KR820001248B1 - Hydraulic seismic suport for nuclear fuel assembly - Google Patents

Abstract

Fuel assembly(10) for a reactor is improved by providing a cellular grill which engages one end of all of the fuel rods. The engaged rod ends being all on one side of the core. Hollow guide posts protrude into the core from biased spring pads(30) and plungers(54) which move with the spring pads plug each end of the guide posts(50). Plates on the end fitting grid have individual holes for fluid discharge and partially block the other end of the hollow guide post. The arrangement provides a hyaraulic shock absorbing effect to reduce damage due to seismic or other longitudinal forces.

Description

Shock Absorber of Nuclear Fuel Assembly

1 is a perspective view showing a part of a nuclear fuel assembly that exhibits features of the present invention.

FIG. 2 is a partial front cross-sectional view of the nuclear fuel assembly shown in FIG.

3 is a partial side cross-sectional view of the nuclear fuel assembly shown in FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nuclear reactors, and more particularly, to hydraulic devices for absorbing shocks applied to nuclear fuel assemblies and the like.

In general, in order to generate effective power from a nuclear reactor, it is necessary to join fissile urinium in a sufficiently concentrated and physical configuration in order to sustain a continuous neutron-induced fission reaction in the uranium nucleus. The heat generated by these cleavage reactions in these aggregates is generally absorbed by the flow of pressurized water, whereby the heated pressurized water is directed to one or more heat exchangers which transfer the absorbed heat to the secondary cooling water.

Of course, the secondary coolant is converted to steam to drive a turbine or other electrical power generator.

Pellets of uranium dioxide are often used to properly concentrate uranium for the reactor core. These pellets (particles) are loaded into long, hollow tubes and when the two ends of the tubes are sealed, they are called nuclear fuel rods. To achieve structural integrity of the reactor core, these fuel rods are arranged in small groups of about 200 nuclear fuel rods, which are called fuel assemblies.

And this assembly is built in an array of employee pillars to make up the reactor core. Naturally, the reactor core is threatened by the surroundings about its structural integrity. Temperature, cooling water, flow velocity, and pressure radiation in the reactor core combine to cause significant deformation of the core material. In the event that the factors around them are severely affected, it should be installed to reinforce the structural aspects of the reactor core so that a suitable device can overcome other forces greater than those applied during normal operation. Earthquakes and thermal shocks can cause accidents in situations where the force is greater than the normal operating force of pressurized water being evaporated or discharged from the reactor core.

A common solution to this problem is to add some material or metal to the reactor core. It has many unnecessary structures, although it can access the necessary structural protection measures. Further construction of other materials in the reactor core also has a "parasitic" effect of absorbing some of the neutrons in the core. The absorbed neutrons are not consumed in energy generation and are either consumed or used inefficiently. Therefore, there is a need to improve the reactor core, which has the advantage that it does not constitute additional material in the core structure that can attenuate or absorb abnormal impacts or other forces to make the core safe and does not increase the parasitic neutron loss.

In the present invention, it is intended to solve these problems of the prior art broadly. For example, an inner pad that supports to limit the longitudinal movement of the fuel assembly is supported so as not to move the spring pad mounted on the fixture of the upper end of each fuel assembly. At least these have some of the spring pads having plungers pinned to each pad, these plungers being slidably inserted into the hollow tubular guide rods. The guide rods are formed with longitudinal slots for inserting the pins so that the plungers can be moved in the longitudinal direction with respect to the guide rods, and the guide rods are mounted on the upper lattice of each fuel assembly. In addition, a disk-shaped plate body having a through hole for closing the open end of each guide rod is formed in the tubular guide rod. Therefore, when there is fine dust, the plunger and the spring pad assembly are moved in the longitudinal direction with respect to each guide rod, and the pressurized water of the guide rod is suppressed in this movement. At this time, the pressurized water ejected into the through hole of the plate allows the guide rod and the spring pad to move in opposite longitudinal directions at a control speed at which external force can be safely absorbed.

However, in the structure of the present invention, the combination of the pin and the plunger causes a gradual effect while moving in the longitudinal direction through the liver guide rod. Thus, the pins connecting the plungers to their spring pads respectively move longitudinally in the slots of the guide rods, so that the pins and connecting plungers gradually close their slots, thereby allowing the pressurized water in the guide rods to flow. Shrink the area continuously.

