Tag gas capsule with thermally based release system

AU2024420398A1Pending Publication Date: 2026-07-30TERRAPOWER LLC

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Patent Information

Authority / Receiving Office: AU · AU
Patent Type: Applications
Current Assignee / Owner: TERRAPOWER LLC
Filing Date: 2024-11-15
Publication Date: 2026-07-30

AI Technical Summary

Technical Problem

Existing tag gas capsules for nuclear fuel pins are large, require moving parts, and are sensitive to rupture during manufacturing, shipping, handling, and installation, which complicates their use and increases the risk of accidental release.

Method used

A thermally sensitive material seals a flow hole in a small tag gas capsule that melts at reactor operating temperatures, allowing the tag gas to escape passively and reducing the capsule's size and eliminating moving parts.

Benefits of technology

The solution provides a compact, reliable, and efficient leak detection system that minimizes the risk of rupture and reduces the overall fuel assembly length, enhancing safety and operational efficiency.

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Abstract

A tag gas capsule utilizes a thermally based release system to allow the tag gas to flow through a fuel pin and to be detectable upon a leak in the fuel pin. A tag gas capsule is fabricated that has an escape pathway for the tag gas wherein the escape pathway is sealed by a thermally sensitive material. During fabrication, the thermally sensitive material is melted into the tag gas capsule and seals a flow hole in the tag gas capsule. The capsule is then filled with a tag gas and sealed to prevent escape of the tag gas. Once the capsule has been installed into a fuel pin, the capsule can be heated to melt the thermally sensitive material and expose the flow hole. The tag gas can then flow out of the flow hole and into the fuel pin.

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Description

TAG GAS CAPSULE WITH THERMALLY BASED RELEASE SYSTEMGOVERNMENT LICENSE RIGHTS

[0001] This invention was made with government support under DOE Cooperative Agreement No. DE-NE0009054 awarded by the U.S. Department of Energy. The government has certain rights in the invention.CROSS REFERENCE

[0002] The present application claim benefit of priority to U.S. Provisional Patent Application No. 63 / 621,097, filed January 15, 2024, titled “TAG GAS CAPSULE WITH THERMALLY BASED RELEASE SYSTEM,” the entire contents of which is hereby incorporated by reference.FIELD OF THE DISCLOSURE

[0003] This disclosure is directed to a tag gas capsule for detecting leaks in nuclear fuel pins that provides simple fabrication, installation, and operation.BACKGROUND

[0004] Tag gases are utilized in nuclear fuel pins as a component of the safety and monitoring systems in nuclear reactors. Nuclear fuel pins contain fissile material, typically enriched uranium, plutonium, or thorium, which undergoes fission reactions to generate heat for power production. Tag gases, such as helium or xenon, are introduced into the fuel pins during the manufacturing process. These gases serve as tracers or markers that can be monitored to assess the integrity of the fuel pin over time.

[0005] Fuel pin leakage is a concern in nuclear reactors, as it can compromise the containment of radioactive materials and pose safety risks. Detecting leaks promptly is essential for ensuring the safe operation of the reactor. Tag gases play a vital role in leak detection, as they are chosen for their inert nature and low reactivity with other substances. In the event of a fuel pin breach or leakage, tag gases are released, and their presence can be monitored using sensitive detectors. The concentration and isotopic composition of these tag gases provide valuable information about the location and severity of the leak.

[0006] The process of tag gas leak detection involves periodic sampling and analysis of reactor coolant or gas from the containment system. Specialized monitoring systems are employed to detect the presence of tag gases and quantify their concentrations. The use of tag gases in leak detection enhances the reliability of safety measures in nuclear reactors, enabling operators to identify and address potential issues before they escalate. This proactive approach to monitoring ensures the continued safe and efficient operation of nuclear power plants, contributing to the overall stability and security of nuclear energy as a viable power source.

[0007] Tag gas capsules that have historically been used for leak detection rely on moving parts, such as a needle that moves by a magnetic force to pierce a capsule containing the tag gas. Once the needle pierces the tag gas, the tag gas is released into the fuel pin, which can then escape in the event of a leak of the fuel pin. The moving parts results in a length of the tag gas capsule necessary to accommodate the movement of the needle, which impinges upon the overall plenum volume of the fuel pin assembly and leads to a tall core assembly. Moreover, the capsule must be carefully manufactured, shipped, handled, and installed to prevent an inadvertent piercing of the capsule.

[0008] It would be advantageous if a tag gas capsule were smaller in size than historical capsules have been, were efficient to manufacture, contained no moving parts, and were not sensitive to rupture during the manufacturing, shipping, handling, and installation procedures. These, and other advantages, will become readily apparent to those of skill in the art by reference to the following description and accompanying figures.SUMMARY

[0009] A tag gas capsule includes a capsule tube having a first end and a second end; a first end cap coupled to the capsule tube and sealing the first end of the capsule tube; a second end cap coupled to the capsule tube and sealing the second end of the capsule tube; a flow hole formed in one or more of the capsule tube, the first end cap, and the second end cap; a tag gas disposed within the capsule tube; and a thermally sensitive material positioned within the tag gas capsule to block the flow hole, the thermally sensitive material configuredto melt at a temperature below a nuclear reactor operating temperature to expose the flow hole and allow the tag gas to escape through the flow hole.

