RU2295786C2 - Method and device for producing uncontaminated mox fuel rods - Google Patents

Abstract

FIELD: production of uncontaminated mixed oxide fuel rods for atomic engineering.

SUBSTANCE: proposed method involves manufacture of uncontaminated MOX fuel rods from pellets in shielding chamber. The latter is held at pressure lower than indoor atmospheric value. Pellets are charged in stacked condition into can provided in advance with first plug on one of its two ends. Various structural components, such as hold-down spring, are charged. Second plug is installed on other end of can and held in position by circular weld, in particular when it is inserted in mentioned can without clamp. Parts of mentioned can or respective rod are at least once inspected for contamination. Safety chamber is divided into certain number of adjacent compartments. Each compartment communicates with adjacent one through sealed passage for can. Some of such passages are relatively aligned to provide for can movement along its longitudinal axis. Cans being charged with pellets are introduced with their open end forward into first compartment through sealed passage or inlet opening of compartment. Cans are moved along axis between sequential compartments until their open end occurs in last compartment. In the latter can is charged with pellets and, if necessary, with various structural members other than hold-down spring through its open end. Upon completion of charging can is partially pulled out along axis to transfer its open end to preceding compartment. In the latter can is at least partially cleaned and checked for probable contamination by pellets in the course of their charging or by atmosphere of last compartment. After that cans are moved to admit their open end to next compartment. Hold-down spring is installed and second plug is fitted in open end within this compartment. Then other required operations are made in this compartment or in another one involving additional movement of can. Parts of rod contaminated in last compartments are checked for condition and potentially decontaminated, as required, in first or second compartment. Rod is removed from first compartment or is crosswise displaced to other shielding chamber through first compartment that joins shielding chambers together. The degree of contamination stepwise changes between different compartments starting from no or negligible dirt in first compartment up to heavy contamination in last one. Gas supplied to these compartments is chosen from group incorporating air, nitrogen, helium, argon, and vacuum. Pressure within compartment is varied in steps to control leakage starting from high pressure in first compartment down to lowest pressure in the last one. In addition, device is proposed for producing uncontaminated MOX fuel rods.

EFFECT: enhanced safety for personnel engaged in manufacture of mixed oxide fuel rods.

19 cl, 12 dwg

Description

The present invention relates to a method for manufacturing uncontaminated MOX fuel rods from tablets in a protective chamber with reduced pressure compared to the atmosphere, comprising the following operations in the manufacture of a single rod:

- loading tablets in successive columns (stacking) into a shell previously provided with a first plug at one of its two ends;

- loading of various structural elements, in particular, a clamping spring;

- installation of a second plug at the other end of the shell;

- welding with an annular seam of the aforementioned second plug and

- at least one cleaning and at least one check for contamination of parts of the aforementioned shell or, accordingly, of the rod, possibly exposed to contamination.

The reuse of plutonium obtained from the reprocessing of nuclear fuel for civilian use or the implementation of nuclear weapons dismantlement programs through the production of fresh uranium-plutonium mixed oxide (MOX) fuels for industrial nuclear reactors is finding wider industrial applications worldwide.

This industrial application requires, in particular, the solution of the following issues:

- automation of technological operations;

- limiting the effects of ionizing radiation on production personnel and

- reduction of liquid and solid waste.

World practice shows that access to this reuse technology has major powers, whether political, economic or demographic (USA, Japan, Russia, India, China, etc.). Western Europe retains some leadership in the development of industrial processes in this area.

The desire of electricity producers to ensure their competitiveness in connection with the liberalization of their market encourages nuclear fuel developers to limit the frequency of overloading the reactor core, providing more and more complete burnup of unloaded fuel, both fuels based on U02 and MOX fuel (for example, 50 GW- day / t). This explains the desire to produce MOX fuel with an ever higher content of fissile plutonium and with reactor plutonium with an increasingly degraded isotopic composition, that is, a fuel with constantly increasing alpha activity.

To control the safety of personnel of MOX fuel production plants (to prevent the risks of ingestion of an operator with food or inhaled air), the safety of vehicles and nuclear power reactors (non-contamination of the primary circuit), it is important that MOX fuel rods loaded as an assembly are not or were only very slightly contaminated from the outside of their shell, which, together with its welded end caps, protects the tablets of MOX fuel.

The present invention relates to operations for the production of MOX fuel rods, in particular, operations for loading heavily soiled tablets into the shell, installation and welding of a second end plug, and also to methods and devices for the industrial production of uncontaminated MOX fuel rods, without the need for operations by their chemical or electrolytic decontamination using the wet method, leading to environmental pollution and increased criticality risks.

Recall that usually the core of a nuclear fuel consists of a metal shell (most often made of zirconium alloy or stainless steel), fuel pellets (usually made of uranium oxide or uranium-plutonium oxide), a pressure spring, and two welded end caps that provide tightness against gas and nuclear fuel protection. These rods are filled with a heat-conducting inert gas (most often helium) under pressure or not. The gap between the tablets and the shell is very small (for example, about 150-200 microns for light-water nuclear reactors). Structural elements other than the aforementioned clamping spring may be loaded from above or below the shaft (for example, an insertion tube, getter insulating tablets, reproduction zone tablets, etc.).

It is important that during the manufacture of fuel rods the method of loading tablets into the shell allows:

- to limit the size of the parts of the shell susceptible to contamination, and the amount of this contamination in order to reduce and possibly eliminate the need for cleaning / decontamination operations; in particular, to prevent the deposition of contamination on the outer surface of the shell, especially on its open end surface, forming the weld of the second plug, since these deposition possibilities contribute to an increase in the proportion of rods rejected due to their non-compliance with the criteria of external pollution;

- to prevent the ceramic tablets from being subjected to excessive stress in order to avoid the formation of fragments that create mechanical blockage during loading, and - as a result of these fragments getting inside the shell - the production of defective rods having excessive gaps between adjacent tablets.

