An original method to determine the onset of conditions for reliabilitycritical hydraulic impacts for reliability analysis of active safety systems of nuclear power installations is proposed. The suggested method is based on determining the effect of head-flow characteristic delay onto hydraulic impact preconditions during the changes of pipeline system hydrodynamic parameters under transitional modes (e.g. in pump start-up). The delay time of responses to change in the hydrodynamic system parameters embodies the determining factor of head-flow characteristic’s inertance, depending on both design and technical parameters of system components (including pumps), and the hydrodynamic parameters change rate under transitional modes. Using the proposed method, the analysis of conditions for critical hydraulic impacts is performed for the primary high-pressure safety injection system of serial WWER-1000 nuclear power plants. The analysis results allow a conclusion that for this system the conditions leading to hydraulic impact due to the pump start are not reached. The developed method can be applied to any thermal and nuclear power facilities’ pipeline systems equipped with pumps.
The analysis of well-known studies in modelling conditions for water hammers in equipment and components of pipeline systems has revealed that definition of conditions and parameters of water hammers in the transonic modes of single-and two-phase flows (at a speed of propagation of acoustic disturbances) is the least studied problem.The original method is proposed for determining the conditions and parameters of water hammers in transonic flow modes subject to the transition of the kinetic energy of the flow stagnation into the energy of the water hammer pulse.It was found that the simulated hydrodynamic loads in transonic modes can significantly exceed the corresponding known recommendations of N. Zhukovsky.The proposed method of equations computer modelling served to determine the criteria range for water hammers due to aperiodic thermohydrodynamic instability in transonic flow modes. K e y w o r d s: water hammer, transonic modes, head-flow characteristic.
Results of known experimental and computed studies of conditions for water hammers (WHs) in reactor pressurizers are analyzed. It is found that when emergency opening of pilot-operated safety valves of the pressurizers of nuclear reactors happens, WHs can be generated on pressurizer elements, and amplitudes of hydrodynamic load pulses significantly override the limiting values. An original method for determination of the WH conditions and consequences in the case of emergency filling of the pressurizers of nuclear reactors is proposed. Unlike the traditional Joukowski formula, the presented method considers the key features and effects of the WH conditions and consequences in the pressurizers of nuclear reactors. The results of computer modeling of the maximum amplitudes of a pressure pulse of WHs using the presented method are in satisfactory agreement with Korolyev's experiments on the pressurizer model of nuclear reactor. The proposed method is universal for all types of water-cooled nuclear reactors (including the Akkuyu reactor plants). Variation calculations using the presented method have found that a considerable increase in total hydraulic resistance of internal elements can be an effective action to prevent WHs in the pressurizers of nuclear reactors.
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