JPS5925996B2 - Damaged fuel detection device in nuclear reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a device for detecting damaged fuel in a nuclear reactor, and particularly to a device for detecting damaged fuel suitable for automating the inspection of fuel assemblies.

Since the fuel assemblies installed in the core of a nuclear reactor are at risk of being damaged during long-term use, the reactor has traditionally been shut down periodically and inspected for abnormalities in the fuel assemblies. things are being done.

The conventional inspection method will be explained based on FIG. It is installed on the grid plate 6.

Next, air is supplied into the cap 5 from an air supply source (not shown) through the air supply pipe 3.

In this state, by looking into the reactor core from above the floor 7 and visually observing that bubbles are coming out evenly from the notches at the four corners of the cap 5, it is confirmed that the device of the cap 5 is complete, At the same time, confirm that the cooling water levels between each fuel assembly 2 are independent.

Thereafter, sample water is collected from each fuel assembly 2 through the sampling tube 4 and analyzed to detect damaged fuel.

As described above, in the conventional detection method, it is necessary to visually observe the equipment condition of the cap 5 before sampling the sample water. If the transparency of the cooling water is reduced, or if there are ripples or light reflections on the surface of the cooling water, visual inspection becomes extremely difficult.

The present invention has been made to eliminate the above-mentioned disadvantages of conventional methods.

That is, the present invention automatically checks the capping device on the fuel assembly and that the cooling water level is independent for each fuel assembly, and then automatically collects sample water. The object of the present invention is to provide a fuel damage detection device.

Hereinafter, the details of the embodiments of the present invention shown in FIG. 2 and subsequent figures will be explained.

In FIGS. 2 and 3, a box-shaped cap 10 that is placed over the upper end of the fuel assembly 2 contains four box-shaped inner caps 11 that isolate each fuel assembly 2 from each other.

This inner cap is provided with a guide pipe 12 at the upper end, and the inner cap 11 and the sampling tube 1 inserted therein.
3 has a structure that allows it to slide vertically along the guide pipe 12.

Each sampling tube 13 is led to the floor 7 by a tube 14, and connected to a pump 15 installed there for sucking up sample water.

An air supply pipe 16 is opened in the cap 10, and an air discharge pipe 17 for water depth measurement is opened in the upper surface of the cap.

These air supply pipes 16 and air discharge pipes 17 are guided onto the floor γ by tubes 18 and 19, respectively, and at the tips of these tubes there are flow meters 20 for controlling and monitoring the pressure and flow rate of the supplied air, respectively. 21, pressure gauge 22, 23, pressure reducing valve 24, 25, and solenoid valve 26 for supplying and stopping air.
27 are connected in order.

A cross-shaped guide plate 28 is provided inside the cap 10 to guide its installation, and a guide plate 29 is provided inside each inner cap 11 to guide its installation.

Detection devices 30 for detecting the fit of the cap 10 are fixed to four locations on the outer wall of the cap 10.

This detection device has a cap 10 as illustrated in FIG.
The cylinder 31 is fixed to the cylinder 31, and the hollow piston 32 is built into the cylinder 31. The hollow piston is always subjected to a downward force by a spring 33.

The push rod 34 fixed to the lower end of the hollow piston is the cylinder 3
It protrudes downward through a through hole 31b provided in the bottom surface of the cap 1, and its lower end has a length sufficient to contact the upper surface of the upper lattice plate 6 and push up the hollow piston 32 when the cap is inserted.

31a indicates an air vent hole.

The hollow piston 32 includes a rubber packing 35 that closes the opening thereof, a rubber receiver 36 that backs up the rubber packing 35, and a spring 37 that constantly presses the rubber receiver 36 upward.

A water-sealing pipe 38 is fixed to the upper part of the cylinder 31 and has a lower end that is water-sealed by contacting the rubber packing 35 when the hollow piston 32 is raised.

The tip of the tube 39 attached to the upper end of this pipe is the second
As shown in the figure, they are grouped into four pieces on the floor 7,
It is sequentially connected to a pressure gauge 40 and a pressure reducing valve 41 for controlling and monitoring the pressure of the supplied air.

The pressure gauge 40 is configured to send a signal 42 to the solenoid valves 26 and 27 to operate them when the set pressure is reached, and also a differential pressure gauge 4 provided between the tubes 18 and 19.
3 sends a signal 44 to the pump 15 when the set pressure is reached;
It is configured to operate this.

The operation of the apparatus of the present invention constructed as described above is as follows.

First, when the cap 10 is gradually lowered from above the core onto the four fuel assemblies 2 in the lattice using a lifting device (not shown), the guide plate 29 in the middle cap 11 moves the fuel assemblies 2 Guided by the handle, approximate positioning is performed.

