JPH022555B2 - - Google Patents

Description

Detailed Description of the Invention The present invention improves the self-sustainability of the nuclear fuel assembly by changing the lower nozzle structure and lower core plate structure of the nuclear fuel assembly, and prevents the lower core plate from being damaged even if it falls over. The present invention also relates to a nuclear fuel assembly configured to facilitate fuel loading even if the nuclear fuel assembly is deformed, and to improve seismic performance during unloading.

The current type PWR nuclear fuel assembly 1 has an upper nozzle 2 at the upper end and a lower nozzle 3 at the lower end, as shown in Fig. 1, and a pair of lower nozzles 3 as shown in Fig. 2 a and b, respectively. Guide pins 4a protrude above the core plate 4 into a pair of holes 3a drilled in the corner corners.
Positioning within the reactor core is performed by passing the

However, although the above-described method for positioning the nuclear fuel assembly 1 can sufficiently withstand the current conditions of use, improvements have been desired from the viewpoint of improving seismic performance during unloading and improving loading performance.

In other words, from the perspective of improving seismic performance at the time of unloading, consideration is only required for the state in which all fuel assemblies are loaded in the reactor core; body is 360°
Because it is surrounded by barriers in all directions and is supported both above and below, it is unlikely that any major earthquake will cause any major displacement, and it is unlikely that its position within the core will change. Ta. However, when loading and unloading nuclear fuel assemblies, 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 aggregate is in a state where there is no barrier 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, even fairly low-intensity earthquakes can cause people to fall.

On the other hand, from the point of view that nuclear fuel assemblies are consumable items, even if the nuclear fuel assemblies are damaged at the time of shutdown of the reactor, even if the probability is low as mentioned above, it will not be a particular problem. ,
If the guide pin 4a provided on the lower core plate 4 is damaged, there are problems such as significant damage to the entire reactor.

In addition, from the viewpoint of improving the latter loading performance mentioned above, in the current nuclear fuel assembly, during use in the reactor core, the growth in the longitudinal direction of the fuel rods 5 due to growth due to neutron irradiation, coefficient of thermal expansion, etc. As a result, the nuclear fuel assembly 1 is bent non-uniformly. In the fuel loading work after the completion of the fuel inspection outside the reactor, loading of the deformed nuclear fuel assembly as described above is caused by the bending of the nuclear fuel assembly 1 itself as shown in Figure 3a, or by the bending of the nuclear fuel assembly 1 as shown in Figure 3b. Due to twisting of the nuclear fuel assembly 1, the positions of the lower nozzle 3 and the guide pin 4a of the lower core plate 4 do not match (the chain line in the figure indicates the normal position), which often causes difficulties.

Further, even if the deformation of the nuclear fuel assembly 1 during loading is slight, loading may become difficult if the deformation of the adjacent loaded nuclear fuel assembly 1 is large, as shown in FIG. 3c.

In other words, in the current joining method, even though it is supported by core plate support pins, the nuclear fuel assembly 1 is actually placed on the lower core plate 4, and the lower nozzle 3 tends to lift up due to lateral loads. Moreover, even if we wanted to make the guide pin longer by making the taper angle at the tip of the guide pin steeper to make it easier to load, we could not expect that much extension due to the relationship with the lower nozzle 3.
The longer the guide pin 4a is made longer, the more the bending stress applied to the guide pin 4a during a fall increases, and the breakage rate increases accordingly.

Therefore, damage to the guide pin 4a results in damage to the lower core plate 4, and unlike damage to a nuclear fuel assembly, it is not a matter of simply replacing it with a new 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 has problems such as the narrow range of compatibility during positioning, which causes considerable difficulty when loading nuclear fuel assemblies. There is.

In order to solve the problems of the current joining method described above, the present invention changes the lower nozzle structure and lower core plate structure of the nuclear fuel assembly, and the legs provided on the lower nozzle side of the nuclear fuel assembly are , the lower core plate is configured to fit into the fitting hole of the lower core plate, the guide pin of the lower core plate is eliminated, and the lower core plate is not damaged.
The purpose of the present invention is to provide a nuclear fuel assembly that aims to improve the self-sustainability of the nuclear fuel assembly and improve earthquake resistance during fuel loading and unloading.

Embodiments according to the present invention will be described below with reference to FIGS. 4 to 6.
This will be explained in detail based on the figures.

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

As shown in the figure, the lower nozzle 3 of the nuclear fuel assembly 1 is provided with relatively long legs 6 at the four corners, and the tips of the legs 6 are formed into a pointed shape to widen the positioning range when loading fuel. ing.

On the other hand, a fitting hole 7 for the leg 6 is bored in the lower core plate 4 into which the leg 6 provided on the lower nozzle 3 of the nuclear fuel assembly 1 is fitted, and the entrance of this fitting hole 7 is used for loading fuel. Chamfering is applied to expand the positioning range.

When loading the nuclear fuel assembly 1 onto the lower core plate 4, as shown in FIGS. In combination with the matching hole 7, the nuclear fuel assembly 1 is positioned and loaded. At this time, since the tips of the legs 6 are pointed, positioning during loading is easy, and the positioning range can be expanded by chamfering the fitting holes 7 of the lower core plate 4 as necessary. It is easier to load.

Also, when loading and unloading the nuclear fuel assembly 1,
The legs 6 provided at the four corners of the lower nozzle 4 allow the nuclear fuel assembly 1 to maintain its independence against lateral loads.

As explained in detail above, in the nuclear fuel assembly according to the present invention, the legs of the lower nozzle are deeply inserted into the fitting holes of the lower core plate, so that the lower nozzle may lift up due to a slight lateral load. In addition, the length of the legs can be freely extended, increasing the independence of the nuclear fuel assembly, and the pointed tips of the legs improve loading performance.
In this case, even if the probability of damage to the leg increases, it is less important than damage to the lower core plate, and it can be replaced with a new nuclear fuel assembly.

In addition, the legs of the nuclear fuel assemblies at the four adjacent corners are
Because it is included in one fitting hole provided in the lower core plate, the structure of the lower core plate is simpler than the current type,
This has effects such as cost reduction.

[Brief explanation of drawings]

FIG. 1 is a front view showing a conventional nuclear fuel assembly;
Figures 2a and b are cross-sectional views of the main parts showing the conventional joining method and cross-sectional views taken along the line A-A. Figures 3a, b, and c are explanations showing examples of problems during loading of conventional nuclear fuel assemblies. 4 is a front view of a nuclear fuel assembly according to the present invention, FIG. 5 is a sectional view of a main part showing a joining method according to the present invention, and FIG. 6 is a sectional view taken along line B--B in FIG. 5. 1~...Nuclear fuel assembly, 2...Upper nozzle, 3...
... lower nozzle, 4 ... lower core plate, 5 ... fuel rod, 6 ... leg, 7 ... fitting hole.

Claims (1)

[Claims] 1 At each lower corner of the nuclear fuel assembly, a leg is formed that protrudes downward and has a pointed tip, and a plurality of adjacent legs are fitted into the lower core plate when the nuclear fuel assembly is loaded in the reactor. 1. A structure for loading a nuclear fuel assembly onto a lower core plate, characterized in that a fitting hole is bored in the lower core plate, and the legs are respectively inserted into the fitting hole.