Patent Application
20210090753
Nuclear reactors with high operating temperatures may use a fluid heat exchange media, such as a liquid metal or molten salt, for coolant. The heat exchange media may transfer heat from a reactor to a heat exchanger and/or turbine for energy extraction and electricity generation as well as act as a heat sink to remove decay heat or other unwanted heat during operation or a shutdown condition. Many reactor designs, including, for example, liquid sodium-cooled fast reactors, such as the PRISM reactor, use multiple loops of heat exchange media to efficiently transfer heat away from a reactor for electrical generation and cooling. One loop may be an intermediate loop that 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, such as liquid lead or sodium, molten salts, etc. may be used for this heat exchange in the intermediate loop.
Intermediate loops using fluid media may benefit from cleanup of the heat exchange media to remove impurities or debris that may accumulate during operation in a nuclear reactor environment.
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Purifier 80 may include chemical reactants, catalysts, and/or mechanical filters like cold traps, mesh, or other filter media that removes impurities or debris, including precipitates that come out of solution, following cooler 70. Bypass valves 81 and 82 may permit flow bypass of purifier 80, allowing flow to be raised or lowered slowly, and otherwise controlled, through purifier 80 during startup or shutdown. Colder, filtered coolant then passes back through regenerative heat exchanger 60 through input 66 to reheat the coolant to near operating temperatures before being returned to an intermediate loop via output 67, typically just downstream from inlet 50 in the intermediate loop. In this way, the coolant passed through system 10 for cleanup minimizes heat loss from the intermediate loop.
Example embodiments include combined cleanup and heat removal systems and coolant loops joined to the such systems. The coolant loops may have a hot leg connecting between the reactor to a heat extractor like a steam generator or heat exchanger and a cold leg opposite the hot leg returning from the heat extractor to the reactor. Example embodiment cleanup and heat sink systems connect to the hot leg and/or cold leg and, depending on plant situation and/or operator input, function to remove impurities or debris from the fluid coolant flowing in the loop and/or remove a substantial amount of heat from the fluid coolant. The combined system may selectively create flow between the hot leg and the cold leg, which may bypass the heat extractor entirely to permit draining and shutdown operations on the same, even as the reactor is still generating large amounts of heat. Similarly, the combined system may work on a single leg and prevent significant heat loss while cleaning the coolant during normal reactor and heat extractor operation. Intermediate modes are also possible, depending on flow path creation, pumping, and/or cooler operations. Purification may be achieved with a cold trap, for example, cooler connected serially with an outlet, and potentially a regenerative heat exchanger, back into the coolant loop, while heat sinking may be achieved by the cooler, potentially operating in a larger-capacity mode, connected in parallel to a bypass outlet back into the coolant loop.
Because the combined system may selectively provide both cleanup and significant cooling to the coolant loop, the system may be structured to operate between both these modes in desired levels of combination. For example, a cooler in the system may switch between modes, or levels of, heat removal. One mode may remove only a small amount of heat from the coolant sufficient to solidify or otherwise precipitate impurities from the coolant, while another mode may sink significant amounts of heat from the coolant, potentially up to full decay heat or even reactor operational levels of heat. Such modality from impurity-removal to heat-sinking levels may be achieved by increasing forced convection, increasing flow path volume flow rate, changing heat sink media, etc. Similarly, inlet volume flow rate may be increased, pumping pressure may be increased, and/or flow paths connecting the hot leg and cold leg of the coolant loop while avoiding a purifier like a cold trap and any regenerative heat exchanger in the system may be created, such as by valves, between these modes.
Example embodiment coolant loops and cleanup/cooler systems are useable in a variety of plants and coolants, including fluid media like a liquid sodium coolant used in a PRISM reactor. Coolant loops may provide for entire bypass of a primary heat extractor like a steam generator by directly connecting hot and cold legs through the cleanup-cooler systems, allowing for isolation and draining of the heat extractor and related pumps for maintenance. The hot leg and cold legs may include portions filled with fluid columns extending vertically higher than cooler, which itself may be above the reactor, and the hot and cold leg in the loop may be positioned with slightly angled horizontal paths that decline back toward the reactor, to prevent backflow into the heat extractor. Example embodiments may thus be installed and operated with several types of coolant loops already existing with purifiers in nuclear reactors, simply by adding additional cooler capacity and/or additional outlets to opposing portions of the loop.
