Nuclear Safety Valves
There are three main types of nuclear safety valves, namely bellows sealed spring safety valves, fully opened spring safety valves with actuators and pilot safety valves with detectors. Although the amount of safety valves in NI is not large, but they are used in every important system pipeline, vessel and equipment, with a size of DN15 to 200mm. The structure of several representative nuclear 1 and 2 safety valves is introduced in this article. Bellows seal spring safety valves adopt a bellows seal structure to prevent the medium from enterin g the upper valve stem and spring working chamber, so that there will be no leakage when the safety valve discharges media. At the same time, to prevent leakage caused by accidental damage to the bellows, the outer wall of the upper chamber is also provided with a tube for discharge liquid. The valve has a manual forced opening handle. The rotating shaft of the handle is provided with a packing sealing box to prevent the leakage of the medium. The valve also has an adjustable lower gear ring to change lifting or seat returning of the disc. Fully opened spring-loaded safety valves with actuators are used in the main steam system. Although there is no radioactive hazard, they are no less important to the safety of the whole plant than the valves used in coolant media. The diameter of the valve is large (DN200mm), and the upper and lower double adjusting ring is adopted to ensure the full lift of the valve disc.
At the same time, to prevent the situation that the valve is not opened or closed well after opening when there is overpressure, the upper part of the valve is also equipped with an actuator. When necessary, the additional force generated by the pressure of the air source on the film can be used to help lift or close the valve clack to ensure safety. The pilot-operated safety valve with a detector is a very critical device in NI. It is used to protect the voltage regulator. It not only has high-pressure parameters and great displacement, but more importantly, the medium is a radioactive coolant. The leakage of the nuclear power plant in Three Mile Island, USA is caused by the fact that the pilot valve in front of the main safety valve is blocked and failed to return to the seat after the pilot valve popped, resulting in nuclear leakage. As for the pilot-operated safety valve with a detector, the principle of changing the two contacts of the position control release and filling medium according to the sensitive relationship between the pressure change and the balance of the spring force avoids jamming from the structure by using a detector. The main valve adopts a positive-acting disc with spring preload and bellows seal, which achieves a reliable sealing effect.
On the primary circuit of a nuclear power plant, the safety valve is generally installed on the volume compensator. In addition to the main safety valve of the primary circuit, an additional safety valve with a small diameter is also installed in the closed part of each circuit of the cold water reactor.
Main applications in nuclear power plants: direct-acting safety valves (full-opening and micro-opening), pilot-operated safety valves with a nominal diameter of DN600mm, operating pressure 1.265MPa), pilot-operated safety valves with auxiliary devices and explosion-proof membrane devices.
Technical parameter range of safety valves for nuclear power plants: nominal diameter of DN15 to 1500mm, nominal pressure PN2.0 to 70MPa and working temperature 253 to 535℃.
At the same time, to prevent the situation that the valve is not opened or closed well after opening when there is overpressure, the upper part of the valve is also equipped with an actuator. When necessary, the additional force generated by the pressure of the air source on the film can be used to help lift or close the valve clack to ensure safety. The pilot-operated safety valve with a detector is a very critical device in NI. It is used to protect the voltage regulator. It not only has high-pressure parameters and great displacement, but more importantly, the medium is a radioactive coolant. The leakage of the nuclear power plant in Three Mile Island, USA is caused by the fact that the pilot valve in front of the main safety valve is blocked and failed to return to the seat after the pilot valve popped, resulting in nuclear leakage. As for the pilot-operated safety valve with a detector, the principle of changing the two contacts of the position control release and filling medium according to the sensitive relationship between the pressure change and the balance of the spring force avoids jamming from the structure by using a detector. The main valve adopts a positive-acting disc with spring preload and bellows seal, which achieves a reliable sealing effect.
On the primary circuit of a nuclear power plant, the safety valve is generally installed on the volume compensator. In addition to the main safety valve of the primary circuit, an additional safety valve with a small diameter is also installed in the closed part of each circuit of the cold water reactor.
Main applications in nuclear power plants: direct-acting safety valves (full-opening and micro-opening), pilot-operated safety valves with a nominal diameter of DN600mm, operating pressure 1.265MPa), pilot-operated safety valves with auxiliary devices and explosion-proof membrane devices.
Technical parameter range of safety valves for nuclear power plants: nominal diameter of DN15 to 1500mm, nominal pressure PN2.0 to 70MPa and working temperature 253 to 535℃.
