JPH09197079A - Asymmetric fuel assemblies for boiling water reactors - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: For a spacer holding fuel rods in a square lattice arrangement, asymmetrical fuel assemblies for boiling water reactors, in which angular water channels are arranged in a biased manner, one corner away from the diagonal line. By selecting the protruding portion of the regulating tab in the body, the thermal margins of the fuel rods are made uniform and the limiting output characteristics of the fuel rods are improved. A prismatic water channel (14A) is biased from a shaft center of a spacer (12) to a corner (12a) side on a diagonal line (19), so that a thermal margin of a fuel rod (13) is increased.
Although it becomes large on the side of 2a, it becomes small at the fuel rods 13 in the region E, and as a result, the limiting output characteristic deteriorates. In the present invention, the regulating tab 20 is provided vertically so as not to move the spacer 12 in the axial direction due to the difference in irradiation expansion between the rectangular water channel 14A and the fuel rod 13 during combustion, and the side wall 14c near the corner 12a of the side wall 14B. , 14d only,
The coolant passage cross section on the region E side is increased to improve the limit output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large number of fuel rods arranged in a square lattice among nuclear fuel assemblies used by being loaded in a core of a boiling water nuclear reactor, which are arranged on a diagonal line of the square lattice. Regarding an asymmetric fuel assembly in which the rectangular water channels are installed so as to be biased toward one corner, the undesired vertical movement of the spacer is restricted by projecting the rectangular water channels. It is intended to improve the limiting output characteristic of the fuel rod by selecting the projecting position of the regulating tab in the appropriate position.

[0002]

2. Description of the Related Art As is known, in order to load a nuclear fuel assembly a into a core of a boiling water nuclear reactor, a core support plate disposed below the core 1 as disclosed in FIG. 2, the lower tie plates 10 of the set of four nuclear fuel assemblies a are seated on the fuel support fittings 3 provided therein, and thereby the nuclear fuel assembly is in a standing state. Each upper side of the body a is inserted into the lattice frame 4a of the upper lattice plate 4 arranged above the core 1.

Here, in FIG. 4 of the above, reference numeral 5 shows a known control rod which is formed in the shape of a cross, which is erected from below the core 1 through the fuel support fitting 3 and is erected. It is configured such that it can be inserted into or withdrawn from the coolant passage G separated from each other among the four nuclear fuel assemblies a,
In this case, the structure of the coolant channel G is as shown in FIG.
As clearly shown in (A) and (B), types called C lattice and D lattice are known. Then, in the above-mentioned C lattice, as shown in the same figure (A), the control rods 5 are formed between _four sets of nuclear fuel assemblies a ₁ , a ₂ , a ₃ and a ₄ into which the control rods 5 are inserted and are separated from each other. Control rod side coolant flow path g ₁ separation width w
₁ and the separation width of the non-control rod side coolant flow passage g ₂ that is formed between 1 and the set of four nuclear fuel assemblies a ₄ , a ₃ , a ₂ , a ₁ in which the control rod 5 is not inserted. w ₂ is equal to w ₂ .

On the other hand, in the so-called D grid, as shown in FIG. 3B, the separation width W ₁ of the control rod side coolant passage G _{1 and} the separation width of the non-control rod side coolant passage G ₂ are separated. The width W ₂ is
It is set such that W ₁ > W ₂ . Here, the above-mentioned nuclear fuel assembly a is held by a plurality of spacers 12 between the upper tie plate 11 and the lower tie plate 10 as understood from FIGS. 5 and 6. In addition, a fuel main body 15 in which a large number of fuel rods 13 and a small number of water channels 14 are vertically installed at a predetermined interval, and the upper tie plate 11 and the lower type that are fitted on the fuel main body 15 are fitted. And a channel box 16 fixed at rate 10.