When the cap 10 is lowered further, the cross-shaped guide plate 28 built into the cap 10 is inserted into the gap of the fuel assembly 2, and accurate positioning is performed, so the cap 10 is placed on the top surface of the upper grid plate 6. Lower it until you reach it.

At this time, when the lower end of the push rod 34 of the wearability detection device 30 comes into contact with the upper surface of the upper grid plate 6, the piston 32 is pushed up by the push rod 34 as shown in FIG. Press the lower end of the holder to close it.

33.degree. 37 functions as a double bar, and even if there is a slight change in height on the upper surface of the upper lattice plate that the push rod touches, this will be absorbed.

Next, the pressure reducing valve 41 is operated to apply the set pressure to the wearability detection device 30 through the tube 39, and the pressure is left for a certain period of time.

During this time, if it is confirmed that there is no pressure drop using the pressure gauge 40, it is determined that the cap 10 has been properly installed.

Also, the signal 42 from the pressure gauge 40 is sent to the solenoid valves 26,27.

When the solenoid valve 26 operates, air at a preset pressure is sent into the cap 10 through the tube 18, and the cooling water in the air is pumped into the area below the upper edge of the fuel channel and below the cap 10. Press down to the notch on the edge.

Similarly, the solenoid valve 27 sends air at a preset pressure through the tube 19 and releases it from the air release pipe 1γ.

Since the air outlet of the air discharge pipe 17 and the air outlet from the cap 10 are separated by a certain distance in the vertical direction, a difference in static pressure occurs, and a difference in air pressure also occurs.

Therefore, the differential pressure between the indicated pressure inside the cap 10 and the indicated pressure 2 of the pressure gauge 23 caused by air discharge at the upper end of the cap 10 is measured with the differential pressure gauge 43, and when this reaches the set pressure, the cooling water of each fuel assembly 2 is It is determined that the liquid level has become independent, and a signal 44 indicating that sample collection is possible is sent to the pump 15.

This causes the pump to operate and sample water is collected through the sampling tube 13.

Once the damaged fuel inspection within one grid is completed in this way,
By raising the cap 10 and moving it onto the next fuel assembly and repeating the same procedure as above, all fuel assemblies 2 in the reactor can be automatically inspected for damaged fuel.

As described above, according to the present invention, it is possible to automatically check the fit of the cap and the independence of the cooling water level before sampling the sample, thereby saving labor and shortening the working time. can be achieved.

In addition, the risk of radiation exposure to workers is reduced, and sampling preparation work can be completed quickly and reliably without being affected by a decrease in the clarity of the cooling water or ripples on the water surface.

Therefore, the total time required to detect damage to nuclear fuel can be shortened, and accuracy can be improved.

In addition, the present invention utilizes changes in air pressure to detect the mounting position of the cap and the reactor water independently for each fuel assembly, so if air leaks occur in the piping of the detection device, it will be detected from the piping. The leak appears in the form of bubbles, and the failure location can be easily detected from its appearance.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of the main parts explaining a conventional nuclear fuel damage detection method, FIG. 2 is a vertical cross-sectional view of the main parts showing an embodiment of the device of the present invention, and FIG. 4 and 5 are longitudinal sectional views showing an embodiment of the wearability detection device used in the present invention, and FIGS.
The figure shows the state before installation, and FIG. 5 shows the state after installation is completed. 1... Cooling water surface, 2... Fuel assembly, 3... Air supply pipe, 4. °13°...Sampling tube, 5,10.
... Cap, 6... Upper grid plate, 7... Floor, 11
...Inner cap, 12...Guide pipe, 14, 1B
, 19.39...Tube, 15...Pump, 16
...Air supply pipe, 17...Air discharge pipe, 20.21
...Flowmeter, 22゜23.40...Pressure gauge, 24,
25.41...Pressure reducing valve, 26.27...Solenoid valve, 2
8.29...Guide plate, 3゜--Wearability detection device, 3
DESCRIPTION OF SYMBOLS 1...Cylinder, 31a...Through hole, 31b...Air vent hole, 32...Hollow piston, 33, 37...
・Spring, 34...Push rod, 35...Rubber gasket,
36...Rubber receiver, 38...Water seal pipe, 42°44
···signal.

Claims (1)

[Claims] 1. A cap with built-in inner caps equal to the number of fuel assemblies inserted in one grid of the reactor, and a cap that is attached to the four sides of this cap and whose tip is closed at the fixed position of the cap and communicates with the water seal pipe. An attachment detection device that determines whether the cap is correctly attached to the fuel assembly based on pressure changes inside the tube, a tube that communicates with the air supply pipe that opens inside the cap, and an air release that opens outside the cap. A differential pressure gauge that detects that the cooling water level is separated for each fuel assembly by the differential pressure between the tubes communicating with the pipe, and a device that starts collecting sample water based on the output of this differential pressure gauge. A device for detecting damaged fuel in a nuclear reactor, comprising: