Nuclear fuel pellet with radially variable enrichment
By designing proximal, intermediate and distal layers of radially variable enrichment in nuclear fuel pellets, the risk of deterioration of the pellet under high temperature and high combustion is solved, and more stable combustion control and safety is achieved.
Patent Information
- Application Number
- CN202380085846.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2022-12-14
- Filing Date
- 2023-12-14
- Publication Date
- 2025-07-29
AI Technical Summary
Nuclear fuel pellets have a risk of deterioration during combustion, especially fuel fragmentation, repositioning and dispersion (FFRD), especially in locally high combustion or high temperature situations.
A nuclear fuel core pellet is designed with a rotationally symmetrical shape about the central axis, including a proximal layer, an intermediate layer and a distal layer. The enrichment of fission material varies radially within the core pellet, and the enrichment of the intermediate layer is higher than that of the proximal and distal layers. The reactivity and combustion degree are controlled by adjusting the enrichment to limit the deterioration caused by local high temperatures and high combustion.
Through the design of radial variable enrichment, the risk of deterioration of the core pellet is limited, energy equivalence is maintained, the risk of excessive temperature in the center and surrounding areas of the core pellet is reduced, and the stability and safety of the core pellet are improved.
Smart Images
Figure CN120390966A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of nuclear fuels, and more particularly to nuclear fuel pellets intended to be integrated into nuclear fuel rods. Background Art
[0002] The core of a light water or heavy water nuclear reactor is generally formed by a plurality of nuclear fuel assemblies arranged side by side. Each nuclear fuel assembly includes a bundle of nuclear fuel rods, and each nuclear fuel rod includes a tubular sheath that houses nuclear fuel. The sheath is sealed at each of its two ends by plugs.
[0003] The nuclear fuel is provided, for example, in the form of nuclear fuel pellets containing fissile material. Each pellet is generally cylindrical, and the pellets are stacked in the sheath.
[0003]
[0004] During the combustion of the nuclear fuel pellets, there is a risk of pellet degradation, in particular the risk of fuel fragmentation, relocation and / or dispersion (or FFRD according to the English term, which stands for "Fuel Fragmentation Relocation and Dispersion").
[0005] This risk is higher in the case of local high combustion or local high temperature within the pellet.
[0004] Summary of the Invention
[0006] One of the objectives of the present invention is to propose a nuclear fuel pellet that allows limiting the risk of degradation of the pellet during its use.
[0007] To this end, the present invention proposes a nuclear fuel pellet having a rotationally symmetric shape about a central axis and containing fissile material. The pellet has concentric layers including a proximal layer, an intermediate layer, and a distal layer, wherein the enrichment of the fissile material within the pellet varies radially, and the intermediate layer includes a high enrichment region having an enrichment strictly higher than the enrichment in the proximal layer and / or the enrichment in the distal layer.
[0005]
[0008] The radially variable enrichment of the fissile material in the pellet allows adjusting the reactivity and the degree of combustion within the nuclear fuel pellet according to the radius, so as to limit the risk of degradation associated with a local high degree of combustion and / or local high temperature.
[0009] In particular, the higher enrichment in the intermediate layer than in the proximal layer allows maintaining energy equivalence while limiting the temperature at the center of the pellet, which limits the risk of melting in case of an accident.
[0010] The higher enrichment in the intermediate layer than in the distal layer allows maintaining energy equivalence while limiting the risk of excessive combustion in the distal layer.
[0006]
[0011] According to certain embodiments, the pellet comprises one or more of the following optional features, either alone or in any technically possible combination:
[0012] - The enrichment increases with the radius in a region of the proximal layer adjacent to the intermediate layer;
[0013] - The increase in enrichment is continuous or discontinuous, and / or gradual;
[0014] - The enrichment decreases with the radius in a region of the distal layer adjacent to the intermediate layer;
[0015] - The decrease in enrichment is continuous or discontinuous, and / or gradual;
[0016] - The enrichment is maximum at the interface between the proximal layer and the intermediate layer;
[0017] - The enrichment decreases from the interface between the proximal layer and the intermediate layer to the interface between the intermediate layer and the distal layer;
[0018] - The decrease in enrichment is continuous or discontinuous, and / or gradual;
[0019] - The enrichment exhibits a flat segment of maximum enrichment in the intermediate layer;
[0020] - The enrichment is constant in the intermediate layer;
[0021] - The enrichment in the proximal layer is greater than or equal to 0.25% and / or less than or equal to 1.0%, and / or the enrichment in the distal layer is greater than or equal to 0.25% and less than or equal to 1.0%;
[0022] - The enrichment in the high enrichment region is greater than or equal to 1.8% and / or less than or equal to 10.0%;
[0023] - The intermediate layer has a volume fraction of the pellet between 60% and 94%, and / or the proximal layer has a volume fraction of the pellet between 5% and 20%, and / or the distal layer has a volume fraction of the pellet between 1% and 20%.