Further, the above-mentioned nuclear fuel assembly a is at a corner upper end of one corner of the channel box 16, and a channel fastener 17 is attached as shown in FIG. Leaf spring 17
a and 17b are one side wall 16a in the channel box 16 and the other side wall 1 which is continuously provided orthogonally thereto.
6b and 6b, respectively. Then, the nuclear fuel assembly a as described above has the nuclear fuel assemblies a ₁ and a ₂ , a ₃ and a ₄ , a ₁ and a ₃ , and a ₁ as shown in FIG. 5 and FIG. ₂ and a ₄ are the respective leaf springs 17 of the channel fastener 17 described above.
By bringing the a and 17b into contact with each other, elastic force based on the a and 17b causes the four nuclear fuel assemblies a ₁ , a ₂ , a
The pair of side walls of each channel box 16 in ₃ and a ₄ are loaded so as to be in elastic contact with the upper lattice plate 4 in the core 1.

When the nuclear fuel assembly a as described above is loaded in the core 1, in the case of the C lattice described in FIG. 3A, the control rod side coolant passage g ₁ and the non-control Since the separation widths w ₁ and w ₂ of the rod-side coolant flow path g ₂ are formed to have the same width length, the flow rate distribution of the coolant becomes uniform, and therefore the concentration distribution of the fuel element is biased. Even if there is not, the output of the nuclear fuel assembly a becomes flat over the entire surface.

However, in the D grid shown in FIG. 3B, the separation width W _{1 of the} control rod side coolant passage G ₁ is as described above.
However, since it is set to be larger than the separation width W ₂ of the non-control rod side coolant passage G ₂ , the control rod side coolant passage G ₁ is more likely to react because the flow rate of the coolant is larger. The output of the fuel rods increases, whereas in the non-control rod side coolant flow passage G ₂ , the flow rate of the coolant is the same as in the above, and the reaction is less likely to occur, so the output tends to decrease. Therefore, there is a latent problem that the local peaking coefficient increases. For this reason, as a means for suppressing the local peaking coefficient, at present, for the fuel near the control rod side coolant flow passage G ₁ which is wide in the nuclear fuel assembly a, the enrichment degree is set to a low level in advance. As for the fuel near the non-control rod side coolant passage G ₂ which is narrow, the output is flattened by increasing the concentration of the fuel.

However, when the countermeasures based on the enrichment distribution as described above are taken, the local peaking coefficient is reduced, so that the overall reactivity is also reduced. Therefore, from the viewpoint of improving the neutron utilization rate, If this is the case, it will not be the optimal measure.

On the other hand, in order to increase the burnup of the nuclear fuel assembly, there is a lattice type as shown in FIG. 6 or a spacer 12 in which the fuel rods are arranged in a square lattice by the ring element type. The fuel rod 13 at its axial center
It is known that a thick rectangular water channel 14A is vertically installed in the space occupied by a plurality of the above. However, even for such a nuclear fuel assembly, from the purpose of suppressing the above-mentioned local peaking coefficient, As shown by the phantom line in FIG. 6, an asymmetric fuel assembly has been proposed in which the arrangement of the rectangular water channels 14A is displaced to the biased position 18.

As can be seen from FIG. 6, this asymmetric fuel assembly has a rectangular water channel 14A which is located on the diagonal line 19 of the spacer 12 and is closer to one corner 12a. According to this structure, prismatic water channel 14A to the non-control rod side coolant passage G ₂ closer with a narrow width is offset, this result, in a state in which the asymmetric fuel assemblies loaded in the core 1 , The control rod side coolant passage G ₁ , the non-control rod side coolant passage G ₂ , and the inside of the channel box 16, the moderator distribution is made uniform in the radial direction, and the local peaking coefficient is obtained. It is effective in suppressing

Also, this type of rectangular water channel 1
The boiling water reactor fuel assembly configured to use 4A has a difference in irradiation elongation between the rectangular water channel 14A and the fuel rod 13 during combustion as known in the art. Since it is necessary to limit the movement of the spacers 12 (7 pieces) in the axial direction to a desired extent, the spacers 12 are sandwiched from above and below on the side wall 14B of the rectangular water channel 14A as shown in FIG. As described above, the pair of regulating tabs 20 is provided so as to project.

