Nuclear fuel pellet with radially variable enrichment
Patent Information
- Application Number
- EP2023828178
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-12-14
- Filing Date
- 2023-12-14
- Publication Date
- 2025-10-22
AI Technical Summary
Nuclear fuel pellets face risks of deterioration, fragmentation, relocation, and dispersion due to locally high combustion and temperature, which existing designs fail to adequately address, particularly in maintaining energy equivalence and preventing melting or excessive combustion.
A radially variable enrichment nuclear fuel pellet with concentric layers, where the intermediate layer has a higher fissile material enrichment than the proximal and distal layers, allowing for adjusted reactivity and combustion profiles to mitigate these risks, featuring varying enrichment profiles that can be continuous or discontinuous, and maximum enrichment zones to preserve energy equivalence.
The radially variable enrichment design effectively limits the risk of deterioration by managing temperature and combustion, ensuring energy equivalence and reducing the likelihood of melting or excessive combustion, thereby enhancing the stability and performance of nuclear fuel pellets.
Smart Images
Figure 1.1
Abstract
Description
[0001] DESCRIPTION
[0002] Radially variable enrichment nuclear fuel pellet
[0003] The present invention relates to the field of nuclear fuel, and in particular to a nuclear fuel pellet intended to be integrated into a nuclear fuel rod.
[0004] A core of a light water or heavy water nuclear reactor is generally formed of a plurality of nuclear fuel assemblies arranged side by side, each nuclear fuel assembly comprising a bundle of nuclear fuel rods, each nuclear fuel rod comprising a tubular cladding containing nuclear fuel, the cladding being closed at each of its two ends by a plug.
[0005] Nuclear fuel is for example provided in the form of nuclear fuel pellets containing fissile material, each pellet being generally cylindrical in shape, the pellets being stacked in the cladding.
[0006] During the combustion of a nuclear fuel pellet, there is a risk of deterioration of the pellet, and in particular a risk of fragmentation, relocation and / or dispersion of the fuel (or FFRD for "Fuel Fragmentation Relocation and Dispersion" in English terminology).
[0007] This risk is higher in the event of locally high combustion within the pellet or locally high temperature within the pellet.
[0008] One of the aims of the invention is to propose a nuclear fuel pellet which makes it possible to limit the risk of deterioration of the pellet during its use.
[0009] To this end, the invention provides a nuclear fuel pellet of symmetrical shape of revolution around a central axis and containing a fissile material, the pellet having concentric layers including a proximal layer, an intermediate layer and a distal layer, in which the enrichment in fissile material within the pellet varies radially, and the intermediate layer comprises a high enrichment zone in which the enrichment is strictly greater than the enrichment in the proximal layer and / or the enrichment in the distal layer.
[0010] Radially variable enrichment of the pellet in fissionable material allows the reactivity and combustion within the nuclear fuel pellet to be adjusted as a function of the radius, so as to limit the risk of deterioration linked to locally high combustion and / or a locally high temperature. In particular, higher enrichment in an intermediate layer than in a proximal layer makes it possible to maintain energy equivalence while limiting the temperature in the center of the pellet, which limits the risk of meltdown in an accidental situation.
[0011] Higher enrichment in an intermediate layer than in a distal layer allows energy equivalence to be preserved while limiting the risk of excessive combustion in the distal layer.