Thus, the production of nuclear fuel rods, in particular MOX fuel rods, includes various, already mentioned operations, which are worth recalling here before describing the prior art. These operations are usually carried out in protective chambers that protect the environment and operators from the action of α (as well as β, γ) emitters:

- supply of a shell equipped with its first sealed plug;

- loading tablets into the shell;

- loading the spring for clamping tablets;

- replacement of air in the shell with an inert gas;

- cleaning / decontamination of the part of the membrane that has been contaminated during tablet loading;

- installation of a second plug;

- welding of the second plug with an annular seam;

- a possible pre-pressing of the shell, performed as a separate operation or simultaneously with the previous welding;

- possible welding of the ventilation hole, in the case of a separate prepress;

- measurement of contamination of the part of the shell exposed to contamination.

The methods used by manufacturers are aimed at achieving various goals, which may sometimes be incompatible. There are several non-exhaustive examples:

- operational safety: in particular, limiting the criticality risk associated with the use of liquid neutron moderators and the risk of fire or explosion due to the non-use of cleaning solutions including volatile substances; the conclusion of radioactive materials, in particular α-emitters, in sealed chambers, for example, such as glove boxes;

- the quality of the manufactured fuel rods: in particular, the quality of welding (the absence of oxidation, inclusions, etc.), the absence of fragments creating gaps between the tablets, the absence of fixed or tolerable external pollution;

- industrialization of technological operations: automation of operations; performance; limiting the effects of ionizing radiation on production personnel (external or internal exposure); limitation of the production of solid and liquid waste during cleaning / decontamination.

The pursuit of these goals may lead to the choice of a special procedure for performing the operations described above or the use of special technological solutions to perform a particular operation in order to facilitate all these operations with regard to safety, efficiency or limitation of waste production or to improve product quality. Some methods that influence the production processes of MOX fuel are given below:

- checking for dust accumulation on tablets before loading them by grinding with or without cooling, removing dust from tablets with mechanical means or a laser, by limiting the proportion of recycled scrap in tablets, by careful handling of tablets, etc .;

- loading tablets into the shell in an air or nitrogen atmosphere, which is associated with dilution of air or nitrogen by repeatedly adding inert gas, or from pumping gas from the shell in order to reintroduce inert gas into it, and with this contamination of the open end of the rod ( already equipped or not with its second plug);

- installation of a second plug with or without a clamp, welded around the perimeter using the most widely used welding process, namely arc welding with a tungsten electrode in an inert gas medium (TIG), which allows the rod to be pressed on another production line or in another machine; or any welding process that provides welding of the second plug and prepress in one operation (resistance resistance welding or laser welding).

Various known inventions related to the field of the present invention are given below as non-exhaustive examples, according to which it is known:

- the use of a centering device for introducing tablets into the shell, in the absence of special protective devices (such as a glove box):

- a stationary centering device of a cylindrical shape or in the form of a truncated cone (see US patent No. 4980119, 4748798, 5251244);

- a triple centering device (one fixed + two intermediate) of circular cross section (see US patent No. 3940908);

- fixed V-shaped centering device (see US patent No. 3907123);

- fixed centering device with a polygonal or square cross section (see US patent No. 4942014)

or

- the use of a centering device for introducing tablets into the shell installed in a protective chamber (such as a glove box):

- a fixed centering device in the form of a truncated cone mounted in the center of the protective chamber (see US patent No. 3925965);

- a centering device mounted on the border of the two zones of the protective chamber, active and inactive, the active zone being intended for loading tablets (see WO 98/26428).

It should be noted that this last document mentions the separation of the protective chamber into only two compartments.

All of the above devices known to the inventors do not satisfy the requirements for the industrial production of uncontaminated MOX fuel rods from ceramic tablets, which, together with the accumulation of dust, can form fragments, which in turn create mechanical jams and plugs during loading operations;

- either these devices do not limit the part of the membrane that is exposed to contamination to a strict minimum, or there is no control of the levels of contamination in the protective chamber (from "heavily contaminated" in the loading zone to "very slightly contaminated" or "uncontaminated" when the rod leaves the protective chamber) moreover, this lack of control leads to excessive and unjustified contamination, which must be removed by additional operations, most often based on liquid treatment, which leads to the formation of various wastes and additional criticality risks;

- either these devices are sensitive to dust and fragments carried away by tablets in columns and / or to those formed during loading of tablets into the shell, and this sensitivity causes mechanical congestion leading to machine downtime, the need for operator intervention in protective chambers, and risks of contamination operators, workshops, and sometimes protective rooms, which should remain only slightly contaminated or unpolluted;

- either these devices to prevent contamination and loading of tablets do not allow the production of plutonium fuel rods that meet the technical conditions for their non-pollution, when the plutonium content in the tablets and the alpha activity of plutonium are high, even during additional liquid decontamination.

The objective of the invention is to create such a method and apparatus for the manufacture of uncontaminated MOX fuel rods, with which you can eliminate the above and other disadvantages, well known to specialists. This problem is solved through the use of an original and non-obvious combination of features that affect, in particular, technological operations, as well as the quality of manufactured products. So:

- various operations for loading tablets, cleaning / decontamination of the end of the shell that has become contaminated, installing a spring and a second plug with or without immediate welding, depending on whether this plug is installed with or without a clamp, cleaning and checking for contamination before Removing the rod from the protective chamber can be carried out mainly on the same production line and in various protective compartments isolated from each other depending on the gas environment used and the level of pollution Ia inherent implement the corresponding operation; moreover, at least the last two named compartments are preferably designed so that their contamination can be kept for a long time, at a low level, for example, due to their suitability for decontamination, well known to specialists, during operation despite the consistent movement of many rods;

- preferably, the dimensions of the parts of the shell introduced into the protective chamber are limited to a strict minimum in order to limit the size of the parts that are contaminated and require checking for contamination at the outlet and their possible cleaning / decontamination;

- preferably, the loading of tablets is carried out using tablets previously introduced into the protective chamber in a helium medium or in vacuum, and into a shell previously filled with helium, or in vacuum, after pumping the air contained therein. Due to the very low dynamic viscosity of helium, it is possible to load tablets into the shell in a helium medium at production speeds of about 100 to 150 mm / s without evacuating the gas contained in the shell, which carries a lot of dust to the open end of the rod;

- the introduction of the tablets into the shell - or loading them - is provided using a loading device, the inside of which is made in the form of a rounded truncated pyramid and with exact tolerances for:

- feeding at the open end of the shell of the tablets precisely aligned in position and orientation to avoid the occurrence of mechanical congestion;

- shielding the open end of the shell from the loaded tablets in order to avoid severe contamination of the shell, possible deposits of contamination and additional mechanical congestion;

- capture and / or collection and / or removal of dust and fragments of tablets that may block the tablets during loading or possibly get into the shell;

- the loading of tablets into the shell is carried out by columns sequentially fed along the V-shaped element along the axis of the shell, using to limit the forces acting on the tablets, a device with a sensitive drive, the force of which is limited depending on the order of the loaded column of tablets, and having a sufficient length to so that the loading depth of any column in the shell is greater than the length of the next loaded column; it should be noted that the pushing forces of the tablets during their loading into the shell are limited, respectively, by both the depth of entry of the pushing device and the order (N) of the loaded column;

- operations to clean parts of the shell that are subject to contamination are carried out immediately after contamination and in a dry manner to avoid the spread of contamination and the need to control the risk of criticality and the formation of contaminated liquid waste.

To overcome the above drawbacks, it is necessary to use at least a partial combination of the above new operations.

To this end, the method according to the invention includes the following sequence of operations:

- separation of the protective chamber into a number of adjacent compartments;

- the connection of each compartment with the adjacent one to create a sealed passage for the shell, and at least some of these passages are aligned with each other in order to allow the shell to move along its longitudinal axis;

- the input loaded by tablets shell, open end forward, into the first compartment through a sealed passage or inlet of the compartment;

- axial movement of the shell between successive compartments until its open end reaches the last compartment;

- loading tablets in the last compartment, as well as, if provided, various structural elements, other than the clamping spring, into the shell through its open end;

- partial axial extraction of the shell at the end of the load in order to move its open end to the previous compartment;

- in this previous compartment, cleaning and checking for possible contamination of at least part of the membrane that has undergone contamination emitted by the tablets during loading, or the atmosphere of the last compartment;

- after this cleaning, the axial movement of the shell so that its open end moves to another compartment;

- loading the clamping spring and installing the second plug in the open end in this other compartment;

- after this installation, the execution of other possible operations, for example, welding with an annular seam, prepressing / welding of the ventilation hole, etc., in the same compartment or in another compartment with possible additional movement of the shell;

- check for contamination of the parts of the rod that have been contaminated in the last compartments, and, as necessary, their potential cleaning in the first or second compartment;

- removing the rod from the first compartment or its transverse movement to another protective chamber through this first compartment connecting these protective chambers to each other;

- stepwise change in the degree of pollution between different compartments, starting from the absence of pollution or very slight pollution in the first compartment and ending with the most severe pollution in the last compartment;

- the choice of gases supplied to the compartments of the protective chambers and to any technological or transport boxes in them from the group of gases, including: air, nitrogen, helium, argon, vacuum; and

- stepwise pressure changes in these compartments in order to order any leaks, starting with the highest pressure in the first compartment and ending with the lowest pressure in the last compartment.

The above method, which is the subject of the present invention, can be advantageously applied both in conventional plants for the production of MOX fuel, and in plants for the production of other nuclear fuel containing in any proportion actinides other than uranium as non-limiting examples : fuel based on uranium / plutonium nitrides or carbides, fuel without a reproducing material, intended for burning or transmutation of actinides, MOX fuel based on thorium / plutonium, MOX fuel with an absorber burning out or no, etc.

According to one example embodiment of the invention for loading tablets and subsequent related operations, namely

- feeding, centering and aligning the pill forming the pillar from the support to the open end of the shell and

- removing from this column dust tablets and debris trapped by these tablets and / or adhering to the loaded tablets and / or formed during feeding, centering and leveling of the tablets,

The following operations are performed:

- between the support and the open end of the shell and alignment of the axis of the tablets with the axis of the shell using a channel, the lower part of which has a V-shaped profile with uniform inclination and partially coinciding with the cylindrical outlet with the diameter of the tablets;

- centering the shell in the chamber, centered on the cylindrical part of this channel;

- shielding the open end of the shell from the loaded tablet;

- capture and / or collection and / or removal of dust and fragments of tablets through the gaps between the tablets and the channel walls under the action of gravity and, optionally, by additional blowing and / or suction.

The present invention also relates to a device for the production of uncontaminated MOX fuel rods from tablets intended for implementing the proposed method. This device includes a protective chamber designed to perform the following operations:

- loading the tablets in columns into a shell open at one end and closed with a first plug at the other end;

- cleaning and potential contamination of a portion of the aforementioned shell exposed to contamination or dust from the above tablets;

- loading of various structural elements, in particular, a clamping spring;

- installation of a second plug;

- potential cleaning and checking for contamination of a portion of the aforementioned casing exposed to contamination.

According to the present invention in the above device:

- the protective chamber is divided into several separate compartments;

- these compartments are preferably arranged sequentially, one after the other, in the direction of movement between them of the loaded shell, open end forward;

- these compartments of the protective chamber are isolated from each other by sealed partitions having, for moving the shell from one compartment to another passage, consisting of a full bore valve and a sealing device around the circumference of the shell, at least some of the aforementioned passages are aligned in the direction of movement of the aforementioned shell, and the first compartment is potentially simply equipped with a hole at its entrance;

- the axial drive mechanism is installed in order to move along the longitudinal axis of the end of the input shell or rod, provided with a second plug in the selected compartment;

- devices for loading tablets with columns and means for loading various structural elements other than the clamping spring and the second plug are installed in the last compartment;

- at least one device for cleaning / decontamination and, possibly, means for checking for contamination of the part of the membrane exposed to contamination during loading of tablets, are installed in any previous compartment;

- means for loading the clamping spring and installing with a clip or without a second plug in the open end of the shell are located in another previous compartment;

- the means necessary to perform possible additional welding and / or prepress operations may be installed in the same compartment or in another compartment;

- Means for checking for contamination and, potentially, cleaning / decontaminating parts of the core that are subject to contamination during previous operations, are installed in the first or second box; and

- means for ventilating the protective chamber, its compartments and any boxes installed in them, as well as means for supplying gas, are installed in order to maintain a reduced pressure in this chamber compared to the atmosphere of the room, and are designed to provide

- gas selection for each compartment and / or box installed in it from the group of gases, including: air, nitrogen, helium, argon, vacuum; and

- stepwise change in reduced pressure in these compartments in order to streamline the direction of any leaks and to facilitate a stepwise change in the degree of contamination, starting with the weakest pressure in the first compartment and ending with the strongest in the last compartment.

As indicated above, the various compartments may also have one or more boxes or chambers installed in them and operating in gas media other than the gas medium of the compartment, and these boxes or inner chambers are usually designed to perform technological operations, for example, loading tablets in a vacuum , welding in helium medium of very high purity, etc., or transportation operations, for example, transverse movement in some container of the open end of the shell in a controlled gas environment.

Among the advantages provided by the invention include:

- production of rods with a high plutonium content, unpolluted, without inclusions in the weld and without excessive inter-gap gaps;

- various implementation options:

- from processes that are fully manual, to fully automated processes;

- from production devices with low / medium productivity, "single-rod" plants that process only one rod at a time, to high-performance devices, "multi-rod" plants that process a number of rods at the same time;

- various compositions of the “shell / second plug” assembly, for example, plugs inserted into the shell with or without a clamp, plugs with an axial or transverse ventilation hole, etc .;

- various methods for performing an annular weld, arc welding with a tungsten electrode in an inert gas medium (TIG), resistance welding, laser welding, etc. and prepress;

- various dry cleaning / decontamination methods, mechanical wiping, laser, etc .;

- loading without special precautions dusty tablets after grinding without cooling or after numerous transportation operations;

- limiting the contamination of the casing, as regards the surface area and size, when loading the tablets and filling the casing with inert gas before welding, allowing to limit the cleaning / decontamination operations only by cleaning, for example, wiping the end of the contaminated rod and checking the absence of tolerated pollution at the outlet also by mechanical rubbing;

- lack of liquid waste; limited generation of solid waste during cleaning and testing for portable pollution by wiping;

- reduced criticality risk, allowing the use of high content and large quantities of fissile material;

- overall savings in production costs.

Other details and features of the invention will be apparent from its other claims and the description of the schematic drawings, at indefinite and various scales, attached to the present description and explaining by non-limiting examples the proposed method and individual variants of the proposed device or its components.

Figure 1 shows an axial section of one embodiment of a fuel rod manufactured according to the proposed method.

On figa-C schematically shows the layout of the compartments of the protective chamber for one example embodiment of the invention, as well as various options for placing equipment inside these compartments, in order to provide the ability to feed the shell forward, or lateral movement of the specified equipment, or its internal placement for axial movement shell.

FIG. 2B schematically shows the insertion of the rod, made according to FIG. 1, into the first compartment of the protective chamber in accordance with various embodiments of the invention, one at a time or grouped together;

- access to the first compartment through a sealed lock chamber, allowing the use of a gas medium other than room air in it;

- the length of the first compartment in excess of the length of the rod;

- transverse movement of the shell / rod with a "multi-rod" design of the device.

On figs schematically shows the input of the rod depicted in figure 1, so that it fits into the last compartment of the protective chamber.

Figure 3 shows a perspective image of an element for introducing tablets into a shell for carrying out the invention.

On figv shows examples of the design of the longitudinal and transverse grooves and gas nozzles G.

On figa-4F shown in plan various operations of the sequence of loading consecutive columns of tablets into the shell according to one embodiment of the invention. 4A also shows a mechanism for driving a pushing device with limited force. As an example, FIGS. 4A-4F show loading two consecutive columns “a” and “b” deep into shell 2 using a long pushing device 53.

In various drawings, the same reference numbers indicate the same or similar elements of the device.

Shown in figure 1, the rod 1 according to the invention contains a shell 2, hermetically closed at one end by a first plug 3, and at the other end by a second plug 4. Between these plugs 3 and 4 in the shell 2 are tablets 6, spring 7 and structural elements, such as one or more inserts 5.

The device and method for the manufacture of uncontaminated MOX fuel rods 1 from tablets 6, which are the subject of the present invention, are explained in the present description together in view of their full relationship.

As explained below, this method consists in performing in the protective chamber 10 (FIG. 2), for example, the type of glove box, the following operations:

- loading the tablets 6 with columns 12 (FIG. 4) into the shell 2 using the loading device 14 shown in FIG. 3 and schematically in FIGS. 2 and 4, consisting of a V-shaped or grooved plate 38, sequentially moved in the transverse direction the axis of the aforementioned columns 12 and shell 2;

- loading of various structural elements, in particular, the clamping spring 7;

- installation of the second plug 4 in the shell 2, either with a clip or without it;

- potential welding with an annular seam of the second plug 4, in particular, if it is inserted into the shell 2 without clamping;

- potential cleaning and checking for contamination of a portion of the aforementioned shell 2 exposed to dust or aerosols produced by the tablets 6.

According to the invention, the following methods and precautions are used for this purpose (Fig.2-4):

- the protective chamber 10 is divided into compartments, for example, I, II, III and IV according to figure 2, in this case, 4 compartments adjacent to each other and hermetically isolated from each other, and the level of contamination by alpha emitters, as well as the type and gas pressure is monitored in each of these compartments;

- operations: loading, cleaning, installing a plug, checking for contamination are performed sequentially on the shell 2 by axially and sequentially moving between these compartments I-IV, the input and output of the aforementioned shell being carried out through the same compartment I;

- tightness between compartments I-IV is ensured at each moment of time by means of a lock chamber 24 (FIG. 2), consisting of a valve 26 with a full bore for the sheath 2, for example, a shut-off or ball type, and a sealing element 28 with elastomeric seals, sealing rings, lip seals or special seals around the sheath 2; this lock chamber 24 allows you to enter the rod 1 from one compartment into another, without violating the tightness between them and changing, if necessary, when passing the internal gas medium of the rod 1, for example, to introduce into the helium or vacuum the shell 2, which was previously in the air. In this latter case, the gas volume is limited by the lock chamber body 24, the valve 26 and the sealing device 28 are pumped out by a pump (not shown) through the valve 32 or any other device and replaced by a gas of the selected type. The sealing element 28 can occupy different positions, it either leaves the entire passage open without touching the shell, or provides static sealing of the shell around the circle when it is stationary, or provides dynamic sealing around the shell with its relative translational or rotational movement, which is necessary for any either transportation or technological operation;

- loading of tablets 6 and loading of structural elements 5, other than the clamping spring 7 and the second plug 4, are made in compartment IV, located farthest from the input compartment I;

- cleaning of the part of the shell 2 that has been contaminated, in particular the surface of its open end 34, is carried out after loading the tablets 6 and other aforementioned structural elements 5, and before loading the spring 2 and the second plug 4, in compartment III, preferably adjacent to the loading compartment IV ; cleaning of allegedly contaminated surfaces is ensured, for example, by wiping them with strips of cloth or non-woven material that are dry or slightly soaked with some liquid, namely water, a solvent or a chemical decontaminant;

- loading the spring 7 and installing a second plug 4 in the shell 2 and potential welding with an annular seam of this second plug 4 are performed in compartment II, located between the treatment compartment III and compartment I;

- cleaning and potential checking for contamination of the parts of the shell 2, which were introduced into the compartments II-IV of the protective chamber 10, are provided in some compartment separated from the compartment 11. Cleaning can be carried out by dry or slightly damp wiping, using, for example, strips of cloth or non-woven material, dry or slightly soaked in liquid (water, solvent or decontaminant). The absence of contamination can be checked by contact or non-contact method, depending on whether it is desirable or not to check for tolerable pollution. In the second case, most often, the test is carried out by taking a smear sample and its examination using any device known to specialists, for example, a ZnS detector. Total contamination can be checked directly, for example, using a ring ZnS detector. It should be noted that other dry cleaning methods are also known, including, for example, illuminating the corresponding surface with a laser light;

- the input of the shell 2 and the check for contamination of the rod 1 can be successfully performed in the same compartment I. This may also be necessary, for example, if the rod 1 needs to be removed and moved to some other piece of equipment located in another chamber, in particular, if the plug 4 is mounted with a clamp in the fuel shell 2 for light-water nuclear reactors and allows its welding in a separate chamber;

- pollution levels stepwise change from compartment IV to compartment I at the outlet of the protective chamber 10; these levels, in particular of the least contaminated compartments I, II, III, are checked continuously or periodically in order to prevent the transfer of excessive contamination to subsequent compartments I, II and to limit the contamination of the casing 2, with the second plug 4 installed or not installed, during its movement to the above output; in case of accidental pollution or gradual accumulation of pollution, it is important to be able to reduce the pollution level of these compartments to an acceptable level by cleaning them and the equipment installed in them; pollution control of the compartments of the protective chamber 10 is also associated with appropriate ventilation and filtration, for example, the minimum refresh rate of the gas environment should be at least 2-, 3 times per hour, without creating turbulence;

- the atmospheres of the various aforementioned compartments I-IV may consist of various gases such as air, N ₂ , Ar, He or even vacuum for the loading compartment IV;

- the pressures in these different compartments I-IV vary stepwise to order the leaks from the least polluted compartments to the most polluted ones; depending on the gases present in these compartments, the pressure cascade is controlled by separately controlling the pressure in each of the compartments relative to the atmosphere of the room where the protective chamber 10 is located, or by arranging the ventilation flow from one compartment to another; it should be noted that in all different compartments, a reduced pressure must be maintained relative to the pressure in the room in which the installation for the production of rods 1 is operating.

The production method proposed above is particularly preferable from the point of view of pollution control when loading the tablets 6, cleaning and installing the plug 4 are carried out in compartments with a helium medium, which is an additional subject of the invention. For this, when it is introduced into the protective chamber 10, the shell 2 without tablets is moved to the first encountered compartment with a helium medium, usually compartment II for installing a plug, after pumping out the room air or nitrogen of the transport box contained in the aforementioned shell 2 and replacing it helium in the lock chamber 24, separating the two corresponding compartments. As noted above, this variant of the method allows you to install, perhaps even weld the plug on the rod 1 in a helium medium and to avoid the need to vacuum the shell 2, filled with tablets 6 and air or nitrogen, to replace it with helium. It should be noted that due to the low dynamic viscosity of helium, compared with the viscosity of air or nitrogen, usually used in a protective chamber, the helium contained in the shell 2 is removed when columns 12 of tablets 6 are introduced without noticeable entrainment of dust and aerosols to the open end of the rod 34 one.

The manufacturing method proposed above also provides an advantage when tablets are loaded in a vacuum; in this case, the shell is supplied without tablets and gas to the inlet of the last compartment with vacuum or containing any box with vacuum, after pumping gas out of it in the lock chamber 24 to access this compartment; it is possible to choose an atmosphere for compartments in which cleaning, installation and welding are carried out; the helium medium in these two compartments, combined with the vacuum in the loading compartment, provides special advantages with regard to pollution control, despite the higher complexity of its implementation.

During the loading of tablets 6 it is important:

- serve tablets 6 to the open end 34 of the shell 2 so that they are precisely aligned in position and orientation in order to avoid the occurrence of mechanical congestion;

- to shield the open end 34 of the shell 2 from the loaded tablets 6 in order to avoid its strong pollution, the occurrence of additional mechanical congestion and interference;

- to capture, and / or collect, and / or remove dust and fragments of tablets that may block tablets 6 during loading or, possibly, cause the manufacture of defective cores, and which are either transferred by the indicated loading tablets 6, or are formed during tablet loading.

To this end, you can use the device 14 (figure 3) for the introduction of tablets 6, most often served by columns 12 on a fixed V-shaped plate or (figure 4) on a known plate 38 with V-grooves and moved laterally; this boot device, which is an additional subject of the invention, includes a hollow fixed metal element 14 made, for example, of two parts, the inner profile 42 of which consists sequentially, in particular, as shown in figure 3, from the entrance of a square section at its end 44, parts 46 with a gradually decreasing square cross section at its tip (T + U), a cylindrical outlet 48 of circular cross section (Y) with a diameter equal to the diameter of tablets 6, with continuous connection with the square cross-section th section 46 and cylindrical bore 49 with an outer diameter equal to the diameter of the shell 2 (Z). The square inlet (T) at its end 44 allows large gaps, up to 1 ÷ 2 mm, for tablets 6 in order to ignore misalignment of a different nature, for example, vertical and horizontal misalignment of the V-groove strip 38, which feeds the columns 12 tablets 6. Detail with the square cross section at tip 46 has gradually decreasing dimensions (T + U) to gradually center the tablets 6; various laws of geometric reduction can be implemented on modern CNC machines, for example (Fig. 3), starting with a linear reduction leading to a truncated pyramid (U), and ending with a non-linear, for example, quadratic reduction (T), thereby allowing correction significant misalignment in short sections and contribute to the removal of dust and debris as a result of a change in the orientation of the tablets with respect to each other. As for the two circular cross sections 48 and 49, both of these holes D _y and D _z are respectively made with the diameters of tablets (D _YHOM. = D _tab. + 0.02 mm, for example) and shells (D _zhom. = D _max . _Max . _. + 0.01 mm, for example) with an alignment of 0.01 mm and tolerances on the diameter of -0 / + 0.01 mm. This input component can also be provided (FIG. 3B) with various nozzles for injecting gas or nozzles for collecting, collecting or removing dust and debris adhering to the tablets or carried by them. In element 14, longitudinal and / or transverse grooves can also be provided in order to improve the capture of debris and dust. It should be noted that in another possible embodiment of the invention, the upper part of the channel 42 may have a shape other than the reverse V.

In addition, it should be noted that the loading device 14 can be used for direct injection of tablets into the shell, as well as centering and aligning the tablets in any intermediate device installed in front of the shell.

When loading columns of tablets 12, it is important to limit the axial forces used to:

- to avoid the transverse forces of the columns 12, experiencing axial pressure and able to occur due to deviations in the perpendicularity of the end surfaces of the tablets 6; these efforts are harmful when the tablets 6 cross the places of mechanical transition (V-shaped or gutter-shaped strip 38 to the input element 14, the input element 14 to the shell 2); and

- to avoid the formation of additional fragments and dust during loading due to excessive local pressure on the edges of the tablets 6 in contact with their end surfaces.

To do this, the following three methods are used separately or in combination with each other:

- loading the tablets 6 in a gas medium with low dynamic viscosity (helium) or in vacuum, in order to limit the pressure in the shell 2 during the supply of columns of tablets 12; it should be noted, for example, that the further the loading of the pillars progresses, the more the gas pressure increases, at the same loading speed, due to an increase in the pressure drop along the pillar 12;

- the supply of tablets loaded with columns 12 (figure 4) into the shell 2, to a depth equal to at least the length of the elementary columns 12; thus, the first tablet 6 of any column N (N, going from “a” to “e” in the example shown in FIG. 4) during its loading into the shell 2 is in contact with the last tablet 6 of the already loaded column (N- 1) and pushes the “composition” (N-1) of the already loaded columns only when the last tablet of the N column is already inside the shell 2; thereby, the transverse forces created by the tablets 6 are minimized and, moreover, render less harm due to the exact mechanical orientation provided by the shell 2;

- the use of any device for pushing tablets 50, equipped with a sensitive drive, in particular, one that, in general, is able to limit the amount of effort it creates only to the necessary; this is necessary because the required forces increase as an increasing number of elementary columns 12 are loaded. These forces are limited, for example, electronically by controlling the power supply of the DC motor or servomotor 52 depending on the input depth of the pushing device and the serial number N of the loaded a column; finally, due to the use of high loading speeds in factories, it will be necessary to prevent inertial effects by using a tablet pushing device 53 with a hollow shaft and a torque limiter 54 with slippage and low inertia, for example, a magnetic powder torque limiter.

Reducing the pushing speed of the “composition” of pillars can preferably be applied to the last pillar or pillars loaded.

Various types of separation of the protective chamber and the distribution of the operations performed therein are possible. Table 1 shows some of their possible examples.

TABLE 1 Possible embodiments of the invention Compartments No. I II III IV V Comments one Shell input
Pollution check
Terminal pin
(Air or helium) Spring loading
Installing the 2nd plug (Welding the plug if it does not have a clamp)
(Helium) Shell cleaning
(Helium) Tablet loading
(Helium) Single rod device 2 Input / output of the shell (Option: moving the shell to another camera)
(Air or N ₂ ) Contamination check Potential cleanup
(Air or N ₂ ) Spring loading
Installing the 2nd plug
(Welding the plug if it does not have a clamp)
(Air or N ₂ ) Shell Cleaning (Air or N ₂ ) Tablet loading
(Air or N ₂ ) Multi-rod device 3 Shell input
Terminal pin
(Air) Contamination check Potential cleanup
(Air) Spring loading
Installing the 2nd plug
(Welding the plug if it does not have a clamp)
(Helium) Loading tablets in a vacuum
(Air) Single rod device four Shell input
Contamination check Shell outlet
(Air) Moving in a vacuum to other devices (installing a plug, welding it, etc.)
(Air) Loading tablets in a vacuum (additional cleaning of the shell in a vacuum)
(Air) Multi-rod device (rotating drum) Note: The alpha-protective chamber is divided into 3-5 compartments, hermetically isolated from each other. In some cases, the gas environment of one compartment may differ from that in which this or that operation is carried out. In this case, such a compartment is provided with a sealed box or chamber (for example, a box for loading in a vacuum or a chamber for welding in a helium medium).

The following is detailed information regarding an example embodiment of the invention No. 1, described in table 1 and implemented by the inventors in practice.

but. Sequence of operations

- loading tablets 6, containing the scrap formed during the manufacture and polished without cooling, onto the trough plate 38, which is transversely moved step by step;

- gas environment and distribution of functions in compartments:

IV: in helium - loading tablets;

III: in gels: - cleaning of the open end;

II: in gels - loading tablets and caps without clamp;

- welding of the second plug with an annular seam;

I: in the air - potential cleaning of the end of the rod;

- taking a smear test to measure tolerated pollution;

- removing the rod in order to prepress it on another piece of equipment;

- isolation of compartments: using a lock chamber 24, which includes a full bore vacuum valve and a double elastomeric seal with a gas or vacuum barrier.

The helium used in various compartments comes from a helium purification (recycling) station pumped out of the protective chamber to maintain reduced pressure in the above chamber, and from a fresh helium source to compensate for leaks, while the welding compartment of compartment II is directly supplied with high helium degree of purity.

There is an option that provides compartment I with helium for the purpose of manufacturing MOX fuel for boiling reactors.

b. Products and specifications (non-limiting)

total plutonium content in tablets,% 9.5 isotopic composition of plutonium Pu ^{238, 239, 240, 241, 242,} % 2-57-27-8-6 the content of Am ²⁴¹ ,% 2 Plutonium α-activity, 10 ¹⁰ Bq / g 1.8 the content of scrap generated during manufacture,% 22 diameter of a tablet, mm 7-12 tablet loading rate, mm / s from 100 to 150 fillet welding tungsten arc welding
electrode in the medium
inert gas (TIG) sheath material Zr alloy α-contamination of the loading compartments,
cleaning, welding and checking for
pollution, respectively, Bq / dm

<10³, 10²-10¹, <1

<10 ³ , 10 ² -10 ¹ , <1 sticky tolerated α-pollution
rods, Bq / dm ² on the smear test
<1 fixed α-contamination of the weld, Bq <20

Claims (19)

1. A method of manufacturing uncontaminated MOX fuel rods (1) from tablets (6) in a protective chamber (10) held at reduced pressure compared to the atmosphere of the room, including the following operations for one rod (I): loading tablets (6) sequentially columns (12) into the shell (2), previously provided with a first plug (3) at one of its two ends; loading of various structural elements, in particular a clamping spring (7); installing a second plug (4) at the other end of the shell (2); potential welding with an annular seam of the second plug (4), in particular if it is inserted into the specified shell (2) without clamping; at least one cleaning and at least one check for contamination of parts of the aforementioned shell (2) or, accordingly, of the rod (1) exposed to contamination, characterized in that the method includes dividing the protective chamber (10) into a number of adjacent compartments ; the connection of each compartment with the adjacent one to create a sealed passage for the shell (2), and at least some of these passages are aligned with each other in order to allow the shell (2) to move along its longitudinal axis; the input shell (2), loaded with tablets, the open end (34) forward into the first compartment through a sealed passage or inlet of the compartment; axial movement of the shell (2) between successive compartments until its open end (34) reaches the last compartment; loading tablets (6) in the last compartment, as well as, if provided, various structural elements (5), other than the clamping spring (7), into the shell through its open end (34); partial axial removal of the shell (2) at the end of the load in order to move its open end (34) to the previous compartment; in this previous compartment, cleaning and checking for possible contamination of at least part of the shell (2) that has undergone contamination emitted by the tablets (6) during loading, or the atmosphere of the last compartment; after this cleaning, the axial movement of the shell (2) so that its open end (34) enters another compartment; loading the clamping spring (7) and installing the second plug (4) in the open end (34) in this other compartment; after this installation, the execution of other possible operations in the same compartment or in another compartment with possible additional movement of the shell; checking for contamination of the parts of the rod (1) exposed to contamination in the last compartments, and their potential cleaning, as necessary, in the first or second compartments; removing the rod (1) from the first compartment or moving it laterally into another protective chamber through the first compartment connecting the protective chambers to each other; stepwise change in the degree of pollution between different compartments, starting from the absence of pollution or very slight pollution in the first compartment and ending with the most severe pollution in the last compartment; the choice of gases supplied to these compartments from the group including: air, nitrogen, helium, argon, vacuum; step change in pressure in these compartments to order any leaks, starting from the highest pressure in the first compartment and ending with the lowest pressure in the last compartment, 2. The method according to claim 1, characterized in that for loading the tablets (6) and the following related operations of feeding, centering and aligning the tablets (6) forming a column (12), from the support (38) to the open end ( 34) shell (2); and the following, the centering error is corrected between the support (38) and the open end (34) of the shell (2), the axis of the tablets (6) are aligned with the axis of the shell (2) using the channel (42), the lower part of which has a V-shaped profile with uniform inclination, and partially coinciding with the cylindrical outlet with the diameter of the tablets (6); centering the shell (2) in any chamber centered on the cylindrical part of this channel; shielding the open end (34) of the shell (2) from the loaded tablets (6); trapping and collecting and / or removing dust and debris carried by tablets (6) and / or adhering to them, and / or formed during their feeding, centering and leveling, through the gaps between the tablets (6) and the walls of the channel and / or grooves , by gravity and additionally by blowing and / or suction. 3. The method according to claim 1, characterized in that the tablets (6) of the column are loaded into the shell (2) to the depth of entry of the last tablet (6) into the shell (2) equal to at least the length of the next column loaded into that same shell (2) 4. The method according to claim 1, characterized in that the loading of tablets (6) in successive columns into the shell (2) is carried out by limiting the maximum pushing forces during loading, depending on the depth of entry of the pushing device and the order (N) of the column loaded in same shell (2). 5. The method according to claim 1, characterized in that dry or slightly wet cleaning of parts of the shell (2) or, respectively, of the rod (1), contaminated, and this method is wiping. 6. The method according to claim 1, characterized in that the protective chamber is divided into four compartments (I-IV), of which the fourth and last compartment (IV) is designed to load tablets (6) and structural elements; the third (III) is designed to clean the part exposed to contamination during loading; the second (II) is intended for loading the spring (7) and installing the second plug (4), as well as for its possible welding with an annular seam, if it is installed without clamping; the first (I) is designed to check for contamination and potential cleaning of parts that have been contaminated in previous compartments, as well as to enter the sheath and withdraw the rod. 7. The method according to claim 1, characterized in that the loading of tablets (6), cleaning of the end of the shell (2) that has been contaminated, and the installation of the second plug (4) are carried out in compartments with helium medium, as well as additionally checking for output pollution; after entering the shell (2) without tablets into the protective chamber (10), its open end (34) is transferred to the first encountered compartment with helium medium only after pumping the gas between this and the previous compartments and replacing the gas contained in the shell (2) with helium. 8. The method according to claim 1, characterized in that the loading of the tablets (6) is performed in the last compartment in a vacuum or in a protective box in a vacuum located in this compartment; after entering the shell (2) without tablets (6) into the protective chamber (10), its open end (34) is moved to this last compartment only after pumping the gas contained in the shell (2) between this compartment and the previous compartment. 