Example embodiments will become more apparent by describing, in detail, the attached drawings, wherein like elements are represented by like reference numerals, which are given by way of illustration only and thus do not limit the terms which they depict.
Because this is a patent document, general, broad rules of construction should be applied when reading it. Everything described and shown in this document is an example of subject matter falling within the scope of the claims, appended below. Any specific structural and functional details disclosed herein are merely for purposes of describing how to make and use examples. Several different embodiments and methods not specifically disclosed herein may fall within the claim scope; as such, the claims may be embodied in many alternate forms and should not be construed as limited to only examples set forth herein.
It will be understood that, although the ordinal terms “first,” “second,” etc. may be used herein to describe various elements, these elements should not be limited to any order by these terms. These terms are used only to distinguish one element from another; where there are “second” or higher ordinals, there merely must be that many number of elements, without necessarily any difference or other relationship. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments or methods. 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” and indicates the inclusion of all other elements belonging to the same group of the preceding items, in any “and/or” combination(s).
It will be understood that when an element is referred to as being “connected,” “coupled,” “mated,” “attached,” “fixed,” etc. to another element, it can be directly connected to the other element, or intervening elements may be present. In contrast, when an element is referred to as being “directly connected,” “directly coupled,” etc. to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). Similarly, a term such as “communicatively connected” includes all variations of information exchange and routing between two electronic devices, including intermediary devices, networks, etc., connected wirelessly or not.
As used herein, the singular forms “a,” “an,” and the are intended to include both the singular and plural forms, unless the language explicitly indicates otherwise. Indefinite articles like “a” and “an” introduce or refer to any modified term, both previously-introduced and not, while definite articles like “the” refer to a same previously-introduced term; as such, it is understood that “a” or “an” modify items that are permitted to be previously-introduced or new, while definite articles modify an item that is the same as immediately previously presented. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when 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” directions are the same up or down directions oriented with gravity. “Transverse” and “horizontal” directions are perpendicular to the “axial” and are side-to-side directions in a plane at a particular axial height.
The structures and operations discussed below may occur out of the order described and/or noted in the figures. For example, two operations and/or figures shown in succession may in fact be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Similarly, individual operations within example methods described below may be executed repetitively, individually or sequentially, to provide looping or other series of operations aside from single operations described below. It should be presumed that any embodiment or method having features and functionality described below, in any workable combination, falls within the scope of example embodiments.
The Inventors have newly recognized that cleanup systems may be used as a heat sink in a nuclear reactor, instead of merely removing impurities from coolant. The Inventors have further newly recognized that cleanup systems may be used as alternative or parallel coolant loops while intermediate coolant loops are drained and worked on, such as during plant maintenance. While these uses of cleanup systems are contrary to their established functions, the Inventors have recognized that they may solve long-standing problems of emergency cooling and operations maintenance that have traditionally been solved by using other systems and/or fully shutting down a plant. Example embodiments described below uniquely enable these solutions to these and other problems discovered by the Inventors.
The present invention is heat-sink purifier systems, nuclear reactors using the same, and methods of using the same. In contrast to the present invention, the few example embodiments and example methods discussed below illustrate just a subset of the variety of different configurations that can be used as and/or in connection with the present invention.
Example embodiment decay heat removal system 100 has increased flow and heat transfer capacity to dissipate or sink a substantial portion of heat in the intermediate loop. As such, system 100 may act as a decay heat removal system by removing such heat form the intermediate loop and ultimately the reactor, instead of avoiding heat loss. To accommodate this large-scale heat sinking, additional or larger-scale cooler 170 and fan 171, as well as additional parallel and/or higher-volume pump 151, may be used to remove a substantial amount of heat from a larger amount of coolant directed through example embodiment system 100. For example, system 100 may remove heat equivalent to about 7% of full rated thermal power of a plant. Of course, the amount of heat varies based on plant, one example may sink 5 megawatt-thermal heat from an 840 megawatt-thermal rated plant. Smaller values may also be achieved through selective activation of cooler and flow paths, such as for partial removal of decay heat in combination with other heat removal systems.
