Tvel nuclear power reactor
(57) Abstract:The inventive TVEL tablet contains the fuel core in a sealed envelope from an alloy of zirconium. End caps are also made of an alloy of zirconium, and one of the plugs through the neck-getter in contact with the fuel. The length of the neck is selected in the range from two to six wall thickness of the shell of a fuel rod, and the ratio of the cross-sectional area of the neck SWto the cross-sectional area of the head Sgselected within 1/7 SW/Sg1/2. Head length-getter lgdetermined from the relation lg/lcu0,001(A/3,5-1), And where the maximum permitted under the conditions of manufacture of the moisture content in the tablets of the fuel within 3.5 A ppm to 7.0 ppm; lcuthe length of the fuel pole of the fuel rod. To prevent the diffusion of hydrogen from the head to the neck and the cap may be running neck of the trim stainless steel pipe. 3 C. p. F.-ly, 5 Il. The invention relates to nuclear engineering, more specifically to the design of industrial fuel rods of nuclear reactors, membranes which are made of zirconium alloys, for example, fuel type RBMK, VVER, AST, etc.A known design of fuel elements with shells from Zr, in which rcone, as the shell of a fuel rod, and spring made from Zr, (but different content), a latch mounted in the compensation volume of the fuel rod 
The lack of such fuel rods (standard design of fuel elements of foreign and domestic reactors types RBMK and VVER) is that the contact plugs and the release of fuel, due to the increase in temperature in contact with the last parts above the temperature of the tube-shell TVEL there are cases of local volumetric ("sunburst") hydrogenation plugs and clamps. Hydrogenation of the stub and the subsequent diffusion of hydrogen in the close button of the coupling zone of the stub with the shell leads to hydrogenation and embrittlement of the latest and ends, as a rule, such "heavy" form of the destruction of the fuel rod, as the gap of the plugs from the shell on the shell near the zone pairing these details.Hydrogenation of the spring retainer promotes embrittlement and breakage of the coils, which is especially harmful to the fuel rods of the lower half of the symmetric bunk FA (fuel assemblies) reactor RBMK-1000 and RBMK-1500. This leads to lowering in these fuel rods of the fuel column in the lower half of the fuel assemblies is based on the spring retainer and the willow leads to increased surge of energy release within the specified area, and as a consequence, to increase the overheating of the shell ends of the fuel rods in the Central part of the active zone, which ultimately activates the processes of hydrogenation of the shells in this, the most dressed up zone of the reactor.These deficiencies in the design of fuel elements lead to decrease in the reliability of their work in the RBMK-type reactors, degrade the environment and cause significant economic damage.Similar to the proposed solution is TVEL, described in the work of Pickman  in which between the fuel column and the bottom plug of a fuel rod and between the fuel column and spring retainer in the upper part of the same fuel rod entered thermal resistance in the form 2 of sintered Al2O3or ZrO2tablets.These thermal resistance prevent overheating, and hence the local hydrogenation of the lower plug and the retainer and the accompanying destruction. (Cases of isolation plugs from the side of the compensation volume of the fuel rods during the operation of the fuel rods has never been observed. Apparently, this is due to lack of contact with this side of the fuel rods, fuel cap, i.e., a large thermal resistance of the gas gap between fuel and plug in this place)
The disadvantages of the under cladding of a fuel rod (principally from moisture, adsorbiruya on tablets of fuel with greater or lesser extent almost always the case) does not exclude hydrogen under cover of a fuel rod. Therefore, potentially increases the risk of hydrogenation and destruction pipe coating of a fuel rod in other places (especially in areas where there will be local overheating, for example, in places where there is a thick oxide film on the outside of the shell, or boiling of the coolant).2. Introduction in the standard fuel rods insulators complicates and increases the cost of their production, as it requires the development of new technology and equipment for compaction and sintering of ceramic tablets, introducing them to the fuel rods, control their presence in the fuel rods, etc.The closest in technical essence to the proposed solution is TVEL  in which one of the plugs through the neck of the role of thermal resistance, and the head that acts as a getter for hydrogen and having a diameter smaller inner diameter of the shell in contact with the fuel. At that the head, neck and body plugs are made as one whole, the ratio of the areas of the cross-section of the neck and head are recommended as 1: 16, and the plug-side compensation of the PA are as follows.1. The recommended ratio of the areas of the cross-section of the neck and head 1: 16 almost corresponds to the ratio of thermal resistances, if instead of the neck was used insulator, for example of Al2O3diameter equal to the diameter of the head-getter.Such a large value of thermal resistance of the cervix virtually eliminates heat from the head-getter, causes heating of the latter to temperatures in excess of 750-800aboutWith that causes the decomposition of zirconium hydride and the allocation of a hydrogen back into vnutrivennoi atmosphere. The latter reduces the efficiency of the head-getter for absorbing hydrogen, bringing this design to the analog and its main drawback.2. Not listed in any limits to achieve the main goal of the invention should choose the length of the cervical thermal resistance.3. A significant factor in determining the reliability of the head-getter is the volume of this metal head, which must be associated with the highest possible content of hydrogen under cover of a fuel rod. Data on the determination of the height of the head-getter, and therefore its volume in the prototype are also missing.
