– materials science of structural materials, operating and promising nuclear and thermonuclear power plants;

– modern simulation experiments, simulation of radiation exposure in structural materials;

– scientific support for the extension of service life for Ukrainian NPP by determining the real state of residual life for the metal of the main equipment of power units;

– studying the effect of microstructural changes induced by hydrogen and helium on the physical and mechanical properties of structural materials.

For the first time, the results on determining the parameters of swelling in structural materials at ultrahigh radiation doses and ultrahigh concentrations of transmutant gases (helium and hydrogen) were obtained. It was established that the behavior of radiation swelling for ferritic-martensitic steels depends on the concentration of helium and hydrogen, which have different effects on the kinetics and magnitude of swelling at different stages (in the incubation period and at the stationary stage).

During the incubation period, helium increases the swelling due to the earlier nucleation of pores. At the stationary stage, helium reduces the swelling, as their size is significantly reduced at high concentration of pores.

In various materials, the effect of helium tends to be similar. Like helium, hydrogen is also effective in accelerating the onset of swelling, but has less effect on pore nucleation. This can even lead to the increase in swelling at the stationary stage due to a moderate increase in the pore concentration. The results expand the understanding of fundamental radiation phenomena and associated radiation consequences, such as swelling and phase instability, as well as the use of this knowledge to develop radiation-resistant alloys for future reactor generations.

T_irr = 480°C

T_irr = 450°C

The effect of radiation damage on the retention and release of hydrogen and helium from austenitic and ferritic-martensitic steels was studied. It was shown that the main factor in the retention of helium is its energy binding with defects. The efficiency of deuterium capture in the region of displacement damage is decreased by two orders of magnitude at the increased irradiation temperatures.

At the power units of the South Ukraine (SU) NPP, the work on the diagnostic control of the metal for the equipment and pipelines was carried out. The main reasons and mechanisms for the fracture of welded joints No.111 between the collector and steam generator casing were found. The leading role of hydrogen, copper and manufacturing technology in the formation and development of discontinuities under the conditions of long-term operation was shown. It was established that in the sludge deposits of the VSG–1000 steam generato (SU NPP power unit No.3), the copper content under the morpholine regime is 5 – 7 times lower than under the standard ammonia water-chemical regime.

The experience gained in the diagnostics and control of the metal for the equipment and pipelines of NPP is used to solve the problems of thermal power plants (TPP). It was found that the reason for boiler destruction at the Starobeshevskaya TPP (power unit No.5) during the low-temperature tests was the increase of the ductile-to-brittle transition temperature of steel up to 70°С during long-term operation. Using the method of microsamples without violating the strength and integrity of the product, the ductile-to-brittle transition temperature of the boiler drum for the Lugansk TPP (power unit No.9) was determined and its performance was substantiated when the service life was extended.

In order to determine the causes and mechanisms for the formation of "internal" discontinuities (without through cracks), for the first time, the studies were carried out using the sample cut out during the repair of the welded joint between the collector and steam generator casing (No.111) at the SU NPP power unit No.3. It is shown that the initiation and development of defects starts with the inclusions of silicon carbide added to the metal during welding. It is from these inclusions that cracks develop when the power unit is cooled at a high speed. A slow controlled shutdown of the power unit during scheduled preventive maintenance in the cold season is recommended.

To substantiate the safe operation of the NPP reactor vessel, the optomechanical module was developed, manufactured and tested at the SU NPP stand for the simultaneous determination of residual stresses and hardness of the WWER–1000 reactor vessel metal. The method will be implemented as the operational control of reactor vessels, equipment and pipelines of Ukrainian NPP power units.

Deuterium retention in steel 316 on various defect structures

Using a special complex of methods, the data on the evolution of the defect microstructure and accumulation levels were obtained, as well as on the temperature range for the content of gas impurity atoms in austenitic and ferritic-martensitic steels. The thermodynamic parameters of the "metal-helium" and "metal-hydrogen" systems were determined. A significant content of hydrogen in traps associated with helium bubbles and voids was determined. This confirms the data obtained for the stainless steels irradiated in light-water reactors.

For the first time in world practice, studies on the evolution of structural and phase changes in metal were carried out using the metal for the main circulation pipeline (MCP) of WWER–1000 reactor after 32  years of operation by the advanced direct methods. The following signs of metal aging after long-term operation were found: structural changes both in the average grain size and composition of granular and lamellar pearlite. The decrease in the average size of carbide precipitates and their location at grain boundaries were revealed. The results of monitoring the mechanical properties and impact toughness (without violating the MCP integrity), together with the structural studies, made it possible to extend the service life of MCP for the SU NPP power unit No.1 until 2031 (technical solution ТР.1.0019.3827 dated 02.12.2016).

A device for determining the ductile-to-brittle transition temperature using small samples was developed, manufactured and tested. The samples were cut out at the operating NPP and TPP power units without violating the integrity and strength of equipment and pipelines. The device allows identifying the risk of occurrence and spread of brittle cracks.

Corrosion of steel 20 in the standby mode

The causes of leakage for the service water pipelines of responsible consumers at SU NPP were established. It is shown that the presence of excess amount of non-metallic inclusions in steel st. 20 for modern production results in the formation and development of corrosion defects, as well as in the subsequent destruction of pipes. It is also shown that the metal magnetic memory method makes it possible to control not only defects, but also the presence of non-metallic inclusions in pipes.

