WO2024145525A2

WO2024145525A2 - Emergency core cooling systems, such as for use in nuclear reactor system, and associated devices and methods

Info

Publication number: WO2024145525A2
Application number: PCT/US2023/086308
Authority: WO
Inventors: Ben BRISTOL; Taylor CODDINGTON; Eric Baker; Derek NOEL
Original assignee: Nuscale Power, Llc
Priority date: 2022-12-29
Filing date: 2023-12-28
Publication date: 2024-07-04
Also published as: WO2024145525A3

Abstract

Passive emergency core cooling systems (ECCSs) for use in nuclear power systems and associated devices and methods are disclosed herein. An ECCS can include a passive chemical dissolution system that passively collects and directs condensate formed on an inner wall of a containment vessel during an emergency event to a dissolver housing containing a neutron-absorbing chemical. The neutron-absorbing chemical, once dissolved by the condensate, can be released into a recirculating coolant to cool down the reactor core. The ECCS can include a passive mixing system that passively collects and directs condensate to a bottom of the containment vessel. The bottom of the open volume may include colder coolant and/or higher concentration of the neutron-absorbing chemical. The condensate can push the colder coolant and/or the concentrated chemical upward for improved circulation.

Description

EMERGENCY CORE COOLING SYSTEMS, SUCH AS FOR USE IN NUCLEAR REACTOR SYSTEM, AND ASSOCIATED DEVICES AND METHODS

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application claims the benefit of U.S. Provisional Patent Application No. 63/435,913, titled “EMERGENCY CORE COOLING SYSTEMS, SUCH AS FOR USE IN NUCLEAR REACTOR SYSTEM, AND ASSOCIATED DEVICES AND METHODS,” and filed December 29, 2022, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] The present technology is related to emergency core cooling systems, such as for use in nuclear reactor systems.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0003] This invention was made with government support under Contract # DE-NE-000- 8928 awarded by the Department of Energy. The government has certain rights in the invention.

BACKGROUND

[0004] In the event of an emergency while operating a nuclear power plant, such as overheating of the reactor core, it is important to reliably and effectively mitigate the consequences of such overheating, which may include the melting of fuel rods and the release of radioactive materials. There is a need for passive emergency core cooling systems that can activate and operate without operator intervention or supervision, at least for some predefined period of time, and address emergencies in a reliable and effective manner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Many aspects of the present technology can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale. Instead, emphasis is placed on clearly illustrating the principles of the present technology. [0006] FIG. 1 is a partially schematic, partially cross-sectional view of a nuclear reactor system configured in accordance with embodiments of the present technology.

[0007] FIG. 2 is a perspective view of a passive chemical dissolution system and a passive mixing system configured in accordance with embodiments of the present technology.

[0008] FIGS. 3A, 3B, and 3C are partially schematic, partially cross-sectional views of the passive chemical dissolution system of FIG. 2 configured in accordance with embodiments of the present technology.

[0009] FIG. 4 is a partially schematic, partially cross-sectional view' of a nuclear reactor system including the passive mixing system of FIG. 2 configured in accordance with embodiments of the present technology.

DETAILED DESCRIPTION

1. Overview

[0010] Aspects of the present technology are directed generally to emergency core cooling systems (ECCSs) for use in nuclear reactor systems. In some embodiments, a nuclear reactor system includes a reactor vessel containing a reactor core, a containment vessel enclosing the reactor vessel, and an ECCS positioned in an open volume defined between the containment vessel and the reactor vessel. In some embodiments, the ECCS includes a passive chemical dissolution system that passively collects condensate formed on an inner wall of the containment vessel, such as condensate formed during an emergency event, and directs the condensate to a dissolver housing containing a neutron-absorbing material or chemical, such as dry' boric oxide. The neutron-absorbing chemical, once dissolved by the condensate, can be released into a recirculating coolant to cool down the reactor core or otherwise contain the emergency event.

[0011] In some embodiments, the ECCS includes a passive mixing system that passively collects a portion of the condensate formed on the inner wall of the containment vessel, and directs the condensate to the bottom of the open volume. The bottom of the open volume may include settled components of the neutron-absorbing chemical and/or an otherwise high concentration of the neutron-absorbing chemical. The collected condensate, once directed to the bottom of the open volume, can promote mixing of the neutron-absorbing chemical by pushing the settled components upward and/or otherwise dilute the concentration of the neutronabsorbing chemical. [0012] Certain details are set forth in the following description and in Figures 1-4 to provide a thorough understanding of various embodiments of the present technology. In other instances, well-known structures, materials, operations, and/or systems often associated with nuclear reactors, power plant systems, emergency core cooling systems (ECCSs), and the like, are not shown or described in detail in the following disclosure to avoid unnecessarily obscuring the description of the various embodiments of the technology. Those of ordinary skill in the art will recognize, however, that the present technology can be practiced without one or more of the details set forth herein, and/or with other structures, methods, components, and so forth. The terminology used below is to be interpreted in its broadest reasonable manner, even though it is being used in conjunction with a detailed description of certain examples of embodiments of the technology.

[0013] The accompanying Figures depict embodiments of the present technology and are not intended to limit its scope unless expressly indicated. The sizes of various depicted elements are not necessarily drawn to scale, and these various elements may be enlarged to improve legibility. Component details may be abstracted in the Figures to exclude details such as position of components and certain precise connections between such components when such details are unnecessary for a complete understanding of how to make and use the present technology. Many of the details, dimensions, angles and other features shown in the Figures are merely illustrative of particular embodiments of the disclosure. Accordingly, other embodiments can have other details, dimensions, angles and features without departing from the present technology⁷. In addition, those of ordinary skill in the art will appreciate that further embodiments of the present technology can be practiced without several of the details described below.

[0014] To the extent any materials incorporated herein by reference conflict with the present disclosure, the present disclosure controls. The headings provided herein are for convenience only and should not be construed as limiting the subject matter disclosed.

