The Application of Shaft Seal In Nuclear Power

The pressurized water reactor is one of the light water reactors. According to statistics, about 60% of the world's nuclear power plants use pressurized water reactor, which uses pressurized boron containing water as reactor coolant and moderator. At present, there is a good balance between the safety and the economy of the nuclear power plant of the million kilowatt - class PWR. At present, the third generation of pressurized water reactor is mainly multi-million kilowatts.
The reactor coolant pump (main pump) is the only large rotating equipment in the circuit system of the pressurized water reactor. Its main function is to provide it that allows the coolant to be forced in a loop system. The heat generated by the core is passed through the coolant to the steam generator, generating steam from the steam turbine for generating electricity. At the same time, the pump shell and other pressure-containing members also bear the safety function of preventing radioactive material from leaking into the containment.

The shaft seal is the key component of the shaft seal pump. Its long-term reliable operation will not only affect the normal production of the nuclear power plant, but also directly affect the safety of the nuclear power plant. The function of shaft seal is to ensure that the leakage amount of the reactor coolant is basically zero from the primary pump shaft to the containment space environment during the normal operation of the power plant. It is required to be in a high pressure differential condition for a long time and maintain a controllable leakage rate. The non-failure operation time is at least 20000hm. Once the shaft seal of the main pump fails, the integrity of the pressure boundary of the primary loop of the nuclear power plant will be lost. If the leakage rate exceeds the capacity of the water replenishment system, it will lead to the occurrence of the potential small fracture water loss, which will eventually lead to the melting of the core.

At present, the main pump of the world's million-kilowatt nuclear power plant can be divided into three-bearing main pump of American style and four-bearing main pump of European style. Among them, the American style main pump is equipped with a hydrodynamic seal, while the European style main pump is equipped with a hydrostatic type. The 2 types of shaft seals are in a non-contact state through the hydrodynamic pressure effect and hydrostatic pressure effect respectively, and the controllable leakage is formed to ensure the long life and reliable operation of the shaft seal.