JPS6221094A - Fuel aggregate for spectral shift - 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 a fuel assembly for spectrum shifting of nuclear reactors used for power generation, heat supply, ships, research, etc.

[Prior Art] Generally, in a fuel assembly for a pressurized water reactor, the seventh
As shown in the figure, a control rod guide simple 1 and an instrumentation simple 2 are connected to the upper nozzle 3 and the lower nozzle 4 to form the framework of the fuel assembly. A number of fuel rods 5 are held fixed in rows at regular intervals with respect to each other by means of a plurality of support grids 6 joined to the mounting simple 2 at longitudinal intervals.

On the other hand, in a nuclear reactor having a fuel assembly of the type described above, plutonium is produced by eliminating the water moderator in the core at the beginning of the reactor operating cycle and reducing the water moderator/fuel ratio. Various methods have been considered to control the amount of moderator in the core in order to perform a spectrum shift that newly increases reactivity by introducing moderator into the reactor core when the reactivity decreases in the later stages. There is.

For example, JP-A-57-124289 discloses an example of a spectrum shifting fuel assembly that mechanically controls the amount of moderator in the reactor core. This fuel assembly, as partially shown in FIG.
Into the cell defined by the straps 6a and 6)), only one of which is shown in the figure, a control rod guide simple 1 is inserted in place together with a fuel rod (not shown). Inside the control rod guide simple 1, a water exclusion rod cluster 7 consisting of a plurality of water exclusion rods 71) assembled into a cluster by a spider part 7a is configured to be received. 7b is inserted into or pulled out from the corresponding control rod guide simple 1 to change the ratio of water moderator/fuel, that is, to perform a spectrum shift.

As is well known to those skilled in the art, in order to increase the spectral shift effect, it is necessary to increase the change in the water moderator/fuel ratio before and after the spectral shift. In the fuel assembly, in order to increase the above-mentioned change, the water removal rod 7b must be made thick, for example, so that it is substantially equivalent to four cells, as seen from No. 8U2J.

[The problem that the invention seeks to solve However, when using such a thick water drain 17b,
Simple control rod guide for water removal rod during spectrum shift 1
The thermal neutron flux in the water hole that occurs after being extracted from the water increases,
In addition to the problem of power peaking occurring in the fuel rods around the water holes, making the water removal rods 3 thicker means that the amount of fuel loaded decreases accordingly, increasing the fuel rod output by 7 Jn l... This causes a problem in that the fuel temperature rises and the margin of reactor operation decreases.

Therefore, an object of the present invention is to provide a fuel assembly for spectrum shifting that can solve these problems.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a fuel rod/water displacement rod assembly having a plurality of fuel elements, and a fuel rod/water displacement rod assembly having a plurality of fuel rods and water displacement rods. a fuel rod/water displacement rod cluster having a plurality of fuel elements insertable into the fuel rod/water displacement rod assembly, each of the fuel elements of the fuel rod/water displacement rod assembly and cluster being integrally connected one above the other to a fuel section. and a water removal portion, the fuel portion and water removal portion of each fuel element of the fuel rod/water removal rod assembly, and the fuel portion and water removal portion of each fuel element of the fuel rod/water removal rod cluster; is characterized by its vertical arrangement being reversed.

[Operation] In the fuel assembly of the present invention, the fuel rod/water exclusion rod cluster is fully inserted into the fuel rod/water exclusion rod assembly when the reactivity of the reactor core has decreased in the middle of its life. This moves the fuel portions of the cluster and assembly from a dense state in which they are substantially at the same axial level to a sparse state in which they are axially offset from each other, and the water displacement portion of the cluster is filled with moderator, so that neutrons deceleration progresses, the neutron flux spectrum shifts to the lower speed side, the reactivity of the fuel assembly increases, and the reactor can be operated further.

Both the cluster and the assembly have a plurality of fuel elements, each fuel element consisting of a fuel section and a water displacement section, and the fuel section and water displacement section of the cluster are vertically connected to the fuel section of the assembly. Since the portion and the water removal portion are opposite, the thickness of each fuel element can be made as thin as possible.

The amount of fuel loaded in the fuel assembly is constant before and after the spectral shift, and only clusters are inserted during the spectral shift.

9 [Example] Next, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings, in which the same reference numerals indicate the same or corresponding parts. .