II. Nuclear Power Systems

[0015] FIG. 1 is a partially schematic, partially cross-sectional view- of a nuclear pow er or reactor system 100 (hereinafter "‘the system 100”) configured in accordance with embodiments of the present technology. The system 100 can include a power module 102 and a power conversion system 140 operably coupled to the power module 102. The pow er module 102 can include a reactor vessel 120 (e.g., a reactor pressure vessel, or a reactor pressure container) defining a volume, a reactor core 104 positioned within the volume, and a containment vessel 110 (e.g., a radiation shield vessel, or a radiation shield container) sized to enclose the reactor vessel 120 such that an open volume 114 is defined between the containment vessel 110 and the reactor vessel 120. The system 100 can also include an emergency core cooling system (ECCS) positioned in the open volume 114. As discussed further herein, the ECCS can include one or more reactor vent valves 134, one or more reactor recirculation valves 136, a passive chemical dissolution system 160, and/or a passive mixing system 170.

[0016] The reactor core 104 can include one or more fuel assemblies 101 having fissile and/or other suitable materials for enabling a controlled nuclear reaction and thereby generating heat. Within the reactor vessel 120, a primary coolant 107 (e.g., water with or without additives) conveys the heat generated by the reactor core 104 to a steam generator 130. For example, as illustrated by arrow s located within the reactor vessel 120, the primary coolant 107 is heated at the reactor core 104 toward the bottom of the reactor vessel 120 and rises through a core shroud 106 and to a riser tube 108. The hot. buoyant primary coolant 107 continues to rise through the riser tube 108, then exits the riser tube 108 and passes downw ardly through the steam generator 130. The steam generator 130 includes a multitude of conduits 132 that are arranged circumferentially around the riser tube 108, for example, in a helical pattern, as is shown schematically in FIG. 1. The descending primary coolant 107 transfers heat to a secondary coolant (e.g., water) within the conduits 132, and descends to the bottom of the reactor vessel 120 where the cycle begins again. The cycle can be driven by the changes in the buoyancy of the primary coolant 107, thus reducing or eliminating the need for pumps to move the primary' coolant 107. The steam generator 130 can include a feedwater header 131 at which the incoming secondary coolant enters the steam generator conduits 132. The secondary coolant rises through the conduits 132, converts to vapor (e.g., steam), and is collected at a steam header 133. The steam exits the steam header 133 and is directed to the power conversion system 140.

[0017] The power module 102 can also include a control system 150 including multiple control components and associated sensors 151. For example, a hollow cylindrical reflector 109 can be positioned to direct neutrons exiting the reactor core 104 back into the reactor core 104 to further the nuclear reaction taking place therein. Control rods 113 can be used to modulate the nuclear reaction, and can be driven via fuel rod drivers 115. A pressurizer plate 117 can control or otherw ise moderate the pressure w ithin the reactor vessel 120 by controlling the pressure in a pressurizing volume 119 positioned above the pressurizer plate 117. The pressurizer plate 117 can also serve to direct the primary coolant 107 downwardly through the steam generator 130. [0018] The sensors 151 can be positioned at a variety of locations within the power module 102 and/or elsewhere, for example, to identify operating parameter values and/or changes in parameter values. The data collected by the sensors 151 can then be used to control the control components described above and thereby control the operation of and/or generate design changes for the system 100. For sensors 151 positioned within the containment vessel 110, a sensor link 152 directs data from the sensors 151 to a flange 153. at which the sensor link 152 exits the containment vessel 110. and further to a sensor junction box 154. The sensor data can then be routed to one or more controllers and/or other data systems via a data bus 155.

[0019] In some embodiments, the open volume 114 is partially or completely evacuated to reduce heat transfer from the reactor vessel 120 to the surrounding environment (e.g., to the cooling pool 103). However, in other embodiments, the open volume 114 is at least partially filled with a gas and/or a liquid that increases heat transfer between the reactor vessel 120 and the containment vessel 110. For example, the open volume 114 can be at least partially filled primary coolant 107 during an emergency operation. Furthermore, as shown, the containment vessel 110 can be housed in a power module bay 156 containing a cooling pool 103 filled with water and/or another suitable cooling liquid. Most of the power module 102 can be positioned below a surface 105 of the cooling pool 103 such that the cooling pool 103 can operate as a thermal sink, for example, during a system malfunction or other emergency event.

[0020] In some embodiments, the containment vessel 110 includes a first portion (e.g.. an upper portion, a first enclosure, a first vessel portion, a top, a head) and a second portion (e.g., a lower portion, a second enclosure, a second vessel portion, a bottom) removably coupled to the first portion via flanges 112 that are, for example, bolted or clamped to secure the first portion to the second portion. Moreover, in the illustrated embodiment, the second portion of the containment vessel 1 10 includes a funnel portion 111 that narrows such that the bottom portion of the containment vessel 110 has a smaller diameter (or other cross-sectional dimension) than other portions of the containment vessel 110. Similarly, in some embodiments, the reactor vessel 120 includes a first portion (e.g.. an upper portion, a first enclosure, a first vessel portion, a top, a head) and a second portion (e.g., a lower portion, a second enclosure, a second vessel portion, a bottom) removably coupled to the first portion via flanges 122 that are, for example, bolted or clamped to secure the first portion to the second portion. To access components housed within the containment vessel 110 (e g., the reactor pressure vessel 120) or housed within the reactor vessel 120 (e.g., the reactor core 104), the flanges 112 and 122, respectively, can be unlocked (e.g., by removing bolts) such that the first and second portions of the containment vessel 110 or of the reactor vessel 120 can be separated from one another (e.g., via a crane).

[0021] The power conversion system 140 can include one or more steam valves 142 that regulate the passage of high pressure, high temperature steam from the steam generator 130 to a steam turbine 143. The steam turbine 143 converts the thermal energy of the steam to electricity via a generator 144. The low-pressure steam exiting the turbine 143 is condensed at a condenser 145 and then directed (e.g., via a pump 146) to one or more feedwater valves 141. The feedwater valves 141 control the rate at which the feedwater re-enters the steam generator 130 via the feedwater header 131.

