A. V. Nosovskyi, G. I. Sharaevsky, N. M. Fialko, I. G. Sharaevsky, L. B. Zimin
Institute for Safety Problems of Nuclear Power Plants, NAS of Ukraine,
12, Lysogirska st., Kyiv, 03028, Ukraine
Hydromechanical and thermophysical conditions for the operation of the mechanical shaft seal system separation stage for the main circulation pumps of the water-water type nuclear reactors first circuit are analyzed. Typical designs and experience of the end type sealing shafts are considered. The physical features of the flow of processes that accompany the pressure water lubrication of the capillary slit channel in the friction pair of the rotor and stator O-rings tribo-tension are determined. Such a cause is most often a change in the friction regime of surfaces of siliconized graphite in the contact zone of the movable and fixed rings of the tribological pair of the separation stage. As these surfaces wear out, potential vaporization centers may appear on them. Therefore, the transition from semi-liquid to dry friction is most often caused by cavitation processes and uncontrolled boiling of blocking water in the capillary slot channel. The specificity of the coolant boiling in the capillary channels and the dynamics of the development of the heat crisis phenomena in such conditions are considered. Applicable to the stated task using the theory of the Rayleigh microbearing, a physical model of the ring surfaces contact zone and a thermo-hydraulic model of the capillary slit microchannel in the zone of tribon-tension of the end seal contact rings of separation stage have been developed. The models take into account the peculiarities of the progress of thermophysical processes in the capillary slot channel and the practical engineering requirements for the developed operational diagnostics system. The necessity to study the possibility of using the data of existing systems with respect to the pressure drop of the sealing water at the separation stage for monitoring and forecasting the technical state of the mechanical shaft seal system was noted.
Keywords: main circulation pump, mechanical shaft seal, separating stage, tribopair, capillary gap, boiling of blocking water.
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