JPH0140078Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a fuel rod end plug for sealing fuel pellets, a plenum spring, and an inert gas in a cladding tube.

[Prior Art] In general, fuel rods used in nuclear reactors include:
As shown in Fig. 4, a large number of fuel pellets 2... are inserted into a cladding tube 1, and plenum springs 3, 3 are installed at one or both ends of these fuel pellets 2... to prevent them from moving or being damaged. It is known that end plugs (fuel rod end plugs) 4 and 5 are welded and fixed to the ends of the cladding tube 1.

By the way, in the fuel rod having the above configuration, in order to prevent deformation of the cladding tube 1 due to external pressure inside the reactor and to improve heat transfer in the gap between the fuel pellets 2... and the cladding tube 1, It is necessary to fill in an inert gas such as helium gas. Therefore, a gas filling hole is formed inside one end plug 4.

That is, the end plug 4 is composed of a small diameter portion 7 in which the end plug body 6 is inserted into the cladding tube 1 and a large diameter portion 8 that projects to the outside of the cladding tube 1. As shown in FIG. 5, a gas filling hole 9 is formed, one end of which opens into the end surface of the small diameter portion 7, and the other end of which opens into the outer periphery of the large diameter portion 8.

When sealing an inert gas into the fuel rod having the above configuration, the end on the end plug 4 side is airtightly inserted into a pressure welding device (not shown) and fed into the pressure welding device. Then, inert gas is filled into the cladding tube 1 through the gas filling hole 9, and then the opening 9a of the gas filling hole 9 is sealed by welding, thereby sealing the inert gas inside the cladding tube. I'm trying to stop it.

[Problems to be solved by the invention] By the way, when sealing inert gas inside the cladding tube using the above-mentioned end plug, a pressurized atmosphere is required to prevent the inert gas inside the cladding tube from coming out. It is necessary to weld the opening of the gas filling hole inside. However, in a pressurized atmosphere, a normal arc is not generated and poor welding is likely to occur. This caused problems such as the risk of gas leakage.

This idea was made to solve the above problem, and after filling the cladding with inert gas,
It is an object of the present invention to provide an end plug for a fuel rod that can melt-seal the opening of an orifice under normal pressure, thereby preventing gas leakage from the fuel rod.

[Means for Solving the Problems] The fuel rod end plug according to this invention has a gas filling hole connected to a large diameter hole on the cladding tube side and a small diameter hole on the outside communicating with the large diameter hole. A valve body having a larger diameter than the small diameter hole is provided in the large diameter hole so as to be movable in the axial direction of the large diameter hole.

[Embodiment] FIGS. 1 and 2 are diagrams showing an embodiment of this invention.

In FIG. 1, reference numeral 10 indicates an end plug body. The end plug main body 10 has a cylindrical shape and is composed of a small diameter part 11 formed at one end and a large diameter part 12 formed at the other end. Small diameter part 11
The diameter of the cladding tube 3 is set to be slightly smaller than the inner diameter of the cladding tube 3, and the tip thereof is formed into a tapered shape. On the other hand, the large diameter portion 12 has a diameter set to be approximately the same as the diameter of the cladding tube 3, and has a tapered tip. Furthermore, a gas filling hole 13 is formed inside the end plug body 10. This gas filling hole 13 is composed of a small diameter hole 14 that opens at the end surface of the large diameter section 12 and a large diameter hole 15 that opens at the end surface of the small diameter section 11 . Large diameter hole 15
The bottom surface 15a is formed into a concave curved surface along a spherical surface.

Further, a valve body 16 is inserted into the large diameter hole portion 15 of the gas filling hole 13 so as to be movable in the axial direction thereof. The radius of the valve body 16 is set to be approximately the same as the radius of curvature of the bottom surface 15a of the large-diameter hole 15, and by contacting the bottom surface 15a, the gap between the large-diameter hole 15 and the small-diameter hole 14 is It is designed to be airtightly shielded.

Further, a rod member 17 is fixed to the surface of the valve body 16 facing the small diameter hole portion 14 side. This rod member 1
7 is formed to have a slightly smaller diameter than the small diameter hole 14 and to be slightly longer than the small diameter hole 14, and when the rod member 17 is inserted into the small diameter hole 14, the valve body 16 is inserted into the bottom surface 15a. The tip end protrudes outside the small diameter hole 14 when brought into contact with the small diameter hole 14.

Further, a protrusion (locking part) 15b that protrudes radially inward is formed on the opening periphery of the large diameter hole 15 to prevent the valve body 16 from coming out from inside the gas filling hole 13. It's getting old. Of course, this protrusion 15b is not provided over the entire circumference in the cross section of the large diameter hole 15, and therefore, when the valve body 16 is engaged with this protrusion 15b, gas is supplied to the large diameter hole. A gap is formed between the protrusions 15b to allow the flow from the cladding tube 3 to the cladding tube 3.

The fuel rod end plug having the above structure has its small diameter portion 11 fitted into the open end of the cladding tube, and the large diameter portion 12 and the cladding tube near the abutting portion are welded and fixed to the open end of the cladding tube. The occlusion is fixed.

Then, in order to fill the cladding tube to which the fuel rod end plug is fixed with an inert gas, the following procedure is performed.

First, the end on the end plug 4 side of the cladding tube to which the end plugs 4 and 5 are fixed is welded using a pressure welding device (not shown).
Airtightly insert the inert gas into the gas filling hole 1.
Pressurize and fill the cladding tube through opening 3. At this time, the inert gas is sent into the cladding tube through the gap between the small diameter hole 14 and the rod member 17, but the pressure of the gas pushes the valve body 16 toward the cladding tube 3 side, causing the protrusion 15
b, and gas is sent into the cladding tube 3 through the gap between the protrusions 15b. When the gas pressure in the cladding tube reaches a predetermined pressure, filling is stopped and the pressure in the pressure welding device is returned to normal pressure. Then, the valve body 16 is pressed by the gas pressure within the cladding tube, and the valve body 16 moves toward the small diameter hole portion 14 side. Then, as shown in FIG. 2, the valve body 16 comes into close contact with the bottom surface 15a of the large diameter hole 15, and the inside of the cladding tube becomes airtight. At this time, the tip of the rod member 17 slightly protrudes from the opening.

