Nuclear fuel assembly with multi-pitch wire wrap

Abstract

The nuclear fuel assembly is composed of fuel assembly components that are wire-wrapped and arranged in multiple hexagonal rings within a fuel assembly duct. The fuel assembly components located in the outermost ring of the fuel assembly are wire-wrapped at a shorter pitch than the fuel assembly components located in the inner rings of the fuel assembly. The shorter pitch in the outer ring of the fuel assembly increases the coolant fluid pressure drop in the edge and corner subchannels, resulting in a reduced temperature gradient across the fuel assembly. This allows for greater reactor power temperatures without a substantial increase in the peak temperature of the fuel cladding.

Description

Detailed Description of the Invention

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 066,778, entitled "MODULAR MANUFACTURE, DELIVERY, AND ASSEMBLY OF NUCLEAR REACTOR," filed August 17, 2020, the entire contents of which are incorporated herein by reference.

[0002] 〔background〕 Typically, nuclear fuel assemblies include wire-wrapped fuel pins to provide a predetermined subchannel size, reduce pin-to-pin interaction, and improve thermal-hydraulic performance. Typically, the fuel pins are helically wrapped with circular wire. The diameter of the wire determines the separation between adjacent fuel pins and between the fuel pins and the adjacent duct wall.

[0003] Typically, when coolant flows within a subchannel, there is a greater pressure drop in the interior subchannels compared to the edge subchannels. As a result, coolant can flow through the edge subchannels at a greater velocity, which removes heat more efficiently and more quickly from the fuel pins adjacent the duct walls than from fuel pins located closer to the center of the fuel assembly.

[0004] This thermodynamically results in a temperature gradient across the fuel pins, with fuel pins closer to the center of the fuel assembly having a greater temperature than fuel pins near the edges of the fuel assembly, which can result in thermodynamic stresses and strains.

[0005] It would be advantageous to reduce this temperature gradient across the fuel pins so that fuel performance improves, pin-to-pin interactions are reduced, and exit temperatures are increased. These and other features will become readily apparent from the following description and by reference to the drawings.

[0006] 〔overview〕 According to some embodiments, a fuel assembly for a nuclear reactor includes a first fuel pin having a first wire wrapping and a second fuel pin having a second wire wrapping, the first wire wrapping having a first pitch and the second wire wrapping having a second pitch, the second pitch being different from the first pitch. Of course, this wire wrapping is equally applicable to other fuel assembly components, such as neutron reflectors, control rods, fertile fuel, etc.

[0007] In some cases, the second pitch is shorter than the first pitch. As an example, the second pitch may be half the first pitch, a quarter of the first pitch, or some other multiplier factor.

[0008] The first fuel pin and the second fuel pin may be disposed within a fuel duct, and the second fuel pin may be positioned closer to a wall of the fuel duct than the first fuel pin. In some cases, a ring of second fuel pins is positioned closer to the wall of the fuel duct than a ring of first fuel pins.

[0009] In some embodiments, the second fuel pin is positioned within a fuel duct to increase the outlet temperature of the reactor.

[0010] According to some embodiments, the first fuel pin has a first clocking angle and the second fuel pin has a second clocking angle that is different from the first clocking angle. In some cases, the clocking angles of the various fuel pins are selected to avoid wire-to-wire interference between adjacent fuel pins.

[0011] In some instances, the fuel assembly includes fissile fuel. In some cases, the fuel assembly includes parent fuel.

[0012] In some embodiments, the fuel assembly includes a neutron absorber, the neutron absorber having a second wire wrapping having the second pitch. The neutron absorber may be configured to be interchangeable with a fuel pin or a control rod.

[0013] A method for increasing coolant fluid pressure drop in edge subchannels within a nuclear fuel assembly includes disposing a first fuel assembly component within an inner ring of the fuel assembly and disposing a second fuel assembly component within an outermost ring of the fuel assembly, the first fuel assembly component being wire wrapped with a first pitch and the second fuel assembly component being wire wrapped with a second pitch less than the first pitch.

[0014] In some cases, disposing a second fuel assembly component in an outermost ring of the fuel assembly includes disposing a plurality of second fuel assembly components in the outermost ring of the fuel assembly, each of the plurality of second fuel assembly components being wire wrapped at the second pitch.

[0015] The method may further include placing a third fuel assembly component within a second outermost ring of the fuel assembly, the third fuel assembly component being wire wrapped at the second pitch.

[0016] In some embodiments, the second pitch includes twice as many wrappings as the first pitch, and in some cases, the second pitch may include four times as many wrappings as the first pitch.

[0017] The first fuel assembly component may have a first clocking angle, in which case positioning the second fuel assembly component further includes positioning the second fuel assembly component to have a second clocking angle different from the first clocking angle.

