# DNPE: Nuclear Facility Safety Department

Structure of the department:

• Reactor physics sector;
• Sector of thermal hydraulics of nuclear installations.

Activities:

• development of theoretical bases and creation of programs for processing experimental data for measuring subcritical characteristics of nuclear systems by neutron noise methods, in particular in fuel-containing materials of the “Shelter” object, in spent nuclear fuel storage facilities, shut down reactors, in subcritical systems controlled by accelerators (ADS);
• development of operating principles and optimization of a new type of nuclear reactors, in particular ADS, nuclear fission reactor;
• modeling of transmutation of radioactive waste (RW) in a subcritical reactor;
• research of special materials for nuclear energy based on basalt fiber;
• investigation of pre-accident heat and mass transfer processes and hydrodynamics in critical elements and systems of basic equipment of nuclear power units, including active zones of nuclear reactors;
• computer simulation of the flow of thermophysical and thermohydraulic processes of various physical nature in the regular, pre-emergency and emergency modes of equipment operation;
• development of mathematical models, algorithmic and software to create fundamentally new methods for operational diagnostics of the current technical condition of the main equipment of nuclear power units.

Results of activities in the scientific areas:

• Reactor physics sector

Head of Sector – PhD in Engineering sciences
Mr. Volodymyr Gulik

A two-group theory of neutron noise was developed for the first time on the basis of the theory of random branching processes, which makes it possible to analyze neutron noise in systems with different neutron spectra (Mr. Pavlovich V. N., Mr. Sanzhur A. I., Mr. Storozhenko S. A.). For the systems with a thermal neutron spectrum, the results of this theory practically do not differ from the generally accepted equations of the Feynman method, but for systems with a fast neutron spectrum the results differ substantially. The corresponding expressions for the ratio of the variance to the mean (analog of the Feynman method) are obtained, suitable for processing the experimental data.

With the help of mathematical modeling based on the Monte Carlo method, the influence of the time interval in which the average and variance is calculated on the accuracy of the determination of the instantaneous neutron decay constant of experimental data (Mr. Pavlovich V.N., Mr. Podnebesnyi A.V.) was analyzed for the first time. A method for the optimal choice of such an interval is proposed directly from the experimental data without a priori knowledge of the degree of subcriticality. The influence of external noise in the form of a monochromatic obstacle, white noise, various color noises, including flicker noise, on the behavior of the Feynman curve at various time intervals is also studied. It is shown that the nonphysical behavior of the experimental Feynman curve at small time intervals can be explained by the influence of flicker noise and the “dead” time of the detector. Methods for recording various noise during the processing of experimental data have been developed.

The idea of manufacturing a special electronic device for obtaining primary information on neutron noise in nuclear materials (time recording of events) was proposed, in particular, for recording the recording time of each neutron by a detector. Such a device was developed and manufactured at the Institute for Nuclear Research, and on its basis a corresponding hardware-software complex (APC) was created in the department of nuclear physics research. It consisted of a detection unit, a signal amplification unit, a pulse analyzer, a digital oscilloscope and a personal computer. The APC was tested and tuned in the laboratory using a Pu-Be neutron source, as well as the neutron detector’s own pulses from the alpha particles of the working material of the detector (enriched uranium). The idea of using IWRM in the agro-industrial complex has a world priority and allows analyzing the sequence of pulses obtained in the measurements with the help of any theoretical approach. Methods of noise neutron diagnostics are being introduced at the Ukrainian NPPs to measure burnout of fuel assemblies.

The work of the sector’s employees also considered the possibility of creating and operating reactors built on principles different from the technological bases on which existing reactors are based. The theoretical bases of antineutrino measurements for the development of remote antineutrino diagnostics of a nuclear reactor are also considered.

The using of nuclear reactors of a new type and the introduction of precision methods for measuring the characteristics of nuclear systems will make it possible in principle to solve such basic problems of nuclear power as the problem of resources, the problem of radioactive waste and the problem of safe operation of nuclear reactors. In 1989, Mr. Feoktistov L.P. proposed the concept of a wave reactor-reactor on a wave of nuclear burning. As fuel in such reactors, depleted uranium, natural uranium, spent fuel of light-water reactors without radiochemical processing, thorium and mixtures of these materials can be used. These circumstances will solve the problem of resources. The problems of radioactive waste and safe operation of the reactor are also being solved, provided, of course, that the cooling issue in wave reactors has been thoroughly developed and solved. Mr. Pavlovich V.N. and Mr. Litvinov D.A. were working on these questions. The safety of subcritical nuclear reactors as another promising type of reactor that is controlled by an external source of neutrons is determined by this external source, and in the event of emergencies, the source of neutrons can be disconnected instantaneously. A very rigid neutron spectrum of such reactors will also allow to get rid of the most dangerous radioactive waste by their nuclear transmutation. Currently, the sector participates in the IAEA project on research of subcritical systems controlled by accelerators, Mr. Gulik V.I. actively participates in these works.