To do this is useless, since the hydrogen will be absorbed by the cylinder only when heated to temperatures of about twice the temperature of the inner surface of the sheath of the fuel element.The purpose of the invention is to remedy these shortcomings of the prototype, to improve the reliability of a fuel rod by increasing the efficiency of the head-getter, as well as to simplify its design and manufacturing technology.The aim is achieved in that in the known fuel rod power reactor containing filled with ceramic pellets fuel shell of an alloy of zirconium, sealed on both sides using made of an alloy of zirconium plugs, one of which is through the neck of the role of thermal resistance and head-getter with a diameter less than the inner diameter of the shell in contact with the fuel, the length of the neck is selected in the range from two to six wall thickness of the shell of a fuel rod, and the ratio of the cross-sectional area of the neck SWto the cross-sectional area of the head Sgselected within:
the length of the head-getter lgdetermined from the relation
where And as permitted under the terms of the forehead of a fuel rod.To simplify technology introduction in the Fe resonance neutron absorber, which is very important for bunk Talnah assemblies of RBMK type reactors), as it allows to suppress the surge of energy release in the most intense part of the reactor core breaks fuel in the center of the active zone on the neck stub of a fuel rod can be placed cut on one side and are crimped on this neck ring made of wire metal hafnium, with an external diameter not exceeding the diameter of the disk head.To ensure realization of benefits of the proposed fuel element on the shell, the diameter of which does not exceed 8 mm, which makes a solid neck is not strong enough, the head and neck can be performed separately from the cover plate.In this case, it is executed in the form of a disk with a Central hole and slots from the fuel, with the tubular neck part on the opposite side of the drive head (the hole and slots in the disk heads are required to report cervical cavity with the atmosphere of a fuel rod).In the mechanical part of the working disk plugs from the fuel runs cylindrical recess diameter less than the outer diameter of the neck (tube her time is ivalsa head-getter.This construction is convenient for insertion into the recess in the tubular part such as getter on iodine, which is necessary to prevent SCC (stress corrosion cracking under tensile stresses) in a medium containing iodine, which is a product of radioactive decay of the fuel.In addition, for practical exclude the possibility of diffusion of hydrogen from the head through the neck and work the drive plugs into the shell cervix can be performed separately from the head of the pipe piece of the material with which the hydrogen does not react, for example, stainless steel, pressed on to the interference fit in a corresponding cylindrical recess in the end portion of the drive head.The invention is illustrated in Fig.1-5.The proposed fuel rod is shown in Fig.1. It consists of filled fuel 1 shell 2 made of an alloy of zirconium, sealed on both sides with plugs 3 and 4, each of which has a thermal resistance between the fuel column and the butt-plugs, with the latch 5 in the compensation amount. The cover 4 is made of an alloy of zirconium. It can be also based alloys, other metals, which are analogues of zirconium by physico-chemical solstice 6, perform the function of thermal resistance and resistance to diffusion of hydrogen, and the head 7, acting as a getter for hydrogen absorption during operation of a fuel rod, i.e., after heating of the fuel column.In Fig.2, and shows a case in which the neck 6 is placed a cut on one side and are crimped on this neck ring 9 made of wire metal hafnium (resonance neutron absorber). The outer diameter of the ring should not exceed the diameter of the disk head. The ring should be installed with clearances of the order of 0.3-0.4 mm, prevent possible diffusion of hydrogen.In Fig.2,b shows a variant of the lower end of a fuel rod with a head 7 and a neck 6, is made separately from the cover plate 4. In this case, the cross-section of cervical selected the same as in the basic version (Fig.1). But the neck is made in the form of a tubular part with an outer diameter corresponding to the diameter of the fitted tightly cylindrical recesses in the working drive stub. The thickness of the wall of the tubular part of the neck is selected so that it ocials diameter surfaces in the cylindrical recess of the working disk stub 4. Practically the wall thickness of the neck in this case, vybere is 0.3-0.4 mm. For messages cavity of the tubular part of the neck with the atmosphere of a fuel rod in the cylinder is the Central hole (with a diameter of 2-2 .5 mm), and at the end of its contact with the fuel, can run slots-slots connecting with the Central hole in the