[0018] In some cases, the method further includes using a second fuel assembly component having a second wire wrap at the second pitch.

[0019] According to some examples of the method, the first fuel assembly component may include one or more of a fissile fuel, a fertile fuel, a neutron absorber, or a neutron reflector.

[0020] In some cases, the first fuel assembly component is wire-wrapped with a first wire having a first diameter, and the second fuel assembly component is wire-wrapped with a second wire having a second diameter smaller than the first diameter. In some cases, the second fuel assembly component wire-wrapped with the second wire having a second diameter smaller than the first diameter has a larger cross-sectional dimension than the cross-sectional dimension of the first fuel assembly component wrapped with a wire having a larger diameter. In other words, the second fuel assembly component may be thicker than the first fuel assembly component, and in some cases, the difference in size may correspond to the difference in wire diameter.

[0021] The method may further include placing a third fuel assembly component within a second outermost ring of the fuel assembly, the third fuel assembly component being wire wrapped at the second pitch.

[0022] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a wire-wrapped fuel pin, according to some embodiments.

[0023] FIG. 2 is a cross-sectional view of a nuclear fuel assembly or a nuclear fission module, according to some embodiments.

[0024] FIG. 3 is a cross-sectional view of multiple side-by-side hexagonal fission modules, according to some embodiments.

[0025] FIG. 4 shows a cross-sectional view of multiple rods, according to some embodiments.

[0026] FIG. 5 shows computational fluid dynamics results illustrating improved thermal-hydraulic performance according to some embodiments.

[0027] Detailed Description The present disclosure relates generally to nuclear fuel pins, nuclear fuel pin bundles, nuclear fuel assemblies, and nuclear reactor cores in which the nuclear fuel pins have wire wrapping of varying pitches depending on their location within the nuclear fuel assembly.

[0028] Wire-wrapped fuel bundles are a type of nuclear fuel assembly that can be used in sodium-cooled fast reactors (SFRs). SFRs often use a high-density triangular array of assembled fuel to slow down and reduce neutron losses. Wire wrapping around the fuel pins is used to improve coolant mixing between subchannels. The wire wrapping provides spacing and support between the fuel pins.

[0029] With reference to FIG. 1, a fuel pin 100 is shown having a circular cross section. At some point during manufacture, nuclear fuel will be placed in the fuel pin 100. A wire 102 is wrapped helically around the fuel pin to create a wire-wrapped fuel pin. The wire has a diameter d 104 and a pitch H 106. In some cases, the pitch 106 is 1:1. In other words, the wire 102 makes one complete revolution around the fuel pin along its length. The pitch may be characterized as the length along the fuel pin required for the wire to make a complete revolution. For example, a pitch of 15 cm indicates the length along the fuel pin required for the wire to make a complete helical revolution. The pitch may also be characterized as the number of complete wire revolutions along the length of the fuel pin.

[0030] With reference to FIG. 2 , a nuclear fuel assembly 200 is shown schematically. The nuclear fuel assembly 200 includes multiple fuel pins 100 a, 100 b, and 100 n arranged within a fuel duct 202. Typically, the fuel pins are arranged in a ring around a central pin. The fuel pins 100 may be arranged in a first ring 204, a second ring 206, a third ring 208, and additional rings. By way of example, the illustrated fuel assembly 200 is arranged in three rings, thereby defining 37 pin fuel bundles. Of course, other fuel bundle architectures are contemplated herein, such as, for example, 19 pin fuel bundles, 61 pin fuel bundles, 91 pin fuel bundles, 127 pin fuel bundles, 169 pin fuel bundles, 217 pin fuel bundles, 271 pin fuel bundles, 331 pin fuel bundles, and other configurations.

[0031] The triangular grouping of fuel pins 100 creates subchannels between the fuel pins through which coolant can flow. The inner subchannel 210 has boundaries defined by three fuel pins. The edge subchannel 212 has boundaries defined by two fuel pins and the assembly duct. The corner subchannel 214 has boundaries defined by one fuel pin and the corner of the fuel duct 202.

[0032] While wire wraps improve coolant mixing in the subchannels and reduce peak fuel cladding temperatures, they also create temperature gradients across the fuel assembly, increasing pressure losses in the fuel assembly.

