Patent Description:
Molten fluoride fuel salts suitable for use in nuclear reactors have been developed using uranium tetrafluoride (UF<NUM>) mixed with other fluoride salts as well as using fluoride salts of thorium. Molten fluoride salt reactors have been operated at average temperatures between <NUM> and <NUM>. Binary, ternary, and quaternary chloride fuel salts of uranium, as well as other fissionable elements, have been described in co-assigned <CIT>, titled MOLTEN NUCLEAR FUEL SALTS AND RELATED SYSTEMS AND METHODS. In addition to chloride fuel salts containing one or more of UCl<NUM>, UCl<NUM>F, UCl<NUM>, Ul<NUM>F<NUM>, and UClF<NUM>, the application further discloses fuel salts with modified amounts of <NUM>Cl, bromide fuel salts such as UBr<NUM> or UBr<NUM>, thorium chloride fuel salts, and methods and systems for using the fuel salts in a molten fuel reactor. Average operating temperatures of chloride salt reactors are anticipated between <NUM> and <NUM>, but could be even higher, e.g., > <NUM>. <CIT> discloses various configurations and components of a molten fuel fast or thermal nuclear reactor for managing the operating temperature in the reactor core. <CIT> discloses a single fluid molten salt nuclear breeder reactor.

Molten fuel reactors and orifice ring plates for molten fuel reactors are described herein. The orifice ring plate is disposed within a low power region of a reactor core and proximate inlet channels that channel fuel salt into the reactor core. The orifice ring plate is oriented substantially orthogonal to the flow of fuel salt and is configured to balance and distribute the flow of fuel salt that enters into an active core region. By conditioning fuel salt flow within the reactor core, stability of the fuel salt flow is increased, which increases temperature uniformity and performance of the reactor. The orifice ring plate is coaxial with the right-circular cylinder shaped reactor core and is configured to direct fuel salt along the sides of the reactor core, direct fuel salt through the plate to provide flow distribution in the azimuthal direction, and allow fuel salt to flow below the plate to reduce or prevent centerline recirculation in the reactor core.

These and various other features as well as advantages which characterize the molten fuel reactors and orifice ring plates described herein will be apparent from a reading of the following detailed description and a review of the associated drawings. Additional features are set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the technology. The benefits and features of the technology will be realized and attained by the structure in the written description and claims hereof, as well as the appended drawings.

It is to be understood that both the foregoing introduction and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

The following drawing figures, which form a part of this application, are illustrative of described technology and are not meant to limit the scope of the technology as claimed in any manner, which scope shall be based on the claims appended hereto.

This disclosure describes molten fuel reactors and orifice ring plates for molten fuel reactors. The orifice ring plate is disposed within a low power region of a reactor core and proximate inlet channels that channel fuel salt into the reactor core. The orifice ring plate is oriented substantially orthogonal to the flow of fuel salt and is configured to balance and distribute the flow of fuel salt that enters into an active core region. By conditioning fuel salt flow within the reactor core, stability of the fuel salt flow is increased, which increases temperature uniformity and performance of the reactor.

In aspects, the orifice ring plate is coaxial with the right-circular cylinder shaped reactor core. The orifice ring plate has a top solid portion that acts a deflector vane to direct fuel salt along side reflectors that define the reactor core and to reduce or prevent reflector recirculation. One or more apertures are formed within the plate that allow fuel salt to flow through the plate and provide flow distribution in the azimuthal direction within the reactor core. Additionally, the plate is configured to allow fuel salt to flow below the plate to reduce or prevent centerline recirculation in the reactor core and support fuel salt drainage from the inlet channel. In aspects, a height of the orifice ring plate is approximately equal to a height of the inlet channel. However, an inside lower corner of the side reflectors that form a boundary between the inlet channel and the reactor core is curved so that fuel salt can flow above the orifice ring plate. In aspects, a radius of the curved corner is about one-third of the height of the inlet channel. Furthermore, the orifice ring plate is spaced from the inlet channel so that fuel salt flow between multiple inlet channels can be balanced upstream of the plate.

As used herein, the terms "axial" and "longitudinal" refer to directions and orientations, which extend substantially parallel to a centerline of the reactor core and the orifice ring plate. Moreover, the terms "radial" and "radially" refer to directions and orientations, which extend substantially perpendicular to the centerline of the reactor core and the orifice ring plate. In addition, as used herein, the term "circumferential" and "circumferentially" refer to directions and orientations, which extend arcuately about the centerline of the reactor core and the orifice ring plate.

This disclosure describes various configurations and components of a molten fuel nuclear reactor. For the purposes of this application, examples of a molten fuel reactor that use a chloride fuel will be described. However, it will be understood that any type of fuel salt, now known or later developed, may be used and that the technologies described herein may be equally applicable regardless of the type of fuel used, such as, for example, salts having one or more of U, Pu, Th, or any other actinide. Note that the minimum and maximum operational temperatures of fuel within a reactor may vary depending on the fuel salt used in order to maintain the salt within the liquid phase throughout the reactor. Minimum temperatures may be as low as <NUM>-<NUM> and maximum temperatures may be as high as <NUM> or higher.