[0022] During an emergency event or operation (e.g.. a loss of coolant event), the reactor core 104 can overheat, converting at least a portion of the coolant 107 to vapor (e.g., steam), which can build up within the pressurizing volume 119. In the illustrated embodiment, the one or more reactor vent valves 134 are fluidly coupled between the reactor vessel 120 and the containment vessel 110 and configured to vent the vapor from the reactor vessel 120 into an upper portion of the containment vessel 110. The coolant 107 in vapor form vented from the reactor vent valve 134 can condense in the open volume 114 (e.g., on the inner wall of the containment vessel 110) during the emergency event. The condensed coolant 107 in liquid form can collect/pool in the lower portion of the open volume 114 to form a pool 116. Also, the one or more reactor recirculation valves 136 are fluidly coupled between the reactor vessel 120 and the containment vessel 110 and positioned within the pool 1 16 during the emergency event to recirculate the coolant 107 from the pool 116 into the reactor vessel 120.

[0023] As described in further detail below with respect to FIG. 2, the passive chemical dissolution system 160 can include one or more condensate channels 162 coupled to and extending along an inner wall of the containment vessel 110. For the sake of simplicity, the description below focuses on condensate formed on the inner wall of the containment vessel 1 10. The condensate channels 162 are positioned to collect a portion of condensate formed on the inner wall of the containment vessel 110 (e.g., the condensed coolant 107 vented via the reactor vent valve 134 during the emergency event). Similarly, the passive mixing system 170 can include one or more condensate channels 172 coupled to and extending along the inner wall of the containment vessel 110 below the flanges 112, and positioned to collect a portion of the condensate formed on the inner wall of the containment vessel 110. In the illustrated embodiment, the condensate channels 172 are positioned below the condensate channels 162. In other embodiments, the condensate channels 172 can be positioned above the condensate channels 162. Moreover, the positions of the condensate channels 162, 172 in FIG. 1 (e.g., above and below the level of the steam generator 130) are merely illustrative, and can be positioned elsewhere along the inner wall of the containment vessel 110.

III. Passive Emergency Core Cooling Systems

[0024] FIG. 2 is a perspective view of two identical passive chemical dissolution systems 1 0 and two identical passive mixing systems 170 configured in accordance with embodiments of the present technology. As described above with respect to FIG. 1, while the passive chemical dissolution systems 160 are shown positioned above the passive mixing systems 170, the relative positions can be reversed in other embodiments. Moreover, the various components of the passive chemical dissolution systems 160 and the passive mixing systems 170 are labeled in FIG. 2 only for one of each system.

[0025] The passive chemical dissolution system 160 can include a main condensate channel 162a and an auxiliary⁷ condensate channel 162b (collectively referred to as “condensate channels 162”; which can also be referred to as condensate rails) coupled to (e.g., via fasteners, welded to) and extending along the inner wall of the containment vessel 110 (FIG. 1 ). As shown, the condensate channels 162 can comprise U-shaped channels 262 (or channels having other geometries) shaped to passively collect condensate (e.g., droplets formed on the inner wall of the containment vessel 110 sliding down the inner wall via gravity). The passive chemical dissolution system 160 can also include a dissolver housing 266 coupled to the inner wall of the containment vessel 110 (FIG. 1) below the condensate channels 162 via one or more fasteners 265 (e.g., brackets, mounts). The main condensate channel 162a can be fluidly coupled to the dissolver housing 266 via a main condensate drop tube 261a and the auxiliary⁷ condensate channel 162b can be fluidly coupled to the dissolver housing 266 via an auxiliary condensate drop tube 261b. The passive chemical dissolution system 160 can further include a hopper 264 positioned in the containment vessel 110 and above the dissolver housing 266, and a hopper feed tube 263 coupled between the hopper 264 and the dissolver housing 266. In some embodiments, the hopper 264 is positioned outside of the containment vessel 110 (e.g., above the surface 105 of the cooling pool 103 shown in FIG. 1) and the hopper feed tube 263 extends through a wall of the containment vessel 110. In the illustrated embodiment, each of the main condensate drop tube 261a, the auxiliary condensate drop tube 261b, and the hopper feed tube 263 are illustrated as extending generally vertically (e.g., along the direction of gravity). However, in other embodiments, the main condensate drop tube 261a, the auxiliary' condensate drop tube 261b, and/or the hopper feed tube 263 can extend at an angle relative to the direction of gravity. The passive chemical dissolution system 160 can further include a dissolver drop pipe 268 fluidly coupled to a bottom portion of the dissolver housing 266. As with all other illustrated components, the dissolver drop tube 268 is not necessarily illustrated to scale. For example, in some embodiments, the dissolver drop tube 268 can extend (e.g., linearly or non-linearly) farther down. The tubes and/or pipes of the passive chemical dissolution system can be formed from common piping parts and/or other elongate structures shaped and sized to direct movement of condensate, material (e.g., a neutron-absorbing chemical), solution of material and condensate, and/or the like. Details of the passive chemical dissolution system 160 and its operation are described in further detail below with reference to FIGS. 3A-3C.

[0026] The passive mixing system 170 can include one or more condensate channels 172 coupled to (e.g., via fasteners, welded to) and extending along the inner wall of the containment vessel 110, a first condensate collector cup 274a coupled to the condensate channels 172, a second condensate collector cup 274b, a reducer 273 coupled between the first and second condensate collector cups 274a-b, a mixing tube 276 extending from the second condensate collector cup 274b toward a bottom portion of the containment vessel 110 (FIG. 1) along the inner wall of the containment vessel 110, and one or more openings or nozzles 278 at a lower end 277b of the mixing tube 276. Similar to the condensate channels 162, the condensate channels 172 can comprise U-shaped channels 272 (or channels having other geometries) shaped to collect condensate. The mixing tube 276 can be coupled to the inner wall of the containment vessel 110 (FIG. 1) via one or more pipe support guides 275. Moreover, the mixing tube 276 can have a funnel portion 277a shaped to align with the funnel portion 111 (FIG. 1) of the containment vessel 110 such that the mixing tube 276 can extend continuously along the inner wall of the containment vessel 110. In some embodiments, the passive mixing system 170 can include additional, alternative, or fewer components (e.g., the first and second condensate collector cups 274a-b can be omitted). Details of the passive mixing system 160 and its operation are described in further detail below with reference to FIG. 4.

