GB2629925A

GB2629925A - Heat exchanger

Info

Publication number: GB2629925A
Application number: GB2408523.5A
Authority: GB
Inventors: J Narborough David
Original assignee: Rolls Royce Submarines Ltd
Current assignee: Rolls Royce Submarines Ltd
Priority date: 2024-06-14
Filing date: 2024-06-14
Publication date: 2024-11-13
Also published as: WO2025256922A1; GB202408523D0

Abstract

A heat exchanger 100 for a heat pipe-based nuclear micro-reactor, the heat exchanger comprising: a first fluid inlet 10 where heat extraction fluid can enter the heat exchanger, a second fluid inlet 20 where heat extraction fluid can enter the heat exchanger, a first fluid outlet 30 where heat extraction fluid can exit the heat exchanger, and a second fluid outlet 40 where heat extraction fluid can exit the heat exchanger; an internal structure 50 configured to provide a first helical flow path between the first fluid inlet and first fluid outlet, and a second helical flow path between the second fluid inlet and second fluid outlet, the first helical flow path and second helical flow path being separate from one another and interlayered with one another; and a plurality of elongate hollow elements 60 oriented so as to pass through both the first helical flow path and the second helical flow path. At least one of the elongate hollow members may be a heat pipe. A generator system comprising the heat exchanger and a nuclear power plant comprising the generator system is also claimed.

Description

HEAT EXCHANGER

FIELD OF THE DISCLOSURE

The present disclosure relates to nuclear power systems, and more specifically to a 5 heat exchanger for a nuclear micro-reactor.

BACKGROUND

Nuclear fission reactors use the fission process which generates heat in the nuclear reactor core as a source of energy which can then be converted into electricity. For example, heat energy can be extracted from the core and used to raise the temperature of a working fluid in an engine, for example a Brayton cycle engine, creating a rotational movement which in turn can be used to rotate coils within a dynamo to generate an electrical current.

An important consideration in designing a nuclear reactor is how to extract heat from the reactor core in such a way as to maximise the efficiency with which fuel in the core is used. One factor that determines the efficiency is the distribution of heat extraction from the core. In the absence of any means to control the distribution of heat extraction, "hot spots" of fuel depletion may develop within the core, which lead to inefficient fuel burnup. Heat pipes have been proposed as a means by which to extract heat from a nuclear reactor core. One advantage of using multiple heat pipes is that each individual heat pipe is self-contained, and so the failure of one heat pipe does not affect the ability of the other heat pipes to function. Alternatively, fluid flow (for example the flow of gasses or liquids) has been used to transport heat out of the core. However, the means for extracting heat energy from the heat pipes or fluid flow(s) needs to be optimised to provide consistent rates of heat extraction across the core. Having heat energy extracted from different parts of the core at different rates can lead to an undesirable heat extraction profile within 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.

Reliability of operation is a further factor which is to be considered in the design of nuclear reactors which are to be deployed in remote environments, either terrestrial or extraterrestrial. One way to improve the reliability and longevity of a nuclear reactor is through redundancy. In terms of redundancy in power generation, it may be desirable to include more than one means to generate electricity. For example, a power generation system could include two or more engines and/or dynamos, such that if one fails, the system can still continue to produce electricity. In this case there is a further challenge of designing a means for achieving a desirable heat extraction profile within the core, whilst simultaneously providing for the ability to supply heat to two or more means for generating electricity. A yet further challenge is developing such a system that will continue to function and provide evenly distributed heat extraction from the core even in the event of the failure of a means for generating electricity.

SUMMARY

The present disclosure provides a heat exchanger as set out in claim 1, a generator system as set out in claim 6, and a nuclear power plant as set out in claim 9. Optional features are included in the dependent claims.

According to a first aspect there is provided a heat exchanger for a heat pipe-based nuclear micro-reactor, the heat exchanger comprising: a first fluid inlet where heat extraction fluid can enter the heat exchanger, a second fluid inlet where heat extraction fluid can enter the heat exchanger, a first fluid outlet where heat extraction fluid can exit the heat exchanger, and a second fluid outlet where heat extraction fluid can exit the heat exchanger; an internal structure configured to provide a first helical flow path between the 25 first fluid inlet and first fluid outlet, and a second helical flow path between the second fluid inlet and second fluid outlet, the first helical flow path and second helical flow path being separate from one another and interlayered with one another; and a plurality of elongate hollow elements oriented so as to pass through both the first helical flow path and the second helical flow path.

