RU2248051C1 - Nuclear reactor fuel assembly - Google Patents

Abstract

FIELD: nuclear power engineering; fuel assemblies for pressurized-water reactors.

SUBSTANCE: proposed fuel assembly has bottom nozzle carrying guide channels, bundle of fuel elements mounted in spacer grids, and removable top nozzle. The latter has upper plate and lower plate with holes which are mounted on guide channels passing through mentioned holes. Guide bushings are provided with collets and face-to-face mounted through inner steps in butt ends of external projections of guide channels. Springs are installed between upper plate and supporting members made on guide bushings. Collets are provided on upper ends of guide bushings and have upper stops and internal bosses engaging external drillings on upper ends of guide channels. Guide bushings are provided with stops to limit downward displacement of mentioned bushings relative to lower plate.

EFFECT: enhanced reliability and facilitated manufacture of fuel assemblies.

1 cl, 8 dwg

Description

Technical field

The invention relates to nuclear energy, and more specifically to fuel assemblies for nuclear pressurized water reactors.

State of the art

Known fuel assembly of a nuclear reactor [RU 2075118 C1], containing a bunch of fuel elements mounted vertically in a frame assembled from spacer grids mounted on tubular guide channels, control rods, as well as a shank and a removable head. The removable head contains a bottom plate with holes, a lower base plate with holes and an upper plate (upper bearing plate) with holes, said plates are mounted on guide bushings passing through said holes, equipped in their lower part with collets made in the form of nozzles having longitudinal cuts. A cylindrical shell is fixed to the upper plate. The guide bushings are mounted on the ends of the guide channels protruding from the beam of fuel elements, abutted by their inner ledges at the ends of the said channels and connected to the channels using ring grooves present in the collets, covering the ring collars on the guide channels. The springs are installed on the guide bushings between the lower base and upper plates in a partially compressed state. The lower and upper stops attached to the guide bushings below the lower and above the upper plates limit the movement of said plates, respectively, up and down. The locking device is made in the form of a plate, covering the walls of its collet openings, located under the base plate and rigidly connected to the said plate by means of a conical guiding shell.

A significant drawback of the known fuel assembly is the lack of reliability associated with the presence of a “step” at the junction of the guide bushings with the ends of the guide channels, because of the ovality and radial clearances between the said elements, the “step” can damage the shell of the control rod vibrating in the heat carrier flow. In addition, the fastening of the upper stops, made in the form of rings or nuts, on the ends of the guide bushings is difficult due to the inconvenience of welding inside the upper cylindrical shell.

Disclosure of invention

The aim of the invention is to increase the reliability and manufacturability of fuel assemblies.

The objective of the invention is to eliminate the junction of the guide channel with the guide sleeve, as well as the exception of operations to secure the upper stops on the ends of the guide bushings.

The technical result of the invention is to simplify the design and improve the manufacturability of the fuel assembly.

The problem is solved in that in the fuel assembly of a nuclear reactor containing a shank, guide channels fixed to the shank, a bundle of fuel elements installed in the spacer grids, as well as a removable head containing an upper plate and a lower plate with holes mounted on passing through said openings guide channels, guide bushings equipped with collets and fixed against their inner ledges at the ends of the outer protrusions of the guide channels, springs, whiskers mounted on the guide bushes, the upper stops to limit the movement of the upper plate up and the lower stop to limit the movement of the lower plate down, installed on the guide channels, it is new that the springs are installed between the upper plate and the support elements made on the guide bushes, collets are made on the upper ends of the guide bushings and are provided with upper stops and inner collars engaged with the outer grooves made at the upper ends of the guide channels, and the sleep guide bushings wife stops for limiting the movement of said sleeves downwardly relative to the lower plate.

This solution to the problem simplifies the design, manufacturing technology, such as: eliminates the need to weld the upper stops to the guide bushings in hard-to-reach spots above the top plate and the possibility of the formation of “steps” at the joints of the guide channels with the guide bushes that can damage the shells of the control rods that are moved in the guides channels.

Brief Description of the Drawings

The invention is illustrated by drawings, on which:

figure 1 is a vertical section of a fuel assembly with a removable head, the coupling device with the guide channels is blocked by the upper plate, the supporting elements for the springs are made integral with the guide bushings, the lower stop of the lower plate is installed on at least one of the guide channels;

figure 2 is a vertical section of a variant of the removable head, the lower emphasis is made in the form of couplers;

figure 3 is a vertical section of a variant of the removable head, the lower emphasis is made in the form of rings mounted on the guide bushings mounted on the protrusions of the guide channels;

figure 4 is a vertical section of a variant of the removable head, the supporting elements are made in the form of washers or bushings mounted on the protrusions of the guide bushings with the possibility of relative movement upward, the lower stop is installed on at least one of the guide channels;

5 is a vertical section of a variant of the removable head, the guide bushings are provided with external protrusions in the region of the lower plate;

6 is a vertical section of a variant of the removable head, the lower emphasis is made in the form of rings mounted on the lower ends of the guide bushings;

Fig.7 is a vertical section of the coupling node of the collet with the guide channel in the locked position with the working preload of the fuel assembly;

Fig. 8 is a vertical section through a collet engagement assembly with a guide channel in an unlocked position.

Embodiments of the invention

The fuel assembly of FIG. 1 comprises a shank (1) on which guide channels (2) are vertically mounted. The fuel elements (3) are combined into a bundle with spacer grids (4). In the upper part, the fuel assembly is equipped with a removable head (5). In the head there are upper (6) and lower (7) plates with holes (8) and (9). Through these holes pass the guide channels (2). The guide bushings (10), mounted on the upper plate (6), are equipped in the upper part with collets (11) in the form of longitudinally cut nozzles and are installed on the ends of the guide channels (2) protruding from the fuel elements (3) to the stop with their internal ledges ( 12) into the ends of the outer protrusions (13) of the guide channels (2). On the guide bushings (10), springs (14) are installed, pressing the upper plate (6) from below and resting on supporting elements (15), made integral with the guide bushings (10). At the upper ends of the collets (11) are placed upper stops (16), which prevent the upper plate (6) from moving upward. At least one of the guide channels serves as the bottom stop (17) to limit the downward movement of the bottom plate (7). At the upper ends of the guide channels (2), external grooves (18) are made, for which the inner collars (19) of the collets (11) engage. The holes (8) of the upper plate (6) cover the collets (11) in the area of the inner shoulders (19). The outer diameter of the upper stops (16) is chosen so that the closer of the collet segments (11) allowed by the longitudinal slots to its longitudinal axis allows the upper stops (16) to pass through the holes (8), and in the head mounted on the fuel assembly, the outer diameter of the upper stops (16) ) was larger than the diameter of the holes (8). The guide bushings (10) are also provided with stops (20), restricting the passage of the guide bushings (10) through the holes (9) of the lower plate (7) down.

In the embodiment of figure 2, in the removable head (5), the lower stop (17) to limit the movement of the lower plate (7) down is made in the form of couplers (21) between the upper plate (6) and the lower plate (7).

In the embodiment of FIG. 3, in the removable head (5), the lower stop (17) for limiting the downward movement of the lower plate (7) is made in the form of rings (22) mounted on the guide bushings (10) mounted on the guide channels (2).

In the embodiment of FIG. 4, in the removable head (5), the supporting elements (15) are made in the form of washers or bushings (23) mounted on the protrusions (24) of the guide bushings (10) with the possibility of relative upward movement. Guide bushings (10) with their lower ends (20), acting as stops, limit their movement through the holes (9) in the bottom plate (7). The lower stop (17) to limit the movement of the lower plate (7) is installed on at least one of the guide channels.

In the embodiment of FIG. 5, in the removable head (5), the lower ends of the guide bushings (10) are made freely passing through the lower plate (7) to the outer protrusions (25), which act as stops, on the guide bushings (10).

In the embodiment of FIG. 6, in the removable head (5), the lower stop (17) to limit the movement of the lower plate (7) down is made in the form of rings (26), mounted on the lower ends of the guide bushings (10).

