Radially variable enrichment nuclear fuel pellet

Abstract

Nuclear fuel pellet with radially variable enrichment The nuclear fuel pellet is of rotationally symmetrical shape about a central axis (B) and contains 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, the intermediate layer (22) comprising a high enrichment zone in which the enrichment is strictly greater than the enrichment in the proximal layer (20) and / or the enrichment in the distal layer (24). Figure for abstract: Figure 3

Description

Title of the invention: Nuclear fuel pellet with radially variable enrichment

[0001] 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.

[0002] 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.

[0003] The nuclear fuel is for example provided in the form of nuclear fuel pellets containing a fissile material, each pellet being generally cylindrical in shape, the pellets being stacked in the cladding.

[0004] 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” according to English terminology).

[0005] This risk is higher in the event of locally high combustion within the pellet or locally high temperature within the pellet.

[0006] One of the aims of the invention is to propose a nuclear fuel pellet making it possible to limit the risk of deterioration of the pellet during its use.

[0007] To this end, the invention proposes 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.

[0008] The radially variable enrichment of the pellet in fissionable material makes it possible to adjust the reactivity and combustion within the nuclear fuel pellet 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.

[0009] In particular, a higher enrichment in an intermediate layer than in a proximal layer allows energy equivalence to be maintained while limiting the temperature at the center of the pellet, which limits the risk of melting in an accidental situation.

[0010] A higher enrichment in an intermediate layer than in a distal layer makes it possible to preserve energy equivalence while limiting the risk of excessive combustion in the distal layer.

[0011] According to particular embodiments, the pellet comprises one or more of the following optional characteristics, taken individually or in all technically possible combinations:

[0012] - enrichment increases with radius in an area of ​​the intermediate layer adjacent to the proximal layer;

[0013] - the increase in enrichment is continuous or discontinuous, and / or gradual;

[0014] - enrichment decreases with radius in an area of ​​the intermediate layer adjacent to the distal layer;

[0015] - the reduction in enrichment is continuous or discontinuous, and / or gradual;

[0016] - the enrichment is maximal at an interface between the proximal layer and the layer intermediate ;

[0017] - enrichment decreases from an interface between the proximal layer and the intermediate layer to an interface between the intermediate layer and the distal layer;

[0018] - the reduction in enrichment is continuous or discontinuous, and / or gradual;

[0019] - the enrichment has a maximum enrichment plateau in the in layer intermediate;

[0020] - the enrichment is constant in the intermediate layer;

[0021] - the enrichment in the proximal layer is equal to or greater than 0.25% and / or equal 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%;

[0022] - the enrichment in the high enrichment zone is equal to or greater than 1.8% and / or less than or equal to 10.0%;

[0023] - the intermediate layer represents a volume fraction of the pellet included between 60% and 94% and / or the proximal layer represents a volume fraction of the pellet between 5% and 20% and / or the distal layer represents a volume fraction of the pellet between 1% and 20%.

[0024] The invention also relates to a nuclear fuel rod, comprising a tubular sheath containing pellets as defined above.

[0025] The invention and its advantages will be better understood on reading the following description, given solely by way of example, and made with reference to the appended drawings, in which:

[0026] - [Fig.l] [Fig.l] is a schematic sectional view of a fuel rod nuclear including nuclear fuel pellets;

[0027] - [Fig.2] [Fig.2] is a schematic sectional view of a fuel pellet nuclear;

[0028] - [Fig.3][Fig.4][Fig.5][Fig.6] Figures 3 to 6 are graphs illustrating different enrichment profiles of a nuclear fuel pellet depending on the radius;

[0029] - [Fig.7] [Fig.7] is a schematic sectional view of a fuel pellet nuclear according to another example of realization.

[0030] [Fig.l] illustrates a nuclear fuel rod 2 intended to be used 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, a "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 com 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 [Fig.2].

[0036] As illustrated in [Fig.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.

[0038] The pellet 8 has a side surface 14 and two opposite end surfaces 16.

[0039] 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.

