DE1551037A1 - Steam generator element - Google Patents

Description

Steam generates element

The development of nuclear power plant technology is increasingly leading is becoming a so-called integrated reactor, i.e. a Reactor with the core and steam generator in the same pressure vessel lie. This principle, of course, already applies to gas-cooled reactors, where there is the option of using, for example, almost Concrete boilers manufactured in limited dimensions to work and advanced marine reactors, but their performance is much lower than that of normal power plant reactors, Entrance found. The problem of construction becomes difficult, however

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of high capacity integrated pressurized water reactors. If However, the steam generator succeeds even with some Ό0 MW To be arranged within the pressure vessel results in very weighty advantages in terms of space and material requirements. In particular for the primary circuit, the space requirement is much smaller and since most of it is within the Reactor pressure vessel runs, the security is also much greater. It is not only possible to save on steel, on the contrary, the effort for the detachment measures is reduced to the same extent. As a result of the more compact coolant flow the return losses in the primary circuit are also significant smaller. This means that the necessary pumps and pump outputs can also be smaller than before.

However, a prerequisite for the construction of such spatially relatively small integrated reactors is a steam generator design, which has a relatively small footprint and also sufficient accessibility to the reactor core guaranteed for the fuel element change.

The present invention relates to an interior of nuclear reactor pressure vessels housed steam generator consisting of a large number of individual elements, each with its own secondary connections consists. The invention is characterized in that the heat-transferring surfaces consist of straight tubes or plates are arranged without their own housing between collecting spaces for the secondary heat carrier and the flow direction

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of the primary heat carrier substantially perpendicular to that of the secondary runs.

This steam generator principle has the advantage that the relatively small individual steam generator elements are built for themselves can be checked, which is much easier than that Creation and testing of a single large steam generator. Should difficulties arise with individual elements during operation occur, it is not a problem to do this without interrupting the entire operation until the next overhaul switch off the entire system. The primary coolant pressure, which acts as the external pressure on the heat transferring surfaces is always greater than the pressure of the secondary cooling medium. This enables different components of the steam generator elements to be supported against one another or against neighboring ones Components at short intervals and thus low wall thicknesses of e.g. tube plates or heat exchanger plates despite high system pressures. This in turn results in a low weight and less sensitivity to thermal stresses and temperature changes. On the other hand, this becomes a The extremely compact design of the heat exchanger enables what is necessary in view of the task at hand. All movable and any components in need of repair, such as Pumps can be arranged at the top of the reactor vessel, i.e. in the most convenient place for accessibility.

These principles of the present invention and other details are explained in more detail with reference to the following figures.

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Figure 1 shows schematically the arrangement of the reactor core 1 and heat exchanger or steam generator 5 in the boiler 3 of a pressurized water reactor. The thermal shield is marked with 2, the pump - a propeller pump - with 4. The coolant flow is represented by flow arrows. You have to imagine that the entire steam generator consists of an approximately annular arrangement consists of individual elements 5, each of which is provided with feedwater supply and steam discharge pipes. Ks it can be advantageous to arrange several narrower steam generator elements radially to the reactor vessel, not as shown, only one. Likewise, instead of the ring-shaped arrangement, one in several e.g. rectangular groups is possible, between which, seen in the circumferential direction, e.g. the coolant pumps are arranged. The heat-transferring surfaces exist not as usual from U-shaped bent tubes, but from tubes, sheets or pockets that are close to each other the medium to be evaporated flows through evenly to the reactor axis, here from bottom to top, while the The reactor coolant flows through it essentially horizontally, that is to say in cross-flow. With such an arrangement compared to a conventional heat exchanger with U-shaped bent tubes and the thick tube plates required there accommodated about 2.5 to 3 times the heat exchanger surface will.

FIG. 2 now shows a possible example of the structure of a steam generator element in elevation. Figures 3 and 4

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represent possible ground plan forms, with reference to this is that, of course, other cross-sections, e.g. hexagons, trapezoids, etc. are also possible. All of these constructions The heat exchanger tubes 6, which are as closely spaced as possible and are welded close together in thin end plates 7, are common are. In spite of the high system pressures, these end plates can be kept thin because of the closely spaced pipes become, which means a significant advantage over previous arrangements. Construction details for FIG. 5 shows the possibility of a very narrow pipe division while at the same time being good weldability with the end plates 7 and 6, FIG. 5 showing, for example, a section of the upper chamber for the steam outlet and FIG. 6 showing a Section from the lower chamber for the feed water inlet shows.

