JPH026010B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a support grid spring force measuring sensor for measuring the spring force of a support grid elastic support portion of a fuel assembly for a nuclear reactor.

Fuel assemblies loaded in pressurized water type light water reactors currently in use are constructed as shown in FIGS. 1 to 4. That is, an upper nozzle 1 and a lower nozzle 2 are arranged vertically apart from each other, and a strap 3 is arranged with a predetermined interval between them.
A plurality of support grids 5 having grid spaces (cells) 4 formed by a plurality of support grids 5 are inserted into the grid spaces 4 of these support grids 5 at predetermined intervals, and are fixed to fixed parts of the support grid 5, and It has a control rod guide tube 6 whose upper and lower ends are connected to an upper nozzle 1 and a lower nozzle 2, a large number of fuel pellets 8 and a pressing spring 9 sealed in a cladding tube 7, and a lattice of a support lattice 5. It is composed of a large number of fuel rods 12 that are inserted into predetermined locations in the space 4 and supported by rigid support portions (dimples) 10 and elastic support portions (spring portions) 11 of the support grid 5.

The holding force at the contact portion within each cell 4 of the support grid 5 that supports the fuel rods 12 is due to thermal expansion of the cladding tube 7 and the support grid 5, irradiation growth, and a decrease in the spring force of the spring portion due to irradiation (also known as relaxation). It is set in consideration of various factors such as the flow rate and flow velocity of the coolant. If this holding force is excessive, the fuel rods 12 inserted into the support grid 5 are likely to be scratched during assembly of the fuel assembly, and the fuel rods 12 may be bent significantly during combustion. On the contrary, if this holding force is too small, the spring portion 11 due to irradiation
Due to relaxation, the holding force for the fuel rods 12 is insufficient, and vibration caused by the cooling water flow causes relative movement between the contact portions of the fuel rods 12 and the support grid 5 and between the fuel rods, resulting in so-called fretting wear. , which rapidly shortens the life of the cladding tube 7.

As described above, the holding force of the support grid 5 is an important factor that affects the performance of the fuel assembly, but since there is no suitable means for measuring this holding force, it has not been possible to actually measure it. The pushing force of the simulated fuel rods etc. into the support grid 5 was measured, and the holding force (also called restraining force) for the actual fuel rods could be indirectly estimated from this pushing force.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a support grid spring force measurement sensor that can directly measure the spring force of the spring portion in each cell of the support grid.

An embodiment of the present invention will be described below with reference to FIGS. 5 to 7. 21 in FIGS. 5 and 6 is a sensor, and this sensor 21 is the deformable bar 2.
2. It consists of a drive shaft 23 and an expansion roller mechanism 24.

The deformable bar 22 has a rectangular cylindrical part 25 formed at the top thereof, and one side of the rectangular cylindrical part 25 extending downward to form a plate-shaped part (plate member) 26, and is made of stainless steel. It's summery. A substantially central portion of the plate-shaped portion 26 is formed particularly thin and serves as a leaf spring portion 27 . The plate-shaped portion 26 has a width 2 of most of the width excluding the upper part thereof.
6a is smaller than the outer diameter of the fuel rod. Further, a substantially rectangular recess 28 is formed on the lower inner surface of the plate-shaped portion 26, and two strain gauges 29, 29 are attached to the bottom surface of the recess 28 spaced apart from each other in the vertical direction. These two strain gauges 29, 29
The center between them is made to coincide with the center between the upper and lower ends of the recess 28. Furthermore, guide grooves 30 extending vertically are formed on both side surfaces of the lower end of the plate-shaped portion 26 .

A flanged bush 31 is fitted into the rectangular cylindrical portion 25 of the deformable bar 22, and the flange 32 is engaged with the upper end surface of the rectangular cylindrical portion 25. A drive shaft (long member) 23 is fitted into the flanged bush 31 . Threaded portions 33 and 34 are formed at the upper and lower ends of the drive shaft 23, respectively. Nuts 35, 35 are screwed into the threaded portion 33.

The expansion roller mechanism 24 is connected to the threaded portion 34 . This expansion roller mechanism 24 consists of an elastic connecting member 36 and a roller mounting body 37. The elastic connecting member 36 has a female threaded portion 38 at its upper portion.
A connecting portion with a male threaded portion 39 is formed at the bottom.
A thin plate-shaped plate spring portion 40 is formed between these two connecting portions, and the female threaded portion 38 is screwed into the threaded portion 34 of the drive shaft 23.
It is attached to the drive shaft 23 by a nut 41 screwed into the threaded portion 34 so as to be vertically adjustable.

The roller mounting body 37 includes a roller box 44 having a female threaded portion 42 and a fitting protrusion 43 shown in FIG.
and a roller 46 fitted into this roller box 44 and rotatably attached to this roller box 44 by a shaft 45. The roller box 44 has a fitting protrusion 43 fitted into the guide groove 30 of the deformation bar 22, a female threaded portion 42 screwed into the male threaded portion 39, and a nut 47 screwed into the male threaded portion 39 to connect the elastic connecting member 36. It is attached so that its vertical position can be adjusted freely.

