Reactor Shutdown System

Abstract

A system for use in shutting down a nuclear reactor includes a housing defining an interior region sealed from the ambient environment and a gate member disposed within the region in a manner such that the gate member separates the region into a first compartment and a second compartment isolated from the first compartment. The gate member is formed from a material having a predetermined melting point. The system further includes a neutron absorbing material disposed within the first compartment and a distribution mechanism disposed within the region. The distribution mechanism is configured to urge the neutron absorbing material from the first compartment to the second compartment.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. patent application Ser. No. 16 / 711,922, filed Dec. 12, 2019, entitled "REACTOR SHUTDOWN SYSTEM," the contents of which are incorporated herein by reference. [Background technology]

[0002] The present invention relates generally to nuclear reactors, and more particularly 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 to a method of providing a system for use in shutting down a nuclear reactor.

[0003] Currently, most water reactor technologies and state-of-the-art reactors rely on a variety of shutdown mechanisms to shut down the reactor. Examples include control rod drive mechanisms (CRDMs), neutron absorber spheres, and boron injection into the primary fluid. Nearly all of these systems operate using mechanical components that are prone to failure and therefore typically require high reliability and qualification. As such, additional redundancy and diversity must be built into the design and safety case, which increases plant complexity and cost. Some of these systems have passive features that use gravity or other potential energy to activate the passive features. However, these systems are large and not attractive for compact reactor designs such as advanced microreactors. Furthermore, such systems are not applicable to horizontal reactors. Reactors with unique shutdown mechanisms, such as the TRIGA research reactor, are design specific and cannot be applied to other reactor designs.

[0004] Therefore, there is room for improvement in reactor shutdown systems. Summary of the Invention

[0005] The embodiments of the invention described herein provide a "solid-state" emergency core shutdown system for nuclear reactors. The system is designed to be inherently activated and is triggered by an adjustable design set-point temperature. Additionally, the system can be run manually by an operator with the use of electrical power. The system is applicable to any nuclear reactor, regardless of coolant type, neutron energy spectrum and size. This technology allows the reactor to be placed in the IAEA Passive Safety Category B for shutdown systems.

[0006] In one aspect of the invention, a system for use in shutting down a nuclear reactor is provided, the system including a housing defining an interior region sealed from an ambient environment, a gate member disposed within the region in a manner such that the gate member separates the region into a first compartment and a second compartment isolated from the first compartment, the gate member including a material having a predetermined melting point, a neutron absorbing material disposed within the first compartment, and a distribution mechanism disposed within the region, the distribution mechanism being structured to urge the neutron absorbing material from the first compartment to the second compartment.

[0007] The predetermined melting point of the material may be about 800°C.

[0008] The gate member may include a number of heater coils embedded within the material that are structured to melt the material upon activation by an electric current.

[0009] The neutron absorbing material may include a phase change material.

[0010] The phase change material may include at least one of an indium / cadmium alloy, lithium, or boron oxide.

[0011] The dispersion mechanism may include a porous matrix structure disposed within the second compartment.

[0012] The second compartment may be held under vacuum.

[0013] The porous matrix structure may be formed from one or more metals.

[0014] The porous matrix structure may be formed from one or more ceramic materials.

[0015] The neutron absorbing material may include a solid material.

[0016] The dispersion mechanism may include a number of springs disposed within the first compartment.

[0017] The system may further include a second gate member disposed within the region in such a manner that the second gate member further separates the region into a third compartment isolated from the second compartment by a second gate member comprising another material having a predetermined melting point, and a neutron absorbing material disposed within the first compartment.

[0018] In another aspect of the invention, a nuclear reactor is provided, the reactor comprising a core structured to contain a nuclear reaction, and a system for use in shutting down the reactor, the system comprising a housing defining an interior region sealed from an ambient environment, a gate member disposed within the region in a manner such that the gate member separates the region into a first compartment and a second compartment isolated from the first compartment, the gate member including a material having a predetermined melting point, a neutron absorbing material disposed within the first compartment, a distribution mechanism disposed within the region, the distribution mechanism being structured to urge the neutron absorbing material from the first compartment to the second compartment, the system being positioned relative to the core such that the first compartment is positioned outside the core and the second compartment is disposed within the core.

