Hydrodynamic pin for centering a nuclear reactor core

Abstract

A centering pin for a nuclear reactor core within a reactor vessel includes a central part having a radially inner edge oriented toward the core and a horizontal thickness along the radially inner edge. The pin includes an upper hydrodynamic profile, which is disposed above the central part and forms a vertical wing leading edge extending from the central part and having an upper height above the central part. The pin includes a lower hydrodynamic profile, which is disposed below the central part and forms a vertical wing trailing edge extending from the central part and having a lower height below the central part. The upper height has a maximum variation of more or less 25% relative to the horizontal thickness. The lower height has a maximum variation of more or less 25% relative to the horizontal thickness.

Claims

1. A centering pin for centering a nuclear reactor core of a nuclear power plant in a reactor vessel, comprising a central part having a radially inner edge oriented towards the nuclear reactor core and a horizontal thickness along the radially inner edge, an upper hydrodynamic profile, which is disposed above the central part and forms a vertical wing leading edge extending from the central part and having an upper height above the central part and defined between an upper end of the central part and an uppermost point of the upper hydrodynamic profile, and a lower hydrodynamic profile, which is disposed below the central part and forms a vertical wing trailing edge extending from the central part and having a lower height below the central part and defined between a lower end of the central part and a lowermost point of the lower hydrodynamic profile, wherein the upper height of the vertical wing leading edge of the upper hydrodynamic profile has a maximum variation of more or less 25% relative to the horizontal thickness of the central part, and wherein the lower height of the vertical wing trailing edge of the lower hydrodynamic profile has a maximum variation of more or less 25% relative to twice the horizontal thickness of the central part.

2. The centering pin according to claim 1, wherein the upper hydrodynamic profile has a shape of a dihedral.

3. The centering pin according to claim 1, wherein the lower hydrodynamic profile has a shape of a pyramid.

4. The centering pin according to claim 1, wherein the upper height of the vertical wing leading edge of the upper hydrodynamic profile is in an order of 0.87 times the horizontal thickness of the central part, while the lower height of the vertical wing trailing edge of the lower hydrodynamic profile is in the order of 1.93 times the horizontal thickness of the central part.

5. A nuclear power plant reactor comprising a reactor vessel, a nuclear reactor core and centering pins according to claim 1, wherein the nuclear reactor core is centered in the reactor vessel by the centering pins, wherein the radially inner edge of the central part of the centering pins is adjacent to the nuclear reactor core, wherein the central part of the centering pins has a radially outer axial face adjacent to the reactor vessel.

6. The nuclear power plant reactor of claim 5, comprising a cooling fluid circulating in a direction of flow in an annular space situated between the nuclear reactor core and the reactor vessel, wherein at least a part of the centering pins are situated in the annular space, wherein the upper hydrodynamic profile of the centering pins is located upstream in the direction of flow of the cooling fluid, wherein the lower hydrodynamic profile of the centering pins is located downstream in the direction of flow of the cooling fluid.

7. The nuclear power plant reactor of claim 6, wherein the lower hydrodynamic profile of the centering pins located downstream in the direction of flow of the cooling fluid reaches a bottom of the reactor vessel in a plenum of the reactor vessel.

Description

QUICK DESCRIPTION OF THE FIGURES

(1) Other characteristics, objects and advantages of the present invention, will become apparent upon reading the following detailed description, and in relation to the appended drawings, given by way of non-limiting example and in which:

(2) FIG. 1 previously described, represents a general view of a conventional nuclear power plant,

(3) FIG. 2 previously described, represents a schematic view in vertical section of a known nuclear power plant reactor,

(4) FIG. 3 previously described, represents a partial schematic view in vertical section of the lower part of a conventional reactor vessel,

(5) FIG. 4 previously described, represents a perspective view at an enlarged scale of a centering pin according to the state of the art,

(6) FIG. 5 represents a partial view in vertical section of a reactor vessel according to the present invention illustrating a pin according to the invention,

(7) FIG. 6 represents a perspective view similar to FIG. 4 of a pin according to the present invention, and

(8) FIG. 7 represents a view in vertical and radial section relative to the vertical central axis of the core, of a centering pin according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(9) As indicated above, the general structure of a nuclear power plant is known to those skilled in the art. It will therefore not be described in detail.

(10) It is simply recalled that the core is centered in the vessel by centering pins.

(11) The appended FIGS. 5, 6 and 7 show a pin 110 according to the present invention.

(12) More specifically, the pin 110 is defined by a radially inner axial face 112 adjacent to the core 20, which conforms to the shape of the core 20 at this level and which is generally stepped.

