System and method for reducing accumulation of non-condensable gas in a coolant system

Abstract

The system reduces non-condensable gases in the coolant system using a recombiner into which the fluid coolant flows. The flow through the recombiner may be reversed relative to the heat exchanger. The recombiner includes a catalyst that combines or decomposes non-condensable gases, such as group 9-11 transition metals that promote the reaction of non-condensable gases. The catalyst may be a liner, plate, aggregate, etc. having an opening through which all of the coolant must flow. The recombiner is insulated to prevent heat exchange and condensation and may be tilted from vertical to promote drainage and fluid flow. The overall system can be passive without operator intervention or moving structures. The system can be made from the emergency condenser system in a nuclear power plant within the emergency condenser pool by adding a recombiner to an existing coolant system. The system can also be made by including a recombiner in a new emergency condenser.

Description

Technical Field

[0001] The present application relates to a system and method for reducing the accumulation of non-condensable gases in the coolant system of a nuclear reactor.

Background Art

[0002] FIG. 1 is an explanatory diagram of an emergency condenser system (ICS) 300 of related art that can be used in a nuclear reactor such as a boiling water reactor 142. As shown in FIG. 1, the system 300 can include one or more emergency condensers 310 in an ICS pool 311 above the nuclear reactor 142, any of which can potentially be present inside a building such as a containment vessel of a commercial nuclear power plant or a nuclear reactor building. The ICS 300 can include a steam inlet 362 from the nuclear reactor 142 and a condensate recovery pipe 363 to the nuclear reactor 142 for passively heat-transferring and condensing the nuclear reactor coolant through a heat absorber of the ICS pool 311. A plurality of valves 200 couple the steam inlet 362 and the condensate recovery pipe 363 to the nuclear reactor 142 and can selectively operate the ICS 300 by opening and closing. Co-pending patent document 1 issued on December 15, 2020 to Hunt et al. describes a related ICS system and is hereby incorporated by reference in its entirety.

[0003] ICS10 can include a plurality of emergency condensers 310 supplied by a single steam inlet 362 that divides between the condensers 310 and further divides into a plurality of supply lines for the condensers 310. Each condenser 310 can include an upper drum 313 that functions as a manifold for all the incoming energy steam. A plurality of heat exchange tubes 314 carry the steam vertically downward and can transfer heat from the coolant to the pool 311 and condense it. The lower drum 315 receives the fluid cooled from the heat exchange tubes and returns the condensate to the condensate recovery pipe 363. This vertically downward one-way arrangement, combined with a higher concentration of coolant achieved by condensation and heat transfer, can facilitate the natural circulation of the coolant through the condenser 310. Thus, the drums 313 and 315 and the tubes 314 are typically manufactured to maximize the heat exchange characteristics with respect to the surrounding pool 311.

[0004] This background provides a useful baseline or starting point for a better understanding of some of the exemplary embodiments described hereinafter. Except for specifically identified third-party subject matter that may be separately filed, this background and the figures are by the inventors and are created for the purposes of this application. What is included in this application is not necessarily known or represented as prior art.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] Exemplary embodiments include a system for limiting the accumulation of non-condensable gases in the power plant fluid coolant and coolant system, such as hydrogen gas and oxygen gas in the water primary coolant of a nuclear power plant. The recombiner connects between two separated volumes within the coolant system, such as between drums, manifolds, plenums, etc. on opposite sides of the heat exchanger tubes. The coolant flows into the upper volume, descends through heat exchange tubes where the coolant may condense, and flows into the lower volume, but may also flow in the reverse direction from the lower volume to the upper volume through the recombiner. The recombiner includes a catalyst that chemically changes the non-condensable gases during this reverse flow, from non-condensable gases such as oxygen and hydrogen, to promote the formation of water and other oxides and hydrides, such as catalytic metals and organic materials. The catalyst can be placed at any position within the recombiner, such as on the inner circumference of the recombiner itself, or on replaceable plates, grids, vanes, etc. for contacting the flow with the catalyst to interact with the flow and non-condensable gases. The recombiner is insulated to generate heat by the chemical change and can prevent the coolant from substantially condensing in this reverse flow, unlike when passing through the heat exchange tubes. The recombiner can be tilted with respect to the vertical and / or the heat exchange tubes so that liquid is drained from the catalyst within the recombiner or so as not to block the catalyst. Power-driven devices such as pumps and fans are not necessary to move the coolant to the recombiner and remove non-condensable gases therefrom. The recombiner can be used with the emergency condenser system of a nuclear power plant and potentially be immersed in the emergency condenser pool along with the condenser. The exemplary embodiment system can be formed by adding a recombiner to an existing coolant system, such as during a modification during a maintenance outage, or can be manufactured together with a new condenser before installation in the plant.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Best Mode for Carrying Out the Invention