[0019] In yet another aspect of the invention, a method is provided for providing a system for use in shutting down a nuclear reaction in a core of a nuclear reactor, the method including positioning a system for use in shutting down a nuclear reactor, the system comprising a housing defining an interior region sealed from an ambient environment, a gate member disposed within the region in a manner such that the gate member separates the region into a first compartment and a second compartment isolated from the first compartment, the gate member including a material having a predetermined melting point, a neutron absorbing material disposed within the first compartment, and a distribution mechanism disposed within the region, the distribution mechanism being structured to urge the neutron absorbing material from the first compartment to the second compartment, and positioning the system includes positioning the housing relative to the core such that the first compartment is positioned outside the core and the second compartment is disposed within the core.

[0020] These and other objects, features and characteristics of the present invention, together with the method of operation and function of the associated structural elements and combination of parts and economy of manufacture, will become more apparent from a consideration of the following description and appended claims, all of which form a part hereof, taken in conjunction with the accompanying drawings in which like reference numerals indicate corresponding parts in the various views, It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention. [Brief description of the drawings]

[0021] A further understanding of the invention can be obtained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings.

[0022] [Figure 1] 1 is a schematic cross-sectional elevation view of a system for use in shutting down a nuclear reactor, according to one exemplary embodiment of the present invention, shown positioned relative to a core region of the reactor. [Diagram 2]FIG. 2 is a perspective cross-sectional view of a furnace arrangement having a system as shown in FIG. 1 according to one exemplary embodiment of the present invention. [Diagram 3] 1 is a schematic cross-sectional elevation view of a system for use in shutting down a nuclear reactor, in accordance with another exemplary embodiment of the present invention. [Figure 4] 4 is an elevated end view of the system of FIG. 3 taken along line 4-4 of FIG. 3. [Diagram 5] 5 is an elevational cross-sectional view of the system of FIG. 3 taken along line 5-5 of FIG. 3. [Figure 6] 4 is a schematic diagram of the system of FIG. 3 shown positioned relative to a nuclear reactor core according to one exemplary embodiment of the present invention, a portion of which is shown disposed in a reactor operating mode. [Figure 7] 4 is another schematic diagram of the system of FIG. 3 shown positioned relative to a nuclear reactor core according to one exemplary embodiment of the present invention, a portion of which is shown disposed in a reactor shutdown mode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] In the following description, like reference numerals designate like or corresponding parts throughout the several views of the drawings. It should also be understood that in the following description, terms such as "front," "rear," "left," "right," "upward," "downward," etc. are used for convenience and should not be construed as limiting terms.

[0024] An exemplary system 4 for use in shutting down a nuclear reactor according to an embodiment of the present invention is shown generally in FIGS. 1 and 2 positioned relative to a core 8 (shown generally in dashed lines) of a nuclear reactor 10. The system 4 includes a housing 12 defining an interior region 14 sealed from the ambient environment within which the system 4 is provided. In the exemplary embodiment of the present invention illustrated in FIG. 1, the housing 12 is generally formed from a tubular member, although it should be understood that the housing 12 may be of other shape(s) and / or relative sizes without departing from the scope of the present invention. The system 4 further includes a first gate member 16 disposed within the region 14 in such a manner that the first gate member 16 separates the region 14 into a first end section 18 that is positioned outside the core 8 when the system 4 is installed in the nuclear reactor 10 and a core section 20 that is positioned within the core 8 when the system 4 is installed in the nuclear reactor 10. In other words, 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 from a material having a predetermined melting point above the normal operating temperature of the reactor 10 but below the critical temperature of the reactor that does not exceed the material design limits of the reactor. The importance of such an arrangement will be understood from further discussion below. Additionally, the first gate member 16 may include a number of heater coils 22 embedded within the material of the first gate member 16 that are structured to melt the material upon actuation by an electrical current provided by an outside power source.

