JPS61207990A - Nuclear fuel aggregate for reactor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to a nuclear reactor, and particularly to a nuclear fuel assembly thereof.

[Prior Art] As shown in FIG. 7, generally during nuclear reactor operation, upper core support plate 4 and lower core support plate 4Err! al
l1m14N141hL&LJ%, j-utpQ-+m
krlI-'pH1 seahLj, and the supported fuel assembly 1 has a considerably large upward flow due to the high-speed coolant flow passing through the flow passage hole 6b of the lower core support plate 6 and the lower nozzle 7, as shown by the arrow. Lifting force is working. Therefore,
During reactor operation, the fuel assembly 1 is securely attached to the lower core support plate 6.
In the fuel assembly 1 of the pressurized wooden reactor, in order to prevent fatigue of various structural members due to vibrations caused by floating of the fuel assembly 1 and fluctuations in the flow rate of the coolant, the fuel assembly 1 of the pressurized wooden reactor is
A hold-down system is adopted in which a holding device 5 consisting of a holding spring 3 is provided at the upper nozzle 2 of the fuel assembly 1, and a downward force is exerted on the fuel assembly 1 through cooperation with the upper core support plate 4. ing.

Although not shown, in the fast breeder reactor, a downward force is exerted from the lower end of the fuel assembly by a hydraulic hold-down mechanism.

However, during transient operation of a nuclear reactor or in a high-power reactor core, the lift force per fuel assembly increases due to the increase in coolant flow rate, and even in the fuel assembly 1 of the current pressurized wooden reactor,
It becomes difficult to ensure stable landing using only the presser spring 3 of the upper nozzle 2, and the design is designed with little leeway.

In addition, in the case of a core such as a high-conversion type pressurized wooden reactor, where the fuel rods are short and dense, the weight of the fuel assembly is relatively light but the lift force is significantly large. A fuel assembly holding device using a hold-down method such as a wooden nuclear reactor cannot hold down the fuel assembly sufficiently because the spring force is limited due to space limitations. Furthermore, hydraulic hold-down mechanisms such as those used in fast breeder reactors,
In a pressurized wooden reactor core, since it is submerged in high-pressure water, no differential pressure is generated, and even if the lower core support plate structure is complicated, sufficient effects cannot be expected.

Additionally, in general, the spring force gradually decreases due to stress relaxation due to irradiation with fast neutrons, but since the fast neutron flux in the Takamatsu Replacement Core is higher than in a normal pressurized wooden reactor core, the above-mentioned tendency increases.

[Problem to be solved by the invention 1 As mentioned above, the conventional hold-down type axial support system has a problem in that the design has a small margin for the increase in lift force and the decrease in spring force due to irradiation. There is. It is an object of the present invention to provide a fuel assembly for a nuclear reactor that promptly solves the problem 7α.

Means for Solving Problem E, α] For this purpose, the present invention is provided between a lower core support plate and an upper core support plate each having a flow passage hole, and the coolant is supplied from the flow passage hole of the lower core support plate. In a nuclear fuel assembly for a nuclear reactor that enters and exits through a passage hole in an upper core support plate, a lower nozzle of the nuclear fuel assembly is configured to move the nuclear fuel assembly in the same direction as the lift force acting on the nuclear fuel assembly due to the flow of the coolant. This device is characterized by being equipped with a pressing device made of an elastic member that applies bias.

[Operation J] Thus, according to the present invention, the holding device is attached to the fuel assembly so that the direction of the biasing force of the holding device acting on the fuel assembly is the same as the direction of the lifting force due to the flow of coolant during operation. It is installed on the upstream side of the coolant flow with respect to the reactor body, and is a hold-up type in which the fuel assembly is pressed against the upper core support plate. As shown in Fig. 6, the forces acting on the fuel assembly include the fuel assembly's own weight W1, buoyancy force B, coolant lift force, presser spring force (biasing force) F, etc. In the hold-down method,
The required downward spring force is defined by F>L+B-W, and as the lift force increases, the spring holding force must also increase. On the other hand, if a hold-up type structure is adopted as in the present invention, if F > W-L-B is satisfied in a weak state, the fuel assembly will be pressed against the upper core support plate, and the lift will be further increased. If , the required pressing force of the pressing spring decreases. That is, the minimum holding force required in this case is determined in a state where there is no flow of coolant and is given by F=W-B, so it can be made much smaller than in the hold-down method. Also, + l + I
＋ L i go lie 1mu ☆ma ↓↓ 顛 shi 11 mu 赫God □ go ill, J-'!
++ force can be significantly reduced, and the reduction in spring force due to irradiation can also be reduced, and thus the nuclear reactor fuel assembly according to the present invention can provide axial support with much greater reliability than conventional ones. It is something to give.

