JPH0219914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fuel support fitting installed on a core support plate of a boiling water nuclear reactor.

In the core of a boiling water reactor, control rods with a cross-shaped cross section are raised and lowered from the bottom of the core between a set of four fuel assemblies, guided by the sides of the fuel assemblies. The lower end of the fuel assembly is supported by a fuel support fitting, and the upper end is supported by an upper grid plate. This fuel support fitting is installed on the core support plate, and has a cross-shaped control rod insertion slit in the center, and four fuel pieces that fit and support the lower end of the fuel assembly around this slit. Equipped with a support hole.

In this way, the control rods are inserted through the control rod insertion slits and moved up and down using the sides of the fuel assembly as guides, so it is necessary to fully insert the control rods into the reactor core, for example when exchanging fuel. If the control rod is moved with no fuel assembly on the fuel support fitting, the blade side of the control rod will slide into the control rod insertion slit and get caught, causing the fuel support fitting to receive upward force. There is a risk of it coming off the core support plate or damaging the blade. Furthermore, if a control rod is inserted in such a state that no fuel assembly is present, there is a risk that the control rod will fall and be damaged because there is no member to support the side surface of the blade. Therefore, a pair of dummies called blade guides are inserted diagonally in place of the fuel assembly to guide insertion of the control rods and to prevent the control rods from falling over. However, inserting the blade guide into the reactor water at the correct position is difficult and requires a long time, which not only causes increased radiation exposure for workers but also contributes to a decrease in reactor operating efficiency. It has also become familiar.

This invention was made based on the above circumstances, and its purpose is to smoothly guide the insertion and withdrawal of the control rod without the blade side surface getting caught in the control rod insertion slit, and to prevent the control rod from falling. An object of the present invention is to provide a fuel support fitting.

Hereinafter, this invention will be described in a first embodiment shown in FIGS. 1 to 3.
An explanation will be given based on an example. In the figure, reference numeral 1 denotes a cylindrical shroud housed in a reactor pressure vessel. An upper grid plate 2 is attached to the upper part of this shroud 1, and a core support plate 3 is attached to the lower part. A control rod guide tube 5 is provided vertically between this core support plate 3 and the bottom part 4 of the reactor pressure vessel, and a control rod 6 moves up and down between this side tube 5 and the above-mentioned upper grid plate 2. It's becoming like that. This control rod 6 has a blade 6a having a cross-shaped cross section and a neutron absorbing material housed inside it.A lifting handle 7 is provided at the upper end of the blade 6a, and a flange-shaped speed control is provided at the lower end of the control rod 6. A fitting 8 and a coupling socket 9 are provided. This coupling socket 9 is connected to the control rod drive mechanism 10.
The control rod 6 can be driven up and down by being connected to the control rod.

A fuel support fitting 1 is attached to the core support plate 3.
1 has been installed. The fuel support fitting 11 is fitted into and supported by the upper end opening of the control rod guide tube 5.
12 is a guide recess for positioning, and this guide recess 12 is used as a guide pin 1 provided in the core support plate 3.
3, the fuel support fitting 11 can be fixed in the correct position. As shown in FIG. 2, the fuel support fitting 11 has a cross-shaped control rod insertion slit 14 in the center,
The control rod 6 is inserted through this slit 14 so as to be able to move up and down. Further, around the slit 14, there are four fuel support holes 16 that vertically fit and support the lower end of the fuel assembly 15.
It is designed so that four fuel assemblies 15 can be loaded as one set by sandwiching the fuel assemblies 15 between them. These fuel assemblies 1
The upper end side surfaces of 5... are supported by the upper lattice plate 2.

Guide support rollers 17 are attached to the upper end of the inner surface of the control rod insertion slit 14 at positions facing each other and sandwiching each side surface of the blade 6a. Of course, the distance between opposing rollers among these rollers 17 is set slightly wider than the thickness of the blade 6a to allow insertion of the blade 6a, and so that the side surface of the blade 6a can roll into contact with these rollers 17. It's getting old. Further, as shown in FIG. 3, the guide support rollers 17 are provided in a plurality of upper and lower stages (two stages in this embodiment), and each guide support roller 17 is
It is a curved roller whose diameter decreases from the center toward both ends.

The fuel support fitting 11 configured as described above is
It is placed on the control rod guide tube 5, and the control rod 6 is inserted from below.
is inserted. That is, when the control rod drive mechanism 10 is driven to raise the control rod 6, the blade 6a
passes through the slit 14 and moves up while being guided by the rollers 17 while rolling in contact with the rollers 17 . Therefore, problems such as the blade 6a getting caught on the inner surface of the slit 14 and being damaged or the fuel support fitting 11 lifting up can be prevented, and the blade 6a can be inserted smoothly. Further, when the control rod is withdrawn, that is, when the blade 6a descends, the blade 6a can be smoothly guided by the rollers 17. Further, in this case, since the guide support rollers 17 are provided in a plurality of upper and lower stages, the blade 6a is supported by the guide support rollers 17 of each stage at a plurality of upper and lower positions so as not to tilt, thereby stably moving the control rod 6. Can be inserted and withdrawn.

