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Source: Novosibirsk State University – Novosibirsk State University – Novosibirsk State University

Researchers of the CCP “Accelerator Mass Spectrometry NSU-NSC” NSU Physics Department together with their colleagues from the Ural Federal University named after the first President of Russia B.N. Yeltsin and the Institute of Industrial Ecology of the Ural Branch of the Russian Academy of Sciences are studying the level of C14 content in annual rings of trees in the area of nuclear power facilities. The Ural scientists take samples in the areas adjacent to the nuclear power plants, while the researchers from NSU prepare samples and conduct radiocarbon analysis of the provided samples on a gas pedal mass spectrometer.

Scientific cooperation began in 2020, when Evgeny Nazarov, a graduate student of the Ural Federal University, sent plant samples collected in the vicinity of the Belarusian Nuclear Power Plant during the pre-operational period to the Accelerator Mass Spectrometry Center of the NSU-NRC. The need for these studies arose to determine the background indicators of C14 content in environmental objects in this area.

C14 is one of the naturally occurring radioactive isotopes. It is formed in the upper layers of the troposphere and stratosphere as a result of absorption by nitrogen-14 atoms of thermal neutrons, which in turn are the result of interaction between cosmic rays and atmospheric matter. In the twentieth century, the major anthropogenic source of 14C was nuclear weapons testing between 1945 and 1980. Currently, the main anthropogenic sources of this radionuclide are nuclear reactors and irradiated fuel reprocessing plants.

The joint work of Novosibirsk and Ural scientists continued with the study of C14 content in annual rings of pine trees growing in the area of Beloyarsk NPP and the Institute of Reactor Materials (Zarechny, Sverdlovsk region), located on the same industrial site.

– The sampling site, located 1200 meters eastward from the Institute of Reactor Materials, was chosen by us based on long-term observations of meteorological parameters: wind direction and strength, cloud cover, precipitation, atmospheric pressure, etc. Based on these data, we determined where exactly theoretically could occur the greatest accumulation of radiocarbon in environmental objects. Further, having calculated the critical area of the terrain, where the maximum radiation impact from nuclear reactor emissions is realized, we selected about 10 pine trees aged from 40 to 70 years and took samples of their wood in the form of cores with a diameter of 5 mm using a Pressler drill at a height of about 130 cm from the soil surface. We carried out this work together with researchers from the Institute of Plant and Animal Ecology of the Ural Branch of the Russian Academy of Sciences. The obtained cores were divided into annual rings. Rings of the same age from ten trees were combined into one sample corresponding to a certain year. We selected 15 different samples for analysis,” said Evgeny Nazarov, a junior researcher at the radiation laboratory of the Institute of Industrial Ecology of the Ural Branch of the Russian Academy of Sciences, Candidate of Technical Sciences.

Novosibirsk scientists had to determine the level of C14 content in these samples and compare them with background values, which were used as data on the activity of this radionuclide in the annual rings of 113-year-old pine trees from the Pirogovsky forest, located near NSU in Akademgorodok, Novosibirsk. This choice was conditioned by several factors. Firstly, both cities – Zarechny and Novosibirsk – are located at approximately the same geographic latitude, and, secondly, Novosibirsk is located at a considerable distance from currently operating and ever-operating nuclear facilities, which means that it was not exposed to anthropogenic sources of radiocarbon, except for nuclear weapons tests. The C14 values in the annual rings of this pine tree corresponded to the average background data for the northern hemisphere.

– We chemically isolated cellulose from pine annual ring samples sent for research by our Ural colleagues and subjected it to graphitization. The obtained graphite-containing targets were placed in a gas pedal mass spectrometer and the concentration of C14 was measured. We analyzed the content of this radionuclide in 30 counting samples (two samples per one year), and in all cases we recorded an excess over the background level by one and a half to two times. And we noticed that starting from 2000s the concentration of C14 in annual rings began to decrease and almost did not exceed the background level. We attribute this fact to the improvement of equipment and the installation of afterburning reactors at nuclear power plants,” explained Ekaterina Parkhomchuk, Director of the Accelerator Mass Spectrometry Center at NSU-NRC.

A similar study was conducted on samples taken in the vicinity of the Kursk nuclear power plant (Kurchatov, Kursk region), which yielded similar results.

– Obtaining information on the content of C14 in each annual ring, we calculated the difference between the anthropogenic and background components, taking into account the correction for its background content. In our opinion, it is caused by the operation of a nuclear power plant or a facility for the use of nuclear energy. Using these data, we were able to calculate the approximate amount of C14 that entered the environment each year during their operation, as well as to estimate the annual effective doses to the population since the 70-80s of the last century. These calculations show that the impact of C14 is negligible. Nevertheless, the data obtained make it possible to estimate this impact from the radionuclide release due to past operation of nuclear industry facilities. This is especially relevant for facilities that were decommissioned before the introduction of mandatory monitoring of C14 in Russian NPP emissions less than 10 years ago. Thanks to this information we can estimate the amount of C14 that was released into the environment as a result of operation of this or that power unit and the whole enterprise during its entire life cycle. The UMS method allows us to perform such studies and we have obtained such unique data for the first time in our country,” said Evgeny Nazarov.

Based on the results of these studies, scientists have published a number of articles in several scientific publications. The joint work of Novosibirsk and Ural scientists continues. The Radiation Laboratory of the Institute of Industrial Ecology of the Ural Branch of the Russian Academy of Sciences sent samples of annual rings taken from areas adjacent to the Bilibino nuclear power plant (Bilibino, Chukotka Autonomous District) to the Accelerator Mass Spectrometry Center of the NSU-NSC. Scientists intend to make a retrospective assessment of C14 emissions from this power plant.

– Operation of any nuclear power plant results in radionuclides entering the environment. This cannot be completely avoided, but by using various filters and purification systems it is possible to minimize radionuclide releases. It is important to clarify that the samples were taken at critical points where the population does not permanently reside. In addition, C-14 is the second most important source (after potassium-40) of unrecoverable intrinsic radioactivity in the human body. It is known that the total internal radioactivity in the human body is 5 times higher than the radioactivity from the radiocarbon contained in it, and the external radioactivity is even several times higher, so a two-fold excess of background radiocarbon in the environment does not carry and, as the experience of the last century showed, did not bring negative consequences for humans, – explained Ekaterina Parkhomchuk.

The described study, which allows retrospective assessment of radiation impact of nuclear reactors on biosphere objects, was conducted for the first time in Russia and became possible only due to the development of UMS in Novosibirsk. The great potential of the UMS method lies in the possibility of analyzing a whole range of rare isotopes, not only radiocarbon, but also Be-10, Al-26, I-129 and others, which is impossible by any other methods and gives unique information. We can only hope that Russian gas pedal mass spectrometry complexes will continue their development and will be in demand for a wide range of fundamental and applied tasks.

The publication was prepared by Elena Panfilo, NSU Press Service.

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Please note; This information is raw content directly from the information source. It is accurate to what the source is stating and does not reflect the position of MIL-OSI or its clients.

EDITOR’S NOTE: This article is a translation. Apologies should the grammar and or sentence structure not be perfect.

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