At least one elongate hollow element of the plurality of elongate hollow elements can comprise a heat pipe.

At least one elongate hollow element of the plurality of elongate hollow elements can be a sleeve.

At least one elongate hollow element of the plurality of elongate hollow elements can comprise one or more protruding elements, the one or more protruding elements being configured to increase the rate at which heat is transferred from the elongate hollow element.

The cross-sectional area of the first flow path can be different to the cross-sectional 10 area of the second flow path.

According to a second aspect, there is a generator system comprising the heat exchanger of the first aspect.

The generator system can comprise a power generation circuit comprising a first generator system and a second generator system, wherein the heat extraction fluid flows from the first fluid outlet to the first generator system, from the first generator system back to the second fluid inlet, through the second helical flow path of the heat exchanger to the second fluid outlet, then from the second fluid outlet to the second generator system.

The generator system can comprise a first generator system and a second generator system, wherein a first heat extraction fluid flows from the first fluid outlet to the first generator system, and from the first generator system to the first fluid inlet, and a second heat extraction fluid flows from the second fluid outlet to the second generator system, and from the second generator system to the second fluid inlet.

According to a third aspect, there is provided a nuclear power plant comprising the 25 generator system of 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: FIG. 1 shows a schematic section view of heat exchanger vessel; FIG. 2 shows a schematic isometric section view of an example heat exchanger vessel; FIG. 3 shows a schematic isometric view of an example heat exchanger vessel; FIG. 4 shows a schematic isometric view of an example heat exchanger vessel; FIG. 5 shows a schematic isometric view of an example heat exchanger vessel; FIG. 6 shows an example elongate hollow element; FIG. 7 shows an example elongate hollow element; FIG. 8 shows an example elongate hollow element; FIG. 9 shows an example elongate hollow element; FIG. 10 shows a close-up view of part of an example heat exchanger; FIG. 11 shows a schematic example of a generator system; FIG. 12 shows a schematic example of a generator system; and FIG. 13 shows a symbolic representation of a nuclear power plant.

DETAILED DESCRIPTION

Aspects and embodiments of the present disclosure will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art.

FIG. 1 shows a schematic sectional side view, and FIG. 2 shows a schematic isometric sectional view, of an example of a heat exchanger 100. The heat exchanger has a first fluid inlet 10 and a second fluid inlet 20, both of which a heat extraction fluid can enter the heat exchanger 100 through. The heat exchanger also has a first fluid outlet 30 and second fluid outlet 40, both of which a heat extraction fluid can exit the heat exchanger through. Within the heat exchanger 100 there is an internal structure 50. The internal structure 50 extends longitudinally through the interior of the heat exchanger 100, and radially across the interior of the heat exchanger 100. In the example heat exchanger 100 of FIG. 1 and FIG. 2, the internal structure 50 divides the heat exchanger into a first helical flow path between the first fluid inlet 10 and first fluid outlet 30, and a second helical flow path between a second fluid inlet 20 and second fluid outlet 40. The internal structure 50 separates the first helical flow path and the second helical flow path from one another, such that heat extraction fluid flowing along the first helical flow path cannot cross into the second helical flow path, and vice versa. In the example heat exchanger 100 the internal structure 50 has a corkscrew-like form, with a helical surface coiled round a central cylindrical pillar 80. However, the skilled person will understand that some variation on this shape is possible whilst still fulfilling the conditions that the flow paths created are helical, and that the first helical flow path and the second helical flow path are kept separate from one another. For example, it is not essential to have a central cylindrical pillar as shown in FIG.s 1 and 2, as the sides of the helical surface can be curved round to join one another to create a boundary between the flow paths at the axis of the helix, as shown in the section of the example internal structure 50 of FIG. 3.

In the example heat exchanger of FIG.s 1 and 2, the first and second helical flow paths are interlayered with one another, which is to say that when the heat exchanger is viewed from one angle, sections of the first flow path are sandwiched between sections of the second flow path, and vice versa, and when the heat exchanger is viewed from another angle, sections of the first flow path are overlaid by sections of the second flow path, and vice versa. The importance of this interlayered arrangement is discussed below.