[0025] Optionally (as discussed further below), the system 4 may further include a second gate member 16' disposed within the region 14 in such a manner that the second gate member 16' further separates the region 14 into a second end section 18' positioned outside the core 8 opposite the first end section 18 when the system 4 is installed within the reactor 10. The second gate member 16' is formed from a material having a predetermined melting point above the normal operating temperature of the reactor 10 but below a critical temperature of the reactor that does not exceed the material design limits of the reactor. Additionally, the second gate member 16' may include a number of heater coils 22 embedded within the material of the second gate member 16' that are structured to melt the material upon actuation by an electric current provided by an outside power source.

[0026] 1, the system 4 further includes a neutron absorbing material 24 disposed within the first end section 18 and the second end section 18' (i.e., outside the core 8) and a distribution mechanism 26 disposed within the core section 20 of the region 14 of the housing 12 (i.e., within the core 8), the distribution mechanism 26 being structured to urge the neutron absorbing material 24 from each of the first end section 18 and the second end section 18' to the core section 20. In the embodiment shown in FIG. 1, the neutron absorbing material 24 is a phase change neutron absorbing material (such as, but not limited to, an indium / cadmium alloy, lithium, or boron oxide) that can be conveyed from the first end section 18 to the core section 20 in a manner described further below to shut down the reactor. In such an embodiment, the distribution mechanism 26 is a porous matrix that may be made from either a metal (such as, but not limited to, stainless steel or niobium zirconium) or a ceramic that does not have a very low neutron absorption cross section (such as, but not limited to, graphite, beryllium oxide, or alumina). To ensure that voids within the porous matrix material are not otherwise occupied by gas that may interfere with liquid adsorption, the core section 20 may be held under vacuum, such as provided via a vacuum port 28 defined in the housing 12, or via any other suitable arrangement.

[0027] Having thus described the general arrangement of the system 4, the operation of the system 4 will not be described here. The normal operating temperature of the reactor 10 as shown in FIG. 2 is above 450° C. At such temperatures, the neutron absorbing material 24 will already be in a liquid phase. The reactor operator can actively operate the system 4 by providing power to the heater coil 22 to melt the first gate member 16 (and / or the second gate member 16′) which will be adsorbed in the porous matrix of the distribution mechanism 26, allowing the neutron absorbing material 24 to access the porous matrix by capillary forces. When the neutron absorbing material 24 is evenly spread in the core section 20 of the system 4 (disposed in the core 8 of the reactor 10), neutron absorption will occur, which will then shut down the reactor 10.

[0028] In an accident scenario where the primary coolant is shut off and the reactor 10 is still in operation, the temperature of the core 8 will increase as the temperature of the core section 20 of the system 4 located therein increases. As the temperature of the core section 20 increases, the heat from the core section 20 will melt the first gate member 16 (and / or the second gate member 16') and adsorb into the porous matrix of the distribution mechanism 26, allowing the neutron absorbing material 24 access into the porous matrix by capillary forces. Once the neutron absorbing material 24 is evenly spread in the core section 20 of the system 4 (disposed in the core 8 of the reactor 10), neutron absorption will occur, thus shutting down the reactor 10. Thus, the system 4 will be passively operated 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').

[0029] It should be understood that the arrangement of a single one of the end sections 18 or 18' with the neutron absorbing material 24 contained therein is sufficient to shut down the reactor 10, but the use of two such sections (if space is available) provides redundancy and thus still further reactor safety.