[0040] Each end surface 16 extends from an end 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 a fissile material, the fissile material preferably being uranium dioxide (UO2).

[0043] The pellet 8 comprises for example a matrix made of a matrix material and the fissile material distributed in the matrix.

[0044] The pellet 8 has several concentric layers.

[0045] In particular, the pellet 8 has a concentric proximal layer 20, an intermediate layer 22 and a distal layer 24.

[0046] 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.

[0047] 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.

[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 to a first radius RI, the layer 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 external radius of the pellet 8, i.e. the radius of the lateral surface 14.

[0051] 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.

[0052] Each of the concentric layers of the pellet 8 has a thickness taken radially.

[0053] The proximal layer 20 has, for example, a thickness of between 700 μm and 2300 μm. The thickness of the proximal layer 20 is equal to the first radius RL

[0054] The intermediate layer 22 has a thickness of 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 RI

[0055] 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.

[0056] Pellet 8 has a concentration of fissile material or “enrichment”.

[0057] The enrichment of the pellet 8 varies radially, i.e. as a function of the distance to 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 of the pellet 8 and over the entire circumference of the pellet 8.

[0059] 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.

[0060] 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.

[0061] Preferably, the enrichment present in the intermediate layer 22, and in particular in the high enrichment zone, a maximum enrichment EMAx-

[0062] 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.

[0063] In the example of [Fig.3], the proximal layer 20 has a constant proximal enrichment EPROx in the proximal layer 20, a constant enrichment in the intermediate layer 22 and a constant distal enrichment ED1ST in the distal layer 24.

[0064] The enrichment in the intermediate layer 22 is strictly higher than the proximal enrichment EPROX of the proximal layer 20 and the distal enrichment ED1ST of the distal layer 24.

[0065] The enrichment in the intermediate layer 22 corresponds to the maximum enrichment EMAX of the pellet 8.

[0066] The intermediate layer 22 has a maximum enrichment plateau EMAX which extends over the entire extent of the intermediate layer 22.

[0067] 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 RI and the second radius R2.

[0068] The proximal enrichment EPROx of the proximal layer 20 and the distal enrichment Ed1st of the distal layer 24 are for example equal.

[0069] Alternatively, the proximal enrichment EPROx of the proximal layer 20 and the distal enrichment ED1ST of the distal layer 24 are different, one being strictly higher than the other.

[0070] In the example of [Fig.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 EMAX and the distal enrichment ED1ST-

[0071] It is possible to provide for a continuous and / or gradual variation of the enrichment.

[0072] 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.

[0073] In an exemplary embodiment illustrated in [Fig.4], the enrichment increases continuously with the radius (i.e. with the distance from the central axis B) in a zone of the intermediate layer 22 adjacent to the proximal layer 20, up to the zone of high enrichment of the intermediate layer 22, for example from the proximal enrichment EPROx up to the maximum enrichment EMAx- The increase is continuous.

[0074] The increase is for example linear. Alternatively, the increase is non-linear.

[0075] 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.

[0076] Alternatively or optionally, as illustrated in [Fig.4], the enrichment decreases continuously with the 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 ED1ST- The decrease is continuous.

[0077] The decrease is for example linear. Alternatively, the decrease is non-linear.

[0078] Said zone of the intermediate layer 22 adjacent to the proximal layer 20 defines a transition zone and the high enrichment zone.

[0079] In a particular embodiment, within the intermediate layer 22, the enrichment increases continuously with the radius in the zone adjacent to the proximal layer, from the proximal enrichment EPROX to the maximum enrichment EMAX, then remains constant, then decreases continuously in the zone adjacent to the distal layer 24 until reaching the distal enrichment ED1ST-

[0080] As illustrated in [Fig.4], the enrichment profile presents an increasing portion from the proximal enrichment EPROX to a maximum enrichment plateau EMAx, then a decreasing portion from the maximum enrichment plateau EMAx to the distal enrichment ED1ST.