Referring back to FIG.1 and FIG.2, passing through the heat exchanger 100 are a number of elongate hollow elements 60, each of which intersects and passes through 5 the first helical flow path and the second helical flow path. The elongate hollow elements of FIG. 1 and FIG. 2 are shown having a cylindrical form, but the exact form of the elongate hollow elements can vary as will be explained. The elongate hollow elements are impermeable, which is to say any heat extraction fluid following along either the first or second helical flow path within the heat exchanger is unable to enter any of the 10 elongate hollow elements, and any fluid in the elongate hollow elements is unable to enter into either of the first or second helical flow paths.

Each helical flow path can cover at least one full 360 degree rotation around the axis of the helical flow path. Preferably each helical flow path covers more than one 360 degree rotation around the axis of the helical flow path. For example, each helical flow path might cover an equivalent of 720 degrees, or 900 degrees, or more, around the axis of the helical flow path. Providing each helical flow path covers at least one full 360 degree rotation around the axis of the helical flow path, each elongate hollow element 60 will pass through both the first and second helical flow paths at least once. In general, an increased number of rotations around the axis of the helical flow path will lead to more heat being extracted from the elongate hollow elements 60, as each helical flow path will flow around each elongate hollow element more than once. In addition, where the number of rotations for a given height of heat exchanger is increased, the commensurate decrease in the cross-sectional area will lead to an increase in the velocity of the fluid flow, which in turn will mean increased turbulence in the fluid flow and an increase in the heat transfer coefficient, leading to an increase in heat extraction from the elongate hollow elements 60.

Furthermore, by having two separate helical flow paths, heat extraction from the core is more evenly distributed. This is because the greatest differential in temperature between an elongate hollow element and the heat extraction fluid is at the first elongate hollow element the heat extraction fluid comes into contact with after entering the heat exchanger, before it has been warmed up by contact with any other elongate hollow elements. In heat exchangers only having a single flow path, helical or otherwise, only a limited number of elongate hollow elements (possibly even just a single elongate hollow element) will make contact with the heat extraction fluid before the heat extraction fluid has been in contact with any other elongate hollow elements. By comparison, in the heat exchanger of FIG.1 and FIG. 2 which has two separate helical flow paths, twice as many elongate hollow elements will interact with heat extraction fluid before it has been in contact with any other elongate hollow elements, which will therefore benefit from the increased heat transfer caused by the maximum temperature differential between the heat extraction fluid and the elongate hollow element(s) 60.

It will be apparent to the skilled person whilst the example heat exchanger 100 of FIG.s 1 and 2 (and FIG.s 11 and 12) shows a heat exchanger 100 with just two separate helical flow paths, it is possible to shape the internal structure 50 so as to create three, four, or more separate helical flow paths within the heat exchanger. FIG. 4 shows a schematic of an example heat exchanger 100 having three separate helical flow paths. The elongate hollow elements 60 have been omitted from FIG. 4 (and FIG. 5) for clarity. Heat exchangers 100 having an increased number of separate flow paths can consequently benefit from further increased evenness of heat extraction distribution from the core.

It will be apparent to the skilled person that whilst the example heat exchangers 100 of FIG. 1, FIG. 2, and FIG. 3 show heat exchangers 100 with helical flow paths having the same cross-sectional area, it is possible to shape the internal structure 50 so as to create helical flow paths having different cross-sectional areas. FIG.5 shows a schematic example where the first helical flow path has a height Z, and the second helical flow path has a height X, which is greater than Z, leading to the second helical flow path having a greater cross-sectional area than the first helical flow path. A heat exchanger having helical flow paths with different cross-sectional areas may allow for different rates of heat exchange across the different helical flow paths, which may be useful depending on (for example) the requirements of the apparatus the different helical flow paths are connected to beyond the heat exchanger.

The elongate hollow elements 60 can take the form of heat pipes. FIG. 6 shows a simplified example where the elongate hollow element 60 takes the form of a heat pipe.

Heat pipes are a known means of transferring heat energy from one location to another. Briefly, heat pipes work by allowing a working fluid sealed within the heat pipe to absorb heat energy and change state at one end of the heat pipe (the "hot" end). The working fluid then travels by convection to the other end of the heat pipe (the "cold" end), where, owing to the cooler temperature, the working fluid releases its heat energy through the external surface of the heat pipe, and in doing so condenses back into a liquid state, before returning to the hot end of the heat pipe via capillary action to begin the process again. When the elongate hollow elements 60 take the form of heat pipes, the "cold" 5 end of the heat pipes will extend into the heat exchanger vessel from a nuclear reactor core, which serves to heat the "hot" end of the heat pipes. The heat energy will then be conveyed into the heat exchanger vessel 100 by the heat pipe, where it will be transferred into the heat extraction fluid as it flows between the heat pipes as it follows the helical flow path between the first fluid inlet and first fluid outlet. As a result, these 10 "cold" ends of the heat pipes will be cooled, and the heat energy will be conveyed away by the heat extraction fluid.