As shown in FIGS. 1 (1) and (b), the fuel assembly 10 of the present invention includes a fuel rod/water exclusion rod assembly 11 and a fuel rod/water exclusion rod cluster insertable into the assembly 11. 12, and the assembly 11 is comprised of an upper core plate 14 and a lower core plate 15 in the reactor vessel 13.
The cluster 12 is connected to a drive device 18 so as to be movable within a cluster guide tube 17 supported by a lower core support plate 16. FIG. 1(a) shows the dense state when the fuel IE+ rod/water exclusion rod cluster 12 is half inserted into the assembly 11, and FIG. 1(b) shows the fuel rod/water exclusion rod cluster 1.
2 is inserted into the assembly 11 for the entire length.

FIG. 2 schematically shows an example of a fuel rod/water displacement rod cluster 12 according to the present invention. As can be seen from FIG. 1, in this embodiment the cluster 12 is connected to the assembly 11.
In FIG. 2, the cluster 12 is shown in the insertion direction because the cluster 12 is inserted from below (of course, it may be inserted in the opposite direction).

In FIG. 2, the cluster 12 is connected to the drive device 1 described above.
8, a plurality of struts or spider sections 20 connected to the drive shaft 19, and a plurality of fuel elements 21 supported by the spider sections 20. Each fuel element 21 consists of an upper fuel section 22 and a lower water displacement section 23 having substantially the same length as the fuel section 22, and the fuel section 22 and the water displacement section 23 are screwed together (not shown). They are connected together by means such as welding.

As is clear from FIG. 2B showing a cross section taken along the line 2[1-211 in FIG. 2, the water removal section 23 is a hollow tube made of a material with low neutron absorption, such as aluminum or Zircaloy. Moreover, the fuel part 22 is 2Δ in FIG.
As is clear from FIG. 28, which shows a cross section along line -2, the fuel rod may have the same structure as a conventionally known fuel rod, and is composed of a Zircaloy cladding tube 24 and fuel pellets 25 stacked therein. ing.

Further, FIGS. 38 and 3 show enlarged cross-sections of regions 38 and 3B of the water removal portion 23 surrounded by chain lines in FIG.
As can be understood from Figure B, through holes 26 are bored in the upper and lower parts of the water removal section 23, allowing the coolant to flow in the direction shown by the arrow during reactor operation. ing.

As will be described later, in this embodiment the support grid of the fuel assembly defines 7×7 cells, and the fuel elements 21 described above
In this case, a total of 24 wires can be inserted at regular intervals within the cell.

FIG. 4 shows a fuel rod/water exclusion rod assembly 11 configured to be able to receive the above-mentioned fuel rod/water exclusion rod cluster 12 from the direction of arrow 12a. The assembly 11
The four control rod guide simples 2) and one instrument simple 28 in the center are connected to the upper nozzle 29 and the lower nozzle 30.
A plurality of support grids 31 are attached to the control rod guide simple 27 and the instrumentation simple 28 by welding.

Furthermore, as can be understood from FIG. 4 and FIG. 48, which shows a cross section taken along line 4^-4 of FIG. 4, and FIG. 4B, which shows a cross section taken along line 411-4f3, The rod assembly 11 includes the fuel elements 21 of the cluster 12 described above.
Each fuel element 40 is provided with a plurality of fuel elements 40 at a position where they do not interfere with each other. Although not shown, the fuel part 33 and water removal part 32 are integrally connected by means such as screwing or welding. As is clear from FIG. 0, which shows a cross section taken along line 48-48 in FIG. 4, the water removal section 32 is a hollow tube made of a material with low neutron absorption, such as aluminum or Zircaloy.

Further, as is clear from FIG. 4B showing a cross-sectional view taken along line 413-4 in FIG.
and fuel pellets 35 stacked therein. Although not shown, the water removal section 32 includes a third
A through hole 26 is provided as described in connection with FIGS. 8 and 3B.

Thus, the structure of the fuel element 40 of the assembly 11 is substantially the same as that of the cluster 12 described above, but
Note that the arrangement of the water removal section 32 and the fuel section 33 is upside down from that of the cluster 12.

Each support grid 31 is constructed in a conventional manner by combining straps to define a number of cells 36, and fuel elements 40 are inserted through these cells 36 at equal intervals every other cell. 36, it is held fixed by a lattice spring 38 and dimples 39. Incidentally, each fuel element 21 of the fuel rod/water exclusion rod cluster 12 shown in FIG. .

