Coolant purification and heat sink systems and methods of operation thereof

Abstract

The combined cleanup and heat sink system operates in conjunction with the reactor coolant loop. The combined system can connect the hot and cold sections of the coolant loop in parallel with any steam generators or other extractors, providing optional heat removal between them. The combined system can also remove impurities and debris from the fluid coolant without significant heat loss from the coolant. The combined system's coolers can be increased in capacity and number to transfer between cleanup cooling and primary heat removal from the coolant water, potentially serving as emergency coolers. The coolers and the hot and cold sections may be connected by valved flow paths depending on the desired function. Sections of the coolant loop may be located entirely above the coolers located above the reactor to facilitate gravity flow and enhance isolation of the coolant loop sections.

Description

[Technical field]

[0001] Reactors with high operating temperatures may use fluid heat exchange media, such as liquid metals or molten salts, as coolants. The heat exchange media may not only transfer heat from the reactor to the heat exchangers and / or turbines for energy extraction and power generation, but may also act as a heat sink to remove decay heat and other unwanted heat during operation and shutdown. Many reactor designs, including liquid sodium-cooled fast reactors such as the PRISM reactor, use multiple loops of heat exchange media to efficiently move heat out of the reactor for power generation and cooling. One loop may be an intermediate loop, where the heat is heated in an intermediate heat exchanger and then passed through a steam generator connected to a turbine and generator. Any fluid heat exchange media may be used for this intermediate loop heat exchange, such as liquid lead, sodium, or molten salts. [Background technology]

[0002] In intermediate loops that use a fluid medium, it may be beneficial to purify the heat exchange medium to remove impurities and debris that may accumulate during operation in a nuclear reactor environment. Figure 1 illustrates a related art purification system 10 that may be used in conjunction with an intermediate loop carrying a fluid heat exchange medium. For example, system 10 may be a sodium purification loop that may be used in conjunction with the intermediate coolant loop of a liquid sodium or molten salt nuclear reactor. Summary of the Invention [Problem to be solved by the invention]

[0003] As shown in FIG. 1, the system 10 includes an input 50 and an output 67 that may be connected to the same leg of the intermediate coolant loop, separated by a sufficient distance, e.g., several feet, to prevent backflow or shorting between them. The input 50 and output 67 are intakes from and returns to the intermediate coolant loop, allowing for the removal and subsequent resupply of relatively small amounts of coolant from / to the intermediate loop. A pump 51 may push the fluid coolant through the system 10. A regenerative heat exchanger 60 is used to initially cool the incoming coolant stream 61, resulting in a cooler exiting coolant that is resupplied to the intermediate loop by output 67. The cooled cooling water stream 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 additional heat. The cooler 70 may reduce the temperature of the coolant sufficiently such that impurities such as oxides solidify or deposit from the fluid coolant.

[0004] Following the cooler 70, the purifier 80 may include a mechanical filter such as a cold trap, screen, or other filter media that traps impurities or debris including chemical reactants, catalysts, and / or sediments that come out of solution. Bypass valves 81 and 82 may bypass the flow through the purifier 80, allowing the flow through the purifier 80 to be ramped up or down or otherwise controlled during start-up or shutdown. The cooler filtered coolant then passes again through the regenerative heat exchanger 60 via input 66, reheating the coolant to near operating temperature before being returned to the intermediate loop via output 67, typically just downstream of the intermediate loop inlet 50. In this manner, the coolant that has passed through the system 10 for purification may minimize heat loss from the intermediate loop. [Means for solving the problem]

