JPH0634074B2 - Fuel channel deformation monitoring system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a fuel channel box deformation monitor for monitoring deformation of a fuel channel box of a fuel assembly of a boiling water reactor (hereinafter referred to as BWR). Regarding the device.

(Prior Art) Generally, the core of a BWR is composed of a plurality of fuel assemblies, control rods, and the like. Therefore, the configuration will be described with reference to FIGS. 8 and 9. In FIG. 8, reference numeral 1 is a fuel assembly, and this fuel assembly 1 is constructed by loading a plurality of fuel rods 3 in a fuel channel box 2 as shown in FIG. The fuel channel box 2 is made of, for example, a zirconium alloy. The upper and lower ends of the fuel rod 3 are supported by an upper tie plate and a lower tie plate (not shown), and an intermediate position between them is held by a spacer. As shown in FIG. 8, the fuel assembly 1 having the above-mentioned structure is used for the upper grid plate 4 1
First, load four bodies, and insert the control rod 5 with a cross-shaped cross section at the center position. This is the unit cell 6. In FIG. 8, reference numeral 7 indicates a gap between the fuel assemblies 1 , and reference numeral 5a indicates a roller attached to the tip of the control rod 5.

In the above structure, the fuel assembly 1 is under severe conditions of high temperature, high pressure, and high radiation, so that the channel box 2 is subject to creep deformation, deformation due to neutron irradiation, and the like. This is shown in FIGS. 10 and 11. FIG. 10 shows a state in which the fuel channel box 2 bulges outward, and FIG. 11 shows a state in which bending occurs in the axial direction.

By the way, the control rod 7 is driven by a control rod drive mechanism to be inserted into or pulled out from the core. At this time, if the fuel channel box 2 is deformed as described above, the gap between the control rod 7 and the fuel channel box 2 of each fuel assembly 1 becomes extremely narrow, and the control rod drive mechanism controls the gap. When trying to insert the rod, it is expected that the control rod 7 will contact the fuel channel box 2. When such a situation occurs, it becomes impossible to control the control rod 7 and thus the core power.

Focusing on such a point, conventionally, when the fuel channel box 2 is used for a long period of time, the deformation amount of each fuel channel box 2 is measured to prevent the above-mentioned situation. The term "use of the fuel channel box 2 for a long time" means that the fuel channel box 2 was conventionally disposed of with the life of the fuel rods 3 etc., but it is reused as much as possible to reduce the cost. Is what you are trying to do.

However, the conventional deformation amount measurement is carried out by removing the fuel channel box 2 and carrying it into the fuel pool installed at the upper part of the reactor and performing remote control there. Therefore, it takes a long time for the measurement and the core is loaded. It has not been possible in time to make such a measurement for all the fuel channel boxes 2 that have been installed. Moreover, the conventional measurement was not performed by directly monitoring the core, but was indirectly performed through various calculations and was not very reliable.

(Problems to be Solved by the Invention) As described above, in the conventional case, the fuel channel box 2
There is a problem in that the reliability of the deformation amount measurement is low, and the measurement takes a long time, and the present invention was made on the basis of this point. It is an object of the present invention to provide a fuel channel box deformation monitoring device capable of performing high deformation amount measurement.

[Configuration of the Invention] (Means for Solving the Problems) That is, the fuel channel box deformation amount monitoring device according to the present invention is a control rod drive mechanism for driving control rods arranged one in four fuel assemblies. A measurement unit that measures the change in frictional force between the control rod and the fuel channel box of the fuel assembly that is mounted, and the fuel channel box with the lapse of time calculated based on the measurement signal and accumulated data from this measurement unit. It is characterized by comprising a deformation amount calculation unit for calculating the deformation amount and an output unit for outputting the result obtained by the deformation amount calculation unit.

(Function) In other words, the fuel channel box is deformed,
The fuel channel box and the control rod come to interfere with each other, and the frictional force between them (when the control rod is driven) changes due to the interference. Therefore, the change of the frictional force is measured by the measuring unit, the deformation amount is calculated based on the data accumulated by the deformation amount calculating unit to calculate the deformation amount with time, and this is output by the output unit. .

