JPH05157866A - Fuel assembly channel box for boiling water reactor - Google Patents

Abstract

PURPOSE:To reduce the bulging, caused by the inner-outer pressure difference, of the channel box of a fuel assembly for a boiling water reactor. CONSTITUTION:On four faces in the horizontal cross-sectional direction of the side faces of a channel box, temporary weld parts are provided by plural electronic beams at the uniform pitch in the axial direction of the channel, or at the small pitch in the lower part and at the large pitch in the upper part so as to reduce the bulging deformation of the channel box.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a boiling water reactor (BW).
The present invention relates to reducing swelling deformation due to a pressure difference between the inside and the outside of a channel box overlaid on a fuel assembly for R) during a reactor loading period.

[0002]

2. Description of the Related Art A fuel assembly for a BWR (FIG. 7) A that has been conventionally used is an upper tie plate 12a, a lower tie plate 12b, a plurality of fuel rods 11, a rod spring 1.
3, a spacer S and a channel box 10 for housing them. Upper and lower tie plate 1
2a and 12b fix the upper and lower ends of a plurality of fuel rods 11. A plurality of spacers S are provided in the channel box 10 at intervals in the axial direction.
Are aligned and supported to form a fuel bundle (see FIG. 6).
Zircaloy 4 is the channel box surrounding the fuel bundle
It is manufactured and has a cylindrical shape with a rectangular horizontal cross section. The channel box provided in the fuel assembly described above forms a flow path isolated for each fuel assembly to prevent cross-flow (cross-flow) of the coolant due to the output mismatch (output mismatch) between the fuel assemblies. It has the functions of preventing the flow of the coolant, ensuring the flow rate of the coolant flowing through the fuel assembly, and allowing the coolant to flow uniformly. In this fuel assembly, due to the pressure loss of the coolant flowing through the fuel assembly during the reactor internal loading period, a pressure difference between the inner and outer sides of the channel box occurs, and as shown in FIG. One side bulges outward. 22 is a state in which four side surfaces of the channel box at the end of fuel are inflated. When the deformation is significant, there is a risk that the insertion of the control rod 23 inserted between the channel boxes is hindered in order to adjust the reactivity of the nuclear reactor. In addition, 24 is a fuel bundle. Currently, in BWRs, in order to reduce fuel cost, higher burnup of fuel is being promoted. However, when irradiation is performed up to such a high burnup, the above-mentioned bulging deformation of the side surface of the channel box to the outside,
It is expected to be larger than before. In addition, Zircaloy-4, which is the material of the channel box, is U2 inside the reactor.
Since it is a neutron absorber required to cause the fission reaction of 35, in order to further reduce the fuel cost, the neutron absorption in the channel box is reduced by reducing the thickness of the channel box. Although it is very effective to improve the neutron economy, it is expected that the deformation due to the internal / external pressure difference will become even larger when the wall thickness is reduced.

[0003]

In view of the above points, the present invention prevents the radial expansion of the BWR fuel assembly having the channel box due to the pressure difference between the inside and the outside of the channel box, and controls even in the final stage of combustion. It is an object of the present invention to provide a channel box for a fuel assembly which has no problem in insertability of rods.

[0004]

