JPS59203986A - Fuel assembly of bwr type reactor - 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] [Technical field of invention] The present invention relates to a fuel assembly for a boiling water nuclear reactor.

[Technical background of the invention and its problems]

Generally, a boiling water reactor has a configuration as shown in FIG. Reference numeral 1 in the figure indicates a reactor pressure vessel. Inside this reactor pressure vessel 1, a plurality of fuel assemblies 2 and a reactor core 3 including control rods (not shown) are installed, and cooling water 4 is accommodated. Above the reactor core 3 is a steam separator 5.
A steam dryer 6 is installed above the steam/water separator 5. A main steam outlet nozzle 7 is connected to the surrounding wall of the reactor pressure vessel 10, and a water supply inlet nozzle 8 is connected above it. The main steam outlet nozzle 7 is connected to a main steam pipe (not shown).

That is, the cooling water 4 rises from the bottom to the top of the reactor core 3, and as it does so, its temperature rises, resulting in a two-phase flow state of water and steam. 2
The cooling water 4 in a phase flow state is separated into water and steam by the steam separator 5, and the steam flows into the steam dryer 6 and becomes dry steam through the main steam outlet nozzle 7 and the main steam pipe. It is introduced into a power generation drive turbine (not shown) and used as a turbine drive source. The steam that has completely passed through the turbine is cooled and liquefied by a condenser (not shown), and then flows into the reactor pressure vessel 1 again through the water supply inlet nozzle 8. - Power water is Annelus part 2
0 and flows into the lower part of the reactor core 3 again, and this cycle is repeated thereafter.

The fuel assembly 2 has a structure as shown in FIG. 2, and reference numeral 9 in the figure indicates a rectangular cylindrical channel box.

Inside this channel box 9, a plurality of fuel rods 10 are arranged in a matrix (for example, 8 rows x 8 columns as shown in FIG. 1 and a lower tie plate 12, respectively. Spacers 13 are provided at multiple locations between the upper tie plate 1 and the lower tie plate 12, and the spacers 13 keep the spacing between the plurality of fuel rods 10 constant. It is configured to do this.

The fuel frame 10 has a structure as shown in FIG. Inside the cylindrical double-covered tube 14, a plurality of cylindrical pellets 15 made by sintering uranium oxide powder into pellets are stacked in the axial direction, and an upper end plug 17 is inserted from above via a spring 16.
This is a configuration that is pressed in place. A lower stopper 18 is attached to the lower end.

Generally, during nuclear reactor operation, about 60 parts of the cooling water 4 in the channel box 9 in the upper part of the fuel assembly 2 is steam.

For this reason, as shown in Figure 5, the infinite multiplication factor Koo is larger in the lower part of the core (point A in the figure) than in the middle part of the core (point B in the figure) and the upper part of the core (point C in the figure). tends to be distorted downward. Therefore, during reactor operation, it is necessary to flatten the axial power distribution, which tends to be distorted downward, by promoting deceleration in the upper part of the core 3 and increasing ω to an infinite multiplication factor.

[Purpose of the invention]

The object of the present invention is to improve the fuel assembly of a boiling water reactor in which it is possible to flatten the axial power distribution by increasing the infinite multiplication factor K C1) f in the upper part of the core during reactor operation. Our goal is to provide the following.

[Summary of the invention]

A fuel assembly for a boiling water reactor according to the present invention comprises a channel box and a plurality of fuel rods each containing fuel and arranged in a grid within the channel box.
ii) In the fuel assembly of the boiling water reactor, some of the plurality of fuel rods are made shorter than all the other fuel rods, and above the fuel rods, at least the inner diameter of the lower part is the same as that of the fuel rods. It consists of a hollow member with a diameter larger than the outer diameter.

Therefore, the amount of fuel in the upper part decreases and the amount of cooling water increases, so the ratio of water to fuel during reactor operation can be increased by 1. It becomes possible to achieve leveling.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 6 to 10. FIG. 6 is a diagram showing a schematic configuration of a boiling water reactor to which the present invention is applied. Reference numeral 101 in the figure indicates a reactor pressure vessel.

A plurality of fuel assemblies 10 are contained within this reactor pressure vessel 101.
A reactor core 103 consisting of 2 and control rods (not shown) is installed, and waste cooling water 104 is accommodated therein. Core 1
A steam/water separator 105 is installed above 03, and a steam dryer 106 is installed above this steam/water separator 105.
ing. A main steam outlet nozzle 107 is connected to the peripheral wall of the reactor pressure vessel 101, and a water supply inlet nozzle 108 is connected below it. A main steam pipe (not shown) is connected to the main steam outlet nozzle 107. That is, the cooling water 104 rises from the bottom to the top of the core 103, and as it does so, its temperature rises, resulting in a two-phase flow state of water and steam. The cooling water 104 in a two-phase flow state is passed through the steam-water separator 1
At step 05, water and steam are separated, and the steam is sent to a steam dryer 106.
The dry steam is introduced into a power generation drive turbine (not shown) through the main steam outlet nozzle 107 and the main steam pipe, and is used as a power source for the turbine. The steam that has passed through the turbine is cooled and liquefied by a condenser (not shown), and then passed through the water supply inlet nozzle 108 again to the reactor pressure vessel 1.
01. - Power water is Annelus part 1
09 and flows again into the lower part of the reactor core 03, and this cycle is repeated thereafter.

The fuel assembly 1θ2 has a configuration as shown in FIG. In the figure, reference numeral 110 indicates a rectangular cylindrical channel box. Inside this channel box 110 is a fuel rod 1.
11 are arranged in a matrix (8 rows x 8 columns). The four fuel rods 111 located at the corners of this circle have a configuration different from that of the other fuel rods 211 as shown in FIG. That is, the fuel rods 111A located at the four corners have a structure in which a hollow tube 22 as a hollow member is connected above the fuel rod 121 which is shorter than the other fuel rods. The axial length of this hollow tube 122 is 10 to 10 times the effective length of the conventional fuel rod.
If the ratio is 50%, especially 25% is optimal. The above fuel rod 12
1 is similar to the conventional fuel rod, in which a plurality of cylindrical pellets 124 are layered around a cladding tube 123 and an upper end plug 126 is attached via a spring 125.
It has a double-pressed configuration, and a lower end plug 127 is attached to the lower end. Further, an upper end plug 128 is attached to the upper end of the hollow tube 122, and is supported between an upper tie plate and a lower tie plate (not shown) via this upper end plug 128 and the lower end plug 127. The inner diameter of the hollow tube 122 is larger than the outer diameter of the fuel rod 12°2. A cooling water inlet 129 is formed between the upper end plug 126 and the upper end plug 128.
A cooling water outflow tube 30 is formed between the two and is configured to efficiently introduce the rising cooling water 104. Now, when we examine the flow of cooling water between each fuel rod, we find that it is as shown in Figure 9. That is, at the bottom, there is no boiling, only water, and as it rises, it boils and steam bubbles 13 are generated. This generated steam bubble 13
As they rise, they gather to form a large number of continuous huge vapor bubbles 132 that rise along the surface of the fuel rod 111. At this time, a liquid film phase (water flow) 133 is formed between the vapor bubbles 132 and the fuel rods 111. In this embodiment, in order to effectively flow the liquid film phase 133 into the hollow tube 122, the inner diameter of the hollow tube 122 is adjusted to the fuel rod 122 as described above.
A cooling water inlet 129 is formed between the upper end plug 126 and the upper end plug 126. In this embodiment, the difference between the outer diameter of the hollow tube 122 and the outer diameter of the fuel rod 121 (the effective diameter of the cooling water inlet 129) is approximately 2=.

Next, the hollow tube 122, the upper end plug 126 and the upper end plug 12
The connection structure with 8 will be explained.

A retaining ring 140 as shown in FIG. 10 is welded to the inner peripheral side of the lower part of the hollow tube 122.

A hole 14 is formed in the center of this stop ring 140, and the upper end plug 1 is inserted into this hole 141 from below.
26 is inserted and welded.