Furthermore, since the guide support roller 17 is a curved roller whose diameter decreases from the central portion toward both ends, the guide support roller 17 rolls into contact with the blade 6a only at the large diameter portion of the central portion. Therefore, since the contact area with the blade 6a is smaller than that of a right cylindrical roller, the frictional resistance caused by the rolling contact of the guide support roller 17 with the blade 6a is reduced, and the control rod 6 can be smoothly inserted and withdrawn. can do. Moreover, if the guide support roller 17 is a curved roller, the control rod 6
Even if the blade 6a rotates in the circumferential direction and the roller contact surface of the blade 6a is inclined with respect to the axis of the guide support roller 17, the blade 6a can be guided and supported by the guide support roller 17.

Moreover, the blade 6a is a connection part with the control rod drive mechanism 10, and the load in the horizontal direction is supported by the rollers 17 at a position spaced upward from the coupling socket 9, that is, at the upper end of the slit 14. It is possible to hold the control rods 6 vertically even if the fuel assemblies 15 are not present.
Therefore, there is no need for the conventional work of inserting a blade guide in place of the fuel assembly, and it is possible to save labor.

The present invention may also be configured such that the rollers 17 are attached only to one side of the inner surface of the control rod insertion slit 14 as shown in FIG. 4 as a second embodiment, or as shown in FIG. 5 as a third embodiment. The rollers 17 may be mounted at two locations facing each other.

As explained above, in this invention, guide support rollers are provided on the inner surface of the cross-shaped slit through which the control rod is inserted, and these rollers guide the vertical movement of the blade and support the horizontal load acting on the blade. Because of this, the control rod can be vertically supported even if no fuel assembly is present on the fuel support fitting, and it is possible to prevent the control rod from falling over. In addition, the rollers can smoothly guide the blade in its upward and downward movements, and it is possible to prevent problems such as damage caused by strong sliding contact of the blade with the inner surface of the slit, and failures such as the fuel support fitting coming off. Therefore, work can be carried out efficiently without relying on the blade guide during fuel exchange, etc., thereby reducing the amount of radiation exposure of workers and contributing to improving the operating rate of the reactor.
Moreover, in the present invention, since the guide support rollers are provided in multiple stages above and below, the blade is supported by the guide support rollers in each stage so that it does not tilt at multiple locations above and below, and the control rod can be stably inserted and withdrawn. be able to. Furthermore, since the guide support roller is a curved roller whose diameter decreases from the center toward both ends, the guide and support roller rolls into contact with the blade only at the large diameter section of the center, so it has a right cylindrical shape. The contact area with the blade is smaller than that of the rollers, so the frictional resistance caused by the rolling contact between the guide and support rollers and the blade is reduced, and the control rod can be smoothly inserted and withdrawn. In addition, if the guide support roller is a curved roller, even if the control rod rotates in the circumferential direction and the roller contact surface of the blade is tilted with respect to the axis of the guide support roller, the blade will not be moved by the guide support roller. Guidance can be supported.

[Brief explanation of drawings]

1 to 3 show a first embodiment of the present invention, in which FIG. 1 is a vertical sectional view showing a part of a boiling water reactor, FIG. 2 is a plan view of a fuel support fitting, and FIG. 2 is a sectional view taken along the line ``-'' in FIG. 2, and FIGS. 4 and 5 are plan views of fuel support fittings showing other embodiments of the present invention, respectively. 3... Core support plate, 6... Control rod, 6a... Blade, 11... Fuel support fitting, 14... Control rod insertion slit, 16... Fuel support hole, 17... Guide support roller.

Claims (1)

[Scope of Claims] 1. A fuel assembly is installed on a core support plate in a reactor pressure vessel and has a cross-shaped control rod insertion slit in the center, and the lower end of the fuel assembly is fitted and supported around this control rod insertion slit. In the fuel support fitting equipped with a fuel support hole, the inner surface of the control rod insertion slit is provided with rotatable guide support rollers in upper and lower stages that roll into contact with the side surface of the blade of the control rod, and the guide support rollers are A fuel support fitting characterized by having a curved roller whose diameter decreases from the center toward both ends. 2. The fuel support fitting according to claim 1, wherein the guide support rollers are each provided at an upper end of the control rod insertion slit.