[0012] According to particular embodiments, the pellet comprises one or more of the following optional features, taken individually or in all technically possible combinations:
[0013] - enrichment increases with radius in an area of the intermediate layer adjacent to the proximal layer;
[0014] - the increase in enrichment is continuous or discontinuous, and / or gradual;
[0015] - enrichment decreases with radius in an area of the intermediate layer adjacent to the distal layer;
[0016] - the reduction in enrichment is continuous or discontinuous, and / or gradual;
[0017] - enrichment is maximal at an interface between the proximal layer and the intermediate layer;
[0018] - enrichment decreases from an interface between the proximal layer and the intermediate layer to an interface between the intermediate layer and the distal layer;
[0019] - the reduction in enrichment is continuous or discontinuous, and / or gradual;
[0020] - enrichment shows a maximum enrichment plateau in the intermediate layer;
[0021] - enrichment is constant in the intermediate layer;
[0022] - the enrichment in the proximal layer is equal to or greater than 0.25% and / or equal to or less than 1.0% and / or the enrichment in the distal layer is equal to or greater than 0.25% and less than or equal to 1.0%;
[0023] - the enrichment in the high enrichment zone is equal to or greater than 1.8% and / or less than or equal to 10.0%;
[0024] - the intermediate layer represents a volume fraction of the pellet of between 60% and 94% and / or the proximal layer represents a volume fraction of the pellet of between 5% and 20% and / or the distal layer represents a volume fraction of the pellet of between 1% and 20%.
[0025] The invention also relates to a nuclear fuel rod, comprising a tubular sheath containing pellets as defined above. The invention and its advantages will be better understood on reading the following description, given solely by way of example, and with reference to the appended drawings, in which:
[0026] - Figure 1 is a schematic sectional view of a nuclear fuel rod comprising nuclear fuel pellets;
[0027] - Figure 2 is a schematic sectional view of a nuclear fuel pellet;
[0028] - Figures 3 to 6 are graphs illustrating different enrichment profiles of a nuclear fuel pellet as a function of radius;
[0029] - Figure 7 is a schematic sectional view of a nuclear fuel pellet according to another exemplary embodiment.
[0030] Figure 1 illustrates a nuclear fuel rod 2 intended for use in a light water reactor, in particular a pressurized water reactor (or PWR for "Pressurized Water Reactor") or a boiling water reactor (or BWR for "Boiling Water Reactor"), a "VVER" type reactor, an "RBMK" type reactor, a heavy water reactor, for example of the "CANDU" type.
[0031] The nuclear fuel rod 2 is elongated along a longitudinal axis A.
[0032] The nuclear fuel rod 2 comprises a cladding 4 containing nuclear fuel. The cladding 4 is tubular and extends along the longitudinal axis A. The cladding 4 is sealed at each of its ends by a plug 6.
[0033] The nuclear fuel is in the form of a stack of nuclear fuel pellets 8 stacked axially inside the cladding 4, each pellet 8 containing fissile material. The stack of pellets 8 is also called a "fissile column".
[0034] The nuclear fuel rod 2 comprises a spring 10 arranged inside the cladding 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. A vacuum or plenum 12 is present between the stack of pellets 8 and the plug 6 on which the spring 10 bears.
[0035] The pellets 8 are similar and only one of the pellets 8 will be described in more detail below, with particular reference to Figure 2.
[0036] As illustrated in Figure 2, the pellet 8 has a shape of revolution 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. The pellet 8 has a lateral surface 14 and two opposite end surfaces 16.
[0038] The lateral surface 14 extends along the central axis B. The lateral surface 14 is cylindrical with a circular cross-section centered on the central axis B.
[0039] Each end surface 16 extends from an end edge of the side surface 14 toward the central axis B.
[0040] Each end surface 16 is for example substantially planar and perpendicular to the central axis B.
[0041] Pellet 8 contains a fissile material, the fissile material preferably being uranium dioxide (UO2).
[0042] The pellet 8 comprises, for example, a matrix made of a matrix material and the fissile material distributed in the matrix.
[0043] The 8 pellet has several concentric layers.
[0044] In particular, the pellet 8 has a concentric proximal layer 20, an intermediate layer 22 and a distal layer 24.
[0045] The proximal layer 20 is the layer of the pellet 8 which is radially closest to the central axis B, and in particular which includes the central axis B. The proximal layer 20 is the radially innermost layer of the pellet 8.
[0046] The distal layer 24 is the layer of the pellet 8 which is radially furthest from the central axis B. The distal layer 24 is the radially outermost layer of the pellet 8. The distal layer 24 is the surface layer of the pellet 8.
