| Reactor Pressure Vessel (RPV) in nuclear power plants is not only an important equipment of the coolant pressure boundary for primary circuit, but also one of the most critical components in nuclear power plants and it is featured by its high temperature, high pressure and strong radiation. Compared with the fatigue failure, buckling failure and cracking failure of RPV, sealing failure is a more common failure mode. The design and manufacture of the seal between RPV head cover and vessel flange is one of the key technologies to guarantee that no radioactive materials leak in the running and testing processes of RPV; in other words, the sealing performance of RPV directly decides whether the nuclear reactor can be started or not.In the present paper, metal O-type seal rings used in CAP 1400 nuclear reactor pressure vessel were taken and tests were conducted to study the compression resilience characteristics of Inconel718 alloy tubes, the influence of silver coating on its deformation characteristics were also analyzed. The elastic-plastic numerical simulations were conducted to help analyze the deformation characteristics of O ring using FEM software ABAQUS and some key factors influencing the sealing ability of O ring were studied; for example, the influence of compression ratio, sizes of the tube (including section diameter d, wall thickness t and outer diameter D) and installation groove clearance on the resilience value and linear pressure of O-type ring were studied.FEM results showed that compression ratio affected the linear pressure of O-type rings in its working process and decided its resilience ability; when compression ratio was in the range of 15%-20%, enough linear pressure and pretty high resilience performance could be got. The size of tubes affected the pressure distribution on the contact area and it not only influenced the resilience value and linear pressure greatly but also caused the collapse of O-type ring in the middle of the contact area. For installation grooves possessing a certain side clearance, linear pressure could be improved by 13.1% and resilience value also be increased. Besides, when O-type ring contacted with the side wall, a secondary seal could be achieved and the collapse of O-type ring can be avoided efficiently with the increment of inner pressure.The correctness of the finite element simulations were validated by a series of sealing-related tests, such as compression-resilience tests, air tight tests and hydrostatic tests. The results showed that the initial pressure ratio of O-type ring decided the its linear pressure value and linear pressure affected the air tightness; linear pressures under varied compression ratios could be got from deformation-load curves and the initial seal load as well as the minimum value of operation load can be got from leakage ratio curve; under different pre-defined compression ratios, initial seal load values for O-type rings were at least 50 percent of the maximum compression loads. |
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