Axial flow heat exchanger

Abstract

A heat exchanger vessel 100 for a heat pipe-based nuclear micro-reactor, the heat exchanger having a fluid input 18 and a fluid output 20 to allow the heat extraction fluid to enter and exit the heat

Description

FIELD OF THE DISCLOSURE The present disclosure relates to nuclear power systems, and more specifically to a heat exchanger vessel for a heat pipe-based nuclear micro-reactor. BACKGROUND Nuclear fission reactors work on the principle that heat generated by the fission process in the core can be used to generate electricity. A number of methods have been proposed for extracting heat from the core of the nuclear reactor. An important consideration in designing a nuclear reactor is how to extract heat from the core in such a way as to maximise the efficiency with which fuel in the core is used. One way to achieve this is to evenly distribute heat extraction from the core. Heat pipes have been proposed as a means by which to extract heat from a nuclear reactor core, and a few nuclear reactors have been built using heat pipes. However, the means for extracting heat energy from the heat pipes have not been optimised to provide consistent rates of heat extraction from each of the heat pipes. Having heat energy extracted from different heat pipes at different rates leads to uneven heat extraction from the core, and uneven fuel expenditure, ultimately either reducing the useful lifetime of the reactor, or increasing the rate at which the fuel within the reactor needs to be replenished, making the reactor more expensive to run. It would therefore be desirable to provide a means for evenly extracting heat energy from a number of heat pipes that are drawing heat from a nuclear reactor core. SUMMARY The present disclosure provides a heat exchanger vessel as set out in claim 1, a nuclear reactor as set out in claim 13, a surface power generator as set out in claim 14, and a satellite as set out in claim 15. Optional features are included in the dependent claims. According to a first aspect there is provided a heat exchanger vessel for a heat pipebased nuclear micro-reactor, the heat exchanger vessel comprising a fluid input configured to allow a heat extraction fluid to enter the heat exchanger vessel, a fluid output configured to allow the heat extraction fluid to exit the heat exchanger vessel, a conditioning plate, the conditioning plate extending across the interior volume of the heat exchanger vessel so as to divide the interior volume of the heat exchanger vessel into a first sub-region and a second sub-region, the conditioning plate comprising a plurality of apertures configured so as to permit the heat extraction fluid to flow between the first sub-region and the second sub-region, the fluid input communicating with the first sub-region and the fluid output communicating with the second subregion, the conditioning plate further comprising a plurality of dividers, the plurality of dividers extending from the conditioning plate, and configured so as to partially enclose one or more heat pipes, such that heat extraction fluid entering the heat exchanger vessel via the fluid input can pass through both the conditioning plate and between at least two dividers before exiting the heat exchanger vessel via the fluid output. Such a heat exchanger vessel helps even out the cooling effect of the heat extraction fluid on the heat pipes within the heat exchanger vessel, which in turn leads to more even heat extraction from the nuclear core of the reactor at the other end of the heat pipes, improving the lifetime and performance of the nuclear core. The plurality of dividers within the heat exchanger vessel may be arranged concentrically, such that one or more heat pipes can be partially enclosed within or between one or more dividers of the plurality dividers. Such a concentric arrangement provides an advantageous distribution of heat extraction fluid with minimal material and mass addition to the system, which is particularly important for microreactors which may be transported between locations, or being sent into space. One or more of the dividers of the plurality of dividers may have a circular crosssection. One or more of the dividers of the plurality of dividers may have a hexagonal cross-section. The particular choice of cross-section shape may depend on factors such as the specific arrangement of the heat pipes within the core, and the shape of the volume available for the heat exchanger vessel. Each divider of the plurality of dividers can be arranged to partially enclose a single heat pipe. Arranging the dividers in this manner provides greater control over the distribution of heat extraction fluid within the heat exchanger vessel. Each of the plurality of dividers can comprise a circular tube configured to partially enclose a heat pipe. Such a divider arrangement may allow for a simpler manufacturing process and / or the use of less material in the creation of the heat exchanger vessel. The plurality of dividers can be configured so as to form a lattice, with each aperture within the lattice configured to partially enclose a heat pipe. Such an arrangement can be beneficial when for example there is a particularly dense distribution of heat pipes to have heat extracted from. One or more dividers of the plurality of dividers can contain a helical accelerator configured to guide the heat extraction fluid around the part of the heat pipe enclosed by the divider. The addition of a helical accelerator increases the velocity of, and turbulence within, the heat extraction fluid, which in turn increases the at which heat is extracted by the heat extraction fluid from the heat pipe. The heat exchanger vessel can further comprise a plurality of pockets, each of the plurality of pockets being configured to partially enclose a heat pipe, and to protrude into the heat exchanger vessel