head.This geometry cervical preferred for fuel rods with shells, outer diameter not exceeding 8 mm But it can be used for fuel for RBMK-1000 and RBMK-1500, as it allows a simple way to enter into the zone of rupture of the fuel bunk FA neutron absorber 10, for example, metal HF or a getter to absorb iodine.In Fig. 2 shows a variant of the lower end of a fuel rod, in which the neck is made separately from the head and from the cover plate, the pipe piece 6 of material, practically areagirls with hydrogen and does not pass it, for example, stainless steel.This variant has been proposed to eliminate even the principal possibility of diffusion of hydrogen from the head in the coupling zone of the shell and the bracket, and therefore, exceptions to the principle of the embrittlement and fracture of this area.In this case, the wall thickness of the pipe segment of stainless steel is similar to the choice that is clever perform in diameter, the smaller outer diameter of the pipe segment-neck on the value of planting with tension.The choice of the pipe wall thickness-neck and planting dimensions of mating parts provides a draught of the diameter of the ends of the tube neck when pressing it into the recess and the head and allows a simple way firmly and securely connect these parts together.Of course, inside the pipe-cervical 6 if necessary, the simplest way can be placed in various absorbers 10, for example, neutrons or iodine. The geometry of the head 7 of the stub 4 was chosen based on the following.The diameter of the disk head Dgselected equal
Dg= d is(0.5-2) where d is the inner diameter of the sheath of a fuel rod; wall thickness of the sheath of the fuel element, based on the fact that, on the one hand, between the head and the shell must exist a gap, excluding the possibility of diffusion of hydrogen directly from the head to the shell, on the other hand, this gap must be sufficient to not hinder the Assembly and welding of the sheath of a fuel rod with cap. And lastly, this gap should not significantly reduce the amount of head, otherwise it will require an increase in its height and, therefore, for fuel assemblies of RBMK type the widening gap fuel that nedous upper shell, which of 0.4 mmThe length (height) of the head lgwas determined using the ratio
-1.This ratio is obtained on the basis of the following considerations.The amount of metal head (minimum should be proportional to the maximum amount of hydrogen that can be stored under the sheath of the fuel element.The maximum amount of hydrogen in the fuel rod is proportional to the fuel mass and the maximum content of moisture, decomposition which gives hydrogen.The first of these conditions is defined as follows.At the same moisture content for all the pellets of fuel the amount of hydrogen in the fuel rod is proportional to the length of the fuel column.This amount of hydrogen must be absorbed either by volume zirconium head Vgor, if the stub is executed without a neck and a head, part of the metal plugs and the metal part of the shell. The latter can be seen from Fig.3, which shows the end of a fuel rod RBMK, razgermetiziruetsya due to the hydrogenation zone mating plugs with the shell during operation (for RBMK fuel rods maximum moisture content in the fuel 7ppm, the length of the fuel column lcu= 3420 mm). It is evident from Fig.3 shows that about what hraneniya hydride in zirconium 1,25 g and the factor by volume of zirconium 2) the volume of the metal ring with an outside diameter d+2, a wall thickness of 2 and a height of 4 , i.e.VZr10 d2.Therefore, a minimal amount VZrmust have head to absorb the maximum amount of hydrogen under the sheath of the fuel element, i.e.Vg10 d2.If the head of the stub has a diameter of Dgequal to the diameter of the tablets of fuel Dtand equal to the inner diameter of the sheath of a fuel rod d, in the first approximation can be taken, since these values vary in practice is negligible, the length (height) of the head lgwill be equal to
lg= and the ratio of the volume of the head Vgto the volume of the fuel column Vcuequal to length of head lgthe length of the fuel column lcu, i.e.< / BR>Considering the ratio, find the numerical value applied to the fuel rods of the RBMK-1000 (d=11.7 mm; D Dg=11.5 mm; 1 mm; lcu=3420 mm):
< / BR>It is obvious that this relation is true for all fuel rods having 7ppm moisture in the fuel and the same density of fuel pellets (DgDt).Given that due to the hydration shell on average fail 2-3 TVEL of 1000, and that the moisture in the fuel ranges from 0 to 7ppm (i.e. word does not affect the destruction, more precisely does not give them (997 rods survive a campaign without damage to the shell and 2-3 TVEL of 1000, in which all, or almost all tablets have fuel 7ppm moisture destroyed).Assuming that the dependence of the number of damage from the moisture content of the fuel in the first approximation, which is sufficient for practice, is linear in relation to the fuel moisture content in fuels other than 7ppm, but over 3.5 ppm, must be added the factor K equal to