The operation of the fuel Assembly is as follows. The coolant enters through the shank (1) into the bundle of fuel elements (2), where it carries out heat removal, and then exits through the head (5) into the upper chamber of the reactor. In the free state (in the absence of pressing the head from above), the springs (14) press the upper plate (6) against the upper stops (16) on the collets (11), and the collets (11) are interlocked by internal collars (19) with grooves (18) on the upper ends of the guide channels (2) and are blocked from being disengaged by the upper plate (6). The head (5) is fixed on the guide channels (2) with the possibility of removal by a special device, which can be used as the device described in [1]. To do this, press the top plate (6) from above, move it down and fix it in this position relative to the bottom plate (7). The holes of the upper plate (8) will come off the collets (11) and will free them from blocking, ensuring the exit of the inner collars (19) from the grooves (18) on the guide channels (2). In this state, applying force to the bottom plate (7) up, you can freely remove the head (5) from the guide channels (2). In this case, the lower plate (7) will come into contact with the stop (20) and raise the guide bushings (10) with collets (11), disengaging them from the grooves (18) of the guide channels (2). Installing the head (5) is performed in the reverse order.

The proposed design of the removable head (5) can significantly simplify the technology of its assembly. When assembling the prototype, a significant difficulty was the operation of fixing the upper stops on the ends of the guide bushings, since the welds had to be performed in a limited volume inside the upper shell, the bottom of which is the upper plate. In the claimed design, the upper stops (16) are made at the upper ends of the collets (11) even before the head assembly (for example, when turning the collets). The diameter of the upper stops (16) is vibrated from the condition of their passage through the holes (8) in the upper plate (6) when the collet segments (11) are closed to their longitudinal axis. After passing through the holes (8), the collet segments (11) diverge under the action of elastic forces, and the diameter of the upper stops (16) becomes larger than the diameter of the holes (8). After installing the head (5) on the fuel assembly, the guide channels (2) are inside the collets (11) and prevent the compression of their segments to the vertical axis.

This solution allows us to simplify the design of the removable head, to extend the guide channels to exclude the joints of the guide channels and guide bushings on their inner surface (as was implemented in the prototype), creating the possibility of the formation of “steps” that can damage the shell of the absorbing rods that are moved in the guide channels of the fuel assembly. Such a device of the removable head also allows for quick removal and installation of the head without the use of any replaceable parts, which ensures a reduction in dose loads for personnel. In addition, in the manufacture of the head, the time-consuming operation of fixing the upper stops on the upper ends of the guide bushings by welding or tightening the nuts with their subsequent locking is excluded.

Thus, it provides increased reliability and manufacturability of the manufacture of the fuel Assembly.

Industrial applicability

It is most appropriate to use the proposed solutions for fuel assemblies of nuclear power reactors with pressurized water.

Claims (1)

A fuel assembly of a nuclear reactor containing a shank (1), guide channels (2) fixed to the shank (1), a bundle of fuel elements (3) installed in the spacer grids (4), as well as a removable head (5) containing the upper plate ( 6) and the bottom plate (7) with holes (8) and (9), respectively, mounted on guide channels (2) passing through the said holes, guide bushings (10), equipped with collets (11) and mounted in an abutment with their internal ledges ( 12) into the ends of the outer protrusions (13) of the channel guides (2), springs (14) installed on the guide bushings (10) between the upper plate (6) and support elements (15) made on the guide bushings (10), the upper stops (16) to limit the movement of the upper plate (6) up and lower stop (17) to limit the movement of the lower plate (7) down, mounted on the guide channels (2), characterized in that the springs (14) are installed between the upper plate (6) and the supporting elements (15) made on the rails bushings (10), collets (11) are made on the upper ends of the guide bushings (10) and provided with upper stops (16) and inner collars (19) hooked to the outer grooves (18) made at the upper ends of the guide channels (2), and the guide bushings (10) are provided with stops (20) to limit the movement of the said bushings down relative to the lower plate (7) )

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