JPS645277Y2 - - Google Patents

Description

[Detailed description of the invention] (Field of industrial application) This invention is a control plate mounting device for controlling the leakage of coolant in the channel box in fuel assemblies, mainly for boiling water reactors. Regarding.

(Prior art) A fuel assembly for a boiling water reactor has a predetermined number of squarely arranged fuel rods supported at regular intervals by upper and lower tie plates and several stages of spacers in the middle, and a channel on the outside. To prevent fuel rods from burning out during reactor operation, coolant flows into the channel box from the lower tie plate side, passes between each fuel rod, and flows out from the upper tie plate. At this time, a portion of the coolant is also allowed to flow out through the leak hole provided in the lower tie plate and the gap between the lower tie plate and the channel box to prevent the water outside the channel box from boiling.

By the way, during the operation of a nuclear reactor, the gap between the lower tie plate and the channel box increases due to outward deformation due to the pressure difference between the inside and outside of the channel box and creep deformation due to neutron irradiation. The amount of leakage increases, and it becomes impossible to expect a cooling effect on the fuel rods.

In order to prevent this phenomenon, a leaf spring member in which a large number of slits and doglegged spring pieces (finger springs) are alternately formed is attached to the lower tie plate, and this leaf spring member is attached to a channel box. A device is generally known that suppresses the amount of coolant leaking by pressing the inner surface of the lower end of the channel box. However, in this device, the spring force of the finger spring must be strong so that it can follow the deformation of the channel box. This results in the channel box being pushed further apart, and the finger springs also become sagging due to the irradiation.
Since it becomes impossible to maintain a constant contact pressure, leakage prevention devices as shown in FIGS. 5 to 7 are used.

That is, recesses 1a having a width and depth capable of accommodating the control plate 3 are formed on the side peripheral surface of the lower tie plate 1 that supports a predetermined number of squarely arranged fuel rods n via lower end plugs, and each The recessed portion 1a is made of a thin plate of the required size as shown in FIG. At the top, there are several slightly elongated locking holes 3a that also serve as coolant inlets, and between them there are slits 3b for leaks from the upper edge to the center, and at the bottom, there are two or three locking holes 3a. A control plate 3 provided with horizontally long locking holes 3c is provided, and each vertically long locking hole of the control plate 3 is provided in the upper part of the recessed part 1a of the lower tie plate 1 in the longitudinal direction as shown in FIG. A stop plate 4 made of stainless steel with a horizontal protrusion 4a that fits loosely into the hole 3a is screwed at three places on the upper edge and two places on the protrusion, while a control plate is attached at the bottom as shown in Figure C. A retaining plate 5 having three oblong horizontal protrusions 5a that loosely fit into each of the oblong locking holes 3c of No. 3 is similarly screwed at three locations on the lower edge and at two locations on the protrusion, and the lower tie plate 1 is assembled. Relatively high-pressure coolant entering the channel box 2 from the side is allowed to flow into the inside of the control plate 3 through the upper locking hole 3a as shown by the arrow in FIG. The bulging part is moved outward as shown in the figure to bring the bulging part into contact with the inner surface of the channel box 2, closing the gap between the lower tie plate 1 and the channel box 2, and keeping the amount of coolant leaking from this part constant. That's what I do.

(Problems to be solved by the invention) Compared to the finger spring type, the control board used does not get in the way when the channel box is inserted into the fuel assembly, and the channel box does not have excessive expansion force. It has the advantage of being able to easily follow the deformation of the channel box without causing stress or settling, but the upper and lower stopper plates are usually made of stainless steel and have a thickness of 0.5 mm to 1 mm.
It is thin, 20mm to 30mm wide, about 10cm long, and the height of the protrusion is about 3mm to 4mm.
Because they are made by milling from a square piece of almost constant thickness, stress from machining remains on the stopper plate, and if used carelessly, it could cause damage to the reactor's high temperatures and high neutron irradiation. As a result, residual strain is released, causing the retaining plate to warp and become wavy, especially in the longitudinal direction, creating a portion that protrudes from the surface of the lower tie plate, which not only collides and impedes the insertion and insertion of the channel box. In the worst case, this will result in damage to the retaining plate and screw.

Therefore, in order to avoid such a phenomenon,
As shown in FIG. 5, the upper and lower retaining plates are screwed at the edges on both sides and at the center, and the intermediate portion is screwed at the protrusion that engages with the locking hole.

However, this method not only requires a large number of screws, making the assembly work cumbersome, but also causes variations in the degree of tightening, making it impossible to sufficiently prevent warping of the stopper plate.

Therefore, the present invention provides a coolant leakage control plate mounting device that does not require many fixing means, allows easy assembly of the stop plate, and sufficiently prevents warping.

