Reactor shutdown system

Abstract

A system for use in shutting down a reactor comprises a housing that defines within it a region sealed from the surrounding environment, and a gate member disposed within the region in such a manner that the region is separated into a first compartment and a second compartment isolated from the first compartment. The gate member is formed of a material having a predetermined melting point. The system further comprises a neutron absorbing material disposed within the first compartment and a dispersion mechanism disposed within the region. The dispersion mechanism is structured to facilitate the neutron absorbing material from the first compartment into the second compartment.

Description

Technology Field

[0001] Cross-reference regarding related applications

[0002] This application claims the benefit of U.S. Patent Application No. 16 / 711,922 filed on December 12, 2019, titled “REACTOR SHUTDOWN SYSTEM”, the contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present invention generally relates to a nuclear reactor, and more specifically, to a system for use in shutting down a nuclear reactor. The present invention also relates to a nuclear reactor having such a shutdown system and a method for providing a system for use in shutting down a nuclear reactor. Background Technology

[0005] Currently, most water reactor technologies and most advanced reactors rely on various shutdown mechanisms to halt the reactor. Examples include the control rod drive mechanism (CRDM), neutron absorber spheres, and boron injection into the primary fluid. Since almost all of these systems operate using mechanical components prone to failure, they generally require high reliability and qualification. Consequently, additional redundancy and variability must be established in the design and safety cases, which complicates the plant and increases costs. Some of these systems feature passive functions that utilize gravity or other potential energy to activate passive features. However, these systems are large and unsuitable for small reactor designs, such as advanced microreactors. Furthermore, these systems are not applicable to horizontal reactors. Reactors with unique shutdown mechanisms, such as the TRIGA research reactor, are design-dependent and cannot be applied to other reactor designs.

[0006] Therefore, there is room to improve the shutdown system for the reactor.

[0007] The embodiments of the invention described herein provide a "solid-state" emergency core shutdown system for a nuclear reactor. The system is designed to be triggered and operated by an essentially adjustable design set temperature. Additionally, the system can be manually activated by an operator using electrical power. The system is applicable to all nuclear reactors regardless of coolant type, neutron energy spectrum, and magnitude. Through this technology, the nuclear reactor can fall under IAEA passive safety category B for the shutdown system.

[0008] In one aspect of the present invention, a system for use in shutting down a nuclear reactor is provided. The system comprises: a housing defining an area sealed from the surrounding environment; a gate member disposed within the area in such a manner that the area is divided into a first compartment and a second compartment isolated from the first compartment, and comprising a material having a predetermined melting point; a neutron absorbing material disposed within the first compartment; and a dispersion mechanism disposed within the area and structured to facilitate the neutron absorbing material from the first compartment into the second compartment.

[0009] The predetermined melting point of the substance can be about 800°C.

[0010] The gate member may include a number of heater coils embedded in the material and structured to melt the material when actuated by an electric current.

[0011] Neutron-absorbing materials may include phase-change materials.

[0012] The phase change material may include at least one of an indium / cadmium alloy, lithium, or boron oxide.

[0013] The dispersion mechanism may include a porous matrix structure disposed within the second compartment.

[0014] The second compartment can be maintained under vacuum.

[0015] The porous matrix structure can be formed from one or more metals.

[0016] The porous matrix structure can be formed from one or more ceramic materials.

[0017] Neutron-absorbing materials may include solid materials.

[0018] The distribution mechanism may include a plurality of springs disposed within the first compartment.

[0019] The system may further include a second gate member disposed within the region in such a manner that the region is further separated into a third section isolated from the second section by a second gate member comprising another material having a predetermined melting point; and a neutron absorbing material disposed within the first section.

[0020] In another aspect of the present invention, a nuclear reactor is provided. The nuclear reactor comprises: a core structured to accommodate a nuclear reaction; and a system for use in shutting down the nuclear reactor. The system comprises: a housing defining an internal region sealed from the surrounding environment; a gate member comprising a material having a predetermined melting point disposed within the region in such a manner that the region is divided into a first compartment and a second compartment isolated from the first compartment; a neutron absorbing material disposed within the first compartment; and a dispersion mechanism disposed within the region and structured to facilitate the neutron absorbing material from the first compartment into the second compartment, wherein the system is positioned relative to the core such that the first compartment is located outside the core and the second compartment is located inside the core.