Next, the small diameter hole 14 is welded using a welding torch 18 of a pressure welding device to seal inert gas inside the cladding tube. In this case, the welding work is performed using the welding torch 18.
Start by bringing the tip of the bar member 17 into contact with the tip of the rod member 17.

Note that the gas pressure filling the cladding tube is
It is set larger than a predetermined value in anticipation of a slight leakage of inert gas to the outside of the cladding tube when 6 moves toward the small diameter hole 14 side. Furthermore, in the figure, the valve body 16 is shown to have a size that is almost fitted into the large diameter hole 15, but since gas flows as described above, the valve body 16 and the large diameter hole 15 are There is a gap between the outer diameter of the valve body 16 and the large diameter hole 15.
This is provided by the difference in the inner diameter of the large diameter hole 15 or by a groove formed along the axis on the inner surface of the large diameter hole 15. In the former case, it will be understood that the rod member 17 has the function of guiding the valve body 16 to be positioned on the axis of the large diameter hole 15 and smoothing its movement. However, since the valve body 16 is spherical in particular, the purpose of the present application can be sufficiently achieved with the guiding function of the large diameter hole portion 15 alone, so the rod member 17 is not an essential requirement for the present application.

As described above, by setting the length of the rod member 17 so that the tip protrudes slightly to the outside when the valve body 16 is on the small-diameter hole 14 side, it is possible to weld the small-diameter hole 14. Easy to ignite. Furthermore, since the valve body 16 is fixed via the rod member 17, the valve body 16 may move during transportation, etc., and the protrusion 15
This prevents situations such as bumping into b.

Moreover, FIG. 3 is a diagram showing still another embodiment of the present invention.

The fuel rod end plug shown in this figure has the bottom surface 19 of the large-diameter hole 15 formed in a conical shape, and the valve body 20 is formed in a conical shape corresponding to the shape of the bottom surface 19. Although the same effects as in the embodiment are achieved, the valve body 20 is small in size, so that the large diameter hole 15 can be short in length. In such a valve body shape,
The rod member 17 has the function of controlling the posture of the valve body.

[Effect of the invention] As explained above, in the fuel rod end plug of this invention, the gas filling hole is connected to the large diameter hole on the cladding side and the small diameter hole on the outside communicating with the large diameter hole. A valve body having a larger diameter than the small diameter hole is provided in the large diameter hole so as to be movable in the axial direction of the large diameter hole, and
A locking part that prevents the valve body from moving into the cladding tube is formed on the cladding tube side of the large diameter hole, and the valve body allows gas flow at the cladding tube side position and at the small diameter hole side position. It is constructed to block the small diameter hole and prevent gas flow, so when the pressurization is stopped after filling the cladding tube with inert gas from the open end of the small diameter hole, the internal pressure automatically closes the inert gas. Since the valve body seals the filling hole, welding can be performed by generating a normal arc at normal pressure, and since welding defects do not occur, gas leaks are less likely to occur and are highly safe.

[Brief explanation of the drawing]

Figures 1 and 2 are views showing one embodiment of the present invention, in which Figure 1 is a fragmented sectional view showing a fuel rod end plug, and Figure 2 shows a valve body attached to the bottom of a large diameter hole. FIG. 3 is a fragmented sectional view showing another embodiment of the present invention, showing an end plug for a fuel rod, and FIGS. 4 and 5 are fragmentary sectional views showing a conventional fuel rod. FIG. 4 is a perspective view of a fuel rod to which a conventional fuel rod end plug is fixed, and FIG. 5 is a side view of the conventional fuel rod end plug. 1... Cladding tube, 2... Fuel pellet, 4... End plug (fuel rod end wire), 5... End plug (fuel rod end plug), 6... End plug body, 9... Gas filling. hole, 1
0... End plug body, 13... Gas filling hole, 14...
...Small diameter hole part, 15...Large diameter hole part, 16...Valve body,
20...Valve body.

Claims (1)

[Claims for Utility Model Registration] (1) An end plug for a fuel rod that is closed and fixed to the open end of a cladding tube in which fuel pellets are charged,
In the fuel rod end plug, the end plug body is provided with a gas filling hole, one end of which is open inside the cladding tube and the other end of which is open to the outside of the cladding tube. It has a large-diameter hole on the side and a small-diameter hole on the outside communicating with the large-diameter hole, and the large-diameter hole has a valve body larger in diameter than the small-diameter hole. The valve body is provided so as to be movable in the axial direction of the cladding tube, and a locking portion that prevents the valve body from moving into the cladding tube is formed in the cladding tube side portion of the large diameter hole, and the valve body is movable in the cladding tube side. 1. An end plug for a fuel rod, characterized in that it is configured to allow gas flow at a side position and block the small diameter hole at a small diameter hole side position to prevent gas flow. (2) The small-diameter hole is formed parallel to the axis of the large-diameter hole, and a rod member is fixed to the valve body and inserted through the small-diameter hole with a gap. An end plug for a fuel rod according to claim 1 of the patent registration claim. (3) The length of the rod member mentioned above is set so that the tip of the rod member protrudes from the outer end of the small diameter hole when the valve body is located on the small diameter hole side of the large diameter hole. An end plug for a fuel rod according to claim 2, characterized in that it is a utility model.