChNPP SRW into the streams. It was established that for such nuclides as 90Sr, 94Nb and 241Am, geometric mean values of SF or correlation function (CF) established on the basis of regression analysis of logarithms of nuclide content, can be used. For the other radionuclides (14С, 3Н and 235, 238U), whose activity levels were higher than the minimum detectable activity (MDA), arithmetic mean values of SF only can be used. For uranium isotopes 235, 238U, a high degree of correlation between their content is observed in all SRW materials, regardless of whether they belong to combustible or non-combustible operational waste of the ChNPP. According to the test results (testing for significance of difference under the null hypothesis) using the Student’s t-statistics, it was established that the same SF values can be applied to the waste temporarily stored in the eastern and western compartments of the ChNPP SRW repository. The waste should be separated into non-combustible and combustible materials only. This follows from the fact that combustible solid waste, if they are to be burned as it is planned, must be re-characterized using the SF value already determined for ash and by a different technique. However, until these wastes are burned, the obtained data allow estimating the expected levels of nuclide content in their ash residue.