[0021] In another aspect of the present invention, a method is provided for providing a system to be used to stop a nuclear reaction within the core of a nuclear reactor. The method comprises the step of positioning a system to be used to stop a nuclear reactor, wherein the system comprises: a housing defining an internal region sealed from the surrounding environment; a gate member disposed within the region in such a manner that the region is divided into a first compartment and a second compartment isolated from the first compartment, and comprising a material having a predetermined melting point; a neutron absorbing material disposed within the first compartment; and a dispersion mechanism disposed within the region and structured to promote the neutron absorbing material from the first compartment into the second compartment, wherein the step of positioning the system comprises the step of positioning the housing relative to the core such that the first compartment is located outside the core and the second compartment is located inside the core.

[0022] These and other objects, features, and characteristics of the present invention, as well as the method of operation and function of related structural elements, and the combination of parts and manufacturing economics, will become more apparent from the following description with reference to the accompanying drawings and the appended claims, all of which form part of this specification, where similar reference numbers designate corresponding parts in various drawings. However, it should be clearly understood that the drawings are for illustrative and illustrative purposes only and are not intended to define the limitations of the present invention. Brief explanation of the drawing

[0023] The present invention can be further understood from the following description of a preferred embodiment when read together with the accompanying drawings. FIG. 1 is a schematic elevation cross-sectional view of a system for use in shutting down a reactor according to an exemplary embodiment of the present invention, which is shown positioned with respect to the core region of a nuclear reactor. FIG. 2 is a perspective cross-sectional view of a nuclear reactor device having a system as shown in FIG. 1 according to an exemplary embodiment of the present invention. FIG. 3 is a schematic elevation cross-sectional view of a system to be used to shut down a nuclear reactor according to another exemplary embodiment of the present invention. Figure 4 is an elevation endview of the system of Figure 3 taken along line 4-4 of Figure 3. Figure 5 is an elevation cross-sectional view of the system of Figure 3 taken along line 5-5 of Figure 3. FIG. 6 is a schematic diagram of the system of FIG. 3, shown as being positioned relative to the core of a reactor according to an exemplary embodiment of the present invention, with a portion arranged in a reactor operating mode. FIG. 7 is another schematic diagram of the system of FIG. 3, shown as being positioned relative to the core of the reactor according to an exemplary embodiment of the present invention, with a portion positioned in a reactor shutdown mode. Specific details for implementing the invention

[0024] In the following description, similar reference numbers designate similar or corresponding parts across various aspects of the drawing. Additionally, it should be understood that in the following description, terms such as "front," "rear," "left," "right," "upward," and "downward" are terms of convenience and should not be interpreted as restrictive terms.

[0025] According to one embodiment of the present invention, one exemplary system (4) for use in shutting down a reactor is schematically illustrated in FIGS. 1 and 2 as being located relative to the reactor core (8) of a reactor (10) (schematically illustrated by dashed lines). The system (4) includes a housing (12) that defines an internal area (14) that is sealed from the surrounding environment where the system (4) is provided. In the exemplary embodiment of the present invention illustrated in FIGS. 1, the housing (12) is generally formed as a tubular member, but it should be understood that the housing (12) may have other shape(s) and / or relative sizes without change from the scope of the present invention. The system (4) further comprises a first gate member (16) disposed within the region (14) in such a manner that the region (14) is separated into a first end section (18) located outside the reactor core (8) when the system (4) is installed in the reactor (10), and a core section (20) located within the reactor core (8) when the system (4) is installed in the reactor (10). That is, the core section (20) is isolated from the first end section (18) by the first gate member (16). The first gate member (16) is formed of a material having a predetermined melting point that exceeds the normal operating temperature of the reactor (10) but is below the critical temperature of the reactor, and does not exceed the material design limits of the reactor. The importance of such a device will be understood from the further discussion below. Additionally, the first gate member (16) may include a plurality of heater coils (22) embedded in the material and structured to melt the material when operated by a current provided by an external power supply.