[0024] The present invention also relates to a nuclear fuel rod comprising a tubular sheath containing the pellets as defined above. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The invention and its advantages will be better understood by reading the following description, given by way of example only and with reference to the drawings, in which:
[0026] - Figure 1 is a schematic cross-sectional view of a nuclear fuel rod including nuclear fuel pellets;
[0027] - Figure 2is a schematic cross-sectional view of a nuclear fuel pellet;
[0028] - Figures 3 to 6 is a graph showing the different enrichment distributions of nuclear fuel pellets varying with the radius;
[0029] - Figure 7 is a schematic cross-sectional view of a nuclear fuel pellet according to another embodiment. Detailed implementation mode
[0030] Figure 1 shows a nuclear fuel rod 2 intended for use in a light water reactor, in particular a pressurized water reactor (or PWR representing "Pressurized Water Reactor") or a boiling water reactor (or BWR representing "Boiling Water Reactor"), a "VVER" type reactor, a "RBMK" type reactor, or a heavy water reactor such as a "CANDU" type.
[0031] The nuclear fuel rod 2 extends along a longitudinal axis A.
[0032] The nuclear fuel rod 2 includes a sheath 4 that houses the nuclear fuel. The sheath 4 is tubular and extends along the longitudinal axis A. The sheath 4 is sealed at each of its ends by plugs 6.
[0033] The nuclear fuel is in the form of a stack of nuclear fuel pellets 8 axially stacked within the sheath 4, and each pellet 8 contains fissionable material. The stack of pellets 8 is also referred to as a "fission column".
[0034] The nuclear fuel rod 2 includes a spring 10 that is disposed inside the sheath 4 between the stack of pellets 8 and one of the plugs 6 to push the stack of pellets 8 towards the other plug 6. There is a void or gas chamber 12 between the stack of pellets 8 and the plug 6 on which the spring 10 rests.
[0035] The pellets 8 are similar, and only one pellet 8 will be described in more detail later, particularly with reference to Figure 2 .
[0036] As Figure 2 shown, the pellet 8 has a rotational shape around a central axis B.
[0037] The pellet 8 preferably has a generally cylindrical shape with a circular cross-section centered on the central axis B.
[0038] The pellet 8 has a side surface 14 and two opposite end surfaces 16.
[0039] The side surface 14 extends along the central axis B. The side surface 14 is cylindrical and has a circular cross-section centered on the central axis B.
[0040] Each end surface 16 extends from the edge of the side surface 14 towards the central axis B.
[0041] Each end surface 16 is, for example, substantially flat and perpendicular to the central axis B.
[0042] The pellet 8 contains fissile material, which is preferably uranium dioxide ((UO2).
[0043] The pellet 8 includes, for example, a matrix formed of a matrix material and fissile material distributed in the matrix.
[0044] The pellet 8 has a plurality of concentric layers.
[0045] In particular, the pellet 8 has concentric proximal layer 20, intermediate layer 22 and distal layer 24.
[0046] The proximal layer 20 is the layer of the pellet 8 that is radially closest to the central axis B, in particular the layer that includes the central axis B. The proximal layer 20 is the innermost radial layer of the pellet 8.
[0047] The distal layer 24 is the layer of the pellet 8 that is radially furthest from the central axis B. The distal layer 24 is the outermost radial layer of the pellet 8. The distal layer 24 is the surface layer of the pellet 8.
[0048] The intermediate layer 22 is located radially between the proximal layer 20 and the distal layer 24.
[0049] The proximal layer 20 extends radially until a first radius R1, the intermediate layer 22 extends radially between the first radius R1 and a second radius R2, and the distal layer 24 extends radially between the second radius R2 and a third radius R3.