As the above-mentioned restricting tab 20 in the past, as shown in FIGS. 7 and 8A, each wall surface 1 of the four side walls 14B of the rectangular water channel 14A.
4a, 14b, 14c, 14d, or the structure shown in FIG.
Wall surface 1 facing the control rod side coolant flow path G ₁ as in (B)
4a and the wall surface 14c facing the non-control rod side coolant flow path G ₂ are provided so as to project from each other.

[0013]

As described above as the prior art, when an asymmetric fuel assembly is used, it can be effective in suppressing the local peaking coefficient, but it is effective in removing heat from the fuel rods 13. Channel Box 1 to contribute
Considering the distribution of the coolant within the fuel cell 6, the fuel rods obviously have an asymmetrical arrangement. Therefore, the thermal margin of the fuel rods 13 in the target fuel assembly surrounded by the channel box 16 is shown in FIG. As will be understood, the non-control rod side coolant flow passage G ₂ side becomes large, and the thermal margin on the control rod side coolant flow passage G ₁ side becomes smaller compared to this, so the thermal margin between the two is large. Difference occurs, and as a result, the marginal output performance deteriorates.

Further, considering the asymmetric fuel assembly, as is known, generally, the steam generated by the heat generation of the fuel rods 13 is cross-sectional direction, that is, in the radial direction of the asymmetric fuel assembly described above. It is known that there is a tendency to shift to the side with a larger flow passage cross-sectional area. Therefore, as illustrated by FIG. 1 according to the present invention, the separation width W ₁ is clearly shown by an imaginary line on the control rod side coolant flow passage G ₁ side which is wider than the non-control rod side coolant flow passage G ₂ . Steam tends to collect on the side of the fuel rods 13 existing in the region E, and as a result, the vapor density in the region E increases and the heat removal property for the fuel rods 13 decreases, so that the thermal margin tends to decrease. Is expected to grow.

In the present invention, based on the above consideration, in this type of asymmetric fuel assembly, the cross sectional area of the coolant passage near the control rod side coolant passage in the channel box can be made as long as possible. It was possible to focus on providing the following configurations from the idea that a large value is effective for improving the limit output of the asymmetric fuel assembly.

That is, in the above-mentioned conventional example, a regulating tab, which is provided in the channel of the coolant in the channel box to reduce the cross-sectional area of the channel, is provided on the side wall of the rectangular water channel. , Not only on the non-control rod side coolant flow path side,
Do not project on the control rod side coolant channel side,
It is not provided on the side wall on the control rod side coolant flow path side, but a pair of upper and lower regulating tabs are selected and protruded only on the wall surface on the non control rod side coolant flow path side.

By doing so, in the present invention, in the conventional asymmetric fuel assembly, the coolant channel cross-sectional area in the channel box on the control rod side coolant channel side is set to be larger than that of the conventional example. The purpose of this is to equalize the distribution of the coolant in the channel box, and thus to avoid the deterioration of the limit output performance due to the thermal margin difference of the fuel rods. Is.

[0018]

