JPH0526081B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steam generator of the type comprising a high pressure resistant vessel containing a bundle of heat exchange tubes and whose upper part constitutes a steam drum. In addition, a feeder, which is usually annular in shape and is connected to a make-up water intake pipe passing through the wall of the container and is equipped with a distribution passage for the inflow of make-up water into the container, is placed in such a container. . The invention is suitable for use in nuclear power plants, in particular in pressurized water reactors (in which case the invention can be used to replenish steam generators) or boiling water reactors (in which case it can be used to supply water for cooling circuits). It is highly effective in power plants.

The steam generator of a pressurized water reactor often has
It has a feeder that is fed from a generally horizontal conduit, shaped like a torus or a lobed torus with a vertical axis. When a nuclear reactor operates normally, the free surface of the water in the vessel is above the conduit and feeder, and the velocity of the water inside the conduit is relatively high. At this time, the operation is satisfactory. However, under various exceptional temporary conditions, the operation may even be disturbed.

In particular, various transient functional stages can cause water hammer and induce overpressures that can cause damage. This is particularly the case when the water level in the steam generator drops below the make-up water level (for example in the case of a hot shutdown). At this time, the feeder is drained. If this situation continues, the feeder and the conduit will be emptied and filled with saturated steam: thus a rapid condensation of the steam and thus the formation of pressure waves rising in the conduit in the form of depressurization and water hammer action will occur. triggered.

Attempts have already been made to solve this problem by preventing the feeder and/or conduit from emptying. For this reason, instead of the distribution holes traditionally made inside the feeder, a spiral tube connected to the top of the feeder was used (FR-A-2 333-200 and US-A-4 502,
419). Although this method solved this problem,
It was complex and difficult to apply to existing steam generators.

Another problem is thermal stratification of the make-up water when operating under very light loads. This phenomenon was particularly observed in 1984 (1985).
NUCLEAR ENGINEERING AND DESIGN
M. Miksch et al. ``Loading conditions in horizontal makeup water pipes of LWRs affected by thermal shock and thermal stratification effects''.
This phenomenon is even more severe for steam generators with a preheated water supply, on the one hand, which is used under normal loads, and, on the other hand, a cold water supply, which is used in accidental situations and under very low loads. Under these circumstances a small flow of cold water is injected into a conduit full of water at the operating temperature of the steam generator. Because the outflow velocity is low, the cold water does not mix with the hot water, but forms a noticeable layer at the bottom of the conduit. This layering maintains a high temperature gradient between the bottom and top of the conduit wall, which creates thermal stresses that can induce cracking, including in the conduit connection weld to the vessel. This phenomenon is exacerbated by vibration-induced fatigue at the interface between the layers.

The vortex tubes used to attenuate the phenomenon of water hammer do not significantly reduce this second phenomenon, which is preserved by the natural convective heat exchange between the hot water occupying the drum and the interior of the conduit. This seems to indicate that it is sagging. Various attempts have been made to solve this second problem. One consists in introducing make-up water into the conduit through an annular drain exiting into a water box where constant mixing occurs.

It has also been proposed to provide an annular or helical low protrusion on the inner surface of the conduit bend to increase the turbulence of the flowing water. The effectiveness of such devices is only very small; in fact, at low flow rates,
In other words, when mixing is desired, the narrow stream of cold make-up water simply jumps over the obstacles thus constructed.

Similar problems occur when using boiling water reactors, especially when cracking occurs.

The object of the invention is to provide a device which makes it possible to solve, at least in a broad sense, the above-mentioned problems of steam generators or only the problems of water hammer. Moreover, this solution is achieved using only purely static and simple equipment, which causes only small load losses during the outflow and which can be installed in existing steam generators without great difficulty.

For this purpose, the invention particularly provides one axial wheel center and a length of more than half a pivot pitch. A steam generator is proposed with a conduit as described above having in its horizontal part one or more deflectors comprising a plurality of helical vanes connecting the ring core to the wall of the conduit.

If it is only desired to avoid emptying the conduit in the case of draining the feeder, it may be sufficient to provide only one helical deflection plate in the conduit or at the intersection between the feeder and the vessel or immediately upstream of the vessel. be. The vanes shall be of such length and pitch that the lower point of the uppermost section of each channel between the vanes is above the upper point of the lowest section of the same channel. It is preferable to have six blades having an angular expansion of one to one and a half revolutions around the axis.