The upper collecting chamber 8 for the steam and the lower chamber 9 for the feed water inlet are on the tube plates 7 vertically standing perforated sheets 1υ and 11 traversed, which have the task of distributing the pressure forces acting from outside evenly on the end plates 7. Without these sheet metal supports 10 and 11 would under certain circumstances inadmissibly high forces on the weld seams between the end plates and the chambers 8 and 9 final lids 12 and 13 act as the primary medium usually a higher one for water reactors Pressure has as a secondary medium. The tubes 6 are through spacers, e.g. simple perforated sheets, supported against each other.

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According to FIG. 2 , feed water flows through the central line 14 from above into the lower chamber, where it is distributed over the pipes 6. The steam that forms in these pipes 6, roughly according to the Benson principle, collects in the upper chamber 6 and is fed to the consumer through line 16, which can possibly be shut off. The fresh water line 14 runs inside the bolt 18, for example. A normal pipe screw connection 21 is indicated above this seal, which can easily be removed for the dismantling of a possibly damaged steam generator element. With the help of the bolt 10, the entire steam generator element is held and at the same time supported and sealed via the wall 12 of the upper chamber 8 in a corresponding recess in the boiler shell 3. Of course, it would also be possible not to supply the feed water concentrically as shown, but via an extra line, which is shown in dashed lines (15).

The evaporator tubes have a clear diameter of 10 mm and spacing around 1.5 mm, so they are smaller and much narrower than previously possible and possible. As already mentioned, this gives one built-up steam generator compared to a similar spatial size, but with the usual pipe arrangements and dimensions 2.5 to 3 times the heating surface. A thawing of one of the

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like heat exchanger rait plate-shaped heating surfaces increases this ratio even about 4 times what for the construction of such steam generators for integrated core reactors is of particular advantage. '-,

Figure 7 shows a partial elevation of such a heat exchanger from individual hats, in dimensions comparable to Figure 2, but with exaggeratedly thick plates. the Figures 8 and j show a partial cross section along the line VIII-VIII from Figure 7. Figure 8 can be seen here, that the heat exchanger is constructed from straight surfaces 23, which by drabvtfärmige, straight or corrugated spacers 22, which run in the direction of flow of the steam formed, are made pressure-resistant against external pressure. In the direction of flow of the primary medium, i.e. horizontal or perpendicular to the steam flow, are horizontal wire-shaped spacers 22a is provided, which at the same time also act as flow guide devices act so that the cross-countercurrent principle is possible well over the entire length or height of the steam generator element remains guaranteed. Like FIG. 8, FIG. 9 shows a cross section through the steam generator element according to FIG Here, however, the heating surfaces 23a are in the manner shown Corrugated and thus are supported directly against one another without additional spacer wires 23.

As already mentioned, such plate heat exchangers are preferred then applicable when outside, i.e. in the horizontal ducts

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the pressure for the primary coolant is higher than in the vertical channels for the secondary coolant. Since the Welded joints are largely subjected to pressure, they are very stable, even defects and not continuous Cracks in these plates can therefore hardly expand into a leak. Compared to heat exchangers with tubes, As described at the beginning, only the long vertical weld seams seem to be a disadvantage. This can not be serious however as all welds are straight and even and closer to being a typical machine work represent. In addition, the sheet metal is much cheaper than the pipes required and the heat transfer surface to be accommodated in the same space are larger, as is the primary pressure loss smaller than with comparable maximum flow velocities.

Plate heat exchangers that are easier to weld are shown in FIGS. 10, 11 and 12. They are characterized by the fact that the wall thickness of the plates at the welds is much larger, e.g. 3 to 5 mm, while the flow channels through corresponding depressions of these strong Plates are formed. The depressions can be made in a manner known per se by machining or non-cutting processing getting produced. The sheet thickness at the thinnest points is about 1 mm. FIG. 10 shows a section from such a steam generator, the individual plates, which are normally welded together, because of the clearer Representation are drawn apart. the

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Outer plates 28 defining the heat exchanger element are smooth and only wear a groove 26 on each of the two welding edges, which act as a throttle skin for the heat dissipation during welding acts and thus causes an improvement in the sweat root. "Plates 24 and 2b are each on one side, like shown, provided with longitudinal and transverse grooves. On their back they in turn have the grooves 26 in the vicinity of the Welding point. This groove 26 is in the last view of the plate 24 »which represents a perspective rear view, better to see. There are also recesses 27 drawn in there, which can be attached to reduce the material thickness between the individual channels. In this sequence shown, the plates are welded together so that the flow paths for the primary coolant and form the secondary coolant. The depth or the width of these flow channels is on the order of 1.9 to 4 mm. Of course, the flow channels can also be provided with a different cross-section, e.g. a rectangular cross-section, whereby another Material savings and an increase in heat conduction between the heat-exchanging media is achieved. A depiction the welded connection between the plates 24 and FIG. 10a shows from which the puncture of the grooves 26 is also shown is seen.