[0030] In an exemplary embodiment of the invention, heat may be transferred to one or both of the first and second end sections 18 and 18' in the housing 12 where the neutron absorbing material 24 resides by use of an integrated heat spreader (generally shown as 27), which may be either (i) a heat pipe or thermosiphon that uses a phase change fluid such as sodium to spread the heat (which may be utilized for any size reactor), or (ii) a solid conductive tube or shell (which may be applicable for smaller reactors). Heat pipe and thermosiphon arrangements as are commonly known may be used. Typically, both arrangements transfer heat from one end to another. In the example of FIGS. 1 and 2, heat is transferred from the core 8 to the region 14 of the housing 12 and out to the first and second end sections 18 and 18' of the system 4.

[0031] If a heat pipe is used, when the core section 20 rises above a certain design temperature, the sodium melts and flows rapidly to the relatively cooler first and second end sections 18 and 18' of the system 4. The heat then melts the gates 16 and 16', allowing the neutron absorbing material 24, now in a liquid state, to flow to the core section 20. As the heat is transferred to the neutron absorbing material, optionally via conductive fins 28, the sodium in the heat spreader condenses and is passively transported back to the core section 20 by the capillary action of the heat spreader wick in a heat pipe (applicable to a horizontal furnace) or gravity in a thermosiphon (applicable to a vertical furnace). The heat spreader maintains an isothermal temperature of the device over its entire length.

[0032] 3-7, another example of a system 104 for use in shutting down a nuclear reactor will be described according to another embodiment of the present invention. The basic layout 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 the same as that of the system 4 described above, and therefore will not be described in further detail herein. The system 104 differs from the system 4 both in the neutron absorbing material and thus in the distribution mechanism employed. Instead of a neutron absorbing material 24 dispersed in a liquid phase by a distribution mechanism 26 in the form of a porous matrix, the system 104 utilizes a solid neutron absorbing material 124 (e.g., but not limited to, boron carbide, boron carbide coated with gadolinium, pure gadolinium). In the example shown in Figures 3-7, 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 other geometries, sizes, or quantities (e.g., multi-elements) without departing from the scope of the present invention. The neutron absorbing material 124 is expelled from the end section 118 by a distribution mechanism 126 disposed within the end section 118 of the region 114 of the housing 112. Unlike the distribution mechanism 26 of the system 4, which utilizes a wicking effect to generally draw the liquid neutron absorbing material 24 into the core section 20 of the system 4, the distribution mechanism 126 of the system 104 utilizes a physical force F to expel the neutron absorbing material from the first end section 118 to the core section 120. Such a physical force F may be provided via any suitable arrangement. In the exemplary embodiment illustrated in Figures 3-5, the physical force F is provided via a number of springs 130. More specifically, in the exemplary embodiment illustrated in Figures 3-5, physical force F is provided to each end section 118 via a total of twelve springs 130 arranged in four spaced-apart stacks, each stack having three springs 130 stacked end-to-end with an alignment plate 132 positioned therebetween.

[0033] The general operation of the system 104 is similar to that of the system 4 discussed above. As shown in FIG. 6, during normal operating temperatures of the reactor, the solid neutron absorbing material 124 will be housed in the end section(s) 118 via the gate member(s) 116. The reactor operator can actively operate the system 104 by providing power to the heater coils 122 of the gate member(s) 116 to melt the gate member(s) 116. As shown in FIG. 7, once the gate member(s) 116 have melted sufficiently, the solid neutron absorbing material 124 will be ejected into the core section 120 (disposed within the core 8) by a physical force F provided by a dispersion mechanism 126. Once in the core section 120, the solid neutron absorbing material 124 will absorb neutrons present in the core 8, thereby shutting down the reactor 10.

[0034] In an accident scenario in which the primary coolant is shut off and the reactor 10 is still operating, the temperature of the core will increase as the temperature of the core section 120 of the system 104 located therein increases. Such heat causes the gate(s) 116 to melt, allowing solid neutron absorbing material 124 to be discharged from the end section(s) 118 into the core section 120, thereby shutting down the reactor 10. Thus, the system 104 provides passive operation.