[0010] The thermally sensitive material may be sodium, tin, or other desired material that can melt at an appropriate temperature and is compatible with the materials and environment in which it is used.

[0011] In some cases, the flow hole is small to reduce the cross section of exposed thermally sensitive material, and in some cases, has a diameter of 0.8mm, or 1mm, or 1.2mm, or 1.5mm or more.

[0012] The tag gas capsule may be configured to be inserted into a nuclear fuel pin, and in some cases has an outer diameter of less than 6.35mm.

[0013] In some embodiments, the flow hole is formed at a location near an upper end of the tag gas capsule such that the thermally sensitive material flows downward once melted and is captured within the tag gas capsule. In this way, the thermally sensitive material remains within the tag gas capsule, even after it is melted.

[0014] In some examples, the flow hole is formed at a bottom end of the tag gas capsule such that the thermally sensitive material flows out of the tag gas capsule once melted. In this case, the thermally sensitive material may flow into the fuel pin and be captured therein.

[0015] A method of forming a tag gas capsule includes the steps of coupling a first end cap to a first end of a capsule tube to seal the first end of the capsule tube; inserting a heat sensitive material into the capsule tube; applying heat to melt the heat sensitive material and cause the heat sensitive material to flow into the first end cap; cooling the heat sensitive material to cause the heat sensitive material to solidify; inserting a tag gas into the capsule tube; and coupling a second end cap to a second end of the capsule tube to seal the second end of the capsule tube and form a tag gas capsule.

[0016] The first end cap may include a flow hole formed therein and the step of applying heat to melt the heat sensitive material may further include the step of causing the heat sensitive material to flow into the first end cap and block the flow hole.

[0017] In some cases, the flow hole is formed prior to the step of inserting the heat sensitive material into the capsule tube. In other cases, the flow hole may be formed after the heat sensitive material is inserted into the capsule tube. For example, once the heat sensitivematerial is melted and flows into the end cap, a hole may be drilled through the end cap to expose a diameter of the solidified heat sensitive material.

[0018] The heat sensitive material may be selected from sodium and tin. Of course, the heat sensitive material may be any suitable material that can be melted to cause the heat sensitive material to flow and subsequently cooled to plug the flow hole.

[0019] The first end of the capsule tube may be an upper end and coupling the second end cap may include coupling the second end cap to the upper end of the capsule tube. In this way, the thermally sensitive material may form a plug near a lower end of the capsule tube.

[0020] In some cases, the first end of the capsule tube is a lower end and coupling the second end cap comprises coupling the second end cap to the lower end of the capsule tube. In this way, the thermally sensitive material may form a plug near an upper end of the capsule tube.

[0021] The method may further include the step of inserting the tag gas capsule into a fuel pin. In some cases, the method includes coupling the tag gas capsule to an upper end cap of a fuel pin.

[0022] In some embodiments, the first end cap is an upper end cap of a fuel pin. This arrangement eliminates a separately form end cap of the tag gas capsule and the upper end cap of the fuel pin becomes an integral part of the tag gas capsule.

[0023] The method may further include step of causing, by applying heat to melt the heat sensitive material, the heat sensitive material to flow away from the first end cap to thereby expose a flow hole formed in the first end cap to allow the tag gas to escape the tag gas capsule through the flow hole.

[0024] According to some embodiments, a method for detecting a leak in a fuel pin, includes the steps of providing a tag gas capsule in a fuel pin, the tag gas capsule formed to have a flow hole formed in the tag gas capsule, a thermally sensitive plug blocking the flow hole, and a tag gas within the tag gas capsule; heating the fuel pin and tag gas capsule to melt the thermally sensitive plug to unblock the flow hole and allowing the tag gas to flow out of the tag gas capsule and into the fuel pin; sampling a primary coolant or a cover gas of anuclear reactor; and detecting, in the primary coolant or the cover gas, a presence of the tag gas.

[0025] The thermally sensitive plug may be sodium, tin, or other desired material that can melt at an appropriate temperature and is compatible with the materials and / or environment in which it is used.

[0026] A method of forming a tag gas capsule may include the steps of coupling a first end cap to a first end of a capsule tube to seal the first end of the capsule tube; inserting a heat sensitive material into the capsule tube; applying heat to melt the heat sensitive material and cause the heat sensitive material to flow into the first end cap; cooling the heat sensitive material to cause the heat sensitive material to solidify; and coupling a second end cap to a second end of the capsule tube to seal the second end of the capsule tube and form a tag gas capsule. The tag gas may be inserted into the capsule at a later step, or by a different company. For instance, a first company may manufacture the capsule, but not load the capsule with a tag gas. That may happen by a different entity at a later time. The tag gas capsule may be loaded, for example, by creating a hole in the tag gas capsule, such as at the plug, filling the tag gas capsule with a gas, and then sealing the hole. In some cases, forming and sealing the hole may be performed by a laser.BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 illustrates various components of a nuclear reactor, according to some embodiments.

