| 摘要 |
A pressurized-water reactor pressure vessel has a plurality of inlet openings through which coolant is introduced from the cold legs of a plurality of main coolant loops, into an annular descent space of restricted radial extent and formed between the inside of the vessel's side wall and the outside of a core barrel on the inside of the vessel. To prevent outward loss of coolant from the vessel in the event of a break in any of the cold legs, the vessel is internally provided with a check valve assembly for each of the inlet openings, and to avoid restriction of the normal inlet coolant flow rate, each assembly comprises a plurality or series of flap valves which are each individually of small dimensions so that they can be fitted into the descent space. Therefore, these flap valves are normally held open by the inlet coolant flow but can snap shut to outward coolant flow. Due to their small dimensions, they are very sensitive to coolant flow in the descent space through the vessel's various inlet openings making it possible for some of these valves to flutter between fully open and partially closed or fully closed positions in regions of low coolant flow velocity. To prevent this fluttering possibility, each valve assembly comprises means for forming a flow-confining chamber extending downwardly from the coolant inlet opening involved, and having an open lower end substantially conforming in contour to a segment of the annular descent space, the flap valves being mounted in the form of a row in this open lower end of the chamber. In this way, the flow is directed in a predeterminable manner also in case of a break, so that the flap valves associated with the broken pipe defenitely close and are prevented from fluttering.
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