[0027] Referring to FIGS. 1 and 2, the two passive chemical dissolution systems 160 can be arranged at generally the same level (e.g., elevation) on the inner wall of the containment vessel 110. More specifically, the condensate channels 162 of each of the passive chemical dissolution system 160 can extend around a portion of the circumference of the containment vessel 110 and the two passive chemical dissolution systems 160 can be positioned on opposite sides of the containment vessel 110. In some embodiments, only one, or more than two (e.g., three, four, five, six, or more) of the passive chemical dissolution systems 160 can be arranged at generally the same level on the inner wall of the containment vessel 110 and/or at different levels. Similarly, in the illustrated embodiment, the two passive mixing systems 170 can be arranged at generally the same level on the inner wall of the containment vessel 110. More specifically, the condensate channels 172 of each of the passive mixing system 170 can extend around a portion of the circumference of the containment vessel 110 and the two passive mixing systems 170 can be positioned on different sides of the containment vessel 110. In some embodiments, only one, or more than two (e.g., three, four, five, six, or more), of the passive mixing systems 170 can be arranged at generally the same level on the inner wall of the containment vessel 110 and/or at different levels.

[0028] FIGS. 3A, 3B, and 3C are partially schematic, partially cross-sectional views of one of the passive chemical dissolution systems 160 of FIG. 2 configured in accordance with embodiments of the present technology. In particular, FIGS. 3A-3C illustrate cross-sectional views of the condensate channels 162, the main condensate drop tube 261a, the auxiliary condensate drop tube 261b, the hopper 264, the hopper feed tube 263, the dissolver housing 266, and the dissolver drop pipe 268. Referring to FIGS. 3A-3C together, in the illustrated embodiment, the passive chemical dissolution system 160 further includes a release mechanism 382 operably coupled to the hopper 264 and/or the hopper feed tube 263, and one or more sensors 388 operably coupled to the dissolver housing 266. The passive chemical dissolution system 160 can further include a dissolver basket 386 positioned within the dissolver housing 266 such that a dissolver volume 387 is defined between the dissolver housing 266 and the dissolver basket 386. In some embodiments, the dissolver basket 386 comprises a mesh backed with a cylindrical structure (e.g., made from metal) with perforations. The main condensate drop tube 261a can extend into the dissolver housing 266 and/or can be fluidly coupled to the dissolver basket 386, and the auxiliary condensate drop tube 261b can extend into the dissolver housing 266 and/or can be fluidly coupled to the dissolver volume 387. The hopper feed tube 263 can extend between the hopper 264 and the dissolver basket 386. In the illustrated embodiment, the dissolver housing 266 further includes a distributor 385 positioned within the dissolver basket 386 toward the main condensate drop tube 261a.

[0029] In the illustrated embodiment, each of the condensate channels 162a, 162b is oriented at an angle 0 (not necessarily illustrated to scale) from horizontal such that condensate collected thereon/therein can be passively transferred (e.g., via gravity) towards the main or auxiliary condensate drop tube 261a, 261b, respectively. The angle 0 can be about 1 degree, about 2 degrees, about 3 degrees, about 4 degrees, about 5 degrees, about 10 degrees, about 15 degrees, about 20 degrees, between about 1-5 degrees, between about 1-10 degrees, between about 1-15 degrees, between about 1-20 degrees, or greater. In some embodiments, the angle 9 can be 0 degrees such that either or both of the condensate channels 162a, 162b are oriented horizontally such that condensate can pool therein before flowing down the main or auxiliary condensate drop tube 261a, 261b. The main condensate channel 162a and the auxiliary condensate channel 162b can be oriented at the same or different angles 0. In some embodiments, the condensate channels 162a, 162b can have shapes other than the illustrated linear shape.

[0030] In some embodiments, the main and auxiliary condensate channels 162a, 162b have different dimensions. For example, the main condensate channel 162a can be longer and/or wider (e.g.. having a wider U-shaped cross-section) than the auxiliary condensate channel 162b. The angles 0 and the dimensions of the mam and auxiliary condensate channels 162a, 162b can be selected such that condensate flows into the dissolver basket 386 at a different (e.g., greater) rate than into the dissolver volume 387.

[0031] The release mechanism 382 can be configurable between a closed state, an open state, and various partially open states. In the closed state, the release mechanism 382 can inhibit or even prevent a neutron-absorbing material or chemical 380 (e g., boron, silver, cadmium, indium, hafnium) in the hopper 264 from moving (e.g., falling) down through the hopper feed tube 263 (e.g., via gravity). In the open state, the release mechanism 382 can allow the neutronabsorbing chemical 380 to move down the hopper feed tube 263 and into the dissolver basket 386 at a maximum rate. In the various partially open states, the release mechanism 382 can allow the neutron-absorbing chemical 380 to move down the hopper feed tube 263 and into the dissolver basket 386 at various rates below the maximum rate.

[0032] In some embodiments, the sensors 388 can be load sensors positioned to measure how much of the neutron-absorbing chemical 380 is present in the dissolver basket 386 (e g., by weight, by volume). The sensors 388 and the release mechanism 382 can be communicatively coupled such that the amount of the neutron-absorbing chemical 380 fed from the hopper 264 and into the dissolver basket 386 is controllable via a feedback loop. The distributor 385 can be a perforated plate, a mesh, or other component designed to distribute the stream of fluid (e.g., condensate) flowing (e.g., falling) down from the main condensate drop tube 261a to a larger area across the cross-section of the dissolver basket 386. Alternatively or additionally, a sprinkler mechanism can be coupled to the outlet of the main condensate drop tube 261a to distribute the fluid.

