Increasing Tightness and Environmental Safety of Npp Pump Seals

Abstract

The determining factor for NPP pumps is safety, as well as the maximum sealing capacity, which imposes additional conditions when choosing the type of seal. Mechanical seals are widely used in pumps in nuclear power plants. The processes occurring at the junction of the contacting end surfaces of a seal in various operating modes are described. Cooling and safety pumps systems that pump radioactive media are subject to requirements, some of which can only be met with the use of special designs. On the basis of mechanical seals, new types of seals have been created, in which the sealing belts are unloaded and operate with a small gap in friction modes close to liquid: hydrodynamic and thermohydrodynamic seals. The principle of operation of thermohydrodynamic seals is based on the use of the deformation of the rings under the force of thermal stresses in the contact zone. At high pressure differentials and rotation speeds, when a long life is required and small leaks are allowed, seals with a continuous liquid film are used - hydrostatic seals. Impulse mechanical seals are self-adjusting non-contacting seals and are an alternative to hydrostatic and hydrodynamic non-contacting mechanical seals. Impulse mechanical seals with self-adjusting gap have a number of advantages over conventional mechanical seals and non-contacting hydrostatic and hydrodynamic mechanical seals. Seals with impulse balancing of the axially moving ring during the rotation of the shaft ensure contactless operation with low leaks, and during standstill — complete tightness. Examples of industrial application of impulse seals in pumping equipment of nuclear power plants were given.