Passively-actuated reactor shutdown system by meltable poison

Abstract

A system for use in shutting down a nuclear reactor without user intervention. The system is actuated by temperature exceeding a pre-determined upset condition and causing the gross failure or phase change of neutron absorbing material and / or additional fuses. When actuated, gravity causes the absorbing material to migrate from a non-active region of the reactor to an active region, shutting down the reactor.

Description

PASSIVELY-ACTUATED REACTOR SHUTDOWN SYSTEM BY MELTABLE POISONINCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

[0001] Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application are hereby incorporated by reference under 37 CFR 1.57. This application claims priority to U.S. Provisional Patent Application No. 63 / 669,881 filed July 11, 2024.BACKGROUNDField

[0002] The present disclosure is directed to a high-temperature passively actuated reactor shutdown system.Description of the Related Art

[0003] There are currently many distinct designs and design concepts for reactor control / shutdown that use different types and arrangements of control / shutdown materials. Modern advanced reactors rely on diverse shutdown mechanisms to shut down the reactor. Examples are control rod drive mechanism (CRDM), neutron absorber spheres, boron injection into primary fluid, etc. Almost all these systems are operated using a mechanical component, which is prone to failure, thus high reliability, and qualification is typically needed. As such, additional redundancy and diversity must be built into the design and safety case, which makes the plant complicated and drives cost up. Most systems proposed are not capable of use in the highest temperature reactors (>900°C) due to irreconcilable material shortcomings, and many rely on the assumption of a bulk flowing reactor fluid to transport shutdown neutron absorbing materials in shutdown situations. A class of emerging heat pipe reactors lack this bulk flow, and so must be actuated by an intransient force. Finally design for horizontal applications are mutually exclusive to vertical orientations due to the need to balance forces and account for gravimetric operation.SUMMARY

[0004] Accordingly, there is a need for improved nuclear reactor shutdown systems.

[0005] In accordance with one aspect of the disclosure, a gravity assist shutdown system is described. Advanced methods such as genetic algorithms or other methodologies that are currently available or become available and the use of artificial intelligence may be used to specify the components, materials, or features of each individual module.

[0006] In accordance with one aspect of the disclosure, a gravity assist shutdown system is provided that incorporates multiple components necessary for the passive shutdown of a high temperature reactor. The same assembly may incorporate solid metallic or ceramic neutron absorbing materials, additionally tuned melting point fuses or diaphragms, partial height filler materials, structural supports, and neutron absorbing materials clad within a ceramic or metallic tube.

[0007] In accordance with another aspect of the disclosure, the configuration of each individual shutdown assembly within a reactor core can be tailored by specifying the type, configuration, and density of reactivity suppression material, actuation location, actuation temperature, and potential presence of dispersion aids. Each shutdown system may be individually designed using advanced optimization algorithms, artificial intelligence, or other methods. Tailoring of each shutdown system results in a reactor core that is walk-away safe without any further intervention by operators of the reactor.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 shows an overview of the components of a shutdown system implemented with meltable neutron control material in a normal (left) and upset (right) conditions.

[0009] Figure 2 shows an example of implementation of this system with ceramic absorber materials in a normal (left) and upset (right) conditions.

[0010] Figure 3 shows a hypothetical axial temperature distribution in an advanced heat pipe reactor.DETAILED DESCRIPTION