[0008] Exemplary embodiments will become more apparent by describing in detail the accompanying drawings in which like elements are presented by like reference numerals. The drawings are for illustrative purposes only and thus do not limit the exemplary embodiments herein. The elements in these drawings are scaled with each other and can accurately depict the shape, position, operation, and / or language of the exemplary embodiments, or some or all of the elements can be out of scale or decorated to show alternative ratios and details.

[0009] Since this document is a patent document, general broad interpretation rules should be applied when reading this document. Everything described and shown in this document is an example of the subject matter belonging to the claims attached below. The specific structural and functional details disclosed in this document are merely for the purpose of explaining how to make and use the examples. Some different embodiments and methods not specifically disclosed in this document 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 in this document.

[0010] Constituent terms such as "comprises", "includes", "has", or "with" reflect the presence of the described features, characteristics, steps, operations, elements, and / or components, but do not, by themselves, exclude the presence or addition of one or more other features, characteristics, steps, operations, elements, components, and / or groups thereof. Rather, exclusive modifiers such as "only" or "singular" may exclude the presence or addition of other subjects in the modifier. The use of permissive terms such as "may" or "can" reflects the optionality such that the modifier need not necessarily be present, but the absence of the permissive term does not reflect a requirement. In the listing of items in an exemplary embodiment, conjunctions and inclusive terms such as "and", "with", "or" include any and all combinations of one or more of the listed items without excluding items not listed. The use of "etc." is defined as "et cetera" and indicates that in any "and / or" combination(s), it includes all other elements belonging to the same group as the preceding item. Modifiers such as "first", "second", "another", etc. do not limit the modified items in any order. These terms are used only to distinguish one element from another. If there is a "second" or higher ordinal number, there must simply be that number of elements, and there need not necessarily be a difference or other relationship between those elements.

[0011] When an element is related to another element such as "connected to", "coupled to", "in the form of", "attached to", "fixed to", etc., it may be directly connected to the other element or there may be intervening elements. In contrast, when an element is referred to as "directly connected to", "directly coupled to", etc. another element, there are no intervening elements. Other words used to express the relationship between elements should be interpreted similarly (e.g., "between" vs. "directly between", "adjacent" vs. "directly adjacent", etc.).

[0012] As used herein, singular forms such as "a", "an", and "the" are intended to include both singular and plural forms unless the context clearly dictates otherwise. Indefinite articles such as "a" and "an" introduce or refer to any modifier, whether previously introduced or not. On the other hand, definite articles such as "the" refer to the same previously introduced term. Relative terms such as "about" and "more", and degree terms such as "approximately" and "substantially", reflect a variance of up to 10% of the modified value, or the full range of inaccuracies that, in the technical context, would still achieve the functionality of the modified term as understood by one of ordinary skill in the art. Precision and non-variation are expressed by contrary terms such as "exactly".

[0013] As used herein, "axial direction" and "vertical direction" are the same up-and-down direction oriented along the long axis of the reactor, and are often the direction oriented in the direction of gravity. The "lateral" direction is perpendicular to the "axial direction" and is the side-to-side direction at a particular axial height, while the "radial direction" extends perpendicular to the long axis of the reactor and is a particular lateral direction directly away from the long axis of the reactor.

[0014] The structures and operations described below may occur out of the order described and / or noted in the figures. For example, two operations and / or figures shown in sequence may actually be executed simultaneously or in the reverse order depending on the relevant functions / acts. Similarly, the individual operations within the exemplary methods described below may be executed iteratively, individually, or sequentially so as to provide looping or other sequences of operations apart from the exact operations described below. Any embodiment or method having the features and functionality described below should be presumed to be included within the scope of the exemplary embodiments in any executable combination.