[0028] FIG. 2 is a schematic sectional view of a core of a sodium-cooled fast reactor, in accordance with some embodiments.

[0029] FIG. 3 is an exploded view of a core assembly, in accordance with some embodiments.

[0030] FIG. 4 illustrates an example embodiment of a tag gas capsule installed within a fuel pin near the upper end cap with a tag gas escape pathway at a lower end of the tag gas capsule, in accordance with some embodiments.

[0031] FIG. 5 illustrates an example embodiment of a tag gas capsule installed within a fuel pin with an escape pathway through a side of the capsule, in accordance with some embodiments.

[0032] FIG. 6 illustrates an example embodiment of a tag gas capsule integral with the upper end cap, in accordance with some embodiments.

[0033] FIG. 7 illustrates a process flow diagram showing a sample process for fabricating a tag gas capsule, in accordance with some embodiments.DETAILED DESCRIPTION

[0034] This disclosure generally relates to method and systems for a tag gas capsule that is simple to fabricate and install, has no moving parts, and is passively activated. These results are obtained by creating a tag gas capsule that relies on a thermal based release system. According to some embodiments, a small tag gas capsule can be fabricated that has an escape pathway, such as a flow hole, for the tag gas wherein the escape pathway is sealed by a thermally sensitive material. For instance, the thermally sensitive material may be a material that melts at a temperature below or near the operating temperature of the nuclear reactor. Such suitable materials may include, without limitation, tin and / or sodium.

[0035] A small thermal plug or fuse can be added at an end of the capsule, and the tag gas can be released from the capsule into the fuel pin by melting the plug or fuse by external heat after fabrication of the fuel pin. The plug or fuse can be formed to be quite small, especially in comparison with previous tag gas capsules, and the entire tag gas capsule can be significantly smaller than prior tag gas capsules. This results in the entire fuel assembly length being reduced in comparison with prior attempts, or the extra space savings can be used for other purposes, such as additional plenum volume for a longer lifetime of the fuel pin.

[0036] Referring to FIG. 1, for additional context, many of the components and subassemblies of a representative nuclear reactor 100 are illustrated. For example, a reactor head 102, reactor vessel 106 and guard vessel 104, and many ancillary reactor components such as structural members, flanges, cover plates, piping, railing, framing, connecting rods, and supports are illustrated. While the illustrated nuclear reactor 100 is a sodium fast reactor(SFR), it should be appreciated that the components and embodiments described herein could be applied to any suitable reactor configuration. For example, the tag gas capsule embodiments described herein could be utilized in any reactor that utilizes fuel pins that may experience a rupture or leak.

[0037] The nuclear reactor 100 is designed to hold a number of nuclear fuel pins (not shown) in a reactor core 108 located near the bottom of the reactor vessel 106. The reactor head 102 seals the radioactive materials within the reactor vessel 106 and guard vessel 104. In the embodiment shown, the reactor core 108 can only be accessed through the reactor head 102. For example, an in-vessel fuel handling machine 116 is provided. The fuel handling machine 116 allows fuel pins and other core components and instruments to be lifted from the core 108 and removed from the vessel 106 via a set of large and small rotating plugs 118 located in the reactor head 102. This design allows the reactor vessel 106 to be unitary and without any penetrations.

[0038] In some cases, sodium, which is a liquid at the nuclear reactor operating temperatures, is the primary coolant for removing heat from the reactor core 108. The reactor vessel 106 is filled to some level with sodium which is circulated through the reactor core 108 using pumps 110. In some embodiments, two or more sodium pumps 110 are provided, which may be electromagnetic pumps. In some cases, one or more pumps 110 may include an impeller which may extend through the reactor head 102 to a location above the reactor head 102.

[0039] In some embodiments, the pumps 110 are configured to circulate the sodium through one or more intermediate heat exchangers (IHX) 112 located within the reactor vessel 106. Sodium from the cold pool 122 near the bottom of the reactor vessel 106 is pumped up into the core 108 where it becomes heated from the nuclear fission reactions taking place therein. The heated sodium travels up out of the core and into the hot pool 124 above the core. The sodium flows upwardly by natural circulation as heated sodium has a lower density than cold sodium in the cold pool, and also by forced pressure from the one or more pumps 110. The heated sodium in the hot pool is drawn into the intermediate heat exchanger(s) 112 which transfer heat from the primary sodium coolant to a secondary coolant flowing through the intermediate heat exchangers. Fresh secondary coolant is pipedthrough the reactor head 102 via one or more heat transport loop pipes 120 to the intermediate heat exchangers 112 where it is heated. Heated secondary coolant then flows out of the reactor head 102 through the heat transport loop piping 120. In some embodiments, the heated secondary coolant is used to generate steam which transferred to a power generation system. The secondary coolant may be a sodium coolant or a salt coolant such as a magnesium sodium coolant.