[0050] The third radius R3 is the outer radius of the pellet 8, i.e., the radius of the side surface 14.
[0051] The pellet 8 has, for example, a height H between 9 mm and 13 mm and / or an outer diameter D between 7 mm and 10 mm measured according to the central axis B.
[0052] Each concentric layer of the pellet 8 has a thickness measured radially.
[0053] The proximal layer 20 has a thickness, for example, between 700 μm and 2300 μm. The thickness of the proximal layer 20 is equal to the first radius R1.
[0054] The thickness of the intermediate layer 22 is between 1.5 mm and 3.9 mm. The thickness of the intermediate layer is equal to the difference between the second radius R2 and the first radius R1.
[0055] The distal layer 24 has a third thickness, for example, between 17 μm and 528 μm. The thickness of the distal layer 24 is equal to the difference between the third radius R3 and the second radius R2.
[0056] The pellet 8 exhibits an accumulation or "enrichment" of fissile material.
[0057] The enrichment of the pellet 8 varies radially, i.e., as a function of the distance from the central axis B of the pellet 8.
[0058] Preferably, the enrichment of the pellet 8 varies only radially. The enrichment of the pellet 8 does not vary axially or circumferentially. For a given radius, the enrichment is the same over the entire height and the entire circumference of the pellet 8.
[0059] The intermediate layer 22 has a high enrichment region in which the enrichment is strictly higher than the enrichment in the proximal layer 20 and / or the distal layer 24, preferably strictly higher than the enrichment in the proximal layer 20 and the distal layer 24.
[0060] For example, if the enrichment is constant in the intermediate layer, the high enrichment region extends, for example, over the entire radial extent of the intermediate layer 22, or, for example, if the enrichment varies within the intermediate layer 22, the high enrichment region extends over a part of the radial extent of the intermediate layer 22.
[0061] Preferably, the enrichment present in the intermediate layer 22 and in particular in the high enrichment region has a maximum enrichment E MAX .
[0062] Figures 3 to 7 is a graph showing different examples of the enrichment profile E of the pellet 8 that varies with the radius R (i.e., as a function of the distance from the central axis B of the pellet 8).
[0063] In Figure 3 the example, the proximal layer 20 exhibits a constant proximal enrichment E PROX in the proximal layer 20, a constant enrichment in the intermediate layer 22, and a constant distal enrichment E DIST in the distal layer 24.
[0064] The enrichment in the intermediate layer 22 is strictly higher than the proximal enrichment E PROX of the proximal layer 20 and the distal enrichment E DIST of the distal layer 24.
[0065] The enrichment in the intermediate layer 22 corresponds to the maximum enrichment E MAX of the pellet 8.
[0066] The intermediate layer 22 has a flat section with the maximum enrichment E MAX extending over the entire extent of the intermediate layer 22.
[0067] The high enrichment region of the intermediate layer 22 corresponds to the entire intermediate layer 22. The enrichment is high over the entire radial extent of the intermediate layer 22 (i.e., between the first radius R1 and the second radius R2).
[0068] The proximal enrichment E of the proximal layer 20 PROX and the distal enrichment E of the distal layer 24 DIST are, for example, equal.
[0069] Alternatively, the proximal enrichment portion E of the proximal layer 20 PROX and the distal enrichment E of the distal layer 24 DIST are different, one being strictly higher than the other.
[0070] In Figure 3 the example of, the enrichment distribution exhibits a discontinuous jump between the proximal enrichment E PROX and the maximum enrichment E MAX at the interface between the proximal layer 20 and the intermediate layer 22, and exhibits a discontinuous jump between the intermediate enrichment E MAX and the distal enrichment E DIST at the interface between the intermediate layer 22 and the distal layer 24.
[0071] A continuous and / or gradual change in enrichment can be provided.
[0072] In particular, the intermediate layer 22 optionally includes a transition region having a continuous and / or gradual change in enrichment between the high enrichment region and the proximal layer 20, and / or a transition region having a continuous and / or gradual change in enrichment between the high enrichment region and the distal layer 24.
[0073] In Figure 4 one embodiment shown, the enrichment continuously increases with radius (i.e., with the distance to the central axis B) in the region of the intermediate layer 22 adjacent to the proximal layer 20, for example, from the proximal enrichment E PROX to the maximum enrichment E MAX . This increase is continuous.
