System for forming a pellets column of a predetermined length and a corresponding method

Abstract

The invention relates to a system for forming a pellets column of a predetermined length, the system comprising: a conveyor belt (3); a first stopper (10), having a closed position, in which the first stopper is configured to block displacement of pellets along a conveying direction (X), and an open position in which the first stopper allows displacement of pellets along the conveying direction; a second stopper (12), positioned downstream the first stopper along the conveying direction, having a closed position, in which the second stopper is configured to block displacement of pellets along the conveying direction (X), and an open position, in which the second stopper allows displacement of pellets (5) along the conveying direction; and a first sensor (14), the first sensor being configured to detect the presence of a pellet (5) on the conveyor belt (3) at a predetermined position (P) of the conveyor belt (3) along its conveying direction (X), wherein the first sensor is adapted to emit a presence signal in case a pellet has been detected at the predetermined position; wherein the system further comprises an second sensor (16) configured for generating a displacement signal representative of the displacement of the conveyor belt (3), and a controller (18) being configured to command the first and second stoppers between their open and closed positions as a function of the displacement signal and the presence signal for forming a pellets column on the conveyor belt (3) with the predetermined length (L) along the conveying direction (X).

Description

[0001] System for forming a pellets column of a predetermined length and a corresponding method

[0002] The present invention concerns a system for forming a pellets column of a predetermined length and a corresponding method.

[0003] During the production of nuclear fuel elements, it is necessary, at several stages of the production, to form stacks (also called columns) of pellets / tablets of a predetermined length.

[0004] EP1882257 A2 relates to a method to load a nuclear fuel rod, comprising, providing nuclear fuel pellets in a bottomless tray; transferring the nuclear fuel pellets from the bottomless tray to a fuel pellet column through the use of a belt, indexing the nuclear fuel pellets in the fuel pellet column to a nuclear fuel pellet loading machine; and pushing the fuel pellet column into a fuel rod cladding.

[0005] JPH09101392A relates to a pellet aligning device is constituted of a vibration feeders, a magazine having a plurality of holes, a stopper plate having a plurality of notches, a stopper plate operation mechanism, a magazine sending mechanism, a magazine rotation mechanism, the first stopper and the second stopper.

[0006] RU2302047 discloses a method for proposed method for horizontal charging of fuel rod cans with pellets.

[0007] Object of the invention is to provide a system producing less damaged fuel pellets.

[0008] According to one aspect, a system is provided for forming a pellets column of a predetermined length, the system comprising:

[0009] - a conveyor belt configured for transporting pellets along a conveying direction;

[0010] - a first stopper, having a closed position, in which the first stopper is configured to block displacement of pellets along the conveying direction, and an open position in which the first stopper allows displacement of pellets along the conveying direction;

[0011] - a second stopper, positioned downstream the first stopper along the conveying direction, having a closed position, in which the second stopper is configured to block displacement of pellets along the conveying direction, and an open position, in which the second stopper allows displacement of pellets along the conveying direction; and

[0012] - a first sensor, the first sensor being configured to detect the presence of a pellet on the conveyor belt at a predetermined position of the conveyor belt along its conveying direction, wherein the first sensor is adapted to emit a presence signal in case a pellet has been detected at the predetermined position; characterized in that the system further comprises an second sensor configured for generating a displacement signal representative of the displacement of the conveyor belt, and a controller being configured to command the first and second stoppers between their open and closed positions as a function of the displacement signal and the presence signal for forming a pellets column on the conveyor belt with the predetermined length along the conveying direction.

[0013] Further embodiments may relate to one or more of the following features, which may be combined in any technical feasible combination:

[0014] • the pellets are fuel pellets, for example nuclear fuel pellets, in particular uranium pellets, or gadolinium pellets;

[0015] • the first sensor is a light barrier;

[0016] • the second sensor is an encoder, in particular placed at an axis of a drive shaft;

[0017] • the system further comprising a driving unit adapted to propel the conveyor belt, wherein the driving unit includes the drive shaft;

[0018] • in the open position the first and / or second stopper is spaced apart from the conveyor belt.

[0019] • the presence signal is emitted as long as a pellet is detected at the predetermined position.

[0020] • the controller is configured to calculate a length a pellets column and for comparing the calculated length with a predetermined length.

[0021] • the length is calculated based on the cumulated displacement of the conveyor belt, while pellets are present at the predetermined position.

[0022] • the controller is configured to maintain second stopper closed and first stopper open until the predetermined length is reached.

[0023] • the controller is configured to open the second stopper and to close the first stopper, when the predetermined length is reached and to maintain the second stopper opened until displacement of belt represented by conveyor signal corresponds at least to the predetermined length; and / or

[0024] • the predetermined position of the conveyor belt along its conveying direction is between the first stopper and the second stopper, in particular adjacent to the first stopper.

[0025] • the conveyor belt is driven at a constant speed.

[0026] According to another aspect, a method is provided for operating a system for forming a pellets column of predetermined length, the system comprising:

[0027] - a conveyor belt configured for transporting pellets along a conveying direction;

[0028] - a first stopper, having a closed position, in which the first stopper is configured to block displacement of pellets along the conveying direction, and an open position in which the first stopper allows displacement of pellets along the conveying direction;

[0029] - a second stopper, positioned downstream the first stopper along the conveying direction, having a closed position, in which the second stopper is configured to block displacement of pellets along the conveying direction, and an open position, in which the second stopper allows displacement of pellets along the conveying direction; and

[0030] - a first sensor, the sensor being configured to detect the presence of a pellet on the conveyor belt at a predetermined position of the conveyor belt along its conveying direction, wherein the first sensor is adapted to emit a presence signal in case a pellet has been detected at the predetermined position; and an second sensor configured for generating a displacement signal representative of the displacement of the conveyor belt; the method comprising: placing the pellets randomly onto the conveyor belt upstream of the first stopper; calculating a length of the pellets column based on the presence signal and the displacement signal; opening a second stopper and closing the first stopper, when it is determined that the predetermined length is reached; and closing the second stopper when displacement of the conveyor belt represented by conveyor signal corresponds at least to the predetermined length.

[0031] Further advantages, features, aspects and details are evident from the dependent claims, the description and the drawings.

[0032] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be read by reference to embodiments. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0033] The accompanying drawings relate to embodiments of the invention and are described in the following:

[0034] Fig. 1 shows a system for forming a pellets column of a predetermined length, in particular during three different situations in Figures Fig. 1 a), Fig. 1 b) and Fig. 1 c); and

[0035] Fig. 2 shows a flow chart for operating a system for forming a pellets column of predetermined length.

[0036] During the production of nuclear fuel elements, it is necessary, at several stages of the production, to form stacks (also called columns) of fuel pellets / tablets of a predetermined length. For example, the columns are formed after the production of the fuel pellets in a pellet press. Such pellets are very prone for being damaged. The fuel pellet column is then arranged or pushed on a tray for further processing, for example sintering.

[0037] In other embodiments, the pellet columns are formed after an inspection of fuel pellets, in particular of sintered fuel pellets. The inspection includes an inspection of the surface and / or a diameter of the fuel pellets. These fuel pellets are then arranged or pushed on a tray for further processing, for example for loading the fuel pellets into fuel rods. Sintered fuel pellets are much more stable than green pellets but they are bridle and surface chipping can happen. Typically, there is not an additional quality inspection after the tray loading. That means all pellet defects, generated after the inspection will not be detected and will go into the fuel rods.

[0038] Fig. 1 shows a system 1 for forming a pellets column of a predetermined length. A pellets column includes a plurality of pellets. The plurality of pellets are aligned in a column and adjacent to each other, in particular such that they touch each other.

[0039] The pellets 5 are for example fuel pellets, for example nuclear fuel pellets, in particular uranium pellets, or gadolinium pellets. Gadolinium pellets are uranium pellets doped with gadolinium.