Instead of the plates 24, according to FIG.

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on the other standing grooves no support ribs, but only support points 30 are formed, which, so to speak, the plate surface divided into a multitude of small, interconnected "vaults". Here the mixing of the steam is better that Exchanger surface is also a little larger, but this is a result the higher flow resistance also the pressure loss is somewhat higher.

Another variation of the plate design is shown in FIG. 12. Here the plates 40 and 50 alternate with one another, the Plate 40 is grooved on either side in different directions for the two fluids and plate 50 respectively is only designed as a cover plate except for the welding groove 26 smooth.

These examples should only show that it is proportionate a simple way of construction is possible, heat exchangers with such a high concentration of heat exchangers To train surfaces. The other figures show in addition to Figure 2 how such heat exchanger elements in a so-called integrated reactor can be accommodated in the same pressure vessel.

According to Figure 13, the lid 31 of the pressure vessel 3, which is about has the same diameter, with the main circulation pumps on it 32 can be withdrawn. The steam generator elements 33 », which are arranged here on two concentric circles, go through

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penetrate ^ * 4 * ge «, with their steam lines a planing ring 34 to which the flow guide devices above the actual reactor core 35 are also attached. When the reactor is overhauled, these components can therefore be lifted off as a unit after the cover has been removed. The flow path of the primary coolant is indicated by arrows. This first flows up through the reactor core, enters the lower half of the heat exchanger elements 33 and flows outwards and from there over the upper half again inwards, is captured by the main circulation pump 3 P in the cooled state and afterwards again along the pressure vessel wall 3 conveyed down to re-entry into the reactor core 1.

The arrangement of the heat exchanger elements in an integrated reactor according to FIG. 14 is similar to that in FIG the heat exchanger elements silt up on the inner ring with the lid 31 of the reactor pressure vessel and can mit.dem same be lifted off. The elements on the outer circle, on the other hand, penetrate the upper flange ring of the with their steam pipes Reactor pressure vessel 3 · They have such an inner diameter that the actual reactor core 1 without dismantling the same can be expanded. The flow course of the primary medium is the same here as in the arrangement according to FIG. 13. The main circulation pump 32 has been omitted for the sake of clarity.

Figure 15 shows an arrangement in which the steam generator elements

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in a ring-shaped pole, each above and below dec actual reactor core are housed in the common reactor pressure vessel. With appropriate distribution of the steam generator elements there is also the possibility with this arrangement that the secondary cooling means in natural circulation through the steam generator elements flows.

Ensure this arrangement of the steam generator elements not only greater safety in the operation of the entire steam generator and a simplification of the manufacturing process of the same, they also avoid large boiler openings and allow one different and significantly more favorable safety planning for the entire primary circuit.

The special design of these steam generators can, however, also be used to advantage in such integrated nuclear reactors in which the fuel channels are passed over the entire length of the reactor pressure vessel, e.g. heavy water moderated nuclear reactors. Such relationships are shown in FIG. Such a structure would be with Steam generators of conventional design not only from the point of view of the too small heat exchanger surfaces, but also purely constructive reasons encounter almost insurmountable difficulties and therefore not be feasible. With the steam generator elements according to the present invention, however, the required heat exchanger surface is ensured and is above all also the structural design of the entire system without special

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Difficulties to carry out. The heavy water content of this Arrangement is smaller than with the usual guidance of the primary coolant by externally arranged conventional heat exchangers,

For the sake of completeness it should be mentioned that the individual ate Heat exchanger elements, preferably those in the radial direction are 'arranged next to each other' with regard to the flow the secondary heat carrier can be connected in series. This creates a counterflow heat exchanger with a distinctive Preheating part and superheating or drying part.

^p igur 17 shows such a steam generator, consisting of the preheater 51, the evaporator 52 and the Üterhitzer 53rd The secondary heat carrier enters at 54 and leaves the reactor as steam at 55. The flow of the primary heat carrier is again directed radially and horizontally from the inside to the outside, so that the heat exchanger element 53 with the hottest and the element

51 comes into contact with the coldest heat transfer medium.

FIG. 18 shows a similar embodiment of such a heat exchanger in section and FIG. 20 in plan. FIG. 19 shows, so to speak in an angled manner, the series connection of the heat exchanger ^{elements 53 »52 and 51, with the heat exchanger c} · 1 between the elements according to FIG

52 and 53 is arranged. In contrast to FIG. 17, here the secondary inlet and outlet lines are at the top, that is far away from the reactor core. When installing or removing a steam

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generating element, the water level in the reactor only needs up to just under. Introductory line 54 to be lowered. This means that more than 6 to 7 meters of water remain above the core as a shield if the secondary input and outlet lines 54 and 55 welding or cutting work must be carried out.