This technique continually increases the resistance to relative longitudinal movement of the plunger and through-hole plate. This resistance is also increased to provide progressive protection of the reactor core structure from violent risk of sudden damping of the applied shocks.

As described above, the external force applied to the reactor core of the present invention can be overcome, but a material that absorbs neutrons parasitically from the core is not used.

When described in more detail by the accompanying drawings illustrating the present invention.

In FIG. 1, the fuel assembly 10 is shown. The fuel assembly 10 is composed of a group of elongated fuel rods 11 arranged in parallel in the longitudinal direction, one end of which is an end portion. It is housed in the congestion 12.

The end fixture 12 has a cellular grid 13 arranged transverse to the longitudinal axis of the fuel rod 11 to engage with the end of the fuel rod, whereby longitudinal movement of the nuclear fuel rod is suppressed. In addition, the end fixture 12 is composed of a unitary end structure 14 for supporting the cellular grid 13. As shown, the end structure 14 is generally in the form of a hollow cube, the transverse ends of which are open and longitudinal slots 15, 16, 17, 20 formed on each side of the cube. have.

The slots 15, 16, 17, 20 are parallel to the longitudinal axis of the fuel rod 11 and the slots are centered on each side of the cube from the transverse sections which are spaced at regular intervals in the longitudinal direction from the grid 13. About two-thirds of the length, and riveted fixtures 21, 22, 23, 24 are slots 15, 16, 17 (at about a quarter of the slot depth from the top). 20) attached separately.

Spring pads 25, 26, 27, 30, which will be described in more detail below, are provided with fuel rods limited by respective fasteners 21, 22, 23, 24 from the hollow interior of the end casting body 14. Through the respective slots 15, 16, 17 and 20 in order to adjust the longitudinal movement of 11) and the movement of the end cast body 14 adjacent to the grid 13 and immediately below the slot. It protrudes.

The entire fuel assembly 10 is excreted in the reactor core (not shown) and only shown as pads 31 and 32 in FIG. 1 but with four internal pads damping the longitudinal motion of the fuel rod 11. Is supported. The pads 31 and 32 are laid in connection with a transverse lattice (not shown) disposed in the upper region of the complete nuclear reactor core. The inner pads are generally arranged in quadrilaterals in groups of four, each of which is confined to one fuel assembly. The inner pads 31, 32 are spring pads 25, 26, 27, 30 protruding through the slots 15, 16, 17, 20 formed on each side of the end cast body 14. ) Is supported opposite to the protruding portion.

In FIG. 2, the end casting body 14 is formed with a transverse shoulder 33 for holding the edge of the cellular grating body 13.

As shown, the slot 15 is closed by the fixture 21, and the spring pad 25 protruding through the slot 15 is an inner pad 34 fixed to a grid (not shown). ) Is supported.

The spring pad 25 has a through hole 35 installed therein, and the hollow guide rod 36 is inserted into the through hole 35 to allow relative movement in the longitudinal direction.

The pin 37 also secures the circumferential plunger 40 to the spring pad 25, and furthermore, the pin 37 is connected to the end of the guide rod 36 to close the open end of the guide rod 36. Let the plunger 40 secure. The circumferential wall surface of the plunger 40 and the inner wall of the guide rod 36 are loose enough to prevent the leakage of the fluid so that the plunger can move freely in the longitudinal direction with respect to the guide rod between them. In addition, the guide rods 36 are parallel to the longitudinal axis of the fuel rods 11, and the slots 41 and 42 of the guide rods are also formed in the longitudinal direction on the wall of the guide rods, and the widths of the guide rod slots 41 and 42 are The pin 37 is of a suitable size to move longitudinally relative to the guide rod 36 when there is longitudinal movement of the guide rod relative to the plunger 40, and the depth of the slots 41 and 42 of these guide rods is guided. It corresponds to about half the length of the rod 36 and the ends of the guide rod slots 41 and 42 are located on the transverse surface of the cellular grid 13. The guide rod 36 is installed while protruding into the cellular structure of the lattice body 13.

As shown in the figure, the upper side 43 of the grating body 13 is cut | disconnected by the depth which penetrated into the grating body 13, and the request | requirement is formed.