The present invention comprises, as shown in FIG. 1, provision of a temporary welded portion 2 by an electron beam in the horizontal sectional direction of a channel box. Caltech Inc. in the United States manufactures a channel box by bending a plate into a rectangular shape by electron beam welding in the center of the surface. Therefore, only one of the four faces is welded. However, on the face that is not welded and the face that is not welded, the elongation in the axial direction is different due to the presence or absence of the thermal effect of welding, and Since the box is bent, a temporary welded portion 1'is also provided in the longitudinal direction by an electron beam on the surface opposite to the welded surface so that the channel box is prevented from bending by exerting a thermal effect. The present invention also utilizes the thermal effect of the electron beam similarly to the above. If the zircaloy heated to the β region or α + β region of the zirconium alloy (zircaloy) by the electron beam is rapidly cooled, β is locally generated.
It will be quenched or α + β quenched. Generally, when a metal material is hardened, its hardness becomes high, so that it becomes strong in deformation and becomes small in elongation. Therefore, by utilizing this, the deformation amount when the pressure difference between the inside and the outside of the channel box is applied is suppressed. The above-mentioned temporary welding is to form a heat-affected zone of welding or a line-shaped partial fusion zone, and is not to bond them by welding. In FIG. 1, 1 is a weld bead, 1'is a temporary welded portion at a symmetrical position to the weld bead 1 for preventing bending, and 2 is a temporary welded portion in the horizontal cross-sectional direction according to the present invention.

[0005]

[Function] When the channel box material Zircaloy is heated to the β region or α + β region by the heat effect of the electron beam, and then rapidly cooled, it is locally β-quenched or α + β-quenched, and the hardness increases. The amount of bulging deformation when the channel box is subjected to a pressure difference between the inside and the outside due to the deformation becoming stronger or the elongation becoming smaller.

[0006]

EXAMPLE Example 1 will be described with reference to FIG. In the figure, C indicates one side surface of the channel box, in which the temporary welding portion 3 is formed by an electron beam in the horizontal sectional direction of the channel box with a uniform pitch in the axial direction of the temporary welding. The second embodiment will be described with reference to FIG. This example is based on the measurement result of axial distribution of swelling of the channel box shown in FIG. That is, the axial pitch of the temporary welded portion 3 ″ in the upper portion is increased. Further, the present invention is applied to a channel box having a thin plate as shown in FIG.
Shown in. In the figure, 4 is a thinned portion and 5 is a normal thickness portion. In this case, the application of the present invention is more effective than the conventional channel box.

From the above, it is desirable that the temporary welding is performed under the following conditions. Atmosphere: Vacuum (10 ^-4 Torr or less) Electron beam accelerating voltage; 100 to 500 kV Electron beam current: 10 to 50 mA However, there are various thicknesses of the channel box, and if the penetration depth of the temporary weld is changed. Since the strength against deformation can be controlled, it is not limited to the above numerical range depending on the target channel box and its usage conditions.

[0008]

EFFECTS OF THE INVENTION Temporary welding with an electron beam in the horizontal cross-sectional direction of the channel box makes it possible to locally quench the material and suppress bulging deformation in the horizontal direction.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a channel box of the present invention.

FIG. 2 is an explanatory diagram of Embodiment 1 of the present invention.

FIG. 3 is an explanatory diagram of a second embodiment of the present invention.

FIG. 4 is a diagram showing measurement results of axial distribution of swelling of a channel box for manufacturing Example 2.

FIG. 5 is an explanatory diagram of Embodiment 3 of the present invention.

FIG. 6 is a modified schematic diagram of a channel box.

FIG. 7 is an explanatory view of a fuel assembly for a boiling water reactor.

[Explanation of symbols]

 1 Welded part (axial direction) 1'Temporary welded part (same as above) 2 Horizontal temporary welded part 3 Axial uniform pitched welded part 3'Temporary welded part at the bottom of channel box 3 "Temporary welded part at the top of channel box 4 Thinned part 5 Normal thickness part 10 Channel box 11 Fuel rod 21 Channel box (at the time of manufacturing) 22 Channel box (end of combustion) 23 Control rod 24 Fuel bundle A Fuel assembly S Spacer C Channel box (one surface)

Claims (1)

[Claims] 1. A channel box covered with a fuel assembly for a boiling water reactor, wherein the axial pitch of temporary welding performed by running an electron beam in the horizontal cross-sectional direction on the side surface of the channel box is uniform in the channel box. A channel box for a fuel assembly for a boiling water reactor characterized in that it is made smaller at the bottom of the channel box and made larger at the top.