The control of the structure and properties for the ferrite-pearlitic steels st. 20, st. 16GS was carried out after 30 years of operation in the heat exchange system of the first SU NPP power unit. The methods of light, electron microscopy and temperature-dependent internal friction in pipe steels revealed changes in the pearlite substructure, which cause the development of local corrosion and destruction of the pipelines under operating conditions. It is proposed to modernize the current procedures for zonal-periodic monitoring of the heat exchange equipment for WWER–1000 power unit by improving the methods of temperature-dependent internal friction and metal magnetic memory.

Microstructural studies, data on electrical resistivity and hydrogen desorption from the base metal for the "cold" thread of the MCP circulation loop for the SU NPP power unit No.1 show the removal of impurities from the grains and their concentration along the boundaries. The increased concentration of impurities along the grain boundaries is also shown by the increase in the internal friction peak.

Dependence of hydrogen thermal desorption rate

Internal friction

Thin-film (V, Te, Mg) nanocrystalline porous Nx absorbents capable of accumulating more than 7 wt.% hydrogen in a short period of time (up to 100 s) at a relatively low pressure (0.3 – 0.4 MPa) were created and investigated. The gravimetric and kinetic characteristics of the films meet the requirements of the US Department of Energy (DOE).

For the first time, the influence of sink strength on the swelling of oxide dispersion strengthened (ODS) austenitic steels under irradiation with heavy ions was established. It is shown that the addition of ZrO₂ and Y₂O₃ nano-oxides in the manufacture of ODS steel results in a significant decrease of the grain size and precipitation of secondary oxides. Also, the uniformity of oxide distribution over the sample is increased. A decrease in the grain size and precipitation of secondary oxides results in swelling decrease by more than 5 times. Swelling suppression is explained by the increase in the probability of point radiation defect recombination for the sinks, which are the “nanooxide-matrix” interfaces and grain boundaries. In this case, sink strength due to oxides is ∼ 4.86×10¹⁴ m^-2, which is almost 35 times greater than the sink strength (∼ 1.41×10¹³ m^-2) provided by the grain boundaries with their average size at the level of ∼ 1.2 microns.

Based on the statistical analysis of the data for the long-term monitoring of heat-exchange tubes (HET) for the SU NPP steam generators and metallurgical studies, the mechanism for the most of the operational damage to the tubes is established: cracking under the action of corrosion fatigue. Crack nuclei are nonmetallic inclusions of titanium carbonitrides on the surface of HET (08Х18Н10Т). Crack growth is stimulated by tensile stresses arising as a result of tube vibrations in the attachment points. Proposals for optimizing the control of HET were substantiated, approaches to plugging defective HET were proposed.

Using a number of experimental techniques (which make it possible to numerically control the kinetics of accumulation, volume distribution and thermally activated desorption of ion-implanted gas atoms), it was first established that the behavior of hydrogen, its mass transfer and accumulation in structural steel 316 are determined by the complex effect of the radiation-induced structure, the state surface and the presence of helium. For the first time, a correlation was established between the structure being developed upon irradiation and the level of hydrogen isotope accumulation. It was shown that the concept of using strong "useful" hydrogen traps capable of reliably retaining hydrogen throughout the entire service life of a nuclear object in the entire operating temperature range is of key importance to neutralize the harmful effects of hydrogen and increase the resistance of materials to hydrogen degradation in the event of exposure to thermo-radiation fields.

Critical levels of hydrogen storage

Energy of hydrogen binding with traps

It was shown for the first time that the radiation hardening of the steel 316 caused by the conservative nature of Frank loops restraining the motion of dislocations is a function of the radiation dose and reaches quasi-saturation with the radiation damage at the level of ∼ 1 dpa. Helium and hydrogen, when implanted to the concentrations of more than 1 at.%, increase the strength by 20 – 30% due to the dislocation component. These two factors (Frank loops and helium/hydrogen) increase the strength and yield strength by ∼ 1.8 times. The obtained results are the step towards the development of the fundamental principles for the correlation between the mechanical properties and radiation-induced microstructure of materials, which is developed under various radiation effects.

Dose dependence of hardening

– Laboratory for electron microscopic studies of irradiated materials.

Investigation of the mechanisms for structural and phase evolution of nuclear-power materials under radiation exposure. Development of the principles for producing materials with high radiation resistance.

– Laboratory of Physics of Ion Beam Interaction with Materials.

Experimental research on the properties of solids being under the influence of plasma and charged particle beams. The research subject is: radiation damage; helium and hydrogen concentration; patterns of defect formation; ion-induced transformations; radiation phenomena depending on the irradiation characteristics and conditions.

– - Laboratory for reactor testing of new materials and investigation of vessel materials.

Performance of work at NPP power units of Ukraine for ensuring safe operation of the metal for equipment, pipelines and service life extension.

– Sector for the development of layered metals and bimetals.

Use of the the vacuum hot rolling method to manufacture the composite materials and products with extremely improved physical and mechanical characteristics. Research and development of the transitional "refractory metal/steel" bimetals, "high-speed steel/structural steel" bimetals, multilayered radiation-absorbing composites, nanostructured composites for various functional purposes.