Coolant cleanup and heat-sinking systems, and methods of operating the same

Abstract

To provide combined cleanup and heat sink systems.SOLUTION: Combined cleanup and heat sink systems work in combination with nuclear reactor coolant loops. The combined systems may join hotter and colder sections of the coolant loops in parallel with any steam generator or other extractor and provide optional heat removal therebetween. The combined systems may also remove impurities and debris from a fluid coolant without significant heat loss from the coolant. A cooler in the combined systems may be increased in capacity or be augmented in number to move between purifying cooling and major heat removal from the coolant water, potentially functioning as an emergency cooler. The cooler may be joined to the hotter and colder sections through valved flow paths depending on desired functionality. Sections of the coolant loops may be fully above the cooler, which may be above the reactor, to promote the flow by gravity and enhance isolation of sections of the coolant loop.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] In nuclear reactors with high operating temperatures, a fluid heat exchange medium such as liquid metal or molten salt may be used as the coolant. The heat exchange medium not only transfers heat from the nuclear reactor to at least one of a heat exchanger and a turbine for energy extraction and power generation, but may also function as a heat sink to remove decay heat and other unwanted heat during operation and shutdown. For example, in many nuclear reactor designs, including liquid sodium-cooled fast reactors such as the PRISM reactor, multiple loops of heat exchange medium are used to efficiently transfer heat from the nuclear reactor for power generation and cooling. One loop may be an intermediate loop that passes through a steam generator connected to a turbine and a generator after being heated in an intermediate heat exchanger. Any fluid heat exchange medium such as liquid lead, sodium, or molten salt can be used for heat exchange in this intermediate loop.

Background Art

[0002] In an intermediate loop using a fluid medium, it may be effective to purify the heat exchange medium to remove impurities and debris that may accumulate during operation in a nuclear reactor environment. FIG. 1 is an explanatory diagram showing a purification system 10 according to related art that can be used in combination with an intermediate loop for transporting a fluid heat exchange medium. For example, the system 10 may be a sodium purification loop that can be used in combination with an intermediate coolant loop of a liquid sodium nuclear reactor or a molten salt nuclear reactor.

Summary of the Invention

Problems to be Solved by the Invention

[0003] As shown in FIG. 1, system 10 includes an input 50 and an output 67 that can be connected to the same leg of the intermediate coolant loop, and are separated by a distance sufficient to prevent reverse flow or short circuit between them, for example, several feet apart. The input 50 and output 67 are the suction from and the return to the intermediate coolant loop, and can effect a relatively small amount of coolant removal from / to the intermediate loop and subsequent re-supply. A pump 51 can push the fluid coolant through system 10. The regenerative heat exchanger 60 is used to initially cool the incoming coolant flow 61, and the resulting cooler discharged coolant is re-supplied to the intermediate loop by the output 67. The cooled coolant flow 62 then flows to a cooler 70, which may be a series of small tubes with fins exposed to an open air fan 71 to convect further heat. The cooler 70 can sufficiently reduce the temperature of the coolant such that impurities such as oxides solidify or deposit from the fluid coolant.

[0004] The purifier 80 can include a mechanical filter such as a cold trap, a screen, or other filter media that removes impurities or debris including deposits from chemical reactants, catalysts, and / or solutions, following the cooler 70. Bypass valves 81 and 82 can bypass the flow through the purifier 80, thereby slowly ramping up or down the flow through the purifier 80 during startup or shutdown and controlling it in other ways. The more cold-filtered coolant then passes back through the regenerative heat exchanger 60 through the input 66, reheats the coolant to near the operating temperature, and is then returned through the output 67 to the intermediate loop, usually immediately downstream of the inlet 50 of the intermediate loop. In this way, the coolant passing through system 10 for purification can minimize heat loss from the intermediate loop.