Alternatively, the elongate hollow elements 60 can take the form of sleeves, into which (for example) heat pipes extending from a nuclear reactor core could be inserted, or hot fluid that has passed through a nuclear reactor core could be flowed. FIG. 7 shows a schematic example where the elongate hollow element 60 takes the form of a sleeve, with a heat pipe inserted into it. It may be beneficial for the elongate hollow elements 60 to take the form of sleeves, as sleeves can be made of any suitable material, whereas (for example) the material used for a heat pipe will depend at least on the working fluid contained within the heat pipe, which in turn is determined by the range of temperatures over which the heat pipe will be operating. As such, the sleeve could be made out of the same material as the rest of the heat exchanger vessel, which maybe be beneficial in terms of dealing with the thermal expansion such vessels might undergo in proximity to a nuclear reactor core. Making the elongate hollow elements 60 out of the same material as the rest of the heat exchanger vessel would make it easier to manufacture the heat exchanger vessel using additive layer manufacturing (ALM) methods, which may allow for greater ease of construction.

As alluded to earlier, the exact form of the elongate hollow elements 60 can vary. This is particularly the case if the elongate hollow elements 60 take the form of sleeves, as the shape of the sleeves can be tailored to best suit their content (i.e. heat pipes or fluid), or to increase the efficiency of heat transfer to the heat extraction fluid. In the case of heat pipes, which are generally straight, the elongate hollow elements 60 will likely also be straight as illustrated in the examples of FIG. 1 and FIG. 2. However, it will be appreciated that if the elongate hollow elements 60 are providing passage for fluid, they do not have to be straight, and instead could have (for example) a non-linear profile, such as illustrated in FIG. 8. It will therefore be understood that whilst for illustrative purposes the elongate hollow elements of FIG. 1 and FIG. 2 have a straight, cylindrical form, the exact form of the elongate hollow elements can vary.

Furthermore, the elongate hollow elements may include one or more protruding 5 elements, which protrude into the helical flow paths so as to increase the surface area of the elongate hollow element which is in contact with the heat extraction fluid flowing through the helical flow path, which can lead to an increased rate of heat transfer from the elongate hollow element to the fluid flowing through the helical flow path. An example of an elongate hollow element 60 having protruding elements is shown in FIG. 10 9. It will be appreciated that the exact form of the protruding elements 90 can vary, and that the shape, size, and arrangement of those shown in FIG.9 are purely for illustrative purposes.

FIG. 10 shows a close-up view of the part of the example heat exchanger 100 within the box A denoted by the dot-dash line in FIG. 1 between a section of the internal structure 50 and a wall of the heat exchanger 100. It is envisaged that a bellows 70, i.e. a section of concertinaed material, can be included between the internal structure and the interior of the heat exchanger 100 in order to account for any difference in the rates of thermal expansion between the internal structure and the walls of the heat exchanger. In the example of FIG. 10 the folds of the bellows are oriented so as to run parallel to the wall of the heat exchanger, which should mean the channels formed by the bellows run in generally the same direction as the flow path of the heat extraction fluid travelling through the heat exchanger, but it will be appreciated this is not essential in order for the bellows to perform their function. Similar such bellows could also be included between the elongate hollow elements 60 and the internal structure 50, if desired. Whilst FIG. 10 shows a section of the example heat exchanger of FIG. 1, it will be appreciated that such bellows 70 could be incorporated into any of the example heat exchangers described herein.

Whether the elongate hollow elements 60 take the form of heat pipes or sleeves, the at least first and second helical (i.e. corkscrew-like) flow paths induced within the heat exchanger 100 by the internal structure mean that the heat extraction fluid can flow around each of the elongate hollow elements 60 several times between entering the heat exchanger vessel 100 via one of the fluid inlets 10, 20 and exiting the heat exchanger vessel 100 via one of the fluid outlets 30, 40. As such, the distribution of heat energy extraction across the plurality of elongate hollow elements 60 is fairly even, which in turn leads to a more even distribution of heat extraction from the nuclear reactor core, which in turn reduces the appearance of hot spots in the nuclear reactor core, leading to the reactor being cheaper to run and having an increased operational lifetime.