FIG. 5, which corresponds to FIG. 1(a), shows a dense state in which the fuel rod/water exclusion rod cluster 12 of FIG. 2 is inserted approximately halfway into the fuel rod/water exclusion rod assembly 11 of FIG. 1 shows the fuel assembly 10 of the present invention in a state (before being carried out). Each fuel element of the assembly 11 has a water removal section 32 in its upper half and a fuel section 33 in its lower half;
Since the upper half of each fuel element 21 in No. 2 is the fuel part 22,
In the dense state shown in FIG. 5, there is no fuel section in the upper half of the fuel assembly 10, and as shown in FIG. 36, one instrumentation simple 28 shown by ◇, four control rod guide simple 27 shown by ◎, and 44 fuel parts 22 and 33 shown by hatching inside ○ are inserted. . The arrangement relationship of the fuel section 22 of the cluster 12 and the fuel section 33 of the assembly 11 with respect to the grid cell 36 is as shown in FIG. 28 and FIG. 4B, respectively. In this embodiment, the 24 fuel sections of the cluster 12 part 22 and assembly 11
20 fuel portions 33 are inserted into the lattice cells 36.

FIG. 6, which corresponds to FIG. 1(1)), shows the fuel assembly 10 of the present invention at the time of spectrum shift, with the cluster 12 of FIG. 2 fully inserted into the assembly 11 of FIG. At this time, the G8-6 line and the 6I! Figures 68 and 6 [! 17I, it can be seen that there are fuel parts indicated by hatching inside the circle and water removal parts indicated by the circle at every other position along the entire length of the fuel assembly 10.

[Effects of the Invention] As described above, the fuel assembly of the present invention has a fuel rod/water displacement rod assembly capable of receiving a one-fuel rod/water displacement rod cluster, and also has Fuel f in each fuel element? By virtue of the fact that the water removal part and the water removal part are integrated and arranged upside down, the following various effects can be obtained.

(1) Since the fuel section and the water removal section are arranged alternately during the spectrum shift 1, and no large water holes are formed during the spectrum shift 1, output peaking does not occur.

(2) Therefore, it is possible to select the lattice pitch, fuel rod cladding tube outer diameter, and water exclusion rod outer diameter to in, without having to worry about power beaking, and the spectrum shift effect can be maximized. , which helps conserve uranium resources and reduce fuel cycle costs.

(3) The fuel loading is substantially the same before and after the spectrum shift, resulting in a low power density.

[Brief explanation of the drawing]

1(a) and (1)) are schematic diagrams showing the states of the fuel assembly according to the present invention loaded in the reactor vessel before and after the spectrum shift, and FIG. 2 is a schematic diagram showing the state of the fuel assembly of FIG. 28 and 2B are cross-sectional views taken along lines 2^-28 and 2[1-2Il in FIG. Figure n and Figure 3B are enlarged cross-sectional views of the area mixture and 3B in the water displacement part of the fuel element in the fuel rod/water displacement rod cluster in Figure 2, and Figure 4 is an enlarged cross-sectional view of the fuel assembly itself in Figure 1. A schematic side view showing the fuel rod/water displacement rod assembly; FIG. 4Δ and FIG. 4B are partial cross-sectional views taken along lines 48-4^ and 4B-48 in FIG. 4; FIG. The fuel rod/water exclusion rod cluster shown in Figure 2 is attached to the fourth
Figure 58 is a cross-sectional view taken along line 5Δ-5 of Figure 5, and Figure 6 is a cross-sectional view of Figure 2. The fire r1
Rods Figures 68-6Δ and 61)- of Figure 6 are side views of the fuel assembly at the time of spectrum shift when the water exclusion rod cluster is inserted into the water exclusion rod assembly of the 4th National Power Fuel Rod. 7 is a side view showing a typical conventional fuel assembly, and FIG. 8 is a perspective view partially showing a conventional Spectrum Shift I water removal rod cluster. 10...Fuel rod assembly 11...Fuel rod/water exclusion rod assembly 12...Fuel rod/water exclusion rod cluster 21...Fuel element 22 of the fuel rod/water exclusion rod cluster...
- Fuel f1 part 23 of fuel element 21...Water removal part 32 of fuel element 21...Water removal part 33 of fuel element 40...Fuel part 40 of fuel element 40...Fuel rod/water removal Fuel element of rod assembly Applicant Mitsubishi Atomic Crab Industry Co., Ltd. Figure 1 (0) (b) J
LJ L Figure 4 Figure 4A Figure 6

Claims (1)

[Claims] The fuel rod/water displacement rod assembly includes a fuel rod/water displacement rod assembly having a plurality of fuel elements, and a fuel rod/water displacement rod cluster having a plurality of fuel elements insertable between the fuel elements of the fuel rod/water displacement rod assembly. Each of the fuel elements of the fuel rod/water displacement rod assembly and cluster consists of a fuel section and a water displacement section that are integrally connected one above the other;
The fuel portion and water displacement portion of each fuel element of the water displacement rod assembly and the fuel portion and water displacement portion of each fuel element of the fuel rod/water displacement rod cluster are arranged in an inverted vertical relationship. A fuel assembly for spectrum shifting characterized by: