JPS6050313B2 - Shipper cap installation status confirmation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a shipper cap attachment status confirmation device used for detecting damaged fuel in a boiling water nuclear reactor.

In boiling water reactors, fuel rods are inspected for damage during periodic inspections. A method for detecting damaged fuel in this case will be explained with reference to FIG. In the figure, a shipper cap 4, which is provided with an air supply pipe 2 and a sampling pipe 3, is lowered from the upper part of the reactor core and installed on a core grid 6 above a fuel assembly 1. At this time, the inner shell 5 of the shipper cap 4 is also mounted onto the channel box 8 via the rubber packing 7. When the installation is completed, pressurized air is sent into the shipper cap 4 through the air supply pipe 2 to push down the liquid level inside. As a result, the flow of cooling water 9 is stopped and isolated from surrounding reactor water. If the fuel is damaged, fission products are released into the cooling water 9 from the damaged part. Several tens of minutes after the shipper cap 4 is attached, the cooling water 9 is sampled through the sampling pipe 3, and the presence or absence of fuel damage is determined by measuring the radioactivity concentration of the sample. When testing with this method, if the shipper cap 4 is not properly installed, the cooling water 9 will not be isolated, resulting in a large error in the measured value.

For this reason, conventionally, multiple notches were provided at the bottom of the side wall of the shipper cap 4, and it was visually confirmed from the top of the reactor core that the air bubbles 10 were coming out evenly from these parts, to ensure that the shipper cap 4 was installed horizontally and correctly. I had determined that there was. However, this method is not only inaccurate because it involves visual observation, but also has the serious problem of exposing the observer to radiation. Another idea is to attach several limit switches to the bottom end of the shipper cap and use electrical contact signals to check whether the shipper cap is attached, but this is preferable in terms of water resistance and radiation resistance. The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a shipper cap attachment status confirmation device that eliminates the conventional difficulties.

In the present invention, a shipper cap is provided with air outlets each having a plurality of sealing mechanisms provided on the bottom surface of the side wall, and an air conduit connected to these air outlets and converged into one pipe joint; an air pipe connected to a pressurized air source and provided with a pressure regulating valve and a pressure switch outside the reactor core on a pipe line, the other end of which extends to a pipe joint provided in the shipper cap, and the set pressure of the pressure regulating valve is set to the The pressure is a suitable pressure higher than the reactor water pressure that the bottom of the shipper cap receives when it is properly installed in the core grate, and the operating pressure of the pressure switch is lower than the set pressure of the pressure regulating valve and higher than the reactor water pressure. The above objectives have been achieved with the feature of the shipper cap attachment status confirmation device. An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram of a shipper cap installation status confirmation device according to the present invention, and FIGS. 3 and 4 are sectional views showing different embodiments of air outlets used in the device shown in FIG. 2. In FIG. 2, a plurality of air outlet ports each having a sealing mechanism are provided on the bottom surface of four side walls of a sipper cap 4 which is shaped like an inverted square tank.

Air conduits 21 branched from pipe joints 20 provided on the upper surface of the shipper cap are connected to each of these air outlet ports. On the other hand, outside the reactor core, a pressure regulating valve 2 is installed on the air piping 25 whose one end is connected to the pressurized air source 22.
3 are provided in series, and a pressure switch 24 is provided in a branched manner. Furthermore, the other end of the pipe 25 is connected to the shipper cap 4.
Connect to the pipe joint 20 provided at the The set pressure of the pressure regulating valve 23 is set so that the shipper cap 4 is on the core grid. Reactor water pressure H to which the bottom of the shipper cap is subjected when installed correctly
(The pressure indicated by the water head H in FIG. 2) is set to a higher appropriate pressure P1. In addition, the operating pressure of the pressure switch 24 is set to an appropriate value that is lower than the set pressure P of the pressure regulating valve and higher than the reactor water pressure H. Set the pressure to P2. Next, details of the air outlet will be explained with reference to FIGS. 3 and 4.