Selective activation may be achieved by, for example, cooler 170 including several parallel channels with fins to selectively accommodate larger flows, and/or fan 171 including several speeds or multiple fans or higher-pressure blowers that can be selectively activated to convect large amounts of heat. Or, for example, larger-scale cooler 170 may include other coolant media, submerged sections, counter-flow heat exchangers, printed-circuit heat exchangers, plate-and-frame heat exchangers, and other heat sinks in parallel that can be turned on to selectively dissipate large amounts of heat from the coolant. In this way, cooler 170 may seamlessly change from a purifying mode that removes little heat, such as 0.5 MW or less, from a coolant to a heat-sinking mode that removes much heat, such as around 5 MW or more, from the coolant.
Example embodiment decay heat removal system 100 may be scaled between increased decay heat removal and lower-level cooling useable for purification, such as cold trapping. For example, connections 150 and 180 may be shut off, such as by valves, during normal plant operations without excess heat loss, and system 100 may act as a purification system with purifier 80, returning flow to outlet 67 and receiving flow from inlet 50 nearby in an intermediate loop. When additional cooling is necessary, such as during a transient involving reactor shutdown or loss of other cooling systems, connections 150 and 180 may be opened to enable larger coolant flows, and pump 151, cooler 170, and/or fan 171 may be increased in speed, number, and/or type, to increase heat dissipation from larger coolant flows. Similarly, valves 81 and/or 82 may be closed to avoid purifier 80 and/or reheater 60 when example embodiment system 100 is selectively scaled to decay heat sink levels. Closing off purifier 80 may create direct and/or exclusive coolant flow between connections 150 and 180, improving heat sinking through example system 100 in the additional cooling state. In this way, example embodiment system is compatible with nearly any coolant loop using a cold trap or other purifier, while still providing optional functionality of a selectively-activatable increased heat sink.
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Example embodiment intermediate coolant loop 200 can also be operable with intermediate pump 7 and steam generator 6, or other heat extractor, drawing heat from the coolant to generate electricity. Intermediate pump 7 and/or steam generator 6 may optionally be deactivated and drained while coolant loop 200 still circulates coolant and sinks heat through inlet 150 and outlet 160. For example, intermediate pump 7, steam generator 6, and/or portions of hot leg 4 and cold leg 8 may be drained into drain tank 5, such as through opening drain valves to drive coolant by gravity into drain tank 5 and/or through active pumping.
Proper sloping of piping in hot leg 4 and cold leg 8 may permit draining of pump 7 and steam generator 6 and their associated piping. For example, horizontal piping of hot leg 4 and cold leg 8 may be at slight angles with respect to the vertical, such as slightly declined toward steam generator 6 and away from reactor 1 at 5-10 millimeters vertical drop per meter length. This decline may further prevent backflowing and ensure coolant looping only through a portion of example embodiment intermediate coolant loop 200 in combination with example positioning discussed below.
Hot leg 4 and cold leg 8 may be arranged such that a column of fluid in hot leg 4 may be at a vertical height 240 and fluid in cold leg 8 may be at a vertical height 280. Columns of fluid in these legs may remain even though other portions of loop 200 are drained. Because of the presence of the columns of fluid at vertical heights 250 and 280 above inlet 150 on hot leg 4 and outlet 180 on cold leg 8, coolant may still be circulated between intermediate heat exchanger 3 and a decay heat removal system 100 (
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Example embodiments and methods thus being described, it will be appreciated by one skilled in the art that example embodiments may be varied and substituted through 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 example embodiments, simply by allowing for different temperatures and coolants. Such variations are not to be regarded as departure from the scope of these claims.