[0015] The inventors have recognized that in coolant systems where the working fluid can decompose into such gases during operation, non-condensable gases can accumulate. These gases impede heat removal by condensation, creating the potential for blockage of coolant flow paths, combustion, and / or other undesirable chemical interactions. Particularly in a radioactive environment such as a nuclear reactor coolant system, radiolysis of the coolant is especially likely to occur. Also, particularly in passive coolant systems that use natural circulation between specially arranged heat sources and sinks to avoid active components and operator intervention, non-condensable gases can resist or block such circulation, deplete the coolant volume, and / or potentially cause combustion, corrosion, or other adverse effects. Thus, a nuclear reactor passive coolant system such as an ICS is particularly likely to experience undesirable accumulation of non-condensable gases. However, blocking the natural circulation path with a recombination structure and / or using active ventilation or pumps can potentially interfere with the desirable natural circulation and passive, simplified configuration of the coolant system. To address these newly recognized problems, as well as other problems, the inventors have developed the exemplary embodiments and methods described below using unique solutions enabled by the exemplary embodiments to address these and other problems recognized by the inventors.

[0016] The present invention is a system and method for reducing non-condensable gases in a coolant system. In contrast to the present invention, the few exemplary embodiments and exemplary methods described below merely show a small part 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 of a recombiner system 100 of an exemplary embodiment that can be used with an emergency condenser 310 such as used in a nuclear power plant ICS. As shown in FIG. 2, the recombiner system 100 of the exemplary embodiment includes a recombiner 160 in fluid communication with an upper drum 313 and a lower drum 315 of the emergency condenser 310. For example, an upper pipe 101 can be coupled between the recombiner 160 and the upper drum 313, and a lower pipe 102 can be coupled between the recombiner 160 and the lower drum 315. Any other connection path can be used between the recombiner 160 and the emergency condenser 310, including direct joining at different locations of the emergency condenser 310. An upper isolation valve 111 and / or a lower isolation valve 112 can be joined between the recombiner 160 and the emergency condenser 310 to isolate, or prevent, the flow of fluid through the recombiner 160, such as for replacement, installation, or maintenance. The recombiner 160 can also be joined to the emergency condenser 310 during manufacture, or added to an existing emergency condenser 310 by creating a flow path through the later-added recombiner 160 from the condenser. For example, the recombiner 160 can be connected to an existing condenser 310 by forming a flow path through the recombiner 160 from the upper drum 313 and the lower drum 315. This can be done at any time, including when the ICS pool 311 (FIG. 1) is at a level below the recombiner 160, such as during a maintenance period or a shutdown of operation.

[0018] As can be seen in FIGS. 2 and 3, the recombiner 160 can be connected such that fluid enters to return to the upper drum 313 at or near the highest vertical point of the lower drum 315 where non-condensable gas and gaseous coolant tend to accumulate. Similarly, the recombiner 160 can be connected to the upper drum 313 at a higher point for gas reflux near where higher energy reactor coolant may enter the upper drum 313. Although only one recombiner 160 is shown in the exemplary embodiment system 100, it is understood that multiple recombiners 160 may be used in connection with the emergency condenser 310. The recombiner 160 can be coupled to the emergency condenser 310, or at other points to the steam inlet 362 (FIG. 1) or other reactor structures, to draw in non-condensable gas therefrom. The recombiner 160 can also be coupled to other structures and volumes where non-condensable gas can collect to assist in their removal.

[0019] The recombiner 160 is a flow conduit that includes and / or is made of a catalyst material that substantially accelerates the recombination of non-condensable gas passing through the recombiner 160. For example, non-condensable gas generated by radiolysis and / or other conditions in an operating power plant can accumulate in the lower drum 315; that is, free gases such as hydrogen and oxygen are typically in diatomic form and can be formed by dissociation from the fluid coolant or introduction into the reactor system. Catalyst materials such as palladium, platinum, rhodium, other Group 9-11 transition metals, organic materials, etc. promote the recombination and / or decomposition of these gases. For example, oxygen gas or hydrogen gas exposed to palladium quickly binds to oxides, hydrides, the liquid coolant itself, etc., reducing the risk of combustion, reducing the risk of introducing gas into the reactor coolant, and / or reducing the risk of causing voids or blockages in the coolant loop.

[0020] The recombiner 160 can include an insulator 150 that limits heat transfer to the surrounding heat sink, in which the recombiner 160 and the emergency condenser 310 can be submerged. For example, the insulator 150 can be a vacuum or air gap or thermal insulation layer wrapped around the outer wall of the recombiner 160 and / or around any connections such as pipes 101 and 102. The insulator 150 can be adapted to in-water operation as well as the temperatures and other conditions encountered in an ICS.

