JPH03267792A - Channel box - Google Patents

Abstract

PURPOSE:To improve neutron economy and to reduce the obstruction of swelling due to a difference between internal pressure and external pressure to the insertion of a control rod by tapering the external flank of the channel box from each corner to an adjacent corner. CONSTITUTION:The external surface of the channel box is tapered 3 linearly or inward convexly 4 from each corner to an adjacent corner, e.g. from a corner 1 to a corner 2 to have thin parts 5 and thick parts 6 at the respective corners. Thus, a material of zircalloy 4 as a neutron absorber is removed in a tapered shape to reduce the weight and then improve the neutron economy, and the external surface is deleted in the tapered shape, so the outward swelling of deformation due to the difference between the internal pressure and external pressure can be suppressed small.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention provides a channel box surrounding a fuel rod bundle of a fuel assembly for a boiling water reactor (hereinafter abbreviated as BWR) to improve the neutron economy of a BWR core. This invention relates to minimizing the swelling deformation of the outer surface caused by the difference in internal and external pressure.

[Prior Art] As shown in the simplified explanatory diagram of FIG. 6, a conventionally used BWR fuel assembly mainly consists of an upper tie plate 11. Lower tie plate 12. A plurality of fuel rods 13, water rods 14. Spacer 15. and a channel box 16 that houses this. The upper and lower tie plates 11.12 fix both ends of the plurality of fuel rods 13. A plurality of spacers 5 are provided in the channel box 16 at predetermined intervals in the axial direction, and align and support a plurality of fuel rods to form a fuel rod bundle 20.

The channel box surrounding this fuel rod bundle is made of Zircaloy-4 and has a cylindrical shape with a square horizontal cross section.

The channel boxes provided in these fuel assemblies prevent coolant cross-flow caused by output mismatch between fuel assemblies by forming isolated coolant flow paths for each fuel assembly, and prevent fuel It has the function of ensuring the flow rate of the coolant flowing inside the assembly and allowing the coolant to flow uniformly.

During the loading period of the fuel assemblies into the reactor, pressure loss of the coolant flowing between the fuel assemblies causes a pressure difference between the inside and outside of the side of the channel box, and as shown in Figure 5, the side faces move outward. Inflates. In the figure, 17 is a channel box at the time of manufacture, 18 is a channel box in the final stage of combustion,
19 is a control rod, and 20 is a fuel rod bundle. If the bulge is significantly deformed, there is a risk that it will interfere with the control rods 19 inserted between the channel boxes in order to adjust the reactivity of the reactor.

Currently, in order to reduce fuel costs in BWRs, efforts are being made to increase the burnup of fuel, but when the fuel is irradiated to such a high burnup, the above-mentioned outward bulging deformation of the side surface of the channel box will occur. It is expected to be larger than before.

In addition, Zircaloy-4, which is the material of the channel box,
is a neutron absorber necessary to cause a 23rU nuclear fission reaction in a nuclear reactor, so in order to reduce the fuel cost of the - layer, the wall thickness of the channel box should be made thinner. It is very effective to reduce neutron absorption and improve neutron economy.

[Problems to be Solved by the Invention] In view of the above points, the present invention improves neutron economy in a BWR fuel assembly provided with a channel box,
To achieve this, we have made the channel box thinner to reduce radial swelling due to the pressure difference between the inside and outside of the channel box.
It is an object of the present invention to provide a fuel assembly provided with a channel box that does not cause problems in inserting control rods for adjusting the reactivity of the nuclear reactor even in the final stage of fuel combustion.

[Means for solving the problem] In order to achieve the above object, as shown in Figs. 1 and 2, the outer surface of the channel box is
A linear taper 3 or an inwardly convex taper 4 is formed from the corner 2 toward the adjacent corner 2, and a thin wall portion 5 is provided at each corner.
and a thick wall portion 6.

[Effects] Since the Zircaloy-4 material, which is a neutron absorber, is removed in a tapered shape, its weight is reduced and the neutron economy is improved. It is possible to suppress outward swelling due to deformation. In other words, since the shape is as described above, even when the channel box is deformed, the amount of protrusion outside the line of the outer surface of the conventional channel box, which is a problem due to contact with the control rod, is reduced.

[Example] In order to compare the deformation amount of the channel box of the present invention, a conventional channel box (wall thickness 2
, 54 mm r - side length 139.14 mm), the results of elastically analyzing the amount of deformation using a finite element method calculation code are shown in FIG.

The analysis conditions are as follows.

Channel box material Zircaloy-4 Coolant temperature 280C Coolant pressure Inside the channel box l bar Outside the channel box Obar As a result of analysis, the maximum deformation amount △ was about 0.7 mm.

Next, when we analyzed the amount of deformation of the channel box of the present invention (Fig. 1) under the same analysis conditions as above, we found that although the weight of the channel box was reduced by about 20% compared to the conventional one, The outer surface of the channel box of the present invention after deformation was comparable to the outer surface of the conventional channel box after deformation.

This is because the channel box of the present invention eliminates the outer surface. In this analysis, the minimum wall thickness was set to approximately 60% of the maximum wall thickness.

As already mentioned, the example shown in Fig. 1 has the outer surface cut in a straight line, but in order to further minimize the amount of deformation, the outer surface has a curved shape that is convex inward. Shown in Figure 2. By forming the tapered shape as shown in FIG. 2, an effect similar to that of the earlier patent application No. 1-313899 can be expected, so that outward deformation can be further suppressed.

[Effects of the Invention] By tapering the outer surface of the co-channel box from each corner to the next corner, the weight of Zircaloy-4, which is a neutron absorber, is reduced and neutron economy is improved. The bulge caused by the pressure differential can reduce the amount of bulging outward from the outer surface during manufacture of conventional channel boxes. Therefore, the insertion of control rods is not obstructed;

[Brief explanation of drawings]

Figures 1 and 2 both relate to embodiments of the outer surface of the channel box of the present invention, and show one in which the taper shape cut from each corner toward the next corner is linear, and the other is a curved shape convex inward. Figure 3 is a simplified diagram of the conventional example of the outer surface of the channel box.
The drawings are an explanatory diagram of the analysis results of FIG. 3, FIG. 5 is an explanatory diagram of deformation of the outer surface of the channel box, and FIG. 6 is a simplified explanatory diagram of the main parts of the BWR fuel assembly. 1.2... Corner, 3... Straight taper 4... Inwardly convex taper, 5... Thin wall part, 6... Thick wall part, 1
3...Fuel rod, 16...Channel box, 17...
Channel box (at the time of manufacture), 18... Channel box (in the final stage of combustion), 19... Control rod, 20... Fuel rod bundle. Figure 6C

Claims (1)

[Claims] 1. In a channel box surrounding a fuel rod bundle of a fuel assembly for a boiling water reactor, the outer surface thereof has a linear or inwardly convex taper from each corner to the next corner. Features a channel box.