9. A device for the production of uncontaminated MOX fuel rods (1) from tablets (6) for implementing the method according to claims 1-8, including a protective chamber (10) for performing the following operations: loading tablets (6) with columns (12) into the shell (2) open at one end and closed with a first plug (3) at the other end; cleaning and potential contamination of a portion of the aforementioned shell exposed to contamination or dust from the above tablets (6); loading of various structural elements, in particular, a clamping spring (7); installation of the second plug (4); checking for contamination and potential cleaning of a part of the aforementioned shell (2) that has been exposed to contamination, characterized in that the protective chamber (10) is divided into several separate compartments; these compartments are preferably arranged sequentially, one after the other, in the direction of movement of the loading shell (2) between them with the open end (34) forward; these compartments of the protective chamber are isolated from each other by sealed partitions having, for moving the shell (2) from one compartment to another, a sealed passage (24) consisting of a full bore valve (26) and a sealing device (28) around the circumference of the shell (2), moreover at least some of the aforementioned passages (24) are aligned in the direction of motion of the aforementioned shell (2), and the first compartment is potentially provided only with a hole at its entrance; at least one axial drive mechanism is mounted with the ability to move along its longitudinal axis the end of the insertion shell (2) or the rod (1) provided with a second plug (4) in the selected compartment; devices for loading tablets (6) with columns (12) and means for loading various structural elements (5), other than the pressing spring (7) and the second plug (4), are installed in the last compartment; at least one cleaning device and, possibly, means for checking for contamination of a portion of the shell (2) exposed to contamination during loading of the tablets (6) are installed in any previous compartment; means for loading the clamping spring (7) and installing, with or without a clamp, a second plug (4) in the open end (34) of the shell (2) is installed in another previous compartment; the means necessary to perform possible additional welding and / or prepress operations may be installed in the same compartment or in another compartment; means for checking for contamination and, potentially, cleaning / decontaminating parts of the rod (1) exposed to contamination during previous operations, are installed in the first or second compartment; means for ventilating the protective chamber (10), its compartments and any boxes installed in them, and means for supplying gas are installed in order to maintain reduced pressure in this chamber (10) compared to the atmosphere of the room, and are configured to provide gas selection for each compartment from the group of gases, including air, nitrogen, helium, argon, vacuum; stepwise pressure changes in these compartments in order to streamline the directions of any leaks and promote a stepwise change in the degree of pollution, starting from the weakest in the first compartment and ending with the strongest in the last compartment. 10. The device according to claim 9, characterized in that the device comprises a device (14) for feeding, centering and aligning the tablets (6) with the aim of loading them into the shell (2), which contains a fixed metal element (14) with a channel (42) ) passing through it, the dimensions of the inlet (44) of which are selected so as to allow displacement of the tablets (6) relative to the axis of the shell (2), and the lower part of which has a V-shaped profile with uniform inclination and partially coinciding with the cylindrical outlet (48) with a diameter equal to the diameter of the tablets (6), and provided ilindricheskoy chamber (49) with a diameter equal to the diameter of the shell (2) and centered on the cylindrical output (48) of the channel; having dimensions and tolerances selected taking into account the dimensions of the tablets (6) and the shell (2), and so that the diameter of the cylindrical outlet (48) of the channel is smaller than the inner diameter of the shell (2) in order to shield the end of the shell (2) from the tablets (6) ; having longitudinal and / or transverse gaps and nozzles for injecting gas in the direction opposite to the direction of loading, and / or suction of dust and fragments. 11. The device according to claim 9, characterized in that for loading tablets (6) and structural elements, the device comprises a pushing device (50) with a sensitive drive; having, on the one hand, an axial transmission carried out by a set of rollers (56), equipped with a force limiter (54) with low inertia, driven by an engine (52), the force of which is limited depending on the insertion depth of the pushing device (53) and the order (N ) a column of tablets (6) loaded into the same shell (2); and on the other hand, a hollow pusher (53) with a small mass and an adaptable length, so that the depth of insertion of the last tablet (6) of the column loaded into the shell (2) is equal to at least the length of the next column loaded into the same shell (2). 12. The device according to claim 9, characterized in that it has at least one device for dry or slightly wet cleaning of the parts of the shell (2) or, accordingly, the rod (1) that have been contaminated. 13. The device according to claim 9, characterized in that at least one of these cleaning devices contains a system with strips of fabric or non-woven material, wiping dry or after lightly moistening parts of the aforementioned shell (2) or, accordingly, the rod (1), exposed to pollution. 14. The device according to claim 9, characterized in that the protective chamber (10) consists of four compartments, of which the fourth and last (IV) contain devices for loading tablets (6) with columns (12) of a means for loading various structural elements, other than the spring (7) and the second plug (4); the third (III) contains means for cleaning part of the shell (2) exposed to contamination during loading; the second (II) contains means for loading the clamping spring (7) and installing with a clip or without a second plug (4); the first inlet / outlet compartment (I) contains means for checking for contamination and, possibly, a cleaning device. 15. The device according to claim 9, characterized in that the sealed passages (24) between the compartments contain at least a valve (26), which can either be completely closed or can contactlessly leave the passage completely open for the shell (2) or respectively rod (1); a sealing connecting element (28), configured to either leave a passage completely open to the shell (2) without contact, or form a seal around the shell (2), which either stops at this point or makes a relative rotational or translational motion; and a device for pumping gas enclosed in a volume contained between the valve (26) and the sealing element (28), both in the closed position, and for possibly filling the same volume with another gas. 16. The device according to claim 9, characterized in that at least one gas supply device is installed for supplying the aforementioned compartments and any boxes installed therein with various gases selected from the group of gases including air, N ₂ , Ar, He and vacuum . 17. The device according to claim 9, characterized in that it includes a system for distributing helium either in an open loop or in a closed loop in recirculation mode, or in a combination of both of them, designed to supply them with compartments for loading tablets (6), for subsequent cleaning and to install a second plug (4). 18. The device according to claim 9, characterized in that the last compartment for loading tablets (6) contains means for loading tablets (6) into the shell (2) in vacuum. 19. The device according to claim 9, characterized in that the compartment, including the assembly means, also comprises a device for welding the second plug (4) to the shell (2) with an annular seam when said plug is installed in the shell (2) without clamping.

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