[0021] When the recombiner 160 is insulated, heat transfer to the surrounding heat sink can be reduced, unlike substantial heat transfer from the heat exchange tubes 314 of the emergency condenser 310. Further, recombination or decomposition of non-condensable gases caused by the catalyst material within the recombiner 160 can generate additional heat. Without heat loss, the recombiner 160 may not substantially condense the fluid coolant flowing through the recombiner 160. The lack of a pressure head from the condensate moving downward can facilitate a vertical upward or reverse flow of gas through the recombiner 160, including gaseous coolant and non-condensable gases from the lower drum 315.

[0022] Figure 3 is an illustration of the recombiner system 100 of an exemplary embodiment from the cross-section of FIG. 2, showing additional alignment that can be used to enhance the vertically upward flow. As seen in FIG. 3, the recombiner 160, and any connections to drums 313 and 315, may be vertical with some offset. If grids or vanes such as honeycomb shapes or axially swirling vanes are used in the catalyst material of the recombiner 160, some angle with respect to the vertical may help any liquid discharged from the shelves or horizontal surfaces of the material. This can prevent the liquid from wetting and preventing contact between the catalyst material and the gas. The liquid may be discharged to the bottom of the recombiner 160 so as not to impede the upward entry and flow of the gas through the recombiner 160 and / or the catalyst material therein, and may return to the lower drum 315. Any inclination may still allow the recombiner 160 to take in liquid near the top of the lower drum 315 where non-condensable gases and gaseous coolant are likely to accumulate and return to the upper drum 313.

[0023] As can be seen from FIGS. 2 and 3, the recombiner 160 operates as a countercurrent path through the emergency condenser 310 and can provide an upward or reverse flow of gas from the lower drum 315 to the upper drum 313. This is contrary to the typical downward flow of the two-phase coolant through the heat exchange tubes 314 driven by condensation from the heat sink. The insulation and reaction heat due to the recombination of non-condensates may further promote the upward flow through the recombiner 160. In this way, the non-condensable gas is returned particularly upward through the recombiner 160 for conversion to less harmful compounds, while the vapor or other gaseous coolant moving in the same way simply re-enters the upper drum 313 for another circuit below through the heat exchange tubes 314. In this way, the recombiner 160 can provide a passive countercurrent path for gases containing non-condensable gases and non-condensing two-phase flows to flow countercurrently through the emergency condenser 310 without movable structures such as power pumps, fans, motors, etc. Such an active driving device for the fluid returning through the recombiner 160 can be used in exemplary embodiments, but the passive configuration occupies less space, has a lower risk of failure, and / or can be more easily arranged within an emergency condenser heat sink such as the ICS pool 311 (FIG. 1).

[0024] Figures 4A and 4B show several different exemplary possibilities regarding the arrangement and configuration of the catalyst material in the recombiner 160. U.S. Patent No. 9,496,058, issued November 15, 2016 to Marquino et al., exemplifies a similarly usable arrangement of the catalyst material from a separate space, which is hereby incorporated by reference in its entirety. As seen in Figure 4A, the cross-shaped catalyst sheet 161 is inserted perpendicular to the recombiner 160 and can occupy its substantial cross-section. The openings 162 or grooves in the catalyst material can facilitate cross-flow of the fluid and recombination or decomposition of the non-condensable gas. As seen in Figure 4B, the catalyst liner 161 can extend about the inner circumference of the recombiner 160. Further, a grid-like or honeycomb-like catalyst insert 161 having several openings 162 can be inserted perpendicular to the recombiner 160 or extend across the region of its complete internal flow path laterally. Still other configurations, such as a pebble bed or filter-style catalyst material including several small pieces packed within the recombiner 160, or radial vanes that force the fluid to move outward, can be used. These configurations and other configurations can each be used in combination with one another or individually. It is also possible to use a single catalyst material such as a palladium plate or grid, or various materials such as platinum vanes or rhodium liners can be used based on the desired chemical properties.

[0025] The exemplary recombiner system 100 can be made of materials suitable for an operating nuclear reactor environment, including, among other things, materials that maintain their physical properties even when exposed to high-temperature fluids and radiation, without substantially changing physical properties such as becoming substantially radioactive, melting, embrittling, retaining / adsorbing radioactive particulates. For example, metals such as austenitic stainless steels 304 or 316, XM-19, alloy 600, and stainless steels and ferrous alloys, nickel alloys, zirconium alloys, etc. can be used for the components of system 100. Similarly, direct connections between separate components and all other direct contact points may be fabricated from lubricated and / or alternately or otherwise compatible materials to prevent seizing, fouling, metal-to-metal reactions, etc.

