JPS6058434B2 - nuclear reactor fuel assembly - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in nuclear reactor fuel assemblies.

Figure 1 shows the basic structure of a nuclear reactor fuel assembly. This fuel assembly includes a plurality of regularly arranged fuel elements 3, spacers 4, both upper and lower tie plates 1 and 5 that support the fuel elements 3 at the upper and lower ends, respectively, and both upper and lower tie plates 1. , 5, and a channel box 2 surrounding a fuel element 3. The cooling member then flows through the channel box 2 from the bottom to the top of the fuel assembly to cool the fuel element 3.
By the way, when a nuclear reactor equipped with the fuel assembly described above is operated, the internal pressure of the channel box 2 becomes higher than the external pressure, so a pressure difference is generated between the inside and outside of the channel box 2.

This pressure difference becomes particularly large near the bottom of the channel box 2 where pressure loss is small within the fuel assembly. Then, the channel box 2 is expanded and deformed outward due to the mechanical bending caused by the above-mentioned relative pressure difference, and the channel box 2 is also expanded and deformed due to the thermal effects and neutron irradiation effects caused by the high-temperature long-term operation of the nuclear reactor. is further encouraged. As a result, coolant leaks from the gap between the lower end of the channel box 2 and the lower tie plate 5,
This will lead to a reduction in the cooling effect on the fuel element 3. Therefore, conventionally, a leaf spring 6 for preventing coolant leakage is interposed between the lower tie plate 5 that supports the fuel element 3 and the channel box 2 that covers the circumferential surface of the lower tie plate 5. This prevents coolant from leaking even if it expands and deforms.

Here, the configuration of the coolant leakage prevention leaf spring 6 is shown in FIGS. 2 to 4, and its installed state is shown in FIGS. 5 and 6.

As is clear from the figure, a flat portion 7 is formed in the center of the leaf spring 6 and is in pressure contact with the inner circumferential surface of the channel box 2, and a lower tie plate circumferential pocket 1 is formed at the tip.
A bent portion 8 is formed in pressure contact with the leaf spring 8, and a plurality of leaves 1 are formed through slits 9 in the width direction of the entire leaf spring.
0 to 17 are formed. And this leaf spring 6
As shown in detail in FIG. 6, one end is fixed to the upper end surface of the lower tie plate 5, and the spring force F is:
Pressure difference P between the inside and outside of the channel box 2 applied to the leaf spring 6
1-PO, and is preset to a value that prevents coolant from leaking between the leaf spring 6 and the channel box 2. By the way, when the above-described leaf spring 6 for preventing coolant leakage is actually incorporated into a fuel assembly and used, the channel box 2 will receive a force commensurate with this spring force F as a reaction of the leaf spring 6. As shown in Figure 5, it deforms into a bow shape using the corner as a fulcrum.

A plurality of leaves 10 to 17 formed on the leaf spring 6 prevent coolant leakage caused by the arcuate deformation of the channel box 2, and each leaf deforms to follow the arcuate deformation of the channel box 2. This is intended to prevent coolant leakage. That is, each leaf 10 to 17 of the leaf spring 6 is in a bent state during assembly before use, and the channel box 2 is bent due to thermal effects and neutron irradiation effects during reactor operation. It closely follows expansion deformation. However, in the conventional configuration described above, the amount of leaf deflection of the coolant leakage prevention leaf spring 6 is set so that it can sufficiently follow the expansion deformation at the portion where the amount of deformation of the channel box 2 is greatest, that is, at the center of the channel box 2. When adjusted, since the amount of expansion deformation of the channel box 2 is small at the corner, the leaves near the corner may receive excessive strain and be damaged.

In consideration of the above points, an object of the present invention is to prevent excessive strain from occurring locally in the leaf near the corner of a leaf spring for preventing coolant leakage, and to prevent damage to the leaf. It was designed to do so.