[0040] FIG. 2 is a schematic sectional view of a core 200 of an SFR. The core 200 is schematically shown and includes a central core region 202 having a plurality of core assemblies 204. The core assemblies 204 may include fissile nuclear fuel assemblies, fertile nuclear fuel assemblies, shield assemblies, reflector assemblies, control assemblies, and standby shutdown assemblies, or material testing assemblies. In general, the contents of the assemblies (e.g., fissile material, control material, etc.) identifies the particular assembly. The structural components of the assemblies that hold such material may be identical, such as to facilitate shuffling the core assemblies around the core to any location, as desired. A peripheral core region 206 includes in-vessel storage pots 208. Throughout the life of the core 200, the fissile nuclear fuel assemblies and fertile nuclear fuel assemblies (as well as certain other assemblies) are shuffled between the central core region 202 and the peripheral core region 206. This is performed at various stages of core life as required or desired to initiate, maintain, accelerate, or terminate nuclear reactions or power generation and / or for safety reasons.

[0041] The assemblies 204 are received by an upper plate 210 of a core support structure 212 at locations sized and configured to receive the core assemblies 204. Sodium coolant is pumped into a plenum 214 disposed below the upper plate 210 and flows upward into the core assemblies 204, where it is heated by the nuclear reactions taking place within the core 200. Structures that channel the flow of sodium through the core 202 and into the various assemblies are described below.

[0042] FIG. 3 is an exploded view of a core assembly 300. The core assembly 300 includes an elongate duct 302 having an axis A. In some cases, the duct 302 has a hexagonal cross section. A handling socket 304 with an internal flow passage is secured to a first end 306 of the duct 302 and has internal or external features that allow it to be grasped bymechanisms within the reactor vessel to lift, lower, and otherwise move the core assembly 300 into, out of, or within the core.

[0043] An inlet nozzle 308 is secured to a second end 310 of the duct 302. A plurality of bearing rings 312 and retaining rings 314 are used to attach the handling socket 304 and inlet nozzle 308 to the duct 302. When configured as a fuel assembly, a bundle of fuel pins 320 may be inserted into the duct 302. The fuel pins 320 are formed as a cladding tube filled with fuel rods. The nuclear fuel rods may include fissile fuel or fertile fuel. A plurality of lock plates 316 (two in this example) and a plurality of pin strip rails 318 may be included proximate an end of the inlet nozzle 308. Together, the lock plates 316 and pin strip rails 318 connect the pin bundle 320 to the inlet nozzle 308. Seal rings 322 and a flow restrictor 324 may also be incorporated. The nozzle 308 defines a plurality of coolant inlet windows 326 that are in flow communication with an interior flow chamber (not shown) that extends through the nozzle 308. Thus, the windows 326 provide a path for sodium to flow into the nozzle 308 and into the duct 302 to flow around the pin bundle 320 disposed therein. Sodium flow continues out of the handling socket 304. Typically, the core assemblies 300 are inserted into the reactor core such that the inlet nozzle 308 is inserted first into the reactor core and is therefore at a lower end of the core assembly and the handling socket 304 is at an upper end of the core assembly.

[0044] FIG. 4 illustrates an example tag gas capsule 400, in accordance with some embodiments. In some cases, a tag gas capsule 400 includes a capsule tube 402 with a top end connector 404 at a first end and a bottom end plug 406 at a second end of the capsule tube 402. The bottom end plug 406 may be securely coupled to the capsule tube, and in some cases, may be coupled to the capsule tube 402 by welding, such as laser welding or resistance pressure welding (RPW). The bottom end plug 406 may have a flow hole 408 formed therein configured to allow the tag gas to escape once the flow hole 408 is exposed to form a flow path for the tag gas. The capsule tube 402 and bottom end plug 406 may then be filled with a small slug, which may be a temperature sensitive material. While there are many temperature sensitive materials available and suitable for use in embodiments disclosed herein, for efficiency, the description will use sodium as an example of a suitable plug material. It should be understood and appreciated that the use of sodium in describedexamples throughout this disclosure should not be limiting. Once sodium is inserted into the capsule tube 402 it may be heated while the capsule tube is in a vertical orientation to melt the sodium so it flows into the bottom end plug 406. The flow hole 408 in the bottom end plug 406 may be occluded during this filling process, to prevent the molten sodium from leaking out of the flow hole 408. Once a sufficient quantity of sodium is melted and the flow hole 408 is plugged, the sodium is cooled and solidified to create a sodium plug 410 that seals the flow hole 408.

[0045] In some embodiments, the tag gas capsule is installed into a fuel pin 412 that has a cladding 414 formed as a tube, an upper end cap 416 that seals one end of the cladding and a shield slug closing a lower end of the cladding 414. The tag gas capsule 400 may be positioned near the upper end cap 416 and may be shaped to cooperate with the upper end cap 416 to hold the tag gas capsule 400 in place. In some cases, the tag gas capsule 400 fits into a recess in the upper end cap 416 and is thereby held in place. The tag gas capsule 400 may have an outer diameter that is smaller than the inner diameter of the cladding 414 such that there is an annular space between the tag gas capsule 400 and the inner diameter of the cladding 414. This annular space may allow the tag gas, once it escapes from the tag gas capsule 400 to reach all welds, connections, and components that make up the fuel pin 412. In some embodiments, the outer diameter of the tag gas capsule is less than(6.35mm) in order to fit within a fuel pin. Of course, other dimensions are contemplated and are only dictated by the inner diameter of the fuel pin into which the tag gas capsule is installed.