[Embodiments] Next, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings, in which the same reference numerals indicate the same or corresponding parts.

1A and 118 show, for example, an embodiment in which the present invention is applied to a fuel assembly 1 having a square cross section and a regular hexagonal cross section, respectively. The lower nozzles 7 of each fuel assembly 1 are of a structure having a holding device of a hold-up mechanism, and the lower nozzle structures can be considered to be substantially the same except for the cross-sectional shape, as shown in FIG. As such, fuel assembly 1
A main body part 8 having an extension part 8a extending downward in the direction of the operator's hand, and the! It includes a hollow body 9 that extends into the main body 8 through the L-long portion 8a, and an elastic member, that is, a spring 10, disposed at the opening between the hollow body 9 and the extension portion 8a. It provides an upward spring force. Main body part 8 and extension part 8
7 flange 1 radially inward from the joint with a.
1 extends radially outward from the upper and lower ends of the hollow body 9, respectively. The upper surface of the 7-run no. 11 functions as a stopper to limit the downward movement of the hollow body 9 in cooperation with the lower surface of the 7-run no. 12.
The upper surface of the flange 13 serves as a support surface for the spring 10. Further, a support 15 is provided in the hollow body 9 of the lower nozzle 7 to support a vertically movable in-core instrumentation guide pipe 14 and protect it from hydraulic vibration.

(A) in FIG. 2 shows the fuel assembly 1 when it is suspended, and under this no-load condition, the spring 10 is moved between the extension part 8a and the hollow body 9 by the engagement of the seven flanges 11 and 12. The fuel assembly 1 is housed in a compressed state, and the spring 10 is given a certain amount of deflection to support the weight of the fuel assembly 1 . Therefore, when landing on the floor in a freestanding state as shown in FIG. 2(B), the spring 10
does not bend even under the weight of the fuel assembly 1,
It is possible to obtain stable seating comfort. Also, in Figure 2 (
As shown in C), after the fuel assembly 1 is placed on the lower core support plate 6, when the upper core support plate 4 and other upper core structures (not shown) are attached, the spring 10 is bent further. The design is such that a predetermined spring force acts between the fuel assembly 1 and the lower core support plate 6 even if there is thermal expansion of the reactor internal structure due to temperature rise during reactor operation.

Regarding the in-core instrumentation guide W14, its lower end protrudes downward from the lower end of the hollow body 9, except when the upper core structure is attached to the upper core structure by fitting the positioning pin 4a provided on the upper core support plate 4 to the upper nozzle 2. It is designed to ensure stable protection of in-core instrumentation.

As mentioned above, although the present invention was applied to fuel assemblies with square and regular hexagonal cross sections, it is of course possible to apply the above-described structure to fuel assemblies with various other cross-sectional shapes. Furthermore, the different embodiments of the present invention shown in FIGS. 3 to 5, which will be described hereinafter, can also have various cross-sectional shapes.

In the embodiment of FIG. 3, a plurality of positioning legs or pins are provided along the bottom of the main body 8 of the lower nozzle 7 at appropriate positions of the runner 11 extending toward the center of the lower nozzle 7. 16 is attached with its point facing downward, while the positioning pin 1 is attached to the lower core support plate 6.
A hole 17 is bored at a position corresponding to 6, and this hole 17 receives the positioning pin 16. A spring 18, which is an elastic member, is installed around each positioning pin 16 between the lower surface of the seven flange 11 and the upper surface of the lower core support plate 6.
Preferably, a spring 18, such as a rib, which is fixed to the lower surface of the 7 flange 11 by welding as indicated by the reference numeral 19, acts in the same manner as the spring 10 of the embodiment shown in FIG. An upward pressing force is applied to the fuel assembly 1. The embodiment shown in FIG. 3 can reduce the axial dimension of the lower nozzle 7 compared to the one shown in FIG. Since it is possible to provide a small hole, it is possible to provide a small hole for guiding the in-furnace instrumentation. , L4 tas l
ltA'FfAme air travel 1-7 is provided with a plurality of spring receivers 2o extending into the lower nozzle 7 through the 7 langes 11 of the main body 8 of the lower nozzle 7, and the spring receivers 2o extend into the lower nozzle 7. A coil spring 21 having a relatively small diameter is mounted around the coil spring 20 in the lower nozzle 7. When the fuel assembly 1 is placed on the floor and transported, the lower end of each spring receiver 20 comes into contact with the lower 7 flange 13 of the hollow body 9. The operation of this embodiment is similar to that of FIG. 2, but by using a plurality of coil springs 21, which are elastic members, to increase the overall spring rigidity,
The axial dimension of the lower nozzle 7 can be reduced, and the projected area required for storing the spring is smaller than when using a large-diameter coil spring, so the space of the flow passage hole 6a of the lower core support plate 6 can be reduced. can also be made larger.

Furthermore, for the same reason as in the case of FIG. 3, the guidance of the in-core instrumentation becomes easier.

In the embodiment shown in the ms diagram, a plurality of leaf springs 22 are disposed as elastic members between the seventh flange 11 of the lower nozzle body 8 and the seventh flange 13 of the hollow body 9.

Its working principle is that the real II6@ in Fig. 2 and m4 is cotton, but by using the leaf spring 22, sufficient spring force can be provided in a narrower space, so the axis of the lower 7x Lua The directional dimension can be further reduced, and the space of the channel hole 6b can be made larger. Furthermore, the guidance of the in-core instrumentation becomes easier.

[Effects of the Invention] As described above, the nuclear fuel assembly for a nuclear reactor according to the present invention has the following effects:
The holding device is installed on the upstream side of the coolant flow with respect to the fuel assembly so that the direction of the urging force of the holding device acting on the fuel assembly is the same as the direction of the lifting force due to the coolant flow during transport. Since it is a hold-up type that presses the fuel assembly against the upper core support plate, it is possible to stably support the fuel assembly in the axial direction regardless of the magnitude of the lift force, and it is possible to achieve stable support in the axial direction of the fuel assembly, compared to the current pressurized wood. It provides sufficient reliability as a support system for cores with a faster coolant flow than that of nuclear reactors, and for fuel assemblies in which fuel rods are arranged more densely. Moreover,
Since the urging force and lifting force of the holding device act in the same direction,
The force applied to the elastic member is smaller than in the past, the stress level of the elastic member can be lowered, and the spring force of the elastic member due to irradiation can be alleviated.

[BRIEF DESCRIPTION OF THE DRAWINGS] Pt51Δ is a side view partially showing a fuel assembly having a square cross section constructed according to the present invention between an upper core support plate and a lower core support plate, and FIG. FIGS. 2(A), 2(B), and 2(C) are side views showing a fuel assembly having a regular hexagonal cross section constructed according to the present invention installed between an upper core support plate and a lower core support plate; ) are cross-sectional views showing the states of the fuel assembly according to the present invention during suspension, landing, and operation, respectively, and FIGS. 3, 4, and 5 are cross-sectional views showing different embodiments according to the present invention, respectively. Figure 6 is an explanatory diagram that compares and contrasts the effects of the hold-up method according to the present invention and the conventional hold-down method, and Figure 7 shows a conventional fuel assembly between the upper core support plate and the lower core support plate. FIG. 3 is a partially sectional side view of the device installed. 1...Fuel assembly 2...Upper nozzle 4...
Upper core support plate 6... Lower core support plate 6b... Channel hole 7... Lower nozzle 10... Elastic member (spring) 18... Elastic member (spring) 21... Elastic member ( Spring) 22...Elastic member (spring) Fig. 1A
Old Figure 3 Figure 4 Heron Figure 7

Claims (1)

[Claims] In a nuclear fuel assembly for a nuclear reactor, which is installed between a lower core support plate and an upper core support plate each having a flow passage hole, and in which coolant enters through the flow passage hole in the lower core support plate and exits to the flow passage hole in the upper core support plate. , in the lower nozzle of the nuclear fuel assembly,
A nuclear fuel assembly for a nuclear reactor, characterized in that it is equipped with a holding device made of an elastic member that urges the nuclear fuel assembly in the same direction as the lift force acting on the nuclear fuel assembly due to the flow of the coolant.