JPH0640140B2 - Reactor fuel assembly - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a nuclear reactor fuel assembly.

[Conventional technology]

Usually, a large number of fuel assemblies used in a boiling water reactor are arranged at a predetermined interval from each other, and each fuel assembly includes a large number of fuel rods, water rods, upper and lower tie plates, spacers. And the channel box.

A fuel assembly of a conventional boiling water reactor which has been conventionally used will be described with reference to FIGS. 3 to 6. 3 and 4
The figures are the vertical section, horizontal section, and fifth section of the fuel assembly, respectively.
Figures (a), (b), and (c) are respectively a plan view, a front view, and a bottom view of the upper tie plate of the current 8 × 8 type fuel assembly.
FIG. 6 (a) is a plan view of the lower tie plate,
(B) is a front view. In the figure, 1 is an upper tie plate, 2 is a lower tie plate, 3a to 3d are corner posts, 12a and 12b are water rods, and 13 is a current 8 ×.
It is an 8 type fuel assembly and is composed of upper and lower tie plates 1 and 2, a channel box 14, a fuel rod 11, a combined fuel rod 15, a spacer 18 and the like. Reference numeral 20 is a channel fusuna, 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 screw hole for the lower end plug of the fuel rod, 28 is The lower end plug boss hole and 29 are upper end plug boss holes.

As shown in FIG. 4, 62 fuel rods 11 and two water rods 12 a and 12 b are assembled in an 8 × 8 array, and the periphery of the fuel assembly 13 is surrounded by a Zircaloy channel box 14. being surrounded. Eight of the 62 fuel rods are combined fuel rods 15 and serve to connect the upper tie plate 1 and the lower tie plate 2. Further, one (12a) of the two water rods 12a and 12b also has a function of determining the axial position of the spacers 18 arranged in seven stages in the vertical direction and is fixedly held. As shown in FIG. 5, the four corner portions of the upper tie plate 1 have four corner posts 3a, 3b, 3c and 3d which serve as guides when the channel box is mounted. The channel box is screwed to the corner post 3a by a channel fastener.

FIG. 7 is a front view of the fuel rod, FIG. 8 (a) is a front view of the water rod, and (b) is a bottom view. Upper end plugs 21a, 21 are provided at the upper and lower ends of the fuel rod 11 and the water rod 12a.
b and the lower end plugs 22a, 22b are fixed by welding,
Boss holes in which upper and lower end plugs 21a, 21b, 22a, 22b are provided in the upper and lower tie plates, especially the water rod 1
The position of the fuel rod 11 and the water rods 12a and (12b) in the fuel assembly is determined by inserting the lower end plug 22b of 2a into the square rod hole for the lower end of the water rod and assembling it. Incidentally, 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 formed uniformly for the purpose of efficiently using the fuel.
%, 4%, etc., the fuel assembly 1
3 has a predetermined enrichment distribution in its height direction (in the present invention, it has nothing to do with the height direction) and in the cross-sectional direction. Therefore, when the individual fuel assemblies 13 are mounted on the core, attention is 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 also to this direction is that each fuel rod 11
This is because the direction is determined in advance according to the difference in the fuel enrichment of the. Whether or not each fuel assembly 13 is arranged at a predetermined mounting position is determined by the identification number 16 stamped on the upper surface of the upper tie plate handle 9 of the upper tie plate 1 shown in FIG. I can confirm. Also, the orientation of the fuel assembly is the upper tie plate handle 9
It can be confirmed by the orientation of the orientation boss 24 provided on the side surface of the.

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 temporarily, the upper tie plate 1 is incorporated in the fuel assembly 13 in the correct orientation. If not, there is a risk of mounting the fuel assembly 13 in the wrong direction and mounting it on the core. In this case, the performance expected in advance cannot be exhibited. On the other hand, as shown in FIG. 6 (b), the conical seat portion of the lower tie plate 2 has cooling water holes 25, and when incorporated into a fuel assembly, it should be oriented in a predetermined direction with respect to the upper tie plate. There is a need. As shown in FIG. 6 (a), the current lower tie plate 2 is provided with a square hole 26 for a water rod lower end plug for incorporating a spacer holding water tube lower end plug 22b (see FIG. 8). ing. Eight screw holes 27 for lower end plugs of the combined fuel rods are provided, 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 plate 2 is non-rotationally symmetrical due to the square hole 26 for the water rod lower end plug which is displaced from the center position.

