**GF KMU1 36 months**

**Implementation period: April 2021 – November 1, 2023.**

**AP09259476 “Simulation of radiation effects and thermophysical properties in the advanced nuclear ceramics irradiated with heavy ions of fission fragment energies”**

| For modern energy, the issue of disposal of radioactive waste generated as a result of the nuclear fuel cycle remains critical. One of the perspective ways of radiotoxicity reduction is neutralization of minor actinides using special diluents (matrices) of nuclear fuel, inert to formation of radioactive isotopes and characterized by high radiation resistance, in particular, to the effects of fission fragments. The study of such effect of fission products on the properties of nuclear fuel diluents, as well as structural materials for nuclear power engineering, seems to be most convenient using the accelerated heavy ion beams decelerated in the electronic energy loss mode, since this allows varying the levels of ionization and nuclear energy losses over a wide range and provides a unique opportunity to obtain a wide range of information for the objective prediction of the long-term radiation stability of new materials. In this case, the most sensitive zone to irradiation with such ions is the near-surface region of matrices, as well as the material-fuel interface region in the multi-component and multilayer structures. It should be noted that the excess potential energy of the surface, the possible exchange of energy and particles with the environment can significantly change the response of material to irradiation with the fast heavy ions, in comparison with the bulk crystal. Therefore, experimental, analytical and numerical study of the effect of irradiation with fast heavy ions (FHI) on possible modification of massive samples, as well as areas at the interface between media in composite materials of power engineering and electronics, is a necessary and urgent task of radiation materials science. To date, the effect of fast heavy ions (FHI, Е>1 MeV/a.m.u.), despite the accumulated amount of experimental data, is still the least studied in comparison with other types of nuclear radiation. The main type of structural damage caused by FHI, and irreproducible for all other types of radiation exposure, are latent tracks. These defects are the extended disordered regions with a transverse size of several nanometers around the ion trajectory. There are practically no quantitative models in the literature that describe the stages of excitation and relaxation of a material in the track of a high-energy heavy ion, and the available approaches are not uniform for different materials. This work is intended for a quantitative study of the processes of defects formation in dielectric ceramic materials (Al2O3, Y3Al5O12, MgO, ZrO2, Si3N4) for nuclear-physical and nano-technological applications, which will enable us to consider the mechanisms of damage formation in the sample depth, on the surface and near the interface regions in dynamics of their development. Structural-phase changes in ceramics around the ion trajectory are supposed to be studied using the previously developed quantitative approach, which combines the Monte Carlo model for describing the excitation of the electronic and ionic sub-systems and modeling by the molecular dynamics methods. The simulation results will be compared with transmission electron microscopy data and used to evaluate the change in the thermal conductivity of materials after irradiation. The results obtained during implementation of the project can be used as the basis for new methods for designing the structure of ceramics (including composite ones) for inert fuel matrices and transmutation of minor actinides, and will also allow developing new approaches for creation of the promising materials with high radiation resistance and corresponding thermo-physical properties. The further prospect of using such materials covers innovative energy, rocket and space technology and various branches of general and special engineering. |

| ## Quantitative study of the mechanisms of defect formation and analysis of available micro-structural data on radiation resistance in candidate materials of inert diluents (matrices) of nuclear fuel based on nitrides and oxides in relation to the impact of high-energy heavy ions, simulating irradiation with fission fragments. |

| ## The main result of the project implementation will be a description of the mechanisms of excitation of the electronic and ionic subsystems and their subsequent relaxation in the surface region of the perspective nuclear power materials (Al2O3, Y3Al5O12, MgO, ZrO2, Si3N4) in fast heavy ion tracks simulating the impact of fission fragments. Determination of the dependences of the structural response of these materials to the introduced excitation on the parameters of the incident ions and the basic properties of solids.## As a result of the project, the multi-scale model will be completed, quantitatively and without the use of fitting procedures describing the kinetics of excitation of the electronic and ionic sub-systems of materials in FHI tracks. The original Monte Carlo model (TREKIS) will be upgraded: transition from cylindrical to three-dimensional geometry; transition from the method of asymptotic trajectories to integration of the equations of motion of charged particles. The use of a new version of the Monte Carlo model will make it possible to obtain the space-time distributions of electrons and holes density and their energies in the FHI track depending on the distance from the sample surface for various geometries, including inhomogeneous structures: in layered materials and materials containing nanosized inclusions of different composition, phase and structure.## Thus, the input parameters will be obtained – the initial conditions for applying the methods for describing lattice relaxation, in particular, the molecular dynamics program (LAMMPS) will be used for describing the following:## 1) Relaxation kinetics of the material lattice and the final structure in bulk samples and their near-surface layer under irradiation at different angles.## 2) Mechanisms of damage formation (crystalline and amorphous nanosized bumps, extended nanostructures formed by irradiation at small angles) on the surface of samples at different parameters of FHI irradiation.## 3) Processes of nanometer-sized defective regions formation in inhomogeneous structures (layered composites, nanosized inclusions).## 4) Change in the thermal conductivity of the studied materials after irradiation. |

| As a result of the study, the original Monte Carlo model was modernized to take into account the processes that occur during interaction of ionizing radiation with surface and near-surface layers of solids. The spatial-time dependences of the excitation parameters of dielectric materials (Al2O3, Y3Fe5O12, MgO, ZrO2, Si3N4) irradiated by heavy ions with fission fragment energies was calculated. The dielectric function of Y3Fe5O12 was selected and tested, which was then used to calculate the cross sections for interaction of charged particles with materials. The interatomic potentials for Al2O3 and Y3Fe5O12 were selected and tested. The modeling of structural damage, caused by FHI, by the method of molecular dynamics in the bulk samples and near the surface of dielectric materials was completed, and the structure of the tracks was analyzed. As a result of the project, the dependence of the thermal conductivity of Al2O3 on the ion fluence was studied for the first time using numerical methods without adjustable parameters. The effect of different track regions on degradation of thermal conductivity after irradiation was studied. – Published: 1 article in the journal included in Q1 according to JCR Web of Science |

| ## 1) Project Manager – Senior Researcher, Rymzhanov R.А. (http://orcid.org/0000-0002-7404-9769); Scopus ID 55648728100## (https://www.scopus.com/authid/detail.uri?authorId=55648728100)## 2) Researcher, Ibrayeva А.D.## (https://www.scopus.com/authid/detail.uri?authorId=55637013100)## 3) Senior Researcher – Volkov А.Е. (Research Center «Kurchatov’s Institute», Moscow, Russia)## (https://www.scopus.com/authid/detail.uri?authorId=55938916900)## 4) Engineer – Mutali А.К.## (https://www.scopus.com/authid/detail.uri?authorId=57216340812)## 5) Engineer – Temir Ә.M.## 6) Engineer – Kurahmedov А.Е.## 7) Engineer – Ungarbaev Е.О. |

| ## Kurakhmedov, A.E.; Alin, M.; Temir, A.M.; Ivanov, I.A.; Bikhert, Y.V.; Ungarbayev, Y.O.; Zdorovets, M.V.; Kozlovskiy, A.L. Study of the Effect of Doping ZrO2 Ceramics with MgO to Increase the Resistance to Polymorphic Transformations under the Action of Irradiation. Nanomaterials 2021, 11, 3172. https://doi.org/10.3390/nano11123172 (ИФ – 5.076) |