[0040] The system 1 includes a conveyor belt 3 configured for transporting pellets 5 along a conveying direction X. The conveyor belt has a first end 3a and a second end 3b. According to embodiments, the first end 3a is an entrance end and the second end 3b is an exit end. The pellets 5 are placed randomly, in particular with a random distance between each other, onto the conveyor belt 3. In an embodiment, the conveyor belt 3 is driven by a shaft 7 at the first end 3a and / or the second end 3b. The shaft 7 is rotated by a motor (not shown), for example an electric motor. In other words, a driving unit is adapted to propel the conveyor belt 3, wherein, in particular, the driving unit 3 includes the drive shaft 7 and / or the motor.

[0041] According to an embodiment, the conveyor belt 3 is driven at a constant speed. The constant speed enables to reduce the damages of the pellets due to acceleration and deceleration.

[0042] The system comprises a first stopper 10, having a closed position, in which the stopper is configured to block displacement of pellets 5 along the conveying direction X, and an open position in which the stopper allows displacement of pellets 5 along the conveying direction X.

[0043] The system comprises a second stopper 12, positioned downstream the first stopper 10 along the conveying direction X. The second stopper 12 having a closed position, in which the stopper is configured to block displacement of pellets 5 along the conveying direction, and an open position, in which the stopper allows displacement of pellets 5 along the conveying direction. The first stopper 10 and / or the second stopper 12 comprises for example a gate, for example a liftable gate, wherein the gate is movable between a closed position and an open position.

[0044] The gates of the first and second stoppers 10, 12 are arranged in the closed position sufficiently close above the conveyer, in order to block the pellets 5 to pass by the respective stopper 10, 12. The gates of the first and second stoppers 10, 12 are spaced apart from the conveyor belt 3 in the open position, such that the pellets 5 are allowed to pass by the respective stopper 10, 12.

[0045] The first and second stopper 12 are spaced apart from each other in the conveying direction X of the conveyor belt 3 with a distance being equal or greater than the predetermined length of the pellets column.

[0046] In an embodiment, the first stopper 10 is for example arranged about in the middle or the middle third of the conveyor belt 3, in the conveying direction X.

[0047] According to an embodiment, the pellets 5 are placed randomly upstream of the first stopper 12 onto the conveyor belt 3. For example, the pellets 5 are placed at the first end or entrance end 3a onto the conveyor belt.

[0048] The pellets 5 have a random distance between each other in conveying direction X upstream of the first stopper 10.

[0049] The system further comprises a first sensor 14, the first sensor 14 being configured to detect the presence of a pellet 5 on the conveyor belt 3 at a predetermined position P of the conveyor belt along its conveying direction X, wherein the first sensor is adapted to emit a presence signal in case a pellet has been detected at the predetermined position.

[0050] According to an embodiment, the distance between the predetermined position and the second stopper 12 corresponds to the predetermined length L. The predetermined position P of the conveyor belt along its conveying direction is between the first stopper and the second stopper, in particular adjacent to the first stopper 10.

[0051] According to an embodiment, the first sensor 14 is a light barrier. The presence signal is emitted as long as a pellet 5 is detected at the predetermined position P.

[0052] The system 1 further comprises a second sensor 16. The second sensor 16 is configured for generating a displacement signal representative of the displacement of the conveyor belt 3. The second sensor 16 is an encoder, in particular placed at an axis of a drive shaft 7. In other embodiments, the second sensor 16, in particular the encoder, can read a code on the belt 3 in order to generate a displacement signal representative of the displacement of the conveyor belt 3. In such a case, a controller, for example the controller described here-below, has only to count pulses received from the second sensor 16. In other embodiments, the second sensor may be a detector adapted to count steps of a stepper motor used to drive conveyor belt.

[0053] In an embodiment, the system includes a controller 18. The controller 18 is only shown in Fig. 1 a), the controller 18 has been omitted in the Fig. 1 b) and 1 c) for clarity reasons.

[0054] The controller 18 adapted to command the first and second stoppers 10, 12 between their open and closed positions. For that purpose, the controller 18 is connected to the first and second stoppers 10, 12, for example wireless or with one or more wires. Further, the controller 18 is adapted to receive the presence signal and the displacement signal, in particular from the first and second sensors 14, 16. For example, the controller 18 is configured to command the moving the first and second stoppers 10, 12 between their open and closed positions as a function of the displacement signal and the presence signal for forming a pellets column on the belt with the predetermined length L along the conveying direction X.

[0055] In order to form the column of pellets, a second stopper 12, located downstream the first stopper 10, is maintained in the closed position while the first stopper 10 is maintained in its open position. For example, the controller 18 commands the first stopper 10 and the second stopper 12 accordingly. The pellets 5, carried by the conveyor belt 3, are then blocked by the second stopper 12 and accumulated to form a pellets column, in particular upstream of the second stopper 12.

[0056] In some embodiments, the controller 18 is configured to calculate a length a pellets column and for comparing the calculated length with a predetermined length L. The length relates to the length a pellet column upstream of the second stopper 12, in particular between the first stopper 10 and the second stopper 12. For example, the length is calculated based on the cumulated displacement of the conveying belt, while pellets 5 are present at the predetermined position. In other words, the lengths of each pellet 5 passing by the first sensor 10 is added. In an example, the calculation of the length is based on the time a plurality of pellets 5 are present at the predetermined position P and the displacement of the conveyor belt 3 during that time.

[0057] According to an embodiment, the displacement is only cumulated, when the first sensor 10 emits the presence signal. For example, controller counts the pulses from the encoder only when the light barrier is “dark”. In other words, the controller 18 knows immediately and exactly when the predetermined length L of the pellets column is reached.

[0058] Thus by combining the information from the displacement signal and presence signal, it is possible to determine the actual length of the pellets column, which then leads to an accurate actuation of the stopper and to a reduction in the number of defective pellets. Fig. 2 shows a flow chart for operating a system, which will be explained with the situations in Figures 1 a) b) and c).

[0059] As shown in Fig. 1 a) and in step 100, the pellets 5 are placed on the conveyor belt 3 randomly upstream of the first stopper 10. The first stopper 10 is opened and the second stopper is closed 12.

[0060] Then, a pellets column is building up upstream of the second stopper 12 and downstream of the first stopper 10.

[0061] In step 110, a length of the pellets column is calculated, in particular by the controller 18, based on the presence signal and the displacement signal. For example, the length is calculated based on the cumulated displacement of the conveyor belt 3, while pellets are present at the predetermined position P. In particular, encoder pulses are counted only when a pellet 5 inhibits the light to pass the light through the light barrier 14. The second stopper 12 is maintained closed and first stopper 10 is maintained opened until the predetermined length is reached, see Fig. 1 b).

[0062] In step 120 it is determined, that the predetermined length L is reached. Then, the second stopper 12 is opened and the first stopper 10 is closed, see Fig. 1 c).

[0063] The second stopper 12 is maintained opened and, in particular the first stopper 10 closed, until displacement of the conveyor belt 3 represented by conveyor signal corresponds at least to the predetermined length. In other words, the second stopper 12 remains open as long as the column has left the conveyor belt.

[0064] In step 130 the second stopper 12 is closed when displacement of the conveyor belt represented by conveyor signal corresponds at least to the predetermined length L, in particular to build up a new pellets column. Then the first stopper 10 opens at the same time. In other words, the second stopper 12 is closed at the same time with the opening of the first stopper 10.

[0065] The system according to the embodiments enables to reduce the defect rate.