A heat exchanger having at least first and second separate helical flow paths has the advantage that at least two separate flows of heat extraction fluid can be passed through the heat exchanger. Consequently, for example, a generator system comprising such a heat exchanger vessel could also employ two or more separate power conversion systems, or converters. A schematic example of a generator system arrangement using a heat exchanger with two separate helical flow paths supplying two converters is illustrated in FIG. 11. In the example generator system 200 of FIG. 11, the heat extraction fluid can flow into the heat exchanger 100 via the first fluid inlet 10 (the arrows indicating the direction of flow of the heat extraction fluid), and then pass through the heat exchanger 100 by flowing along a first helical flow path (represented by the dotted line in FIG. 11), absorbing heat from the elongate hollow elements (not shown in FIG. 11) that it flows past within the heat exchanger 100, eventually exiting the heat exchanger via the first fluid outlet 30. Thus heated, the heat extraction fluid can then flow from the first fluid outlet 30 to the first converter 110, where (for example) the heat energy carried by the heat extraction fluid can be extracted and converted into mechanical energy for converting into electrical energy, with some remaining heat being ejected via, for example, a heat radiation means (not shown). As a result of the energy extraction and heat radiation processes, the heat extraction fluid will be cooler than when it left the heat exchanger 100. The heat extraction fluid can then travel back to the heat exchanger 100, this time entering via the second fluid inlet 20. The heat extraction fluid will then pass through the heat exchanger via the second helical flow path (represented by the dashed line in FIG. 11), to be re-heated as a result of passing over the elongate hollow elements 60 contained within the heat exchanger 100. The heat extraction fluid, having been re-heated within the heat exchanger 100, will then exit the heat exchanger 100 via the second fluid outlet 40, and travel to the second converter 120, where (for example) the heat energy carried by the heat extraction fluid can be extracted and converted into mechanical energy for converting into electrical energy, with further heat removal via a further heat extraction means, such as a radiator (not shown). Once the second converter has extracted work from the heat extraction fluid, and it has been further cooled by the further heat extraction means, the heat extraction fluid can flow back to the heat exchanger and re-enter the heat exchanger via the first fluid inlet 10, thus completing the cycle.

An advantage of such a generator system is that the distribution of heat extraction across the nuclear reactor core (not shown) is such that hot spots are less likely to occur, even if the heat energy required by the first converter is different to the heat energy required by the second converter, as all of the elongate hollow elements are involved in the heating of the heat extraction fluid passing through both the first and second helical flow paths. By comparison, an alternative system having two (or more) converters which instead uses separate heat exchangers, with each heat exchanger encompassing only a subset of elongate hollow elements as a means of adding heat energy into the system, is likely to result in a more uneven distribution of heat extraction from the nuclear reactor core in all circumstances except that where both the first and second converters require the same amount of heat energy, because the amount of heat extracted from the nuclear reactor core via each subset of elongate hollow elements will only be dependent on the energy demands of the converter they are supplying heat energy to. Consequently, such an alternative system would likely require refuelling more often, and would therefore have a shorter operating lifetime, or be more expensive to run. By comparison, a system such as that shown in FIG. 11 may make the reactor safer, as the commensurate reduction in temperature variation within the core reduces the chances of the material limits within the core being exceeded.

It will be apparent to the skilled person that similar systems to that shown in FIG. 11 can be created to work with three, four, or more converters when used with a heat exchanger having the same number (i.e. three, four, or more) of separate helical flow paths.

FIG. 12 shows an alternative generator system 200 comprising the heat exchanger vessel 100. In the example of FIG. 12, the generator system comprises two separate heat extraction fluid circuits. In the first circuit, the heat extraction fluid enters the heat exchanger 100 through the first fluid inlet 10, and flows through the heat exchanger 100 via the first helical flow path (represented by the dotted line in FIG. 12), and exits the heat exchanger via the first fluid outlet 30. The heat extraction fluid then flows from the first fluid outlet to the first converter 110, where (for example) the heat energy carried by the heat extraction fluid can be extracted and converted into mechanical energy for converting into electrical energy. As a result of this energy extraction process, when the heat extraction fluid leaves the first converter 110, it will be cooler than when it entered the first converter 110. If required, the heat extraction fluid can then pass through an excess heat extraction means, before travelling back to the heat exchanger 100, reentering the heat exchanger via the first fluid inlet 10 to flow through the heat exchanger 100 via the first helical flow path once again, thus completing the circuit.