[0074] This increase is, for example, linear. Alternatively, this increase is non-linear.
[0075] The region of the intermediate layer 22 adjacent to the proximal layer 20 defines a transition region between the proximal layer 20 and the high enrichment region.
[0076] Alternatively or optionally, as Figure 4 shown, the enrichment continuously decreases with radius in the region of the intermediate layer 22 adjacent to the distal layer 24, for example, from the maximum enrichment E MAX to the distal enrichment E DISTThe decrease is continuous.
[0077] The reduction is, for example, linear. Alternatively, the reduction is non-linear.
[0078] The region of the intermediate layer 22 adjacent to the proximal layer 20 defines a transition region and a high enrichment region.
[0079] In a particular embodiment, within the intermediate layer 22, the enrichment increases in the region adjacent to the proximal layer as the radius increases from the proximal enrichment E PROX Continuously increase to the maximum enrichment E MAX , then remains constant and then decreases continuously in the region adjacent to the distal layer 24 until the distal enrichment E is reached. DIST .
[0080] like Figure 4 As shown, the enrichment distribution shows that the enrichment E PROX To the maximum enrichment E MAX The plateau increases, and then presents an increase from the maximum enrichment E MAX The plateau to the distal enrichment E DIST the reduced part.
[0081] The increasing portion is linear. It takes the shape of an ascending ramp with a constant slope. Alternatively, the increasing portion is nonlinear. It takes a variable slope.
[0082] The decreasing portion is linear. It takes the shape of a descending ramp with a constant slope. Alternatively, the decreasing portion is nonlinear. It has a variable slope.
[0083] In one embodiment, the enrichment exhibits a gradual increase.
[0084] For example, the gradual increase is achieved by one or more intermediate steps. For example, the gradual increase is achieved in a continuous manner (with a slope between two consecutive steps) and / or discontinuously (with a discontinuous jump between two consecutive steps).
[0085] In one embodiment, the enrichment exhibits a gradual decrease.
[0086] For example, the gradual reduction is achieved by one or more intermediate steps.For example, the gradual reduction is achieved in a continuous manner (with a ramp between two consecutive steps) and / or discontinuously (with a jump between two consecutive steps).
[0087] Figure 5 The enrichment distribution shown is similar to Figure 4 The enrichment distribution of the proximal enrichment E PROX and the maximum enrichment E MAXThe increase between the flat segments is gradual, with two intermediate steps here, and the maximum enrichment E MAX of the flat segment and the distal enrichment E DIST The decrease between them is gradual, with two intermediate steps here.
[0088] The enrichment distribution does not necessarily exhibit a flat segment with the maximum enrichment in the intermediate layer 22.
[0089] When presenting a high-enrichment region where the enrichment is strictly higher than the proximal enrichment E PROX and / or the distal enrichment E DIST the enrichment distribution can increase from the proximal enrichment E PROX to the maximum enrichment E MAX and / or decrease from the maximum enrichment E MAX to the distal enrichment E DIST in the intermediate layer 22.
[0090] In Figure 6 In one embodiment shown, the enrichment is maximum at the interface between the proximal layer 20 and the intermediate layer 22, and then gradually decreases towards the interface between the intermediate layer 22 and the distal layer 24.
[0091] The enrichment decreases continuously and particularly linearly towards the interface between the intermediate layer 22 and the distal layer 24 here. Alternatively, the enrichment decreases gradually towards the interface between the intermediate layer 22 and the distal layer 24.
[0092] In an alternative, the maximum enrichment E MAX is reached near the interface between the intermediate layer 22 and the distal layer 24, preferably having a continuous or discontinuous and / or gradual change between the proximal enrichment E PROX and the maximum enrichment E MAX over a small thickness (e.g., a thickness between 50 μm and 500 μm).
[0093] The enrichment at the interface between the intermediate layer 22 and the distal layer 24 is strictly higher than the distal enrichment E DIST here. The enrichment exhibits a discontinuous jump at the interface between the intermediate layer 22 and the distal layer 24.
[0094] Alternatively, as shown by the dashed line in Figure 6 the enrichment decreases in the intermediate layer 22 until it reaches the distal enrichment E DIST at the interface between the intermediate layer 22 and the distal layer 24.
[0095] In this case, the intermediate layer 22 presents a high-enrichment region, followed by a transition region between the high-enrichment region and the distal layer 24.
[0096] The present invention is not limited to what is described above andFigures 3 to 6 For the embodiments shown, other embodiments can be contemplated, especially Figures 3 to 6 combinations of embodiments.
[0097] In one embodiment, the enrichment degree shows a continuous and / or gradual increase between the proximal enrichment degree E PROX and the maximum enrichment degree E MAX in the intermediate layer 22, and then shows a flat segment until the interface between the intermediate layer 22 and the distal layer 24 at the maximum enrichment degree E MAX At the interface between the intermediate layer 22 and the distal layer 24, the enrichment degree shows a discontinuous jump between the maximum enrichment degree E MAX and the distal enrichment degree E DIST (it is not a continuous or gradual decrease between the maximum enrichment degree E MAX and the distal enrichment degree E DIST ).
[0098] In one embodiment, the enrichment degree shows a discontinuous jump between the proximal enrichment degree E PROX and the maximum enrichment degree E MAX at the interface between the distal layer 20 and the intermediate layer 22, then shows a flat segment at the maximum enrichment degree E MAX and then shows a continuous and / or gradual decrease between the maximum enrichment degree E MAX and the distal enrichment degree E DIST .
[0099] In addition, continuous increase can be combined with discontinuous decrease, and discontinuous increase can be combined with continuous decrease.
[0100] In one embodiment, where the enrichment degree E shows a discontinuous gradual increase between the proximal enrichment degree E PROX and the maximum enrichment degree E MAX and shows a continuous decrease between the maximum enrichment degree E MAX and the distal enrichment degree E DIST .
[0101] In one embodiment, the enrichment degree E shows a continuous increase between the proximal enrichment degree E PROX and the maximum enrichment degree E MAX and shows a discontinuous gradual decrease between the maximum enrichment degree E MAX and the distal enrichment degree E DIST .
[0102] In one embodiment where the enrichment degree shows a linear increase and a linear decrease, the absolute values of the slope of the linear increase and the slope of the gradual decrease are, for example, equal.
[0103] Alternatively, the absolute values of the slope of the linear increase and the slope of the gradual decrease are different.
[0104] In one embodiment where the enrichment continuously increases and then continuously decreases, the increase and decrease are linear. Alternatively, the increase is linear while the decrease is non-linear, or the increase is non-linear while the decrease is linear.
[0105] In one embodiment, and as Figures 3 to 6 shown, the proximal enrichment E PROX and the distal enrichment E DIST are substantially equal.
[0106] In this case, preferably, the proximal enrichment E PROX and the distal enrichment E DIST are equal to the minimum enrichment of the pellet 8.
[0107] Alternatively, the proximal enrichment E PROX and the distal enrichment E DIST are different.
[0108] In this case, preferably, one of the proximal enrichment E PROX and the distal enrichment E DIST is lower than the other, and the lower one is the minimum enrichment of the pellet 8.
[0109] In one embodiment, the proximal enrichment E PROX is strictly higher than the distal enrichment E DIST . In this case, preferably, the distal enrichment E DIST is the minimum enrichment of the pellet 8.
[0110] In one embodiment, the proximal enrichment E PROX is strictly lower than the distal enrichment E DIST . In this case, preferably, the proximal enrichment E PROX is the minimum enrichment of the pellet 8.
[0111] Generally speaking, the enrichment shows a discontinuous jump between the high-enrichment regions of the proximal layer 20 and the intermediate layer 22, or there is a transition region with continuous and / or gradual increase between the proximal layer 20 and the high-enrichment region, and shows a discontinuous jump between the high-enrichment region of the intermediate layer 22 and the distal layer, or there is a transition region with continuous and / or gradual increase between the high-enrichment region and the distal layer 24.
[0112] In addition, the enrichment in the high-enrichment region is constant and shows a flat segment of the maximum enrichment E MAX , or varies radially. In this case, the enrichment varies continuously and / or gradually in the high-enrichment region, thus forming, for example, one or more flat segments.
[0113] The radially variable enrichment within pellet 8 allows for the provision of the required amount of fissile material within pellet 8 while limiting the risk of pellet 8 degradation, in particular the "FFRD" risk.
