JPH01494A - nuclear reactor 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 [Field of Industrial Application] The present invention relates to improvements in nuclear reactor fuel assemblies.

[Conventional technology]

Usually, a large number of fuel assemblies used in a boiling water reactor are arranged at a predetermined distance from each other, and each fuel assembly consists of a number of fuel rods, water rods, upper and lower tie plates. , a spacer and a channel box.

4 to 7, fuel assemblies for boiling water nuclear reactors currently in use will be explained. Figures 4 and 5 are longitudinal and horizontal sectional views of the fuel assembly, respectively, and Figures 6 (a), (b), and (c) are of the upper tie plate of the current 8x8 type fuel assembly, respectively. Plan view, front view, bottom view, Figure 7 (a) is the same plan view of the lower tie plate, (
B) is a front view. In the figure, 1 is the upper tie plate 1, 2 is the lower tie plate, 3a to 3d are corner posts, 12a and 12b are Waterlots 1-113 are the current 8
×8 type fuel assembly, upper and lower tie plates 1°2, channel box 14. Fuel rod 11, combined fuel rod 15. It is implanted from spacers 18 and the like.

20 is a channel fastener, 9 is an upper tie plate handle, 24 is an orientation boss, 25 is a cooling water hole,
26 is a square hole for the lower end plug of the water rod, 27 is a threaded hole for the lower end plug of the combined fuel rod, 28 is a boss hole for the lower end plug, and 29 is a boss hole for the upper end plug.

As shown in FIG. 5, 62 fuel rods 11 and two water rods 12a, 12b are assembled in an 8×8 array, and a channel box 14 made of Zircaloy surrounds the fuel assembly 13. being surrounded. Eight of the 62 fuel rods are joint fuel rods 15, which serve to connect the upper tie plate 1 and the lower tie plate 2. Further, one of the two water rods 12a and 12b (12a) also has the function of determining the axial position of the spacers 18 arranged in seven stages in the vertical direction, and holds them fixedly. As shown in FIG. 6, four corner posts 3a, 3b, 3c, and 3 are provided at the four corners of the upper tie plate 1 to serve as guides when installing the channel box 14.
There is d. The channel box 14 is screwed to the corner post 3a by a channel fastener 20.

FIG. 8 is a front view of the fuel rod 11, FIG. 9(A) is a front view of the water rod 12a, and FIG. 9(B) is a bottom view. Fuel rod 11. Upper end plugs 2 are provided at the upper and lower ends of the water rod 12a.
1a, 21b and 22a.

22b is fixed by welding, and the upper and lower end plugs 21a.

b, 22a, b are boss holes provided in the upper and lower tie brakes 1-1.2, especially the lower end plug 22 of the water rod 12a.
b is fitted into the square hole 26 for the water rod lower end plug and assembled, so that the fuel rod 11 and the water rod 12
The positions of a and 12b in the fuel assembly 13 are determined. It is also known that the water rod is mounted only by supporting the lower end plug on the lower tie plate.

The fuel material (uranium) enrichment of each of the fuel rods 11 of the fuel rod group arranged in the fuel assembly 13 is not necessarily uniform for the purpose of efficient fuel use, and is 3%.
, 4%, etc., and the fuel assembly 13
is the height direction (the height direction is irrelevant in the present invention).

and has a predetermined concentration distribution in the cross-sectional direction.

Therefore, when mounting individual fuel assemblies 13 in the core, attention must be paid not only to the position of the fuel assemblies 13 in the core, but also to the orientation of the fuel assemblies 13 at each position. The reason for paying attention to this direction is that the direction is determined in advance in accordance with the fact that the fuel concentration of each fuel rod IL is different as described above. Whether or not each fuel assembly 13 is placed in a predetermined mounting position can be determined by checking the identification number 16 stamped on the upper surface of the upper tie plate handle 9 of the upper tie plate 16 shown in FIG. 6(a). This can be confirmed by

Further, the orientation of the fuel assembly 13 can be confirmed by the orientation of the orientation boss 24 provided on the side surface of the upper tie plate handle 9.

As described above, the orientation of the fuel assembly 13 is determined by the orientation of the orientation boss 24 of the upper tie plate 1, and if the upper tie plate 1 is assembled into the fuel assembly 13 in the correct orientation. If there is no fuel assembly 13, there is a risk that the fuel assembly 13 will be installed in the core in the wrong direction, and in this case, the performance expected in advance will not be achieved. - On the other hand, as shown in FIG. 7(B), there is a cooling water hole 25 in the conical seat part of the lower tie plate 2, and when it is assembled into the fuel assembly 13, it is oriented in a predetermined direction with respect to the upper tie plate 1. It is necessary to do so. As shown in FIG. 7(a), the current lower tie plate 2 has a spacer holding water tube lower end plug 22b (see FIG. 9).
A square hole 26 for a water rod lower end plug is provided for incorporating the water rod. The combined fuel rod lower end plug screw holes 27 are provided at eight locations as shown in FIG. 7(a), and all the other fuel rod boss holes 28 have the same diameter. As described above, the boss hole arrangement of the current lower tie brakes 1 and 2 is non-rotationally symmetrical due to the square hole 26 for the water rod lower end plug hole located at a position offset from the center position.