(Means for Solving the Problems) Based on the above-mentioned purpose, in this invention, a large number of fuel rods arranged in a square arrangement are erected on the upper base plate of the lower tie plate, and the outside thereof is covered with a channel box. In a fuel assembly in which coolant is introduced from the lower end of the lower tie plate to cool each fuel rod and rise, recesses of the required width and depth are provided on the sides of the lower tie plate, and each recess is A hanging wall of the required length is provided on the upper edge of the part, and an upper bag groove approximately equal to the thickness of the stop plate is formed inside the wall, and the lower edge is approximately at the height of the lower flat part of the control plate. Each upright wall of matching height is provided, and a lower bag groove wider than the thickness of the control plate is formed inside each wall, and each recess has a flat upper and lower end and a lower tie plate in the center. A control plate with several locking holes and slits alternately arranged on the upper part of the bulge to match the outer surface of the control plate, and the lower flat part of each control plate is connected to the lower bag of each recess The horizontal protrusions provided on the flat plate part of the stop plate, whose upper part is bent into an L shape to form a raised edge, are loosely fitted into each locking hole of each control plate. It is characterized in that the upright edge is engaged with the upper bag groove of each recessed part, and the two horizontal protrusions on both sides are screwed to the lower tie plate.

(Function) During operation of the reactor, coolant flows into the lower tie plate from below, and a portion of it flows out of the channel box through the leak hole on the side of the tie plate, and coolant flows inside the lower tie plate. The coolant enters the inside of the channel box through the holes in the upper bedplate, cools the fuel rods, and rises.
A portion of the coolant flows inward through the locking holes, and the control plate abuts against the inner surface of the channel box due to the pressure difference between the inside and outside, sealing off the gap between the lower tie plate and the channel box.

At this time, since the lower flat part of the control plate is simply inserted into the lower bag groove of the recessed part, it can move freely and follow the deformation of the channel box.
Further, since the upper upstanding edge of the stop plate engages with the upper bag groove of the recessed portion, warping and deformation thereof is suppressed.

(Embodiment) An embodiment of this invention will be described with reference to FIGS. 1 to 3. Reference numeral 11 is a lower tie plate in the fuel assembly, and as usual, the lower end is provided with a support grid in the furnace. A large number of fuel rods arranged in a square arrangement are erected on the upper base plate (grid) through a lower end plug, A channel box 12 is fitted on the outside thereof.

A control plate 13 is provided on the side peripheral surface of the lower tie plate 11.
A recessed portion 11a having a width and depth capable of accommodating the
As shown in the figure, a relatively short hanging wall 15 is provided, and an upper bag groove 15a approximately equal to the thickness of the stopper plate 14 is formed inside the wall, and the lower edge of each recessed portion 11a has a surface. hanging wall 1
Upright walls 16 that match the surface of the control board 13 and have heights that approximately match the length of the lower flat part of the control board 13 are provided, and a lower bag groove 16a that is larger than the thickness of the control board 13 is provided inside them. are formed respectively.

As mentioned above, the control plate 13 is made of a thin plate material of the required size, and the upper and lower ends are flat, and the center part bulges out to match the surfaces of the hanging wall 15 and the upright wall 16 of the lower tie plate, forming an arcuate side surface. None, the upper part is provided with several slightly elongated locking holes 13a that also serve as coolant inflow ports, and the slit 13b is provided between them, but the lower part is provided with horizontally elongated locking holes as described above. is not provided.

Reference numeral 14 denotes a stop plate made of stainless steel, the upper end of which is bent in an L-shape toward the recess 11a of the lower tie plate 11, and is provided with an upright edge 14b to be engaged with the upper bag groove 15a. , the lower flat part is provided with several horizontal protrusions 14a that loosely engage with the locking holes 13a of the control plate 13, as in the prior art, and each of the second horizontal protrusions 14a from both ends has screws inserted therein. A hole 14c is bored.

Thus, the control plate 13 is disposed in each of the recesses 11a on the peripheral surface of the lower tie plate 11, with the bulge facing outward and the lower flat part fitting into the lower bag groove 16a. , their respective locking holes 1
3a, the horizontal protrusions 14a of the stopper plates 14 are loosely engaged with each other, and each stopper plate 14 is connected to the upright edge 14.
b is fitted into the upper bag groove 15a of the recessed part 11a, and the screw insertion hole 14 of the horizontal protrusion 14a on both sides
It is screwed to the lower tie plate 11 via c.