• Sector of thermal hydraulics of nuclear installations

Head of the sector – Doctor of Sciences in Engineering sciences,
Prof. Sharaevsky Igor

The main aims of the sector are the investigating of the pre-accidental thermophysical processes in critical elements and systems of basic equipment of nuclear power units, including active zones of nuclear reactors, turbo-generators, main circulation pumps, etc.; creating intelligent computer software and hardware for operational diagnostics of this equipment, providing the possibility of early automatic recognition of its potentially hazardous operation states.

Within the framework of research topics, the sector conducts and develops studies of thermal and hydrodynamic processes in the critical elements of the design of the main equipment of nuclear power units with VVER-1000 reactors. The most important and promising areas of the sector’s research are the development of mathematical models for automatic computer recognition of operational anomalies and violations in the elements and systems of the indicated equipment, as well as the creation of intelligent algorithms and software and hardware systems for improving in-system monitoring systems, as well as diagnostics and information support for operational personnel of the block control panel. At the same time, these developments are aimed at qualitative improvement of the existing systems for monitoring and diagnosing nuclear power plants (NPPs) in order to reduce the information load affecting operational personnel, based on the automation of procedures for the formation of diagnostic solutions developed by intelligent diagnostic tools. This provides a transition from existing ineffective deterministic methods for analyzing the signals of the systems for the diagnosis and monitoring of nuclear power plants, for which only the limits for changing the levels of these signals are monitored, to intelligent diagnostic algorithms, including the methodology of artificial neural networks. Obvious advantages of the proposed approach should be considered the possibility of automatic detection in real time of the initial phases of the onset of operational anomalies and damages in conditions when by modern technical means these potentially dangerous non-globular states can not yet be detected. In addition, the implementation of the developed approaches creates the necessary prerequisites for optimizing the functions of the operational personnel of the nuclear power unit for managing the nuclear power unit, provides a transition to performing repair operations of equipment based on its real technical condition, facilitating the reasonable use of its resource, reduces the time required for making operational decisions, and also minimizes the possible negative impact of the human factor on the safety of nuclear power plants.

The following fundamental scientific results were also received:

1. Based on the use of a new tool, that was created in the sector, – an intelligent computer diagnostic complex for automatic recognition of the modes of generation of the vapor phase on the heat transfer surface of fuel element, in accordance with actual operating conditions, estimates of the reliability of known empirical design dependencies for the determination of crises of the 1st and 2nd kind , as well as the boiling point of the heat carrier in the steam generating channels of various geometries, including rod assemblies with an equinoctial and unequal heat-hydraulic honeycombs.
2. The maps of the flow regimes of the vapor-liquid structures in the reactor channels that are widely used in the RELAP-5 / MOD3 thermal and hydraulic design code, as well as in other versions of the modern calculation codes for improved estimation, the main component of the operational means of complying with the operational safety of modern reactor installations, have been verified.
3. Based on the results of the automatic classification of the spectra-realizations of thermoacoustic diagnostic signals, the adequacy of the known results of investigating the structural limits separating the main classes of flow regimes of the two-phase diabatic vapor-liquid flow in the steam-generating channels is obtained.

The main scientific and technical result is the algorithmic and program support developed and tested on test problems and full-scale experimental data, which should be used by incorporating into existing systems of automatic control of NPP power units and by optimizing operating conditions. The developed methods, technical and software tools for diagnostics, monitoring and forecasting of the state of the main heat-and-power equipment of NPP units should be used in the form of a subsystem of the APCS of NPPs in Ukraine to manage their technical condition, improve safety, energy and environmental efficiency.

Main achievements:

• Publication in 2010-2017 series of monographs “Thermal physics of nuclear power plants”:
• Thermophysics of safety of nuclear power plants / A. A. Klyuchnikov, I. G. Sharaevsky, N. M. Fialko, L. B. Zimin, G. I. Sharaevsky – 2010. – 484 p.;
• Thermophysics of nuclear reactor accidents / A. A. Klyuchnikov, I. G. Sharaevsky, N. M. Fialko, L. B. Zimin, E. I. Sharaevskaya – 2012. – 528 p.;
• Thermophysics of damages of reactor installations / A. A. Klyuchnikov, I. G. Sharaevsky, N. M. Fialko, L. B. Zimin, N. I. Sharaevskaya – 2013. – 528 p.;
• Thermophysics of the reliability of active zones / A. A. Klyuchnikov, I. G. Sharaevsky, N. M. Fialko, L. B. Zimin, G. I. Sharaevsky – 2015. – 772 p .;
• Thermophysics of the resource of nuclear power plants / A. V. Nosovsky, I. G. Sharaevsky, N. M. Fialko, L. B. Zimin, G. I. Sharaevsky – 2017. – 624 p.
• Patent of Ukraine in 2010 for invention No. 32071. Computer program “Neural network software complex for automatic diagnostics of complex process equipment” (G. I. Sharaevsky).

The Monograph: The Physics of Nuclear Reactors / V. M. Pavlovich. – 2009. – 224 p.

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