Moreover, the upper end plug 21 of each fuel rod 11 of the fuel rod group
The diameter of a is different depending on the concentration level, so the boss hole 29 for the upper end plug of the one-part tie plate 1 shown in FIG. 6 is a hole that matches the diameter of the end plug. As a result, the boss hole arrangement of the upper tie plate 1 is generally non-rotationally symmetrical.

In this way, with the current fuel, there was no possibility that the upper and lower tie plates 1.2 would be incorrectly attached to the fuel assembly 13.

However, improvements to the fuel assembly structure are currently being considered from an economic standpoint, and plans are being made to put into practical use a future fuel assembly 17 with the structure shown in Figure 10. It has a structure in which a large diameter water rod 30 is incorporated. FIG. 1(a) is a plan view of the upper tie plate 1 of the future type fuel assembly 17, and FIG. 1(b) is a plan view of the lower tie plate 2. The upper tie plate 1 has a pressure drop (coolant flow 9
The boss diameter 33 and web thickness 34 are optimized for the purpose of reducing the pressure loss (at 1:00). That is, the stress generated in the upper tie plate 1 is evaluated when the fuel assembly 13 is handled (when lifted by the upper tie brake 1 to the handle 9), and the stress generated in the upper tie plate 1 is evaluated, and the upper end plug of the combined fuel rod corresponding to the position where the stress is severe is determined. boss 31
, and the boss and web thickness 34 near the root of the upper tie plate handle 0 are made large, and conversely, the thickness of the boss and web 34 in the vicinity of the root part of the upper tie plate handle 0 is made small, and on the contrary, the thickness of the boss and the web 34 are made small in the vicinity of the base part of the upper tie plate handle 0. In the lower tie plate 2, 19 is a boss hole for a large-diameter water rod lower end plug, and 23 is a tapped hole for a combined fuel rod lower end plug.

In addition, for the boss hole, reduce the number of upper end plug parts and make the boss outer diameter smaller (if the boss is made larger, it is necessary to increase the boss outer diameter and boss wall thickness to ensure boss strength, which is not desirable in terms of pressure loss. ) For this purpose, the hole diameters are unified, and the hole diameters are made small within a range that does not affect the strength of the end plug.

However, since the upper end plug for the combined fuel rod is required to be stronger than other fuel rods, the diameter of the end plug is large, and therefore the hole diameter of the boss 31 for the two-part end plug of the combined fuel rod is also formed large. ing. The hole diameters of the eight combined fuel rod upper end plug bosses 35 are unified to have the same diameter. As described above, the upper tie plate 1 is optimally designed in terms of strength, but the boss hole arrangement has no directionality and is rotationally symmetrical.

The lower tie plate 2, which has the possibility (danger) of being incorrectly attached to the channel box 14, has a structure in which a boss hole (square hole) 19 for a large-diameter water rod lower end plug is provided in the center. Therefore, there is no directionality in the boss hole arrangement, and as with the upper tie plate 1, there is a possibility that the fuel rod group may be incorrectly installed.

[Problem that the invention seeks to solve]

In the future type fuel assembly 17, a large-diameter water rod 30 is arranged at the center of the fuel rod group, and no consideration has been given to making it non-rotationally symmetrical, and the fuel rod group is arranged in an upper and lower type. For a rate of 1.2, there is a problem in that there is a possibility of incorrect attachment.

The present invention has been made in view of the above situation, and an object of the present invention is to provide a nuclear reactor fuel assembly that can prevent fuel rod groups from being incorrectly attached to upper and lower tie plates.

[Means for solving problems]

The above object includes an upper tie plate and a lower tie plate disposed at upper and lower end positions, and an upper end plug and a lower end plug respectively connected and held to the upper and lower tie plates, and
A fuel rod group consisting of a plurality of fuel rods each of which is filled with fuel pellets, a water rod disposed between the fuel rods and held by at least the lower tie plate, and a spacing between the fuel rods. A plurality of spacers arranged to hold the fuel rods and a channel box containing the fuel rod group are provided, and the large-diameter water rod is arranged at the center of the fuel rod group, and the water rod has a large diameter. The diameter of the upper and lower end plugs of only the fuel rods disposed at the corner posts at predetermined positions of the upper and lower tie plates or the boss portions at the base of the upper tie plate handles of the upper tie plates is the same as that of the other fuel rods. The upper and lower end plugs are formed to have a larger diameter than the upper and lower end plugs so that the fuel rod group is connected to the upper and lower tie plates non-rotationally symmetrically at the center position, or the upper and lower end plugs of the large diameter water rod The cross-sectional shapes of the plugs are formed non-rotationally symmetrically with respect to their respective centers, so that the fuel rod group is formed to be coupled to the upper and lower tie plates non-rotationally symmetrically with respect to the center position. This can be achieved by using nuclear reactor fuel assemblies.