[0011] Figure 1 provides a schematic cross-sectional diagram that indicates some of the configurations of the assembly. In accordance with aspects of the disclosure, a gravity assist shutdown system 100 is provided. During normal operation (e.g., shown in left image of FIG. 1), a sleeve 15 of ceramic or metallic material sits along the active core region 12 of a nuclear reactor 10, protruding some distance above that region. While the system 100 as implemented is a single-use device, the sleeve 15 may have features to facilitate its removal and replacement upon triggering or for inspection. An axial spacer material 20 may be present to control the fill behavior of neutron absorbing materials 40, as well as to optimize neutronics behavior during all other conditions. By choosing a material that is either a reflector or absorber, or situationally between the two, this axial spacer 20 is an optimization tool for those skilled in the art. At a predetermined height near to or above the active core region 12 of the reactor 10, there may be present retaining features 30 on the sleeve 15 which provide structure upon which a retaining interface 32 (e.g., platform 32 above retaining features 30) is housed or supported. These have the effect of determining the temperature interfaces at which actuation of the system 100 may occur. In this implementation, one or more retaining barriers 35 may be present, which physically hold a neutron absorbing material 40 out of the active core region 12. These barriers 35 may be tuned to structurally degrade / melt at the same or lower temperatures as the neutron absorbing material 40. These barriers 35 may have features such as meshing or conical structures designed to breach surface tension of a melting neutron absorbing material 40 or to optimize the filling behavior of the region below. The neutron absorbing material 40 in this implementation is tuned in composition, together with the temperature behavior of the reactor and the height of the barrier interface, such that it only melts in an upset condition (e.g., shown in right image in FIG. 1). By tuning the composition of the neutron absorbing material or neutron poison 40, a wide variety of implementations can be supported. For example, while pure gadolinium metal melts in excess of 1300°C, a 78 wt% gadolinium-aluminum eutectic melts at under 800°C, and thus compositions between that range offer similar neutron control capacity, but with substantively different melt triggers (e.g., temperature at which the neutron absorbing material 40 melts). Further insights as to how one can tune such things follows in the discussion of Figure 3. When the temperature of the system 100 at the retaining barrier 35 exceeds the designed threshold, an upset condition occurs, andthe melting burnable neutron absorbing material falls into the active core region 12 and shutdowns the reactor 10. Advantageously, the system 100 operates automatically to shut down the reactor 10 as described herein without requiring user intervention.

[0012] Figure 2 provides another implementation of this gravity assist shutdown system 100’ using a ceramic burnable neutron absorber material 30 and structurally degrading fuse. During normal operation (e.g., image on left in FIG. 2), a sleeve 15 of ceramic or metallic material sits along the active core region 12 of a nuclear reactor 10, protruding some distance above that region. While the system 100’ as implemented is a single-use device, the sleeve 15 may have features to facilitate removal and replacement upon triggering or for inspection. At a predetermined height near to or above the active core region 12 of the reactor, there may be present retaining features 20 on the sleeve which provide structure upon which a retaining interface 32 (e.g., platform 32 above retaining features 20) is housed or supported. These have the effect of determining the temperature interfaces at which actuation of the system 100’ may occur. In this implementation, one or more retaining barriers 25 may be present, which physically hold the neutron absorbing material 30 out of the active core region 12. These barriers 25 should be chosen out of materials such that they can withstand very long durations at nominal operating conditions, but rapidly fail at upset conditions (e.g., shown on right in FIG. 2). For example, nickel-chrome based super alloys often have useful creep resistance at or above 1000°C, but melt at ~1300°C. In cooler implementations, use of copper or aluminum alloys which melt at ~660°C and 1080°C respectively. By careful choice of the geometries of the system 100’ sleeve 15 and neutron absorber material 30, one can rely on the statistically consistent packing fractions of simple shapes to design an effective shutdown system. Use of complex shapes or poly dispersed shapes may yield higher packing fractions where desirable. Axial spacers like axial spacer 20 in Figure 1 may also be used with this system 100’ to further optimize packing behavior at specified heights. Advantageously, the system 100’ operates automatically to shut down the reactor 10 as described herein without requiring user intervention.