FIG. 3 is a sectional view showing the internal structure of the air outlet port, and shows the state when the shipper cap 4 is correctly installed on the core grid 6. A spindle with a conical head and a flange 12a at the bottom is slidably fitted into a bearing 13 provided concentrically with the air conduit 21, and the flange 12a and the bearing 1
3, a spring 14 is installed between it. Further, the spindle ±I has a concentric hole 12b, and a spring 1 is inserted into this hole 12b.
6 is loosely fitted, and the pin 15 is slidably fitted. Further, a stopper 17 is provided to regulate the positions of the spindle ±2 and the pin 15 when they are free. Further, a plurality of air holes 18 are provided in each of the bearing 13 and the stopper 17. In the air outlet configured as described above, when the air outlet is free, the spindle spindle and pin 15 move to positions where they respectively abut against the stopper 17 due to the repulsive forces of the springs 14 and 16, and the air is sent through the air conduit 21. The pressure-regulated air is discharged from the lower end of the air outlet. In addition, when the shipper cap 4 is correctly attached to the core grate 6, the pin 15 is attached to the core grate due to the shipper cap's own weight.
It is pushed by the top surface of the child and moves to the position shown. This movement is transmitted to the spindle ±λ via the spring 16, which moves upward in the figure while compressing the spring 14, and its conical top abuts the lower end of the air conduit 21, sealing the air conduit 21. At this time, since a spring 16 is interposed between the pin 15 and the spindle J prong, the pin 15 is
It will not be deformed or destroyed by force applied to it. Next, FIG. 4 is a cross-sectional view showing another embodiment of the air outlet port, showing the state when the shipper cap 4 is correctly installed on the core grid 6.

A counterbore hole 30 with a large diameter is provided on the bottom of the side wall of the shipper cap 4 concentrically with the air conduit 21, and a packing 31 made of relatively good radiation resistance, for example silicone rubber, and having a hole in the center is inserted into the counterbore hole as appropriate. Attach the cap so that it protrudes from the bottom of the shipper cap 4 by the compression amount. In the air outlet configured in this way, when the air outlet is free, the pressure-regulated air sent through the air conduit 21 is released from the lower end,
When the shipper cap 4 is properly mounted on the core grate 6, the air outlet port is sealed by the upper surface of the core grate and the packing 31. Next, the operation and effect of the shipper cap attachment status confirmation device constructed as described above will be explained with reference to FIGS. 2, 3, and 4.

The shipper cap 4 is installed on the core grate 6, and the pressure regulating valve 2 is installed.
The air regulated to the pressure P1 in step 3 is sent from the air pipe 25 to the air outlet through the pipe joint 20 and the air conduit 21. At this time, if the shipper cap 4 is correctly installed on the core grate 6, all air outlet ports will be sealed.
Since the air pressure in the pressure switch 24 rises to near the set pressure P1 of the pressure regulating valve 23 and exceeds the operating pressure P2 of the pressure switch 24, the pressure switch 24 is activated, and this signal confirms that the shipper cap 4 is correctly installed. . If the shipper cap 4 is not installed correctly, one or more of the air outlets will not be sealed, and the air pressure at the pressure switch 24 will not rise above a pressure close to the core pressure H. Since the operating pressure P2 has not been reached and therefore no signal is output from the pressure switch, it can be determined that the shipper cap 4 is not installed normally. As described in detail above, according to the shipper cap attachment status confirmation device of the present invention, it is possible to determine whether or not the shipper cap attachment status is good or bad much more accurately than visual confirmation, so the problem of radiation exposure of supervisors is solved, and It can contribute to improving the efficiency of damaged fuel inspection and measurement accuracy.

Furthermore, since the air outlet is constructed so that a material with sufficient water resistance and radiation resistance can be selected, there is no problem in practical use. It should be noted that the device of the present invention is not limited to the shipper cap, but can be applied to an internal shell attached to the inside of the shipper cap to obtain exactly the same effect.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the main part of the upper part of the fuel assembly in the core to explain the method of detecting damaged fuel, FIG. The figures are cross-sectional views showing different embodiments of the air outlet used in the apparatus of FIG. 2, respectively. 4... Shipper cap, 6... Core lattice, ±± air outlet, ±I... Spindle, 14
, 16... Spring, 15... Zen, 20...
... Pipe joint, 21 ... Air conduit, 22 ...
- Pressurized air source, 23... Pressure regulating valve, 24...
...Pressure switch, 25...Air piping] pipe, 31
······rubber seal.

Claims (1)

[Claims] 1. A shipper cap equipped with air outlets each having a plurality of sealing mechanisms provided on the bottom of the side wall and an air conduit connected to these air outlets and converged into one pipe joint, and one end of which is equipped with pressurized air. a pressure regulating valve and a pressure switch are provided on a pipe line outside the reactor core, and the other end is connected to a pipe joint provided in the shipper cap, and the set pressure of the pressure regulating valve is set when the shipper cap The pressure is an appropriate pressure that is higher than the reactor water pressure that the bottom face of the grate receives when it is correctly installed in the grate, and the operating pressure of the pressure switch is lower than the set pressure of the pressure regulating valve and higher than the reactor water pressure. A device to check the installation status of the shipper cap.