(13) The pin 110 also includes a radially outer axial face 114 adjacent to the vessel 10 and which conforms to the shape of the vessel at this level. Thus, the face 114 is preferably curved. It converges toward the radially inner axial face 112 downwards.

(14) The central part 111 of each pin 110 is completed with two radial faces 116, 118 generally planar and radial relative to the vertical central axis of the core.

(15) As indicated above, according to the invention, each pin 110 is equipped with a hydrodynamic upper profile 120 and a hydrodynamic lower profile 130, disposed respectively above and below the central part 111.

(16) The hydrodynamic upper profile 120 located upstream in the direction of flow of the fluid entering the annular space 11, has the shape of a dihedral 121.

(17) More specifically, this dihedral 121 is formed of two symmetrical main facets 126, 128 which extend the radial faces 116 and 118 upwards. The facets 126, 128 are preferably generally flat and meet at a radial ridge 129 relative to the axis of the core.

(18) The upper profile 120 is completed with two radially inner 122 and outer 124 secondary facets respectively adjacent to the outer face of the core and to the inner face of the vessel.

(19) The lower hydrodynamic profile 130 has the general shape of a pyramid 131. It comprises two symmetrical main facets 136, 138 which extend the radial faces 116 and 118 downwards. The radially outer edges 135 of the main facets 136, 138 follow the contour of the vessel 10 and meet at the radially inner edge 137 at a point of convergence 139. The lower hydrodynamic profile 130 also comprises two radially inner 132 and outer 134 secondary facets. The radially outer 135 and radially inner 137 edges of the main facets 136, 138 converge to join the two secondary facets 132 and 134 of the pyramid 131 composing the lower profile, at the tip 139.

(20) Of course, the present invention is not limited to the particular embodiment that has just been described, but extends to all variants according to its spirit.

(21) Particularly, the hydrodynamic profiles 120 and 130 can be of angular or rounded geometry.

(22) The best possible embodiment of a hydrodynamic device is a shape that eliminates any stagnation space (low-flow area) in the vicinity of the centering pins 110.

(23) The present invention makes it possible to reduce or even totally eliminate turbulence at the bottom of the vessel.

(24) The invention makes it possible to stabilize the flow on its passage at the centering pins 110 and therefore reduce the heterogeneity of the flow upstream of the core and thus make the distribution of the heat transfer fluid more homogeneous in the core.

(25) FIG. 3 proposes an example of a pin 110 consisting of angular geometries. For this case, the pin 110 is defined by two parameters b and c.

(26) The parameter b (illustrated in FIG. 7) corresponds to the vertical height of the upper profile 120.

(27) The parameter c (illustrated in FIG. 7) corresponds to the vertical height of the lower profile 130.

(28) These parameters b and c are defined in relation to the thickness a of the centering pin 110 (illustrated in FIG. 6) considered in a horizontal section and along the radially inner edge of the central part 111 of the pin 110.

(29) In the example illustrated in FIGS. 5 to 7, the height b of the hydrodynamic upper part 120 of the pin 110 is in the same order of magnitude (0.87 times) as the thickness a of the centering pin 110. The height c of the hydrodynamic lower part 130 of the pin 110 is about twice (1.93 times) the thickness a of the centering pin 110.

(30) This shape is chosen to make the centering pin 110 hydrodynamic for the water flowing down through the annular space 11. The centering pin 110 with the hydrodynamic devices 120 and 130 thus takes the shape of a wing. The upper part 120 of the pin 110 represents a leading edge of the wing and the lower part 130 represents a trailing edge of the wing.

(31) The inventors have found that: If the height b of the upper part 120 tends to zero, the device 120 has no more effect. If the height b of the upper part 120 becomes too large, the device 120 blocks the rotation of water in the annular space 11. The rotation of water in the annular space is however significant because it mixes the water coming from the cold branches. This is an effect that stabilizes the circulation in the event of flow rate imbalance that may occur between cold branches. With the choice of a height b in the order of magnitude of the thickness a of the centering pin 110, an effective hydrodynamic shape is obtained without blocking the mixture in the annular space. The height c of the lower part 130 of the device, in the order of twice the thickness a of the centering pin 110, is chosen so that the pin is extended vertically up to the bottom of the vessel. The device is made less effective if it does not extend up to the bottom of the vessel. The device 130 can induce space requirement and even a source of instability if it takes a larger shape that does not follow the vertical axis and approaches the center of the vessel.

(32) Within the framework of the invention, it is meant by “same order of magnitude” a maximum variation of more or less 25% relative to a reference value.