If it is also desired to obtain a mixing that avoids thermal stratification, a second deflection plate can be provided in the part of the conduit outside the container. The first deflection plate and this second deflection plate placed upstream of the crossing point of the container can have vanes whose angular development is only half a turn. It can also have four blades regularly distributed around the shaft.
It is preferable that the two deflection plates have blades of the same pitch.

Alternatively, two deflection plates can be combined and mounted on the same wheel core. In any case, the single deflection plate or the front part of the upstream deflection plate is placed longitudinally so as to only gradually transmit the winding motion to the flowing water.

In still other cases deflection plates are there to avoid thermal stratification. In this case, an angular development of the blades of at least half a turn is sufficient. The blades do not have a length and pitch, i.e., an angular development of more than one revolution around the axis, such that the lower point of the highest part of each interbladder channel is above the highest point of the lowest section of the same channel. This should only be done if you want to prevent the conduit from emptying when draining the feeder.

In any case, it is desirable to impose load losses on the central part of the flowing water that are significantly greater than those caused by the helical vanes around the flowing water.

In practice, 2 to 5 times the diameter of the conduit to the vane.
This often results in twice the flow pitch and a diameter for the ring core of 0.25 to 0.5 times the diameter of the conduit.

In a special manufacturing style, the second helix overlaps the first
It is placed between the norasa and the wheel. If only anti-laminarization is desired, these two helices often have different directions of rotation. Conversely, when trying to reduce the water hammer effect, the turning direction may be the same.

The annular core exhibits a shape that diverges from front to back in the normal outflow direction, and in the case of stratification, tends to rise, mixing the lower outflow portion of the conduit closest to the upper generator with hot water. In this case, the ring core has a particularly conical or ogive shape.

It is believed that the invention will be better understood by reading the description of specific embodiments given below by way of example and not limitation. Note that the description is based on the attached drawings.

The feeder and water supply pipes shown in Figure 1 can be used in particular in steam generators for pressurized water reactor nuclear power plants with generators having the general structure shown in the aforementioned document FR-A-2333200. It is something. In the embodiment shown, the feeder 10 consists of a toroidal loop. However, a lobe shape is also possible. This feeder is placed in the upper part of the pressure vessel 12 and coaxially therewith. Water flows from the feeder into the container through regularly distributed passages, which may be simple holes or volutes. The horizontal right side portion of the makeup water intake pipe 14 to the feeder 10 is connected to the sleeve 1 at the crossing point of the cover 12.
It is fixed at 6. This conduit is extended at the connecting portion 18 with the feeder 10 to form a T-shaped joint.

The conduit 14 is provided with a main water supply that can be shut off by a gate valve 20 that accepts already preheated water, and likewise an emergency water supply is provided in the intake pipe with a gate valve 22 that is closed during normal operation. I'm awake.

The exchanger includes in the connecting part 18 a first deflection plate 24 whose function is to prevent the conduit from emptying in the event of an interruption of the water supply. For this purpose, the deflection plate 24 includes a wheel core 26 with regularly distributed vanes 28 wound around it. Each blade 28
has a rear rectifying portion of the outflow whose surface contacting the leakage edge is parallel to the axis, and a helical front portion. There are at least four of these vanes, and in the example shown there are six. Each blade has a spiral shape with a constant pitch.

This requires that the lower point of the uppermost section of each channel between vanes, such as channel 30 shown in FIG. 4, be above the upper point of the lowest section of the same channel; It is necessary that the length and pitch ratio be sufficient. In reality, a length between 1 pitch and 1.5 pitches is sufficient.
In order to enable the siphon formed by the helix to be stopped, communication mechanisms are provided between the helical flow tubes, which are defined at least in the open part by those of the vanes passing over the top of the conduit. In the embodiment shown, these mechanisms are constituted by holes 31 drilled in the upper part of the vane 28, where it passes through the upper point of the conduit. When the level falls after reaching the upper generator of the wheel core, the stop holes 31 equalize the steam pressure upstream and downstream of the vanes. The level in the upper part of the inter-vane channel, which is restricted by the perforated vanes 28, decreases at the same time as the level downstream. As soon as this downstream level reaches the ring center, the level stabilizes upstream of the deflection plate until the conduit is completely empty.

The load loss carried by the deflection plate 24 is an increasing function of the slope of the vane relative to the axis of the conduit. However, the vertical space required for the deflection plate increases as the pitch becomes longer. On the other hand, the required number of pitches varies depending on the number of blades. A compromise is therefore made between the lowest number of vanes and the smallest possible slope compatible with the length available.

The exchanger shown in FIG. 1 also includes a second deflector plate 32 located within a portion of conduit 14 outside vessel 12 and upstream of the first deflector plate.

This second deflection plate has the purpose of acting as a mixer to prevent stratification. Deflection plate 32 includes a ring core 34 having the same diameter as ring core 26 and a plurality of vanes 36 (four in the illustrated embodiment) that connect the ring core to the wall of conduit 14. each feather 3
6 has a rear helical portion with a rectified leakage lip, preferably of the same pitch as the vanes 28, and a front portion for rotating the flowing water, whose surface contacting the leading edge of the blade is parallel to the axis. Thus conduit 1
4 is divided into four independent inter-blade waterways.
The length of each vane corresponds to half a helical turn.

If the deflection plate 32 is omitted, the blade 2 has a front part that gradually rotates the flowing water.
It is 8.

The role of the deflection plate 32 becomes immediately apparent when the conduit is filled with a liquid consisting of two constituent parts with different densities, and even when injecting through the conduit a liquid of a different density than the liquid previously filled: density When the flow rate of a liquid with a high temperature is low, a stratified flow tends to occur. However, each vane 28 induces a half-turn tilting motion which causes the heavier components to be routed from the bottom to the top of the conduit and vice versa. The natural layer order is therefore reversed at the exit of the deflection plate 32, which causes mixing by diffusion.

The role of the deflection plate 24 is to prevent the conduit from being emptied by the feeder when the water supply is interrupted.
If the wheel core dimensions are appropriate and the pitch of the blades is short enough, the lower point of the upper section of each blade channel will be the 4th point.
Above the upper point of the lower section as shown in the figure. Thus, each channel between the blades that rotates at least once constitutes one siphon. In each of the channels, the free surface 38 is above the axis of the wheel core, and the tap remains at the bottom to prevent steam from passing through, i.e., from emptying the conduit.

Instead of using separate deflection plates, it is also possible to use a single deflection plate of sufficient length to allow the blades to make more than 1.5 revolutions.

It can be seen that the installation of the above-described mechanism into existing exchangers is simple. The deflection plate 32 is mounted by unwelding a portion of the conduit 14 and then reassembling this portion after insertion of the deflection plate without entering the interior of the steam generator. The deflection plate 24 can also be inserted externally, for example by mounting it in a liner that is slid through the sleeve 16.

Regardless of the embodiment employed, the deflection plate 24 reduces the severity of the water hammer effect caused by the injection of cold water and further directs the conduit between the hot water or water coming directly from the vessel or between the steam and make-up water in the drum. protection from stubborn stratification due to natural convection. The deflection plate 24 actually prevents the development of natural convection in the vicinity of the conduit and stops the propagation of temperature oscillations at the interface between the cold and hot layers.

Thus a device of pure static and hydrodynamic shape,
This means creating a device that has a long service life and has negligible load losses in spills under normal conditions.

The layering further forms the portion 18 that constitutes the water supply T-shaped pipe.
This can be prevented by providing small blades at the bottom of the feeder 10 for increasing heat conduction. Such vanes may be in the form of regularly distributed arches 40 (FIGS. 7 and 9) or in the form of longitudinal plates 42 welded along the generator to the lower part of the T-tube. You can leave it there. Since these vanes increase heat exchange at the bottom of the feeder, they tend to reduce the temperature difference between the cold and hot layers.

The exchanger shown in FIG. 11 differs from that of FIG. 1 in that it includes only one deflection plate 32, which is placed within a portion of conduit 14 outside vessel 12. The purpose of this deflection plate is to at least fulfill the role of a mixer that prevents stratification.

The deflection plate shown in FIGS. 12 and 13 includes a heat shield having an outer diameter that matches the inner diameter of the conduit 14 and which allows the block-shaped deflection plate to be installed in the conduit 14 in an airtight manner. An outer sleeve forming the cover is included. The deflection plate can be thought of as having a annulus 46 or central core and regularly distributed vanes 28 secured to the sleeve 44 and wrapped around the annulus. Each vane 28 has a helical portion and optionally a water-rectifying rear section in which the vane transitions from a helical to a radial shape.
or having a front part. To enable the siphon formed by the vanes to be stopped, a communication mechanism can be provided between the helical flow tubes, which are at least defined by the flow tubes of the vanes 28 passing through the upper part of the conduit. These features may be just one hole (not shown). If the vane makes more than one revolution, the passage is generally located at the most downstream upper point.

The cylindrical ring center or center core 46 is streamlined at the front to reduce load losses. The core has two or more winged spirals whose outer edges are fixed to a cylindrical septum. Spiral 4
8. The connection between the core 46 and the septum 50 must be airtight to prevent air from passing through. 12th
In the embodiment shown in FIGS. and FIG.
is slid into a similarly cylindrical septum 52, which is integral with the vane 28, which is connected in a gas-tight manner to the septum 52 and sleeve 44. This arrangement facilitates the manufacture of the deflection plate; in fact, the sleeve 4
4. Two subassemblies, one containing the vane 28 and bulkhead 52 and the other containing the inner portion, can be made separately and then the two can be sleeved together. Fixation can be done by sleeve joints. However, completely different assembly methods can also be used which ensure the tightness of the connection between the partition walls 50 and 52, for example butt welding.

If only the stratification prevention effect is desired, it is sufficient that the blades 28 and the small blades 48 have a length corresponding to half a rotation. Vanes 28 placed around the deflection plate
captures water completely and concentrates the cold water in one direction,
Raise it to the top of the conduit closest to the generator. These vanes thus complement the effect of the two or more vaned helix, which allows the water to rise only to the level of the upper generator of the core 46 when the thickness of the cold water section is small.

It is possible to provide the blade 28 with a direction of rotation opposite to that of the small blade 48 . If a deflection plate is provided to alleviate the water hammer effect, the blade 2
8 and the small blade 48 at least once, preferably
It has a length equivalent to 1.5 revolutions.

Each vane 36 and vane 48 may exhibit a helical general section and have a rectified leakage lip and a forward section that rotates the flowing water such that its tangential plane to the wing leading edge is parallel to the axis. This reduces load losses. However, if a second device with helical wings with pitches in the same direction is placed in the conduit inside the container, the leak lip of the first device and the entry lip of the second device are You don't have to prepare.

The vanes are designed to impose load losses on the water flow across the annular space between the bulkhead 50 and the core 46 over and above those caused by the vanes 28 to favor the passage of cold water along the vanes 28. 48 must be provided.

The deflection plate 32 of FIGS. 14 and 15 is in the form of an ogive connected to the sleeve 44 by four angularly regularly distributed vanes 28 (only one of which is shown in FIG. 14). solid wheel core 3
It has 4. The deflection plate causes the incidental stratified cold water portion to rise toward the upper generator of the conduit while mixing with the hot water. Due to the rearward widening of the wheel core, the passage cross section is reduced and the speed is therefore increased, which favors the mixing of cold and hot water.

If a deflection plate of the type shown in FIGS. 14 and 15 is used only to prevent stratification, two vanes 28 with a minimum of half a turn are sufficient. but,
In practice, it is desirable to use three or four blades. If the sole purpose is to reduce the water hammer effect, a device with two vanes each having one or more revolutions is used. Finally, if these two phenomena are to be prevented, it is desirable to use a four-bladed device that rotates at least one revolution, preferably one and a half revolutions.

In order to maintain excellent airtightness around the blade 28, it should be made into a spiral along with the end of one belt.
It can then be welded to form the sleeve 44.

In the application of the invention to a boiling water reactor (FIG. 16), the deflection plate 32 is placed above the water supply pipe 14, upstream of the crossing point of the tank 12 forming the pressure-tight vessel. The reactor further includes a feeder 10 located below the separator 60 and dryer 62. Steam exits the tank through tube 64. Circulation within the reactor itself is accomplished by ejector loop 66 in a conventional manner.

It will be appreciated that the invention is not limited to the particular construction described by way of example, and the scope of this patent extends to all equivalent variants as well as to non-nuclear steam generators. It extends to the field of use.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a make-up water feeder of a steam generator and its water supply pipe having a configuration according to the present invention. FIG. 2 is an elevational view of one of the deflection plates mounted within the conduit of FIG. 1, with only one vane shown. FIG. 3 is a view from the left of the feeder in FIG. FIG. 4 is a diagram showing a siphon equivalent to one of the inter-blade water channels of the deflection plate of FIG. 2. Figures 5 and 6 are the same as Figures 2 and 3.
Figure 3 shows a second deflection plate on the conduit shown in the figure. FIGS. 7 and 8 are principle diagrams showing a portion of a water supply pipe equipped with small heat exchange vanes to alleviate stratification. FIGS. 9 and 10 are views seen from the right side of FIGS. 7 and 8, respectively. FIG. 11, like FIG. 1, shows a steam generator and its water supply pipe equipped with a mechanism according to the invention. FIG. 12 is a front perspective view of a portion of a water supply pipe equipped with a mechanism according to another embodiment; 13th
The figure is an elevational view of the deflection plate of FIG. 12. Figures 14 and 15 show yet another embodiment (only one blade is shown in Figure 14). FIG. 16 is an elevational view showing the application of the present invention to a boiling water nuclear reactor. Number of main components, 10...Feeder, 1
2... Container, 14... Water intake pipe, 16... Sleeve, 20... Gate valve, 22... Gate valve, 24
... Deflection plate (deflector), 26 ... Wheel center, 28
...Blade, 30...Waterway, 32...Deflection plate (deflector), 38...Free surface, 40...Archid blade, 42...Flat blade, 44...Sleeve, 4
6... Nucleus, 48... Spiral (feather), 50...
Cylindrical wall, 52... partition, 64... tube, 66...
...Egiecta Loop.

Claims (1)

[Scope of Claims] 1. A steam generator including a container 12 containing a bundle of tubes for heat exchange, wherein the upper part of the container 12 constitutes a steam drum, and a steam generator that passes through the wall of the container into the steam drum. A feeder 10 connected to a make-up water intake pipe 14 and provided with a passage for flowing water into the container.
In the steam generator in which the make-up water intake pipe 14 houses a deflection device in its horizontal portion, the deflection device includes an axial wheel center 26 and the wheel center of the make-up water intake pipe. a first deflector 24 having a plurality of uniformly spaced helical vanes 28 coupled to a wall;
8 is at least half the winding pitch, and the first deflector 24 further connects the flow path with the spiral flow path defined by the vane 28, so that the first deflector 24 has a length that is at least one half of the winding pitch. the deflection device is further located upstream of the first deflector outside where the make-up water intake pipe passes through the vessel, and is also located upstream of the first deflector; 3
4 and a plurality of spiral blades 36.
A steam generator characterized in that it includes a deflector 32 of. 2. The first deflector 24 is disposed within the make-up water intake pipe between the feeder and a location where the make-up water intake pipe passes through the container 12. The steam generator according to item 1. 3 The first deflector 24 rotates from one rotation to one rotation.
Steam generator according to claim 2, characterized in that it has at least four uniformly spaced vanes (28) having an angular expansion of half a turn. 4 The first deflector has at least one blade.
The steam generator according to claim 2 or 3, characterized in that it has a rotating winding. 5. Claims 2 to 4, characterized in that the blades of the second deflector 32 have the same pitch as the blades of the first deflector 24.
The steam generator according to any one of paragraphs. 6. The steam generator of claim 5, wherein the second deflector vanes have an angular expansion of approximately half a turn. 7. The steam generator according to claim 5 or 6, wherein the second deflector has four blades. 8. A steam generator according to any one of claims 1 to 7, wherein the second deflector has a longitudinally oriented forward portion. 9. Any one of claims 1 to 8, wherein the blade of the first deflector arranged downstream has an exit lip in a radially oriented plane. Steam generators as described in Section. 10 the wheel core is separated from the vane 28 by a cylindrical partition 50 connected to the vane 28 and a helix 48 having at least two vanes, the helix 48 connecting the wheel core and the cylinder A steam generator according to claim 1, characterized in that the blades of the helix (48) have a length of at least one half of the winding pitch. 11 The helix 48 and the first deflector 2
11. The steam generator according to claim 10, wherein the steam generator has a winding direction different from that of the four blades.