The expansion of the steam generator elements can be according to the following Play steps: Loosen the '/ bindings with the inlet and outlet lines 54 and 55, radial displacement of the loose steam generator elements inside and then remove them through the upper small boiler opening. Afterward the respective preheater 51 can also be removed in the same way, e.g. between the elements according to FIG 53 and 5? is arranged. The installation of these Kiemente is to be accomplished in reverse order, whereby it is expedient is, the connection with the supply and discharge lines 54 and 55 from outside the boiler via the interior of this Conduct lines. Fastening elements suitable for this belong to the state of the art and will not be described in more detail here will. This technique is also indicated in FIG. 19, where reference numeral 60 indicates such a point will. In this construction, a plug 59 is also inserted from the outside in the supply line 54, the direction of flow of the secondary heat carrier represented by arrows in the sense of a series connection of the three Ensures steam generator elements. The flow of the primary

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The heat transfer medium is indicated by the arrows in FIGS. 18 and 20 refer to. This flows horizontally outward through the elements 53 and 52, reverses according to the arrow on the wall 56 and flows through the preheater 51, this time from the outside to the inside. In the triangular rooms recognizable in the floor plan 57 the primary heat transfer medium then flows up to where it is by the pumps 4 between the guide wall 56 and the inside wall of the boiler is moved down to under the reactor core. In this package it is necessary to have the elements 52 and 53 with Provide side baffles for the primary heat transfer medium so that the flow around the preheater is even.

Finally, FIG. 21 shows a further detail of the steam generator elements. In the area of the low flow velocity of the secondary heat transfer medium, i.e. at the beginning of the evaporator zone, it is advisable to increase the speed and thus achieve a stabilizing effect. this will achieved through the insert 61, which is inserted into the evaporator tubes 6 is plugged. These throttles narrow the flow of the secondary heat carrier and thus force it to run at higher speeds. They expediently only extend over part of the length of the evaporator tubes 6 and can serve at the same time with their heads as a support for the wall 13 of the collecting spaces 8. ■

These only schematically shown arrangements of heat exchangers in integrated nuclear reactors make no claim

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on scale. Above all, the distance between the steam generator and the actual reactor core can also be larger be when replacing the fuel assemblies with the aid of a loading machine without removing the steam generator elements beforehand to be held.

10 claims
21 figures

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Claims (1)

) 6 / iO66 Claims H Steam generator housed inside nuclear reactor pressure vessels, which consists of a large number of individual elements, each with its own secondary connections, characterized in that that the heat-transferring surfaces of straight tubes or plates without their own housing between collecting spaces for the secondary heat carrier are arranged and the direction of flow of the primary heat carrier is substantially perpendicular to that of the secondary runs. Steam generator according to claim 1, characterized in that _f - that it is in its entirety substantially "ring-cylindrical shape, wherein the individual elements may be arranged parallel to the reactor axis heat exchanger surfaces radially and / or concentrically and the mutual distance of the heat exchanging surfaces in the order of about 2 mm. 3. Steam generator according to claim 1 and 2, characterized in that that the free interior of the ring cylindrical steam generator is dimensioned for the introduction and movement of a loading machine. 4. Steam generator according to claim 1 to 3, characterized in that that the secondary connections of the individual elements as concentric Passages through the pressure vessel wall. 3 8-31 / ^ 0 ^ 7 9 8 Mü / Fra BATH L 5. Steam generator according to claim 1 to 3 _f, characterized in that the secondary connections of the individual elements pass sealingly through an inserted ring between the actual container and its cover and open into manifolds outside the container, and that the individual elements in their entirety with this ring can be removed from the container after removing the lid. 6. Steam generator according to claim 1, characterized in that the individual elements with the help of also built into the reactor vessel Sina flows through control devices from the primary heat transfer medium. 7. Steam generator according to claim 1, characterized in that the Above and below the heat-exchanging surfaces of the individual elements, ■ storage spaces provided by built-in support bodies or sheets are made pressure-resistant against external pressure. 8. Steam generator according to claim 1 to 7, characterized in that that the heat-exchanging surfaces consist of straight tubes arranged close together. 9. Steam generator according to claim 1 to 7, characterized in that that the heat-exchanging surfaces consist of mutually supported metal pockets, which are also inside Support elements included. - 18 - ^ _n _ Mü / Fra 909883/0798 10. Steam generator according to claim 1 to 9, characterized in that that the individual elements are preferably flow-wise in the radial direction are connected in series so that they are in the order from the outside to the inside as a preheater, evaporator and superheaters work. - 19 - Mü / FrE 909883/0798 BATH ORIGINAL L e r s e i t e