The disc-shaped plate body 44 is installed at the transverse surface position of the grid body 13 in the guide rod 36, and the diameter of the plate body 44 is inserted into the guide rod 36 so that the guide rod 36 can be inserted. The through-hole 45 is sized to close the end of the plate body as a means for fluid flow between the guide rod volume 46 formed between the plunger 40 and the plate body 440 and the remainder of the reactor core volume. 44)

The operation of the present invention is described in detail in FIG. 3, which is explained in conjunction with FIG. 2, wherein the longitudinal component of the force for the impact is applied to the nuclear reactor assembly 10 when an impact such as an earthquake or the like is applied to the reactor core. Move to pad 32. Since the pad 32 is pressed against a portion of the spring pad 30 protruding from the end casting body 14 through the slot 20, the movement of the nuclear fuel assembly 10 through the elastic characteristic of the coil spring 47 is performed. In addition to suppressing the pressure, the movement of the nuclear fuel assembly is suppressed by the force of the hydraulic pressure generated in the guide rod 50.

In this way, the pressurized water coolant in the reactor core filled in the guide rod volume 51 acts as a shock absorber, and the pressurized water flows from the volume 51 through the through hole 52 of the plate 53. Dissipate power One of the features of the present invention, however, is that the guiding rod slot (shown with only one guiding rod slot 55 in FIG. 3) is progressively formed in the discharge zone formed by the relative longitudinal movement of the plunger 54 passing therethrough. To decrease.

Thus, when the impact is first applied to the reactor core, the coolant flow from the volume 51 is relatively unrestricted and the inhibitory effect on the longitudinal movement of the plunger and guide rod assembly appears relatively light. This initial mild deterrent protects the reactor core's components from the risk of sudden impact.

As the fuel assembly 10 moves longitudinally toward the inner pad, the plunger 54 gradually guides the flow path formed by the guide rod slot 55 and the pair of slots of the guide rod 50 from the plane of FIG. To close. The gradual decrease in the area of this flow path has the effect of increasing the flow resistance from the volume 51 to the remainder of the reactor core, thereby absorbing this force rather than abruptly absorbing this force. To gradually attenuate the force caused. The progressive force attenuation, which is a feature of the present invention, protects the core from the possibility of danger caused by unexpected forces.

In addition, after the plunger 54 completely closes the slot of the guide rod, the antistatic fluid and the discharge from the volume 51 continue through the through hole 52 of the plate body 53 until the applied force is completely absorbed. It also serves to attenuate a portion of the impact applied to the coil spring 47. Obviously, the progressively varying passage exit area formed by the linking effect of the coil springs 47, the through holes 52 and the plunger 54 and the associated guide rod slots, may be used to fully absorb the expected load of the machine, Even if no parasitic neutron absorbing material is used from the reactor core, one or two of them are much more effective than a means of overcoming impact forces. As described above, the hollow guide rod which is a feature of the present invention improves the structural integrity of the reactor core and eliminates inefficient neutron absorption.

After the impact is dissipated in the above manner, the energy accumulated in the compressed coil spring 47 is longitudinally displaced from the inner pad 32 until its movement is stopped by the action of the spring pad 30 and the fixture 24. The nuclear fuel assembly 10 is pressed.

As such, the present invention works to overcome most of the impact forces that need to be supported by all of the impact damping guide rods of the reactor core.

Claims (1)

In a shock absorber of a nuclear reactor fuel assembly in which a plurality of elongated fuel rods 11 having two ends are separated from each other at regular intervals and arranged in parallel to each other, the cellular grid 13 is formed in each of the cell lattice bodies. At least one slot 41 is formed therein while engaging the one end of the fuel rod 11 to be adjacent to each other, and engaging the hollow guide rods 36 and 50 to one end of the grid moving therewith. 42 and 55, wherein the slots are formed to extend from there through a portion of the guide rod at regular intervals from the grid, and the plates 43 and 53 to the guide rod ends adjacent to the grid. Insert and install on the end in the guide rod, and arrange the pads (25) and (30) in the transverse direction with respect to the guide rod slots to form a through hole (35) therein to receive the guide rods and guide the pads. Shock absorption of the nuclear fuel assembly that allows the relative movement between the plunger and the guide rod by progressively closing and opening the guide rod slot by fixing the plungers 40 and 54 to the pad in the guide rod. Device.

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