[0046] After adding the sodium to occlude the flow hole 408, the top end connector 404 may be coupled to the capsule tube 402, such as by welding. In some cases, connecting the top end connector 404 may be performed in an atmosphere of the tag gas, such that the tag gas is captured within the capsule tube 402 as the top end connector 404 is attached, thus capturing the tag gas within the capsule tube 402. In some examples, a seal weld hole is formed at the interface of the top end connector 404 and the capsule tube 402, and the tag gas can be inserted through the seal weld hole and the seal weld hole can then be filled to trap the tag gas within the capsule tube 402.

[0047] Once the tag gas capsule is formed, the sodium oxidation of the sodium plug 410 is relatively minor due to the small diameter of the sodium plug exposed by the flow hole408. In some cases, the flow hole 408 is formed of a diameter suitable to allow the tag gas to escape, and may be on the order of 1 / 32” (0.8mm). In some cases, the flow hole is less than 1mm in diameter and provides a sufficient aperture for allowing the tag gas to escape. Of course, the disclosed diameter is given as an example, and it should be appreciated that any suitable flow hole diameter may be used with the inventive concepts and embodiments described herein. In some cases, the tag gas is pressurized within the tag gas capsule such that its pressure is higher than that of the fuel pin environment. In this way, the tag gas may be encouraged to flow out of the tag gas capsule once the plug 410 is removed from the flow hole 408.

[0048] In some cases, the fuel pin is heated before installing the fuel pin into a fuel assembly, or before installing a fuel assembly into the reactor, or after the fuel assembly has been installed into the reactor. In any case, as the fuel pin is heated, which may be performed during fueling (e.g., sodium bonding) or heat treatment, the sodium plug 410 will melt and flow into the fuel pin and eventually flow downward to the bottom of the fuel pin near a shield slug that seals the bottom of the fuel pin. Of course, the sodium plug 410 may also be melted during operation of the reactor.

[0049] In some embodiments, the bottom end plug 406 and the capsule tube 402 could be formed as a unity component and thus omit the step of coupling the bottom end plug 406 to the capsule tube 402. The disclosed components may be formed of any suitable material, and in some cases, may include stainless steel, HT9 steel, or some other suitable material that is compatible with the reactor core environment.

[0050] It should be appreciated that the tag gas capsules described herein may be inserted into any core assembly. For example, a tag gas capsule may be inserted into a control pin within a control assembly and may be used to monitor the integrity of the control pin. This provides confidence that any material within the control pin, such as neutron-absorbing material, is not leaked out due to failures of the control pin.

[0051] FIG. 5 illustrates another embodiment of a tag gas capsule 400. In the illustrated embodiment, the sodium plug 502 may be formed within the top end connector 404 of the tag gas capsule 400. In fabricating this embodiment, the top end connector 404 may first be coupled to the capsule tube 402 through any suitable method, and sodium may then beinserted into the capsule tube 402 while the capsule tube is inverted. The capsule tube 402 and top end connector 404 may then be heated to melt the sodium and the material would flow and settle into a space within the top end connector 404. The top end connector may be formed with one or more flow holes 504 that become plugged by the molten sodium before it solidifies into the sodium plug 502. In some cases, a single flow hole 504 is sufficient to allow the tag gas to escape once the sodium plug is melted, although it should be apparent that additional flow holes 504 may be provided to allow the tag gas to escape faster. In some cases, two, three, four, or six holes are formed in the top end connector 404 in a radial direction.

[0052] Once the sodium plug 502 is formed, the capsule may be filled with the tag gas and the bottom end plug 506 can be attached to the capsule tube 402. In some cases, the bottom end plug 506 may be formed with a small hole that can be used to load the tag gas after bottom end plug 506 is coupled to the capsule tube, and the small hole can then be closed, such as by a light laser weld once the tag gas is added to the capsule tube 402. By using a bottom end plug 506, as shown, as the sodium plug melts while in the orientation shown, the sodium will flow down the capsule tube until it rests against the bottom end plug 506 and will not be able to enter the fuel pin.

[0053] FIG. 6 illustrates another embodiment of a tag gas capsule 400 in which the upper end cap 416 of the fuel pin 412 is formed integrally with the tag gas capsule 400. In this embodiment, the top end cap of the tag gas capsule 400 shown in the previous embodiments may be omitted and the capsule tube 402 may be coupled directly to the upper end cap 416 of the fuel pin 412.

[0054] The upper end cap 416 may have a first section 602 having a first diameter that equals the diameter of the cladding 414 to facilitate coupling the upper end cap 416 with the cladding 414. The upper end cap 416 and the cladding 414 may be coupled together through any suitable method, which includes welding. The upper end cap 416 may further include a second section 604 having a second diameter smaller than the first diameter and configured to allow the second section 604 to be inserted into the cladding 414. The second section 604 may have a hollow space 606 (e.g., counterbore) that is configured to contain the sodium plug 502.

[0055] The second section 604 of the upper end cap 416 may be formed with one or more flow holes 504 through the sidewall of the second section 604 to allow tag gas to escape therethrough upon melting of the sodium plug 502. During fabrication, the weldment of the upper end cap 416 and the capsule tube 402 can be inverted and solid sodium can be placed therein, which may be in a sufficient quantity to fill the hollow space 606 in the second section 604 of the upper end cap 416. The weldment may then be heated to liquify the sodium so that it flows to occupy the hollow space 606. The second section 604 of the upper end cap 416 may then be drilled to create one or more flow holes 504 for the tag gas to escape the tag gas capsule 400 once the sodium plug 502 melts. Of course, the flow holes 504 may be created before the sodium is inserted, or after the sodium plug has been formed.

[0056] Once the sodium plug 502 is in place, the capsule tube 402 may be filled with tag gas and the bottom end cap 506 may then be affixed to the capsule tube 402. After fabrication, the combination of the upper end cap 416 with capsule tube 402 and bottom end cap 506 may together form the tag gas capsule 400 which can be inserted into the fuel pin cladding 414 and be permanently affixed thereto.

[0057] As with any of the embodiments described herein, a tag gas capsule provides a tag gas within a fuel pin that is only released once the tag gas capsule is exposed to heat in order to melt the sodium plug and release the tag gas so that it flows within the fuel pin. Thereafter, upon a leak of the fuel pin, the tag gas will exit the fuel pin through the leak, which can then be detected in the primary coolant or in the cover gas within the reactor vessel.

[0058] In any of the embodiments described herein, the tag gas may be pressurized to encourage the tag gas to flow out of the capsule and into the fuel pin. In some embodiments, the fuel pin has an internal pressure of about 1 atm, and the tag gas capsule can be pressurized to be slight above 1 atm, such as 1.1 atm, 1.2, 1.3 atm, 1.5, atm or higher. This may be accomplished, for example, by inserting the tag gas capsule into a chamber pressurized with the tag gas, puncturing a hole, allow the pressurized tag gas to flow through the hole, then seal the hole. In some cases, the entire tag gas capsule is fabricated and sealed without the tag gas. At a later step, the tag gas capsule can be punctured, filled with tag gas, and then resealed. As described above, this may be accomplished by putting the tag gascapsule in a chamber pressurized with the tag gas, puncturing the capsule, then sealing the puncture within the chamber.

[0059] FIG. 7 illustrates a process flow diagram showing a sample process 700 for fabricating the tag gas capsules described herein. At block 702, a capsule tube is provided. The capsule tube may be circular in cross-section, but may also have other cross sectional shapes, such as hexagonal, octagonal, elliptical, or some other suitable shape.

[0060] At block 704, a first end cap is coupled to the capsule tube to seal the first end of the capsule tube. The first end cap may be coupled through any suitable method, such as welding, adhesives, threaded, or otherwise.

[0061] At block 706, heat sensitive material is inserted into the capsule tube. The heat sensitive material may be any suitable material that is solid at ambient temperature, and is able to melt with applied heat. Such suitable materials may include, without limitation, sodium, tin, a tin-containing alloy, or other metal or nonmetal materials with melting temperatures below reactor operating temperatures. In some cases, the heat sensitive material is first melted and then poured into the capsule tube, where it flows to the bottom of the capsule tube and assumes the shape of the first end cap. In some cases where the flow hole is already formed in the first end cap, the heat sensitive material does not exit through the flow hole by virtue of the size of the flow hole in combination with the viscosity of the molten heat sensitive material, based on the surface tension of the heat sensitive material, or a combination. In some cases, the flow hole may be blocked from outside the capsule tube to inhibit the heat sensitive material from flowing out of the flow hole.

[0062] At block 708, heat is applied to the capsule tube to melt the heat sensitive material and cause it to flow to the first end cap. In some cases, the first end cap includes a recess into which the heat sensitive material flows. In addition, the first end cap may also be formed with one or more flow holes. The flow holes may be formed either before the heat sensitive material is added, or after the heat sensitive material is added to the capsule tube.

[0063] At block 710, a tag gas is inserted into the capsule tube. In some cases, the tag gas is inserted at a predetermined pressure that is greater than 1 atm so as to pressurize the tag gas within the capsule tube.

[0064] At block 712, a second end cap is coupled to the capsule tube to seal the second end of the capsule tube. The second end cap may be coupled through any suitable method, such as welding, adhesives, threaded, interference, or some other suitable coupling method. In some instances, either the first end cap or the second end cap may be the upper end cap of a fuel cladding tube and used to seal the end of the fuel cladding tube. In other cases, the first end cap or second end cap may be coupled to the upper end cap of the fuel cladding tube and held in place by any suitable method, such as welding, adhesives, friction, threaded, pinned, or otherwise.

[0065] At block 714, the tag gas capsule is inserted into a fuel pin. For example, the tag gas capsule may be attached to the upper end cap of the fuel pin and inserted into the fuel cladding as the upper end cap is affixed to the fuel cladding.