at least partially between one or more dividers. One advantage of a configuration including pockets for the heat pipes is that it removes the need for a fluid-tight seal between the heat pipes and the heat exchanger vessel where the heat pipes enter the heat exchanger vessel. One or more of the plurality of pockets can comprise one or more fins, the fins being connected to the surface of the pocket within the heat exchanger vessel. Having one or more fins protruding from a pocket increases the surface area of the pocket within the heat exchanger vessel, therefore increasing the volume of heat extraction fluid that can be in contact with the surface of the pocket, which in turn can increase the rate at which heat can be extracted from the pocket, and therefore the rate at which heat can be extracted from the heat pipe that is partially enclosed within the pocket. One or more of the one or more fins can be configured as a helical fin. Having one or more of the one or more fins configured as a helical fin can beneficially influence the speed and flow direction of the heat extraction fluid as it passes over the pocket, to increase the rate of heat transfer from the heat pipe to the heat extraction fluid. The heat exchanger vessel can further comprise a flow restrictor plate, the flow restrictor plate extending across the interior volume of the heat exchanger between the plurality of dividers, the flow restrictor plate comprising a plurality of holes to allow the heat extraction fluid to flow from one side of the flow restrictor plate to the other side of the flow restrictor plate, such that heat extraction fluid entering the heat exchanger vessel via the fluid input can pass between at least two dividers between passing through the flow restrictor plate and passing through the conditioning plate before exiting the heat exchanger vessel via the fluid output. The addition of a flow restrictor plate provides a further control on the flow rate and distribution of the heat extractor fluid through the interior of the heat exchanger vessel, as the flow rate is affected by the size and number of the holes in the flow restrictor plate. In a second aspect there is provided is a nuclear reactor comprising a heat exchanger vessel according to the first aspect. Also provided is a surface power generator comprising a nuclear reactor according to the second aspect. Also provided is a satellite comprising the nuclear reactor according to the second aspect. The skilled person will appreciate that except where mutually exclusive, a feature described in relation to any one of the above aspects may be applied mutatis mutandis to any other aspect. Furthermore, except where mutually exclusive, any feature described herein may be applied to any aspect and / or combined with any other feature described herein. BRIEF DISCRIPTION OF THE DRAWINGS Embodiments will now be described by way of example only, with reference to the Figures, in which: Figure 1 is a schematic cross-section side view of a heat exchanger vessel; Figure 2 is a schematic cross-section plan view along the line A-A’ of Figure 1; Figure 3 is schematic cross-section plan view of another heat exchanger vessel; Figure 4 is schematic cross-section plan view of a further heat exchanger vessel; Figure 5 is a schematic cross-section side view of a further exchanger vessel; Figure 6 is a schematic cross-section side view of a further exchanger vessel; Figure 7 is schematic cross-section plan view of a further heat exchanger vessel; Figure 8 is schematic cross-section plan view of a further heat exchanger vessel; Figure 9 is schematic cross-section plan view of a further heat exchanger vessel; Figure 10 is a schematic oblique view of a heat pipe within a channel; Figure 11 is schematic cross-section side view of a further heat exchanger vessel; Figure 12 is schematic cross-section side view of a further heat exchanger vessel; Figure 13 is schematic cross-section side view of a further heat exchanger vessel; Figure 14 is schematic cross-section side view of a further heat exchanger vessel; Figure 15 is a schematic oblique view of a single pocket within a channel; Figure 16 is schematic cross-section side view of a further heat exchanger vessel; Figure 17 is schematic cross-section side view of a further heat exchanger vessel; Figure 18 is schematic cross-section plan view of the heat exchanger vessel of Figure 17; Figure 19 is schematic cross-section side view of a further heat exchanger vessel; Figure 20 is a simplified schematic of a nuclear reactor; Figure 21 is a simplified schematic of a surface power generator; and Figure 22 is a simplified schematic of a satellite. DETAILED DESCRIPTION Aspects of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects will be apparent to those skilled in the art. Figure 1 shows a schematic cross-sectional side view of an example of a heat exchanger vessel 100 according to the present disclosure. A plurality of heat pipes 12 extend up from the nuclear core (not shown) through a layer of shielding 16 and into the heat exchanger vessel 100. The heat exchanger vessel has a fluid input 18, through which a heat extraction fluid can enter the heat exchanger vessel, and a fluid output 20, through which a heat extraction fluid can exit the heat exchanger vessel. In Figure 1 the fluid input 18 is at the top of the heat exchanger vessel, and the fluid output 20 is on the side of the heat exchanger vessel, level with the bottom of the heat exchanger vessel, but the skilled person will appreciate these positions can be varied, as will be shown. The heat exchanger vessel has a conditioning plate 22 which extends across the interior volume of the heat exchanger vessel, so as to effectively divide the heat exchanger vessel into two sub-regions. The first sub-region 24 is defined as the sub-region in fluid communication with the fluid input 18, and the second sub-region 26 is defined as the sub-region in fluid communication with the fluid output 20. In other words, the first subregion 24 is the sub-region entered first by heat extraction fluid from the fluid input 18, and the second sub-region 26 is the last sub-region the heat extraction fluid passes through before it leaves the heat exchanger vessel via the fluid output 20. In the example of Figure 1 therefore, the first sub-region 24 is the upper region of the heat exchanger vessel as shown in the figure, and the second sub-region 26 is the lower portion of the heat exchanger vessel as shown in the figure. The conditioning plate 22 has a number of apertures 23 within it so as to allow the heat extraction fluid to pass from the first sub-region 24 into the second sub-region 26. By including the conditioning plate 22 within the heat exchanger vessel, the flow of the heat extraction fluid is dispersed more evenly throughout the volume of the heat exchanger vessel 100. Without the conditioning plate, the heat extraction fluid would tend to establish a main flow path between the fluid input and fluid output, with regions of the heat exchanger vessel away from this main flow path experiencing a lower throughput of heat extraction fluid, and consequently lower amounts of heat being extracted from the heat pipes within those regions, leading to uneven heat extraction from the nuclear core. Attached to the conditioning plate are a number of dividers 28. The dividers extend away from the conditioning plate 22 so as to create elongated channels within the heat exchanger vessel which can partially enclose, which is to say enclose a part of, one or more heat pipes 12. Including such dividers 28 creates separation of the heat extraction fluid within the heat exchanger vessel 100, such that the heat pipes no longer all share a common body of heat extraction fluid, but rather each heat pipe 12, or each group of heat pipes, has its own supply of heat extraction fluid in contact with a portion of its length which has not previously interacted with other heat pipes I groups of heat pipes. This subdivision of heat extraction fluid flow into multiple channels helps even out the extraction of heat from the heat pipes within the heat exchanger vessel, which in turn leads to more even heat extraction from the nuclear core of the reactor at the other end of the heat pipes, improving the lifetime and performance of the nuclear core. Figure 2 shows a schematic plan sectional view along the line A-A’ in Figure 1 of one possible arrangement of the dividers 28 within the heat exchanger vessel 100. In the example of Figure 2, both the dividers 28 have circular cross-sectional profiles, and have been arranged in concentric circles, such that the heat pipes 12 are effectively divided into groups of rings of heat pipes, each within a circular channel formed between the dividers. This arrangement provides a trade-off between being simple to construct and still providing a more evenly distributed heat extraction effect by comparison to the known systems of the prior art. Variations on this design will be apparent to the skilled person. For example, further dividers 28 could be added to the arrangement of Figure 2 in order to further subdivide the circular channels into smaller channels, each containing a smaller number of heat pipes 12. An example of such an arrangement is shown in the schematic plan sectional view of Figure 3, where further dividers have been introduced in order to divide up the circular channels created between the circular dividers into smaller subsections, and therefore divide up the heat pipes into smaller groups. Alternatively or additionally, one or more of the dividers 28 could have a hexagonal cross-sectional profile. The schematic plan sectional view of Figure 4 shows an example where both dividers have hexagonal profiles. The skilled person will appreciate that dividers having a hexagonal profile could also incorporate further dividers in order to further subdivide the hexagonal channels into smaller channels, each containing a smaller number of heat pipes 12. The skilled person will further appreciate that, whilst for the sake of clarity the examples shown herein contain only a limited number of heat pipes and a limited number of dividers, the principle can be applied to a great number of heat pipes and dividers. For example, whilst Figures 2, 3, and 4 show only nineteen heat pipes and two concentric dividers, a heat exchanger vessel could contain more or fewer heat pipes, and more or fewer concentric dividers, depending on, for example, the size of the core, the rate of heat release from the core, or the energy levels required from the device containing the heat exchanger vessel. Figure 5 shows a schematic cross-sectional view of another example configuration of the heat exchanger vessel 100, where the fluid input 18 has been located on the side of the heat exchanger vessel. It will be apparent to the skilled person that the location of the fluid input 18 and fluid output 20 can vary, providing that the heat extraction fluid entering the heat exchanger vessel 100 via the fluid input 18 will always pass through the conditioning plate 22 and the dividers 28 before it can exit the heat exchanger vessel via the fluid output 20. Figures 6 and 7 show, respectively, a schematic cross-sectional view, and a schematic plan sectional view along line B-B’, of an alternative conditioning plate and divider arrangement within the heat exchanger vessel 100. In Figures 6 and 7, the dividers 28 are arranged around each individual heat pipe 12, so that each individual heat pipe is partially enclosed by a divider. In other words, each divider creates a channel through which heat extraction fluid can flow around a single heat pipe, with each such channel being fed with heat extraction fluid from the first sub-region 24 of the heat exchanger vessel by at least one aperture 23 through the conditioning plate 22. By having each individual heat pipe partially enclosed by a divider, the space between each heat pipe and the divider partially enclosing it can be reduced. The effect of this is that, for a given flow rate of heat extraction fluid at the fluid input 18, the heat extraction fluid has to flow more quickly through the partial enclosure. This is advantageous as it leads to an increase in the amount of heat energy transferred from the heat pipe into the heat extraction fluid per unit time. In Figure 7, the dividers 28 are formed into cylindrical shapes (i.e. channels having a circular cross-section), but it will be apparent to the skilled person that the dividers could have other cross-sectional profiles, such as hexagons, squares, or ovals, depending on such factors as the space available, the required packing density, or the manufacturing method used to create the dividers and / or heat exchanger vessel. Figure 8 shows a schematic sectional plan view of an alternative arrangement of dividers 28 within the heat exchanger vessel. As with the examples shown in Figures 6 and 7, each individual heat pipe 12 is partially enclosed by a divider. However, in the example of Figure 8, the dividers are arranged so as to create a lattice, with the channels in the lattice being sized so as to be able to fit a section of an individual heat pipe 12 within them. In the example of Figure 8, the lattice of dividers forms hexagonal-shaped channels, but the skilled person will appreciate the lattice could equally create channels of a different shape, such as a square or rectangular shape. Figure 9 shows a schematic sectional plan view of a further alternative arrangement of dividers 28 within the heat exchanger vessel. In this example, the dividers (indicated by the diagonal hatching in Figure 9) create channels within a block or blocks of material, so as to create a lattice of channels within each of which a section of heat pipe 12 can be inserted. As with the examples of Figures 7 and 8, it will be appreciated that the circular cross-sectional shape of the channels is exemplary, and that the channels could have other cross-sectional profiles. Again, because in this arrangement each individual heat pipe is partially enclosed by a divider, the space between each heat pipe and the divider partially enclosing it can be reduced, causing the heat extraction fluid to flow more quickly through the partial enclosure, and therefore increasing the amount of heat energy transferred from the heat pipe into the heat extraction fluid per unit time. Figure 10 shows a schematic oblique view of a single heat pipe 12 within a channel. In this example the channel has a circular cross-sectional shape, formed by a divider 28 housing a section of a single heat pipe. Attached to the divider is a helical accelerator 30, which serves to guide the heat extraction fluid around the part of the heat pipe within the channel formed by the divider. The addition of the helical accelerator increases the velocity of, and turbulence within, the heat extraction fluid, which in turn increases the amount of heat extracted by the heat extraction fluid from the heat pipe compared with a divider arrangement that does not have the helical accelerator. The skilled person will appreciate it is not essential the channel has a circular cross-sectional shape in order to incorporate a helical accelerator, and that it is possible to incorporate a helical accelerator into a channel having a different shape, for example a channel having a square or hexagonal cross-sectional shape. Figure 11 shows a schematic cross-sectional side view of a further example of the heat exchanger vessel 100, in which the location of the conditioning plate 22 and the dividers 28 has been inverted, such that the heat pipes 12 now pass through apertures 23 in the conditioning plate 22 before entering the channels between the dividers 28. In this orientation, the fluid input 18 is still in fluid communication with the first sub-region 24, but the first sub-region is now in the lower portion of the heat exchanger vessel as shown in the figure, with the heat pipes passing through the first sub-region into the second sub-region. In the example of Figure 11, the heat extraction fluid passes through the conditioning plate 22 and then around the edge of the heat pipes 12, but it will be understood extra apertures in the conditioning plate may be present to allow heat extraction fluid to pass though the conditioning plate from the first sub-region 24 to the second sub-region 26 at an increased rate. Then, as with the other examples, the heat extraction fluid passes between the dividers 28, which are now in the upper region of the heat exchanger vessel as shown in the figure, before exiting the heat exchanger vessel 100 via the fluid output 20. It will be apparent that this configuration has advantages over the known art, in that the flow of the heat extraction fluid is dispersed more evenly throughout the volume of the heat exchanger vessel 100, leading to more even heat extraction from the heat pipes, and consequently more even heat extraction from the nuclear core. Furthermore, as with other examples where each individual heat pipe is partially enclosed by a divider, the space between each heat pipe and the divider partially enclosing it can be reduced, causing the heat extraction fluid to flow more quickly through the partial enclosure, and therefore increasing the amount of heat energy transferred from the heat pipe into the heat extraction fluid per unit time. In an alternative configuration of the examples of the heat exchanger vessel where each individual heat pipe is partially enclosed by a divider, such as the examples shown in Figures 6, 7, 8, 9, and 11, the channels formed by the dividers which do not partially enclose a heat pipe can be sealed off, as shown in Figure 12. This effectively recreates the channel arrangement shown in Figure 9, but with the block or blocks of material that form the dividers being hollow. The advantage of blocking off the space in the second sub-region between the dividers is that it eliminates the possibility of heat extraction fluid getting stuck in a location away from the flow path, and consequently not removing the heat energy it absorbs from the heat exchanger vessel. This is particularly relevant in the configuration shown in Figure 11 if the heat exchanger vessel is working in an environment with a downwards gravitational pull, as this would make it more difficult for the heat extraction fluid to reach the fluid output if flowed into one of the spaces between the channels formed by the dividers. Figure 13 shows a schematic cross-section side view of another example of the heat exchanger vessel 100. In this example, the heat exchanger vessel incorporates a plurality of pockets 32, each of the plurality of pockets being configured to partially house a heat pipe 12, and to protrude into the heat exchanger vessel at least partially into the channels formed between two or more dividers 28, or (in the case of the channels at the edge of the heat exchanger vessel) between a divider and the wall of the heat exchanger vessel. Forming a seal between the heat pipes 12 and the heat exchanger vessel 100 can be challenging to implement, particularly where the heat extraction fluid is a gas such as helium. The advantage of a configuration including pockets for the heat pipes is that it removes the need for a fluid-tight seal between the heat pipes 12 and the heat exchanger vessel 100 where the heat pipes enter the heat exchanger vessel. The pockets 32 also help accommodate heat expansion that the heat pipes might undergo when they start operating. The pockets can be filled with a heat conducting medium (not shown), which will vary depending on the operating environment. Examples of possible heat conducting mediums include helium, nitrogen, molten salts, or liquid metals, which allow the heat to be transferred from the heat pipe to the wall of the heat exchanger vessel, through the wall of heat exchanger vessel 100 and into the heat extraction fluid within the heat exchanger vessel. It will be apparent to the skilled person that the incorporation of pockets in the heat exchanger vessel is compatible with any of the other examples of the heat exchanger vessel included herein, providing the channels between the dividers is of a size that can accommodate such a pocket. Figure 14 shows a schematic cross-section side view of another example of the heat exchanger vessel 100. In this example, the heat exchanger vessel incorporates a plurality of pockets 32, wherein each pocket has had fins 38 connected to the surface of the pocket within the heat exchanger vessel. The addition of such fins increases the surface area of the pocket within the heat exchanger vessel, therefore increasing the volume of heat extraction fluid that can be in contact with the surface of the pocket, which can increase the rate at which heat can be extracted from the pocket, and therefore the heat pipe that is partially enclosed within the heat pipe. Whilst Figure 14 shows each of the pockets 32 having the same number of fins 38 extending from the pockets at similar locations on the pocket surface, it will be apparent to the skilled person that not every pocket needs to have the same number of fins attached to it (or indeed have any fins attached to them), nor do each of the fins have to have the same profile or be in the same location. For example, it may be beneficial for only those pockets next to the edge of the heat exchanger vessel to have fins attached to them, and / or it may be beneficial for the fins to adopt a helical profile, i.e. as a helical fin, much like the helical accelerator, so as to beneficially influence the speed and flow direction of the heat extraction fluid as it passes over the pocket. Figure 15 shows a schematic oblique view of a single pocket 32 within a channel, with the channel in this example having a circular cross-sectional shape, formed by a divider 28 housing a section of a pocket 32. Attached to the pocket 32 is a helical accelerator 30, which serves to guide the heat extraction fluid around the part of the heat pipe within the channel formed by the divider. This example takes advantage of the fact that it is easier to attach a helical accelerator to a pocket than it is to attach it directly to a heat pipe. Having the helical accelerator directly attached to the pocket allows for improved heat transfer from the heat pipe, as the pocket and the helical accelerator are now in physical contact, meaning heat can be transferred into the helical accelerator by conduction. Furthermore, as with the example of Figure 10, the addition of the helical accelerator increases the velocity of, and turbulence within, the heat extraction fluid, which in turn increases the amount of heat extracted by the heat extraction fluid from the heat pipe compared with a divider arrangement that does not have the helical accelerator. The skilled person will appreciate that, as with the example of Figure 10, it is not essential the channel has a circular cross-sectional shape in order to incorporate a helical accelerator, and that it is possible to incorporate a helical accelerator into a channel having a different shape, for example a channel having a square or hexagonal cross-sectional shape. Figure 16 shows a schematic cross-section side view of another example of the heat exchanger vessel 100. In this example, the heat exchanger vessel has two fluid inputs 18, each being in fluid communication with the first sub-region 24. The skilled person will understand additional fluid inputs could be added at other locations in fluid