Fuel element rod type and method of its manufacture

 

(57) Abstract:

The inventive fuel rod rod type contains a shell and welded onto the stage door. Inside the shell is loaded ceramic fuel in the form of on-screen tablets and fuel bushings. Plug, sealing the shell side loading of nuclear fuel, is made of a smooth, axisymmetric, with the same truncated cones, and the cylindrical surface of the extruded annular band, minimum outer diameter which is equal to the maximum inner diameter of the shell, and the maximum diameter greater than the greatest internal diameter of the casing on the tolerance of its inner diameter. Smooth cylindrical plug with a stamped ring band is more efficient and requires no additional orienting devices when installing in the shell with mass production of the fuel element and the belt clears the internal cavity of the shell surfaces of the plug and forms a dense fixed connection stub with sheath, capable of a long time to keep the gas pressure in the shell to weld the shell with cover and excludes fuel dust in the welding zone. 2 S. and 2 C. p. F.-ly, 10 ill.

Isaih nuclear power reactors of the type bn, VVER, RBMK, etc.

TVEL nuclear power reactor typically contains the fuel core, recruited from pellets of uranium dioxide, is placed inside the shell, sealed on the ends of the end caps by welding. In the upper part of a fuel rod is formed of a compensation amount for the collection of gaseous fission products, which houses the latch that is designed to prevent displacement of the fuel core relative to the shell during transport-technological operations and enable the elongation of the fuel core during operation of a fuel rod in the reactor.

Known fuel rod of a nuclear reactor, consisting of a tubular shell, filled with fissile fuel, end plugs, inserted on both ends of the shell and welded thereto, characterized in that one of the plugs has a cylindrical shape and a conical surface on both sides, and the angles are different with a smaller angle from the input plugs in the skin /1/.

A disadvantage of the known design is the stepped shape of the plugs from the side of the equipment shell fuel, which is not producible in the manufacture of fuel elements for automated flow-l is the most closest technical solution of the essence and the achieved technical result is the design of the fuel elements for the reactor bn-350 /2/, the prototype.

TVEL rod type consists of a shell with welded thereto speed shutter inside the shell loaded post screen tablets depleted UO2then the sleeve of the fuel and then the top screen of the same tablets depleted UO2. The entire post of tablets based on the glass at the bottom and at the top is limited by the retainer from moving post when transporting the fuel rods. In the fuel element is provided by the compensation cavity volume, located in the colder parts of the fuel elements and designed for gaseous fission products during irradiation of the fuel and the pressure increases. End cap, the sealing membrane from the side of the loading of nuclear fuel, has a stepped shape in the form of a flange on its end face. The disadvantage of a fuel rod is stepped configuration of the upper stub, since the presence of the flange on the end affects the manufacturability of its production and become more complex automation to insert it into the shell for mass production TVEL on automated lines. Not excluded the possibility of the fuel particles in the weld zone of the shell and end caps and discontinuity of a welded joint, as the removal of the fuel particles with the UB>2due to insufficient temperature conditions (for evaporation by sublimation or the other way).

The known method of "Siemens", which has patented a device for mechanically Stripping the ends of the fuel cladding weld, using as a wiper element tape, rewindable with the coils on the coil. TVEL contaminated with plutonium, is entered in a special device and there turns on the supporting pulley. At this point, the tape clears the surface of the shell. By the same principle, other devices, allowing you to clean not only the external surface, but also on a certain site from the inside /2/. The disadvantage of this method is the complexity of the automation of the operation of Stripping the inner surface of the shell for mass production of products on the production lines.

The closest in technical essence and the achieved technical result is a method that is based on the detention of dust in the pumping process /2/ the prototype. He uses a metal tube-wad, which, for example, is made from a fine metal mesh, rolled into a ball or cylinder. This wad is injected into the shell after fuel loading, then crush it with some of the lib in the sealing area. This method is widely used in our country in the manufacture of fuel elements, in which the cap is made with the shoulder. The disadvantage of this method is the complexity of the automation inserts the plug into the shell for mass production of fuel rods and not enough high efficiency dedusting zone of the weld, as the wad eliminates dust only of the inner part of the membrane, but does not eliminate the dust on the side of the shell and under the collar stub, resulting weld may be leaking.

The claimed fuel rod is aimed at enhancing the technological effectiveness and ease of automation when inserting the plugs into the shell, and the inventive method of its manufacture to reduce scrap for tightness.

This technical result is achieved by the fact that the rod type fuel elements containing tubular envelope filled inside the ceramic fuel resting on the spacer, retainer for retaining the fuel pole plugs to seal welded on both sides of the shell, one of the plugs inserted from the side of the equipment nuclear fuel, is made of a smooth and cylindrical surface of the extruded annular band outer mi is ishaat the greatest internal diameter of the casing on the tolerance of its inner diameter, this belt is made of the M-shaped and are placed symmetrically with respect to the chamfering of the ends of the stub.

Thus, these distinctive essential features allow us to conclude about the technical solutions according to the criterion of novelty.

The comparison of the proposed solutions with other analogues, where the blank is made with the shoulder, showed that the proposed cap without collar and with a wiper belt is more efficient and requires no additional orienting device when it is installed in the shell, and a wiper belt, deformed, forming with the inner surface of the shell thick fixed connection, capable of a long time to keep the pressure of the gas to the welding of the shell blank.

Thus, the proposed TVEL meets the criterion of inventive step.

This technical result is achieved in that in the method, including welding the lower plug shell, install spacers, equipment ceramic fuel, insert clamp, vacuum, leak helium, welding the top of the stub and the spacer wire before welding of the end seam of the upper stub with sheath produce cleaning internally is edenia inside of the shell, moreover, the cover set with a protrusion relative to the end face of the shell on the length of the tapered part of the plug.

These distinctive essential features allow to conclude that the criterion of novelty. Comparison of proposed method with other models, and prototype, where the removal of dust are carried out either plug or tape, showed that the use of Bezborodova stub, and specifically its wiper ring belt for scraping the inner surface of the shell of dust has increased the efficiency of this operation and allowed to combine cleaning with insert, reduce waste, leak tightness 8-10 times by eliminating the ingress of fuel particles in the weld zone.

Thus, the technical solution meets the criterion of inventive step.

One of the causes of leaks in the fuel is getting into the end seams of the fuel particles. This is confirmed by studies of thin sections of welded joints with end joints of defective fuel rods held in the x-ray microanalyzer "CAMEC" MS-46 UCand other

Are two possible pathways by which the fuel particles in the weld zone. But podgotovlennosti fuel deposited on the wall of the shell of a fuel rod in the channel of the degassing device. When the press-fit plugs with collar wrapped the collar performs the function of a scraper and under it at the site of contact with the end face of the shell focusing particles of fuel that the melting of the plug and shell are naturally in the weld pool. The second way appears in the end seams of oxide inclusions due to the presence of fuel dust on the inner surface of the shell. During welding, performing perimeter or edge seam, these oxide particles having a higher density than the alloy (of 10.2 to 10.6 g/cm3) against (7,8 g/cm3) steel in the weld pool does not come up, almost staying in the same position as before welding. In seam forming a channel-type defects, leading to leakage of fuel elements.

To reduce the accumulation of fuel particles at the end of the shell in the weld zone, the natural transition to the plug, no collar.

The optimal solution when performing a sealing connection of the end seam is achieved by using axisymmetric stub having on the ends of the shape of truncated cones, and the cylindrical part of its extruded annular band, outside NaViSet the greatest internal diameter of the casing on the tolerance of its inner diameter. The cap should be set relative to the end face of the shell with the protrusion on the length of the conical part.

In that case, if the fuel particles are inside the shell, when the press-fit plugs ring belt clears away these particles from the end and moves them into the shell, and if the fuel particles or dust will be on the protruding part of the door, and at the end of the shell, they, first, blown off by a stream of inert gas welding torches before the initiation of the arc and, secondly, remaining on these surfaces of the fuel particles evaporate in the arc having a temperature of column (10-12)1030K.