Separately, in the second circuit, the heat extraction fluid flows through the heat exchanger 100 via the second helical flow path (represented by the dashed line in FIG. 12), and exits the heat exchanger via the second fluid outlet 40. The heat extraction fluid then flows from the second fluid outlet to the second converter 120, where (for example) the heat energy carried by the heat extraction fluid can be extracted and converted into mechanical energy for converting into electrical energy. As a result of this energy extraction process, when the heat extraction fluid leaves the second converter 120, it will be cooler than when it entered the second converter 120. If required, the heat extraction fluid can then pass through an excess heat extraction means, before travelling back to the heat exchanger 100, re-entering the heat exchanger via the second fluid inlet 20 to flow through the heat exchanger 100 via the second helical flow path once again, thus completing the second circuit.

As with the generator system 200 of FIG. 11, the generator system 200 of FIG. 12 also evenly distributes heat extraction from the nuclear reactor core, even if the heat energy required by the first converter is different to the heat energy required by the second converter, as all of the elongate hollow elements are involved in the heating of the heat extraction fluid passing through both the first and second helical flow paths. A further advantage of the generator system 200 of FIG. 12 is that even if one of the converters 110, 120 stops working or needs to be shut down, such that the heat extraction fluid no longer flows through one of the helical flow paths, all of the elongate hollow elements will continue to be cooled by the heat extraction fluid flowing through the other of the helical flow paths, and in such a way heat continues to be extracted from the nuclear reactor core (not shown) in an evenly distributed manner. In this way, the heat exchanger allows for redundancy within the means of electricity generation, without sacrificing optimal heat extraction distribution form the nuclear reactor core.

As with the generator system 200 of FIG. 11, it will be apparent to the skilled person that similar systems to that shown in FIG. 12 can be created to work with three, four, or more converters when used with a heat exchanger having the same number (i.e. three, four, or more) of separate helical flow paths.

A generator system 200 comprising the heat exchanger 100 can be used as part of a nuclear power plant. FIG. 13 shows a symbolic representation of such a nuclear power plant 300. Such a nuclear power plant comprising any of the heat exchangers 100 described herein may benefit from a longer operational lifetime, safer operation, and/or cheaper running costs, plus the benefit of potential redundancy measures.

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 disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.

Claims

Claims 1. A heat exchanger for a heat pipe-based nuclear micro-reactor, the heat exchanger comprising: a first fluid inlet where heat extraction fluid can enter the heat exchanger, a second fluid inlet where heat extraction fluid can enter the heat exchanger, a first fluid outlet where heat extraction fluid can exit the heat exchanger, and a second fluid outlet where heat extraction fluid can exit the heat exchanger; an internal structure configured to provide a first helical flow path between the first fluid inlet and first fluid outlet, and a second helical flow path between the second fluid inlet and second fluid outlet, the first helical flow path and second helical flow path being separate from one another and interlayered with one another; and a plurality of elongate hollow elements oriented so as to pass through both the first helical flow path and the second helical flow path.
2. The heat exchanger of claim 1, wherein at least one elongate hollow element of the plurality of elongate hollow elements comprises a heat pipe.
3. The heat exchanger of claims 1, wherein at least one elongate hollow element of the plurality of elongate hollow elements is a sleeve.
4. The heat exchanger of any preceding claim, wherein at least one elongate hollow 20 element of the plurality of elongate hollow elements comprises one or more protruding elements, the one or more protruding elements being configured to increase the rate at which heat is transferred from the elongate hollow element.
5. The heat exchanger of any preceding claim, wherein the cross-sectional area of the first flow path is different to the cross-sectional area of the second flow path.
6. A generator system comprising the heat exchanger of any preceding claim.
7. The generator system of claim 6, comprising a power generation circuit comprising a first generator system and a second generator system, wherein the heat extraction fluid flows from the first fluid outlet to the first generator system, from the first generator system back to the second fluid inlet, through the second helical flow path of the heat exchanger to the second fluid outlet, then from the second fluid outlet to the second generator system.
8. The generator system of claim 6, comprising a first generator system and a second generator system, wherein a first heat extraction fluid flows from the first fluid 5 outlet to the first generator system, and from the first generator system to the first fluid inlet, and a second heat extraction fluid flows from the second fluid outlet to the second generator system, and from the second generator system to the second fluid inlet.A nuclear power plant comprising the generator system of claim 7 or claim 8.