[0026] Optionally (as further discussed below), the system (4) may additionally include a second gate member (16') when installed in a reactor (10), and the second gate member (16') may be positioned within the region (14) in such a way that the region (14) is further separated into a second end section (18') located opposite the first end section (18) and outside the reactor core (8). The second gate member (16') is formed of a material having a predetermined melting point that exceeds the normal operating temperature of the reactor (10) but is below the critical temperature of the reactor, and does not exceed the material design limits of the reactor. Additionally, the second gate member (16') may include a plurality of heater coils (22) embedded in the material and structured to melt the material when operated by a current provided by an external power supply.

[0027] Referring further to FIG. 1, the system (4) further comprises a neutron absorbing material (24) disposed within the first and second end sections (18, 18') (i.e., outside the reactor core (8)) and a dispersion mechanism (26) disposed within the core section (20) of the region (14) of the housing (12) (i.e., inside the reactor core (8)), wherein the dispersion mechanism (26) is structured to promote the neutron absorbing material (24) from each of the first and second end sections (18, 18') into the core section (20). In the example illustrated in FIG. 1, the neutron absorbing material (24) is a phase change, neutron absorbing material (e.g., without limitation, indium / cadmium alloy, lithium, or boron oxide) which is transferred from the first end section (18) to the core section (20) to stop the reactor in a manner as described below. In this example, the dispersion mechanism (26) is a porous matrix that can be made of a metal (e.g., stainless steel or niobium zirconium, without limitation, etc.) or a ceramic (e.g., graphite, beryllium oxide or alumina, without limitation) that does not have a very low neutron absorption cross-section. To ensure that voids within the porous matrix material are not filled with gas that could interfere with liquid adsorption, the core section (20) can be maintained under vacuum, such as through a vacuum port (28) defined in the housing (12) or through any other suitable device.

[0028] Now that the general arrangement of the system (4) has been described, its operation will now be described. The normal operating temperature of the reactor (10) as illustrated in FIG. 2 is above 450°C. At this temperature, the neutron absorbing material (24) will already be in a liquid state. The reactor operator can actively activate the system (4) by supplying power to the heater coil (22) to melt the first gate member (16) (and / or the second gate member (16')), and the first gate member is adsorbed into the porous matrix of the dispersion mechanism (26), allowing the neutron absorbing material (24) to access the porous matrix by capillary force. As the neutron absorbing material (24) is uniformly diffused into the core section (20) of the system (4) (which is placed within the reactor core (8) of the reactor (10)), neutron absorption will occur and the reactor (10) will be stopped.

[0029] In an accident scenario where the primary coolant is cut off and the reactor (10) is still operating, the temperature of the reactor core (8) will rise, as will the temperature of the core section (20) of the system (4) located therein. As the temperature of the core section (20) increases, heat from the core section (20) will cause the first gate member (16) (and / or the second gate member (16')) to melt and be adsorbed into the porous matrix of the dispersion mechanism (26), causing the neutron absorbing material (24) to approach the porous matrix by capillary force. As the neutron absorbing material (24) spreads uniformly into the core section (20) of the system (4) (placed within the reactor core (8) of the reactor (10)), neutron absorption will occur, causing the reactor (10) to stop. Accordingly, the system (4) will be passively activated in the event of an emergency where the temperature of the reactor (10) exceeds a predetermined operating limit (i.e., the melting point of the gate member(s) (16 and / or 16').

[0030] It should be understood that while the device of one of the end sections (18 or 18') and the neutron-absorbing material (24) contained therein is sufficient to cause the reactor (10) to stop, the use of two of these sections (where space is available) provides a margin and thus provides greater reactor safety.

[0031] In an exemplary embodiment of the present invention, heat may be transferred to one or both of the first and second end sections (18 and 18') within a housing (12) containing a neutron-absorbing material (24) using an integrated heat diffuser, and the integrated heat diffuser (generally illustrated as 27) may be (i) a heat pipe or thermosiphon that diffuses heat using a phase change fluid such as sodium (which can be utilized in reactors of any size), or (ii) a solid conductive tube or shell (applicable to small reactors). Heat pipe and thermosiphon devices as generally known may be used. Typically, both devices transfer heat from one end to the other. In the example of FIGS. 1 and 2, heat is transferred from the reactor core (8) to the area (14) of the housing (12) and to the first and second end sections (18 and 18') of the system (4).

