Radionuclides contamination of leaves of woody plants growing within the CHNPP cooling pond

The data on the state of radioactive contamination of leaves of plants growing directly on the territory of the drained part of the cooling pond of the Chernobyl NPP are presented. It was shown that the main source of contamination is the root intake of radionuclides (137Cs and 90Sr). This contamination is larger in previously drained areas compared to recently exposed ones. Hot particles were found on the leaf surface by autoradiography. Their total β-activity is a few percent of the total pollution. Possible sources of hot particles – resuspension in the air in the region of the northern part of the cooling pond are discussed.

The nature of Pu-bearing particles from the Maralinga nuclear testing site, Australia

The high-energy release of plutonium (Pu) and uranium (U) during the Maralinga nuclear trials (1955–1963) in Australia, designed to simulate high temperature, non-critical nuclear accidents, resulted in wide dispersion µm-sized, radioactive, Pu–U-bearing ‘hot’ particles that persist in soils. By combining non-destructive, multi-technique synchrotron-based micro-characterization with the first nano-scale imagining of the composition and textures of six Maralinga particles, we find that all particles display intricate physical and chemical make-ups consistent with formation via condensation and cooling of polymetallic melts (immiscible Fe–Al–Pu–U; and Pb ± Pu–U) within the detonation plumes. Plutonium and U are present predominantly in micro- to nano-particulate forms, and most hot particles contain low valence Pu–U–C compounds; these chemically reactive phases are protected by their inclusion in metallic alloys. Plutonium reworking was observed within an oxidised rim in a Pb-rich particle; however overall Pu remained immobile in the studied particles, while small-scale oxidation and mobility of U is widespread. It is notoriously difficult to predict the long-term environmental behaviour of hot particles. Nano-scale characterization of the hot particles suggests that long-term, slow release of Pu from the hot particles may take place via a range of chemical and physical processes, likely contributing to on-going Pu uptake by wildlife at Maralinga.

To a Burst of 137Cs Activity in the Air under the “Arch” Object on October 17, 2019

The construction of a New Safe Confinement (NSC) is one of the main stages in the transformation of the Chornobyl nuclear power plant 4th power unit into an ecologically safe system. On the one hand, this system is designed to ensure the safety of personnel, the population and the environment, on the other — to allow safe work with the remnants of the unit. At the same time, the project allows quite high levels of bulk activity of radioactive aerosols inside the NSC — up to 210 Bq/m3 for total β-activity. The sharp increase in the volumetric air activity, observed on October 17–19, 2019 in a number of rooms of the Shelter object and in the space under the “Arch” object in the absence of a burst of activity outside these objects, can be considered as a successful kind of spontaneous test of the NSC isolation systems. The chronology of the dynamics of volume activity according to the act of official investigation of the precedent is given. The results of studies of aerosol filters exposed in the near zone of the Chornobyl NPP before and after the burst of activity in the air under the “Arсh” object are presented. Autoradiograms of fragments of these filters demonstrate a significant (≈2 orders of magnitude) increase in the number of hot particles immediately after the fall of the concrete fragment of the floor in the room 402/3. The analysis of features of the hot particles after the collapse indicates a significant contribution to the total activity of a large number of low-activity particles (0.005÷5 Bq), and the low 137Cs/241Am ratio that indicates their fuel nature. Based on the assumption about the fuel nature of hot particles, their minimum possible aerodynamic diameters were calculated, which are in the range 2.91<d<36.7 μm, which does not exclude the presence of smaller hot particles on the filter that are not visible using this method. The contribution of particles with aerodynamic diameters less than 10 μm, determined using the impactor, did not exceed 20% of the total beta activity of the aerosol.

Fuel particles in consequences of the accident at the ChNPP

As a result of the nuclear explosion at the fourth block of the Chornobyl NPP (ChNPP), the radioactive cloud containing an aerodispersed system with aerosols formed at the explosion appeared in air above the ChNPP territory. The accident occurred at the end of the reactor company before the assumed reloading of the active zone. Thus, the cloud composition included the products of fission and activation of uranium that were accumulated in the reactor fuel during the company. On that night, the east wind carried the radioactive cloud to the west, by leaving the aerosol fallouts on Earth’s surface as a radioactive trace. The results of the own studies (1986–1990) of aerosol fallouts on the west trace formed at once after the explosion at the ChNPP are presented. On this basis, the characteristics [physico-chemical forms, radionuclidic composition, activity median aerodynamic diameters (AMADs), etc.] of the aerodispersed system created at once after the explosion of the active zone of the reactor are reconstructed. In the frame of the respiratory model given in ICRP Publication 66, the contributions caused by the inhalation of fuel particles (microscopic particles which are fragments of exploded fuel elements and have conserved mainly their radionuclidic characteristics) to the doses of irradiation of parts of respiratory organs and gastrointestinal tract (GIT) are evaluated. It is shown that the cause for a mass cough in the summers of 1986 and 1987 on territories underwent the action of emergency fallouts was the inhalation of radionuclides of ruthenium in the form of RuO4 that was formed in “hot” particles contacting with air and then evaporated from them. The “hot” particles are compact inclusions formed by fission products. They consist mainly of atoms close to noble metals (molybdenum, ruthenium, rhodium, etc.) formed during a regular operating period in fuel tablets and released from the latter at the explosion of the active zone. The reasons for the disagreement between the clinic consequences and the ascribed values of the dose for the sufferers who were present in premises of the NPP at the emergency time and then died from acute radiation sickness in three-four weeks after the accident are explained.