K 1.Thus, finally, we obtain
1, where a permissible moisture content in the fuel, in excess of 3.5 ppm.The geometry of the neck 6 of the stub 4 was determined as follows.Thermal resistance cervical RWshould be large enough to prevent heating located below the working drive cover plate (welded to the shell) to temperatures, large temperature on the inner surface of the shell more than 30-50aboutWith practically eliminates the absorption of hydrogen scratch disk stub of the free volume of the fuel rod, the greater the absorption of hydrogen by the shell.On the other hand, RWshould not be too large; otherwise, if the contact of the head with fuel and, moreover, n the days of hydrides, will be partially allocated from hydrides back in vnutrivennoi atmosphere, i.e. the head as the getter will work poorly.Therefore, the lower bound of the ratio of the area Poperechnaya section cervical SWto the cross-sectional area of the head Sgi.e., which is determined by the diameter of the neck D and, accordingly, RWwas determined by calculation (on the computer using a specially developed program, finite element method, applied to the conditions of RBMK fuel rods) with the condition that the temperature in the contact of the fuel with the cylinder must not exceed 700aboutC.Calculations (with respect to the fuel rods RBMK) showed (head diameter Dg= 10 mm and the length of the neck lW=lg=4.0 mm) that this condition satisfies the inequality
DW3,8 mm, i.e.
When this is taken into account that during operation, due to the different temperatures axis (up to 1500about) and in the periphery (up to 650aboutS) of fuel pellets, and therefore different thermal expansion of these zones, and also due to possible deformation of the softened core tablets fuel thermo-mechanical interaction of the fuel with shell (ratchet effect) possible clearance in the hole tablets toplevelwindow ring.(Assuming the head has a contact with the tablet fuel only ring outer diameter of the latter, i.e. in the zone where even in the absence of contact with the cylinder, the temperature of the cylindrical surface tablets fuel due to radial heat transfer in the coolant does not rise above 650aboutSince then, according to the calculations of RWmay be taken equal to Randthermal resistance of the insulator of ZrO2.In this case, the
RW= Rand= Zr= 0,2; = 0,012.Assuming: RW= Rand; lW=landand Dand=Dtwhere land; Dand; Sandlength, diameter, cross sectional area (respectively) tablets insulator;
lW; DW; SWlength, diameter, cross sectional area of the neck stub;
Dtthe diameter of the fuel tablets;
the conductivity of Zr and ZrO2find
< / BR>For RBMK fuel rods with shell size 13,was 6x11,7 mm, assuming Dand=Dt=11.5 mm and given that
DW=2,8 mmIf so RWnote that the contact of the fuel with possible head around the side of the head, it will cause the temperature rise of the contact, as shown by raschu this case on the side of the head may be made hollow, precluding contact of fuel all over the side of the head.In addition, DW=2.8 mm (Dg=11.5 mm or DW=2.5 mm for Dg=10 mm) is not sufficient to counteract axial bending and flattening under the action of possible axial forces compression of the fuel column.The upper limit of the ratio (or the lower limit of RW), given the complexity and uncertainty of its determination by checking, driven mainly by the need to define the boundaries of hydrogenation, having radial in nature, different in different planes of the cross sections were determined in the reactor experiment on the sections of the ends of the fuel rods fully experienced assemblies of RBMK-1000. One of these rods razgermetiziruetsya (longitudinal crack in the shell), probably due to fuel swelling and increase the diameter of the shell (up to 14.5 mm).Photograph of the longitudinal section of the lower sealing connection leaking fuel rod shown in Fig.4, b.In Fig. 4,and shows a longitudinal section of a stub in the form of "glasses" with a Central "core" and "foot" used to seal these fuel rods (if the tests were simultaneously solved and a number of other issues).It is evident from Fig. 4, b shows that hydrorad almost only began to arrive. The inner deburring and weld seam zone pairing shell cover from hydrogen free. Thus, in this case, the head in the form of "glasses" played the role of the getter and protected from the hydrogenation inner Burr weld and the coupling zone of the shell blank, despite the fact that the amount of hydrogen in this razgermetiziruetsya Fe, it is most likely from the heat carrier is steam, it was big enough.No doubt that if the fuel was in contact with the inner Burr (Fig.3), the hydrogenation of the latest and zone pair with the shell would happen, and then the test would have ended the isolation plugs on the shell.At the same time for quite a long time from loss of containment, i.e., when there is a hydrogen, until you stop the test, the hydrogen has not reached the "actual" caps, which allows us to assert that this will not happen and for the entire campaign, although at much larger times campaign, due to the diffusion of hydrogen can reach the plug and the shell.To prevent failure at a significantly greater duration of the campaign operation, you should use the solution, practically excluding the hydrogen diffusion and the goal of the staff of the measurements was found, what ratio This corresponds to what is taken as the upper limit of this ratio.It should be noted that the identity of the equations of heat conduction and diffusion allows us to consider the neck not only as heat resistance, but also as a diffusion resistance, i.e., as a barrier to diffusion, in this case hydrogen from the head to the working drive stub welded to the shell that contributes to the concentration of hydrogen in the cylinder and prevents the hydrogenation and embrittlement of the membrane in the area adjacent to the door.Thus, to accomplish the task, the ratio should be within
< / BR>If < RWis large enough to prevent overheating and hydrogenation of the working disk plugs and the adjacent part of the shell, but in this case, the possible overheating of the head and exit as a result of hydrogen from hydride head, which is unacceptable.If > , the head temperature is below 700aboutAnd decomposition of the hydride head will be removed, but RWto be insufficient, the temperature of the working disk cap will rise above the temperature of the shell and the absorption of hydrogen in this area can go in parallel with the absorption of bodoro is walking, that the disk head is guaranteed must not come into contact with the inner beads of the weld, and the neck should have sufficient thermal and diffusion resistance. However, the neck should be sufficiently durable and resistant to axial bending under the action of possible axial forces of the fuel column and the height of it should not lead to a significant increase in rupture of the fuel in the RBMK.While the smaller size of the selected limit (2-6) refers mainly to the shells with more and most to shells with less .The proposed fuel rod works as follows.After filling the active zone cassettes with the fuel rods and reactor startup (or overload of fuel elements "on the fly" in RBMK reactors) leads to heating of fuel pellets, and the contact of the fuel with the head lower plug reaches a temperature of 450-600aboutS, while the inner surface of the shell along its entire length, including the zone pairing it with the plugs is heated only to 330-350aboutC.As a result, all the hydrogen available under the shell of a fuel rod and eye-catching in the process of operation, for example, by decomposition of fuel moisture, cracked, tablets, etc. is absorbed by the head zapusk overheating of the plugs relative to the shell, eliminates the possibility of hydrogen absorption by the cover and the adjacent part of the shell of nutritionai atmosphere, and "diffusion" resistance cervix, acting as a barrier to diffusion of hydrogen from the head-getter, protects scratch disk stub from the infiltration of hydrogen from the head due to the diffusion.In addition, the HF ring, reducing the burst of neutrons in the area of the gap of fuel, reduces overheating in this area, to enhance security and manageability of the reactor.If you use the getter on iodine, dramatically reduces the possibility of the development processes of corrosion stress cracking (SCC) in a medium containing this element, which protects the membrane of the fuel rod from damage during operation.The proposed solution allows, through the use of getter properties of Zr with respect to hydrogen and the location of the disk head, which acts as a getter, in the zone where its temperature (100-200)aboutWith the above cladding of a fuel rod, in conjunction with the Department head-getter from the cover plate thermal resistance in the form of cervical reduced (compared to the disk head) cross-section, substantially reduce the content of free hydrogen in Swabi stub, as this is a prototype, but the shell along its entire length, and a spring clamp.In addition, the proposed technical solution simplifies design and manufacturing technology of fuel elements and allows virtually no increase in length of the rupture zone of the fuel in the reactors of the RBMK type to enter in this, the most energopetrol zone of the reactor resonance neutron absorber that in addition to reducing the temperature and a corresponding reduction in the possibility of local processes of hydrogenation of the fuel cladding in the area, increases the controllability of the reactor and its safety.The specified technical solution does not require the establishment of new industries, such as insulators and getters, as well as changes in the technology of fabrication of fuel elements, including their sealing. For its implementation need only change the program of machining, lathe machines, which are manufactured plugs, and change the number of overpass supply plugs into the welding zone in the welding machines in automated production lines of the fuel rods.The stated ratio of the drive of the head and neck at the lower end plugs provide the amount of heat weather resistance is of erator, allowing effective use of getter properties of zirconium head in contact with the fuel, and thereby the achievement of the main objectives of the invention reduce the content of hydrogen in the free volume of a fuel rod during operation, and therefore, prevention of hydrogenation of the shell throughout its length. This allows us to conclude that the claimed features of the invention are connected by a single concept. These differences from the prototype allows to establish their compliance with the criterion of "novelty".The study of other known technical solutions in this field of technology features that distinguish the proposed solutions from the prototype, not identified. Therefore, they provide the proposed technical solution according to the criterion of "significant differences".The effectiveness of the proposed solutions is proved by the following:
1. In detected cases of fracture zone pairing shell and plugs on the fuel rods of the type RBMK, due to hydrogenation and embrittlement of these zones (Fig. 3), it is established that causes destruction of the presence of hydrogen under cover of individual fuel rods overheating and plugs in contact with her fuel. In other words, in the presence of hydrogen under cover, Mesa is in the first place.2. The fact that the contact plugs with fuel absorbs hydrogen in the first place, it has been proved experimentally in laboratory scale simulation of the behavior of the end of a fuel rod during operation when the hydrogenation tselnolityh samples, simulating the weld site. The results of these experiments in which simulated operating temperature gradients and the amount of hydrogen corresponding to the decomposition of moisture fuel 7ppm in each tablet, illustrated in Fig.5A, b.3. Increased hydrogen absorption with increasing temperature the zirconium sample and the partial pressure of hydrogen. In this work we present the corresponding graph, which shows that compared with a temperature of 350about(The temperature of the shell during operation) at a temperature of about 450-500about(The temperature of butt plugs during operation), the ability of zirconium to absorb hydrogen increases by about an order.4. Direct confirmation of the effectiveness of the proposed solution was obtained in the reactor experiment at the experimental reactor during the test Assembly of fuel elements of type RBMK. One of the fuel rods of the Assembly razgermetiziruetsya (longitudinal crack in the shell), apparently AFL is and the lower sealing connection leaking fuel rod shown in Fig.4, B.No doubt that if the fuel was in contact with the inner Burr, the hydrogenation of the latest and zone pair with the shell would happen, and then the test would have ended the isolation plugs on a shell (similar to Fig.3).Economic efficiency proposals obvious, as the omission of only one cassette RBMK half of the campaign on electricity brings great loss. 1. TVEL NUCLEAR POWER REACTOR containing filled with ceramic pellets fuel shell of an alloy of zirconium, sealed on both sides using made of an alloy of zirconium plugs, one of which is through the neck and head-getter with a diameter less than the inner diameter of the shell in contact with the fuel, characterized in that, to improve the reliability of a fuel rod by increasing the efficiency of the head-getter, the length of the neck is selected in the range from two to six wall thickness of the shell tela, and the ratio of the cross-sectional area of the neck SWto the cross-sectional area of the head Sgselected within
< / BR>the length of the head-getter lgdetermined from the relation
< / BR>where A maximum/BR>ltwiththe length of the fuel pole of the fuel element.2. TVEL under item 1, characterized in that, to facilitate introducing the resonant neutron absorber in bunk fuel assemblies, on the neck stub of a fuel rod placed cut on one side and are crimped on this neck ring made of wire metal hafnium.3. TVEL under item 1, characterized in that the head and neck is made with a Central hole and is separate from the bracket, and at the end of the last side fuel made depression with a diameter less than the outer diameter of the neck on the value of planting with tension, while the neck is pressed into the recess of the insert.4. TVEL under item 3, characterized in that, to avoid diffusion of hydrogen from the head through the neck and the cap to the shell, the neck is made separately from the head of the pipe piece stainless steel, pressed on to the interference fit in a corresponding cylindrical recess of the head.
FIELD: nuclear power engineering, possibly automatic line for producing fuel elements of fuel assemblies of power nuclear reactors.
SUBSTANCE: aggregate is provided with detachable device for measuring electric resistance of fitting. Said device is arranged between collet chucks being in open position and it is made of two dielectric members spring-loaded one relative to other. End of one of said members has shape corresponding to contour of annular turning formed coaxially on end of collet chuck for plug. End of second member has shape corresponding to contour of annular turning formed coaxially on end of fitting in collet chuck for fuel element envelope. Said device has spring-loaded contacts for measuring electric resistance between fitting inside collet chuck and collet chuck itself. Caprolactam is used as dielectric material.
EFFECT: enhanced efficiency and quality of contact butt welding at sealing fuel element.
2 cl, 3 dwg
FIELD: nuclear industry.
SUBSTANCE: proposed method is used for manufacturing fuel elements of type VVER-1000 and VVER-440 reactors when sealing them in resistance butt welding machine using expanding chuck. Novelty is that spent chucks cleaned from uranium dioxide are used as charge to be melted for producing new ones of sufficient strength and flexibility. Spent chucks are melted at 1300 - 1350°C for 20 - 25 min., melt is degassed at pressure of 4.5 x 10-3 of mercury; when cleaning molten bronze from nonmetallic admixtures, the latter are upset on cooled crucible walls in the course of short-time disconnection and connection of inductor load; ingots obtained are hardened in water at 780 ±10°C and annealed at 320 - 340 °C for 3 - 3.5 h to make them flexible; then expanding chucks are manufactured by mechanical method.
EFFECT: provision for using spent chucks to produce new ones.
2 cl, 2 dwg
FIELD: nuclear power engineering.
SUBSTANCE: proposed rod billet designed for use in compacting nuclear-reactor fuel core rods has zirconium alloy tube, nuclear fuel and matrix material fill, as well as two cylindrical plugs with annular drillings for localizing excess solder placed in the form of paste. Plugs are installed in tube in guaranteed space relation to the latter. Cylindrical surface of each plug has two annular drillings spaced 5 to 7 mm apart; drillings external with respect to fill are filled with paste. Provision is made for combining degassing and sealing processes by raising temperature directly upon completion of degassing operation.
EFFECT: enhanced productivity and reduced cost of process equipment and rigging.
3 cl, 2 dwg
FIELD: nuclear power engineering.
SUBSTANCE: proposed method that can be used, for instance, to manufacture ceramic rods for fuel cores of miscellaneous nuclear-reactor fuel elements involves following procedures. Zirconium alloy tube is filled with definite amount of nuclear fuel powder and matrix material. Zirconium alloy caps are attached to butt-end surfaces of cylindrical plugs provided with annular drillings. Inner surfaces of caps are coated with layer of paste prepared from powder of metal oxide, such as aluminum oxide. Tube is closed with plugs and assembly obtained is degassed at high temperature; solder in the form of, say, paste is placed on butt-end surfaces of tube, assembly is heated to soldering temperature and subjected to isostatic compression. Tube is heated in vicinity of plug drillings until metal oxide is opened, and tube ends are removed together with plugs.
EFFECT: enhanced yield of rods which is important in mass production.
1 cl, 4 dwg
FIELD: nuclear power engineering; fuel assemblies of pressurized-water reactors.
SUBSTANCE: proposed device designed for entrapping solid particles in fuel assembly has perforated plate which is undulatory in direction transversal to coolant flow. Mentioned plate in first design alternate of proposed device is saw-toothed in direction transversal to coolant flow. Mentioned plate in second design alternate of device is made in the form of concentric perforated truncated cones alternately installed with their vortices up and down. Mentioned plate in third design alternate of device is made in the form of concentric truncated pyramids alternately installed with their tops up and down.
EFFECT: enlarged total coolant flow section of device installed at fuel assembly inlet.
8 cl, 4 dwg
FIELD: welding works.
SUBSTANCE: present invention pertains to welding, particularly to the method of sealing fuel elements of a nuclear reactor using contact-butt welding. Contact-butt welding is done on a fuel element casing with an end-cap, with maximum diametre less than the outer diametre of the casing, and greater than its inner diametre. The end of the casing is put into an expanding mounting with a depression. Welding is done with rate of increase of welding current to maximum value in the initial welding moment in the range of 1-3 kA/ms and its density in that period from 1.5 to 2.5 kA/mm2 with specific pressure of 35-80 kg/mm2 for a period of 10-60 ms. The end cap is moved deep into the casing at a distance of 2-5 times the thickness of the wall of the casing. If necessary, the displacement of the end cap can be limited due to restriction of the movement of the electrode linked to the actuator of the welding force of the installation.