Means for Solving the Problems

[0005] Exemplary embodiments include a system that combines purification and heat removal, and a coolant loop joined to such a system. The coolant loop may have a hot leg connecting between a nuclear reactor and a heat extractor such as a steam generator or a heat exchanger, and a cold leg on the opposite side of the hot leg that returns from the heat extractor to the nuclear reactor. The purification and heat sink system according to the exemplary embodiments connects to at least one of the hot leg and the cold leg, and depending on at least one of the plant situation and the operator input, performs at least one of the functions of removing impurities or debris from the fluid coolant flowing in the loop and removing a substantial amount of heat from the fluid coolant. The composite system may selectively cause flow between the hot leg and the cold leg, thereby bypassing the heat extractor completely and enabling drainage and shutdown operations even if the nuclear reactor is still generating a large amount of heat. Similarly, the composite system can operate with one leg and prevent substantial heat loss while cleaning the coolant during normal operation of the nuclear reactor and the heat extractor. Also, an intermediate mode is possible depending on operations such as flow path formation, liquid feeding, and / or cooling. Purification can be achieved by a cold trap, for example a cooler connected in series with the outlet, and potentially a regenerative heat exchanger that returns to the coolant loop, while heat absorption can be achieved by a cooler connected in parallel with the bypass outlet and returning to the coolant loop, potentially operating in a high-capacity mode.

[0006] The composite system can selectively perform both purification and substantial cooling for the coolant loop, so the system may be configured to operate between both of these modes in a desired level combination. For example, the cooler within the system can switch the mode or level of heat removal. In one mode, only a small amount of heat sufficient to solidify or deposit impurities from the coolant is removed from the coolant, and in another mode, a substantial amount of heat can be removed from the coolant, potentially reaching decay heat or reactor operating level heat. Such modulation from impurity removal level to heat sink level can be achieved by an increase in forced convection, an increase in channel volumetric flow rate, a change in heat sink medium, etc. Similarly, by increasing the inlet volumetric flow rate, increasing the pump pressure, and / or forming a flow path connecting the hot leg and cold leg of the coolant loop between these modes by means of a valve or the like while avoiding purifiers such as cold traps and any regenerative heat exchangers within the system.

[0007] The coolant loop and purification / cooler system according to the embodiment can be used in various plants and coolants including fluid media such as liquid sodium coolant used in a PRISM reactor. The coolant loop can provide a bypass of the entire primary heat extractor such as a steam generator by directly connecting the hot leg and cold leg through the purification cooler system, allowing the heat extractor and associated pumps to be separated and drained for maintenance. The hot leg and cold leg may include portions filled with a fluid column that extends vertically higher than a cooler that is itself above the reactor, and the hot leg and cold leg within the loop may be arranged by a slightly angled horizontal path that retreats towards the reactor to prevent backflow to the heat extractor. Thus, an exemplary embodiment can be installed and operated in combination with some existing types of coolant loops along with the reactor purifier by simply adding cooler capacity and / or adding an outlet to the opposite portion of the loop.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

DETAILED DESCRIPTION OF THE INVENTION

[0009] Exemplary embodiments will become more apparent by describing the accompanying drawings in detail. Here, like elements are represented by like reference numerals, but these reference numerals are given for the purpose of illustration and thus do not limit the terms they describe.

[0010] Since this is a patent document, general and broad rules of interpretation should be applied when reading it. Everything described in this document is an example of the subject matter included in the claims appended below. The specific structural and functional details disclosed herein are merely for the purpose of explaining how to form and use the examples. Some different embodiments and methods not specifically disclosed herein may be included in the claims. Therefore, the claims may be embodied in many alternative forms and should not be construed as limited only to the examples described herein.

[0011] In this specification, ordinal terms such as "first", "second", etc. may be used to describe various elements, but it should be understood that these elements should not be limited to any order by these terms. These terms are only used to distinguish one element from another. When there are ordinals of "second" or higher, there must simply be that number of elements, and there does not necessarily have to be a difference or other relationship. For example, without departing from the scope of the illustrated embodiments or methods, the first element can be called the second element, and similarly, the second element can be called the first element. In this specification, the terms "and", "or", and "and / or" include all combinations of one or more of the related listed items unless it is clearly indicated that only a single item, a subgroup of items, or all items exist. The use of "etc." is defined as "et cetera" and indicates that it includes all other elements belonging to the same group as the previous item in any combination of one or more of "and / or".

[0012] When an element is referred to as "connected to", "coupled to", "fitted to", "attached to", "fixed to", etc. another element, it should be understood that the element may be directly connected to the other element or there may be intervening elements. On the other hand, when an element is expressed as "directly connected to", "directly coupled to", etc. another element, there are no intervening elements. Other terms representing the relationship between elements should be interpreted similarly (e.g., "between" and "direct between", and "adjacent" and "direct adjacent", etc.). Similarly, terms such as "communicatively connected to" include all variations of information exchange and routing between two electronic devices, including intermediate devices and networks, regardless of whether they are wirelessly connected or not.