[Effect]

As described in the description of the examples below, the first
In the embodiment, the corner post boss hole 5 of only a predetermined corner post 3a is formed with a large diameter, and the upper and lower end plugs 21a, 2 of only the fuel rod 11 disposed at the position of the corner boss 3a are formed.
2a is formed to have a larger diameter than that of the other fuel rods 11, and corresponding corner plate boss holes 5. The boss 66 is also formed to have a large diameter. Therefore, the positions where the fuel rod group is connected to the upper and lower tie plates 1 and 2 are the large-diameter upper and lower end plugs 21a and 2.
2a is the corner plate boss hole 5. It is limited to the position where it fits into the boss 66. That is, it is non-rotationally symmetrical and can prevent incorrect attachment. In other embodiments, incorrect mounting can be similarly prevented by non-rotation symmetry.

〔Example〕

Examples of the nuclear reactor fuel assembly of the present invention (first example) are as follows:
The same parts as in FIGS. 4 to 11 are designated by the same reference numerals, and explanations of the structures of the same parts are omitted in FIG. 1(A).

This is explained by (b). FIGS. 1(a) and 1(b) are \V side views of the upper tie plate and the lower plate, respectively.

In the figure, 4 is a boss, 5 is a corner post boss hole for fixing the channel box, and 6 is a lower tie plate boss hole corresponding to the corner post boss hole 5. The diameters of the upper and lower end plugs of the fuel rods 11 (not shown in FIG. 1) disposed at the channel fixing corner posts 3a of the upper tie plate 1 are the same as those of the other fuel rods 11 except the combined fuel rods 15. The diameter of the end plug is larger than that of the end plug, and the boss hole arrangement of the upper and lower tie plates is made non-rotationally symmetrical.

For its function, the corner post 3a has a larger diameter than the other corner posts 3b, 3c, 3d or other bosses 4 to ensure strength, so the corner posts 3b to 3d
It is possible to drill large boss holes that cannot be drilled in other bosses. Further, since the boss corresponding to the corner post 3a of the lower tie plate 2 has sufficient strength, it is possible to make a somewhat large lower tie plate boss hole 6.

As described above, the reactor fuel assembly of this embodiment has the corner post boss holes 5 of the upper tie plate 1 for holding fuel rods and the lower type of the lower tie plate 2 arranged at the corner posts 3a for fixing the channels. The rate boss hole 6 is formed to be slightly larger than the boss hole of the other fuel rod holding bosses 4 except for the combined fuel rod 15, and the upper and lower end plugs of the corresponding fuel rods are also thicker than the other fuel rod end plugs. Therefore, incorrect attachment can be prevented without impairing the pressure loss reduction effect of the upper and lower tie boots at all. In other words, non-rotational symmetry can be achieved with a very simple structure in which the diameter of one fuel rod end plug at the corner is made slightly larger than the other fuel rods, as described above, and there is no misalignment with respect to the large-diameter water rod at the center. The fuel rod group can be reliably mounted to the upper and lower tie plates at predetermined positions without any mounting.

FIG. 2 shows another embodiment (second embodiment), (A), (
B) is a plan view of the upper and lower tie plates, respectively. The difference from the above embodiment is that the above embodiment has corner posts 3a of the upper and lower tie plates 1 and 2 due to non-rotational symmetry.
Corner post boss hole 5 and lower tie plate boss hole 6
In addition, the diameter of the end plug of the fuel rod 11 fitted into these boss holes is increased. On the other hand, in this embodiment, the inner diameter of the boss hole 8 of one of the bosses 7a and 7b corresponding to the base of the upper tie plate handle 9 is increased, and the end of the fuel rod 11 is made thicker than the fuel rod 11 at the other position. This is because the structure into which the stopper is inserted is non-rotationally symmetrical.

The upper tie plate handle 9 is formed to have the strength required for handling the fuel assembly 13, and the outer diameter of the boss hole 8 at the base of the upper tie plate handle 9 is set to the diameter of the boss hole 8 near the base of the upper tie plate handle 9. Even if the thickness is increased, the pressure loss reducing effect of the upper tie plate 1 will not be deteriorated in any way. Incidentally, the upper and lower end plugs 21a of the fuel rod 11 are arranged at the boss 68 position.

Needless to say, the diameter of 22a is larger than the diameter of the other fuel rod end plugs except for the combined fuel rod 15, and the corresponding lower tie plate boss hole 10 is also formed to have a larger inner diameter. This example also has the same effects as the above example.

In both of the above embodiments, the upper and lower end plugs 21a of one fuel rod 11 are
, 22a, and the corner post boss holes 5, lower tie plate boss holes 6, and bosses 68 of the upper and lower tie plates 1 and 2 into which they are inserted. The lower tie plate boss hole 10 has a larger diameter. However, it is possible to prevent incorrect mounting on the upper and lower tie plates 1 and 2 by targeting multiple 1% LL fuels, increasing their end plug diameters and boss hole diameters, and arranging them so that they do not rotate. It's obvious. In this case, the upper and lower tie plates 1 and 2
It goes without saying that it is important to target a boss that does not deteriorate the optimal conditions for the ), (c)
are cross-sectional views of the upper and lower end plugs for water rods, (b)
, (d) are a bottom view and a plan view of the fitting holes of the upper and lower tie plates into which the end plugs of (a) and (c) are fitted, respectively.

In this embodiment, the upper and lower end plugs 21b of a large-diameter water rod 30 are arranged at the center of the fuel assembly 13.

The cross-sectional shape of 22b is non-rotatable as shown in (A) and (C). And upper and lower end plugs 21b.

The hole shapes of the boss hole (not shown) opened in the upper tie plate 1 into which the 22b is inserted and the boss hole 19 for the large diameter water rod lower end plug of the lower tie plate 2 are also as follows: (B), (
As shown in d), the upper and lower end plugs 21b.

The shape corresponds to the cross section of 22b. By aligning the straight portions 32 provided in each, they are similarly restricted to non-rotating objects, and have the same effects as the above embodiments in addition to being unrelated to the pressure loss reduction effect.

〔Effect of the invention〕

As described above, the nuclear reactor fuel assembly of the present invention is as follows.

This has the effect of preventing fuel rods from being incorrectly attached to the upper and lower tie plates.

[Brief explanation of drawings]

Figures 1 (a) and (b) are plan views of the upper tie plate and lower tie plate, respectively, of the embodiment of the nuclear reactor fuel assembly of the present invention, and Figures 2 (a) and (b) are plan views of other examples, respectively. Plan views of the upper tie plate and lower tie plate of the embodiment,
Figures 3 (a) and (1)) are sectional views of the upper and lower end plugs for water rods of other embodiments, respectively, and (b) and (d) are sectional views of (a) and (c), respectively. A bottom view and a plan view of the hole portions of the upper tie plate and lower tie plate into which the end plugs are inserted. Figure 4 is a longitudinal sectional view of a conventional fuel assembly, Figure 5 is a horizontal sectional view of Figure 4, and Figures 6 (A), (B), and (C) are each a towed 8x8 type fuel assembly. Top view, front view, and bottom view of the bottom tie plate, Figure 7 (a). (B) is also a plan view and front view of the lower tie plate, Figure 8 is a front view of the fuel rod in Figure 5, and Figures 9 (A) and (B).
is also a front view of the water rod. Bottom view, Figure 10 is a vertical cross-sectional view of the future fuel assembly, Figure 1
1(a) and 1(b) are a bottom view and a plan view of the upper and lower tie plates of FIG. 10. 1. Upper tiebrae 1~. 2...Lower tie plate, 3a...Corner post 59...Upper tie plate handle, 11...Fuel rod, 12a, 12b...Waterrock+<, ta...Fuel assembly, 14...・Channel box, 18・・Spacer, 21a, 22a・
... Upper end plug, 21b, 22b... Lower end plug, 3o.
...Thick diameter water rod.

Claims (1)

[Claims] 1. An upper tie plate and a lower tie plate are arranged at the upper and lower end positions, and an upper end plug and a lower end plug are connected and held by the upper and lower tie plates, respectively, and the inside is filled with fuel pellets. A fuel rod group consisting of a plurality of fuel rods, a water rod disposed between the fuel rods and held by at least the lower tie plate, and a plurality of fuel rods formed to maintain a spacing between the fuel rods. spacer and a channel box containing the fuel rod group, the large-diameter water rod is disposed at the center of the fuel rod group, and the corner post at a predetermined position of the upper and lower tie plates is provided. or, the diameter of the upper and lower end plugs of only the fuel rods disposed at the boss portion at the base of the upper tie plate handle of the upper tie plate is larger than the upper and lower end plugs of the other fuel rods. so that the fuel rod group is connected to the upper and lower tie plates non-rotationally symmetrically at the center position, or the cross-sectional shapes of the upper end plug and lower end plug of the large diameter water rod are respectively A nuclear reactor characterized in that the group of fuel rods is formed non-rotationally symmetrically with respect to the center so that the group of fuel rods is coupled to the upper and lower tie plates non-rotationally symmetrically with respect to the center position. fuel assembly.