[0033] Referring to FIGS. 1 and 3A, the hopper 264 can be loaded with the neutronabsorbing chemical 380 (e.g., in the form of pelletized boron oxide) by operators during a non- operational period of the nuclear power system 100, such as during a refueling stage and/or prior to sealing the containment vessel 110. Referring next to FIGS. 1 and 3B, during a startup sequence of the nuclear power system, once the containment vessel 110 is sealed properly, the release mechanism 382 can be operated (e.g., remotely via a wireless or wired connection) to release some or all of the neutron-absorbing chemical 380 from the hopper 264 into the dissolver basket 386. As discussed above, the sensors 388 can measure and indicate when a sufficient quantity of the neutron-absorbing chemical 380 has reached the dissolver basket 386. The nuclear power system 100 can then initiate operation to generate power. In some aspects of the present technology, the neutron-absorbing chemical 380 can be selected based on the operating conditions of the nuclear power system 100. For example, the neutron-absorbing chemical 380 can entirely or in part comprise boric oxide, which, compared to boric acid, is more chemically stable in high temperature environments (e.g., such as in the containment vessel 110 during an emergency event or normal operation), less volatile, and has a higher melting temperature.

[0034] If there is no emergency event during operation of the nuclear power system 100, the neutron-absorbing chemical 380 remains in the dissolver basket 386 unused. However, referring to FIGS. 1 and 3, during an emergency event (e.g., overheating of the reactor core 104, loss of coolant), the coolant 107 can be vented into the open volume 114 through the reactor vent valve 134 and condense to form condensate 107 on the inner wall of the containment vessel 110 that is collected by the condensate channels 162. In particular, the main condensate channel 162a can collect a first portion of the condensate and the auxiliary condensate channel 162b can collect a second portion of the condensate. The first portion of the condensate can flow along the main condensate channel 162a, down the main condensate drop tube 261a, and into the dissolver basket 386. The first portion of the condensate 107 entering the dissolver basket 386 is distributed by the distributor 385 over the neutron-absorbing chemical 380 in the dissolver basket 386 and dissolves the neutron-absorbing chemical 380 to form a solution 307. The dissolver basket 386 can be a mesh such that the neutron-absorbing chemical 380 in its dry and/or pelletized form cannot pass through, but can when dissolved by the condensate 107. The main condensate channel 162a can be sized to collect a sufficient amount of condensate to completely dissolve the neutron-absorbing chemical 380 in the dissolver basket 386 over time. The solution 370 of the neutron-absorbing chemical 380 dissolved into the condensate 107 (e.g., diluted boric acid) then flows out of the dissolver basket 386, into the dissolver volume 387, and out of the dissolver housing 266 via the dissolver drop pipe 268.

[0035] The second portion of the condensate flows along the auxiliary condensate channel

162b, down the auxiliary condensate drop tube 261b, and into the dissolver volume 387. The second portion of the condensate from the auxiliary condensate channel 162b can help promote flow of the dissolved neutron-absorbing chemical out of the dissolver housing 266. The second portion of the condensate from the auxiliary condensate channel 162b can also further dilute the solution 307 of the neutron-absorbing chemical 380, which may approach or reach the saturation limit if the main condensate channel 162a is used alone. The solution 307 of the neutronabsorbing chemical 380 is then released into the open volume 114 and the pool 116 where it can mix with the recirculating coolant 107 in the pool 116 toward the bottom of the containment vessel 110. and can enter the reactor vessel 120 via the submerged reactor recirculation valves 136 to maintain subcriticality by reducing or shutting down the nuclear fission reaction within the core 104.

[0036] In some aspects of the present technology, the chemical dissolution system 160 can operate in a passive manner to cool the core 104 by reducing the nuclear fission reaction therein without operator input or control. As described in detail above, the chemical dissolution system 160 passively directs condensate formed in the open volume 114 toward and through the neutron-absorbing chemical 380 which, once dissolved, passively mixes with the coolant 107 for recirculation through the reactor recirculation valves 136. Furthermore, the neutronabsorbing chemical 380 remains unused if there is no emergency event, avoiding unnecessary interference with the nuclear fission reaction during operation of the nuclear power system 100. In addition, by positioning the passive chemical dissolution system 160 in the open volume 114 as opposed to, for example, submerging the passive chemical dissolution system 160 in the pool 116 of the coolant, the flow rate of the condensate fluid down the condensate channels 162 can be predicted more accurately and easily. In some aspects of the present technology, knowing the flow rate can allow for improved analysis and/or simulation of the operation of the passive chemical dissolution system 160, which can help operators properly size the various components, such as the length and/or width of the condensate channels 162. This can ensure proper passive activation of the passive chemical dissolution system 160 while also avoiding dissolving all of the neutron-absorbing chemical 380 at once or at an undesirably high rate. [0037] FIG. 4 is a partially schematic, partially cross-sectional view of the nuclear reactor system 100 including the passive mixing system 170 configured in accordance with embodiments of the present technology. As described in detail above with reference to FIG. 2, the passive mixing system 170 can include the one or more condensate channels 172 positioned above the pool 116 of the vented coolant 107, and the mixing tube 276 extending from the condensate channels 172. The mixing tube 276 can extend downward into the pool 116 toward a bottom portion 414 of the containment vessel 1 10, and the one or more nozzles 278 at the lower end 277b of the mixing tube 276 can be positioned at the bottom portion 414 of the containment vessel 110.