[0005] Exemplary embodiments include combined purification and heat rejection systems and coolant loops joined to such systems. The coolant loop may have a hot leg connecting between the reactor and a heat extractor such as a steam generator or heat exchanger, and a cold leg opposite the hot leg returning from the heat extractor to the reactor. Exemplary embodiment purification and heat sink systems connect to the hot leg and / or cold leg and function to remove impurities or debris from the fluid coolant flowing through the loop and / or remove a significant amount of heat from the fluid coolant depending on plant conditions and / or operator inputs. The combined system may selectively provide flow between the hot leg and cold leg, thereby bypassing the heat extractor entirely while the reactor is still generating a large amount of heat, allowing for draining and shutdown operations. Similarly, the combined system may operate with one leg to prevent significant heat loss while still cleaning the coolant during normal reactor and heat extractor operation. Intermediate modes are also possible depending on operations such as flow channeling, pumping, and / or cooling. Purification can be achieved by a cold trap, e.g. a chiller connected in series with the outlet and back to the coolant loop, potentially a regenerative heat exchanger, while heat absorption can be achieved by a chiller connected in parallel with the bypass outlet and back to the coolant loop, potentially operating in a bulk mode.

[0006] Since the composite system can selectively provide both purification and significant cooling to the coolant loop, the system may be configured to operate between both of these modes in any desired level combination. For example, a cooler in the system may switch between modes or levels of heat removal. In one mode, it may only remove a small amount of heat from the coolant, enough to solidify or deposit impurities from the coolant, and in another mode, it may remove a significant amount of heat from the coolant, potentially reaching decay heat or reactor operating levels of heat. Such modulation from impurity removal levels to heat sink levels may be accomplished by increasing forced convection, increasing flowpath volumetric flow rates, changing heat sink media, etc. Similarly, inlet volumetric flow rates may be increased, pump pressures may be increased, and / or flowpaths connecting hot and cold legs of the coolant loop may be formed, such as by valves, between these modes while avoiding purifiers such as cold traps and any regenerative heat exchangers in the system.

[0007] The example coolant loop and purification / chiller system can be used with a variety of plants and coolants, including fluid media such as the liquid sodium coolant used in PRISM reactors. The coolant loop can provide a bypass of the entire primary heat extractor, such as a steam generator, by directly connecting the hot and cold legs through the purification / chiller system, allowing the heat extractor and associated pumps to be isolated and drained for maintenance. The hot and cold legs may include portions filled with fluid columns that extend vertically higher than the cooler, which itself is above the reactor, and the hot and cold legs in the loop may be arranged with horizontal paths that are angled slightly back toward the reactor to prevent backflow into the heat extractor. Thus, the example embodiment can be installed and operated in combination with several types of existing coolant loops with reactor purifiers by simply adding cooler capacity and / or outlets to opposing portions of the loop. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram showing a coolant purification system according to the related art. [Diagram 2] FIG. 2 is a diagram illustrating a coolant purification and heat rejection system according to one embodiment. [Diagram 3] FIG. 3 is an illustration of an intermediate loop that may be used in conjunction with a nuclear reactor according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Exemplary embodiments will become more apparent from a detailed description of the accompanying drawings, in which like elements are represented by like reference numerals, which are given for purposes of illustration and therefore not for the purposes of limiting the terms they depict, and in which:

[0010] Because 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 covered by the claims appended below. Specific structural and functional details disclosed herein are merely intended to illustrate how to make and use the examples. Several different embodiments and methods not specifically disclosed herein may be included within the scope of the claims. Thus, the claims may be embodied in many alternative forms and should not be interpreted as limited to only the examples set forth herein.

[0011] In this specification, ordinal terms such as "first," "second," and the like may be used to describe various elements, but it will be understood that these elements should not be limited to any order by these terms. These terms are used only to distinguish one element from another element. When there is an ordinal number of "second" or higher, there simply must be that number of elements present, not necessarily a difference or other relationship. For example, a first element can be referred to as a second element, and similarly, a second element can be referred to as a first element, without departing from the scope of the illustrated embodiment or method. As used herein, the terms "and," "or," and "and / or" include all combinations of one or more of the associated listed items, unless it is clearly indicated that only a single item, subgroup of items, or all items are present. The use of "etc." is defined as "et cetera," indicating the inclusion of all other elements belonging to the same group of the preceding item, in any one or more combinations of "and / or."