[0066] At block 716, the fuel pin is heated, which melts the heat sensitive material, which then flows downward through gravity and exposes one or more flow holes through which the tag gas escapes into the fuel pin and around the fuel volume with the fuel pin. In some cases, this step of melting the heat sensitive material and causing the tag gas to flow out of the tag gas capsule and into the fuel pin is performed during the fuel pin fabrication and before the fuel pin is integrated into a fuel assembly. The tag gas capsule may be inspected for proper operation such as by performing an eddy current inspection, which will show a magnetic cross section response that can identify a sodium plug blocking the flow hole and further identify when the sodium plug has melted and exposed the flow hole.

[0067] Eddy current inspection is a non-destructive testing method used to assess the integrity of conductive materials. It relies on the generation of eddy currents - circulating electrical currents induced by a changing magnetic field. An alternating current is passed through a coil, creating this magnetic field. When the coil is brought near a conductive material, such as metal, it induces eddy currents in the material.

[0068] The interaction between these induced currents and the material's properties is then analyzed. Changes in the electrical conductivity, permeability, or geometry of the material, often associated with defects like cracks or corrosion, affect the eddy currents. The inspection is typically performed using a probe or sensor coil, and specialized instruments measure parameters like impedance and phase angle to identify and characterize defects.Eddy current inspection can thus determine whether the sodium plug is in a location to block the flow hole, or whether it has melted and migrated to a location where the flow hole is unobstructed.

[0069] Subsequently, during reactor operation, if there is ever a leak or breach of the fuel pin, the tag gas will escape the fuel pin and be detectable from outside the fuel pin.

[0070] While some examples describe adding the tag gas capsule to an upper end of a fuel pin, it is contemplated that the tag gas capsule could be installed near a lower end of the fuel pin, or at any location along the fuel pin. However, in many cases, the tag gas capsule is installed at one end of the fuel pin or the other end of the fuel pin. In some examples, each fuel pin within a fuel assembly is outfitted with a tag gas capsule.

[0071] The foregoing description of specific embodiments will so fully reveal the general nature of embodiments of the disclosure that others can, by applying knowledge of those of ordinary skill in the art, readily modify and / or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of embodiments of the disclosure. Therefore, such adaptation and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. The phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the specification is to be interpreted by persons of ordinary skill in the relevant art in light of the teachings and guidance presented herein.

[0072] The breadth and scope of embodiments of the disclosure should not be limited by any of the above-described example embodiments but should be defined only in accordance with the following claims and their equivalents.

[0073] Conditional language, such as, among others, “can,” “could,” “might,” or “may,” unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain implementations could include, while other implementations do not include, certain features, elements, and / or operations. Thus, such conditional language generally is not intended to imply that features, elements, and / or operations are in any way required for one or more implementations or that one or more implementations necessarily include logic for deciding, with or without user input orprompting, whether these features, elements, and / or operations are included or are to be performed in any particular implementation.

[0074] Throughout the instant specification, the term “substantially” in reference to a given parameter, property, or condition may mean and include to a degree that one of ordinary skill in the art would understand that the given parameter, property, or condition is met with a small degree of variance, such as within acceptable manufacturing tolerances. By way of example, depending on the particular parameter, property, or condition that is substantially met, the parameter, property, or condition may be at least approximately 90% met, at least approximately 95% met, or even at least approximately 99% met.

[0075] As used herein, the terms “about” and “approximately” may, in some examples, indicate a variability of up to ±5% of an associated numerical value, e.g., a variability of up to ±2%, or up to ±1%.

[0076] A person of ordinary skill in the art will recognize that any process or method disclosed herein can be modified in many ways. The process parameters and sequence of the steps described and / or illustrated herein are given by way of example only and can be varied as desired. For example, while the steps illustrated and / or described herein may be shown or discussed in a particular order, these steps do not necessarily need to be performed in the order illustrated or discussed.

[0077] The various exemplary methods described and / or illustrated herein may also omit one or more of the steps described or illustrated herein or comprise additional steps in addition to those disclosed. Further, a step of any method as disclosed herein can be combined with any one or more steps of any other method as disclosed herein.

[0078] It is, of course, not possible to describe every conceivable combination of elements and / or methods for purposes of describing the various features of the disclosure, but those of ordinary skill in the art recognize that many further combinations and permutations of the disclosed features are possible. Accordingly, various modifications may be made to the disclosure without departing from the scope or spirit thereof. Further, other embodiments of the disclosure may be apparent from consideration of the specification and annexed drawings, and practice of disclosed embodiments as presented herein. Examples put forward in the specification and annexed drawings should be considered, in all respects, as illustrativeand not restrictive. Although specific terms are employed herein, they are used in a generic and descriptive sense only, and not used for purposes of limitation.

[0079] Unless otherwise noted, the terms “a” or “an,” as used in the specification, are to be construed as meaning “at least one of.” Finally, for ease of use, the terms “including” and “having” (and their derivatives), as used in the specification, are interchangeable with and have the same meaning as the word “comprising.”

[0080] From the foregoing, and the accompanying drawings, it will be appreciated that, although specific implementations have been described herein for purposes of illustration, various modifications may be made without deviating from the spirit and scope of the appended claims and the elements recited therein. In addition, while certain aspects are presented below in certain claim forms, the inventors contemplate the various aspects in any available claim form. For example, while only some aspects may currently be recited as being embodied in a particular configuration, other aspects may likewise be so embodied. Various modifications and changes may be made as would be obvious to a person skilled in the art having the benefit of this disclosure. It is intended to embrace all such modifications and changes and, accordingly, the above description is to be regarded in an illustrative rather than a restrictive sense.

Claims

CLAIMSWhat is claimed is:

1. A tag gas capsule, comprising: a capsule tube having a first end and a second end; a first end cap coupled to the capsule tube and sealing the first end of the capsule tube; a second end cap coupled to the capsule tube and sealing the second end of the capsule tube; a flow hole formed in one or more of the capsule tube, the first end cap, and the second end cap; a tag gas disposed within the capsule tube; and a thermally sensitive material positioned within the tag gas capsule to block the flow hole, the thermally sensitive material configured to melt at a temperature below a nuclear reactor operating temperature to expose the flow hole and allow the tag gas to escape through the flow hole.

2. The tag gas capsule as in claim 1, wherein the thermally sensitive material is sodium.

3. The tag gas capsule as in claim 1, wherein the thermally sensitive material is tin or a tin-containing alloy.

4. The tag gas capsule as in claim 1, wherein the flow hole is formed with a diameter of less than 1mm.

5. The tag gas capsule as in claim 1, wherein the tag gas capsule is configured to be inserted into a nuclear fuel pin.

6. The tag gas capsule as in claim 5, wherein the tag gas capsule has an outer diameter of less than 6.35mm.

7. The tag gas capsule as in claim 1, wherein the flow hole is formed at a location near an upper end of the tag gas capsule such that the thermally sensitive material flows downward once melted and is captured within the tag gas capsule.

8. The tag gas capsule as in claim 1, wherein the flow hole is formed at a bottom end of the tag gas capsule such that the thermally sensitive material flows out of the tag gas capsule once melted.

9. A method of forming a tag gas capsule, comprising the steps of coupling a first end cap to a first end of a capsule tube to seal the first end of the capsule tube; inserting a heat sensitive material into the capsule tube; applying heat to melt the heat sensitive material and cause the heat sensitive material to flow into the first end cap; cooling the heat sensitive material to cause the heat sensitive material to solidify; inserting a tag gas into the capsule tube; and coupling a second end cap to a second end of the capsule tube to seal the second end of the capsule tube and form the tag gas capsule.

10. The method of claim 9, wherein the first end cap includes a flow hole formed therein and the step of applying heat to melt the heat sensitive material further includes causing the heat sensitive material to flow into the first end cap and block the flow hole.

11. The method of claim 10, wherein the flow hole is formed prior to the step of inserting the heat sensitive material into the capsule tube.

12. The method of claim 9, wherein the heat sensitive material is selected from sodium and tin.

13. The method of claim 9, wherein the first end of the capsule tube is an upper end and coupling the second end cap comprises coupling the second end cap to a lower end of the capsule tube.

14. The method of claim 9, wherein the first end of the capsule tube is a lower end and coupling the second end cap comprises coupling the second end cap to an upper end of the capsule tube.

15. The method of claim 9, further comprising inserting the tag gas capsule into a fuel pin.

16. The method of claim 9, further comprising coupling the tag gas capsule to an upper end cap of a fuel pin.

17. The method of claim 9, wherein the first end cap is an upper end cap of a fuel pin.

18. The method of claim 9, further comprising the step of causing, by applying heat to melt the heat sensitive material, the heat sensitive material to flow away from the first end cap to thereby expose a flow hole formed in the first end cap to allow the tag gas to escape the tag gas capsule through the flow hole.

19. A method for detecting a leak in a nuclear fuel pin, comprising the steps of providing a tag gas capsule in the fuel pin, the tag gas capsule formed to have a flow hole formed in the tag gas capsule, a thermally sensitive plug blocking the flow hole, and a tag gas within the tag gas capsule; heating the fuel pin and tag gas capsule to melt the thermally sensitive plug to unblock the flow hole and allowing the tag gas to flow out of the tag gas capsule and into the fuel pin; sampling a primary coolant or a cover gas of a nuclear reactor; and detecting, in the primary coolant or the cover gas, a presence of the tag gas.

20. The method as in claim 19, wherein the thermally sensitive plug is sodium, tin, or a tin-containing alloy.ABSTRACT OF THE DISCLOSUREA tag gas capsule utilizes a thermally based release system to allow the tag gas to flow through a fuel pin and to be detectable upon a leak in the fuel pin. A tag gas capsule is fabricated that has an escape pathway for the tag gas wherein the escape pathway is sealed by a thermally sensitive material. During fabrication, the thermally sensitive material is melted into the tag gas capsule and seals a flow hole in the tag gas capsule. The capsule is then filled with a tag gas and sealed to prevent escape of the tag gas. Once the capsule has been installed into a fuel pin, the capsule can be heated to melt the thermally sensitive material and expose the flow hole. The tag gas can then flow out of the flow hole and into the fuel pin.CLAIMSWhat is claimed is: