The problem of coordination of short-circuit (fault) currents is considered. Data on the dynamics of variation of the levels of single-phase and three-phase short-circuit currents (their highest values) in networks rated for different voltage are presented for a long-term period. The main factors (integral parameters of the networks) affecting the values of short-circuit currents are listed. Statistics of variation of rated parameters of electrical equipment in past years and in the recent period is presented and predictions for the future are made. Basic methods and means for limiting short-circuit currents are discussed. A method of automatic and stationary network separation and a method of circuit design are described in detail. The efficiencies of different methods are compared. The effect of integral parameters of the network on the maximum level of short-circuit currents is shown. The aspects of the switching life of breakers and of allowance for probabilistic characteristics of faults and for the risk factor of decision-making are considered. It is shown that coordination of the levels of short-circuit currents is a possible means for raising the reliability of power installations and systems.Keywords: short-circuit current, coordination of levels of short-circuit currents, level of short-circuit current, limitation of short-circuit currents, parameters of electrical equipment, structure and parameters of power systems, influencing factors, standardization of parameters of electrical equipment, methods and means for limiting short-circuit currents.Statement of the problem. In different-voltage networks of power systems the level of short-circuit (fault) currents increases continuously to this or that degree. The requirements on electrical equipment, conductors, line (auto)transformers, and design of switchgears become more and more rigid. The problem of optimum agreement between the dynamics of the parameters of electrical equipment and the requirements of power systems or of coordination of the parameters of electrical equipment with the existing or expected levels of short-circuit (SC) currents becomes urgent [1].The problem is comparatively new; it appeared in the 1960 -1970s due to the rapid development of the power industry manifested by growth in the unit power of generating units, power plants, substations, and power systems rated for medium, high, extrahigh, and ultrahigh voltages. The problem should be solved by a system approach with allowance for the dynamics of variation of SC currents and parameters of electrical equipment, results of new developments in electrical power engineering, and requirements on the reliability and efficiency of operation of power systems. This is part of the more general problem of designing the structure, parameters, and operating conditions of power systems and their components, which is solved in all stages of power system control from prediction and planning to design and operation. The problem is quite complex and requires consideration of interrelated aspects. ...

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As one of the safety barriers, the main vessel of a fast reactor must be strong enough to prevent radionuclides from entering the environment during any type of accident, including hypothetical accidents. The most serious accident is an impulsive release of energy with melting of the fuel and boiling of the coolant (liquid sodium). The rate of emission of the boiling sodium from the core determines the growth of excess reactivity, i.e., the rate of energy release in an accident. Some of the energy is transferred through the sodium and the intrareactor equipment to the vessel, which in the process is subjected to dynamical loads, predominantly impulsive loads which are characteristic of explosions. Therefore, one of the most important characteristics of the strength of a vessel is its explosion-resistance.The need for engineering methods of guaranteeing nuclear power plant safety has made it necessary to study experimentally the vessel strength and to develop methodological principles for analyzing it numerically. The All-Russia ScientificResearch Institute of Electrophysical Apparatus (Arzamas-16) and the Special Office of Machine Design (Nizhnii Novgorod) have performed investigations which have made it possible to assess the static strength and explosion-resistance of the vessel of an operating BN-600 reactor and at the design stage of future reactors, and the possible consequences of impulsive loading of the reactors in a hypothetical accident. The experimental part of the investigations was directed toward the solution of several problems.1. Study of the scale effect [i] accompanying the explosive destruction of models or prototypes of the vessel. This is necessary in order to determine the validity of transferring the results of model experiments to a full-scale vessel, since it is impossible to experiment with a full-scale vessel in this manner.2, Study of the properties of chromium-nickel steel (the main material used in fast-reactor vessels) with rapid deformation, characteristic of accidents. It is well known that under a dynamical load the characteristics of steel differ substantially from the static characteristics.3. Study of the effect of the characteristics of an internal impulsive load on the behavior of the reactor vessel: character and rate of impulsive energy release (for correct simulation of energy release in an accident); degree of filling of the vessel with liquid coolant or its analog (for example, water in the case of reactors with liquid sodium); displacement of the focus of impulsive energy release from the center of the core (this degrades the explosionresistance of the vessel); and, intrareactor equipment, which strongly influences the parameters of an impulsive load on the vessel. 4. Study of the explosion-resistance of models of a vessel with detonation of high explosives in the models. 5. Estimation of the explosion-resistance of a full-scale vessel and its carrying capacity under the conditions of offdesign accidents.6. Mathematical analysis of the experiment and comparison of the ...

The main vessel of a BN-600 fast reactor is fabricated from chrome-nickel steel in the form of a thin-walled tank with a cylindrical shell, elliptic (BN-600) or spherical (BN-800) bottom, and a conical cover. The shell is connected to the bottom through a support ring, on which rests a rigid support collar, on which, in turn, the reactor equipment is mounted. The neck of the cover supports a large rotating plug. The reactor is filled with liquid sodium, and the cavity above it is filled with argon.Experimental and theoretical-computational investigations [1] have shown that the static strength of the vessel is sufficient for reliable and safe operation. However, the question of the strength during an accident under dynamical loading as a result of, for example, sudden explosive release of energy in the fuel core, remains open. Thus it is important to study the dynamic strength of the vessel. In this connection, we propose a method, which we have developed, that makes it possible to assess, on the basis of data from model explosive tests, the blast-resistance and, on the basis of these tests, the carrying capacity of the vessel in an unspecified accident.The experiment was conducted on two BN-800 models with a scale of 1:10, in one of which (model I) the intrareactor outfitting* was not modeled. The model vessels (inner radius of 643 mm; thickness of 3 mm) were welded, just as the prototype, using 12Khl8N10T steel (Fig. 1). The construction of the model, together with the simulation of the intrareactor outfitting (model II), is simplified (without increasing the carrying capacity of the vessel) as follows:the fuel core and the breeding zone, the intratank shielding, displacers, displacement pumps, elevator compartments, the pressure pipelines, the gas blow-through system, the collectors, and the accident containment vessel, are excluded; the vessel is welded using the smallest number of sheet panels; the simulators of the intrareactor outfitting are fabricated from carbon steel; the bellows are replaced by thin (0.5 mm) shells; a massive shell case, welded to the neck in order to simulate the hydraulic seal, is used for the large rotating plug; the small rotating plug and the rotating column were replaced by a single stepped hollow-core plug, bolted in the shell case; the inner radiation shielding consists of two coaxial 4 mm thick shells, welded to the supporting collar.The construction of the model-I vessel was virtually identical, but the neck was covered with a plate on bolts, the protuberances of the heat exchangers on the cover were replaced by capped pipe stubs, and the supporting collar was replaced by a massive disk with radial stiffening ribs.A diagram of the experimental arrangement is displayed in Fig. 1. The models, placed on the supports (similar to a reactor), were filled with water, the cavity above which remained filled with air at atmospheric pressure. In this manner we simulated the presence of liquid sodium and the gas cushion above it in the reactor. The high temperatures (-400-600~ and the...

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