[0035] From the foregoing examples, it should be appreciated that embodiments of the present invention provide a shutdown system that can be actively operated or passively actuated. The passive systems described herein are generally simple and can be scaled for use in both micro-reactors and larger reactors (hundreds of megawatts), regardless of coolant type, reactor design, orientation, etc. The material forming the gate is chosen based on the reactor design and the set point temperature at which the reactor needs to be shut down without operator intervention. For example, in a sodium heat pipe micro-reactor with a stainless steel 316 monolith core, reactor shutdown should be initiated at approximately 800°C. Thus, gates formed from bronze, brass, or aluminum alloys are generally preferred.

[0036] Although specific embodiments of the present invention have been described in detail, it will be understood that various modifications and alternatives to these details may be developed by those skilled in the art in light of the overall teachings of the present disclosure. Accordingly, the specific embodiments disclosed are intended to be illustrative only and not limiting as to the scope of the invention, which is to be given the full scope of the appended claims and any and all equivalents thereof.

Claims

1. 1. A system for use in shutting down a nuclear reactor, comprising: The system further comprises: a housing defining an interior region sealed from the ambient environment; a gate member disposed within the region in a manner such that the gate member separates the region into a first compartment and a second compartment isolated from the first compartment, the gate member comprising a material having a predetermined melting point; a neutron absorbing material disposed within the first compartment; a dispersion mechanism disposed within the region; Equipped with the dispersion mechanism is structured to urge the neutron absorbing material from the first compartment to the second compartment; The system wherein the dispersion mechanism comprises a porous matrix structure disposed within the second compartment.

2. The system of claim 1 , wherein the predetermined melting point of the material is about 800° C.

3. 10. The system of claim 1, wherein the gate member comprises a number of heater coils embedded within the material that are structured to melt the material upon activation by an electric current.

4. The system of claim 1 , wherein the neutron absorbing material comprises a phase change material.

5. The system of claim 4 , wherein the phase change material comprises at least one of an indium / cadmium alloy, lithium, or boron oxide.

6. The system of claim 1 , wherein the second compartment is held under vacuum.

7. The system of claim 1 , wherein the porous matrix structure is formed from one or more metals.

8. The system of claim 1 , wherein the porous matrix structure is formed from one or more ceramic materials.

9. The system of claim 1 , wherein the neutron absorbing material comprises a solid material.

10. The system of claim 9 , wherein the dispersion mechanism comprises a number of springs disposed within the first compartment.

11. a second gate member, the second gate member comprising another material different from the gate member material and having a predetermined melting point, disposed within the region in a manner to further separate the region into a third compartment isolated from the second compartment; The system of claim 1 further comprising:

12. A nuclear reactor, a reactor core structured to contain a nuclear reaction; and a system for use in shutting down the nuclear reactor, the system comprising: a housing defining an interior region sealed from the ambient environment; a gate member disposed within the region in a manner such that the gate member separates the region into a first compartment and a second compartment isolated from the first compartment, the gate member 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; Equipped with the dispersion mechanism is structured to urge the neutron absorbing material from the first compartment to the second compartment; the system is positioned relative to the core such that the first compartment is positioned outside the core and the second compartment is disposed within the core; The nuclear reactor, wherein the distribution mechanism comprises a porous matrix structure disposed within the second compartment.

13. 1. A method of providing a system for use in terminating a nuclear reaction in a core of a nuclear reactor, comprising: the method includes positioning the system for use in shutting down the nuclear reactor; the system comprising: a housing defining an interior region sealed from an ambient environment; a gate member disposed within the region in a manner to separate the region into a first compartment and a second compartment isolated from the first compartment, the gate member 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; Equipped with the dispersion mechanism comprises a porous matrix structure disposed within the second compartment and structured to urge the neutron absorbing material from the first compartment to the second compartment; The method, wherein positioning the system includes positioning the housing relative to the core such that the first compartment is positioned outside the core and the second compartment is disposed within the core.

14. 2. The system of claim 1, wherein the system is positioned relative to the reactor core such that the first compartment is positioned outside the core and the second compartment is disposed within the core.

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