[0047] The intermediate layer 22 is located radially between the proximal layer 20 and the distal layer 24.
[0048] The proximal layer 20 extends radially to 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.
[0049] The third radius R3 is the external radius of the pellet 8, i.e. the radius of the lateral surface 14.
[0050] The pellet 8 has, for example, a height H, taken along the central axis B, of between 9 mm and 13 mm and / or an external diameter D of between 7 mm and 10 mm.
[0051] Each of the concentric layers of the pellet 8 has a thickness taken radially.
[0052] The proximal layer 20 has for example a thickness between 700 pm and 2300 pm. The thickness of the proximal layer 20 is equal to the first radius R1. The intermediate layer 22 has a thickness 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.
[0053] The distal layer 24 has, for example, a third thickness of 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.
[0054] Pellet 8 has a concentration of fissile material or “enrichment”.
[0055] The enrichment of the pellet 8 varies radially, ie as a function of the distance from the central axis B of the pellet 8.
[0056] 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 of the pellet 8 and over the entire circumference of the pellet 8.
[0057] The intermediate layer 22 has a high enrichment zone in which the enrichment is strictly higher than in the proximal layer 20 and / or in the distal layer 24, preferably strictly higher than in the proximal layer 20 and in the distal layer 24.
[0058] The high enrichment zone extends for example over the entire radial extent of the intermediate layer 22, for example if the enrichment is constant in the intermediate layer, or over a fraction of the radial extent of the intermediate layer 22, for example if the enrichment varies within the intermediate layer 22.
[0059] Preferably, the enrichment has in the intermediate layer 22, and in particular in the high enrichment zone, a maximum enrichment EMAX.
[0060] Figures 3 to 7 are graphs illustrating different examples of enrichment profiles E of the pellet 8 as a function of the radius R, i.e. as a function of the distance from the central axis B of the pellet 8.
[0061] In the example of Figure 3, the proximal layer 20 has a proximal enrichment E PRO constant x in proximal layer 20, constant enrichment in intermediate layer 22 and constant distal EDIST enrichment in distal layer 24.
[0062] The enrichment in the intermediate layer 22 is strictly higher than the proximal EPROX enrichment of the proximal layer 20 and the distal EDIST enrichment of the distal layer 24.
[0063] The enrichment in the intermediate layer 22 corresponds to the maximum enrichment EMAX of the pellet 8. The intermediate layer 22 has a maximum enrichment plateau EMAX which extends over the entire extent of the intermediate layer 22.
[0064] The high enrichment zone 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.
[0065] For example, the proximal EPROX enrichment of proximal layer 20 and the distal EDIST enrichment of distal layer 24 are equal.
[0066] Alternatively, the proximal EPROX enrichment of the proximal layer 20 and the distal EDIST enrichment of the distal layer 24 are different, one being strictly higher than the other.
[0067] In the example of Figure 3, the enrichment profile has a non-continuous jump at the interface between the proximal layer 20 and the intermediate layer 22, between the proximal enrichment EPROX and the maximum enrichment EMAX, and a non-continuous jump at the interface between the intermediate layer 22 and the distal layer 24, between the intermediate enrichment E AX and the distal enrichment EDIST.
[0068] It is possible to predict a continuous and / or gradual variation of enrichment.
[0069] In particular, the intermediate layer 22 optionally comprises a transition zone with continuous and / or gradual variation of the enrichment between the high enrichment zone and the proximal layer 20 and / or a transition zone with a continuous and / or gradual variation of the enrichment between the high enrichment zone and the distal layer 24.
[0070] In an exemplary embodiment illustrated in Figure 4, the enrichment increases continuously with the radius (i.e. with the distance from the central axis B) in an area of the intermediate layer 22 adjacent to the proximal layer 20, up to the high enrichment area of the intermediate layer 22, for example from the proximal enrichment EPROX up to the maximum enrichment EMAX. The increase is continuous.