[0012] When an element is referred to as being "connected," "coupled," "mated," "mounted," "secured," or the like, to another element, it will be understood that the element may be directly connected to the other element, or there may be intervening elements. In contrast, when an element is referred to as being "directly connected," "directly coupled," or the like, to another element, there are no intervening elements present. Other terms expressing 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" include all permutations of information exchange and routing between two electronic devices, whether wirelessly connected or not, including intermediary devices, networks, etc.

[0013] As used herein, the singular forms "a," "an," and "the" are intended to include both the singular and the plural, unless the language explicitly indicates 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" or "an" is understood to modify an item that has been previously introduced or is acknowledged to be new, and the definite article is understood to modify the same item as that immediately preceding it. It will be further understood that the terms "comprises," "comprising," "includes," and / or "including," as used herein, specify the presence of 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" and "vertical" refer to the same up-down direction oriented along the force of gravity. "Transverse" and "horizontal" are directions perpendicular to the "axial" direction and are lateral to a given plane at a particular axial height.

[0014] The structures and operations described below may differ from the order depicted in the figures. For example, two operations and / or figures shown in succession may in fact be performed simultaneously or in reverse order depending on the functions / acts involved. Similarly, individual operations in the exemplary methods described below may be performed individually or repeatedly in succession to provide loops or other sequences of operations apart from the single operations described below. Any embodiment or method having the features and functions described below, in any operable combination, should be presumed to be within the scope of the exemplary embodiments.

[0015] The inventors have newly recognized that the purification system may be used as a heat sink for the reactor, rather than simply removing impurities from the cooling water. The inventors have further newly recognized that the purification system may be used as an alternative or parallel coolant loop while the intermediate coolant loop is drained and worked on, such as during plant maintenance. Although these uses of the purification system go against its established functions, the inventors have recognized that they may solve long-standing problems of emergency cooling and operational maintenance that have traditionally been solved using other systems and / or by shutting down the plant completely. The exemplary embodiments described below uniquely enable the solving of these and other problems discovered by the inventors.

[0016] The present invention is a heat sink purification system, a nuclear reactor using the same, and a method of using the same. In contrast to the present invention, the several exemplary embodiments and exemplary methods described below represent only a subset of the various different configurations that may be used as and / or in conjunction with the present invention.

[0017] FIG. 2 is a diagram illustrating an example embodiment of a decay heat removal system 100 that can be used in a commercial nuclear power plant. As shown in FIG. 2, some elements of the example embodiment system 100 may be similar to the related art system 10 of FIG. 1. Thus, the example embodiment system 100 may be used in conjunction with an intermediate loop carrying a molten heat transfer medium in a number of different nuclear power plant designs. The example embodiment system 100 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 side or hot leg 4 (FIG. 3) of the intermediate loop where the coolant exits the reactor. Similarly, the outlet 180 may be, for example, a valved connection to the colder side or cold leg 8 (FIG. 3) of the intermediate loop where the coolant enters the reactor. The inlet 150 and the outlet 180 may be far apart, 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 of the mid-loop. In this way, the system 100 can function as a decay heat removal system by avoiding heat loss and instead removing such heat from the mid-loop and thus the reactor. To accommodate this large heat sink, additional or larger coolers 170 and fans 171, as well as 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 may remove heat equivalent to about 7% of the full rated thermal output of the plant. Of course, the amount of heat varies from plant to plant, but as an example, 5 megawatts of heat may be absorbed from a plant rated at 840 megawatts. Smaller values ​​may also be achieved by selective activation of the coolers and flow paths, such as in combination with other heat removal systems to partially remove the decay heat.

[0019] Selective activation may be accomplished, for example, by cooler 170 including multiple parallel channels with fins to selectively accommodate larger flows, and / or fan 171 including multiple speed or multiple fans or high pressure blowers that can be selectively activated to convect significant amounts of heat. Alternatively, for example, larger scale cooler 170 may include other coolant media, immersions, counterflow heat exchangers, printed circuit heat exchangers, plate-frame heat exchangers, and other heat sinks in parallel that can be turned on to selectively dissipate significant amounts of heat from the coolant. In this manner, cooler 170 may seamlessly change from a purification mode that removes a small amount of heat from the coolant, such as 0.5 MW or less, to an absorption mode that removes significant heat from the coolant, such as 5 MW or more.

[0020] Example embodiment decay heat removal system 100 may be tuned between increased decay heat removal and a lower level of cooling available for cleanup, such as cold traps. For example, connections 150 and 180 may be shut off, such as by valves, during normal plant operation without excessive heat loss, and system 100 may function as a cleanup system with purifier 80, returning flow to outlet 67, and receiving flow nearby from inlet 50 in an intermediate loop. When additional cooling is needed, such as during a transient involving a reactor shutdown or loss of other cooling systems, connections 150 and 180 may be opened to allow for a larger coolant flow, and the speed, number, and / or type of pump 151, cooler 170, and / or fan 171 may be increased to increase heat dissipation with the larger coolant flow. Similarly, valves 81 and / or 82 may be closed to avoid purifier 80 and / or reheater 60 when example embodiment system 100 is selectively tuned to a decay heat sink level. Closing purifier 80 may result in direct and / or dedicated coolant flow between connections 150 and 180 to improve heat absorption through example system 100 in additional cooling conditions. In this manner, example embodiment systems are compatible with nearly any coolant loop that uses cold traps or other purifiers, while still providing the optional functionality of selectively activatable incremental heat sink.

[0021] FIGURE 3 is a diagram illustrating an example embodiment of an intermediate coolant loop 200 that may be used in nuclear reactors, including high temperature reactors such as PRISM reactors and molten salt reactors. As shown in FIGURE 3, an example embodiment of an intermediate coolant loop 200 may interface with a number of related or conventional reactor components, including a nuclear reactor 1 that contains a core 2 having nuclear fuel. An intermediate heat exchanger 3 transfers heat from the nuclear reactor 1 to the intermediate coolant loop 200, from where it may transfer heat to an extractor, such as a steam generator 6, or to a heat exchanger for power generation.

[0022] As shown in FIG. 3, the intermediate coolant loop 200 is interfaced with the decay heat removal system 100 (FIG. 2) according to the example embodiment via the inlet 150 and the outlet 180. For example, the inlet 150 may take the coolant from the bottom of the hot leg 4 where the coolant first leaves 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 a typical cold trap purge, the inlet 50 and the outlet 67 (FIG. 2) may be from the same or nearby locations on the same leg to prevent heat loss, unlike the inlet 150 and the outlet 180 which may be separated at temperature extremes in the intermediate coolant loop 200 according to the example embodiment. In transient conditions or when greater heat absorption is desired, the inlet 50 and / or the outlet 67 may be closed and the inlet 150 and the outlet 180 may be opened or enabled to remove heat from the coolant flowing back through the intermediate heat exchanger 3 and ultimately cool the reactor 1.

[0023] Example embodiment intermediate coolant loop 200 can be operated in combination with intermediate pump 7 and steam generator 6, or other heat extractors, to extract heat from the coolant and generate electricity. Intermediate pump 7 and / or steam generator 6 can be optionally idled and drained while coolant loop 200 still circulates coolant and extracts heat through inlet 150 and outlet 180. For example, intermediate pump 7, steam generator 6, and / or portions of hot leg 4 and cold leg 8 can be drained to drain tank 5 by opening drain valves to drive coolant to drain tank 5 by gravity and / or by active pump drive.

[0024] Proper slope of the piping in the hot and cold legs 4 and 8 can facilitate draining of the pump 7 and the steam generator 6 and its associated piping. For example, the horizontal piping in the hot and cold legs 4 and 8 can be at a slight angle to the vertical, such as a slight drop toward the steam generator 6 and a vertical drop of 5 to 10 millimeters per meter of length away from the reactor 1. This downward slope, in combination with the example positioning described below, can further prevent backflow and ensure that the coolant loops through only a portion of the intermediate coolant loop 200 in accordance with example embodiments.