[0033] The amount of temperature distribution in a fuel bundle is proportional to the subchannel area. The edge subchannels 212 typically have a larger cross-sectional area than the interior subchannels 210. Therefore, the edge subchannels 212 typically have a lower temperature because a larger volume of coolant can flow through them with less restriction. As a result, different thermodynamic results occur for each pin in the fuel assembly depending on the ring in which the pin is located. As an example, a hexagonal fuel assembly will be shown and described. However, the concepts presented herein are not limited to hexagonal fuel assemblies, as the phenomena and concepts are similarly applicable to fuel assemblies having other cross sections and configurations. Additionally, as an example, a sodium-cooled fast reactor will be described. However, the concepts and techniques described herein are not limited to sodium fast reactors, as the concepts may be applicable to other types of nuclear reactors in both the thermal and fast spectrums, as well as to reactors utilizing other types of coolants.

[0034] 3 illustrates multiple fission modules including fuel assembly components (e.g., one or more fuel pins containing fissionable fuel, parent fuel, or a combination thereof; control rods; and / or neutron reflectors). While any of the components within a fission module may be wire wrapped, for ease of explanation, the wire wrapping will be described in connection with fuel pins. However, when referring to wire-wrapped fuel pins, it should be understood that the description could also apply to other fuel assembly components, and that the specific description of fuel pins is an example of application.

[0035] Regardless of the configuration selected for the core, a plurality of spaced, longitudinally extending, and longitudinally movable control rods 302 may be symmetrically arranged within control rod guide tubes or cladding (not shown) to extend the length of a predetermined number of fission modules 304. The control rods 302 are shown arranged within a predetermined number of hexagonal-shaped fission modules 304. The control rods 302 control the neutron fission reactions occurring within the fission modules 304. The control rods 302 include a suitable neutron absorber material having an acceptably large neutron absorption cross section. In this regard, the absorber material may be substantially a metal or metalloid selected from the group consisting of lithium, silver, indium, cadmium, boron, cobalt, hafnium, dysprosium, gadolinium, samarium, erbium, europium, and mixtures thereof. Alternatively, the absorber material may be substantially a compound or alloy selected from the group consisting of silver-indium-cadmium, boron carbide, zirconium diboride, titanium diboride, hafnium diboride, gadolinium titanate, dysprosium titanate, and mixtures thereof. The control rods 302 controllably supply negative reactivity to the core. As such, the control rods 302 provide reactivity management capabilities to the core. In other words, the control rods 302 can control or are configured to control the neutron flux profile throughout the core. As such, the control rods 302 affect the temperature profile throughout the core. As described herein, the control rods may be wire-wrapped, and a first control rod may be wire-wrapped with a first pitch and a second control rod may be wire-wrapped with a second pitch.

[0036] It should be understood that the fission module 304 need not be neutronically radioactive. In other words, the fission module 304 need not include any fissionable material. For example, the fission module 304 may be a purely reflective assembly, a purely fertile assembly, or a combination of both. Regarding the above, the fission module 304 may be a breeder nuclear fission module including nuclear breeding material, or a reflective nuclear fission module including reflective material. In this case, the fission module 304 may include fission module components wire-wrapped with a fixed pitch and clocking angle. Alternatively, in one embodiment, the fission module 304 may include fuel pins 306 in combination with breeder or reflector rods. For example, the fission module 304 may include multiple breeder rods in combination with the fuel pins 306. Control rods 302 may also be present. The fertile breeding material in the breeder rods may be thorium-232 and / or uranium-238, or any other suitable fertile breeding material. In this manner, the fission module 304 may define a fertile breeder assembly. In some cases, the fission module 304 includes a plurality of neutron reflector rods in combination with the fuel pins 306. Control rods 302 may also be present. The reflector material may be substantially a material selected from the group consisting of beryllium (Be), tungsten (W), vanadium (V), depleted uranium (U), thorium (Th), lead alloys, and mixtures thereof. The reflector rods may also be selected from a variety of steel alloys. In this manner, the fission module 304 may define a neutron reflector assembly. Furthermore, those skilled in the art of in-core nuclear fuel management will understand that the fission module 304 may include any suitable combination of nuclear fuel pins 306, control rods 302, breeder rods, and reflector rods. As disclosed herein, the individual rods in any combination of the disclosed nuclear fuel assembly components may be wire wrapped.The combination of rods may be formed in a hexagonal matrix and may depend, at least in part, on the wire wrapping to create various inter-rod spacings. The wire wrapping on the fuel assembly component may be wrapped in a first pitch, a second pitch, a third pitch, a fourth pitch, or some other configuration.

[0037] The temperature changes proportionally to the pressure change across the fission module. The pressure loss due to friction for flow along a smooth pipe can be calculated as follows:

[0038]

number

[0039] where ρ is the density, v is the average velocity of the coolant, L is the length of the tube, and d h is the hydraulic diameter of the channel. The friction factor can be calculated as a function of the Reynolds number. However, it is generally accepted that smaller pitch wire wrap values ​​correlate with greater friction along the subchannel. Thus, smaller pitch values ​​result in larger friction factors.