EFFECT: invention can be used in nuclear power engineering.
2 cl, 9 dwg, 1 ex
FIELD: welding works.
SUBSTANCE: invention is related to method of contact-butt welding of pipe with plug and may find application in manufacturing of rod fuel elements of nuclear plants. Method includes placement and fixation of pipe end with deepening in welding auxiliaries. Heating of pipe end and plug pressed by butts by welding current, at that plug has section welded into pipe wall, with diametre that is larger than internal one, but is less than external diametre of pipe, and further welding of plug into pipe wall with alternating speed of plug motion. Pipe end on section with length of 1.5-3 of pipe wall thickness is placed on section of welding auxiliaries, electric resistance of which is less than resistance of pipe section material in zone of welding. Heating of pipe end and plug pressed by butts by welding current is carried out due to contact resistance in butt between end of pipe and plug and area of welding current supply into pipe, which is arranged at the distance equal to 1.5-3 of pipe wall thickness from its end. Besides heating of welded parts in process of welding to arrange zone of thermal effect, which is common in length of welded joint with width in central part of welded joint, which is equal to 0.1-3 of pipe wall thickness.
EFFECT: simplified welding technology without deterioration of quality properties of welded joints.
2 cl, 3 dwg, 1 ex
FIELD: technological processes.
SUBSTANCE: invention is related to method for manufacturing of fuel element (FE) of nuclear reactor and may find application in nuclear engineering. Method includes fixation of its shell end in welding installation equipment, creation of atmosphere with specified composition and pulling pressure by means of vacuumising, filling with high pressure inertial gas with further sealing with plug using contact-upset welding for its welding into shell, and its diametre is more than internal diametre of shell, and monitoring of gas pressure under shell. Monitoring is realised directly in welding installation. For this purpose prior to vacuumising clearance is created between ends of shell and plug arranged in welding installation, and its value is measured at continuous measurement of gas pressure value. Value of clearance is first measured till filling of fuel element shell with gas, then after application of welding force. Afterwards produced results are compared, and permits for welding are issued, if difference in produced measurements corresponds to specified values.
EFFECT: invention provides for improved serviceability of fuel elements.
6 cl, 3 dwg
FIELD: power engineering.
SUBSTANCE: invention refers to manufacturing method of nuclear fuel elements and may be used in nuclear power engineering during manufacturing, using contact-butt welding of fuel elements and guide channels of rod type for fuel assemblies of nuclear power reactors. Method includes fixing of end of can (1) of fuel element installed with embedding in welding fixture (2), welding to at least one edge of can (1) of plug (6) by contact-butt welding with its simultaneous displacement inside can (1) on section warmed by welding current, and quality control of welding and stability of process of welded joint sealing. Edge of plug (6) end installed in welding fixture is fixed with respect to edge of welding fixture (2) at a specified position. During plug (6) displacement inside can (1), control of voltage value on section of secondary circuit of welding set, generated by welding fixture with fuel element can end located in it, is performed. Obtained values of voltage are compared to values of voltage specific to conditions of optimum warming of weldments at analogous position of can (1) edge in welding fixture, and according to difference of obtained values quality of welding and stability of sealing process is determined.
EFFECT: improvement of fuel elements quality.
2 cl, 2 dwg, 1 ex
FIELD: power engineering.
SUBSTANCE: welded part of plug additionally contains mould flash in form of face at 45° to generatrix of surface of plug in its welded part. The face is located at (4÷6)·δ distance, where δ is thickness of cladding, from surface of cold contact of the welded part of the plug with the end of cladding. A transition part of the plug has cylinder and conic elements. Surface of the face is conjugated with surface of the cylinder element of the plug transition part, which in its turn is conjugated with surface of the conic element of the plug transition part through radius (0.7÷2)·δ. Angle between generatrix of surface of the cylinder element of the plug transition part and a base of the conic element of the plug transition part with bigger diametre is 45°, while distance from the base of the conic element of the plug with smaller diametre to surface of cold contact of the welded part of the plug with the end of cladding is equal to (8÷10)·δ.
EFFECT: increased reliability of fuel element operation, reduced expenditures for its production.