[0025] The hot leg 4 and the cold leg 8 may be arranged such that the fluid column in the hot leg 4 is at a vertical height 240 and the fluid column in the cold leg 8 is at a vertical height 280. The fluid columns in these legs may remain even if other parts of the loop 200 are drained. Due to the presence of 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 (FIG. 2) through the lower parts of the hot leg 4 and the cold leg 8. In this way, it is possible to carry out repairs or other work on the emptied steam generator 6, the intermediate pump 7, and / or any other drained parts of the coolant loop 200 while still removing heat from the reactor 1 through the intermediate heat exchanger 3. 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, system 100, or at least cooler 170 (FIG. 2) of system 100, may be located at vertical height 230 above intermediate heat exchanger 3 at vertical height 231. The difference between vertical height 230 and vertical height 231 may create a natural circulation driving force for cooling water heated in heat exchanger 3 to rise due to reduced concentration, flow to cooler 170 where it is cooled and increased in concentration, and return to heat exchanger 3 due to the concentration difference. This configuration and the natural circulation associated with it may eliminate or reduce the need for active pumping, such as pumps 151 and 7. Natural circulation occurs in loop 200 through heat exchanger 3 by gravity and by the absence of voids below system 100, provided all other coolant charges in system 100 are below coolant column elevations 240 and 280.

[0027] As shown in Figures 2 and 3, the example embodiment intermediate coolant loop 200 and example embodiment decay heat removal system 100 can be used in conjunction with several types of reactors and existing components. Some functions of the loop 200 and system 100 can be achieved simply by increasing the capacity of the inlet 50 to that 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 system 100 can be used during typical reactor operation to clear impurities and / or debris from a relatively small flow of coolant, and can be selectively adjusted to remove all or a substantial portion of the decay heat or even operating heat from the reactor 1 during transient or non-electrical generating conditions, such as during an accident or plant maintenance. Similarly, multiple loops 200 and systems 100 can be used in conjunction with a single reactor 1 to provide additional significant heat transfer and absorption from the reactor 1.

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

Claims

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 generating electricity, 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:

2. The system (100) of claim 1, further comprising at least one valve (81, 82) configured to close all flow to the purifier (80) and the first outlet (67).

3. 2. The system (100) of claim 1, wherein the inlet and the first outlet (67) are positioned to join a same leg (4) of the coolant loop (200) and the second outlet (180) is positioned to join an opposing leg (8) of the coolant loop (200).

4. 2. The system (100) of claim 1, wherein the cooler (170, 171) is configured to absorb approximately 0.5 megawatts of heat from the fluid coolant in a first mode and to absorb approximately 5 MW or 7% of the rated thermal power of the reactor (1) from the fluid coolant in a second mode.

5. The system (100) of claim 4, wherein the cooler (170) comprises a plurality of finned heat exchange tubes and at least one fan (171) that blows a convective fluid against the plurality of finned heat exchange tubes.

6. The system (100) of claim 4, wherein the inlet is configured to change volumetric flow rate upon a mode change of the cooler (170).

7. 2. The system of claim 1, further comprising a heat exchanger (60) in series with the purifier (80) connected between the inlet and the first outlet (67) to reduce a temperature of the fluid coolant entering the heat exchanger (60) from the inlet and to increase a temperature of the fluid coolant entering the heat exchanger (60) from the heat exchanger (60) to the first outlet (67).

8. The system (100) of claim 7, further comprising valves (81, 82) configured to allow flow of the fluid coolant to the purifier (80), the heat exchanger (60), and the first outlet (67).

9. 2. A method of operating the purifier and heat sink system (100) of claim 1, comprising: A method of operating the purifier and heat sink system (100) comprising flowing the fluid coolant from the inlet, through the purifier (80) and out the first outlet (67).

10. changing the mode of the coolers (170, 171); stopping the flow of the fluid coolant through the purifier (80) and exiting the first outlet (67); flowing the fluid coolant to exit the second outlet (180); The method of claim 9 further comprising:

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