[0038] During an emergency event, condensate formed on the inner wall of the containment vessel 110 can be collected by the condensate channels 172 and flow down the mixing tube 276. In some embodiments, the nuclear reactor system 100 includes both the passive chemical dissolution system 160 and the passive mixing system 170, and the condensate channels 162 and the condensate channels 172 can collect different portions of the condensate. Hydrostatic forces from condensate collected in the mixing tube 276 can help drive the flow of the collected condensate down through the mixing tube 276 such that the condensate can reach the bottom portion 414 and exit the mixing tube 276 into the pool 116 through the one or more nozzles 278. The pool 1 16 at the bottom portion 414 may contain a higher concentration (or settled portions) of a neutron-absorbing chemical (e.g., in the case of using the passive mixing system 170 of FIGS. 1-3C with the passive chemical dissolution system 160 or other chemical release systems). The pool 116 at the bottom portion 414 may also contain colder portions of the recirculating coolant 107 (e.g.. regardless of whether the passive mixing system 170 is used with the passive chemical dissolution system 160 or other chemical release systems). The condensate exiting from the one or more nozzles 278 can push such colder coolant and/or concentrated chemical upward through the pool 116 and to ard the submerged reactor recirculation valves 136 (as indicated by arrows in FIG. 4). The passive mixing system 170 can thereby promote improved mixing of the coolant and/or the chemical, which can increase the effectiveness of the ECCS operation and the safety level of the nuclear pow er system 100.

[0039] In some aspects of the present technology, the passive mixing system 170 can address issues associated with stagnant fluid during an emergency event in a passive manner. As discussed in detail above, the passive mixing system 170 passively directs condensate formed in the open volume 114 toward the bottom portion 414 (e.g., via hydrostatic forces). Furthermore, one of ordinary skill in the art will appreciate that the nuclear power system 100 can include only one or both of the passive chemical dissolution system 160 and the passive mixing system 170.

[0040] Many embodiments of the technology described herein may take the form of computer- or machine- or controller-executable instructions, including routines executed by a programmable computer or controller. Those skilled in the relevant art will appreciate that the technology can be practiced on computer/controller systems other than those shown and described below. The technology' can be embodied in a special-purpose computer, controller or data processor that is specifically programmed, configured or constructed to perform one or more of the computer-executable instructions described below. Accordingly, the terms “computer’ and “controller” as generally used herein refer to any data processor and can include Internet appliances and hand-held devices (including palm-top computers, wearable computers, cellular or mobile phones, multi-processor systems, processor-based or programmable consumer electronics, network computers, mini-computers and the like). Information handled by these computers can be presented at any suitable display medium, including a liquid crystal display (LCD).

[0041] The technology can also be practiced in distributed environments, where tasks or modules are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules or subroutines may be located in local and remote memory storage devices. Aspects of the technology described below may be stored or distributed on computer-readable media, including magnetic or optically readable or removable computer disks, as well as distributed electronically over networks. Data structures and transmissions of data particular to aspects of the technology are also encompassed within the scope of the embodiments of the technology.

IV. Additional Examples

[0042] The following examples are illustrative of several embodiments of the present technology:

1. A nuclear power system, comprising: a reactor vessel defining a volume: a reactor core positioned within the volume, wherein the reactor core includes one or more nuclear fuel assemblies configured to generate a nuclear fission reaction; a containment vessel sized to enclose the reactor vessel such that an open volume is defined between the containment vessel and the reactor vessel; and a passive chemical dissolution system positioned in the open volume, wherein the passive chemical dissolution system includes: a condensate channel coupled to and extending along an inner wall of the containment vessel, wherein the condensate channel is configured to collect condensate formed on the inner wall of the containment vessel; a dissolver housing coupled to the condensate channel to receive the condensate from the condensate channel; and a neutron-absorbing chemical positioned in the dissolver housing, wherein the dissolver housing is configured to direct the condensate to dissolve at least a portion of the neutron-absorbing chemical and to release the dissolved neutron-absorbing chemical into the open volume.

2. The nuclear power system of example 1 , wherein the passive chemical dissolution system further includes a dissolver basket positioned within the dissolver housing such that a dissolver volume is defined between the dissolver housing and the dissolver basket, and wherein the neutron-absorbing chemical is positioned in the dissolver basket.

3. The nuclear power system of example 2, wherein the condensate channel is a first condensate channel, wherein the condensate channel is configured to collect a first portion of the condensate, and wherein: the passive chemical dissolution system further comprises a second condensate channel coupled to and extending along the inner wall of the containment vessel, the second condensate channel is configured to collect a second portion of the condensate formed on the inner wall of the containment vessel, the dissolver basket is coupled to the first condensate channel to receive the first portion of the condensate, and the dissolver volume is coupled to the second condensate channel to receive the second portion of the condensate.

4. The nuclear power system of any of examples 1-3, wherein the passive chemical dissolution system further comprises a hopper coupled to the dissolver housing, wherein the neutron-absorbing chemical is configured to be positioned in the hopper and routed to the dissolver housing.

5. The nuclear power system of example 4, wherein the passive chemical dissolution system further comprises a hopper release mechanism coupled between the hopper and the dissolver housing, and wherein the hopper release mechanism is operable to selectively release the neutron-absorbing chemical from the hopper such that the neutron-absorbing chemical is routed to the dissolver housing.

6. The nuclear power system of any of examples 1-5, wherein the passive chemical dissolution system further comprises one or more sensors coupled to the dissolver housing and configured to measure an amount of the neutron-absorbing chemical positioned in the dissolver housing.

7. The nuclear power system of any of examples 1-6, wherein the passive chemical dissolution system further comprises a distributor positioned inside the dissolver housing and configured to distribute the condensate from the condensate channel across the dissolver housing.

8. The nuclear power system of any of examples 1-7, wherein the condensate channel is angled downward toward the dissolver housing at an angle of between 1-5 degrees.