[0071] The increase is, for example, linear. Alternatively, the increase is non-linear.
[0072] Said zone of the intermediate layer 22 adjacent to the proximal layer 20 defines a transition zone between the proximal layer 20 and the high enrichment zone.
[0073] Alternatively or optionally, as illustrated in Figure 4, the enrichment decreases continuously with radius in an area of the intermediate layer 22 adjacent to the distal layer 24, for example from the maximum enrichment EMAX to the distal enrichment EDIST. The decrease is continuous.
[0074] The decrease is, for example, linear. Alternatively, the decrease is non-linear.
[0075] Said zone of the intermediate layer 22 adjacent to the proximal layer 20 defines a transition zone and the high enrichment zone.
[0076] In a particular embodiment, within the intermediate layer 22, the enrichment increases continuously with the radius in the area adjacent to the proximal layer, from the proximal enrichment EPROX to the maximum enrichment EMAX, then remains constant, then decreases continuously in the area adjacent to the distal layer 24 until reaching the distal enrichment EDIST.
[0077] As illustrated in Figure 4, the enrichment profile shows an increasing portion from proximal enrichment EPROX to a maximum enrichment plateau E AX, then a decreasing portion from the maximum enrichment plateau EMAX to distal enrichment EDIST.
[0078] The increasing portion is linear. It has the shape of an upward ramp with a constant slope. Alternatively, the increasing portion is non-linear. It has a variable slope.
[0079] The decreasing portion is linear. It has the shape of a downward ramp with a constant slope. Alternatively, the decreasing portion is non-linear. It has a variable slope.
[0080] In one exemplary embodiment, the enrichment exhibits a gradual increase.
[0081] A gradual increase is, for example, achieved with one or more intermediate stages. A gradual increase is achieved, for example, continuously (with a ramp between two successive stages) and / or non-continuously (with a discontinuous jump between two successive stages).
[0082] In one exemplary embodiment, the enrichment exhibits a gradual decrease.
[0083] A gradual decrease is, for example, achieved with one or more intermediate stages. A gradual decrease is achieved, for example, continuously (with a ramp between two successive stages) and / or non-continuously (with a jump between two successive stages).
[0084] The enrichment profile illustrated in Figure 5 differs from that of Figure 4 in that the increase between proximal enrichment EPROX and the maximum enrichment plateau EMAX is gradual, here with two intermediate steps, and in that the decrease between the maximum enrichment plateau EMAX and distal enrichment EDIST is gradual, here with two intermediate steps.
[0085] The enrichment profile does not necessarily show a maximum enrichment plateau in the intermediate layer 22.
[0086] The enrichment profile may increase in the intermediate layer 22 from the proximal enrichment EPROX to the maximum enrichment EMAX and / or decrease from the maximum enrichment E AX to the distal enrichment EDIST, presenting a zone of high enrichment in which the enrichment is strictly higher than the proximal enrichment EPROX and / or the distal enrichment EDIST.
[0087] In an exemplary embodiment illustrated in Figure 6, the enrichment is maximum at the interface between the proximal layer 20 and the intermediate layer 22 then gradually decreases to the interface between the intermediate layer 22 and the distal layer 24.
[0088] The enrichment here decreases continuously, and in particular linearly, up to the interface between the intermediate layer 22 and the distal layer 24. Alternatively, the enrichment gradually decreases up to the interface between the intermediate layer 22 and the distal layer 24.
[0089] In a variant, the maximum enrichment EMAX is reached near the interface between the intermediate layer 22 and the distal layer 24, with a continuous or discontinuous and / or gradual variation between the proximal enrichment EPROX and the maximum enrichment EMAX, preferably over a small thickness, for example a thickness of between 50 μm and 500 μm.
[0090] The enrichment at the interface between the intermediate layer 22 and the distal layer 24 is here strictly greater than the EDIST distal enrichment. The enrichment presents a non-continuous jump at the interface between the intermediate layer 22 and the distal layer 24.
