Thorium-based fuel design for pressurized heavy water reactors

Abstract

The present invention provides thorium-based fuels for pressurized heavy water reactors (e.g., fuel pellets, fuel pins, and / or fuel bundles), as well as methods for manufacturing and using the same. [Solution] The fuel composition of the bundle consists of 60 wt% or more thorium, with the remaining fuel being low-enriched uranium (LEU) of 235U with an enrichment level of 13-19.95%. The use of such a thorium-based fuel bundle provides a non-brederate spent fuel bundle having (1) 100% of the nominal power throughout the entire lifecycle of the core, (2) high burnup, and (3) a total isotope uranium concentration of less than 12 wt%. Reprocessing of spent fuel can also be avoided.

Description

Technical Field

[0001] Cross - reference to Related Applications This application claims priority based on U.S. Provisional Patent Application No. 63 / 186,990 (filing date: May 11, 2021, title: "Thorium - based Fuel Design for Pressurized Heavy Water Reactors"), the content of which is incorporated herein by reference.

[0002] Various embodiments generally relate to fuel pellets, pins, bundles, and core loading for pressurized heavy water reactors ("PHWRs"), and in particular to thorium - based fuel compositions for such pellets, pins, bundles, and cores.

Background Art

[0003] A 220MWe pressurized heavy water reactor is a heavy - water moderated and heavy - water cooled reactor having a reactor vessel 10. The reactor includes 306 fuel channels in the form of horizontal pressure tubes through which high - pressure coolant flows. Each channel has 12 fuel bundles, but only 10 are in the core. To isolate the high - temperature fuel channels from the low - temperature moderator, the pressure tubes are loaded into calandria tubes surrounded by heavy - water moderator. The pressure tubes are arranged in a square lattice with a lattice pitch of 22.84 cm. The shape of the core 20 including the heavy - water moderator reflector and an exemplary fuel bundle is shown in FIG. 1. In FIG. 1, only two exemplary bundles are shown, but it should be understood that additional fuel bundles (not shown in FIG. 1) are provided in each of the 306 channels.

[0004] A fuel bundle is an assembly of 19 fuel pins per bundle. The overall length of the fuel bundle is 49.53 cm. The fuel is in the form of uranium dioxide pellets clad with zircaloy - 4 pins. The length of the fuel stack is 48.1 cm, and the fuel pins are sealed with end caps welded to the ends of the fuel pins. To maintain the structural integrity of the fuel bundle, two end plates are welded to the end caps of the fuel pins.

[0005] In addition to the fuel channels, the reactor core contains numerous reactivity control devices. All reactivity devices are perpendicular to the fuel channels and penetrate the reactor pressure vessel from top to bottom. Reactor power adjustment is performed by two power adjustment rods, which are normally inserted 80%. Four additional adjustment rods are installed for power shape control and xenon override, and these are normally fully inserted. Reactor shutdown is performed by a primary shutdown system consisting of 14 shutdown rods, which are normally stored outside the core. In emergencies or failures of the primary shutdown system, a secondary shutdown system consisting of 12 liquid poison compartments can independently provide shutdown functionality. These liquid compartments are normally filled with helium gas and, if necessary, can be injected with liquid neutron poison for a short time to safely shut down the reactor. Furthermore, the reactor has two shim rods to support shim mode operation if necessary. These are normally stored outside the core.

[0006] Canadian Patent Application Publication No. 2810133 discloses a thorium-containing nuclear fuel bundle and a nuclear reactor containing said nuclear fuel bundle. See also U.S. Patent Application Publication No. 2016 / 0035441. [Overview of the project]

[0007] One or more non-limiting embodiments are disclosed herein and claimed to provide thorium-based fuels for pressurized heavy water reactors (e.g., fuel pellets, fuel pins, and / or fuel bundles), as well as methods for manufacturing and using the same.

[0008] One or more non-limiting embodiments provide fresh fuel pellets configured for use in a pressurized heavy water reactor. The fuel pellets contain thorium fuel and uranium fuel. The fuel composition of the fuel pellets is 55–90 wt% thorium and 10–45 wt% uranium. The enrichment level of uranium-235U is 10.5% to 20%.

[0009] According to one or more of these embodiments, the pellet is annular in shape with through holes.

[0010] According to one or more of these embodiments, the through hole has a diameter of 0.3 to 1.0 cm.

[0011] According to one or more of these embodiments, the fuel composition is 70-90 wt% thorium.

[0012] According to one or more of these embodiments, the uranium's 235U enrichment is 15-19%.

[0013] One or more non-limiting embodiments provide a fuel pin configured for use in a pressurized heavy water reactor. The fuel pin comprises a sealed tube and a plurality of fuel pellets according to one or more embodiments disclosed herein. The plurality of fuel pellets are arranged inside the sealed tube.

[0014] According to one or more of these embodiments, the fuel composition of the fuel pin is 70-85 wt% thorium.

[0015] According to one or more of these embodiments, each of the plurality of fuel pellets contains a flammable poison.

[0016] One or more non-limiting embodiments provide a fuel bundle configured for use in a pressurized heavy water reactor. The fuel bundle includes a plurality of fuel pins according to one of the embodiments disclosed herein. The fuel composition of at least one of the plurality of fuel pins differs from the fuel composition of at least one other of the plurality of fuel pins.

[0017] According to one or more of these embodiments, the fuel bundle is shaped and configured for use in a 220 MWe pressurized heavy water reactor, and the plurality of fuel pins comprises exactly 19 fuel pins, including one central fuel pin, six intermediate fuel pins arranged radially outward from the one central fuel pin, and twelve outer fuel pins arranged radially outward from the six intermediate fuel pins. The weight percentage of thorium in the fuel composition of the central fuel pin is lower than the weight percentage of thorium in the fuel composition of each of the twelve outer fuel pins.

[0018] According to one or more of these embodiments, the fuel composition of the central fuel pin and the six intermediate fuel pins has a thorium content of 55-75 wt%, the fuel composition of the twelve outer fuel pins has a thorium content of 65-90 wt%, and each of the twelve outer fuel pins has a higher weight thorium content than each of the central fuel pin and the six intermediate fuel pins.

[0019] According to one or more of these embodiments, the fuel composition of the central fuel pin has a lower weight percentage of thorium than that of each of the six intermediate fuel pins, and the fuel composition of each of the six intermediate fuel pins has a lower weight percentage of thorium than that of each of the twelve outer fuel pins.

[0020] According to one or more of these embodiments, the fuel composition of the central fuel pin has a thorium content of 55-70 wt%, the fuel composition of each of the six intermediate fuel pins has a thorium content of 60-80 wt%, and the fuel composition of each of the twelve outer fuel pins has a thorium content of 65-90 wt%.

[0021] According to one or more of these embodiments, the fuel bundle further includes a flammable poison placed in the sealed tube of each of the six intermediate fuel pins.

[0022] According to one or more of these embodiments, no flammable toxic material is placed inside the sealed tube of any of the outer fuel pins.