[0013] As used herein, the singular forms "a", "an", and "the" are intended to include both the singular and the plural forms unless the language clearly dictates otherwise. Indefinite articles such as "a" and "an" introduce or refer to any modified term, whether previously introduced or not, and definite articles such as "the" refer to the same term previously introduced. Thus, "a" and "an" are understood to modify an item that has been previously introduced or is newly recognized, and the definite article modifies the same item as that presented immediately before. The terms "comprises", "comprising", "includes", and / or "including" as used herein specify the presence of the stated features, characteristics, steps, operations, elements, and / or components, but do not themselves preclude the presence or addition of one or more other features, characteristics, steps, operations, elements, components, and / or groups thereof. As used herein, "axial direction" and "vertical direction" are the same up-and-down direction oriented along gravity. "Transverse direction" and "horizontal direction" are directions perpendicular to the "axial direction" and are the lateral directions in a given plane at a given height in a particular axial direction.

[0014] The structures and operations described below may be in a different order than that shown in the figures. For example, at least one of two operations and figures shown consecutively may actually be performed simultaneously or in the reverse order depending on the related functions / acts. Similarly, individual operations in the exemplary methods described below may be repeated individually or consecutively and, apart from the single operations described below, loops or other series of operations may be provided. Any embodiment or method having the features and functions described below should be presumed to be within the scope of the exemplary embodiments in any executable combination.

[0015] The inventors newly recognized that the purification system can not only simply remove impurities from the cooling water, but also be used as a heat sink for the nuclear reactor. The inventors further newly recognized that the purification system can be used as an alternative coolant loop or a parallel coolant loop while the intermediate coolant loop is discharged and worked on, such as during plant maintenance. These uses of the purification system are contrary to its established functions, but the inventors recognized that they can solve the long-standing problems of emergency cooling and operation maintenance that have conventionally been solved by using other systems and / or completely shutting down the plant. The exemplary embodiments described below uniquely enable the solution of these and other problems discovered by the inventors.

[0016] The present invention relates to a heat sink purification system, a nuclear reactor using the same, and a method of using the same. In contrast to the present invention, some of the exemplary embodiments and exemplary methods described below show merely subsets of the various different configurations that can be used as the present invention and / or in connection with the present invention.

[0017] FIG. 2 is an explanatory diagram showing a decay heat removal system 100 according to an exemplary embodiment that can be used in a commercial nuclear power plant. As shown in FIG. 2, some elements of the system 100 according to the exemplary embodiment may be the same as those of the system 10 according to the related art of FIG. 1. Thus, the system 100 according to the exemplary embodiment can also be used in connection with an intermediate loop that conveys a molten heat transfer medium in a plurality of different nuclear power plant designs. The system 100 according to the exemplary embodiment includes an additional, higher-capacity inlet 150 from the intermediate loop and an additional, higher-capacity outlet 180 to the intermediate loop. The inlet 150 may be, for example, a valved connection to the hot leg 4 (FIG. 3) of the intermediate loop where the coolant exits the nuclear reactor. Similarly, the outlet 180 may be, for example, a valved connection to the colder leg 8 (FIG. 3) of the intermediate loop where the coolant enters the nuclear reactor. The inlet 150 and the outlet 180 may be widely spaced apart and potentially on opposite sides of the intermediate loop.

[0018] The decay heat removal system 100 according to the exemplary embodiment has an increased flow rate and heat transfer capacity to dissipate or absorb a significant portion of the heat in the intermediate loop. Thus, instead of avoiding heat loss, the system 100 can function as a decay heat removal system by removing such heat from the intermediate loop and thus from the reactor. To accommodate this large heat sink, additional or larger coolers 170 and fans 171, and additional parallel and / or larger capacity pumps 151 may be used to remove a significant amount of heat from the larger amount of coolant directed through the system 100 according to the exemplary embodiment. For example, the system 100 can remove heat corresponding to about 7% of the full rated heat output of the plant. Of course, the amount of heat varies by plant, but as an example, it may absorb 5 megawatts of heat from a plant rated at 840 megawatts. Also, smaller values can be achieved, such as by selectively activating the cooler and flow path to partially remove decay heat in combination with other heat removal systems.

