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 ∙ 1010, 154Eu – n ∙ 106, 239 + 240Pu – 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, рН 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.

The results of five-year studies in Shelter subreactor rooms are summarized. At height elevations from 0 to 12 m, the mean volume activity (VA) of 212Pb-bearing aerosols is about 10 Bq m−3. The main source of 220Rn and of its daughter 212Pb is 232Th contained in the building structures. The maximal 212Pb VA is observed in the warm period of a year, and the minimal VA, in the cold period. In ventilation releases through the Bypass system, VA of 212Pb is 4–5 times lower than in subreactor room. The activity median aerodynamic diameter (AMAD) of 212Pb-bearing aerosols in most cases was within the range 0.06–0.4 µm. During works in subreactor space, the irradiation via 212Pb inhalation can amount to 3–5% of the annual effective dose limit (20 mSv) adopted in Ukraine.

An adsorbent for Cs removal from contaminated water based on phosphotungstic acid (PTA) embedded in SiO2 network was synthesized and granulated with γ-Al2O3. PTA/SiO2 had a high adsorption capacity towards Cs while the binder provided excellent mechanical characteristics of the material. It was shown that small particles of PTA/SiO2 with the sizes of 0.1–1 µm occupied space between larger particles of the binder (up to 5 µm). Chemical interaction between PTA and γ-Al2O3 during the adsorbent preparation also took place. The obtained porous material with the specific surface area of 286.9 m2/g contained 4.73% of PTA. Presence of Keggin units in the structure was confirmed by solid state NMR spectroscopy. Study of the adsorbent in Cs+ adsorption from solutions demonstrated its high adsorption capacity. The concentrations of Cs+ in the solutions after the column tests decreased by 3.3–5.2 times. The presence of Na+ and K+ as competing ions did not affect the adsorption. The material was tested in clean-up of radioactive water from the shelter of Chernobyl nuclear power plant (Ukraine). A significant decrease of 137Cs radioactivity was detected in all samples of radioactive water, especially in acidic solutions. Thus the adsorbent can be used for water treatment after incidents resulting in release of radioactive isotopes 134Cs and 137Cs.

Представлены радионуклидный состав и объемные активности аэрозолей в 2017-2018 гг.в помещении 012/15 объекта «Укрытие».Пробы отбирали в 5 м от северного края лавообразных топливосодержащих материалов (ЛТСМ).Установлено, что суммарная концентрация аэрозолей-носителей 90 Sr + 90 Y и 137 Cs колебалась в диапазоне 0,025-4,5 Бк/м 3 .При этом на долю 137 Cs приходилось 54 %.Гамма-спектрометрические измерения и радиохимические анализы показали, что усредненные отношения труднолетучих радионуклидов-продуктов аварии 4-го блока Чернобыльской атомной электростанции в аэрозольных пробах соответствуют составу ЛТСМ в помещении.Это свидетельствует о процессе деструкции ЛТСМ и частичном переходе материалов в аэрозольное состояние.Их носителями были

During studies performed in 2010–2014, in the under-reactor rooms and deaerator stack of the sarcophagus at the Chernoby NPP, the average volume activity of radon was ~100 Bq/m3 and the average coefficient of equilibrium of radon and its daughter products was ~0.7. The maximum volume activity of radon reached 666 Bq/m3. The daughter products complicate radiation monitoring of the aerosol situation. In the inspected rooms of the under-reactor space and deaerator stack, the radiation exposure of workers due to inhalation of radon, thoron, and their daughter products can exceed 10% of the maximum admissible effective dose. It was determined that the carrier aerosols of the daughter products are submicron aerosols with active median aerodynamic diameter ~0.1 μm. The arch erected above the sarcophagus at the end of 2016 can degrade the radon radiation situation because of reduction of the natural ventilation.

