Brief Analysis of Nuclear Power Plant Main Loop System

Most of the main circuit systems of nuclear power plants operate at high temperature and high pressure, but they also operate in a vacuum state, and are mainly pressure shell sandwiches, steam turbine condensers, and so on.

(1) Pressure shell sandwich

The pressure shells of modern large-scale pressure reactors are double-layered. In order to increase safety, in recent years, some large-scale pressure reactors in foreign countries have adopted pressure-coated shells with a vacuum sandwich. The purpose is that the vacuum sandwich can prevent the radioactive gas in the pressure shell from leaking out of the shell through the sandwich. Because the pressure shell is not absolutely leakproof, the foreign nuclear power plant pressure shell design allows the leakage rate: 1% (volume) of the total amount of air in the pressure shell per day. With a vacuum sandwich, the sandwich gas can be pumped by a large vacuum pump to a high-efficiency filter, which is purified and discharged into the atmosphere.

(2) Steam turbine condensing system

Nuclear power plant turbine has a huge condenser under it, it is in a vacuum state. For example, the steam turbine condenser of the French 900,000 kW nuclear power plant is a heat exchanger consisting of a titanium tube. The outer shell is a secondary circuit medium under a vacuum of 4×10 4 Pa. General nuclear power plant turbine condensers are cylindrical or box-shaped, with tens of thousands of tubes arrayed inside, and cooling water passes through the tubes. The second-loop steam drives the impeller to function as a shield. It is sucked into the condenser by a vacuum pipette, cooled by the outer wall of the pipe and falls into ice, and is sent back to the evaporator for evaporation. Nuclear power plant steam turbines are different from thermal power plants because the steam pressure of nuclear power plants is lower than that of thermal power plants and the temperature is lower than that of thermal power plants. Therefore, small water droplets are easily formed. These small water droplets are very harmful to steam turbines, and when the condenser is in a vacuum state, the nozzle wall can be The water film is sucked into the condenser. The working conditions of the condenser are very bad. It has many special requirements for the vacuum maintenance equipment. The most important thing is to work reliably for a long time.