[0032] When a heat pipe is used, if the core section (20) exceeds a specific design temperature, the sodium melts and flows down to the first and second end sections (18 and 18') of the relatively colder system (4). Then, the heat melts the gates (16 and 16') and causes the neutron-absorbing material (24), now in a liquid state, to flow into the core section (20). As heat is transferred to the neutron-absorbing material, optionally through the conductive pin (28), the sodium in the heat diffuser condenses and is passively transferred back to the core section (20) by the capillary action of the heat diffuser wick in the heat pipe (applicable to a horizontal reactor) or by gravity in the heat siphon (applicable to a vertical reactor). The heat diffuser maintains the isothermal temperature of the device throughout its entire length.

[0033] Now, referring to FIGS. 3 through 7, another example of a system (104) for use in shutting down a reactor according to another embodiment of the present invention will be described. The basic apparatus of the system (104) (i.e., housing (112), region (114), first end section (118), second end section (118') (optional), core section (120), gate member(s) (116, 116'), and heating element(s) (122)) is generally identical to the apparatus of the previously described system (4) and is therefore not described in further detail herein. The system (104) differs from the system (4) in both the neutron-absorbing material and the dispersion mechanism used accordingly. Instead of a neutron absorbing material (24) distributed in a liquid state by a dispersion mechanism (26) in the form of a porous matrix, the system (104) utilizes a solid neutron absorbing material (124) (e.g., boron carbide, boron carbide coated with gadolinium, pure gadolinium, without limitation). In the examples illustrated in FIGS. 3 through 7, the neutron absorbing material (124) is in the form of a single solid cylindrical rod, but it should be understood that the neutron absorbing material may be of a different geometric structure, size, or quantity (e.g., multi-element) without change from the scope of the invention. The neutron absorbing material (124) is released from the end section (118) by a dispersion mechanism (126) placed within the end section (118) of the region (114) of the housing (112). Unlike the dispersion mechanism (26) of the system (4) which generally utilizes a wicking effect to draw the liquid neutron-absorbing material (24) into the core section (20) of the system (4), the dispersion mechanism (126) of the system (104) utilizes a physical force (F) to release the neutron-absorbing material from the first end section (118) into the core section (120). This physical force (F) can be provided through any suitable device.In the exemplary embodiment illustrated in FIGS. 3 to 5, the physical force (F) is provided through a plurality of springs (130). More specifically, in the exemplary embodiment illustrated in FIGS. 3 to 5, the physical force (F) is provided to each end section (118) through a total of 12 springs (130) arranged in four spaced stacks, each stack having three springs (130) stacked end-to-end with an alignment plate (132) positioned between them.

[0034] The general operation of the system (104) is similar to the operation of the previously discussed system (4). As shown in FIG. 6, during the normal operating temperature of the reactor, the solid neutron absorbing material (124) will be contained in the end section(s) (118) through the gate member(s) (116). The reactor operator can actively activate the system (104) by providing power to the heater coil (122) of the gate member(s) (116) to melt the gate member(s) (116). As shown in FIG. 7, when the gate member(s) (116) have melted to a sufficient degree, the solid neutron absorbing material (124) is released into the core section (120) (placed within the reactor core (8)) by a physical force (F) provided by the dispersion mechanism (126). Once the solid neutron-absorbing material (124) in the core section (120) absorbs the neutrons present in the reactor core (8), the reactor (10) will be stopped.

[0035] In an accident scenario where the primary coolant is cut off and the reactor (10) is still operating, the reactor core temperature will rise to the same temperature as the core section (120) of the system (104) located therein. This heat melts the gate(s) (116) and causes the solid neutron-absorbing material (124) to be released from the end section(s) (118) into the core section (120), thereby stopping the reactor (10). Thus, the system (104) provides passive activation.