[0013] Figure 3 provides a hypothetical temperature profile within a graphite moderated heat pipe reactor. Embodiment of this reactor are not limited to any particular temperature profile, or reactor cooling technology, and the figure is demonstrative. Within the active core region, temperature profiles are desirably flat, and a designer attempting to build asafe reactor will specify a maximum temperature for components within this and all other regions of the reactor. Within a graphite moderated heat pipe reactor, there may be a relatively small gradient of temperature throughout a reflector mounted above the active core. The largest temperature gradient exists in a final shielding region near the top of the core which protects non-high temperature reactor components from the extreme heat generated within the core. Depending on many factors, the gradient in the reflector and shielding increases during upset conditions, but the temperature does increase and thus provides the trigger for this system. Embodiments of this invention that reside within a high thermal gradient may use lower temperature materials and fuses. Additionally, it may be desirable to have a neutron absorbing material as high out of the core / reflector as possible to minimize parasitic losses during operation. In this situation, a lower temperature fuse higher above the core could be utilized as a first layer which then drops the neutron absorbing material into a higher temperature region to initiate melting itself or an ultimate fuse.

[0014] While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the disclosure. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the systems and methods described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure. Accordingly, the scope of the present inventions is defined only by reference to the appended claims.

[0015] Features, materials, characteristics, or groups described in conjunction with a particular aspect, embodiment, or example are to be understood to be applicable to any other aspect, embodiment or example described in this section or elsewhere in this specification unless incompatible therewith. All features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such components, materials, and features and / or steps are mutually exclusive. The protection is not restricted to the details of any foregoing embodiments. The protection extends to any novel one, or any novel combination, of the components, materials, and features disclosed inthis specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0016] Furthermore, certain components, materials, and features that are described in this disclosure in the context of separate implementations can also be implemented in combination in a single implementation. Conversely, various components, materials, and features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable combination. Moreover, although components, materials, and features may be described above as acting in certain combinations, one or more components, materials, and features from a claimed combination can, in some cases, be excised from the combination, and the combination may be claimed as a subcombination or variation of a subcombination.

[0017] Moreover, while components, materials, or components, materials, and features may be depicted in the drawings or described in the specification in a particular order, such components, material, or components, materials, and features need not be implemented in the particular order shown or in sequential order, or that all components, material, or components, materials, and features be implemented, to achieve desirable results. Other components, material, or components, materials, and features that are not depicted or described can be incorporated in the example methods and processes. For example, one or more additional components, material, or components, materials, and features can be implemented before, after, simultaneously, or between any of the described components, material, or components, materials, and features. Further, the components, materials, or features may be rearranged or reordered in other implementations. Those skilled in the art will appreciate that in some embodiments, the actual components, material, or components, materials, or features taken in the processes illustrated and / or disclosed may differ from those shown in the figures. Depending on the embodiment, certain of the components, materials, or features described above may be removed, others may be added. Furthermore, the components, materials, or features and attributes of the specific embodiments disclosed above may be combined in different ways to form additional embodiments, all of which fall within the scope of the present disclosure. Also, the separation of various system components in the implementations described above should not be understood as requiring such separation in all implementations,and it should be understood that the described components and systems can generally be integrated together in a single product or packaged into multiple products.

[0018] For purposes of this disclosure, certain aspects, advantages, and novel components, materials, or features are described herein. Not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the disclosure may be embodied or carried out in a manner that achieves one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

[0019] Conditional language, such as “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain components, materials, or features. Thus, such conditional language is not generally intended to imply that components, materials, or features are in any way required for one or more embodiments or that one or more embodiments necessarily include logic for deciding, with or without user input or prompting, whether these components, materials, or features are included or are to be implemented in any particular embodiment.

[0020] Conjunctive language such as the phrase “at least one of X, Y, and Z,” unless specifically stated otherwise, is otherwise understood with the context as used in general to convey that an item, term, etc. may be either X, Y, or Z. Thus, such conjunctive language is not generally intended to imply that certain embodiments require the presence of at least one of X, at least one of Y, and at least one of Z.

[0021] Language of degree used herein, such as the terms “approximately,” “about,” “generally,” and “substantially” as used herein represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms “approximately”, “about”, “generally,” and “substantially” may refer to an amount that is within less than 10% of the stated amount.