[0019] Selective activation can be achieved, for example, by the cooler 170 including a plurality of parallel channels having fins for selectively accommodating a larger flow, and / or the fan 171 including a plurality of speeds or a plurality of fans or high-pressure blowers that can be selectively activated to convect a significant amount of heat. Alternatively, for example, the larger cooler 170 can include in parallel other coolant media, immersion sections, countercurrent heat exchangers, printed circuit heat exchangers, plate-frame heat exchangers, and other heat sinks that can be turned on to selectively dissipate a significant amount of heat from the coolant. Thus, the cooler 170 can seamlessly change from a purification mode of removing little heat, such as less than 0.5 MW, from the coolant to a heat absorption mode of removing significant heat, such as about 5 MW or more, from the coolant.

[0020] The decay heat removal system 100 according to an exemplary embodiment can be adjusted between increased decay heat removal and low-level cooling available for purification such as a cold trap. For example, the connections 150 and 180 may be blocked by a valve or the like during normal plant operation without excessive heat loss, and the system 100 may function as a purification system with a purifier 80, return the flow to the outlet 67, and receive the flow near the inlet 50 in an intermediate loop. When additional cooling is required, such as during a transient condition involving a reactor shutdown or loss of another cooling system, the connections 150 and 180 may be opened to allow a larger coolant flow, and the speed, number, and / or type of the pump 151, cooler 170, and / or fan 171 may be increased to increase heat dissipation by the larger coolant flow. Similarly, at least one of the valve 81 and the valve 82 may be closed to avoid at least one of the purifier 80 and the reheater 60 when the system 100 according to an exemplary embodiment is selectively adjusted to a decay heat sink level. By closing the purifier 80, a direct and / or dedicated coolant flow may occur between the connections 150 and 180, and the endothermic through the exemplary system 100 in an additional cooling state may be improved. Thus, the system according to an exemplary embodiment is compatible with almost all coolant loops using cold traps and other purifiers and still provides an optional function of an increased heat sink that can be selectively activated.

[0021] FIG. 3 is an explanatory diagram showing an intermediate coolant loop 200 according to an exemplary embodiment that can be used in a nuclear reactor including a high-temperature reactor such as a PRISM reactor or a molten salt reactor. As shown in FIG. 3, the intermediate coolant loop 200 according to an exemplary embodiment can interface with several related or conventional nuclear reactor components including a nuclear reactor 1 that houses a core 2 having nuclear fuel. The intermediate heat exchanger 3 may transfer heat from the nuclear reactor 1 to the intermediate coolant loop 200 and then transfer the heat to an extractor such as a steam generator 6 or a heat exchanger for power generation.

[0022] As shown in FIG. 3, the intermediate coolant loop 200 is interconnected with a decay heat removal system 100 (FIG. 2) according to an exemplary embodiment via an inlet 150 and an outlet 180. For example, the inlet 150 may take in coolant from the bottom of the hot leg 4 where the coolant first exits the reactor 1 and has the highest energy, and the outlet 180 may return the coolant to the bottom of the cold leg 8 where the coolant is returned to the reactor 1 and has the lowest energy. In the case of typical cold trap purification, the inlets 50 and outlets 67 (FIG. 2) may be taken from the same or nearby positions on the same leg to prevent heat loss, unlike the inlets 150 and outlets 180 which may be separated at the extreme temperature points in the intermediate coolant loop 200 according to an exemplary embodiment. If a transient state or greater heat absorption is desired, at least one of the inlets 50 and outlets 67 may be closed and the inlets 150 and outlets 180 may be opened or activated to finally remove heat from the coolant flowing in reverse through the intermediate heat exchanger 3 and cool the reactor 1.

[0023] The intermediate coolant loop 200 according to an exemplary embodiment is operable in combination with an intermediate pump 7 and a steam generator 6, or other heat extractors, and it is also possible to extract heat from the coolant to generate electricity. At least one of the intermediate pump 7 and the steam generator 6 can optionally be paused and drained while the coolant loop 200 still circulates the coolant and absorbs heat through the inlets 150 and outlets 180. For example, the intermediate pump 7, the steam generator 6, and / or a part of the hot leg 4 and the cold leg 8 can drain to the drain tank 5 by opening a drain valve to drive the coolant by gravity and / or by active pump drive.