[0036] From the foregoing embodiments, it should be understood that embodiments of the present invention provide a shutdown system that can be operated actively or passively. The passive system described herein is generally simple and can be scaled for use in both microreactors and larger reactors (hundreds of megawatts), regardless of the type of coolant, reactor design, orientation, etc. The material forming the gate is selected based on the reactor design and the set temperature at which the reactor must be shut down without operator intervention. For example, in a sodium heat pipe microreactor with a stainless steel 316 monolith core, reactor shutdown must be initiated at approximately 800°C. Therefore, a gate formed of bronze, brass, or aluminum alloy is generally suitable.

[0037] Although specific embodiments of the present invention have been described in detail, those skilled in the art will understand that various modifications and alternatives to these details may be developed in light of the entire teaching of this disclosure. Accordingly, the specific embodiments disclosed are merely illustrative and are not intended to limit the scope of the invention to which the full scope of the appended claims and any and all equivalents thereof should be given.

Claims

Claim 1 A system for using to shut down a nuclear reactor comprises: a housing that defines an area sealed from the surrounding environment; a gate member disposed within the area in such a manner that the area is separated into a first compartment and a second compartment isolated from the first compartment, and comprises a material having a predetermined melting point; a neutron absorbing material disposed within the first compartment; and a dispersion mechanism disposed within the area and structured to promote the neutron absorbing material from the first compartment into the second compartment, wherein the dispersion mechanism comprises a porous matrix structure disposed within the second compartment. Claim 2 A system according to claim 1, wherein the predetermined melting point of the substance is 800°C. Claim 3 A system according to claim 1, wherein the gate member is structured to melt the material when actuated by an electric current and comprises a plurality of heater coils embedded in the material. Claim 4 In claim 1, the system comprises a neutron absorbing material including a phase change material. Claim 5 In paragraph 4, the system comprises at least one of the phase change material, indium / cadmium alloy, lithium, or boron oxide. Claim 6 delete Claim 7 In claim 1, the system, wherein the second compartment is maintained under vacuum. Claim 8 A system according to claim 1, wherein the porous matrix structure is formed of one or more metals. Claim 9 A system according to claim 1, wherein the porous matrix structure is formed of one or more ceramic materials. Claim 10 In claim 1, the system comprises a neutron absorbing material including a solid material. Claim 11 In paragraph 10, the above-mentioned dispersion mechanism comprises a plurality of springs disposed within the first compartment, a system. Claim 12 A system comprising: a second gate member disposed within the region in such a manner that the region is further separated into a third section isolated from the second section, and a neutron absorbing material disposed within the first section, wherein the second gate member comprises another material having a predetermined melting point; and a neutron absorbing material disposed within the first section. Claim 13 A nuclear reactor comprising: a core structured to accommodate a nuclear reaction; and a system for use in shutting down the nuclear reactor, wherein the system comprises: a housing defining an internal region sealed from the surrounding environment; a gate member comprising a material having a predetermined melting point disposed within the region in such a manner that the region is separated into a first compartment and a second compartment isolated from the first compartment; a neutron absorbing material disposed within the first compartment; and a dispersion mechanism disposed within the region and structured to promote the neutron absorbing material from the first compartment into the second compartment, wherein the system is positioned relative to the core such that the first compartment is located outside the core and the second compartment is located inside the core, and the dispersion mechanism comprises a porous matrix structure disposed within the second compartment. Claim 14 A method for providing a system for use in stopping a nuclear reaction within a reactor core, comprising the step of positioning the system for use in stopping the reactor, wherein the system comprises: a housing defining an internal region sealed from the surrounding environment; a gate member comprising a material having a predetermined melting point disposed within the region in such a manner that the region is divided into a first compartment and a second compartment isolated from the first compartment; a neutron absorbing material disposed within the first compartment; and a dispersion mechanism disposed within the region and structured to promote the neutron absorbing material from the first compartment into the second compartment, wherein the step of positioning the system comprises the step of positioning the housing relative to the core such that the first compartment is located outside the core and the second compartment is located inside the core, and the dispersion mechanism comprises a porous matrix structure disposed within the second compartment.

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