JPS5985993A - Nuclear fuel assembly - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention relates to a lower nozzle structure and a lower nozzle structure of a nuclear fuel assembly.

The structure of the lower core plate has been changed to improve the self-sustainability of the nuclear fuel assembly, to prevent the lower core plate from loosening even in the event of an overturn, and to ensure that fuel can be easily loaded even if the nuclear fuel assembly is deformed, and that This article relates to a nuclear fuel assembly configured to improve seismic performance during deployment.

The current type PWR nuclear fuel assembly 1 has an upper nozzle 2 at the upper end and two lower nozzles 3 at the lower end, as shown in FIG. 2 (a) and (b), respectively. Positioning within the core is achieved by connecting guide pins 4a protruding from the core plate 4 to a pair of holes 3a formed at diagonal corners of the lower nozzle 3.

But inside. Although the above-mentioned positioning method for the nuclear fuel assembly 1 can sufficiently withstand the current usage conditions, improvements have been desired from the viewpoint of improving seismic performance during loading and unloading and improving loading performance.

In other words, from the perspective of improving seismic performance during unloading, consideration is only required for the state in which all fuel assemblies are loaded in the reactor core; in such a state, each nuclear fuel assembly must be The body is surrounded by barriers for 360 degrees, and is supported both above and below, so even in the event of any major earthquake, it will not undergo large displacements, and it is unlikely that its position within the core will change. I couldn't. However, when a nuclear fuel assembly is loaded and viewed, the upper core plate is removed and no longer supported by the upper nozzle 2, and generally a portion of the entire fuel assembly is outside the core. The nuclear fuel assembly becomes free of barriers in a certain direction.

It is extremely rare for earthquakes to occur in such conditions, and there are currently no public requests for evaluation of these conditions.

However, according to actual evaluations, people are accustomed to falling (up to 1) even in fairly low-intensity earthquakes.

On the other hand, from the point of view that nuclear fuel assemblies are consumable items, there is a low probability as mentioned above, and moreover, when the reactor is shut down (-
Even if the nuclear fuel assembly is damaged, it will not cause any damage to the entire nuclear reactor (2). There are problems such as severe damage.

In addition, from the perspective of improving the latter loading performance mentioned above,
In current nuclear fuel assemblies, during use in the reactor core (2. Growth due to neutron irradiation ζ2, thermal expansion coefficient, etc.) Assembly 1 (1 bending occurs. Fuel loading work after fuel inspection outside the reactor (2) is carried out as described above (2-liquid nuclear fuel assembly is loaded as shown in Figure 3 (a)). C bending of the two-sheet fuel assembly 1 itself, or as shown in FIG. The positions do not match (the dashed line in the figure indicates the normal position), which often causes difficulties.

Furthermore, even if the deformation of the nuclear fuel assembly 1 during loading is slight, as shown in FIG. be.

In other words, in the current joining method, even though it is supported by the core plate support bin, in reality it is placed on the lower core plate 4 (the two-ply fuel assembly l), and the lower nozzle 3 is lifted due to the lateral load. Even if you want to make the 5 guide bin longer to make it easier to climb up and make it easier to load, you cannot expect it to be as long as the one above, due to the relationship with the lower nozzle 3. The longer it is, the wider the guide bin 4a will be when it falls over.
The bending stress applied to the steel increases and the failure rate increases.

Therefore, damage to the guide bin 4a results in damage to the lower core plate 4 (1), and is not something that can be solved by simply replacing it with a new fuel assembly (1), like damage to the nuclear fuel assembly.

From the above point of view, the current method of joining the lower nozzle 3 and the lower core plate 4 using the guide pin 4a causes considerable difficulty when loading the nuclear fuel assembly C1 because the compatibility range during positioning is narrow. There are problems such as

In order to solve the problems of the current joining method mentioned above (-2 lower nozzle structure of nuclear fuel assembly, lower nozzle structure
This is a modification of the core plate structure, in which the lower nozzle side of the nuclear fuel assembly (two legs) are configured to fit into the lower core plate's fitting holes (two legs), and the guide bin on the lower core plate is eliminated. The purpose of the present invention is to provide a nuclear fuel assembly that is free from damage to the lower core plate, improves the self-sustainability of the nuclear fuel assembly, and improves seismic resistance during fuel loading and unloading.