<FIG> illustrates, in a block diagram form, some of the basic components of a molten fuel reactor <NUM>. In general, the molten fuel reactor <NUM> includes a reactor core <NUM> containing a fissionable fuel salt <NUM> that is liquid at the operating temperature. Fissionable fuel salts include salts of any nuclide capable of undergoing fission when exposed to low-energy thermal neutrons or high-energy neutrons. Furthermore, for the purposes of this disclosure, fissionable material includes any fissile material, any fertile material or combination of fissile and fertile materials. The fuel salt <NUM> may or may not completely fill the core <NUM>, and the example shown is illustrated with an optional headspace <NUM> above the level of the fuel salt <NUM> in the core <NUM>. The size of the reactor core <NUM> may be selected based on the characteristics and type of the particular fuel salt <NUM> being used in order to achieve and maintain the fuel in an ongoing state of criticality, during which the heat generated by the ongoing production of neutrons in the fuel causes the temperature of the molten fuel to rise when it is in the reactor core <NUM>. The performance of the reactor <NUM> is improved by providing one or more reflectors <NUM> around the core <NUM> to reflect neutrons back into the core. As illustrated, the reactor <NUM> may include an upper reflector <NUM>, a lower reflector <NUM>, and at least one radial side reflector <NUM>. Additionally, the reflectors <NUM> may shield components positioned radially outward from the core <NUM>. The molten fuel salt <NUM> is circulated in a fuel loop <NUM> between the reactor core <NUM> and one or more primary heat exchangers <NUM> located outside of the core <NUM>. The circulation may be performed using one or more pumps <NUM>.

The primary heat exchangers <NUM> transfer heat from the molten fuel salt <NUM> to a primary coolant <NUM> that is circulated through a primary coolant loop <NUM>. In an example, the primary coolant may be another salt, such as NaCl-MgCh, lead, or other liquid metal. Other coolants are also possible including Na, NaK, Na mixtures, supercritical CO<NUM>, liquid lead, and lead bismuth eutectic. In the example, the radial side reflector <NUM> extends between the upper reflector <NUM> and the lower reflector <NUM> and is positioned between each primary heat exchanger <NUM> and the reactor core <NUM> as shown in <FIG>. In an aspect, the reactor core <NUM> has substantially a right-circular cylinder shape with a diameter of <NUM> meters (m) and a height of <NUM> or greater, and is oriented vertically along a longitudinal axis <NUM> so that the flat ends of the cylinder are on the top and bottom, and adjacent the upper reflector <NUM> and the lower reflector <NUM>, respectively. The radial side reflectors <NUM> are substantially parallel to the longitudinal axis <NUM> and at least partially define an inner diameter <NUM> of the reactor core <NUM>.

The entire reactor core <NUM> is surrounded by reflectors <NUM> between which are provided radial channels for a flow of fuel salt <NUM> into (e.g., inlet channels <NUM>) and out (e.g., outlet channels <NUM>) of the reactor core <NUM>. In an aspect, eight side reflectors <NUM> and primary heat exchangers <NUM> are circumferentially spaced around the reactor core <NUM> and about the longitudinal axis <NUM>, with each primary heat exchanger <NUM> provided with the pump <NUM> to drive circulation of the fuel salt <NUM> and generate the fuel loop <NUM>. In alternative examples, a different number of side reflectors <NUM> and primary heat exchangers <NUM> may be used as required or desired. For example, examples having <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> reflectors and primary heat exchangers are contemplated. Additionally, in some examples, circulation of the fuel salt <NUM> may be naturally driven (e.g., fuel circulation via the density differential created by the temperature differences within the fuel loop). This configuration can obviate the need for fuel salt pumps <NUM>. Furthermore, it should be appreciated that while the inlet channel <NUM> is shown adjacent the lower reflector <NUM> in <FIG>, the fuel loop <NUM> can be reversed and the inlet channel <NUM> can be adjacent the upper reflector <NUM> as required or desired.

In the embodiment shown in <FIG>, in normal (power generating) operation, the fuel salt <NUM> is pumped from the reactor core <NUM>, through the primary heat exchanger <NUM>, and cooled fuel salt <NUM> is returned back to reactor core <NUM>. Heated primary coolant <NUM> from the primary heat exchangers <NUM> is passed to a power generation system <NUM> for the generation of some form of power, e.g., thermal, electrical or mechanical. The reactor core <NUM>, primary heat exchangers <NUM>, pumps <NUM>, molten fuel circulation piping (including other ancillary components that are not shown such as check valves, shutoff valves, flanges, drain tanks, etc.) and any other components through which the molten fuel circulates or contacts during operation can be referred to as the fuel loop <NUM>. Likewise, the primary coolant loop <NUM> includes those components through which primary coolant circulates, including the primary heat exchangers <NUM>, primary coolant circulation piping (including other ancillary components that are not shown such as coolant pumps <NUM>, check valves, shutoff valves, isolation valves, flanges, drain tanks, etc.).

Salt-facing elements of the molten fuel reactor may be formed and/or clad to protect against corrosion. Other protection options include protective coatings, loose fitting liners, or press-fit liners. Based on the operating conditions, which will at least in part be dictated by the fuel selection, any suitable high temperature and corrosion resistant steel, such as, but not limited to, <NUM> stainless, HT-<NUM>, a molybdenum alloy, a zirconium alloy (e.g., ZIRCALOY™), SiC, graphite, a niobium alloy, nickel or alloy thereof (e.g., HASTELLOY™), or high temperature ferritic, martensitic, stainless steel, or the like, may be used.

The molten fuel reactor <NUM> further includes at least one containment vessel <NUM> that contains the fuel loop <NUM> to prevent a release of molten fuel salt <NUM> in case there is a leak from one of the fuel loop components. The containment vessel <NUM> is often made of two components: a lower, vessel portion <NUM> that takes the form of a unitary, open-topped vessel with no penetrations of any kind; and an upper, cap portion <NUM> referred to as the vessel head that covers the top of the vessel portion <NUM>. All points of access to the reactor <NUM> are from the top through the vessel head <NUM>.

Broadly speaking, this disclosure describes multiple alterations and component configurations that improve the performance of the reactor <NUM> described with reference to <FIG>. For example, when the flow of fuel salt <NUM> within the fuel loop <NUM> enters the reactor core <NUM> from the inlet channel <NUM>, the flow turns sharply (e.g., approximately <NUM>°) to flow in an upward direction through the core <NUM>. This change of direction of the flow of fuel salt <NUM> and the relative cross-section of the incoming channels as compared to the diameter of the core region can induce formation of jet-like flow recirculation vortexes and flow behavior that reduces performance of the molten fuel reactor <NUM>. These recirculation vortexes result in relatively stationary flow within the middle of the vortex that heats up, and via buoyancy, the fuel salt can move through the reactor core and induce unstable flow and possibly reactivity instabilities within the fuel loop <NUM>. With respect to reactor core's that have a right-circular cylinder shape and high flow rates, these vortexes can be formed along an inside wall of the side reflector <NUM> and proximate the lower corner with the inlet channel <NUM>.

In some known reactor configurations, the shape and size of the reactor core and the inlet channel has been modified to reduce the sharp corners in the fuel loop. For example, the reactor core can take on a more hourglass shape with a modified inlet channel. These reactor cores, however, increase the volume of the reactor core, which then requires more fuel salt. In other known reactor configuration, a horizontal plate (e.g. in relation to the longitudinal axis) is positioned across the reactor core. This plate, however, is positioned close to the active core and absorbs a large amount of neutrons, and thereby also increases the amount of fuel salt required. Accordingly, a flow conditioner as described further below is disposed within the reactor core <NUM> and proximate the inlet channels <NUM> within a low power region of the core. The flow conditioner ensures the fuel salt flows entering the active core are well-distributed, without jet-like behavior or major recirculations, as the flow turns the corner inside the lower edge of the reflector <NUM>. In the examples described herein, the flow conditioner is an orifice ring pate designed to optimize the flow, and thus, the heat distribution of the fuel salt <NUM> as it flows through the core. In additional or alternative examples, the flow conditioner may take an alternative form such as directional baffles, tube bundles, honeycombs, porous materials, and the like. The flow conditioner also reduces the impact of reactor geometry so that the volume of fuel salt needed for operation is not increased.

It should be appreciated that the molten fuel reactor <NUM> described in <FIG> can take many different forms. For example, the reactor <NUM> can be a molten chloride fast reactor that is used to generate power as described above. In other examples, the reactor <NUM> can be a reactor that does not generate power and that only generates heat. This reactor can be utilized to study the fuel salt <NUM> as required or desired.

<FIG> is a perspective sectional view of one possible physical implementation of a reactor core system <NUM>. In this example, the reactor core system <NUM> includes a single molten salt pump assembly <NUM> to circulate fuel salt through a central active core <NUM> and into four individual flow channels <NUM> that define a flow loop <NUM> of fuel salt. The flow loop <NUM> is described in further detail in <FIG> below. The pump assembly <NUM> includes a pump motor <NUM>, a pump flange <NUM>, and a pump impeller <NUM>. Rotation of the impeller <NUM> drives the flow of fuel salt upward through the core <NUM> and downward within the flow channels <NUM> and along an interior surface of a reactor vessel <NUM>. In alternative examples, the flow direction may be reversed as required or desired. The reactor vessel <NUM> can include fins <NUM> on the exterior surface to assist in transferring heat from the reactor vessel <NUM>. As such, in this example a primary coolant loop is not provided and power is not generated from the reactor core system <NUM>.

Within the reactor vessel <NUM> one or more reflectors surround the active core <NUM>. In this example, a lower reflector <NUM> is disposed on the bottom side of the core <NUM> and one or more side reflectors <NUM> surround the lateral sides of the core <NUM>. Additionally, a vessel head <NUM> acts as a reflector at the top side of the core <NUM>. In other examples, an upper reflector may be disposed adjacent the vessel head <NUM>. The reactor core system <NUM> also includes one or more independently rotated control drums <NUM>. In this example, there are four control drums <NUM> that are cylinders of a reflector material with a partial face made of a neutron absorber <NUM>. The side reflectors <NUM> define a receiving space for each control drum <NUM> so that the control drums <NUM> can be inserted into the reactor vessel <NUM> adjacent the active core <NUM>. The control drums <NUM> can be independently rotated within the reflector <NUM> so that the neutron absorber <NUM> is closer to or farther away from the active core <NUM>. This controls the amount of neutrons that are reflected back into the core <NUM>, and thus, available for fission. When the absorber <NUM> is rotated to be in proximity to the core <NUM>, neutrons are absorbed rather than reflected and the reactivity of the reactor is reduced. Through the rotation of the control drums <NUM>, the reactor may be maintained in a state of criticality, subcriticality, or supercriticality, as required or desired.

Additionally, an orifice ring plate <NUM> is disposed within the active core <NUM> and proximate the inlet flow of fuel salt from the flow channels <NUM>, adjacent the lower reflector <NUM>. The orifice ring plate <NUM> is configured to condition the flow of fuel salt entering the active core <NUM> so as to reduce or eliminate fuel salt flow recirculation inside the lower active core region. The orifice ring plate <NUM> is described in further detail below.

<FIG> is a perspective view of the fuel salt flow loop <NUM> of the reactor core system <NUM> (shown in <FIG>). <FIG> is an enlarged partial perspective view of the exemplary orifice ring plate <NUM> and an inlet channel <NUM> of the fuel salt flow loop <NUM>. <FIG> is an enlarged partial perspective view of the orifice ring plate <NUM>. Referring concurrently to <FIG>, the components of the reactor core system from <FIG> have been removed to detail the fuel salt flow loop <NUM> and the orifice ring plate <NUM>. The flow loop <NUM> is full of fuel salt and the flow direction is illustrated by arrows <NUM>. The flow loop <NUM> is defined by the active core <NUM>, which is substantially a right-circular cylinder shape, and the flow channels <NUM> that are formed around the side reflectors <NUM> (shown in <FIG>).

In this example, four flow channels <NUM> are circumferentially spaced around the active core <NUM>, and include a radially extending inlet channel <NUM> configured to channel fuel salt into a lower portion of the active core <NUM> and a radially extending outlet channel <NUM> configured to channel fuel salt out of an upper portion of the active core <NUM>. Each inlet channel <NUM> and outlet channel <NUM> are coupled in flow communication with an axial channel <NUM> that is substantially parallel to the active core <NUM>, but separated from the core by one or more of the reflectors (not shown). As illustrated in <FIG>, each of the four flow channels <NUM> are discrete and spaced apart from one another. It should be appreciated that any other number of discrete flow channels can be utilized as required or desired. In some examples, a portion (e.g., the inlet channel, the outlet channel, and/or the axial channel) of each of the flow channels <NUM> may be coupled in flow communication with each other so that the fuel salt flow can be balanced prior to entering the active core <NUM>. Additionally, in an aspect, the fuel salt flow loop <NUM> may include a single flow channel that extends approximately <NUM>° around the active core <NUM> so that the fuel salt flow can be balanced prior to entering the core. Upstream of the outlet channel <NUM> directing vanes <NUM> are provided so as to condition the fuel salt flow coming out of the pump assembly <NUM> (shown in <FIG>).

In some examples, a flow restriction device <NUM> configured to control the flow of fuel salt may be located in one or more of the flow channels <NUM>. As illustrated in <FIG>, the flow restriction device <NUM> is located at the top of one of the four fuel salt flow channels <NUM> between the active core <NUM> and the reactor vessel. Although only one flow restriction device <NUM> is shown, in alternative examples, some of the other, or all of the other, flow channels <NUM> may be furnished with such devices. The flow restriction device <NUM> can include a valve, a gate valve, sluice gate, pinch valve, or the like, and allows the flow rate of the fuel salt to be reduced with the channel <NUM>. Additionally, an expansion volume <NUM> is provided for the fuel salt at least partially within the pump assembly <NUM>. The expansion volume <NUM> allows heated fuel salt to expand and enter the volume during reactor operation. The volume <NUM> can be filled with an inert gas and have a cover gas management system (not shown) to control the pressure of the gas within the expansion volume <NUM> and clean the gas as required or desired.

The orifice ring plate <NUM> is disposed within the active core <NUM> and proximate the inlet channels <NUM>. The orifice ring plate <NUM> extends circumferentially about a longitudinal axis <NUM> of the active core <NUM> and includes a top end <NUM> and a bottom end <NUM>. As contemplated herein, the orifice ring plate <NUM> can be circular or substantially circular, whereby the ring plate <NUM> is formed from a plurality of linear sections that when coupled together form a ring like shape. When the orifice ring plate <NUM> is within the active core <NUM>, an axial axis of the orifice ring plate <NUM> aligns with the longitudinal axis <NUM> of the active core <NUM> so that the core <NUM> and the plate <NUM> are coaxial. The top end <NUM> and the bottom end <NUM> extend is a direction along the longitudinal axis <NUM> such that the orifice ring plate <NUM> is substantially parallel to the longitudinal axis <NUM> of the active core <NUM>. The top end <NUM> and the bottom end <NUM> define a height H<NUM> of the orifice ring plate <NUM>. The orifice ring plate <NUM> has a plurality of first apertures <NUM> that are configured to allow a flow of fuel salt through the plate, and the greater number of apertures <NUM> the more fuel salt is allowed to flow through the plate. In the example, the first apertures <NUM> are circumferentially spaced around the orifice ring plate <NUM> and extend in a radial direction relative to the longitudinal axis <NUM>. In an aspect, the apertures <NUM> are spaced approximately every <NUM>°. The first apertures <NUM> are substantially circular in shape, however, it is appreciated that the shape of the apertures can have any other shape (e.g., oval, rectangular, etc.) that enables the orifice ring plate <NUM> to function as described herein.

In the example, the orifice ring plate <NUM> is downstream of the inlet channel <NUM> and at least partially covers the inlet channel <NUM> with respect to the active core <NUM>. In an aspect, the bottom end <NUM> of the orifice ring plate <NUM> is directly adjacent the lower reflector <NUM> (shown in <FIG>). In other aspects, the bottom end <NUM> of the orifice ring plate <NUM> may be offset and raised above the lower reflector <NUM> so that a gap is formed between the bottom end <NUM> and the lower reflector <NUM>. Additionally, the orifice ring plate <NUM> has an inner radial surface <NUM> and an opposite outer radial surface <NUM>. The outer radial surface <NUM> faces the inlet channel <NUM>. The inner radial surface <NUM> is axially aligned with an inner circumferential perimeter <NUM> of the active core <NUM> formed by the reflectors. That is, the inner radial surface <NUM> has a diameter <NUM> that is approximately equal to an inner diameter <NUM> of the core <NUM>. The inner diameter <NUM> of the core <NUM> is formed at least partially by the side reflectors <NUM> (shown in <FIG>). Because the orifice ring plate <NUM> has a thickness Ti, the diameter of the outer radial surface <NUM> is greater than the inner diameter <NUM> of the core <NUM>.

The inlet channels <NUM> and the outlet channels <NUM> extend in a radial direction relative to the longitudinal axis <NUM> of the active core <NUM>. The inlet channels <NUM>, however, are radially offset <NUM> from the circumferential perimeter <NUM> of the active core <NUM>. As such, an upstream gap <NUM> in the radial direction is formed between the inlet channel <NUM> and the outer radial surface <NUM> of the orifice ring plate <NUM>. The gap <NUM> enables each of the inlet channels <NUM> to be in flow communication with each other upstream of the orifice ring plate <NUM> and increase flow distribution around the perimeter <NUM> of the active core <NUM>. By allowing the fuel salt flow from each of the inlet channels <NUM> to be balanced prior to entering the active core <NUM> (because flow velocities in each inlet channel may be different), flow imbalance within the core <NUM> is reduced or prevented.

The inlet channel <NUM> has a perimeter <NUM> at the active core <NUM>. The perimeter <NUM> has a height H<NUM> and a width W<NUM>. In the example, the height H<NUM> of the orifice ring plate <NUM> is approximately equal to the height H<NUM> of the inlet channel <NUM>. This size and shape of the orifice ring plate <NUM> would generally completely cover the inlet channel <NUM>, however, an intersection edge <NUM> of the inlet channel <NUM> and the active core <NUM> is rounded and has a radius <NUM>. In the example, the side reflectors <NUM> defines the boundary of the flow loop <NUM> between the inlet channel <NUM> and the active core <NUM>. As such, the side reflectors <NUM> have a lower inside corner <NUM> (shown in <FIG>) that has a rounded surface and which corresponds to the radius <NUM>. In an aspect, an aspect ratio (e.g., the ratio of width to height) of the inlet channel <NUM> at least partially defines the radius <NUM>. For example, for inlet channel geometries with an aspect ratio about <NUM>, the radius <NUM> may be about one-third of the height H<NUM> of the inlet channel <NUM>. In the example illustrated in <FIG>, the inlet channel <NUM> is relatively narrow (e.g., the width W<NUM> greater than the height H<NUM>), and as such, the radius <NUM> is greater than one-third of the height H<NUM> so that the rounding radius of edge <NUM> is increased.

In operation and during flow of fuel salt within the flow loop <NUM>, the position of the orifice ring plate <NUM> enables the fuel salt exiting the inlet channel <NUM> to flow above the plate <NUM>, through the plate <NUM> via the first apertures <NUM>, and below the plate <NUM> in order to enter the active core <NUM>. The first apertures <NUM> are offset from the top end <NUM> of the orifice ring plate <NUM> such that a solid portion <NUM> is formed. The solid portion <NUM> induces at least a portion of the fuel salt to flow above the orifice ring plate <NUM>, and the larger the solid portion <NUM> the more flow is directed above the plate <NUM>. Additionally, the bottom end <NUM> has a plurality of second apertures <NUM> that are partially defined in the plate <NUM> and that are configured to allow fuel salt to flow under the bottom of the plate. In the example, the second apertures <NUM> are circumferentially spaced around the orifice ring plate <NUM> and extend in a radial direction relative to the longitudinal axis <NUM>. The second apertures <NUM> are substantially semi-circular in shape, however, it is appreciated that the shape of the apertures can have any other shape (e.g., oval, rectangular, etc.) that enables the orifice ring plate <NUM> to function as described herein.

In the example, the first apertures <NUM> form a row of apertures with a centerline positioned along the height H<NUM> of the plate <NUM>. The first apertures <NUM> are similarly sized and shaped and are equally circumferentially spaced. The second apertures <NUM> also form a row of apertures with a centerline positioned along the height H<NUM> of the plate <NUM> but offset from the row of first apertures <NUM> so that they do not axially overlap. The second apertures <NUM> are similarly sized and shaped and are equally circumferentially spaced. The row of first apertures <NUM> are circumferentially offset from the row of second apertures <NUM> so that the first apertures <NUM> are positioned between the second apertures <NUM> and vice-versa. In other examples, the apertures <NUM>, <NUM> may have different sizes and/or shapes as required or desired. The apertures <NUM>, <NUM> may also have different dimensions (e.g., diameter for a circular apertures) as needed in either the circumferential and/or axial directions of the orifice ring plate <NUM> so as to provide the desired flow distribution corrections for target conditions of interest.

<FIG> is a fuel salt flow vector plot for the fuel salt flow loop <NUM> shown in <FIG>. <FIG> is a fuel salt flow vector and temperature plot for the fuel salt flow loop <NUM> shown in <FIG>. Referring concurrently to <FIG>, certain components are described above, and thus, are not necessarily described further. From fuel salt modeling, the orifice ring plate <NUM> enables fuel salt flow to be balanced and distributed when entering the active core <NUM> so as to increase reactor performance. For example, a portion of the flow is directed in an upwards direction from the inlet channel <NUM> and reduces or prevents flow recirculation along the inner perimeter <NUM> of the active core <NUM>. A portion of the flow is channeled through the orifice ring plate <NUM> to distribute flow in the azimuthal direction. Additionally, a portion of the flow is channeled under the orifice ring plate <NUM> to reduce or prevent recirculation proximate the centerline of the active core <NUM>.

Turning first to <FIG>, the vector plot illustrates fuel salt flow velocity through the orifice ring plate <NUM>. The orifice ring plate <NUM> enables fuel salt to pass through the plate <NUM> (e.g., via apertures <NUM>) so as to provide flow distribution in the azimuthal direction, enables fuel salt to go over the plate <NUM> and up the reflector wall to reduce or prevent flow recirculation, and enable fuel salt to go below the plate <NUM> to reduce or prevent centerline recirculation and enable fuel salt drainage from the inlet channel <NUM>. Generally, the largest flow velocity of the fuel salt is retained by going over the top of the orifice ring plate <NUM>. The reactor modeled has a flow velocity of fuel salt that is considered to be low and is generally around <NUM> meter/second. Because of the low flow velocity, more flow is directed through the orifice ring plate <NUM> since flow recirculations are not very large.

Additionally, the fuel salt flow velocity upstream and downstream of the orifice ring plate <NUM> is substantially maintained. In the example, the pressure drop across the orifice ring plate <NUM> is less than or equal to approximately <NUM> kilopascal (kPa). In other examples, the pressure drop is less than or equal to approximately <NUM> kPa. Generally, pressure drop across the orifice ring plate <NUM> is between about <NUM>-<NUM>% of the overall fuel salt flow loop pressure. By reducing the pressure drop across the orifice ring plate <NUM>, flow velocity of the fuel salt within the flow loop <NUM> is improved and performance of the active core <NUM> is increased. Additionally, reducing the pressure drop across the orifice ring plate <NUM> increases the efficiency of the pump assembly <NUM> (shown in <FIG>) that induces the flow of fuel salt. The orifice ring plate <NUM> as described herein enables a variety of parameters (e.g., height, size of apertures, aperture spacing, solid portion sizes, etc.) to be tuned so that the plate <NUM> can increase performance of the reactor.

Turning now to <FIG>, the vector plot illustrates fuel salt flow velocity through the entire flow loop <NUM>, and the orifice ring plate <NUM> enables the fuel salt to maintain its velocity throughout the loop <NUM> more effectively because flow recirculations are reduced or prevented. For example, if there is not even pressure distribution within the core and there is increased flow pressure in the center, recirculations are induced at the sides of the core. Conversely, with increased flow pressure on the sides, recirculations are induced at the center of the core. Additionally, temperature distribution of the fuel salt within the active core <NUM> improves because flow recirculations are reduced or prevented. Accordingly, the orifice ring plate <NUM> improves performance of a molten fuel reactor.

<FIG> is a partial perspective view of another orifice ring plate <NUM> and an inlet channel <NUM> of another fuel salt flow loop <NUM>. In this example, the flow loop <NUM> includes a reactor core <NUM> that is substantially a right-circular cylinder shape with the inlet channel <NUM> proximate the bottom. The inlet channel <NUM> is connected to a channel <NUM> that includes a heat exchanger (not shown) and is on the opposite side of a reflector (now shown) from the reactor core <NUM>. The flow loop <NUM> in this example has eight inlet channels <NUM> that channel fuel salt into the reactor core <NUM>. The inlet channel <NUM> has an aspect ratio (e.g., width to height ratio) that is not as severe at the inlet channel described above in reference to <FIG>, however, fuel salt flow velocities are significantly higher (e.g., around <NUM> meters/second). As such, an edge <NUM> between the inlet channel <NUM> and the reactor core <NUM> has a radius <NUM> that is about one-third of the height of the inlet channel <NUM>.

In this example, the orifice ring plate <NUM> has a top end <NUM> that is formed with a solid portion and a bottom end <NUM> that has a plurality of second apertures <NUM> that are partially defined within the plate <NUM>. In this example, however, the bottom end <NUM> of the plate <NUM> is raised above the lower reflector (not shown) by a longitudinal offset <NUM>. This offset <NUM> allows more fuel salt to pass under the orifice ring plate <NUM> to avoid centerline recirculation and support drainage in higher flow velocities. Additionally, a plurality of first apertures <NUM> are fully defined within the plate <NUM>. In this example, the first apertures <NUM> are formed in two rows that are circumferentially offset from one another. By having two rows of apertures <NUM> more fuel salt can pass through the plate <NUM> to provide flow distribution in the reactor core <NUM>.

In an aspect, the configuration of the orifice ring plate <NUM> may be as follows. An original height of the plate <NUM> is set to be approximately equal to the height of the inlet channel <NUM> and four rows of apertures are sized within the plate <NUM>. As such, the diameter of the apertures may be at least partially based on the height of the inlet channel <NUM>. Then the top row of apertures are removed to form the solid portion at the top end <NUM>. In this example, because of the larger flow rate of the fuel salt, the solid portion is larger than the examples described above so that more flow is directed up the sides of the reactor core <NUM> since recirculations are larger. At the bottom end <NUM>, the plate forming half of the apertures <NUM> is cut off, and this forms the offset <NUM> with a final height of the plate <NUM> being less than the height of the inlet channel <NUM>. By increasing the amount of flow below the orifice ring plate <NUM>, flow recirculation from the plate <NUM> itself is reduced or prevented for high flow velocities. The plurality of first apertures <NUM> in the middle can be two rows of uniformly sized holes. In other aspects, the orifice ring plate <NUM> may be formed with multiple rows of apertures with decreasing size going up the rows from the bottom (e.g., largest apertures in the bottom row and smallest apertures in the top row), and in some examples, without including a raised gap at the bottom and an aperture free row at top.

<FIG> is a partial perspective view of another orifice ring plate <NUM> and an inlet channel <NUM> of another fuel salt flow loop <NUM>. In this example, the flow loop <NUM> includes a reactor core <NUM> that is substantially a right-circular cylinder shape with the inlet channel <NUM> proximate the top. As such, in this example the flow loop <NUM> is reversed when compared to the examples described above with the fuel salt being pumped downward through the reactor core <NUM>, and the fuel salt exits the reactor core <NUM> at the bottom and enters from the top. Thus, the inlet channel <NUM> is disposed adjacent an upper reflector (not shown). In this example, by reversing the flow direction, the pump is disposed on the cold side of the flow loop <NUM> which increases pump efficiencies.

Similar to the example described above in <FIG>, the inlet channel <NUM> is connected to a channel <NUM> that includes a heat exchanger (not shown) and is on the opposite side of a reflector (now shown) from the reactor core <NUM>. The flow loop <NUM> has eight inlet channels <NUM> that channel fuel salt into the reactor core <NUM>. The inlet channel <NUM> has an aspect ratio (e.g., width to height ratio) that is not as severe at the inlet channel described above in reference to <FIG>, however, fuel salt flow velocities are significantly higher (e.g., around <NUM> meters/second). As such, an edge <NUM> between the inlet channel <NUM> and the reactor core <NUM> has a radius <NUM> that is about one-third of the height of the inlet channel <NUM>.

In this example, because the flow loop <NUM> is reversed, the orifice ring plate <NUM> has a top end <NUM> that has a plurality of second apertures <NUM> that are partially defined within the plate <NUM> and a bottom end <NUM> that is formed with a solid portion. The top end <NUM> of the plate <NUM> is lowered below the upper reflector (not shown) by a longitudinal offset <NUM>. Additionally, a plurality of first apertures <NUM> are fully defined within the plate <NUM>. In this example, the first apertures <NUM> are formed in two rows that are circumferentially offset from one another. In this flow loop <NUM>, the orifice ring plate <NUM> increases fuel salt flow distribution in the reactor core <NUM> and reduces and/or prevents flow recirculation as described above. Additionally, the orifice ring plate <NUM> counteracts the buoyant forces from fuel salt heating in an upwards directions. For example, the size and spacing of the apertures <NUM>, <NUM> can be different than the example described in <FIG>. Additionally, a partial solid portion <NUM> may be formed on the top end <NUM> of the plate <NUM> between apertures <NUM>. In some examples, the partial solid portion <NUM> may extend all the way to the upper reflector. In an aspect, the configuration of the orifice ring plate <NUM> with relating the sizes of the apertures <NUM>, <NUM> to the height of the inlet channel <NUM> may be similar to the plate <NUM> described above in reference to <FIG>.

<FIG> is an elevation view of another possible physical implementation of a reactor core system <NUM>. In this example, the reactor core system <NUM> can be a demonstration reactor that is a nuclear reactor designed to allow for efficient testing and assessment of the reactor's design and technology or a commercial reactor as required or desired. Both demonstration and commercial reactors generate heat, however, the dissipation of the heat generated during operation includes the generation of useable power in commercial reactors, while the generation of useable power may or may not occur in demonstration reactors.

The reactor core system <NUM> is a pool-type reactor having an enclosed vessel <NUM> with no bottom penetrations that contains reactor fuel salt <NUM>, a fuel pump assembly <NUM>, reflectors <NUM>, heat exchangers <NUM>, and control elements (not shown). The molten fuel salt <NUM> fills in all the space within the vessel <NUM> that is not taken up by components (e.g., reflectors <NUM>, pump assembly <NUM>, and heat exchangers <NUM>), shielding, or fuel displacement elements. This forms a central 'active' critical core region <NUM> as well as fuel channels <NUM> connecting the active core <NUM> with the pump assembly <NUM> and heat exchangers <NUM>. Reactor control elements (not shown) enter through a vessel head <NUM> and are positioned within the radial reflector region surrounding the active core <NUM>. Multiple fuel circuits operate in parallel to circulate the fuel salt <NUM>, and in the event of a loss of forced flow, the reactor core system <NUM> is capable of retaining the fuel salt safely in the vessel <NUM> and removing decay heat via robust natural circulation.

The critical, `active core' region <NUM> of the system <NUM> includes an open central, cylindrical chamber <NUM> defined by an annular draft tube <NUM> and a downcomer duct <NUM> defined outside of the draft tube <NUM> (e.g., between the draft tube <NUM> and the reflectors <NUM>). In operation, the pump assembly <NUM> drives the fuel salt <NUM> upwardly out of the active core <NUM> and through the heat exchanger <NUM>. A coolant flow <NUM> is channeled through an exchanger head <NUM> to extract heat from the active core <NUM>. The fuel salt <NUM> exits from the bottom of the heat exchanger <NUM> and into the annular downcomer duct <NUM> between the draft tube <NUM> and the reflectors <NUM> re-entering the active core <NUM>. The fuel salt <NUM> transitions around the bottom of the submerged draft tube <NUM> that separates the upward flowing fuel salt <NUM> within the chamber <NUM> from the downward flowing fuel salt <NUM> within the downcomer duct <NUM>.

Additionally, an orifice ring plate <NUM> is disposed within the active core <NUM> and proximate the transition of the fuel salt <NUM> between the downcomer duct <NUM> and the chamber <NUM> of the active core <NUM>. The orifice ring plate <NUM> is configured to condition the flow of fuel salt <NUM> moving around the bottom of the submerged draft tube <NUM> so as to reduce or eliminate fuel salt flow recirculation inside the lower active core region. The orifice ring plate <NUM> is described in further detail below.

<FIG> is a partial perspective view of a fuel salt flow loop <NUM> of the reactor core system <NUM> (shown in <FIG>). The flow loop <NUM> is full of fuel salt and the flow direction is illustrated by arrows <NUM>. The flow loop <NUM> is at least partially defined by the draft tube <NUM> and the reflectors <NUM>. In the active core <NUM> the fuel salt turns approximately <NUM>° from the downcomer duct <NUM> to the chamber <NUM>. The orifice ring plate <NUM> is disposed within the active core <NUM> proximate the bottom end of the draft tube <NUM>. The orifice ring plate <NUM> has a plurality of apertures <NUM> arranged in rows configured to allow a flow of fuel salt through the plate and a top solid portion <NUM> that directs at least a portion of the fuel salt flow above the orifice ring plate <NUM>. Additionally, the orifice ring plate <NUM> has a diameter that is less than a diameter of the draft tube <NUM> so that the orifice ring plate <NUM> is inwardly offset from the draft tube <NUM>. A height of the orifice ring plate <NUM> is about equal to or less than the height of the bottom end of the draft tube <NUM> above the bottom reflector <NUM>. The orifice ring plate <NUM> is coupled to and extends from the bottom of the core. In some example, a portion of the top of the orifice ring plate <NUM> may be supported by the draft tube <NUM> as required or desired.

The orifice ring plate <NUM> enables the fuel salt flow <NUM> to be balance and distributed when entering the chamber <NUM> so as to increase reactor performance. For example, a portion of the flow is directed in an upwards direction along the inner surface of the draft tube <NUM> and reduces or prevents flow recirculation along the draft tube <NUM>. A portion of the flow is channeled through the orifice ring plate <NUM> to distribute flow in the azimuthal direction. Additionally, a portion of the flow is channeled under the orifice ring plate <NUM> to reduce or prevent recirculation proximate the centerline of the active core <NUM>. The spacing, sizing, and configuration of the apertures <NUM> and top solid portion <NUM> can be adjusted as described herein to balance and distribute the fuel salt flow.

In general, increased fuel salt flow balance and distribution within the reactor core and the reduction and/or prevention of flow recirculation is enabled by the orifice ring plate designs as described above. It should be appreciated that modifying one or more design parameters of the orifice ring plate, for example, but not limited to, inner ring diameter, ring thickness, aperture diameter, aperture angular spacing, etc. can be done to tailor the orifice ring plate to specific reactor core designs and fuel salt flow velocities. For example, the aperture size and spacing can be adjusted to tailor the amount of flow directed along the reflector wall. The size of the solid portion can also change the amount of flow directed along the reflector wall. The partial aperture size and spacing and/or the bottom offset can change the amount of flow directed underneath the plate and towards the centerline of the core. Aperture size and spacing also changes pressure drop and flow distribution within the core. For example, large diameter apertures enable more flow through the plate than smaller diameter apertures. Aperture sizes can be modified by location relative to the inlet channel (e.g., smaller diameters closer to the inlet channel and larger diameters farther away), and/or modified by location on the plate (e.g., smaller diameter at the bottom and larger diameters at the top). The thickness of the orifice ring plate can change the amount of pressure drop across the plate.

It is to be understood that this disclosure is not limited to the particular structures, process steps, or materials disclosed herein, but is extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts. It should also be understood that terminology employed herein is used for the purpose of describing particular examples only and is not intended to be limiting. It must be noted that, as used in this specification, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

Claim 1:
A molten fuel reactor (<NUM>) comprising:
a reactor core (<NUM>, <NUM>) defined at least partially by an upper reflector (<NUM>), a lower reflector (<NUM>), and at least one side reflector (<NUM>, <NUM>), wherein the reactor core is substantially a right-circular cylinder shape, and wherein the reactor core has a longitudinal axis (<NUM>) and an inner diameter (<NUM>);
at least one inlet (<NUM>) configured to channel fuel salt into the reactor core;
at least one outlet (<NUM>) configured to channel fuel salt out of the reactor core, wherein the at least one inlet and the at least one outlet at least partially define a flow loop (<NUM>) of fuel salt with respect to the reactor core; and
an orifice ring plate (<NUM>) disposed within the reactor core and proximate the at least one inlet, wherein the orifice ring plate is configured to condition a flow of fuel salt entering the reactor core from the at least one inlet, wherein the orifice ring plate forms a continuous ring and extends circumferentially about the longitudinal axis and has a height defined in a direction along the longitudinal axis, and wherein the orifice ring plate includes a plurality of radial apertures configured to allow the flow of fuel salt therethrough.