communication with the first sub-region. This might be useful if space around the first sub-region is limited, such that it is not possible to attach one fluid input of sufficient cross-sectional area to provide the flow rate of heat extraction fluid necessary to extract the required amount of heat from the heat pipes in a given time. In this situation, multiple smaller fluid inputs could be used to cumulatively provide the necessary flow rate of heat extraction fluid. Figure 16 also has two fluid outputs 20, each being in fluid communication with the second sub-region 26. The skilled person will understand additional fluid outputs could be added at other locations in fluid communication with the second sub-region, if, for example, there is no space for a single fluid output capable of providing the necessary flow rate of heat extraction fluid. Figure 17 shows a schematic cross-section side view, and Figure 18 shows a schematic cross-section plan view from the line C-C’ (in the direction indicated by the arrows at the ends of the line C-C’) in Figure 17, of another example of the heat exchanger vessel 100. In the example of Figures 17 and 18, a flow restrictor plate 34 extends across the interior volume of the heat exchanger between the plurality of dividers, which is to say the flow restrictor plate 34 extends across the interior volume of the heat exchanger in the spaces between the channels formed by the plurality of dividers. The flow restrictor plate has a plurality of holes 36 going through it which allow the heat extraction fluid to flow from one side of the flow restrictor plate to the other side of the flow restrictor plate. In the example of Figures 17 and 18, the heat extraction fluid enters the first sub-region 24 via the fluid input 18, where it flows around the outside of the channels formed by the dividers 28. The heat extraction fluid will then flow through holes 36 in the flow restrictor plate, in the direction of the open ends of the channels (i.e. the ends of the channels furthest from the conditioning plate) formed by the dividers 28. Upon reaching the open ends of the channels, the heat extraction fluid can then enter the channels formed between the dividers, and flow along the edge of the heat pipe (or pocket, if pockets have been incorporated into the heat exchanger vessel, although this option is not shown here) until it reaches the conditioning plate 22, at which point it will flow through one the apertures in the conditioning plate 22 into the second sub-region 26, and then out of the heat exchanger vessel 100 via the fluid output 20. The advantage of introducing a flow restrictor plate is that it provides a further control on the flow rate of the heat extractor fluid through the interior of the heat exchanger vessel, the flow rate being affected by the size and number of the holes in the flow restrictor plate. Figure 19 shows a schematic cross-section side view of an example heat exchanger vessel where the flow direction is reversed compared to that shown in Figure 17, such that the heat extraction fluid passes through the apertures 23 in the conditioning plate 22 first, then alongside the heat pipes (which in this example are within pockets 32) in the channel between dividers 28 second, before passing through the holes 36 in the flow restrictor plate 34 and then out through the fluid output 20. In the example of Figures 17 and 18, this would be the equivalent of swapping the positions of the fluid input 18 and the fluid output 20. Whichever way the fluid input 18 and fluid output 20 are arranged, the heat extraction fluid entering the heat exchanger vessel via the fluid input can pass between at least two dividers (i.e. through the channels formed by the plurality of dividers) between passing through the conditioning plate and passing through the flow restrictor plate before exiting the heat exchanger vessel via the fluid output. Figure 20 shows a simplified schematic view of a nuclear reactor 200. Within the nuclear reactor there is, among other components, a nuclear core 10 and a heat exchanger vessel 100. A nuclear reactor comprising a heat exchanger vessel 100 according to any of the example heat exchanger vessels included herein will benefit from the improved performance and lifetime of the nuclear core 10 resulting from the features of said heat exchanger vessel 100 outlined above. Figure 21 shows a simplified schematic view of a surface power generator 300. Within the surface power generator there is, among other components, a nuclear reactor 200 comprising a heat exchanger vessel 100 according to any of the example heat exchanger vessels included herein. Such a surface power generator will benefit from the improved performance and lifetime of the nuclear reactor 200 resulting from the features of said heat exchanger vessel. Figure 22 shows a simplified schematic view of a satellite 400. Within the satellite there is, among other components, a nuclear reactor 200 comprising a heat exchanger vessel 100 according to any of the example heat exchanger vessels included herein. Such a satellite will benefit from the improved performance and lifetime of the nuclear reactor 200 resulting from the features of said heat exchanger vessel. The skilled person will appreciate that the choice of materials used to make the heat 5 exchanger vessel, and the sub-components such as the conditioning plate 22, the dividers 28, the pockets 32, and the flow restrictor plate 34, will depend on the environment in which, and the temperature range at which, the heat exchanger vessel is operating. Some examples of suitable materials from which the heat exchanger vessel and its sub-components could be made include Alloy 617, 316 Stainless steel, 10 Alloy 800H, Alloy 625, and 9-12Cr Steel. It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the 15 disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