[0091] Alternatively, as illustrated in dashed lines in Figure 6, the enrichment decreases in the intermediate layer 22 until reaching the distal enrichment EDIST at the interface between the intermediate layer 22 and the distal layer 24.
[0092] The intermediate layer 22 in this case has a high enrichment zone followed by a transition zone between the high enrichment zone and the distal layer 24.
[0093] The invention is not limited to the exemplary embodiments described above and illustrated in Figures 3 to 6, other exemplary embodiments being conceivable, in particular combinations of the exemplary embodiments of Figures 3 to 6.
[0094] In an exemplary embodiment, the enrichment in the intermediate layer 22 has a continuous and / or gradual increase between the proximal enrichment EPROX and the maximum enrichment EMAX, then a plateau at the maximum enrichment EMAX up to the interface between the intermediate layer 22 and the distal layer 24 where the enrichment has a discontinuous jump between the maximum enrichment EMAX and the distal enrichment EDIST (without a continuous or gradual decrease between the maximum enrichment E AX and the distal enrichment EDIST).
[0095] In an exemplary embodiment, the enrichment exhibits a discontinuous jump at the interface between the distal layer 20 and the intermediate layer 22 between the proximal enrichment EPROX and the maximum enrichment EMAX, then a plateau at the maximum enrichment EMAX then a continuous and / or gradual decrease between the maximum enrichment EMAX and the distal enrichment EDIST.
[0096] Furthermore, it is possible to combine a continuous increase with a non-continuous decrease and a non-continuous increase with a continuous decrease.
[0097] In an exemplary embodiment in which the enrichment E has a non-continuous gradual increase between the proximal enrichment EPROX and the maximum enrichment EMAX and a continuous decrease between the maximum enrichment EMAX and the distal enrichment EDIST.
[0098] In an exemplary embodiment, the enrichment E has a continuous increase between the proximal enrichment EPROX and the maximum enrichment EMAX and a non-continuous gradual decrease between the maximum enrichment EMAX and the distal enrichment EDIST.
[0099] In an exemplary embodiment in which the enrichment exhibits 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.
[0100] Alternatively, the absolute values of the slope of the linear increase and the slope of the gradual decrease are different.
[0101] In an exemplary embodiment in which the enrichment exhibits a continuous increase and a continuous decrease, the increase and decrease are linear. Alternatively, the increase is linear and the decrease is non-linear, or the increase is non-linear and the decrease is linear.
[0102] In an exemplary embodiment, and as illustrated in Figures 3 to 6, the proximal EPROX enrichment and the distal EDIST enrichment are substantially equal.
[0103] In this case, preferably, the proximal EPROX enrichment and the distal EDIST enrichment are equal to a minimum enrichment of the pellet 8.
[0104] Alternatively, the proximal enrichment EPROX and the distal enrichment EDIST are different. In this case, preferably, the one of the proximal enrichment EPROX and the distal enrichment EDIST that is lower than the other is the minimum enrichment of the pellet 8.
[0105] In an exemplary embodiment, the proximal enrichment EPROX is strictly greater than the distal enrichment EDIST. In this case, preferably, the distal enrichment EDIST is the minimum enrichment of the pellet 8.
[0106] In an exemplary embodiment, the proximal enrichment EPROX is strictly less than the distal enrichment EDIST. In this case, preferably, the proximal enrichment EPROX is the minimum enrichment of the pellet 8.
[0107] Generally, the enrichment has a discontinuous jump between the proximal layer 20 and the high enrichment zone of the intermediate layer 22 or a transition zone with a continuous and / or gradual increase between the proximal layer 20 and the high enrichment zone, and has a discontinuous jump between the high enrichment zone of the intermediate layer 22 and the distal layer or transition zone with a continuous and / or gradual increase between the high enrichment zone and the distal layer 24.
[0108] Furthermore, the enrichment in the high enrichment zone is constant and has a maximum enrichment plateau EMAX or varies radially, in which case the enrichment varies in the high enrichment zone, for example, continuously and / or gradually, for example, forming one or more plateaus.
[0109] The radially variable enrichment within pellet 8 makes it possible to predict the quantity of fissile material required in pellet 8 while limiting the risk of degradation of pellet 8, in particular the “FFRD” risk.
[0110] A higher enrichment in the intermediate layer 22 than in the proximal layer 20 makes it possible to predict the quantity of fissile material required while limiting the risk of reaching too high a temperature in the center of the pellet 8, in particular in accident conditions.
[0111] A higher enrichment in the intermediate layer 22 than in the distal layer 24 makes it possible to predict the quantity of fissile material while limiting the risk of excessive combustion of the combustible material at the periphery of the pellet 8.
[0112] The enrichment of the pellet 8 is preferably adjusted so as to provide a required quantity of fissile material contained in the pellet 8, and preferably so as to maintain an energy equivalence between the pellet 8 and a reference pellet having a uniform EREF reference enrichment and having substantially the same geometry, in particular having the same volume as the pellet 8. Considering the example enrichment profile of Figure 3, the following equation must be respected:
[0113] EREF = EP OX x (FVP OX) + EMAX x (FVINT) + EDIST x (FVDIST) in which:
[0114] EREF is the reference enrichment of the reference pellet;
[0115] EPROX is the enrichment of the proximal layer 20;
[0116] EMAX is the enrichment of the intermediate layer 22;
[0117] EDIST is the enrichment of distal layer 24;
[0118] FVPROX 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 the pellet 8;
[0119] FVINT 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 the pellet 8; and
[0120] 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.
[0121] In a particular example where EREF = 4%, EPROX = EDIST = 0.3%, FVPROX = 10%, FVDIST = 5% and FVINT = 85%, we obtain a maximum enrichment EMAX = 4.65%.
[0122] Preferably, the volume fraction of the proximal layer 20 is between 5% and 20%.
[0123] Preferably, the volume fraction of the intermediate layer 22, in particular of the high enrichment zone of the intermediate layer 22, is between 60% and 94%.
[0124] Preferably, the volume fraction of the distal layer 24 is between 1% and 20%.
[0125] Preferably, the enrichment in the proximal layer 20 is equal to or greater than 0.25% and / or equal to or less than 1.0%.
[0126] Preferably, the enrichment in the distal layer 24 is equal to or greater than 0.25% and / or equal to or less than 1.0%.
[0127] Preferably, the enrichment in the high enrichment zone of the intermediate layer 22 is equal to or greater than 1.8% and / or equal to or less than 10.0%.
[0128] Preferably, the ratio between the maximum enrichment E AX and the proximal enrichment EPROX is for example between 1.8 and 40.
[0129] Preferably, the ratio between the maximum enrichment EMAX and the distal enrichment EDIST is for example between 1.8 and 40. Compliance with the dimensions and / or proportions, taken individually or in combination, makes it possible to obtain a pellet 8 containing an appropriate quantity of fissile material while limiting the risks of deterioration.
[0130] Reducing the risk of degradation of the pellet 8 possibly makes it possible to at least partially overcome the geometric constraints of conventional pellets, and in particular the presence of a chamfer at the junction between the lateral surface 14 and each end surface 16 and / or the presence of a depression in the center of each end surface 16.
[0131] As illustrated in particular in Figure 2, the pellet 8 may be provided with a cylindrical shape, in particular without a chamfer at the junction between the lateral surface 14 and each end surface 16 and with flat end surfaces 16.
[0132] This simplifies the manufacture of the pellet 8.
[0133] As illustrated in Figure 7, the invention can also be applied to a pellet of generally cylindrical shape whose geometry differs from that of Figure 2 in that it comprises a chamfer 30 at the junction between the lateral surface 14 and each end surface 16 and / or a depression 32 in the center of each end surface 16.
[0134] A pellet 8 comprising a matrix and a fissile material contained in the matrix with a radially varying enrichment (i.e. a radially varying fissile material concentration) is obtained for example by sintering.