[0081] The increasing portion is linear. It has the form of an ascending ramp of constant slope. Alternatively, the increasing portion is non-linear. It has a variable slope.

[0082] The decreasing portion is linear. It has the form of a descending ramp with a constant slope. Alternatively, the decreasing portion is non-linear. It has a variable slope.

[0083] In an exemplary embodiment, the enrichment exhibits a gradual increase.

[0084] A gradual increase is for example carried out with one or more intermediate stages. A gradual increase is carried out for example continuously (with a ramp between two successive stages) and / or non-continuously (with a discontinuous jump between two successive stages).

[0085] In an exemplary embodiment, the enrichment exhibits a gradual decrease.

[0086] A gradual decrease is for example carried out with one or more intermediate stages. A gradual decrease is carried out for example continuously (with a ramp between two successive stages) and / or non-continuously (with a jump between two successive stages).

[0087] The enrichment profile illustrated in [Fig.5] differs from that of [Fig.4] in that the increase between the 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 the distal enrichment ED1ST is gradual, here with two intermediate steps.

[0088] The enrichment profile does not necessarily present a maximum enrichment plateau in the intermediate layer 22.

[0089] 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 EMAX to the distal enrichment ED1ST, presenting a high enrichment zone in which the enrichment is strictly greater than the proximal enrichment EPROX and / or the distal enrichment EdIST.

[0090] In an exemplary embodiment illustrated in [Fig.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.

[0091] The enrichment decreases here continuously, and in particular linearly, up to the interface between the intermediate layer 22 and the distal layer 24. Alternatively, the enrichment decreases gradually up to the interface between the intermediate layer 22 and the distal layer 24.

[0092] In a variant, the maximum enrichment EMAX is reached near the interface between the intermediate layer 22 and the distal layer 24, with a variation continuous or discontinuous and / or gradual between the proximal enrichment EPROX and the maximum enrichment EMAX, preferably over a small thickness, for example a thickness between 50 pm and 500 pm.

[0093] The enrichment at the interface between the intermediate layer 22 and the distal layer 24 is here strictly greater than the distal enrichment ED1ST- The enrichment presents a non-continuous jump at the interface between the intermediate layer 22 and the distal layer 24.

[0094] Alternatively, as illustrated in dotted lines in [Fig.6], the enrichment decreases in the intermediate layer 22 until reaching the distal enrichment ED1ST at the interface between the intermediate layer 22 and the distal layer 24.

[0095] 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.

[0096] 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.

[0097] In an exemplary embodiment, the enrichment exhibits in the intermediate layer 22 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 exhibits a discontinuous jump between the maximum enrichment E MAX and the distal enrichment ED1ST (without a continuous or gradual decrease between the maximum enrichment EMAX and the distal enrichment ED1ST).

[0098] In an exemplary embodiment, the enrichment presents 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 ED1ST-

[0099] Furthermore, it is possible to combine a continuous increase with a non-continuous decrease and a non-continuous increase with a continuous decrease.

[0100] 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 ED1ST.

[0101] 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 distal enrichment ED1ST-

[0102] 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.

[0103] Alternatively, the absolute values ​​of the slope of the linear increase and the slope of the gradual decrease are different.

[0104] 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.

[0105] In an exemplary embodiment, and as illustrated in Figures 3 to 6, the proximal enrichment EPROX and the distal enrichment ED1ST are substantially equal.

[0106] In this case, preferably, the proximal enrichment EPROx and the distal enrichment Edist are equal to a minimal enrichment of the pellet 8.

[0107] Alternatively, the proximal enrichment EPROx and the distal enrichment ED1ST are different.

[0108] In this case, preferably, the one of the proximal enrichment EPROx and the distal enrichment ED1ST which is lower than the other is the minimum enrichment of the pellet 8.

[0109] In an exemplary embodiment, the proximal enrichment EPROX is strictly greater than the distal enrichment ED1ST. In this case, preferably, the distal enrichment ED1ST is the minimum enrichment of the pellet 8.

[0110] In an exemplary embodiment, the proximal enrichment EPROX is strictly less than the distal enrichment ED1ST- In this case, preferably, the proximal enrichment EPROX is the minimum enrichment of the pellet 8.

[0111] 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.

[0112] 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.

[0113] The radially variable enrichment within the pellet 8 makes it possible to predict the quantity of fissile material required in the pellet 8 while limiting the risk of degradation of the pellet 8, in particular the “FFRD” risk.

[0114] 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.

[0115] 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.

[0116] 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 reference enrichment Eref and having substantially the same geometry, in particular having the same volume as the pellet 8.

[0117] Considering the example of enrichment profile of [Fig.3], the following equation must be respected:

[0118] Eref — Eprox x (FVprox) + EMax x (FVjnt) + Ed1st x (FVdist)

[0119] in which:

[0120] Eref is the reference enrichment of the reference pellet;

[0121] EpROx is the enrichment of the proximal layer 20;

[0122] Emax is the enrichment of the intermediate layer 22;

[0123] ED1ST is the enrichment of the distal layer 24;

[0124] FVprox is the volume fraction of the proximal layer 20, i.e. the ratio of the volume of the proximal layer 20 on the volume of the pellet 8;

[0125] FV^p 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

[0126] FVd1st 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] In a particular example in which Eref = 4%, EPROx = ED1ST = 0.3%, FVprox = 10%, FVd1st = 5% and FV^t = 85%, we obtain a maximum enrichment EMAX = 4.65%.

[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 of the high enrichment zone 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 equal to or greater than 0.25% and / or equal to or less than 1.0%.

[0132] 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%.

[0133] 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%.

[0134] Preferably, the ratio between the maximum enrichment EMAX and the proximal enrichment EpROX is for example between 1.8 and 40.

[0135] Preferably, the ratio between the maximum enrichment EMAX and the distal enrichment ED1ST is for example between 1.8 and 40.

[0136] 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.

[0137] 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.

[0138] As illustrated in particular in [Fig.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.

[0139] This makes it possible to simplify the manufacture of the pellet 8.

[0140] As illustrated in [Fig.7], the invention can also be applied to a pellet of generally cylindrical shape whose geometry differs from that of [Fig.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.

[0141] 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.

[0142] 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 [Fig.3].

[0143] As a variant, 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] Additive manufacturing is carried out for example by one or more of the following methods: selective laser sintering (or SLS), electron beam melting (or EBM), direct metal laser sintering (or DMSL), direct energy deposition (or "Direct Energy Deposition" according to English terminology) and flash sintering (or SPS).

Claims

Claims

1. Nuclear fuel pellet intended to be integrated into a nuclear fuel rod, the pellet being 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).

2. A pellet according to claim 1, wherein the enrichment in the high enrichment zone is strictly greater than the enrichment in the distal layer (24).

3. A pellet according to claim 1 or 2, wherein the enrichment increases with radius in an area of ​​the intermediate layer (22) adjacent to the proximal layer (20).

4. A pellet according to claim 3, wherein the increase in enrichment is continuous or discontinuous, and / or gradual.

5. 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).

6. A pellet according to claim 5, wherein the decrease in enrichment is continuous or discontinuous, and / or gradual.

7. 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).

8. 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).

9. A pellet according to claim 8, wherein the decrease in enrichment is continuous or discontinuous, and / or gradual.

10. A pellet according to any preceding claim, wherein the enrichment has a maximum enrichment plateau in the intermediate layer (22).

11. A pellet according to claim 1 or 2, wherein the enrichment is constant in the intermediate layer (22).

12. A pellet according to any preceding claim, wherein the enrichment in the proximal layer (20) 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 (24) is equal to or greater than 0.25% and less than or equal to 1.0%.

13. A pellet according to any preceding claim, wherein the enrichment in the high enrichment zone is equal to or greater than 1.8% and / or less than or equal to 10.0%.

14. 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%.

15. A nuclear fuel rod, comprising a tubular sheath containing pellets according to any one of the preceding claims.

Images