Also, the upper end plugs 21 of the fuel rods 11 of the fuel rod group are
The diameter of a is different depending on the degree of enrichment, and accordingly,
Boss hole 2 for upper end plug of upper tie plate 1 shown in FIG.
9 is a hole corresponding to the diameter of the end plug, and as a result, the boss hole arrangement of the upper tie plate 1 is generally non-rotationally symmetric. Thus, with the current fuel, the upper and lower tie plates 1 and 2 are unlikely to be erroneously attached to the fuel assembly 13.

However, at present, improvement of the fuel assembly structure is being considered from the viewpoint of economic efficiency, and the future fuel assembly of the structure shown in FIG. 9 is planned to be put into practical use. It has a structure incorporating a large diameter water rod 30. FIG. 10A is a bottom view of the upper tie plate of the future fuel assembly, and FIG. 10B is a plan view of the lower tie plate. The upper tie plate 1 has a boss diameter 33 and a web thickness 3 for the purpose of reducing the pressure loss (pressure loss when the coolant flows).
4 has been optimized. That is, the stress generated in the upper tie plate 1 at the time of handling the fuel assembly (when being lifted by the upper tie plate handle) or the like is evaluated, and the boss 31 for the upper end plug of the coupled fuel rod corresponding to the stressful position is formed. , And the boss and web thickness 34 near the root of the upper tie plate handle
Is large and, conversely, the one corresponding to a position having a stress margin is small. 19 in lower tie plate 2
Is a boss hole for a large diameter water rod lower end plug, and 23 is a screw hole for a combined fuel rod lower end plug.

In addition, the boss hole reduces the number of upper end plug parts and reduces the outer diameter of the boss (when the boss is increased, it is necessary to increase the outer diameter of the boss to increase the boss wall thickness to secure the boss strength, which is not preferable in terms of pressure loss. ) For the purpose, the hole diameter is unified, and the hole diameter is reduced within a range that does not hinder the end plug strength. However, since the upper end plug for the combined fuel rod is required to have higher strength than other fuel rods, the end plug diameter is large, and accordingly, the hole diameter of the combined fuel rod upper end plug boss 31 is also formed to be large. There is. In addition, the hole diameters of the eight bosses 31 for the upper end plugs of the combined fuel rods are unified to the same diameter. Thus the upper tie plate 1
Is optimally designed from the standpoint of strength, but has no directivity with respect to the boss hole arrangement and has rotational symmetry, so there is a possibility of incorrect mounting on the upper tie plate of the fuel rod group, that is, the channel box 14 ( There is a risk. Lower tie plate 2
Has a structure in which a large diameter water rod lower end plug boss hole (square hole) 19 is provided in the center, so there is no directionality in the boss hole arrangement, and the fuel rod group is erroneously mounted as in the upper tie plate 1. there's a possibility that.

[Problems to be solved by the invention]

In the future fuel assembly 17, the large diameter water rod 30 is arranged at the center of the fuel rod group, and no consideration is given to making it non-rotationally symmetric. There is a problem in that there is a possibility of erroneous mounting for 1 and 2.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a reactor fuel assembly capable of preventing erroneous mounting of the fuel rod group on the upper and lower tie plates.

[Means for solving problems]

The above object is to hold an upper tie plate and a lower tie plate disposed at upper and lower end positions, and to hold an upper end plug and a lower end plug respectively on the upper and lower tie plates, and
A fuel rod group consisting of a plurality of fuel rods filled with fuel pellets, a water rod disposed between the fuel rods and held at least in the lower tie plate, and an interval between the fuel rods. In which a plurality of spacers arranged to hold the fuel rod group and a channel box containing the fuel rod group are provided, the water rod having a large diameter is arranged at the center position of the fuel rod group, One corner post at a predetermined position of the upper and lower tie plates, or the upper and lower end plug diameters of only the fuel rods arranged at one boss portion of the root portion of the upper tie plate handle of the upper tie plate is the other fuel. This is achieved by forming the fuel rod group so as to be non-rotationally symmetrically connected to the upper and lower tie plates at the central position formed with a diameter larger than the upper and lower end plugs of the rod.

[Action]

As described in the description of the embodiments below, the first
In the embodiment (see FIG. 1), the corner post boss hole 5 of only the predetermined corner post 3a is formed to have a large diameter, and the upper and lower end plugs of only the fuel rod arranged at the position of the corner post 3a are formed. The diameter of the fuel rods is larger than that of the fuel rods, and the corner plate boss holes 5 and the boss holes 6 provided in the upper and lower tie plates 1 and 2 corresponding thereto are also formed to have a larger diameter. Therefore, the position where the fuel rod group is joined to the upper and lower tie plates 1 and 2 is limited to the position where the large diameter upper and lower end plugs are fitted into the corner plate boss holes 5 and 6. That is, it has non-rotational symmetry, and erroneous mounting can be prevented. In the other embodiments as well, erroneous mounting can be prevented with non-rotational symmetry.

〔Example〕

Embodiments of the reactor fuel assembly according to the present invention (first embodiment)
The same parts as those in FIGS. 3 to 10 are designated by the same reference numerals, and the description of the structure of the same parts is omitted, and the description will be made with reference to FIGS. 1 (a) and 1 (b) are plan 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 a channel box, and 6 is a lower tie plate boss hole corresponding to the corner post boss hole 5. The upper and lower end plugs of the fuel rods arranged at the positions of the channel fixing corner posts 3a of the upper tie plate 1 are formed to have a diameter larger than the end plug diameters of the other fuel rods except the combined fuel rods. The rate 1 and 2 boss holes are arranged to have non-rotational symmetry. Due to its function, the corner post 3a has other corner posts 3b, 3
Since the diameter is made larger than that of the c, 3d or the other boss 4 to ensure the strength, it is possible to form a large boss hole that cannot be formed in the bosses of the corner posts 3b to 3d. In addition, since the boss corresponding to the corner post 3a of the lower tie plate 2 has a margin in strength, it is possible to make the lower tie plate boss hole 6 to some extent large.

As described above, the reactor fuel assembly according to the present embodiment has the corner post boss hole 5 of the upper tie plate 1 for holding the fuel rod and the lower tie plate of the lower tie plate 2 arranged at the corner post 3a for fixing the channel. Since the boss holes 6 are formed to be slightly larger than the boss holes of the other fuel rod holding bosses 4 except the joint fuel rods, and the corresponding upper and lower end plugs of the fuel rods are made thicker than the other fuel rod end plugs. The erroneous mounting can be prevented without impairing the pressure loss reducing effect of the upper and lower tie plates. That is, non-rotational symmetry can be achieved with a very simple structure in which one fuel rod end plug at the corner portion is made slightly thicker than the other fuel rods as described above, and it is erroneously attached to the central large diameter water rod. The fuel rod group can be surely attached to the upper and lower tie plates at a predetermined position without causing.

FIG. 2 shows another embodiment (second embodiment).
(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 a corner post 3 of upper and lower tie plates 1 and 2 due to non-rotational symmetry.
The corner post boss hole 5 and the lower tie plate boss hole 6 of a are enlarged, and the end plug diameters of the fuel rods fitted into these boss holes are enlarged. On the other hand, in the present embodiment, the inner diameter of the boss hole 8 of one of the bosses 7a, 7b corresponding to the root portion of the upper tie plate handle 9 is made larger to make the fuel rod larger than the fuel rods at other positions. The point is that the structure in which the end plug is fitted is non-rotationally symmetric. The upper tie plate handle 9 is formed so as to have a strength required for handling the fuel assembly, and the boss outer diameter of the boss hole 8 at the base of the upper tie plate handle 9 is set to a thickness near the base of the upper tie plate handle 9. Even if it is increased to the above level, the pressure loss reducing effect of the upper tie plate 1 is not deteriorated at all. The diameters of the upper and lower end plugs of the fuel rods arranged at the positions of the boss holes 8 are, of course, larger than the diameters of the other fuel rod end plugs except for the combined fuel rods. The rate boss hole 10 also has a large inner diameter. This embodiment also has the same effects as the above embodiment.

In both of the above embodiments, the diameters of the upper and lower end plugs of one fuel rod and the corner post boss holes 5 of the upper and lower tie plates 1 and 2 into which they are inserted, the lower tie plate boss hole 6 and the boss hole 8, the lower part The tie plate boss hole 10 has a large hole diameter.

〔The invention's effect〕

As described above, the reactor fuel assembly of the present invention has the effect of preventing erroneous mounting of fuel rods on the upper and lower tie plates.

[Brief description of drawings]

1 (a) and 1 (b) are plan views of the upper tie plate and the lower tie plate of the embodiment of the reactor fuel assembly of the present invention, and FIGS. A plan view of the upper tie plate and the lower tie plate of the embodiment,
FIG. 3 is a vertical sectional view of a conventional fuel assembly, FIG. 4 is a horizontal sectional view of FIG. 3, and FIGS. 5 (a), 5 (b) and 5 (c) are current 8 × 8 type fuel assemblies. Of the upper tie plate of FIG. 6, front view, bottom view, FIG. 6 (a), (b) are the same as the lower tie plate of FIG. 4, front view, front view of the fuel rod of FIG. 8 (a) and 8 (b) are also a front view and a bottom view of the water rod, FIG. 9 is a longitudinal sectional view of the future fuel assembly, and FIGS. 10 (a) and 10 (b) are shown in FIG. It is a bottom view and a top view of an upper and lower tie plate. 1 ... Upper tie plate, 2 ... Lower tie plate, 3a ...
Corner post, 9 ... Upper tie plate handle, 11 ...
Fuel rods, 12a, 12b ... Water rods, 13 ... Fuel assemblies, 14 ... Channel boxes, 18 ... Spacers,
21a, 21b ... Upper end plug, 22a, 22b ... Lower end plug, 30 ... Large diameter water rod.

Claims (3)

[Claims] 1. An upper tie plate and a lower tie plate disposed at upper and lower end positions, an upper end plug and a lower end plug being coupled and held to the upper and lower tie plates, respectively, and
A fuel rod group consisting of a plurality of fuel rods filled with fuel pellets, a water rod disposed between the fuel rods and held at least in the lower tie plate, and an interval between the fuel rods. In which a plurality of spacers arranged to hold the fuel rod group and a channel box containing the fuel rod group are provided, the water rod having a large diameter is arranged at the center position of the fuel rod group, One corner post at a predetermined position of the upper and lower tie plates, or the upper and lower end plug diameters of only the fuel rods arranged at one boss portion of the root portion of the upper tie plate handle of the upper tie plate is the other fuel. An atom having a diameter larger than that of the upper and lower end plugs of the rod and formed so that the fuel rod group is coupled to the upper and lower tie plates in a non-rotationally symmetrical manner at the central position. The fuel assembly. 2. A corner post boss hole at a predetermined position of the upper and lower tie plates, which is provided in each of the upper and lower tie plates, has an end of the large-diameter fuel rod disposed in the boss hole. The reactor fuel assembly according to claim 1, wherein the reactor fuel assembly is sized so that a plug can be inserted therein. 3. One of the boss holes in the base portion of the upper tie plate handle is formed to have a size into which the end plug of the fuel rod formed in the boss hole and having the large diameter is inserted. The nuclear reactor fuel assembly according to claim 1.