[0026] In this way, several exemplary embodiments and methods have been described, but it will be understood by those skilled in the art that the examples can be varied through routine experimentation without further inventive activity. For example, in some of the exemplary systems, a recombiner with a vertical emergency condenser is used, but it is understood that other systems, such as a passive containment cooling system, can be used with the exemplary embodiments. Variations are not regarded as departing from the spirit and scope of the exemplary embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.

Claims

1. A system for removing non-condensable gas from a coolant, comprising: A condenser having an upper volume configured to receive the coolant, a lower volume configured to return the coolant, and a plurality of heat exchange tubes connecting the upper volume and the lower volume and configured to condense the coolant; A recombiner connected between the upper volume and the lower volume and configured to allow the coolant to flow from the lower volume to the upper volume, the recombiner including a catalyst material configured to remove non-condensable gas from the coolant flowing into the recombiner from the lower volume; The system comprising the same.

2. The system according to claim 1, wherein the recombiner further comprises an insulator configured to prevent condensation of the coolant.

3. The system according to claim 1, wherein the catalyst material is at least one of platinum and palladium.

4. The system according to claim 1, wherein the catalyst material is arranged along an internal flow path of the recombiner.

5. The system according to claim 1, wherein the catalyst material is a plate having an opening crossing an internal flow path of the recombiner.

6. The system according to claim 1, wherein a plurality of heat exchange tubes are arranged in parallel between the upper volume and the lower volume, and the recombiner is angled between the upper volume and the lower volume so as not to be parallel to the heat exchange tubes.

7. The system according to claim 1, wherein the upper volume is an emergency condenser upper drum, the lower volume is an emergency condenser lower drum, and further comprising an emergency condenser pool surrounding the condenser and the recombiner.

8. A steam supply line configured to carry the coolant from a nuclear reactor to the condenser; A condensate return line configured to carry the condensed coolant to the reactor The system according to claim 7, further comprising the same. **Claim 9** The system according to claim 1, wherein the system does not include a movable structure for driving the coolant. **Claim 10** A reactor emergency condenser system with reduced risk of accumulation of non-condensable gas, comprising: A relief line configured to receive steam as a primary coolant from a reactor; A condensate return line configured to supply water to the reactor as the primary coolant; A plurality of emergency condensers immersed in at least one emergency condenser pool, the plurality of emergency condensers being connected between the relief line and the condensate return line, each of the emergency condensers being connected to the relief line and having an upper manifold for receiving steam from the relief line, a lower manifold connected to the condensate return line for returning the water to the condensate return line, and a plurality of heat exchange tubes connecting the upper manifold and the lower manifold and configured to condense the coolant. A recombiner connected to at least one of the emergency condensers, the recombiner including a catalyst material configured to remove non-condensable gas from the coolant flowing from the at least one emergency condenser into the recombiner. An emergency condenser system for a reactor, comprising the same. **Claim 11** The system according to claim 10, wherein the recombiner is a heat insulation flow path passing through a pool connecting the lower manifold and the upper manifold. **Claim 12** The system according to claim 10, wherein the catalyst material is at least one of platinum and palladium. **Claim 13** The system according to claim 10, wherein the catalyst material is arranged along the internal flow path of the recombiner.

14. The system according to claim 10, wherein the catalyst material is a plate having an opening that crosses an internal flow path of the recombiner.

15. The system according to claim 10, wherein the plurality of heat exchange tubes are substantially vertical and the recombiner is a flow path that forms an angle with respect to the vertical.

16. The system according to claim 10, wherein the system does not include a movable structure for driving the coolant.

17. A method of forming the system of claim 1, comprising: Connecting the recombiner between the upper volume and the lower volume of the condenser, the condenser having been previously installed in an emergency condenser pool of a nuclear power plant.

18. The method according to claim 17, wherein the connection is performed while the emergency condenser pool is being drained below the recombiner.

19. The method according to claim 17, wherein the connection is performed during a maintenance shutdown of the nuclear power plant.

20. The method according to claim 17, wherein the recombiner is insulated from the emergency condenser pool.

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