[0066] List of reference signs

[0067] 1 System

[0068] 3 Conveyor belt

[0069] 5 Pellet

[0070] 7 Shaft

[0071] 10 First stopper

[0072] 12 Second stopper

[0073] 14 First sensor

[0074] 16 Second sensor

[0075] 18 Controller X conveying direction

[0076] P Predetermined position

[0077] L Predetermined length

Claims

CLAIMS1. System (1 ) for forming a pellets column of a predetermined length, the system comprising:- a conveyor belt (3) configured for transporting pellets (5) along a conveying direction (X);- a first stopper (10), having a closed position, in which the first stopper is configured to block displacement of pellets along the conveying direction (X), and an open position in which the first stopper allows displacement of pellets along the conveying direction;- a second stopper (12), positioned downstream the first stopper along the conveying direction, having a closed position, in which the second stopper is configured to block displacement of pellets along the conveying direction (X), and an open position, in which the second stopper allows displacement of pellets (5) along the conveying direction; and- a first sensor (14), the first sensor being configured to detect the presence of a pellet (5) on the conveyor belt (3) at a predetermined position (P) of the conveyor belt (3) along its conveying direction (X), wherein the first sensor is adapted to emit a presence signal in case a pellet has been detected at the predetermined position; characterized in that the system further comprises an second sensor (16) configured for generating a displacement signal representative of the displacement of the conveyor belt (3), and a controller (18) being configured to command the first and second stoppers between their open and closed positions as a function of the displacement signal and the presence signal for forming a pellets column on the conveyor belt (3) with the predetermined length (L) along the conveying direction (X).

2. System according to claim 1 , wherein the pellets are fuel pellets, for example nuclear fuel pellets, in particular uranium pellets, or gadolinium pellets.

3. System according to claim 1 or 2, wherein the first sensor (14) is a light barrier.

4. System according to any one of the preceding claims, wherein the second sensor (16) is an encoder, in particular placed at an axis of a drive shaft (7).

5. System according to any one of the preceding claims further comprising a driving unit adapted to propel the conveyor belt, wherein the driving unit includes the drive shaft (7).

6. System according to any one of the preceding claims, wherein in the open position the first and / or second stopper (10, 12) is spaced apart from the conveyor belt.

7. System according to any one of the preceding claims, wherein the presence signal is emitted as long as a pellet (5) is detected at the predetermined position (P).

8. System according to any one of the preceding claims, wherein the controller (18) is configured to calculate a length a pellets column and for comparing the calculated length with a predetermined length (L).

9. System according to claim 8, wherein the length is calculated based on the cumulated displacement of the conveyor belt (3), while pellets are present at the predetermined position (P).

10. System according to any one of the preceding claims, wherein the controller is configured to maintain second stopper (12) closed and first stopper (10) open until the predetermined length (L) is reached.1 1 . System according to any one of the preceding claims, wherein the controller is configured to open the second stopper (12) and to close the first stopper (10), when the predetermined length (L) is reached and to maintain the second stopper opened until displacement of belt represented by conveyor signal corresponds at least to the predetermined length.

12. System according to any one of the preceding claims, wherein the predetermined position (P) of the conveyor belt along its conveying direction is between the first stopper and the second stopper, in particular adjacent to the first stopper (10).

13. System according to any one of the preceding claims, wherein the conveyor belt (3) is driven at a constant speed.

14. Method for operating a system for forming a pellets column of predetermined length, the system comprising:- a conveyor belt (3) configured for transporting pellets along a conveying direction;- a first stopper (10), having a closed position, in which the first stopper is configured to block displacement of pellets along the conveying direction, and an open position in which the first stopper allows displacement of pellets along the conveying direction;- a second stopper (12), positioned downstream the first stopper along the conveying direction, having a closed position, in which the second stopper is configured to block displacement of pellets along the conveying direction, and an open position, in which the second stopper allows displacement of pellets along the conveying direction; and- a first sensor (14), the sensor being configured to detect the presence of a pellet on the conveyor belt at a predetermined position of the conveyor belt along its conveying direction, wherein the first sensor is adapted to emit a presence signal in case a pellet has been detected at the predetermined position; and an second sensor (16) configured for generating a displacement signal representative of the displacement of the conveyor belt; the method comprising: placing the pellets randomly onto the conveyor belt upstream of the first stopper; calculating a length of the pellets column based on the presence signal and the displacement signal; opening a second stopper (12) and closing the first stopper (11 ), when it is determined that the predetermined length (L) is reached; and closing the second stopper (12) when displacement of the conveyor belt represented by conveyor signal corresponds at least to the predetermined length.

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