When using plugs with collar there is no direct effect of the arc on the fuel particles under him, and the arc melts both the cap and the collar. The temperature of the weld pool, which stuck fuel particles, is only 1750-1950 K, which is considerably lower than the melting temperature UO2or mixture UO2PuO23000 K and 2730 K, the more the temperature of evaporation.

Thus, the proposed form of stub meets the conditions of metal, automation, transportation, collection shell, minimal surface Sorbie fuel castilo); in Fig. 2 General view of the fuel elements for the reactor bn-350 (prototype) and the fuel elements of the proposed design, differing only in the upper cover; and Fig. 3-cover with clamp after welding with the shell; Fig. 4 plug the offer of a fuel rod after welding with the shell; Fig. 5 cover with clamp after Assembly with the shell with the possible appearance of the fuel particles in the zone of the weld of Fig. 6-relative positions of plugs and shell offer of a fuel rod of Fig. 7 procurement of the proposed caps; Fig. 8 configuration of the proposed caps with embossed belt; Fig. 9 the formation of the seam: (a) a stationary arc, b) due process of Fig. 10 is an example of inclusion of the fuel between the shell and plug directly into the end seam, showing leakage during testing: (a) clot concentration in the solid solution; b) fuel particles between the shell and the plug below the wiper belt.

TVEL rod type (Fig. 2) comprises a tubular shell 1, welded to the stepped cap 2, the inside of the shell is loaded ceramic fuel in the bottom of the screen tablets 3 depleted UO2and fuel bushings 4 and again the top of the display 3 tablets. The entire post of tablets based on the spacer 5, and the top granitegreenstone volume, located in the colder part of the fuel rod and designed to collect gaseous fission products during irradiation of the fuel and increasing the pressure. The upper cover 7, the sealing membrane 1 side loading of nuclear fuel, has a smooth cylindrical Bezborodova configuration with grinding belt 8. On the outer surface of the shell of a fuel rod with a certain step is wrapped around the spacer wire 9, the ends of which are welded to the caps.

Is a method as follows.

The method of manufacture of a fuel rod includes the following operations: welding the lower plug shell, the installation of the support glass, equipment fissile and fertile fuel, insert clamp, vacuum, leak helium, welding the top of the stub and the spacer wire.

Before you weld the top cover 7 of the casing 1, it is necessary to clean the inner surface of the shell from the fuel dust. With the introduction of the plugs 7 in the casing 1, and further pressing the grinding belt 8 makes its crest of the fuel dust from the inner surface of the shell, starting from the end, and moves from the zone of the weld. Originally it was installed on the samples cut the camera can pity were held with metallographic studies on a representative batch of samples of welded joints, made stationary arc. 10 viewed welded samples by x-ray analysis detected only one sample of a small accumulation of uranium not in the form of inclusion of the fuel, and in the solid solution (Fig. 10 a). Small particles found outside of the seam, in the area below the Stripping zone of the belt (Fig. 10 b), which may be known proof of execution by the band on the cover laid him wiper functions.

The greatest efficiency of the proposed method for the sealing of a fuel rod can be achieved only in the case when excluded the possibility of the fuel dust not only in the internal cavity of the shell, but also on the ends of the stub and the shell, so the cap is installed with the protrusion relative to the end face of the shell on the length of the tapered portion, thereby providing direct access arc to the end of the entire surface, which can be adsorbed fuel particles. Under the action of high temperature of the arc during welding of small particles of fuel evaporate.

Proposed construction of a fuel rod with a modified cover and the manufacturing method recommended for mass production TVEL on an automated production line, starting with the 1st quarter of 1996.

2. TVEL under item 1, characterized in that the annular belt made in the form of the crest of the M-shaped.

3. TVEL under item 1, characterized in that the cover is made osesimmetrichnoi with the same truncated cones.

4. The method of manufacture of a fuel rod, including welding the lower plug shell, the installation of the support glass, equipment fissile and fertile fuel, insert clamp, vacuum, leak helium, welding the top of the stub and the spacer wire, characterized in that before the welding of the end seam of the upper stub with sheath produce sweep the inner surface of the shell, from the end of the annular flanges stub by an axial AC is and shell on the length of the tapered part of the plug.

 

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