[0040] At the contact area between the fuel pin and the spacer wire, the coolant flow velocity is significantly reduced, especially behind the spacer wire. In these locations, the fuel pin surface may heat up above the coolant vapor temperature, which can affect neutron flux. Related literature indicates that, in the absence of a mixing device, deviation from nucleate boiling occurs first on the center fuel pin, followed by preferentially at locations facing azimuthally adjacent fuel pins. With a mixing device, such as a wrapped wire, the critical heat flux is greater; however, the location of deviation from nucleate boiling depends at least on the coolant pressure and mass velocity. According to some embodiments, the coolant is directed from the edge subchannels toward the inner subchannels to mitigate the effects of deviation from nucleate boiling and increase the critical heat flux.

[0041] Coolant flow in a fission module is primarily axially directional, with secondary flows in the subchannels. This directional flow can be disrupted by spacer wires, which cause turbulence in the wake of the wires as the flow follows the spacer wire's rotation around the fuel pin. In many conventional designs, the clocking of the wire wraps remains constant across the fuel pins in a fuel assembly. The clocking, or clocking angle, indicates the starting point of the wire wrap on the fuel pin. For example, as shown in Figure 2, the fuel pin has a constant starting clocking angle. The starting clocking angle indicates the wire wrap is at the 2:00 position. Furthermore, the pitch of the wire wraps is constant across all fuel pins, forming a hexagonal mesh that avoids wire-to-wire interference contact points.

[0042] Considering these parameters, the fuel pin reaches a local maximum temperature T max and the fuel assembly may be exposed to an average exit temperature T avg Generally, the T to which the fuel pins are exposed is determined so as not to exceed thermomechanical stress and strain limits on the fuel pins and so that pin-to-pin interactions caused by radial expansion, axial deformation, bending, etc. are managed. max would have to be controlled.

[0043] The fuel assembly as a whole is at a specific hot spot. max Preferably, the particular hot spot is constrained to remain below the thermomechanical limits of the components within the fuel assembly. max and T avg It would be advantageous to reduce the temperature difference (ΔT) between max While maintaining this, the overall outlet temperature will increase without substantially increasing the peak temperature of the fuel pin cladding.

[0044] To achieve these advantages, according to some embodiments, at least some of the fuel assembly components (e.g., fuel pins, control rods, etc.) within a fuel assembly may be wire-wrapped at a different pitch than the other fuel assembly components. For example, according to some examples, the outermost ring of wire-wrapped fuel assembly components may have a shorter pitch than the innermost rings of the fuel assembly components. Similarly, the second-to-outermost ring of wire-wrapped fuel assembly components may have a shorter pitch than the innermost rings of the fuel assembly components. In particular, the second-to-outermost ring of wire-wrapped fuel assembly components may have a different pitch than the outermost ring of the fuel assembly components. As used herein, the term "fuel assembly component" is a broad term and refers to any component that may be disposed within a fuel assembly. Fuel assembly components include, but are not limited to, fissionable fuel rods, parent fuel rods, neutron reflectors, and control rods. In many cases, each of these fuel assembly components may be configured to be interchangeable with other fuel assembly components. The description will primarily use fuel pins and exemplary fuel assembly components, however, it should be understood that the description using fuel pins as an example should not be so limited, particularly where the fuel pins are sized and shaped to be interchangeable with other fuel assembly components.

[0045] In some examples, the pitch difference between adjacent fuel assembly components is a half-pitch difference. For example, the inner rings of the fuel assembly components may have, as an example, a 50 cm pitch. In other words, the wire wrapping makes one full revolution every 50 cm along the axial length of the fuel pin. The second-to-outermost ring of the fuel assembly components may have a 25 cm (one-half of 50 cm) pitch, and the outer ring of the fuel assembly components may have a 12.5 cm (one-half of 25 cm) pitch. Of course, other pitches are contemplated herein, such as different numbers of pitches, including but not limited to three different pitches or two different pitches.

[0046] As shown in FIG. 4, a fuel assembly 200 implementing multiple pitch wire wraps allows for the T max The outlet temperature can be increased without exceeding

[0047] According to some embodiments, the central fuel pin 400 and the first ring of fuel pins 402 may be formed with wire wrapping having a first clocking angle and a first pitch. The outer ring of fuel pins 410 may be formed with one or more fuel pins in the outer ring of fuel pins 410 being wire wrapped with a second pitch. In some cases, one or more fuel pins in the outer ring of fuel pins 410 have a clocking angle different from the first clocking angle. In a typical wire-wrapped fuel assembly, wire is helically wrapped around the fuel pins with a constant pitch and a constant clocking angle, which directly avoids wire-to-wire interference. However, varying the clocking angle or pitch of the wire wrap makes it more difficult to avoid wire-to-wire interference. Similarly, one or more fuel pins in the second-to-outermost ring of fuel pins 404 may have a second pitch or a third pitch.

[0048] According to some embodiments, a solution is presented for avoiding wire-to-wire interference while utilizing more than one pitch by varying the clocking angle. Such a solution is illustrated in FIG. 4 for an exemplary fuel bundle of 37 pins. In some cases, many or most of the fuel pins among the plurality of fuel pins that cooperate to define multiple internal subchannels are formed with a consistent first pitch and a typical wire wrap. The typical wire wrap may include one, two, three, four, five, six, seven, eight, nine, or more turns of wire wrap helically wrapped along the length of the fuel pin. By way of example, some typical wire wrap pitches are between about 8 cm and about 100 cm. That is, the wire wrap makes a complete helical turn around the fuel pin about every 8 cm to about every 100 cm of the axial length of the fuel pin. Of course, these values ​​are examples, and other pitches are entirely possible based on the concepts presented herein.

[0049] In some cases, one or more fuel pins in the outer ring 410 may be wire wrapped at a second pitch that is different from the first pitch. In some cases, the second pitch varies from the first pitch by a factor of 0.5 or some other integer multiplier. For example, if the first pitch is 40 cm, the second pitch may be 20 cm. In some cases, the second pitch is half the first pitch, a quarter of the first pitch, or some other integer multiplier. Similarly, one or more fuel pins in the second-to-outermost ring 404 may be wire wrapped at the second pitch or at a third pitch that is different from the first and second pitches. Of course, other factors may be used to vary the pitch between fuel pins, and solutions to avoid wire-to-wire interference may be achieved by varying the clocking angle.

[0050] In some embodiments, the fuel pins associated with the outer ring 410 of fuel pins have a shorter pitch than the inner rings of fuel pins. In some cases, the two outermost rings have a shorter pitch than the inner rings of fuel pins. In some embodiments, the shorter pitch toward the outer rings increases the pressure drop in the edge and corner subchannels. This has been shown to more uniformly distribute temperature throughout the fuel assembly, resulting in a reduced ΔT and increased exit temperature. In many cases, a significant increase in exit temperature occurs without increasing the peak cladding temperature, providing substantial benefits. For example, in some cases, increasing the pressure drop in the subchannels adjacent to the fuel assembly duct has been shown to increase exit temperature by 20°C. This can result in a 1% increase in plant operating efficiency.

[0051] Additionally, there are numerous advantages over thermal hydraulics. For example, reducing the pitch of the outer ring of fuel pins reduces the pin-duct interaction forces by adding additional contact points along the fuel duct. The pin-duct interaction is spread over a larger surface area due to the additional contact points between the wire and the duct. As a practical result, the fuel pins can undergo increased thermal strain without causing excessive pin-duct interaction.

[0052] With reference to Figure 5, computational fluid dynamics ("CFD") modeling was performed on a 19-pin fuel assembly. Here, the pitch length of the outer ring of fuel pins was modeled as half the pitch length of the inner ring of fuel pins. This results in more flow being directed at an angle away from the main flow direction. This creates a greater pressure drop in the outer channels, and the cooler edge fluid tends to be pushed back into the assembly, away from the edge channels. This results in more efficient coolant mixing and a reduced ΔT throughout the fuel assembly.

[0053] In one example, the outer ring of fuel pins and the penultimate ring of fuel pins were modeled as half-length pitches. max and T avg A 7.6°C reduction occurred between the inner and outer rings of fuel pins. In another example, a pitch of one-quarter the length of the outer ring of fuel pins was modeled compared to the inner rings of fuel pins. This resulted in a 21°C reduction in ΔT. The area of ​​the edge and corner subchannels compared to the area of ​​the interior subchannels is believed to indicate that this approach is also valid for larger bundle sizes (e.g., 169-pin, 217-pin, 271-pin, or other sized bundles).

[0054] In some embodiments, increasing the pressure drop in the edge and corner subchannels forces coolant flow toward the inner subchannels of the fuel bundle. The increased pressure drop may be achieved by providing one or more fuel pins with wire wound at a shorter pitch than the other fuel pins. The increased pressure drop in the edge and corner subchannels may also be achieved by providing one or more fuel pins with wire having a smaller diameter toward the outer ring or the ring next to the outermost ring. Additionally or alternatively, fuel assembly components wound with wire having a smaller diameter may be fabricated with a larger cross-sectional diameter compared to other fuel assembly components with relatively thicker wire. As a result, the edge and corner subchannels become smaller because the fuel assembly components are closer together due to the smaller diameter spacer wire. This further increases the neutron flux (and temperature) at these locations. In other examples, one or more of d-spacers, dummy pins, or other displacement elements may be applied to reduce flow in the edge and corner subchannels, optionally maintaining the same wire pitch across all fuel assembly components.

[0055] While the discussion focuses on the wire wrap pitch of the fuel pins, it should be understood that solutions for multiple-pitch wire-wrapped fuel bundles may also include multiple-pitch wire wrapping of other components within the fuel bundle, such as control rods, parent fuel rods, reflector rods, etc. These terms may also be referred to as "fuel assembly components." Inner fuel assembly components may be wire-wrapped with a first pitch, and outer fuel assembly components may be wire-wrapped with a second pitch that is shorter than the first pitch. Outer fuel assembly components include fuel assembly components located in the outer ring of the plurality of fuel assemblies, the second-to-outermost ring of the plurality of fuel assemblies, and / or the third-to-outermost ring of the plurality of fuel assemblies. For clarity, the second-to-outermost ring refers to the hexagonal ring of the plurality of fuel assembly components adjacent to the outermost ring. The third-to-outermost ring refers to the hexagonal ring of the plurality of fuel assembly components that is third from the outermost ring. The fourth ring from the outermost ring is the fourth hexagonal ring of fuel assembly components from the outermost ring. According to some embodiments, one or more fuel assembly components in the third ring from the outermost ring are wire wrapped at a different pitch than the fuel assembly components in the inner rings. According to some embodiments, one or more fuel assembly components in the fourth ring from the outermost ring are wire wrapped at a different pitch than the fuel assembly components in the inner rings. In some cases, one or more fuel assembly components of the plurality of fuel assembly components in the outer ring, the second ring from the outermost ring, the third ring from the outermost ring, and / or the fourth ring from the outermost ring are wire wrapped at a different pitch than other fuel assembly components in adjacent rings and may be wrapped at a different pitch than fuel assembly components disposed in the inner rings.For example, the inner fuel assembly component may be wire wrapped with a first pitch, the third fuel assembly component from the outermost ring may be wire wrapped with a second pitch that is shorter than the first pitch, the second fuel assembly component from the outermost ring may be wire wrapped with a third pitch that is shorter than the second pitch, and / or the outermost fuel assembly component may be wrapped with a fourth pitch that is shorter than the third pitch.

[0056] In some embodiments, the inner rings are hexagonal rings of the fuel assembly components that are positioned closer to the center of the fuel assembly than the outer rings of the fuel assembly components. According to some embodiments, the inner rings of the fuel assembly components are wire wrapped with a first pitch and the outermost rings of the fuel assembly components are wire wrapped with a second pitch that is less than the first pitch. In some cases, the second from the outermost rings of the fuel assembly components are also wire wrapped with the second pitch.

[0057] As shown in Figure 4, the clocking angle of one or more fuel assembly components may be offset relative to one or more other fuel assembly components to avoid wire-to-wire interference. Solutions may exist for each wire-wrapped fuel assembly that utilizes more than one pitch by varying the clocking angle to avoid wire-to-wire interference. Clocking angle solutions for multiple-pitch wire-wrapped fuel assembly components are shown in Figures 4 and 5. One solution is presented and modeled in Figures 4 and 5, which shows a substantial effect on exit temperatures.

[0058] According to some examples, one or more inner rings of the plurality of fuel assembly components are wire wrapped with a first pitch, an outer ring of the plurality of fuel assembly components is wire wrapped with a second pitch different from the first pitch, and one or more other fuel assembly components is wire wrapped with a third pitch different from the first and second pitches. In some embodiments, the first fuel assembly component is wire wrapped with the first pitch, the second fuel assembly component is wire wrapped with the second pitch, and the third fuel assembly component is wire wrapped with the third pitch. For example, the pitch may be half between the first fuel assembly component, the second fuel assembly component, and the third fuel assembly component. This results in a solution for avoiding wire-to-wire interference between adjacent pins. As an example, one or more internal fuel assembly components may be wire wrapped at a 30 cm pitch, the second to outermost ring of the fuel assembly components may be wire wrapped at a 15 cm pitch (one-half of 30 cm), and the outer ring may be wire wrapped at a 7.5 cm pitch (one-half of 15 cm), which may result in a solution for avoiding wire-to-wire interference between adjacent fuel assembly components.

[0059] In some examples, inner rings of the fuel assembly components are wire wrapped at a first pitch and start at a first clocking angle. According to some embodiments, outermost rings of the fuel assembly components are wire wrapped at a second pitch different from the first pitch and at a variable clocking angle. The variable clocking angle is either a clocking angle equal to the first clocking angle or a clocking angle rotated in 30° or 60° increments from the first clocking angle. In some embodiments, the second pitch is either equal to the first clocking angle or rotated in 30° increments from the first clocking angle. In some embodiments, the second pitch is either equal to the first clocking angle or rotated in 60° increments from the first clocking angle. In some embodiments, the second pitch is either equal to the first clocking angle or rotated in 120° increments from the first clocking angle. In some embodiments, the second pitch may be the same as the first clocking angle or may be rotated from the first clocking angle in 45° increments.

[0060] The described embodiments are particularly relevant to nuclear reactor designs in which the reactor exit temperature may be less than a desired temperature. As described herein, utilizing wire wraps of different pitches on at least some of the fuel pins may increase the exit temperature to the desired exit temperature.

[0061] According to some embodiments, a method for increasing pressure drop in edge and corner sub-channels includes providing fuel assembly components in an outer ring position within the fuel assembly that are wire-wrapped at a second pitch that is smaller than the second pitch at which the fuel assembly components in the inner ring positions are wire-wrapped.

[0062] The present disclosure presents exemplary embodiments. Therefore, the present disclosure is not intended to limit the scope of the embodiments of the present disclosure and the appended claims in any way. The embodiments have been described above with the aid of functional building blocks illustrating implementation of specified functions and relationships thereof. In this specification, the boundaries of these functional components have been arbitrarily defined for the convenience of description. Alternative boundaries may be defined to the extent that the specified functions and relationships thereof are appropriately implemented.

[0063] The general nature of the embodiments of the present disclosure will be sufficiently apparent from the foregoing description of such specific embodiments that others may readily modify and / or adapt the specific embodiments for various applications without undue experimentation by applying the knowledge of those skilled in the art without departing from the general spirit of the embodiments of the present disclosure. Such adaptations and modifications are therefore 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 used herein is intended to be illustrative, not limiting, as the term or terminology would be interpreted by one of ordinary skill in the art in light of the teaching and guidance presented herein.

[0064] The breadth and scope of the presently disclosed embodiments should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

[0065] Unless otherwise specified or understood differently within the context in which they are used, conditional words such as "may," "would," "may," or "may," among others, are generally intended to convey that particular implementations may include particular features, elements, and / or operations, while other implementations do not include particular features, elements, and / or operations. As such, such conditional words generally do not intend that features, elements, and / or operations are in any way required in one or more implementations, or that logic for determining whether these features, elements, and / or operations are included in any particular implementation, or whether these features, elements, and / or operations should be performed in any particular implementation, with or without user input or prompting, is necessarily included in one or more implementations.

[0066] The specification and accompanying drawings disclose examples of systems, apparatus, devices, and techniques that can provide control and optimization of separation equipment. It is, of course, impossible to describe every conceivable combination of elements and / or methodologies for purposes of describing various features of the present disclosure. However, those skilled in the art will recognize that many additional combinations and permutations of the disclosed features are possible. Accordingly, various modifications can be made to the present disclosure without departing from the scope or spirit of the present disclosure. Moreover, other embodiments of the present disclosure will become apparent from consideration of the specification and accompanying drawings and from the practice of the disclosed embodiments presented herein. The examples presented in the specification and accompanying drawings are to be considered in all respects as illustrative and not restrictive. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

[0067] Those skilled in the art will understand that in some implementations, the functionality provided by the processes, systems, and configurations discussed above may be provided in alternative ways. The various methods, configurations, and arrangements shown and described herein represent exemplary embodiments. From the foregoing, it will be understood that, while specific implementations have been described herein for illustrative purposes, various modifications may be made without departing from the spirit and scope of the appended claims and the requirements recited therein. In addition, while certain aspects are presented below in certain claim forms, the inventors contemplate various aspects in any available claim form. For example, while only some aspects may currently be described as embodied in a particular configuration, other aspects may similarly be embodied in such a manner. Various modifications and changes may be made as would be apparent to those skilled in the art having the benefit of this disclosure. All such modifications and changes are intended to be encompassed. The foregoing description, therefore, should be considered in an illustrative, rather than a limiting, sense. [Brief explanation of the drawings]

[0068] [Figure 1] FIG. 2 is a schematic diagram of a wire-wrapped fuel pin according to some embodiments. [Figure 2] 1 is a cross-sectional view of a nuclear fuel assembly or a nuclear fission module according to some embodiments. [Figure 3] FIG. 10 is a cross-sectional view of multiple side-by-side hexagonal shaped fission modules, according to some embodiments. [Figure 4] 1 illustrates a cross-sectional view of a plurality of rods, according to some embodiments. [Figure 5] 10 shows computational fluid dynamics results illustrating improved thermal-hydraulic performance according to some embodiments.

Claims

1. A fuel assembly for a nuclear reactor, comprising: a first set of fuel assembly components forming an inner ring of the fuel assembly; a second set of fuel assembly components forming an outermost ring of the fuel assembly; and Including, each of the plurality of fuel assembly components having a longitudinal axis and wire wrappings in the same rotational direction about the longitudinal axis; the wire wrapping of each fuel assembly component of the first set has a first pitch; the wire wrapping of each fuel assembly component of the second set has a second pitch that is shorter than the first pitch and is formed from a single wire; 10. A fuel assembly, wherein the wire wrapping of each of a plurality of the fuel assembly components has a clocking angle that avoids contact with wire wrapping of an adjacent fuel assembly component.

2. 2. The fuel assembly of claim 1, wherein the inner ring is the second ring from the outermost ring of the fuel assembly.

3. A fuel assembly for a nuclear reactor, comprising: a first set of fuel assembly components forming an inner ring of the fuel assembly; a second set of fuel assembly components forming an outermost ring of the fuel assembly; and Including, each of the plurality of fuel assembly components having a longitudinal axis and wire wrappings in the same rotational direction about the longitudinal axis; the wire wrapping of each fuel assembly component of the first set has a first pitch; the wire wrapping of each fuel assembly component of the second set has a second pitch that is shorter than the first pitch and is formed from a single wire; a wire of the wire wrapping of each fuel assembly component of the first set has a first diameter; a wire of the wire wrapping of each fuel assembly component of the second set has a second diameter smaller than the first diameter; a cross-sectional dimension of each fuel assembly component of the second set that is greater than a cross-sectional dimension of each fuel assembly component of the first set.

4. 3. The fuel assembly of claim 1, wherein the fuel assembly comprises fissile fuel.

5. 3. The fuel assembly of claim 1, wherein the fuel assembly comprises a parent fuel.

6. further comprising a neutron absorber; 3. The fuel assembly of claim 1, wherein the neutron absorber comprises a wire wrapping having the second pitch.

7. 1. A method for increasing pressure drop of a coolant fluid within a nuclear fuel assembly in an edge subchannel, comprising: placing a first fuel assembly component within an inner ring of the nuclear fuel assembly; placing a second fuel assembly component within an outermost ring of the nuclear fuel assembly; the first fuel assembly component is wire wrapped in a first rotational direction at a first pitch; the second fuel assembly component is wire wrapped with a single wire in the first rotational direction at a second pitch that is smaller than the first pitch; wherein placing the first fuel assembly component further includes positioning the first fuel assembly component to have a first clocking angle that avoids contact with wire wrapping of an adjacent fuel assembly component; the step of positioning the second fuel assembly component further comprises positioning the second fuel assembly component to have a second clocking angle that avoids contact with wire wrapping of an adjacent fuel assembly component.

8. disposing a second fuel assembly component within an outermost ring of the nuclear fuel assembly includes disposing a plurality of second fuel assembly components within the outermost ring of the nuclear fuel assembly; each of the plurality of second fuel assembly components is wire wrapped with one wire in the first rotational direction at the second pitch; 8. The method of claim 7, wherein arranging the plurality of second fuel assembly components further comprises positioning the plurality of second fuel assembly components to have a clocking angle that avoids contact with wire wrapping of adjacent fuel assembly components.

9. further comprising disposing a third fuel assembly component within a second to outermost ring of the nuclear fuel assembly; the third fuel assembly component is wire wrapped in the first rotational direction at the second pitch; 8. The method of claim 7, wherein placing the third fuel assembly component further comprises positioning the third fuel assembly component to have a third clocking angle that avoids contact with wire wrapping of an adjacent fuel assembly component.

10. The method of claim 7 , wherein the second pitch includes twice the number of turns of the first pitch.

11. 8. The method of claim 7, wherein the second pitch includes four times as many turns as the first pitch.

12. 8. The method of claim 7, wherein the second fuel assembly component includes a second wire wrap at the second pitch.

13. 8. The method of claim 7, wherein the first fuel assembly component comprises one or more of the following components: fissile fuel, fertile fuel, a neutron absorber, or a neutron reflector.

14. further comprising disposing a third fuel assembly component within a second to outermost ring of the nuclear fuel assembly; the third fuel assembly component is wire wrapped at a third pitch in the first rotational direction; the third pitch is smaller than the first pitch and larger than the second pitch; 8. The method of claim 7, wherein placing the third fuel assembly component further comprises positioning the third fuel assembly component to have a third clocking angle that avoids contact with wire wrapping of an adjacent fuel assembly component.

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