(Embodiment) An embodiment of the present invention will be described below with reference to FIGS. 1 to 7. The same parts as those of the prior art are designated by the same reference numerals and the description thereof will be omitted. Reference numeral 11 in the drawing denotes a control rod drive mechanism, and the control rod 5 is connected to the tip of the piston 12 of the control rod drive mechanism 11. Pressure switches 14 and 15 are installed on the upper surface side and the lower surface side of the piston 12 of the housing 13 of the control rod drive mechanism 11, respectively. The difference between the outputs of these two pressure switches 14 and 15 is a differential pressure signal (meaning the pressure difference between the upper and lower surfaces), which is output to the deformation amount calculator 16 as shown in FIG. The deformation amount calculation unit 16 calculates and processes the input differential pressure signal to calculate the deformation amount of the fuel channel box 2, and outputs it from the output unit (for example, the printing device) 17.

Here, the reason why the differential pressure detection by the pressure switches 14 and 15 leads to the measurement of the deformation amount of the fuel channel box 2 will be described. As described above, the control rod 5 is inserted into the core by raising the piston 12 of the control rod drive mechanism 11, and the driving water drives the piston 12. This drive water is made to act on the lower surface side of the piston 12 to raise the piston 12. The piston 12 that has risen rises slightly above the target position and then stops at the target position by natural fall. Such an operation is called settling, and the differential pressure between the upper and lower surfaces of the piston 12 at that time is called settling differential pressure. Assuming that the fuel channel box 2 is deformed on the plate and comes into contact with the control rod 5, the control rod 5 and the fuel channel box 2 interfere with each other to increase the frictional force. When the friction force increases, during the settling operation,
That is, the pressure acting on the piston 5 when the control rod 5 falls naturally decreases. This is also a reduction in settling differential pressure. Therefore, it is possible to detect that the fuel channel box 2 is deformed by detecting the pressure on the upper and lower surfaces of the piston 12, calculating the differential pressure, and detecting that the differential pressure has decreased. Also, the amount of deformation can be controlled by the degree of the reduction.

The measured differential pressure is stored in the deformation amount calculation unit 16 for each control rod and for each measurement. Further, the deformation amount calculation unit 16 stores in advance a database obtained by an interference test between the control rod 5 and the fuel channel box 2, and the deformation amount is calculated based on this database.

Therefore, an example of the above interference test is shown in FIG. FIG. 3 shows a pattern of the result of the interference test, in which the position of the piston 12 is plotted on the horizontal axis and the differential pressure is plotted on the vertical axis. First, the line a shows the case where there is no frictional force, that is, the case where there is no interference between the control rod 5 and the fuel channel box 2, and the line b shows the case where the interference between the control rod 5 and the fuel channel box 2 is small. Moreover, the line diagram c is the final stage where the interference between the two is large. As is apparent from this figure, when there is no interference, the differential pressure is substantially constant regardless of the position of the piston 12. At the initial stage of the interference, the pressure difference in the central portion is reduced, which causes the fuel channel box 2 to deform near the center thereof, causing interference with the control rod 5 (particularly the roller 5a that is most protruding). It means that you are doing. At the end of the interference period, the differential pressure at the central portion is zero, which means that settling is impossible near the central position of the control rod 5. Diagram b
In both of the cases of c and c, the differential pressure is recovered at the tip part, which means that the roller 5a is in the fuel channel box 2
It is due to passing through the central part (at the point where the deformation is largest). A database patterned in this way is already stored, and it is possible to determine the amount of deformation and its position by comparing the actually measured value with this database.

Next is the specification of the fuel channel box 2. That is, the control rod 5 is inserted between the four fuel assemblies 1 , and therefore it is necessary to specify which fuel channel box 2 of the four fuel assemblies 1 is interfering with. This will be described with reference to FIGS. 4 and 5. First, FIG. 4 (A) shows the case where there is no interference between the control rod 5 and the fuel channel box 2, and it is assumed that the state is changed to the state shown in FIG. 4 (B). This control rod 5 is expected to be interfering with the fuel channel box 2 of any of the fuel assembly 1 of the fuel assembly 1 of 4 body. Here, these four fuel assemblies 1 are referred to as e, f, g and d, respectively, as shown in FIG. 4 (C). When the fuel is exchanged, the four fuel assemblies e,
f, g and d are arranged in separate unit cells, and the differential pressure is measured again in that state. As a result, if the results shown in FIGS. 5A to 5D are obtained, it is possible to specify that the fuel assembly in which the deformation has occurred is g.
Even if it cannot be specified by one refueling, it is easy to estimate if the data is accumulated in consideration of the shuffling (movement) history for each refueling. Further, since it takes a long time from the occurrence of a slight change in frictional force until the settling operation is disturbed, there is no problem even if the estimation takes a certain amount of time.

In this way, the deformation amount calculation unit 16 specifies the deformation amount and the fuel channel box 2 based on the differential pressure. The result is output by the output unit 17.

According to this embodiment, the following effects can be obtained.

(1) That is, according to the monitoring device of the present embodiment, the deformation amounts of the fuel channel boxes 2 of all the fuel assemblies 1 can be grasped at any time and can be stored. As a result, the life of the fuel channel box 2 can be accurately grasped, and the fuel channel box 2 can be used to the maximum extent based on the data.

(2) Further, the monitoring work is extremely easy, the time required for the work is significantly shortened, and the movability can be improved.

(3) Further, since the measurement according to the present embodiment is a direct measurement, its reliability is sufficiently high.

Next, another embodiment will be described with reference to FIGS. 6 and 7. First, FIG. 6 shows the control rod drive mechanism 11
The pressure transmitting pipes 23 are connected to the inserting driving water pipe 21 and the extracting driving water pipe 22, respectively, and the pressure converter 24 is connected to these pressure transmitting pipes 23. Is measured. Further, FIG. 7 shows the case of the electric control rod drive mechanism 11 ', in which the torque change of the electric motor 25 is measured by the torque change measuring device 26. In any of these cases, the calculation is the same as in the case of the one embodiment. Reference numeral 27 in the figure indicates a reactor pressure vessel. Therefore, the same effect as that of the above-mentioned embodiment is obtained.

It should be noted that the detection of the differential pressure and the detection of the torque change are not limited to during settling, but may be during normal driving.

[Effects of the Invention] As described in detail above, according to the fuel channel box deformation monitoring device of the present invention, the deformation amount of all the fuel channel boxes is measured directly and at any time with a simple configuration and simple operation. Therefore, the management of the fuel channel box becomes easy and reliable, which is extremely effective in maintaining the soundness of the plant and reducing the cost.

[Brief description of drawings]

1 to 4 are views showing an embodiment of the present invention.
FIG. 4 is a diagram showing a mounting state of a pressure switch, FIG. 2 is a diagram showing a configuration of a calculation unit and an output unit, FIG. 3 is a diagram showing an example of a database, and FIGS. 4A to 4C and 5 are shown. (A) to (D) are views showing the specification of the fuel channel box, FIGS. 6 and 7 are views showing a control rod drive mechanism and its vicinity according to another embodiment, and FIGS. 8 to 11 are FIG. 8 is a view used for explaining the conventional example, FIG. 8 is a plan view showing a part of the core, FIG. 9 is a perspective view of a fuel channel box,
10 and 11 are views showing modifications of the fuel channel box. 1 ... Fuel assembly, 2 ... Fuel channel box, 5 ...
... control rod, 11 ... control rod drive mechanism, 14, 15 ... pressure switch, 16 ... deformation amount calculation unit, 17 ... output unit.

Claims (3)

[Claims] 1. A measuring unit attached to a control rod drive mechanism for driving a control rod arranged in one of four fuel assemblies, for measuring a change in frictional force between the control rod and the fuel channel box of the fuel assembly. , A deformation amount calculation unit that calculates the deformation amount of the fuel channel box over time by calculating based on the measurement signal from this measurement unit and the accumulated data, and outputs the result obtained by this deformation amount calculation unit And a fuel channel box deformation monitoring device. 2. The fuel according to claim 1, wherein the measuring unit measures the change in frictional force by measuring the pressure difference between the upper and lower surfaces of the piston of the control rod drive mechanism. Channel box deformation monitoring device. 3. The friction measuring device according to claim 1, wherein the measuring unit measures a frictional force change by measuring a torque change of an electric motor for vertically moving a piston of a control rod drive mechanism. Fuel channel box deformation monitoring device.