[0024] If the gradients of the pipes of the hot leg 4 and the cold leg 8 are appropriate, the pump 7, the steam generator 6, and their associated pipes can be drained. For example, the horizontal pipes of the hot leg 4 and the cold leg 8 form a slight angle with respect to the vertical, for example, they slightly descend towards the steam generator 6 and may have a vertical drop of 5 to 10 millimeters per meter of length in the direction away from the reactor 1. This descending slope, in combination with the exemplary positioning described later, can further prevent backflow and ensure a coolant loop that passes only through a part of the intermediate coolant loop 200 according to the exemplary embodiment.

[0025] The hot leg 4 and the cold leg 8 may be arranged such that the fluid column in the hot leg 4 has a vertical height of 240 and the fluid column in the cold leg 8 has a vertical height of 280. Even if other parts of the loop 200 are drained, the fluid columns of these legs may remain. Since there are fluid columns at vertical heights 250 and 280 above the inlet 150 of the hot leg 4 and the outlet 180 of the cold leg 8, the coolant can still be circulated between the intermediate heat exchanger 3 and the decay heat removal system 100 (Figure 2) through the lower parts of the hot leg 4 and the cold leg 8. In this way, while still removing heat from the reactor 1 through the intermediate heat exchanger 3, it is possible to perform repairs or other operations on the emptied steam generator 6, the intermediate pump 7, and / or any other drained part of the coolant loop 200. Of course, the coolant 200 according to the exemplary embodiment with the system 100 can also be used in a fully filled loop.

[0026] Similarly, in FIG. 3, the system 100, or at least the cooler 170 (FIG. 2) of the system 100, may be disposed at a vertical height 230 above the intermediate heat exchanger 3 at a vertical height 231. Due to the difference between the vertical height 230 and the vertical height 231, the cooling water heated by the heat exchanger 3 rises as its concentration decreases, flows to the cooler 170 to be cooled and its concentration increases, and a natural circulation driving force that returns to the heat exchanger 3 due to the concentration difference can be generated. With this configuration and the accompanying natural circulation, the need for an active pump such as pumps 151 and 7 may be eliminated or reduced. If all other coolant filling parts of the system 100 are below the elevations 240 and 280 of the coolant columns, natural circulation occurs through the heat exchanger 3 into the loop 200 due to gravity and the absence of voids formed under the system 100.

[0027] As shown in FIGS. 2 and 3, the intermediate coolant loop 200 according to an exemplary embodiment and the decay heat removal system 100 according to an exemplary embodiment can be used in combination with several types of reactors and existing components. Some functions of the loop 200 and the system 100 can be achieved only by increasing the capacity of the inlet 50 to the capacity of the inlet 150, increasing the heat absorption capacity of the cooler, and adding a dedicated return outlet 180 to the cold leg 8. The loop 200 and the system 100 can be used during typical reactor operation to remove at least one of impurities and debris from a relatively small flow of coolant, and can also be selectively adjusted to remove all or a significant portion of the decay heat or even the operating heat from the reactor 1 during transient or non-power generating states such as accidents or plant maintenance. Similarly, multiple loops 200 and systems 100 can be used in combination with one reactor 1 to effect a further significant amount of heat transfer and heat absorption from the reactor 1.

[0028] Although the exemplary embodiments and methods have been described as above, those skilled in the art will understand that the exemplary embodiments can be modified or substituted by routine experiments while still falling within the scope of the following claims. For example, by merely allowing for different temperatures and coolants, any number of different reactor types and thermodynamic cycles can be used in the exemplary embodiments. Such variations are not considered to depart from the scope of the present claims.

Claims

[Claim 1] 1. A purifier and heat sink system (100) for a coolant loop (200) having a hot leg (4) that transports fluid coolant from a nuclear reactor (1) to a steam generator (6) that extracts heat from the fluid coolant for power generation, and a cold leg (8) that transports the fluid coolant from the steam generator (6) to the nuclear reactor (1), comprising: an inlet configured to join the coolant loop (200), the inlet including two separate connections (50, 150) with different flow rates, the connections (50, 150) configured to join the hot leg (4); a first outlet (67) configured to join the coolant loop (200); a second outlet (180) configured to mate with the coolant loop (200); a cooler (170, 171) configured to remove heat from the fluid coolant flowing through the inlet; a purifier (80) configured to remove impurities from the fluid coolant exiting the cooler (170, 171), the purifier (80) being in series flow with the first outlet (67) and in parallel flow with the second outlet (180); A purifier and heat sink system (100) comprising:

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