The gist of the present invention is to provide a lower tie plate, a plurality of fuel rods whose lower ends are held by the lower tie plate, a channel box surrounding the bundle of fuel rods and the lower tie plate; A coolant leakage prevention plate having a plurality of leaves arranged in a gap formed between the lower tie plate and the channel box, and the leaves being arranged in the width direction of the lower tie plate. In a nuclear reactor fuel assembly having a spring, the lower tie plate has a hole on its side surface into which a lower end of each of the leaves is inserted, and the depth of the hole from the side surface of the lower tie plate is is made deeper at the corner portion of the lower tie plate than at the center portion of the side surface of the lower tie plate in a cross section of the lower tie plate.

Hereinafter, the present invention will be explained with reference to an embodiment shown in FIGS. 7 to 9. The same reference numerals as in the prior art indicate the same parts, and in the present invention, as shown in FIGS. 8 and 9, a lower tie plate is used. By making the depth δ1 of the corner portion of the circumferential pocket 18 (depth from the side surface of the lower tie plate) deeper than the depth δ2 of the center portion (depth from the side surface of the lower tie plate), The leaf spring 6 for preventing coolant leakage is arranged closer to the side surface of the lower tie plate at the corner portion of the tie plate 5 than at the center portion. Therefore, according to the present invention having the above configuration, the amount of leaf deflection of the coolant leak prevention plate spring 6 is adjusted to match the central portion of the channel box 2, that is, the portion of the channel box 2 where the amount of deformation is greatest. However, since the corner leaves 10, 17 and the center leaves 13, 14 of the plate spring 6 can be set to approximately the same deflection state during reactor operation, the corner leaves 1
0 and 17 are not subjected to excessive strain.

Further, according to the present invention, the reaction force that the channel box 2 receives from the leaf spring 6 is small, and the amount of deformation in the initial assembly state is small, so that it is accelerated by the thermal effect and neutron irradiation effect during reactor operation. The leaf spring 6 can easily and reliably follow the enlarged deformation of the channel box 2. As described above, the present invention prevents local excessive strain from occurring in the leaves near the corners of the coolant leakage prevention plates, and prevents damage to the leaves before operating the reactor. It is possible to improve the safety of the above, and if this is implemented, the industrial effect will be very large.

[Brief explanation of drawings]

Figure 1 is a longitudinal sectional view showing the basic structure of a nuclear reactor fuel assembly;
Fig. 2 is a plan view of a leaf spring for preventing coolant leakage that is incorporated into a fuel assembly, Fig. 3 is a front view of Fig. 2, and Fig. 4 is a view taken along the line A-A in Fig. 3. , Fig. 5 is a partial plan view showing the interposition of the coolant leakage prevention plate spring on the fuel assembly and the arcuate deformation of the channel box during reactor operation, and Fig. 6 is the line B-B in Fig. 5. 7 is a sectional view corresponding to FIG. 5 showing an embodiment of the present invention, FIG. 8 is a sectional view taken along line C-C in FIG. 7, and FIG. 9 is a sectional view taken along line DD in FIG. 7. be. 2...Channel box, 3...Fuel element, 5.
...Lower tie plate, 6...Coolant leakage prevention plate, 10 to 17...Leaf.

Claims (1)

[Claims] 1. a lower tie plate, a plurality of fuel rods whose lower ends are held by the lower tie plate, a channel box surrounding the bundle of fuel rods and the lower tie plate, the lower tie plate and the channel box. A nuclear reactor fuel assembly having a plurality of leaves arranged in a gap formed between the lower tie plate and a leaf spring for preventing coolant leakage, the leaves being arranged in the width direction of the lower tie plate. In the body, the lower tie plate has a hole on its side surface into which the lower end of each leaf is inserted, and the depth of the hole from the side surface of the lower tie plate is determined by the width of the hole across the lower tie plate. A nuclear reactor fuel assembly characterized in that a corner portion of the lower tie plate is deeper than a center portion of a side surface of the lower tie plate.