1. A heat exchanger vessel for a heat pipe-based nuclear micro-reactor, the heat exchanger vessel comprising:a fluid input configured to allow a heat extraction fluid to enter the heat exchanger vessel;a fluid output configured to allow the heat extraction fluid to exit the heat exchanger vessel;a conditioning plate, the conditioning plate extending across the interior volume of the heat exchanger vessel so as to divide the interior volume of the heat exchanger vessel into a first sub-region and a second sub-region, the conditioning plate comprising a plurality of apertures configured so as to permit the heat extraction fluid to flow between the first sub-region and the second sub-region, the fluid input communicating with the first sub-region and the fluid output communicating with the second sub-region;the conditioning plate further comprising a plurality of dividers, the plurality of dividers extending from the conditioning plate, and configured so as to partially enclose one or more heat pipes, such that heat extraction fluid entering the heat exchanger vessel via the fluid input can pass through both the conditioning plate and between at least two dividers before exiting the heat exchanger vessel via the fluid output.

2. The heat exchanger vessel of claim 1, wherein the plurality of dividers are arranged concentrically, such that one or more heat pipes can be partially enclosed within or between one or more dividers of the plurality dividers.

3. The heat exchanger vessel of claim 2, where one or more of the dividers of the plurality of dividers have a circular cross-sectional profile.

4. The heat exchanger vessel of claim 2, where one or more of the dividers of the plurality of dividers have a hexagonal cross-sectional profile.

5. The heat exchanger vessel of claim 1, wherein each divider of the plurality of dividers is arranged to partially enclose a single heat pipe.

6. The heat exchanger vessel of claim 5, wherein each of the plurality of dividers comprises a circular tube configured to partially enclose a heat pipe.

7. The heat exchanger vessel of claim 5, wherein the plurality of dividers are configured so as to form a lattice, with each aperture within the lattice configured to partially enclose a heat pipe.

8. The heat exchanger vessel of claim 5, 6, or 7, wherein within one or more dividers of the plurality of dividers contains a helical accelerator configured to guide the heat extraction fluid around the part of the heat pipe enclosed by the divider.

9. The heat exchanger vessel of any preceding claim wherein the heat exchanger vessel further comprises a plurality of pockets, each of the plurality of pockets being configured to partially enclose a heat pipe, and to protrude into the heat exchanger vessel at least partially between one or more dividers.

10. The heat exchanger vessel of claim 9, wherein one or more of the plurality of pockets comprises one or more fins, the fins being connected to the surface of the pocket within the heat exchanger vessel.

11. The heat exchanger vessel of claim 10, wherein one or more of the one or more fins is configured as a helical fin.

12. The heat exchanger vessel of claim 5, 6, 7, or 8, further comprising a flow restrictor plate, the flow restrictor plate extending across the interior volume of the heat exchanger between the plurality of dividers, the flow restrictor plate comprising a plurality of holes to allow the heat extraction fluid to flow from one side of the flow restrictor plate to the other side of the flow restrictor plate, such that heat extraction fluid entering the heat exchanger vessel via the fluid input can pass between at least two dividers between passing through the flow restrictor plate and passing through the conditioning plate before exiting the heat exchanger vessel via the fluid output.

13. A nuclear reactor comprising the heat exchanger vessel of any preceding claim.

14. A surface power generator comprising the nuclear reactor of claim 13.

15. A satellite comprising the nuclear reactor of claim 13.

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