9. The nuclear power system of any of examples 1-8, wherein the condensate channel is a first condensate channel, wherein the condensate channel is configured to collect a first portion of the condensate, and wherein the nuclear power system further comprises a passive mixing system positioned in the open volume, wherein the passive mixing system includes: a second condensate channel coupled to and extending along an inner wall of the containment vessel, wherein the second condensate channel is configured to collect a second portion of the condensate formed on the inner wall of the containment vessel; and a tube extending between the second condensate channel and a bottom portion of the open volume, wherein the tube is configured to deliver the condensate from the second condensate channel to the bottom portion of the open volume. 10. A method for controlling a nuclear fission reaction, comprising: operating a nuclear power system to generate a nuclear fission reaction, the nuclear power system comprising: a reactor vessel defining a volume; a reactor core positioned within the volume, wherein the reactor core includes one or more nuclear fuel assemblies configured to generate a nuclear fission reaction: a coolant in the reactor vessel; a containment vessel sized to enclose the reactor vessel such that an open volume is defined between the containment vessel and the reactor vessel; and a passive chemical dissolution system positioned in the open volume; and during an emergency operation of the nuclear power system — venting the coolant in vapor form from the volume of the reactor vessel to the open volume; permitting the coolant in vapor form to condense into a condensate on an inner wall of the containment vessel within the open volume; collecting a portion of the condensate with a condensate channel of the passive chemical dissolution system; directing, via the condensate channel of the passive chemical dissolution system, the portion of the condensate to a dissolver housing of the passive chemical dissolution system; dissolving a neutron-absorbing chemical positioned in the dissolver housing with the condensate; and releasing the dissolved neutron-absorbing chemical into the open volume.

11. The method of example 10, wherein the passive chemical dissolution system further includes a dissolver basket positioned within the dissolver housing such that a dissolver volume is defined between the dissolver housing and the dissolver basket, and wherein the neutron-absorbing chemical is positioned in the dissolver basket. 12. The method of example 11, wherein the condensate channel is a first condensate channel, wherein the condensate channel is configured to collect a first portion of the condensate, and wherein the method further comprises: directing, via a second condensate channel of the passive chemical dissolution system, a second portion of the condensate formed on the inner wall of the containment vessel into the dissolver volume.

13. The method of any of examples 10-12, wherein the method further comprises: depositing, before operating the nuclear power system, the amount of neutron-absorbing chemical in a hopper of the passive chemical dissolution system, wherein the hopper is coupled to the dissolver housing.

14. The method of example 13, wherein the method further comprises: actuating, prior to operating the nuclear power system, a hopper release mechanism of the passive chemical dissolution system to release the neutron-absorbing chemical from the hopper such that the neutron-absorbing chemical is routed to the dissolver housing.

15. The method of any of examples 10-14, wherein the method further comprises: measuring, via one or more sensors of the passive chemical dissolution system, an amount of the neutron-absorbing chemical positioned in the dissolver housing.

16. The method of any of examples 10—15, wherein the passive chemical dissolution system further comprises a distributor positioned inside the dissolver housing and configured to distribute the condensate from the condensate channel across the dissolver housing.

17. The method of any of examples 10-16. wherein the condensate channel is angled downward toward the dissolver housing at an angle of between 1-5 degrees.

18. The method of any of examples 10-17, wherein the condensate channel is a first condensate channel, wherein the condensate channel is configured to collect a first portion of the condensate, and wherein the nuclear power system further comprises a passive mixing system positioned in the open volume, and wherein the method further comprises: directing, via a second condensate channel and a tube of the passive mixing system, a second portion of the condensate formed on the inner wall of the containment vessel to a bottom portion of the open volume, wherein the second condensate channel is coupled to and extends along the inner wall of the containment vessel, and wherein the tube extends between the second condensate channel and the bottom portion of the open volume.

19. A nuclear power system, comprising: a reactor vessel defining a volume: a reactor core positioned within the volume, wherein the reactor core includes one or more nuclear fuel assemblies configured to generate a nuclear fission reaction; a containment vessel sized to enclose the reactor vessel such that an open volume is defined between the containment vessel and the reactor vessel; and a passive mixing system positioned in the open volume, wherein the passive mixing system includes: a condensate channel coupled to and extending along an inner wall of the containment vessel, wherein the condensate channel is configured to collect condensate formed on the inner wall of the containment vessel; and a tube extending between the second condensate channel and a bottom portion of the open volume, wherein the tube is configured to deliver the condensate from the second condensate channel to the bottom portion of the open volume.

20. The nuclear power system of example 19, wherein the containment vessel includes a funnel portion, and wherein the tube extends along the funnel portion of the containment vessel. V. Conclusion

[0043] All numeric values are herein assumed to be modified by the term about whether or not explicitly indicated. The term about, in the context of numeric values, generally refers to a range of numbers that one of skill in the art would consider equivalent to the recited value (e.g., having the same function and/or result). For example, the term about can refer to the stated value plus or minus ten percent. For example, the use of the term about 100 can refer to a range of from 90 to 110, inclusive. In instances in which the context requires otherwise and/or relative terminology is used in reference to something that does not include, or is not related to, a numerical value, the terms are given their ordinary meaning to one skilled in the art.

[0044] The above detailed description of embodiments of the present technology are not intended to be exhaustive or to limit the technology to the precise forms disclosed above. Although specific embodiments of, and examples for, the technology are described above for illustrative purposes, various equivalent modifications are possible within the scope of the technology, as those skilled in the relevant art will recognize. For example, although steps may be presented in a given order, in other embodiments, the steps may be performed in a different order. The various embodiments described herein may also be combined to provide further embodiments.

[0045] From the foregoing, it will be appreciated that specific embodiments of the technology have been described herein for purposes of illustration, but w ell-known structures and functions have not been shown or described in detail to avoid unnecessarily obscuring the description of the embodiments of the technology. Where the context permits, singular or plural terms may also include the plural or singular term, respectively.

[0046] As used herein, the phrase “and/or” as in “A and/or B” refers to A alone, B alone, and A and B. Additionally, the term “comprising” is used throughout to mean including at least the recited feature(s) such that any greater number of the same feature and/or additional ty pes of other features are not precluded. It will also be appreciated that specific embodiments have been described herein for purposes of illustration, but that various modifications may be made without deviating from the technology. Further, while advantages associated with some embodiments of the technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology⁷ can encompass other embodiments not expressly shown or described herein.

Claims

CLAIMS I/We claim:

2. The nuclear power system of claim 1, wherein the passive chemical dissolution system further includes a dissolver basket positioned within the dissolver housing such that a dissolver volume is defined between the dissolver housing and the dissolver basket, and wherein the neutron-absorbing chemical is positioned in the dissolver basket.

3. The nuclear power system of claim 2, wherein the condensate channel is a first condensate channel, wherein the condensate channel is configured to collect a first portion of the condensate, and wherein: the passive chemical dissolution system further comprises a second condensate channel coupled to and extending along the inner wall of the containment vessel, the second condensate channel is configured to collect a second portion of the condensate formed on the inner wall of the containment vessel, the dissolver basket is coupled to the first condensate channel to receive the first portion of the condensate, and the dissolver volume is coupled to the second condensate channel to receive the second portion of the condensate.

4. The nuclear power system of claim 1, wherein the passive chemical dissolution system further comprises a hopper coupled to the dissolver housing, wherein the neutronabsorbing chemical is configured to be positioned in the hopper and routed to the dissolver housing.

5. The nuclear power system of claim 4, wherein the passive chemical dissolution system further comprises a hopper release mechanism coupled between the hopper and the dissolver housing, and wherein the hopper release mechanism is operable to selectively release the neutron-absorbing chemical from the hopper such that the neutron-absorbing chemical is routed to the dissolver housing.

6. The nuclear power system of claim 1, wherein the passive chemical dissolution system further comprises one or more sensors coupled to the dissolver housing and configured to measure an amount of the neutron-absorbing chemical positioned in the dissolver housing.

7. The nuclear power system of claim 1, wherein the passive chemical dissolution system further comprises a distributor positioned inside the dissolver housing and configured to distribute the condensate from the condensate channel across the dissolver housing.

8. The nuclear power system of claim 1, wherein the condensate channel is angled downward toward the dissolver housing at an angle of between 1-5 degrees.

9. The nuclear power system of claim 1, wherein the condensate channel is a first condensate channel, wherein the condensate channel is configured to collect a first portion of the condensate, and wherein the nuclear power system further comprises a passive mixing system positioned in the open volume, wherein the passive mixing system includes: a second condensate channel coupled to and extending along an inner wall of the containment vessel, wherein the second condensate channel is configured to collect a second portion of the condensate formed on the inner wall of the containment vessel; and a tube extending between the second condensate channel and a bottom portion of the open volume, wherein the tube is configured to deliver the condensate from the second condensate channel to the bottom portion of the open volume.

10. A method for controlling a nuclear fission reaction, comprising: operating a nuclear power system to generate a nuclear fission reaction, the nuclear power system comprising: a reactor vessel defining a volume; a reactor core positioned within the volume, wherein the reactor core includes one or more nuclear fuel assemblies configured to generate a nuclear fission reaction; a coolant in the reactor vessel; a containment vessel sized to enclose the reactor vessel such that an open volume is defined between the containment vessel and the reactor vessel; and a passive chemical dissolution system positioned in the open volume; and during an emergency operation of the nuclear power system — venting the coolant in vapor form from the volume of the reactor vessel to the open volume; permitting the coolant in vapor form to condense into a condensate on an inner wall of the containment vessel within the open volume; collecting a portion of the condensate with a condensate channel of the passive chemical dissolution system; directing, via the condensate channel of the passive chemical dissolution system, the portion of the condensate to a dissolver housing of the passive chemical dissolution system; dissolving a neutron-absorbing chemical positioned in the dissolver housing with the condensate; and releasing the dissolved neutron-absorbing chemical into the open volume.

1 1 . The method of claim 10, wherein the passive chemical dissolution system further includes a dissolver basket positioned within the dissolver housing such that a dissolver volume is defined between the dissolver housing and the dissolver basket, and wherein the neutronabsorbing chemical is positioned in the dissolver basket.

12. The method of claim 11, wherein the condensate channel is a first condensate channel, wherein the condensate channel is configured to collect a first portion of the condensate, and wherein the method further comprises: directing, via a second condensate channel of the passive chemical dissolution system, a second portion of the condensate formed on the inner wall of the containment vessel into the dissolver volume.

13. The method of claim 10, wherein the method further comprises: depositing, before operating the nuclear power system, the amount of neutron-absorbing chemical in a hopper of the passive chemical dissolution system, wherein the hopper is coupled to the dissolver housing.

14. The method of claim 13, wherein the method further comprises: actuating, prior to operating the nuclear power system, a hopper release mechanism of the passive chemical dissolution system to release the neutron-absorbing chemical from the hopper such that the neutron-absorbing chemical is routed to the dissolver housing.

15. The method of claim 10, wherein the method further comprises: measuring, via one or more sensors of the passive chemical dissolution system, an amount of the neutron-absorbing chemical positioned in the dissolver housing.

16. The method of claim 10, wherein the passive chemical dissolution system further comprises a distributor positioned inside the dissolver housing and configured to distribute the condensate from the condensate channel across the dissolver housing.

17. The method of claim 10, wherein the condensate channel is angled downward toward the dissolver housing at an angle of between 1-5 degrees.

18. The method of claim 10, wherein the condensate channel is a first condensate channel, wherein the condensate channel is configured to collect a first portion of the condensate, and wherein the nuclear power system further comprises a passive mixing system positioned in the open volume, and wherein the method further comprises: directing, via a second condensate channel and a tube of the passive mixing system, a second portion of the condensate formed on the inner wall of the containment vessel to a bottom portion of the open volume, wherein the second condensate channel is coupled to and extends along the inner wall of the containment vessel, and wherein the tube extends between the second condensate channel and the bottom portion of the open volume.

20. The nuclear power system of claim 19, wherein the containment vessel includes a funnel portion, and wherein the tube extends along the funnel portion of the containment vessel.