The stop ring 140 has a circulation hole 1 through which cooling water flows.
42 is formed. On the other hand, a similar retaining ring 140 is welded to the upper circumferential side of the hollow tube 122, and an upper end plug 128 is inserted from above and welded into the hole 141 formed in the center thereof. There is.

According to the boiling water reactor of this embodiment, the fuel assembly 1
The fuel rods 111A located at the four corners of the reactor 111A lack fuel in the upper part, and a hollow pipe 122 is installed to introduce the cooling water 104f, so the ratio of water to fuel in the upper part of the core during reactor operation is reduced. It is possible to increase the infinite multiplication factor KO), thereby making it possible to level out the core power distribution. In particular, the inner diameter of the hollow tube 122 is made larger than the outer diameter of the fuel rod 121 by about 2g11.
Since the cooling water inlet 129 is formed between the fuel rod 1 and the upper end plug 126 of the fuel rod 121, the liquid film phase 133 formed near the outer periphery of the fuel rod 121 can be effectively introduced.

In the above embodiment, 111 fuel rods and 1 hollow tube were installed at the four corners.
22, but the present invention is not limited to this. For example, the hollow tubes 122 may be attached to the two fuel rods 111B or the four fuel rods 111B and 111C located in the center in FIG.
may be provided. The number of pieces to be cut is not limited to 2 or 4.

Furthermore, the hollow member is not limited to a circular pipe, but may be a rectangular pipe with a square cross section, or a part of the pipe, for example, only the cooling water inlet may be made larger than the outside diameter of the control rod. good.

〔Effect of the invention〕

The fuel assembly for a boiling water nuclear reactor according to the present invention is a boiling water reactor equipped with a channel box and a plurality of fuel rods each containing fuel and the channels arranged in a lattice shape in the box. In a fuel assembly of a nuclear reactor, some of the plurality of fuel rods are made shorter than other fuel rods, and above the fuel rods there is provided a hollow shape in which the inner diameter of at least the lower part is larger than the outer diameter of the fuel rods. This is a configuration in which members are arranged.

Therefore, the amount of fuel in the upper part can be reduced and cooling water can be effectively introduced into the hollow member, and the ratio of water to fuel in the upper part of the core during reactor operation is high, thereby achieving an infinite multiplication factor. Since ω can be increased, it is possible to flatten the output distribution. In particular, since the inner diameter of at least the lower part of the hollow member is made larger than the outer diameter of the fuel rod, cooling water can be introduced effectively.

[Brief explanation of drawings]

Figures 1 to 4 are diagrams showing conventional examples, in which Figure 1 is a vertical cross-sectional view of a boiling water reactor, Figure 2 is a perspective view of a fuel assembly,
Figure 3 is a cross-sectional view of the fuel assembly, Figure 4 is a partial longitudinal cross-sectional view of a fuel rod, Figure 5 is a diagram showing the relationship between the water/uranium ratio and the infinite multiplication factor, and Figures 6 to 10. 6 is a longitudinal cross-sectional view of a boiling water reactor, FIG. 7 is a cross-sectional view of a fuel assembly, and FIG. 8 is a partial longitudinal cross-sectional view of a fuel rod. , Figure 9 is a diagram showing the state of flow of cooling water between fuel rods, Figure 1
Figure 0 is a perspective view of the clasp ring. 102... Fuel assembly, 104... Cooling water, 110
... Channel box, 111 ... Fuel rod, 11
1 person: Fuel rods at the four corners, 122: Hollow member. Applicant's representative Patent attorney Takehiko Suzue Figure 1 Figure 2 t<s Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 ヱVI8 Figure TS9 Figure 10

Claims (1)

[Claims] In a fuel assembly for a boiling water reactor comprising a channel box and a plurality of fuel rods each containing fuel and the channels arranged in a lattice in the box, the plurality of fuel rods are Fuel for a boiling water reactor, characterized in that some fuel rods are made shorter than other fuel rods, and a hollow member is disposed above the fuel rod, the inner diameter of at least the lower part being larger than the outer diameter of the fuel rod. Aggregation.