[0114] The higher enrichment in the intermediate layer 22 than in the proximal layer 20 allows for the provision of the required amount of fissile material while limiting the risk of reaching an excessive temperature at the center of pellet 8, especially in the event of an accident.
[0115] The higher enrichment in the intermediate layer 22 than in the distal layer 24 allows for the provision of the required amount of fissile material while limiting the risk of excessive burning of the burnable material at the periphery of pellet 8.
[0116] Preferably, the enrichment of pellet 8 is adjusted to provide the required amount of fissile material contained in pellet 8 and preferably to maintain the energy equivalence between pellet 8 and a reference pellet that exhibits a uniform reference enrichment E REF and has a substantially identical geometry, in particular having the same volume as pellet 8.
[0117] Considering Figure 3 an example of the enrichment distribution, the following equation must be complied with:
[0118] E REF = E PROX × (FV PROX ) + E MAX × (FV INT ) + E DIST × (FV DIST )
[0119] where:
[0120] E REF is the reference enrichment of the reference pellet;
[0121] E PROX is the enrichment of the proximal layer 20;
[0122] E MAX is the enrichment of the intermediate layer 22;
[0123] E DIST is the enrichment of the distal layer 24;
[0124] FV PROX is the volume fraction of the proximal layer 20, i.e., the ratio of the volume of the proximal layer 20 to the volume of pellet 8;
[0125] FV INT is the volume fraction of the intermediate layer 22, i.e., the ratio of the volume of the intermediate layer 22 to the volume of pellet 8; and
[0126] FVDIST is the volume fraction of the distal layer 24, i.e., the ratio of the volume of the distal layer 24 to the volume of the pellet 8.
[0127] At E REF = 4%, E PROX = E DIST = 0.3%, FV PROX = 10%, FV DIST = 5% and FV INT = 85% in a specific example, the maximum enrichment E MAX = 4.65% is obtained.
[0128] Preferably, the volume fraction of the proximal layer 20 is between 5% and 20%.
[0129] Preferably, the volume fraction of the intermediate layer 22, in particular the volume fraction of the high enrichment region of the intermediate layer 22, is between 60% and 94%.
[0130] Preferably, the volume fraction of the distal layer 24 is between 1% and 20%.
[0131] Preferably, the enrichment in the proximal layer 20 is greater than or equal to 0.25% and / or less than or equal to 1.0%.
[0132] Preferably, the enrichment in the distal layer 24 is greater than or equal to 0.25% and / or less than or equal to 1.0%.
[0133] Preferably, the enrichment in the high enrichment region of the intermediate layer 22 is greater than or equal to 1.8% and / or less than or equal to 10.0%.
[0134] Preferably, the ratio between the maximum enrichment E MAX and the proximal enrichment E PROX is, for example, between 1.8 and 40.
[0135] Preferably, the ratio between the maximum enrichment E MAX and the distal enrichment E DIST is, for example, between 1.8 and 40.
[0136] Compliance with the above dimensions and / or ratios taken alone or in combination allows obtaining pellets 8 containing an appropriate amount of fissile material while limiting the risk of degradation.
[0137] The reduction of the degradation risk of the pellets 8 can ultimately at least partially allow overcoming the geometric constraints of conventional pellets, in particular the presence of chamfers at the junctions between the side surfaces 14 and each end surface 16 and / or the presence of depressions at the centers of each end surface 16.
[0138] As shown, in particular, in Figure 2In [the context], the pellet 8 can have a cylindrical shape. In particular, there is no chamfer at the junction between the side surface 14 and each end surface 16 and the end surface 16 is flat.
[0139] This allows for simplifying the manufacture of the pellet 8.
[0140] As Figure 7 shown, the present invention can also be applied to a generally cylindrical pellet, the geometry of which differs from the geometry of Figure 2 in that it includes a chamfer 30 at the junction between the side surface 14 and each end surface 16 and / or a recess 32 at the center of each end surface 16.
[0141] For example, the pellet 8 is obtained by sintering. The pellet 8 includes a matrix and a fissile material contained in the matrix, and the fissile material has a radially varying enrichment (i.e., the concentration of the fissile material varies radially).
[0142] In this case, the enrichment is constant, for example, in the proximal layer 20, constant in the intermediate layer 22, and / or constant in the distal layer 24, for example as in the example of Figure 3 [the reference].
[0143] Alternatively, for example, by additive manufacturing (or 3D printing), a pellet 8 including a matrix and a fissile material with a radially varying enrichment contained in the matrix is obtained from a powder. The powder includes, for example, a first powder composed of the fissile material and a second powder composed of the matrix material, and the pellet 8 is additively manufactured by changing the ratio between the first powder and the second powder.
[0144] For example, the pellet 8 is manufactured by successive concentric manufacturing layers by changing the ratio between the first powder and the second powder between the manufacturing layers.
[0145] Each concentric layer (proximal layer 20, intermediate layer 22, and distal layer 24) of the pellet 8 is formed by a plurality of superimposed manufacturing layers.
[0146] Each possible change (continuous or discontinuous) in the enrichment within the intermediate layer 22 is obtained by changing the ratio between the first powder and the second powder between the manufacturing layers of the intermediate layer 22.
[0147] Additive manufacturing is carried out, for example, by one or more of the following methods: selective laser sintering (or SLS from the English "Selective Laser Sintering"), electron beam melting (or EBM from the English "Electron Beam Melting"), direct metal laser sintering (or DMSL from the English "Direct Metal Laser Sintering"), direct energy deposition (or, according to the English term, "Direct Energy Deposition"), and spark plasma sintering (or SPS from the English "Spark Plasma Sintering").
[0148] In the above, the pellet is considered before irradiation. The pellet is considered at the end of pellet manufacturing, especially before integrating the pellet into a nuclear fuel rod and / or before using the pellet in a nuclear reactor. The enrichment value is expressed as a percentage by mass.
Claims
1. A nuclear fuel pellet having a rotationally symmetric shape about a central axis (B) and containing fissile material, the pellet having concentric layers including a proximal layer (20), an intermediate layer (22), and a distal layer (24), wherein the enrichment of the fissile material within the pellet varies radially, and the intermediate layer (22) includes a high-enrichment region in which the enrichment is strictly greater than the enrichment in the proximal layer (20) and / or strictly greater than the enrichment in the distal layer (24).
2. The pellet according to claim 1, wherein, The enrichment increases with radius in a region of the intermediate layer (22) adjacent to the proximal layer (20).
3. The pellet according to claim 2, wherein, The increase in enrichment is continuous or discontinuous, and / or gradual.
4. The pellet according to any one of the preceding claims, wherein, The enrichment decreases with radius in a region of the intermediate layer (22) adjacent to the distal layer (20).
5. The pellet according to claim 4, wherein, The decrease in enrichment is continuous or discontinuous, and / or gradual.
6. The pellet according to any one of the preceding claims, wherein, The enrichment is maximum at the interface between the proximal layer (20) and the intermediate layer (22).
7. The pellet according to any one of the preceding claims, wherein, The enrichment decreases from the interface between the proximal layer (20) and the intermediate layer (22) to the interface between the intermediate layer (22) and the distal layer (24).
8. The pellet according to claim 7, wherein, The decrease in enrichment is continuous or discontinuous, and / or gradual.
9. The pellet according to any one of the preceding claims, wherein, The enrichment exhibits a plateau of maximum enrichment in the intermediate layer (24).
10. The pellet according to claim 1, wherein, The enrichment is constant in the intermediate layer (24).
11. The pellet according to any one of the preceding claims, wherein, The enrichment in the proximal layer (20) is greater than or equal to 0.25% and / or less than or equal to 1.0% by mass, and / or the enrichment in the distal layer (24) is greater than or equal to 0.25% and less than or equal to 1.0% by mass.
12. The pellet according to any one of the preceding claims, wherein, The enrichment in the high-enrichment region is greater than or equal to 1.8% and / or less than or equal to 10.0% by mass.
13. The pellet according to any one of the preceding claims, wherein, The intermediate layer (22) has a volume fraction of the pellet between 60% and 94%, and / or the proximal layer (20) has a volume fraction of the pellet between 5% and 20%, and / or the distal layer (24) has a volume fraction of the pellet between 1% and 20%.
14. A nuclear fuel rod comprising a tubular sheath containing a pellet according to any one of the preceding claims.