[0022] The scope of the present disclosure is not intended to be limited by the specific disclosures of preferred embodiments in this section or elsewhere in this specification, and may be defined by claims as presented in this section or elsewhere in this specification or as presented in the future. The language of the claims is to be interpreted broadly based on thelanguage employed in the claims and not limited to the examples described in the present specification or during the prosecution of the application, which examples are to be construed as non-exclusive.

[0023] Of course, the foregoing description is that of certain components, materials, or features, aspects and advantages of the present invention, to which various changes and modifications can be made without departing from the spirit and scope of the present invention. Moreover, the devices described herein need not feature all the objects, advantages, components, materials, or features and aspects discussed above. Thus, for example, those of skill in the art will recognize that the invention can be embodied or carried out in a manner that achieves or optimizes one advantage or a group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. In addition, while a number of variations of the invention have been shown and described in detail, other modifications and methods of use, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. It is contemplated that various combinations or subcombinations of these specific components, materials, or features and aspects of embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various components, materials, or features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the discussed devices.

Claims

WHAT IS CLAIMED IS:

1. A single-use passively-actuated nuclear reactor shutdown system, comprising: a sleeve having a first portion configured to be disposed within an active core region of a nuclear reactor, a second portion of the sleeve configured to extend above and outside the active core region; one or more retaining features in the second portion of the sleeve, the retaining features configured to support a retaining interface; and a volume of neutron absorbing material disposed in the second portion of the sleeve and supported a distance above the first portion by the retainer interface so that the neutron absorbing material is out of the active core region, wherein during an upset condition of the nuclear reactor when a temperature of the active core region increases above a predetermined threshold temperature, the retainer interface is configured to structurally degrade or melt to allow the volume of neutron absorbing material to move into the first portion of the sleeve under force of gravity to automatically shut down the nuclear reactor without user intervention.

2. The system of claim 1, wherein the volume of neutron absorbing material in the first portion is solid and is configured to melt at the threshold temperature and to flow under gravity into the first portion of the sleeve during the upset condition of the nuclear reactor.

3. The system of claim 2, wherein the neutron absorbing material is a metallic material.

4. The system of any preceding claim, further comprising a retaining barrier between the neutron absorbing material and the retaining interface, the retaining barrier configured to structurally degrade or melt at or below the threshold temperature.

5. The system of claim 4, wherein the retaining barrier has a conical structure configured to breach a surface tension of the neutron absorbing material when the neutron absorbing material is melting.

6. The system of any preceding claim, wherein a composition of the nuclear absorbing material is tuned so that the nuclear absorbing material melts at the predetermined threshold temperature corresponding to the upset condition.

7. The system of claim 1 , wherein the volume of neutron absorbing material comprises a plurality of discrete ceramic units of neutron absorbing material configured to move into the first portion of the sleeve under gravity during the upset condition.

8. The system of claim 7, wherein the neutron absorbing material is a ceramic burnable neutron absorber material.

9. The system of any of claims 7-8 wherein the plurality of discrete ceramic units of neutron absorbing material are ceramic spheres of neutron absorbing material.

10. The system of any preceding claim, wherein the retainer interface is configured to structurally degrade or melt at or below the threshold temperature, allowing the volume of neutron absorbing material to move into the first portion of the sleeve.

11. The system of any preceding claim, further comprising a spacer disposed in the first portion of the sleeve.

12. The system of claim 11, wherein the spacer is an axial spacer configured to control a fill level of the neutron absorbing material in the first portion of the sleeve.

13. The system of any of claims 11-12 wherein the spacer comprises a neutron absorbing material or neutron reflecting material.

14. The system of any preceding claim, wherein the sleeve is sealed and configured to retain gaseous absorption products released by the neutron absorbing material in the sleeve and configured to retain the neutron absorbing material in the first portion of the sleeve following the upset condition.

15. The system of any preceding claim, wherein the sleeve includes a gas plenum.

16. The system of any preceding claim, wherein the sleeve is removable from the core and replaceable.

17. The system of Claim 1 , wherein the neutron absorbing material comprises a ceramic or metallic compound containing gadolinium, erbium, hafnium, cadmium, or boron.

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