Data on the radionuclide composition, volume activity, and dispersity of aerosols taken in 2010–2014 using Petryanov’s filters in rooms 012/7, 012/15, and 210/7 of the Shelter object, into which the lava-like fuel-containing materials (LFCMs) flew after the accident, are presented. In room 012/7, the volume activities of aerosols carrying the Chernobyl accident products are higher by an order of magnitude than those in rooms 012/15 and 210/7. In all the rooms, the carriers of the radioactive products of the accident are, as a rule, aerosols with the activity median aerodynamic diameter larger than 1 µm. This value suggests the dispersion origin of the aerosols. In room 012/7, the aerosols are larger than in the other two rooms. The identity of the radionuclide composition of aerosols and LFCMs in room 012/7 shows that aerosols arise from the degradation of the lava. Considerable difference in the radionuclide compositions of aerosols and LFCMs in rooms 012/15 and 210/7 shows that the lava degradation in these rooms is less intense and that the aerosol generation from the lava surface does not influence the radionuclide composition of aerosols.

Presented are the results of observations of the impact of fog and haze on the operation of filtering units for the sampling of radioactive aerosols in the process of monitoring radiation conditions in the Chernobyl exclusion zone. It is revealed that the performance of installations decreases in the case of the formation of fog and mist (as a rule, at the relative air humidity of more than 90%). This is associated with the settling of finest water droplets on the fibers and with the clogging of the filter. As the fog disappears, the droplets evaporate from the filtering fibers and the performance of the unit increases. In the case of fog and haze at night in November 2012, the performance of AURA-02.11 installation decreased almost by three times as compared with the initial one. To reduce the negative impact of fog and haze on the operation of units, it is reasonable to use the filters made of hydrophobic fibers.

Decontamination of liquid radioactive waste (LW) from transuranium elements (TUEs) and uranium by complexation with phosphorus-containing and guanidine phosphate oligoethers and by ultrafiltration was studied. The rejection coefficient of TUEs and U on these oligomers reaches 99.0–99.6% of the initial concentration.

At present, the direct radiation exposure to the environment from the 4 th block of the Chernobyl plant has been reduced significantly due to radioactive decay. However, the molten fuel material within the concrete shelter, the so-called “Sarcophagus”, is continuously releasing atmospheric aerosols, mostly due to the crystallization of the amorphous lava-like materials, fastened by its radioactivity and the repelling of these micro-crystals due to electric charging of the surface layer of the lava because of the alpha-radioactivity. These aerosols might at present constitute the major hazard from Chernobyl, not only locally but also over distances of many hundreds of km. Analysis of the aerosols can give important information to research and forecast of substance properties and state of materials containing the nuclear fuel.

In 2003–2007, the content of 212Pb (220Rn daughter product) inside the Shelter was, as a rule, in the range 0.5–5 Bq m−3. No seasonal and time dynamics of the 212Pb concentration and no relationship with the technical activity were revealed. At simultaneous sampling of aerosols, the volume activities of 212Pb in the bypass were higher by 1–2 orders of magnitude than in the surrounding medium (local zone). Hence, the sources of 220Rn emanation, in particular, 232U are inside the Shelter. Among 220 samples taken in the bypass, 94% had the activity median aerodynamic diameter of aerosol particles bearing 222Rn and 220Rn daughter products in the range from 0.05 to 0.4 μm. For the Shelter staff members, 222Rn and 220Rn daughter products, and also submicron size of their carriers are negative factors which were not taken into account previously when determining ionizing irradiation doses. The additional inhalation doses can reach tens of percents of the permissible annual dose.

The volume activity of 90Sr, 137Cs, 238Pu, 239+240Pu, 241Am, and 244Cm in water taken from unorganized water accumulations on lower marks of the Shelter was determined. Separate water accumulations are characterized by their specific radionuclide activity ratios 238Pu/239+240Pu, 241Am/239+240Pu, and 244Cm/241Am. The activity ratios 241Am/239+240Pu and 244Cm/239+240Pu in the water accumulations are 5–10 times higher than in the irradiated fuel of the 4th Unit of the Chernobyl NPP and in lava-like fuel-containing materials.