Dynamics of changing of volumes and radiation properties of radioactive contaminate water in the Shelter object in the condition of the New Safe Confinement

In November 2016 the "Arch" of the New Safe Confinement (NSC) was installed into design position over the Shelter object (SO). Installation of the NSC in design position stipulated the changes of the mode of water inflow into underroof space of the SO. The conditions of the SO rooms ventilation as well as temperature-humidity conditions have changed inside the SO. It resulted in the considerable changes of formations conditions of the radioactively contaminated water (RCW) unorganized accumulations in the complex NSC–SO rooms. Aim of the work is to study the dynamics of changes of RCW volumes, concentration of uranium, macrocomponets, as well as radionuclides activity concentration in the RCW unorganized accumulations in rooms at the bottom marks of the SO under conditions of the NSC operation for 2017−2020. Experimental data on the determination of the volumes and radiation characteristics of radioactively contaminated water in unorganized accumulations of liquid radioactive waste at the bottom marks of the SO after the NSC installation into the design position are presented. The biggest accumulations of RCW are in the room 001/3 at the mark −2.60 m. Volume of the accumulation is approximately 270 m³ . During the last decade a water level at the control point is about 1.1 m and does not change practically. During December 2016 – June 2020 the volume of radioactively contaminated water in rooms 017/2, 012/5–8 and 012/13–16 decreased by more than 10 times. In rooms 009/4, 013/2, 014/2 and 210/5–7, the water has dried completely. A decrease of radioactively contaminated water volume occurs due to the evaporation of water during the autumn-winter seasons and is not compensated by the formation of condensation moisture in the summer. Due to the water evaporation, concentrations of macrocomponents and uranium, as well as the activity concentration of radionuclides ⁹⁰Sr, ¹³⁷Cs, ¹⁵⁴,¹⁵⁵Eu, ²³⁸,²³⁹,²⁴⁰Pu, ²⁴¹Am and ²⁴⁴Cm in the radioactively contaminated water increased significantly. The activity concentrations of radionuclides are ⁹⁰Sr — n ∙ 10⁹ , ¹³⁷Cs — n ∙ 10^{10, 154}Eu – n ∙ 10⁶ , ^{239 + 240}Pu – n ∙ 10⁶ , ²⁴¹Am — n ∙ 10⁷ , ²⁴⁴Cm — n ∙ 10⁵ Bq/m³ . As a result of drying out of radioactively contaminated water accumulations, highly active deposits are formed, which are a source of radioactive aerosols in the rooms of the SO. During water evaporation there is an increase of RCW alkaline, pH increases to the values of 9.5–10.2. It is due to the increase of concentration of carbonates of CO₃^2– and hydro carbonates of HCO₃^– in water. (author)