In nuclear power plants, the sealing performance of reactor pressure vessel is highly related to the spring back properties of the seal ring installed between the closure head flange (upper flange) and the vessel flange (lower flange). In the finite element analysis, the sealing performance is usually described by the separation value of the upper and lower flange at the seal ring.

Considered the test results of spring back capability of seal ring in combination with a certain safety factor, the limitation of the separation between upper and lower flange at the seal ring is usually 0.2 mm. There are many design parameters, which have a huge influence on the sealing performance of pressure vessel, such as design size, material performance, bolt preload, etc.

As the reactor coolant loop is a complete, and highly relevant design system, some design parameters of pressure vessel changed may affect the whole system. Therefore, the effects of several design parameters on the sealing performance of the pressure vessel were analyzed in this paper. The results indicated that angle of the upper flange seal surface and the preload of the bolts have a big influence on the sealing performance of the pressure vessel, and they have nothing to do with the design of the whole system. The research results might guide the pressure vessel designers to optimize the pressure vessel design on improving the sealing performance.

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