Furthermore, a plate-shaped arm 48, for example, is fixed to a predetermined location of the rectangular tubular portion 25 of the deformable bar 22 by appropriate means. 5 in FIGS. 6 and 7 is a fuel assembly support grid into which the sensor 21 is inserted;
10 is its rigid support part (dimple), 11 is its elastic support part (spring part), and 4 is its lattice space (cell). The width 49 shown in FIG. 7 of the roller box 44 corresponds to the dimple 10 in the cell 4,
The distance 46a from the outer surface of the plate-like part 26 to the outer peripheral surface of the roller 46 which is the farthest from the outer surface of the plate-like part 26 in FIG.
is the same diameter as or slightly smaller than the outer diameter of the fuel rod. When the sensor 21 is inserted into the grid space 4 of the support grid 5, it is inserted slightly away from the rigid support part 10 so as not to damage the rigid support part 10. At this time, the square cylindrical part 25, the leaf spring part 27, the deformation bar 22
The surface on the rigid support portion 10 side is straight and processed to ensure accuracy during insertion. When measuring the spring force, the deformable bar 22 is connected to the upper and lower rigid supports 1.
0, the lower outer surface of the deformable bar 22 (left side surface in FIG. 6) moves toward the rigid support part with respect to the left side surface of the rectangular tubular part 25 in FIG. When the plate springs come into contact with the rigid support part, they become parallel with two inflection points at the plate spring 27 section. At this time, there is a slight gap between the left side surfaces of the square tubular part 25 and the lower part of the deformable bar 22 in FIG. The reason why the leaf spring part 40 is provided on the elastic connecting member 36 is to move the roller 46 to follow the elastic support part 11 in the same way as the leaf spring part 27 is provided on the deformable bar 22. The pushing force is also transmitted by this leaf spring 40.

Therefore, the thickness of these leaf spring parts 27 and 40 is set to be the minimum thickness necessary for inserting the sensor 21 into the grid space 4 of the support grid 5 and transmitting the pushing force of the roller 46 in order to improve measurement accuracy. There is.

Next, the operation of the support grid spring force measuring sensor configured as described above will be explained.

(1) First, place the support grid 5 at a predetermined location on the rigid support section 1.
0. Fix by appropriate means so that the elastic support part 11 is positioned in the state shown in FIG.

(2) Next, the arm 48 is driven by a suitable driving means to insert the lower end of the sensor 21 into the desired cell 4 as shown in FIG. At this time,
The plate-shaped portion 26 lightly contacts the surfaces of the upper and lower dimples 10, and the two strain gauges 2
The sensor 21 is located at a position where the center line M between 9 and 29 shown in FIG.
Adjust the position and fix it by appropriate means.

(3) Next, when the drive shaft 23 is lowered by a lifting tool (not shown) connected to the upper part of the drive shaft 23, the roller box 44 is moved to the elastic connecting member 36.
The roller 46 descends along the plate-shaped portion 26 through the
The outer circumferential surface of the spring portion 11 contacts the spring portion 11 .

(4) When the drive shaft 23 further descends and the shaft 45 reaches the height position of the peak of the chevron of the spring portion 11, the force applied between the upper and lower dimples 10 becomes maximum, deforming the plate-like portion 26. . This results in
Since the resistance values of the two strain gauges 29, 29 change, this change in resistance value causes the strain gauges 29, 2
It is indicated as a spring force to a strain gauge (not shown) connected to 9. Then, the spring force of the spring section 11 when the fuel rod is inserted between the dimple 10 and the spring section 11 is directly measured using the data from this strain meter.

(5) Next, after pulling up the drive shaft 23 by a suitable distance using a pulling tool, the arm 48 is driven upward to extract the sensor 21 from inside the cell 4.

(6) Thereafter, repeat the operations (2) to (5) above to measure the spring force of the flared portion 11 in the other cells 4.

In the above embodiment, the spring force of the spring portion 11 in each cell 4 is measured sequentially, but the sensor 21 is not limited to this.
A plurality of them may be arranged on the arm 48 in accordance with the arrangement pitch of the cells 4. In this way,
By the operations (2) to (5) above, the spring forces of the plurality of spring parts 11 can be measured simultaneously.

As explained above, according to the present invention, a long member is provided along one side of the elastic plate member that extends in the vertical direction and has a strain gauge attached to the lower end, and is connected to the long member. It has a roller and is movable up and down along the plate member, and is configured to move up and down the expansion roller mechanism with an elastic part formed in the middle part, so it is small and lightweight. The spring force of the spring part of the support grid can be directly measured in a short time, and since the roller only rolls into contact with the spring part of the support grid when measuring the spring force, damage and deterioration of this spring part can be prevented. be able to. Furthermore, by arranging a plurality of sensors, for example, on the arm, in accordance with the arrangement pitch of the cells of the support grid, it is possible to simultaneously measure the spring forces of the plurality of spring parts of the support grid.

[Brief explanation of drawings]

Fig. 1 is a partially cutaway sectional view showing an example of a nuclear reactor fuel assembly, Fig. 2 is a sectional view taken along the - line in Fig. 1, and Fig. 3 is an enlarged sectional view of the circular part in Fig. 2. FIG. 4 is a sectional view taken along the line - in FIG. 3, FIG. 5 is a front view showing an embodiment of the present invention, and FIG. 6 is a side sectional view showing the sensor inserted into the support grid. FIG. 7 is a view taken along the arrows in FIG. 4... Grid space (cell), 5... Support grid, 10...
Rigid support part (dimple), 11... Elastic support part (spring part), 22... Deformation bar, 23... Drive shaft (long member), 24... Expansion roller mechanism, 26... Plate-shaped part (plate member), 27, 40... Leaf spring part, 29... Strain gauge, 36... Elastic connection member, 37... Roller mounting body,
44...Rolla Box, 46...Lola.

Claims (1)

[Claims] 1. An elastic plate member extending in the vertical direction and having a strain gauge attached to the lower end, a long member provided on one side of the plate member so as to be movable up and down along the plate member, and a member connected to the long member. and is rotatably attached to a roller mounting body which is fitted into the plate member and is movable up and down along the plate member so that the outer peripheral surface protrudes from the roller mounting body on the opposite side to the plate member. and an elastic connecting member having an elastic portion formed in the intermediate portion thereof, and is characterized in that it is inserted into a support grid to deform the spring portion of the support grid and the plate member. Support grid spring force measurement sensor.