In order to achieve the above-mentioned object, the present invention is held between a top tie plate and a bottom tie plate by a spacer, which is a plurality of square lattice arrays arranged vertically. A large number of fuel rods and a single rectangular water channel, which is located on a diagonal line of the spacer and is biased toward one corner, are vertically installed at a predetermined interval. A fuel body and a channel box fitted to the fuel body and fixed to the upper tie plate and the lower tie plate are provided, and a side wall of the rectangular water channel is provided above and below the spacer. It is provided with a restricting tab for restricting the axial movement of the spacer due to the difference in irradiation expansion between the rectangular water channel and the fuel rod in the fuel within a predetermined range. versus In the fuel assembly, the above-mentioned restriction tab, when loaded into the core of a boiling water reactor, in the side wall facing the wide control rod-side coolant flow channel side into which the control rod having a cross shape is inserted. Of the pair of wall surfaces and the other pair of wall surfaces directed toward the narrow non-control rod side coolant flow path side where the control rod is not inserted, the latter pair of wall surfaces, and only one or both wall surfaces. The asymmetric fuel assemblies for boiling water reactors are characterized in that they are respectively provided at the upper and lower positions of the spacer as mentioned above.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a case of using a lattice type spacer in FIG. 1 and an asymmetric fuel assembly for a boiling water reactor using a ring element type spacer in FIG. Will be described in detail below. The basic structure is the same as the structure already described in detail with reference to FIGS. 5 and 6, and the same constituent members are the nuclear fuel assembly and the asymmetric fuel assembly in the conventional example, and the members in the core explicitly shown in FIG. , The same code is adopted. That is, the fuel main body 15 and the channel box 16 fitted and fixed to the fuel main body 15 are provided, and the fuel main body 15 is provided between the upper tie plate 11 and the lower tie plate 10 and is provided with a plurality of spacers arranged vertically. A large number of fuel rods 13 held by 12 and a rectangular water channel 14A are vertically mounted and held while being separated from each other by a predetermined distance.

Further, similarly to the above-mentioned conventional example, at the corner upper end which is one corner of the channel box 16,
A pair of leaf springs 17a, 17b branched from the channel fastener 17 are attached to the core 1 of the boiling water reactor, and the control rod 5 is inserted into each of the wide widths. The control rod side coolant passage G ₁ is projected toward the side of the coolant passage G, and of course, the adjacent nuclear fuel assembly a is mounted.
_As described above, the leaf springs 17a and 17b of the channel fasteners 17 of ₁ and a ₂ are loaded in the core 1 in the elastically contacting state with each other.

The above-mentioned rectangular water channel 1 is also used.
On the side wall 14B of 4A, the rectangular water channel 14A during combustion and the axial direction of the spacer 12 due to the difference in irradiation expansion of the fuel rod 13 are provided by projecting above and below the spacer 12. Is provided with a restriction tab 20 for restricting the movement to a predetermined range, and the rectangular water channel 14A is located on the diagonal line 19 of the spacer 12 and is biased toward one corner 12a. The asymmetrical fuel assembly is configured by vertically mounting.

In FIGS. 1 and 2, reference numeral 12b denotes an inner frame plate fixed to the spacer 12 for inserting and supporting the rectangular water channel 14A as is known, and is shown in FIG. 12c is a square outer frame plate, and 12d is a vertical and horizontal lattice plate internally fixed to the outer frame plate 12c. In FIG. 2, a large number of ring elements 12e are provided inside the outer frame plate 12c. It is fixed in the circumscribed state.

In the present invention, in such an asymmetric fuel assembly for a boiling water reactor, as shown in FIGS. 1 and 2, when loaded in the core 1 of the boiling water reactor, The regulating tab 20 is located on the side wall 14B of the rectangular water channel 14A and is directed to the side of the wide control rod side coolant passage G ₁ into which the cross-shaped control rod 5 is inserted. , 14b and another pair of wall surfaces 14c, 14d directed toward the narrow non-control rod side coolant flow path G ₂ side in which the control rod 5 is not inserted, the latter pair of wall surfaces 14c, 14d are provided. Then, only the selected one wall surface or both side walls as shown in the drawing is arranged so as to project at the vertical position of the spacer 12 as described above.

In the present invention, since the regulating tab 20 is provided only at the selected position, that is, on the non-control rod side coolant passage G ₂ side, the control rod side coolant is provided. In the flow channel G ₁ , the rectangular water channel 14A
Since there is no regulating tab 20 on the side wall 14B of the control bar that hinders the flow of the coolant that is the cooling water, the flow passage cross-sectional area on the side of the control rod side coolant flow passage G _{1 is} therefore set. As a result, the limit output performance of the asymmetric fuel assembly can be improved.

Therefore, not only the local peaking coefficient of the asymmetric fuel assembly can be suppressed, but also the problem of the deterioration of the critical output performance, which is a defect of the conventional example of this kind, can be solved.

[0026]

Since the present invention is constructed as described above, the regulating tab in the rectangular water channel, which has not been considered at all, is provided on the side wall on the control rod side coolant passage side. Since this is not projected, but is selectively projected only on the side wall on the non-control rod side coolant flow path side, of course, the original effect of the regulation tab can be achieved, and the control rod side can be achieved. It is possible to supply a larger amount of coolant to the fuel rods on the coolant channel side than in the conventional example. Therefore, even though it is an asymmetric fuel assembly, there is a thermal margin for the fuel rods in the channel box. A large difference does not occur, and as a result, the heat removal of the fuel rods can be promoted and the thermal margin can be increased, which can improve the marginal output performance.

[Brief description of drawings]

FIG. 1 is an explanatory plan view showing a square lattice type spacer portion in a core loaded state of an asymmetric fuel assembly for a boiling water reactor according to the present invention.

FIG. 2 is a plan view showing a square ring element type spacer portion in the core-loaded state of the asymmetric fuel assembly for a boiling water reactor.

FIG. 3 is a plan view showing the arrangement positions of the nuclear fuel assemblies with respect to the upper lattice plate in the boiling water reactor core, (A) is a C lattice type, and (B) is a D lattice type.

FIG. 4 is a schematic perspective view of a main part showing an installed state of a nuclear fuel assembly in a conventional boiling water reactor core.

FIG. 5 is a partially cutaway vertical front view showing a core loaded state of a conventional boiling water nuclear reactor nuclear fuel assembly.

FIG. 6 is a schematic plan view showing a square lattice type spacer portion in a core loaded state of a nuclear fuel assembly in which conventional rectangular water channels are vertically installed at an axial center position and a biased position, respectively.

FIG. 7 is a schematic perspective view showing an insertion support state of a conventional rectangular water channel with respect to a spacer for an asymmetric fuel assembly in which the rectangular water channel is arranged at a biased position.

FIG. 8A is an explanatory plan view showing a protruding portion of a regulating tab provided on a side wall of a rectangular water channel in a conventional asymmetric fuel assembly, and FIG. It is a plane explanatory view same as the above.

[Explanation of symbols]

1 core 5 control rod 10 lower tie plate 11 upper tie plate 12 spacer 12a corner 13 fuel rod 14A square water channel 14B side wall 14a wall surface 14b wall surface 14c wall surface 14d wall surface 15 fuel body 16 channel box 19 diagonal wire 20 regulation tab G ₁ Control rod side coolant channel G ₂ Non-control rod side coolant channel

Claims (1)

[Claims] 1. A large number of fuel rods held by a spacer, which is a plurality of square lattice arrays arranged vertically, between an upper tie plate and a lower tie plate, and a diagonal line of the spacer. There is a fuel main body in which a single rectangular water channel, which is arranged so as to be biased toward one corner, is vertically installed at a predetermined distance, and the upper tie plate fitted to the fuel main body. And a channel box fixed to the lower tie plate. The side wall of the rectangular water channel is located above and below the spacer so as to project from the rectangular water channel in the fuel and the rectangular water channel. In an asymmetric fuel assembly provided with a regulating tab for limiting the movement of the spacer in the axial direction due to the irradiation expansion difference of the fuel rod to a predetermined range, the regulating tab is a boiling water source. When loaded into the core of the sub-reactor, a pair of wall surfaces in the side walls facing the wide control rod side coolant flow path side where a control rod having a cross shape is inserted, and a narrow non-control in which the control rod is not inserted Of the other pair of wall surfaces directed to the rod-side coolant flow path side, the latter pair of wall surfaces is projected on only one wall surface or both wall surfaces at the vertical position of the spacer as described above. An asymmetric fuel assembly for a boiling water reactor characterized by being installed.