With this configuration, during operation of the nuclear reactor, coolant flows into the interior from the nose-shaped portion at the lower end of the lower tie plate 11, and a portion of the coolant flows into the channel through the leak hole 17 on the side of the tie plate. It flows out of the box 12. The coolant that has entered the inside of the lower tie plate 11 enters the inside of the channel box 12 through a hole (not shown) provided in the upper base plate, and rises while cooling the fuel rods n.
A part of the coolant flows into the inside of the control plate 13 through the locking hole 13a as indicated by the dotted line arrow in FIG.

Thus, the pressure of the coolant is highest inside the lower tie plate 11, then inside the channel box 12, and then outside the box 12. The same pressure will be applied to it, and a lower external pressure will be applied to its lower surface.

Therefore, the control plate 13 is oscillatingly moved to the position indicated by the dotted line in FIG. become.

At this time, each control plate 13 is loosely engaged with the horizontal protrusion 14a of the upper stop plate 14 through the locking hole 13a, and the lower flat part is connected to the tie plate 11.
Since the control plate 13 is freely inserted into the lower bag groove 16a, which is wider than the plate thickness formed in Due to the elastic deformation and free rocking of the channel box 12, the deformation that occurs during irradiation can be well compensated for, and the contact state with the channel box 12 is maintained to prevent leakage of coolant from the bottom side of the box in a constant state. Keep it.

Further, the upper part of each stop plate 14 that restrains the control plate 13 between them is bent into an L shape to provide rigidity, and the upright edge 14b is recessed into the recessed part 11a.
It engages with the upper bag groove 15a provided in the hanging wall 1.
5 suppresses warping and deformation, the upper edge of the stopper plate 14 does not protrude from the surface of the lower tie plate 11, and does not interfere with the insertion and insertion of the channel box 12 during regular fuel inspections. .

(Effect of the invention) As described above, in this invention, the lower flat part of the control plate disposed in each recess on the peripheral surface of the lower tie plate is fitted into the lower bag groove formed in each recess,
The stop plate for restraining the upper flat part has its upper part bent into an L-shape to provide a raised end edge, and the raised end edge is engaged with the upper bag groove of each recessed part, and the upper part is bent into an L shape, and the raised end edge is engaged with the upper bag groove of each recessed part.
Since the screws are fixed to the lower tie plate using only one horizontal protrusion, the number of retaining plates and screws for installing the control board can be reduced, making assembly of the control board extremely easy and efficient. In addition, it can sufficiently prevent the waving phenomenon in the longitudinal direction of the stop plate due to use, and since it does not protrude from the surface of the lower tie plate, it will not interfere with the insertion and insertion of channel boxes during periodic inspections. do not have.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of an embodiment of this invention. Figure 2 is a partially cutaway front view with the channel box removed. FIG. 3 is a sectional view taken along the line XX. FIG. 4 is a perspective view of the stop plate. FIG. 5 is a front view showing how a conventional control board is installed. FIG. 6 is a sectional view taken along the Y-Y line. FIG. 7A is a perspective view of the control board. Figures B and C are perspective views of the upper and lower stop plates. In the figure, 11...lower tie plate, 11a...
Recessed part, 12...Channel box, 13...
...control plate, 13a...locking hole, 13b...slit, 14...stopping plate, 14a...horizontal protrusion, 14
b... Standing edge, 15... Hanging wall, 15a... Upper bag groove, 16... Standing wall, 16a... Lower bag groove.

Claims (1)

[Scope of utility model registration request] A large number of fuel rods n arranged squarely are set upright on the upper base plate of the lower tie plate 11, the outside of which is covered with a channel box 12, coolant is introduced from the lower end of the lower tie plate 11, and each fuel rod n is In the fuel assembly, the lower tie plate 11 is provided with recesses 11a of a required width and depth on the side surfaces thereof, and a hanging wall of a required length is provided at the upper edge of each recess 11a. 15, and an upper bag groove 15a approximately equal to the plate thickness of the stop plate 14 is formed inside thereof, and an upright wall 16 having a height approximately equal to the height of the lower flat part of the control plate 13 is provided at the lower edge. A lower bag groove 16a wider than the thickness of the control plate 13 is formed inside each recessed part 11a. Control plates 13 each having several locking holes 13a and slits 13b alternately disposed on the upper part of the bulge to the extent that the bulge corresponds to A horizontal protrusion is inserted into each side bag groove 16a, and each locking hole 13a of each control plate 13 is provided with a horizontal protrusion provided on a flat part of a stop plate 14 whose upper portion is bent into an L shape to form a raised edge 14b. 14a, respectively, and the upright edge 14b is inserted into each recessed portion 11.
A mounting device for a coolant leakage control plate which engages with the upper bag groove 15a of a and screws two horizontal protrusions 14c on both sides to the lower tie plate 11.