[0135] In this case, the enrichment is for example constant in the proximal layer 20, constant in the intermediate layer 22 and / or constant in the distal layer 24, as for example in the example of Figure 3.
[0136] Alternatively, a pellet 8 comprising a matrix and a fissile material contained in the matrix with a radially varying enrichment is obtained for example by additive manufacturing (or 3D printing) from powders, including for example a first powder consisting of the fissile material and a second powder consisting of a matrix material, the pellet 8 being manufactured additively by varying the proportions between the first powder and the second powder.
[0137] The pellet 8 is manufactured for example by successive concentric manufacturing layers by varying the proportions between the first powder and the second powder between the manufacturing layers.
[0138] Each of the concentric layers of the pellet 8 (proximal layer 20, intermediate layer 22 and distal layer 24) is formed from several superimposed manufacturing layers.
[0139] Each possible variation in the enrichment within the intermediate layer 22, continuous or not, is obtained by varying the proportions between the first powder and the second powder between the manufacturing layers of the intermediate layer 22.
[0140] Additive manufacturing is carried out, for example, by one or more of the following methods: selective laser sintering (SLS), electron beam melting (EBM), direct metal laser sintering (DMSL), direct energy deposition (Direct Energy Deposition) and spark plasma sintering (SPS).
[0141] In the above, the pellet is considered before irradiation of the pellet. The pellet is considered after pellet manufacturing, in particular before integration of the pellet into a nuclear fuel rod and / or before use of the pellet in a nuclear reactor. The enrichment values are expressed in mass percentages.
Claims
CLAIMS 1. Nuclear fuel pellet of symmetrical shape of revolution around a central axis (B) and containing a fissile material, the pellet having concentric layers including a proximal layer (20), an intermediate layer (22) and a distal layer (24), in which the enrichment in fissile material within the pellet varies radially, and the intermediate layer (22) comprises a high enrichment zone 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. A pellet according to claim 1, wherein the enrichment increases with radius in an area of the intermediate layer (22) adjacent to the proximal layer (20).
3. A pellet according to claim 2, wherein the increase in enrichment is continuous or discontinuous, and / or gradual.
4. A pellet according to any preceding claim, wherein the enrichment decreases with radius in an area of the intermediate layer (22) adjacent to the distal layer (20).
5. A tablet according to claim 4, wherein the decrease in enrichment is continuous or discontinuous, and / or gradual.
6. A pellet according to any preceding claim, wherein the enrichment is greatest at an interface between the proximal layer (20) and the intermediate layer (22).
7. A pellet according to any preceding claim, wherein the enrichment decreases from an interface between the proximal layer (20) and the intermediate layer (22) to an interface between the intermediate layer (22) and the distal layer (24).
8. A tablet according to claim 7, wherein the decrease in enrichment is continuous or discontinuous, and / or gradual.
9. A pellet according to any preceding claim, wherein the enrichment has a maximum enrichment plateau in the intermediate layer (24).
10. A pellet according to claim 1, wherein the enrichment is constant in the intermediate layer (24).
11. A pellet according to any preceding claim, wherein the enrichment in the proximal layer (20) is, in mass percentage, equal to or greater than 0.25% and / or equal to or less than 1.0% and / or the enrichment in the distal layer (24) is equal to or greater than 0.25% and less than or equal to 1.0%.
12. A pellet according to any preceding claim, wherein the enrichment in the high enrichment zone is, in mass percentage, equal to or greater than 1.8% and / or less than or equal to 10.0%.
13. A pellet according to any preceding claim, wherein the intermediate layer (22) represents a volume fraction of the pellet of between 60% and 94% and / or the proximal layer (20) represents a volume fraction of the pellet of between 5% and 20% and / or the distal layer (24) represents a volume fraction of the pellet of between 1% and 20%.
14. Nuclear fuel rod, comprising a tubular sheath containing pellets according to any one of the preceding claims.