Embodiments of the present invention will now be described in detail based on FIGS. 4 to 6.

FIG. 4 is a front view of a nuclear fuel assembly 1 according to the present invention (2), where 2 is an upper nozzle and 3 is a lower nozzle.

The lower nozzle 3 (2) of the nuclear fuel assembly 1 is provided with two relatively long corners (2) as shown in the figure, and the tips of the legs 6 are formed into a pointed shape (2).

On the other hand, the lower core plate 4 into which the lower nozzle 3 (two provided legs 6) of the nuclear fuel assembly 1 is fitted has a fitting hole 7 for the leg 6, and this fitting hole 7 (two is necessary). (The chamfer is applied accordingly.

Therefore, when loading the lower core plate 4C with two nuclear fuel assemblies 1, as shown in Figs. Combination with the fitting hole 7 of the plate 4 [Secondly, the nuclear fuel assembly l is positioned and loaded.At this time, the tips of the legs 6 are pointed (bent), so positioning during loading is easy. In addition, it is easier to load the fitting hole 7 of the lower core plate 4 (which is easier than the two) by making the fitting hole 7 of the lower core plate 4 (two sides).

In addition, when the nuclear fuel assembly 1 is loaded and taken out, the nuclear fuel assembly 1 can maintain its independence against lateral loads (2) due to the legs 6 provided at the four corners (2) of the lower nozzle 4. It is.

μ Details (- As explained in (2) In the nuclear fuel assembly according to the present invention (-), the legs of the lower nozzle are deeply interlocked with the fitting holes (2) of the lower core plate, so that a slight lateral load can cause the lower part of the nuclear fuel assembly to Not only does the nozzle not lift up, but the length of one leg can be extended freely (2), so loading performance can be improved. Also, damage to the lower core plate (which is less important than the other two)
All you have to do is replace it with a new nuclear fuel assembly.

In addition, since the legs of the nuclear fuel assemblies at the four adjacent corners are included in one fitting hole (1) split into two parts of the lower core plate, the structure of the lower core plate is made heavier than the current model, reducing costs. It has the following effects.

[Brief explanation of the drawing]

Figure 1 is a front view showing a conventional nuclear fuel assembly.
a)', (b) are cross-sectional views of the main parts showing the conventional joining method, cross-sectional views taken along line A-A, and Figures 3 (a), (b), and (c).
) is an explanatory diagram illustrating an example of a malfunction during loading of a conventional nuclear fuel assembly. Figure 4 is a front view of a nuclear fuel assembly according to the present invention (second method), and Figure 5 is an illustration of the main parts of the present invention (two joint method). The cross-sectional diagram, Fig. 6, is the B-B line diagram of Fig. 5. 1... Nuclear/fuel assembly, 2... Upper nozzle, 3...
・Lower nozzle, 4... Lower core plate, 5... Fuel rod,
6...Leg 57...Fitting hole Patent applicant: Mitsubishi Atomic Crab Industry Co., Ltd. Patent attorney: Hideaki Sato

Claims (2)

[Claims] (1) At the joint where the lower nozzle portion of the nuclear fuel assembly is loaded onto the lower core plate, relatively long legs are provided at the four corners of the lower nozzle, and the legs of the lower nozzle of the nuclear fuel assembly are provided on the lower core plate. A nuclear fuel assembly characterized by having a fitting hole for fitting. (2) The legs at the four adjacent corners of the above nuclear fuel assembly. Claim No. 1 is characterized in that it is configured so that it can be located and housed in a fitting hole of one lower core plate.
Nuclear fuel assembly described in ).