[0023] According to one or more of these embodiments, the fuel bundle further includes a burnable poison disposed in the hermetic tubes of each of the central fuel pin and the six intermediate fuel pins, and no burnable poison is disposed in the hermetic tubes of any of the outer fuel pins.

[0024] According to one or more of these embodiments, the burnable poison disposed in the hermetic tubes of each of the central fuel pin and the six intermediate fuel pins contains europium.

[0025] According to one or more of these embodiments, the fuel bundle includes a burnable poison disposed in the hermetic tube of each of the twelve outer fuel pins.

[0026] According to one or more of these embodiments, no burnable poison is disposed in the hermetic tube of any of the central fuel pin or the intermediate fuel pins.

[0027] According to one or more of these embodiments, no burnable poison is disposed in the hermetic tube of any of the fuel pins of the fuel bundle.

[0028] According to one or more of these embodiments, the 235U enrichment of uranium in each of the central fuel pin, the intermediate fuel pins, and the outer fuel pins is at least 12%.

[0029] According to one or more of these embodiments, the 235U enrichment of uranium in each of the fuel pellets of each of the central fuel pin, the intermediate fuel pins, and the outer fuel pins is at least 15%.

[0030] According to one or more of these embodiments, the 235U enrichment of uranium in each of the fuel pellets of each of the twelve outer fuel pins is lower than the 235U enrichment of uranium in each of the fuel pellets of each of the central fuel pin and the six intermediate fuel pins.

[0031] According to one or more of these embodiments, the fuel bundle is shaped and configured for use in a CANDU-type pressurized heavy water reactor, and the plurality of fuel pins consists of exactly 37 fuel pins, the 37 fuel pins including one central fuel pin, six first ring fuel pins arranged radially outward from the one central fuel pin, twelve second ring fuel pins arranged radially outward from the six first ring fuel pins, and eighteen outer ring fuel pins arranged radially outward from the twelve second ring fuel pins.

[0032] According to one or more of these embodiments, the weight percentage of thorium in the fuel composition of the central fuel pin is lower than the weight percentage of thorium in the fuel composition of the second ring fuel pin and the outer ring fuel pin.

[0033] According to one or more of these embodiments, the weight percentage of thorium in the fuel composition of the central fuel pin and the first ring fuel pin is 50-70 wt%, the weight percentage of thorium in the fuel composition of the second ring fuel pin is 60-90 wt%, and the weight percentage of thorium in the fuel composition of the outer ring fuel pin is 75-99 wt%.

[0034] According to one or more of these embodiments, the 235U enrichment of uranium in the central fuel pin and the first ring fuel pin is higher than the 235U enrichment of uranium in the second ring fuel pin or the outer ring fuel pin.

[0035] According to one or more of these embodiments, the 235U enrichment of uranium in the second ring fuel pin is higher than the 235U enrichment of uranium in the outer ring fuel pin.

[0036] According to one or more of these embodiments, the central fuel pin, the first ring fuel pin, and the second ring fuel pin each contain a flammable poison.

[0037] According to one or more of these embodiments, the flammable poison comprises europium oxide.

[0038] According to one or more of these embodiments, the outer ring fuel pin does not contain flammable toxins.

[0039] One or more non-limiting embodiments provide a pressurized heavy water reactor comprising a reactor vessel and a core disposed within the reactor vessel. The core includes a plurality of fuel bundles according to one or more embodiments disclosed herein. The plurality of fuel bundles include a first type of fuel bundle and a second type of fuel bundle. The first type of fuel bundle contains a flammable toxic substance. The second type of fuel bundle does not contain a flammable toxic substance.

[0040] According to one or more of these embodiments, the first and second types of fuel bundles are identical to each other, except that the second type of fuel bundle contains a flammable poison.

[0041] One or more embodiments provide fuel pellets configured for use in a pressurized heavy water reactor. The fuel pellets contain thorium fuel and uranium fuel. The fuel composition of the fuel pellets is 55-90 wt% thorium and 10-45 wt% uranium. The uranium-235U enrichment is 5-20%. The fuel pellets are annular in shape with through holes.

[0042] According to one or more of these embodiments after the bundles, pins, and / or pellets have been removed from the reactor, the total isotopic uranium concentration (by weight) in the spent fuel pellets, pins, and / or bundles is less than 12, 11, 10, 9, 8, and / or 7%.

[0043] One or more of these and / or other embodiments of the various embodiments of the present invention, as well as the methods and functions of the related structural elements, and the combination and economy of the parts in manufacturing, will become clearer by considering the following description and the appended claims with reference to the accompanying drawings. These all constitute part of this specification. In this specification, similar reference numerals represent corresponding parts in various drawings. In one embodiment, the structural components illustrated herein are drawn to an accurate scale. However, the accompanying drawings are for illustrative and explanatory purposes only and are not intended to be used as definitions of the inventive features of the present invention. Furthermore, it should be understood that any structural features shown or described in any one embodiment herein may also be used in other embodiments. As used herein and in the claims, the singular forms "a," "an," and "the" include references to plural things, unless the context makes it clear that they should be interpreted differently.

[0044] All closed ranges of values ​​(e.g., "between A and B") and open ranges of values ​​(e.g., "greater than C") disclosed herein expressly include all ranges within that range. For example, a range disclosed as 1 to 10 is understood to also disclose ranges such as 2 to 10, 1 to 9, 3 to 9, and so on. Similarly, where multiple parameters (e.g., parameter C, parameter D) are separately disclosed as having ranges, embodiments disclosed herein expressly include embodiments in which any value within the disclosed range of one parameter (e.g., parameter C) is combined with any value within the disclosed range of any other parameter (e.g., parameter D). [Brief explanation of the drawing]

[0045] To better understand the various embodiments, their other purposes, and further features, the following description is provided with reference to the attached drawings.

[0046] [Figure 1]This is a schematic end view of a pressurized heavy water reactor according to one or more embodiments.

[0047] [Figure 2] This is a schematic end view showing the fuel bundle and a portion of the reactor in Figure 1.

[0048] [Figure 3A] Figure 2 is a perspective view of the fuel pellets in the fuel bundle shown.

[0049] [Figure 3B] Figure 3A is a side view of a fuel pellet.

[0050] [Figure 3C] This is a cross-sectional view of the fuel pellet in Figure 3A, along the line 3C-3C in Figure 3B.

[0051] [Figure 4] This table shows the composition of the pellets, pins, and fuel bundles of Figures 2-3 according to one or more non-limiting embodiments.

[0052] [Figure 5] This table shows the composition of the pellets, pins, and fuel bundles of Figures 2-3 according to one or more non-limiting embodiments.

[0053] [Figure 6] This is a schematic end view of a fuel bundle and a portion of a reactor according to one or more non-limiting alternative embodiments of a CANDU reactor.

[0054] [Figure 7] Figure 6 is a table showing the composition of pellets, pins, and fuel bundles in one or more non-limiting embodiments of the reactor shown. [Modes for carrying out the invention]

[0055] The 220 MWe pressurized heavy water reactor is a standardized pressurized heavy water reactor design developed and operated in India. This well-known type of reactor will be referred to as the "220 MWe pressurized heavy water reactor" below, even though it is not physically located in India.

[0056] The Indian-type 220 MWe pressurized heavy water reactor uses natural uranium (i.e., unenriched uranium) in a low-burnup open fuel cycle. Due to the use of natural uranium, its potential use for plutonium production, and concerns about radioactive waste, the current design is not favored for export and its use is limited to domestic power production. In the 220 MWe pressurized heavy water reactor, the burnup of spent fuel is low. Various non-limiting embodiments of the present invention provide alternative fuel cycles for use in the 220 MWe pressurized heavy water reactor to address concerns about nuclear proliferation and nuclear waste. Various non-limiting embodiments of the present invention are based on adaptations of the 220 MWe design for a thorium-based high-burnup once-through fuel cycle and provide a 220 MWe thorium pressurized heavy water reactor 5 having a reactor 10 housing a core 200 containing thorium-LEU fuel bundles 100.

[0057] As shown in Figure 2, the reactor 10 includes a plurality of calandria tubes 30 and pressure tubes 40 that define channels in which fuel bundles 100 are placed. Since the calandria tubes 30 and pressure tubes 40 are well-known components of the conventional 220 MWe pressurized heavy water reactor to which one or more embodiments apply, a comprehensive description of these conventional components of the 220 MWe pressurized heavy water reactor is omitted.

[0058] According to various embodiments, thorium-based fuel cycles reduce or eliminate nuclear proliferation risks. This is because the breeding of fissile plutonium is not significant, and uranium-233 is not practical for use in nuclear weapons due to the contamination of associated uranium-232. On the other hand, high burnup fuel cycles are preferred because they significantly reduce the amount of radioactive waste generated. According to various non-limiting embodiments, thorium-LEU fuel in pressurized heavy water reactors can provide the best nuclear proliferation resistance among all water reactor types.

[0059] According to various non-limiting embodiments of the present invention, the overall system and plant design of the 220 MWe pressurized heavy water reactor (see Figure 1) is maintained from the current 220 MWe pressurized heavy water reactor when forming the 220 MWe thorium pressurized heavy water reactors 5 and 10. According to various non-limiting embodiments of the present invention, the fuel bundle 100 provides a high burnup thorium fuel cycle.

[0060] According to various non-limiting embodiments of the present invention, the impact of the design change (converting a 220 MWe pressurized heavy water reactor to a 220 MWe thorium pressurized heavy water reactor 5, 10) is limited to the characteristics of the core 20 rather than the entire plant 5, thus reducing the effort required to implement and license the modified design.

[0061] According to various non-limiting embodiments of the present invention, the effects of design changes may include one or more of the following: i) The reactor physical properties of the core 20 of the 220 MWe thorium pressurized heavy water reactor 5,10 are completely different due to the change in fuel composition and the neutron properties unique to thorium fuel. ii) Adapting to a high-burnup cycle may present challenges to the structural integrity of fuel bundle 100, given that the current / conventional fuel bundle structure is used in a low-burnup fuel cycle.

[0062] According to various non-limiting embodiments of the present invention, the thorium fuel cycle is subject to the following limitations. i) Design modifications to the fuel bundle are limited to the internal dimensions of the fuel pins, while the overall shape and structure of the fuel bundle remain the same as the current / conventional design. This limitation allows much of the core safety and design analysis to be applied to various non-limiting embodiments of the present invention. ii) When optimizing the fuel bundle and core design, the current power limits imposed on the operating 220 MWe pressurized heavy water reactor will also be respected in the 220 MWe thorium pressurized heavy water reactor 10. This limit means that the current design of the heat transfer system and thermohydrdynamics will apply to various non-limiting embodiments of the present invention without requiring modifications.

[0063] According to various non-limiting embodiments of the present invention, a once-through high-burnup reactor cycle using thorium fuel is provided.

[0064] One or more non-limiting embodiments maintain, as much as possible, all the design features of the 220 MWe pressurized heavy water reactor. Such an approach minimizes the effort required to establish a safe state for the reactor and will make it possible to put one or more non-limiting embodiments into practical use in the near future. On the core side, there are no changes to the core shape, the number of fuel channels, or the size of the core. On the fuel bundle side, there are no changes to the external dimensions of the fuel pins or the shape of the fuel bundle. That is, one or more non-limiting embodiments provide a fuel bundle 100 that accommodates 19 fuel pins with a total length of 49.53 cm. The design modifications of the fuel bundle 100 in the various non-limiting embodiments may be limited to the following: i) Fuel composition, and / or ii) Internal design and structure of fuel pin 200.

[0065] As will be described in more detail below, the thorium-pressurized heavy water reactor 5 includes a reactor and reactor vessel 10 (shown as a circle in Figure 1) that houses a core 20 consisting of fuel bundles 100. The fuel bundles 100 consist of fuel pins 200. The fuel pins 200 include sealed tubes 210 filled with fuel pellets 300.

[0066] The fuel composition of each pellet 300 in one or more embodiments is a thorium-uranium mixed oxide containing low-enriched uranium (LEU). In the initial design studies, the fuel composition was specified as 80 wt% thorium and 20% uranium enrichment.

[0067] In this specification, the terms “thorium” and “thorium oxide” are used interchangeably and both refer to thorium oxide (ThO2). Similarly, in this specification, the terms “uranium” and “uranium oxide” are used interchangeably and both refer to uranium oxide (UO2).

[0068] Fuel performance analysis indicates that, under high burnup conditions, significant fission gas emissions and internal fuel pin pressure are expected with the current design. Furthermore, excessive cladding damage was also predicted. To address these two issues, the design of fuel bundle 100 was modified as follows. i) A central hole 310 was introduced into the fuel pellet 300 to contain the fission gas and reduce the internal pressure of pin 200 (see Figures 2 and 3). ii) To reduce the interaction between the cladding and the pellets, the initial fuel-cladding gap was increased. iii) The cladding thickness was increased to reduce the impact of irradiation damage on the integrity of the fuel pins. iv) Finally, advanced cladding materials with a proven track record of high burnup (such as zirconium and Zirlo™) were selected.

[0069] Fuel pellets 300

[0070] As shown in Figure 3, each fuel pellet 300 has a generally cylindrical annular shape with a through hole 310 extending axially through the center. According to various non-limiting embodiments, the fuel pellet 300 has the following physical parameters. i) Outer diameter of fuel pellet 300: at least 0.9, 1.0, 1.1, 1.2, and / or 1.3 cm, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, and / or 1.0 cm or less, between any two such values ​​(e.g., 0.9–2.0 cm, 1.1–1.7 cm, 1.2–1.4 cm, 1.3–1.4 cm, approximately 1.376 cm). ii) Fuel pellet center hole diameter: at least 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, and / or 0.9 cm, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, and / or 0.3 cm or less, and / or between any two such values ​​(e.g., 0.1-1.1 cm, 0.2-1.0 cm, 0.4-0.8 cm, 0.5-0.7 cm, approximately 0.6 cm). iii) Fuel pellet axial length: at least 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, and / or 1.5 cm, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, and / or 0.7 cm or less, and / or between any two such values ​​(e.g., 0.6 to 2.0 cm, 0.8 to 1.2 cm, 0.9 to 1.1 cm, approximately 1.0 cm). iv) True density of fuel pellet 300: 97%. v) Surface roughness of fuel pellets: 0.76 μm, similar to commercial pressurized heavy water reactor fuel. vi) Fuel pellet particle size: 10-60 μm.

[0071] As shown in Figure 3, the intersection between the hole and the axial end of the pellet 300 is chamfered, which reduces chipping of the pellet during loading and handling and reduces strain on the pellet and / or tube when the pellet expands as a result of irradiation.

[0072] According to various embodiments, the fuel composition (on a weight % basis) of each pellet 300 (and by extension, each fuel pin 200 composed of such pellets 300) consists of the following: i) at least 50, 55, 60, 65, 70, 75, 80, 85, and / or 90 wt% of thorium (e.g., thorium oxide), 100, 95, 90, 85, 80, 75, 70, 65, 60, and / or 55% or less of thorium, and / or between any two such values ​​(e.g., 50-95 wt% of thorium, 60-90 wt% of thorium, 65-85 wt% of thorium), ii) at least 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 and / or 50 wt% uranium oxide LEU, 50, 49, 48, 47, 46, 45, 44, 43, 42, 41, 40, 39, 38, 37, 36, 35, 34, 33, 32, 31, 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, and / or uranium oxide LEU of 5 wt% or less, and / or between any two such values ​​(e.g., uranium oxide LEU of 5-50 wt%, uranium oxide LEU of 10-40 wt%, uranium oxide LEU of 10-30 wt%, uranium oxide LEU of about 30 wt%, uranium oxide LEU of about 15 wt%), and iii) Optionally, a flammable poison (e.g., boron oxide) in concentrations of at least 0.0, 0.05, 0.1, 0.15, 0.2, and / or 0.3 wt% (percentage of the total weight of the pellet), less than 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, and / or less than 0.2 wt% of the pellet, and / or between any two such values ​​(e.g., 0.0-1.0 wt% of the pellet, 0.5-0.3 wt% of the pellet, 0.1-0.3 wt% of the pellet, 0.15-0.3 wt% of the pellet, 0.2-0.3 wt% of the pellet, approximately 0.22 wt% of the pellet). If a flammable poison other than boron oxide is used, an equivalent amount / concentration of such other material may be used. As described below, such flammable toxins may be present in certain fuel pellets 300a' used in certain fuel pins (e.g., the intermediate ring fuel pin 200b described below). Unless otherwise specified, all compositional percentages described herein are in weight percent (wt%).

[0073] As will be explained in more detail below, some fuel pellets 300 have all the uranium removed, resulting in pellets 300c with a fuel composition of 100% thorium. As will be explained below, pellets 300c are used in thorium fuel pins 200d, which are used in thorium bundles 100c.

[0074] According to various embodiments, fuel pellets 300 with different fuel compositions can be used within a single pin 200, or within different pins 200a, 200b, 200c, and 200d. For example, as shown in Figure 4, according to one or more embodiments, i) The fuel composition of fuel pellet 300a used in the central fuel pin 200a is 70% thorium and 30% uranium. ii) The fuel composition of the fuel pellet 300a' used in the intermediate ring fuel pin 200b is approximately 70% thorium, approximately 30% uranium, and 0.22 wt% boron oxide (or other flammable poison). iii) The fuel composition of the fuel pellet 300b used in a specific outer fuel pin 200c is 85% thorium and 15% uranium. iv) The fuel composition of fuel pellet 300c used in other specific fuel pins 200d and fuel bundles 300c is 100% thorium.

[0075] According to various embodiments, the LEU of the fuel pellet 300 has a 235U enrichment of at least 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and / or 16%, a 235U enrichment of 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, and / or 6% or less, and / or any value between any two such values ​​(e.g., a 235U enrichment of 5-20%, 10-18%, 12-16%, about 13%, about 15%). According to various embodiments, the 235U enrichment of the LEU differs among different fuel pellets 300 within a single pin 200. According to various embodiments, as shown in Figure 4, the LEU enrichment of fuel pellets 300a, 300a' used in one or more pins 200a, 200b is 235U (e.g., 13.0% enrichment), which is lower than the LEU enrichment of fuel pellets 300b used in one or more other pins 200c (e.g., 15% enrichment). In the embodiment shown in Figure 4, the enrichment difference is 2.0 absolute percent (13% vs. 15%). However, according to alternative embodiments, the absolute difference in enrichment may be higher or lower. For example, at least 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 7.0, 8.0, 9.0, and / or 10.0 absolute percent difference, 10.0, 9.0, 8.0, 7.0, 6.0, 5.5, The differences are 5.0, 4.5, 3.0, 2.5, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, and / or differences of less than 0.2 absolute percent, and / or between any two such values ​​(e.g., a difference of 0.2 to 10.0 absolute percent, a difference of 1.0 to 8.0 absolute percent, a difference of about 2 absolute percent). As used herein, the difference in concentration means an absolute difference, not a relative difference in percentages. Thus, the difference between 5% concentrated LEU and 15% concentrated LEU is 10% (15% minus 5%), not 200%.

[0076] Fuel pin 200

[0077] As shown in Figure 2, each fuel pin 200 includes a sealed cladding tube 210. According to various embodiments, the sealed tube 210 consists of an annular tube with end caps attached to each end (e.g., via welding). Forty to fifty (e.g., 48) fuel pellets 300 are arranged axially within the sealed tube 210, but more or fewer pellets 300 can be used per pin 200 without departing from the scope of the present invention. For example, the number of pellets 300 can be reduced to make space for the accumulation of fission gas. For example, more pellets 300 can be used by shortening the pellets 300 axially. According to various embodiments, the tube 210 has an inner diameter of 1.40 cm and a thickness of 0.06 cm. The tube 210, including its end caps, can be made of any suitable material (e.g., zirconium alloy). According to various embodiments, the internal cavity of the sealed tube 210 is pressurized to 0.5 MPa via a filler (e.g., helium).

[0078] As shown in Figure 4, different variations of the pin 200 are filled with different types of fuel pellets 300, as follows: i) Fuel pin 200a is composed of fuel pellet 300a so that its fuel composition matches that of fuel pellet 300a (e.g., 70% thorium, 30% uranium (13% enrichment)). ii) Fuel pin 200b

[0079] Fuel bundle 100

[0080] As shown in Figure 2, each fuel bundle 100 is composed of multiple fuel pins 200. In the case of a 220 MWe thorium pressurized heavy water reactor 10 according to one embodiment, the fuel bundle 100 includes 19 fuel pins 200, namely one central fuel pin 200a, six intermediate fuel pins 200b arranged in a ring radially outward from the central fuel pin 200a, and twelve outer fuel pins 200c arranged in a ring radially outward from the intermediate ring of pins 200b.

[0081] Similar to conventional fuel bundles, circular end plates with openings for coolant passage are welded or otherwise attached to the axial ends of fuel pins 200a, 200b, and 200c, maintaining the pins 200 in the position shown in Figure 2.

[0082] Taking these factors into consideration, the fuel composition of the fuel bundle 100a according to one or more embodiments was determined as follows, as shown in Figure 4. i) The central fuel pin 200a contains fuel having a composition of 70 wt% thorium and 30 wt% uranium (specifically, uranium enriched to 13% 235U). This fuel composition is achieved by filling the fuel pin 200a with fuel pellets 300a according to various embodiments. ii) The fuel pin 200b of the intermediate ring is generally similar to the fuel pin 200a, but differs in that it is filled with fuel pellets 300a' which also contain flammable toxins (e.g., 0.22 pellet wt% boron oxide or other equivalent material and arrangement combinations) rather than fuel pellets 300a which have flammable toxins removed. Therefore, the fuel pin 200b and fuel pellets 300a' contain slightly less thorium and uranium than the fuel pin 200a and fuel pellets 300a, as small amounts of thorium and uranium are replaced by flammable toxins. iii) The fuel composition of the outer ring fuel pin 200c is 85 wt% thorium and 15 wt% uranium (specifically, uranium enriched to 235U 15%). This fuel composition is achieved by filling the pin 200c with fuel pellets 300b having a matching fuel composition, according to various embodiments.

[0083] The fuel composition of fuel bundle 100 is summarized in Figure 4.

[0084] According to various alternative embodiments, the fuel composition of fuel pins 200, 200a, and 200b can all be varied by using fuel pellets 300 having any of the above-described fuel compositions (or further alternative fuel compositions) without departing from the scope of the present invention.

[0085] The results of these various combinations are as follows: i) The Th / U fuel bundle 100a is configured as follows: (1) The Th / U central fuel pin 200a is composed of fuel pellet 300a (70% Th, 30% U (13% enrichment)) and does not contain any flammable toxic substances. (2) The six Th / U intermediate fuel pins 200b are composed of fuel pellets 300a' (fuel composition of 70 wt% Th, 30 wt% U (enrichment level 13%), and 0.22 wt% boron oxide pellets). (3) The 12 outer fuel pins 200c are composed of fuel pellets 300b (85 wt% Th, 15 wt% U (15% enrichment)) and do not contain flammable toxic substances. ii) The Th / U fuel bundle 100b may be substantially identical to the Th / U fuel bundle 100a, except that the pellets 300a' of the six intermediate fuel pins 200b do not contain flammable toxins (thus making these intermediate fuel pins 200b substantially identical to the central fuel pin 200a). As a result, the fuel bundle 100b is free of flammable toxins and has the following configuration: (1) The Th / U central fuel pin 200a is composed of fuel pellet 300a (70% Th, 30% U (13% enrichment)) and does not contain any flammable toxic substances. (2) The six Th / U intermediate fuel pins 200b are composed of fuel pellets 300a (70 wt% Th, 30 wt% U (13% enrichment)) and do not contain flammable toxic substances. (3) The 12 outer fuel pins 200c are composed of fuel pellets 300b (85 wt% Th, 15 wt% U (15% enrichment)) and do not contain flammable toxic substances. iii) The Th fuel bundle 100c consists of a fuel pin 200d containing Th fuel pellets 300c (100% thorium) and does not contain flammable toxic substances.

[0086] Alternative compositions for fuel bundles, pins, and pellets

[0087] The compositions of the fuel bundles 100a, 100b, pins 200a, 200b, 200c, and pellets 300a, 300a', 300b described herein can be modified in various ways according to various alternative embodiments.

[0088] According to one or more alternative embodiments of the fuel bundles 100a, 100b, and / or fuel pins 200a, 200b, 200c, the fuel pellets 300a, 300a', 300b can utilize uranium of a higher enrichment than one or more of the embodiments described above (e.g., (a) 235U enrichment of at least 15, 16, 17, and / or 18%, (b) 235U enrichment of 19.95, 19, and / or 18%, and / or (c) between any two such upper and lower limits (e.g., 235U enrichment of 15-19.95%, 235U enrichment of 16-19%, 235U enrichment of about 17.8%)).

[0089] According to one or more of these embodiments, the 235U enrichment level of uranium in each of pellets 300a, 300a', and 300b can be standardized across many or all of fuel bundles 100a, 100b, fuel pins 200a, 200b, 200c, and / or fuel pellets 300a, 300a', and 300b.

[0090] According to one or more of these embodiments, the flammable poison can be placed on the outer ring pin 200c and pellet 300b, rather than on the intermediate ring fuel pin 200b and pellet 300a'. According to various embodiments, the flammable poison used in the outer ring pin 200c and pellet 300b comprises erbium oxide, the concentration of which is (a) at least 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, and / or 1.3 wt% of the pellet, (b) 3.0, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, and / or 1.3 wt% or less of the pellet, and / or (c) between any two such values ​​(e.g., 0.1 to 3.0 wt% of the pellet, 1.0 to 2.0 wt% of the pellet, and about 1.3 wt% of the pellet).

[0091] According to one or more of these embodiments, the thorium concentration of the fuel in the pellets 300a, 300a' of the intermediate ring pin 200b may be higher than in one or more of the embodiments described above, for example, (a) at least 71, 72, 73, 74, and / or 75 wt% of the fuel, (b) 84, 83, 82, 81, 80, 79, 78, 77, 76, and / or 75 wt% or less of the fuel, and / or (c) between any two such values ​​(e.g., 71-84 wt% of the fuel, 72-78 wt% of the fuel, about 75 wt% of the fuel).

[0092] Figure 5 shows the compositions of fuel bundles 100a and 100b according to one or more of these embodiments.

[0093] According to various alternative embodiments, the Th / U fuel bundle 100 may have the following configuration: i) Th / U central fuel pin 200a including the following: (1) A fuel pellet 300a having a fuel composition of 60% Th and 40% U (enrichment level 15%), (2) 0.6 wt% europium (Eu) flammable poison. ii) Six Th / U intermediate fuel pins 200b, including the following: (1) A fuel pellet 300a' having a fuel composition of 65 wt% Th and 35 wt% U (enrichment level 15%), (2) 0.6 wt% europium (Eu) flammable poison. iii) 12 outer fuel pins 200c, including the following: (1) A fuel pellet 300b having a fuel composition of 70 wt% Th and 30 wt% U (enrichment 10%), (2) Does not contain flammable poisons. According to various non-limiting embodiments, instead of the aforementioned bundles 100a, 100b, and 100c having different compositions, the same type of fuel bundle (for example, one like the one described above) can be used at all locations within the reactor.

[0094] According to various alternative embodiments, the Th / U fuel bundle 100 may have the following configuration: i) Th / U central fuel pin 200a including the following: (1) A fuel pellet 300a having a fuel composition of 60% Th and 40% U (enrichment 16%), (2) 0.6 wt% europium (Eu) flammable poison. ii) Six Th / U intermediate fuel pins 200b, including the following: (1) A fuel pellet 300a' having a fuel composition of 65 wt% Th and 35 wt% U (enrichment 16%), (2) 0.6 wt% europium (Eu) flammable poison. iii) 12 outer fuel pins 200c, including the following: (1) A fuel pellet 300b having a fuel composition of 80 wt% Th and 20 wt% U (enrichment 15%), (2) Does not contain flammable poisons. According to various non-limiting embodiments, instead of the aforementioned bundles 100a, 100b, and 100c having different compositions, the same type of fuel bundle (for example, one like the one described above) can be used at all locations within the reactor.

[0095] Embodiment of a CANDU-type 600 MWe nuclear reactor

[0096] Figure 6 shows one or more non-limiting alternative embodiments of reactor 1005. The illustrated reactor 1005 is generally similar to the embodiments described above, so redundant descriptions of similar or identical structures and features are omitted. As shown in Figure 6, the reactor vessel 1010 of reactor 1005 houses a core 1020 consisting of a plurality of calandria tubes 1030 and pressure tubes 1040 that define channels in which fuel bundles 1100 are placed.

[0097] In the illustrated embodiments, the reactor 1005, reactor vessel / housing 1010, calandria tube 1030, and pressure tube 1040 are well-known components of a CANDU reactor covered by one or more non-limiting embodiments; therefore, a comprehensive description of these conventional components of a CANDU reactor is omitted. Similarly, the dimensions and configurations of the fuel bundle 1100 and pins 1200a, 1200b, 1200c, and 1200d are also well-known in relation to CANDU reactors covered by various non-limiting embodiments; therefore, a comprehensive description of such dimensions and configurations is omitted.

[0098] As shown in Figure 6, each fuel bundle 1100 consists of 37 fuel pins, which include one central fuel pin 1200a containing a fuel pellet 1300a, six first ring fuel pins 1200b containing fuel pellets 1300a, twelve second ring fuel pins 1200c containing fuel pellets 1300b, and eighteen outer ring fuel pins 1200d containing fuel pellets 1300c.

[0099] As shown in the non-limiting embodiments shown in Figure 7, the composition of the fuel pellets 1300a, 1300b, and 1300c of the fuel pins 1200a, 1200b, 1200c, and 1200d of the fuel bundle 1100 in one or more embodiments differs from the composition in a conventional 37-pin CANDU fuel bundle.

[0100] According to one or more embodiments of the fuel bundle 1100 and / or fuel pins 1200a, 1200b, 1200c, and / or 1200d, the uranium enrichment levels available to the fuel pellets 1300a, 1300b, and / or 1300c are: (a) 235U enrichment levels of at least 13, 14, 15, 16, 17, and / or 18%, (b) 235U enrichment levels of 19.95, 19, 18, and / or 17%, and / or (c) between any two such upper and lower limits (e.g., 235U enrichment levels of 13–19.95%, 16–19%, and approximately 16, 17, 18, or 19%).

[0101] According to various non-limiting embodiments, the 235U enrichment of the fuel pellets 1300a in the central fuel pin 1200a and / or the first ring fuel pin 1200b is equal to that of the others. However, according to one or more alternative embodiments, the enrichment of the fuel pellets in the central pin 1200a may be higher or lower than the enrichment of the fuel pellets in the first ring fuel pin 1200b.

[0102] According to various non-limiting embodiments, the 235U enrichment of fuel pellets 1300a in the central fuel pin 1200a and / or the first ring fuel pin 1200b is higher than the 235U enrichment of fuel pellets 1300b in the second ring pin 1200c and / or the outer ring pin 1200d, the difference being (a) at least 0.1. 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.5, 5 0.0, 5.5, 6.0, 6.5, 7.0, 7.5, and / or 8.0 absolute%, (b) 8.0, 7.5, 7.0, 6.5, 6.0, 5.5, 5.0, 4.5, 4.0, 3.9, 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1, 3.0, 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, and / or 0.2 absolute%, and / or (c) any value between such upper and lower limits (e.g., 0.1 to 8.0 absolute%, 0.5 to 1.5 absolute%, 1.5 to 2.5 absolute%, about 1 absolute%, about 3 absolute%). As used herein, “absolute%” of enrichment means a percentage of enrichment, not a percentage of deviation from another enrichment value. As a result, fuel pellet 1300a with an enrichment of 19% has an enrichment of 2 absolute% higher than pellet 1300b with an enrichment of 17%.

[0103] According to various non-limiting embodiments, the 235U enrichment of the fuel pellet 1300b in the second ring pin 1200c is higher than the 235U enrichment of the fuel pellet 1300c in the outer ring pin 1200d, and the difference is (a) at least 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, 4.5, 5.0, 5.5, 6.0 , 6.5, and / or 7.0 absolute%, (b) 7.0, 6.5, 6.0, 5.5, 5.0, 4.5, 4.0, 3.9, 3.8, 3.7, 3.6, 3.5, 3.4, 3.3, 3.2, 3.1, 3.0, 2.9, 2.8, 2.7, 2.6, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1. 7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, and / or less than or equal to 0.2 absolute percent, and / or (c) any value between such upper and lower limits (e.g., 0.1 to 7.0 absolute percent, 0.5 to 1.5 absolute percent, about 1 absolute percent).

[0104] According to one or more non-limiting embodiments, the fuel pellets 1300a and / or 1300b and / or pins 1200a, 1200b, and / or 1200c contain a flammable poison. According to various embodiments, the flammable poison used in pellets 1300a and / or 1300b and / or pins 1200a, 1200b, and / or 1200c comprises europium oxide, the concentration of which europium oxide is (a) at least 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, and / or 1.3 wt% in pellets, and (b) 3.0, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.15, 0.14, 0.13, 0.12, 0.11, 0.1, 0.09, 0.08, 0.07, 0.06, and / or less than or equal to 0.05 wt%, and / or (c) between any two such values ​​(e.g., 0.05 to 3.0 wt% of the pellet, 1.0 to 2.0% of the pellet, about 1.2 wt%, 0.05 to 0.2 wt%, 0.05 to 0.15 wt%). According to various embodiments, the concentration of flammable toxins in fuel pellet 1300a and / or the central and first pins 1200a, 1200b is higher than the concentration of flammable toxins (e.g., europium oxide) in fuel pellet 1300b and / or the second ring pin 1200c, the difference being (a) at least 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, and (b) less than 1.0 absolute wt%, (b) 2.0, 1.9, 1.8, 1.7, 1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, and / or less than 0.1 absolute wt%, and / or (c) between any two such values ​​(e.g., 0.1 to 2.0 absolute wt%, 0.5 to 1.7 absolute wt%, approximately 1.1 absolute wt%).According to one or more non-limiting embodiments, fuel pellet 1300a has a europium oxide concentration of 1.2 wt%, and fuel pellet 1300b has a europium oxide concentration of 0.1 wt%. Thus, pellet 1300a has a europium oxide concentration that is 1.1 absolute wt% higher than pellet 1300b. According to one or more alternative embodiments, any other flammable poison (e.g., erbium oxide) can be used additionally and / or alternatively.

[0105] According to various alternative embodiments, a flammable poison (e.g., europium oxide and / or erbium oxide in the concentrations described in any of the embodiments above) may be additionally and / or alternatively placed within the fuel pellet 1300c and / or pin 1200d.

[0106] According to one or more embodiments, the thorium fuel concentration (i.e., wt%) of thorium as part of the total weight of fuel) in the fuel pellet 1300a of the central pin 1200a and / or the first ring pin 1200b is (a) at least 45, 50, 55, 57.5, 60, 62.5, and / or 65 wt%, (b) 90, 85, 80, 75, 70, 65, 62.5, and / or 60 wt% or less, and / or (c) between any two such values ​​(e.g., 45-90 wt%, 50-70 wt%, 55-65 wt%, 57.5-62.5 wt%, about 65 wt%). According to various non-limiting embodiments, the remainder of the fuel composition of the pellet is uranium (e.g., 65 wt% thorium and 35 wt% uranium).

[0107] According to one or more embodiments, the thorium fuel concentration in the fuel pellet 1300b of the second ring pin 1200c (i.e., wt%) of thorium as part of the total weight of the fuel is (a) at least 55, 60, 65, 70, 72.5, 75, and / or 77.5 wt%, (b) 95, 90, 85, 80, 77.5, 75, and / or 72.5 wt%, and / or (c) between any two such values ​​(e.g., 55–95 wt%, 65–85 wt%, 70–80 wt%, 72.5–77.5 wt%, about 75 wt%). According to various non-limiting embodiments, the remainder of the fuel composition of the pellet is uranium (e.g., 75 wt% thorium and 25 wt% uranium).

[0108] According to one or more embodiments, the thorium fuel concentration in the fuel pellet 1300c of the outer ring pin 1200d (i.e., wt%) of thorium as part of the total weight of the fuel is (a) at least 55, 60, 65, 70, 75, 80, 82.5, 85, and / or 87.5 wt%, (b) 99, 95, 90, 87.5, 85, and / or 82.5 wt%, and / or (c) between any two such values ​​(e.g., 55-99 wt%, 75-95 wt%, 80-90 wt%, 82.5-87.5 wt%, about 85 wt%). According to various non-limiting embodiments, the remainder of the fuel composition of the pellet is uranium (e.g., 85 wt% thorium and 15 wt% uranium).

[0109] According to one or more of these embodiments, the thorium fuel concentration in the pellet 1300c of the outer ring pin 1200d is higher than the thorium fuel concentration in the fuel pellets 1300b and / or 1300c of the second ring pin 1200c, the first ring pin 1200b, and / or the central pin 1200a. According to various non-limiting examples, the thorium fuel concentration in pellet 1300c (i.e., wt%) of thorium as part of the total weight of the fuel) is higher than the thorium fuel concentration in pellet 1300b, the difference being (a) at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, and / or 15 absolute wt%, (b) less than 25, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, and / or 1 absolute wt%, and / or (c) a value between any two such values ​​(e.g., 1 to 25 absolute wt%, 5 to 15 wt%, about 10 wt%). According to various non-limiting examples, the thorium fuel concentration in pellet 1300c is higher than that in pellet 1300a, and the difference is (a) at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, and / or 30 absolute (b) wt%, (b) 30, 29, 28, 27, 26, 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, and / or less than 1 absolute wt%, and / or (c) a value between any two such values ​​(e.g., 1 to 30 absolute wt%, 20 to 30 wt%, approximately 25 wt%).

[0110] According to one or more embodiments, the thorium fuel concentration in the pellet 1300b of the second ring pin 1200c is higher than the thorium fuel concentration in the fuel pellet 1300a of the first ring pin 1200b and / or the central pin 1200a. According to various non-limiting examples, the thorium fuel concentration in pellet 1300b is higher than the thorium fuel concentration in pellet 1300a, the difference being (a) at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and / or 20 absolute wt%, (b) less than 30, 25, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, and / or 1 absolute wt%, and / or (c) a value between any two such values ​​(e.g., 1 to 30 absolute wt%, 5 to 25 absolute wt%, 10 to 20 absolute wt%, and / or about 15 whole wt%).

[0111] As used herein, "absolute wt%" refers to the percentage of the total fuel content and does not represent a deviation from other values. As a result, fuel pellet 1300a with a thorium fuel concentration of 60 wt% has a concentration 15 absolute wt% lower than fuel pellet 1300b with a thorium fuel concentration of 75 wt%.

[0112] According to various non-limiting embodiments, the composition (e.g., 235U enrichment, thorium / uranium concentration, toxic substance concentration) of all fuel pellets 1300a in the central pin 1200a and / or the first ring pin 1200b may be the same. According to various non-limiting embodiments, the composition of all fuel pellets 1300b in the second ring pin 1200c may be the same. According to various non-limiting embodiments, the composition of all fuel pellets 1300c in the outer ring pin 1200d may be the same. According to various alternative embodiments, different pins in a given ring may utilize pellets of different compositions. According to various alternative embodiments, the fuel pellets in a given pin may have different compositions from one another.

[0113] According to various non-limiting embodiments, the fuel is used in an open fuel cycle in which thorium transitions to U233, which is then burned in situ. According to various non-limiting embodiments, the fuel is burned to levels unattainable with current CANDU / pressurized heavy water reactor fuels. According to various non-limiting embodiments, the amount of fissile material remaining is not sufficient for use in non-power reactor applications. This fuel is characterized by inherent safety features such as a strong negative fuel temperature reactivity coefficient and reduced coolant void reactivity.

[0114] alternative reactor

[0115] The embodiments described above relate to fuels 100, 200, and 300 for a 220 MWe pressurized heavy water reactor, or fuels 1100, 1200, and 1300 for a CANDU-type 600 MWe reactor. However, various embodiments can be used in other types of pressurized heavy water reactors without departing from the scope of the present invention. For example, the various embodiments described above can be applied to other Indian-type pressurized heavy water reactors (e.g., Indian-type 540 MWe pressurized heavy water reactor, Indian-type 700 MWe pressurized heavy water reactor) or other CANDU reactors (e.g., 300 MWe or 900 MWe), and fuel bundles having more or fewer pins than the 19-pin and 37-pin embodiments in the embodiments described above can be used.

[0116] Unless otherwise specified, the composition of pellets, pins, and fuel bundles herein (e.g., wt%, fuel, flammable toxins, etc.) refers to the composition of fresh, unirradiated pellets, pins, and fuel bundles before use in a reactor, not the composition after irradiation in a reactor. Fresh pellets may consist of recycled uranium, depleted uranium, natural uranium, and / or uranium from any other source, including previously irradiated uranium sources. Similarly, fresh pellets may consist of thorium from any source, including previously irradiated sources.

[0117] The exemplary embodiments described above are presented to illustrate the structural and functional principles of various embodiments and are not intended to limit them. Rather, the principles of the present invention are intended to include any and all modifications, alterations, and / or substitutions thereof (e.g., any modifications within the spirit and scope of the following claims).

Claims

1. Fresh fuel pellets configured for use in a pressurized heavy water reactor, containing thorium fuel and uranium fuel, The fuel composition of the aforementioned fuel pellet is 55-90 wt% thorium. The aforementioned fuel composition is 10 to 45 wt% uranium. The uranium-235U enrichment level of the aforementioned uranium is 10.5-20%, and the fuel pellets are of this type.

2. The fuel pellet according to claim 1, wherein the fuel pellet is annular in shape and has a through hole.

3. The fuel pellet according to claim 2, wherein the diameter of the through hole is 0.3 to 1.0 cm.

4. The fuel pellet according to claim 1, wherein the fuel composition is 70 to 90 wt% thorium.

5. The fuel pellet according to claim 1, wherein the uranium has a 235U enrichment level of 15 to 19%.

6. A fuel pin configured for use in a pressurized heavy water reactor, A sealed tube and A plurality of fuel pellets according to claim 1, comprising: The aforementioned plurality of fuel pellets are arranged inside the sealed tube, forming a fuel pin.

7. The fuel pin according to claim 6, wherein the fuel composition of the fuel pin is 70 to 85 wt% thorium.

8. The fuel pin according to claim 6, wherein each of the plurality of fuel pellets contains a flammable poison.

9. A fuel bundle configured for use in a pressurized heavy water reactor, wherein the fuel bundle comprises a plurality of fuel pins as described in claim 6, wherein the fuel composition of at least one of the plurality of fuel pins is different from the fuel composition of at least one other fuel pin.

10. The fuel bundle is molded and configured for use in a 220 MWe pressurized heavy water reactor. The aforementioned plurality of fuel pins consist of exactly 19 fuel pins, including one central fuel pin, six intermediate fuel pins arranged radially outward from the central fuel pin, and twelve outer fuel pins arranged radially outward from the six intermediate fuel pins. The weight percentage of thorium in the fuel composition of the central fuel pin is lower than the weight percentage of thorium in the fuel composition of each of the twelve outer fuel pins. The fuel bundle according to claim 9.

11. The fuel composition of the central fuel pin and the six intermediate fuel pins is such that the thorium content is 55 to 75 wt%, The fuel composition of each of the 12 outer fuel pins is such that the thorium content is 65 to 90 wt%, Each of the twelve outer fuel pins has a higher weight percentage of thorium than each of the central fuel pin and each of the six intermediate fuel pins. The fuel bundle according to claim 10.

12. The fuel composition of the central fuel pin has a lower weight percentage of thorium than that of each of the six intermediate fuel pins. The fuel composition of each of the six intermediate fuel pins has a lower weight percentage of thorium than the fuel composition of each of the twelve outer fuel pins. The fuel bundle according to claim 10.

13. The fuel composition of the aforementioned central fuel pin has a thorium content of 55-70 wt%, The fuel composition of each of the six intermediate fuel pins is such that the thorium content is 60-80 wt%, The fuel composition of each of the 12 outer fuel pins is such that the thorium content is 65 to 90 wt%. The fuel bundle according to claim 12.

14. The fuel bundle according to claim 10, further comprising a flammable poison disposed in the sealed tube of each of the six intermediate fuel pins.

15. The fuel bundle according to claim 14, wherein no flammable poison is placed inside the sealed tube of any of the outer fuel pins.

16. The fuel bundle according to claim 10, further comprising a flammable poison disposed in the sealed tube of each of the central fuel pin and the six intermediate fuel pins, wherein no flammable poison is disposed in the sealed tube of any of the outer fuel pins.

17. The fuel bundle according to claim 16, wherein the flammable poison disposed in the sealed tubes of each of the central fuel pin and the six intermediate fuel pins is europium.

18. The fuel bundle according to claim 10, further comprising a flammable poison disposed within the sealed tube of each of the twelve outer fuel pins.

19. The fuel bundle according to claim 18, wherein no flammable toxic material is placed in the sealed tube of either the central fuel pin or the intermediate fuel pin.

20. The fuel bundle according to claim 10, wherein no flammable poison is placed inside the sealed tube of any of the fuel pins of the fuel bundle.

21. The fuel bundle according to claim 10, wherein the uranium enrichment of each of the central fuel pin, the intermediate fuel pin, and the outer fuel pin is at least 12%.

22. The fuel bundle according to claim 10, wherein the uranium 235U enrichment of each fuel pellet of the central fuel pin, the intermediate fuel pin, and the outer fuel pin is at least 15%.

23. The fuel bundle according to claim 22, wherein the 235U enrichment of each uranium in each of the fuel pellets of each of the twelve outer fuel pins is lower than the 235U enrichment of each uranium in each of the fuel pellets of the central fuel pin and the six intermediate fuel pins.

24. The fuel bundle is molded and configured for use in a CANDU-type pressurized heavy water reactor. The aforementioned plurality of fuel pins consist of exactly 37 fuel pins, and these 37 fuel pins are, One central fuel pin, Six first ring fuel pins are arranged radially outward from the aforementioned single central fuel pin, Twelve second ring fuel pins are arranged radially outward from the six first ring fuel pins, Includes 18 outer ring fuel pins arranged radially outward from the 12 second ring fuel pins, The fuel bundle according to claim 9.

25. The fuel bundle according to claim 24, wherein the weight ratio of thorium in the fuel composition of the central fuel pin is lower than the weight ratio of thorium in the fuel composition of the second ring fuel pin and the outer ring fuel pin.

26. The weight percentage of thorium in the fuel composition of the central fuel pin and the first ring fuel pin is 50 to 70 wt%, The weight percentage of thorium in the fuel composition of the second ring fuel pin is 60-90 wt%, The weight percentage of thorium in the fuel composition of the outer ring fuel pin is 75 to 99 wt%. The fuel bundle according to claim 24.

27. The fuel bundle according to claim 24, wherein the uranium 235U enrichment of the central fuel pin and the first ring fuel pin is higher than the uranium 235U enrichment of the second ring fuel pin or the outer ring fuel pin.

28. The fuel bundle according to claim 27, wherein the uranium 235U enrichment of the second ring fuel pin is higher than the uranium 235U enrichment of the outer ring fuel pin.

29. The fuel bundle according to claim 24, wherein the central fuel pin, the first ring fuel pin, and the second ring fuel pin each contain a flammable poison.

30. The fuel bundle according to claim 29, wherein the flammable poison is europium oxide.

31. The fuel bundle according to claim 29, wherein the outer ring fuel pin does not contain a flammable poison.

32. The reactor vessel and A reactor core disposed within the reactor vessel, comprising a reactor core containing a plurality of fuel bundles as described in claim 9, The plurality of fuel bundles include a first type of fuel bundle and a second type of fuel bundle, The first type of fuel bundle contains a flammable poison, The second type of fuel bundle described above does not contain flammable toxic substances. Pressurized heavy water reactor.

33. The pressurized heavy water reactor according to claim 32, wherein the first and second types of fuel bundles are identical to each other, except that the second type of fuel bundle contains a flammable poison.

34. A fuel pellet configured for use in a pressurized heavy water reactor, comprising thorium fuel and uranium fuel, The fuel composition of the aforementioned fuel pellet is 55-90 wt% thorium. The aforementioned fuel composition is 10 to 45 wt% uranium. The uranium-235U enrichment level is 5-20%. A fuel pellet having a through hole and being an annular in shape.

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