JPS60230090A - Fuel aggregate - 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 the Invention] The present invention relates to a fuel assembly for a fast breeder reactor, and more particularly to a wire spacer type fuel assembly in which a wire is wound around a fuel pin.

[Technical background of the invention and its problems] A wire spacer type fuel assembly used in a fast breeder reactor will be explained in detail with reference to FIGS. 6 to 8.

FIG. 6 is a longitudinal sectional view of the wire spacer type fuel assembly, FIG. 7 is an enlarged cross-sectional view of the cross section taken along line A-A in FIG. 6, and FIG. 8 is a partial cross-sectional view of the wire spacer type fuel assembly. This is an enlarged view.

As shown in FIG. 6, the fuel assembly is constructed by connecting an entrance nozzle section 1, a fuel bundle section 2, and a handling head section 3. This fuel bundle portion 2 has a structure in which a plurality of fuel pins 5 each having a wire 4 wound thereon are fixed to a support plate 6, and this support plate 6 is fixed to a trumpet tube 7. As shown in FIG. 7, the basic flow path shape is a counterflow path α formed at the corner of the trumpet tube 7, and as shown in FIG. There are three types: a flow path β and a central flow path γ formed by three fuel pins.

The coolant flow within the fuel assembly flows into the entrance nozzle section 1 from a pressure chamber formed in the reactor vessel through a plurality of entrance nozzle holes 8 of the entrance nozzle section 1 . Then, it flows into the fuel bundle part 2 and flows into the fuel bundle part 2.
Then, the flow is branched into each flow path represented by three types of flow path shapes, and these flow together in front of the handling head section 3 and flow out from the handling head outlet hole to the upper plenum.

However, if the coolant flows into the fuel assembly, the eighth
As shown in the figure, if the diameter of the fuel pin 5 is 281 and the diameter of the wire is 2b, or if the bottle, wire, and wrapper tube 7 are in a positional relationship in which they are in close contact with each other without any gaps, the pressure loss in the basic flow path of the fuel bundle part 2 is is generally expressed by the following formula % (pressure loss in central flow path γ) ΔPr=ΔAr flr ” ' /53r−...(
1) (Pressure loss in peripheral flow path β) ΔP4=ΔAs Jla ” 5/S'−・・・・・・
(2) Here, A+ = BQ dish 175 (i = γ, β)
... (3) Q: flow rate, B: constant, ΔP: pressure loss βr=πa...
・・・・・・・・・・・・・・・(4) fla=< π +
1) a + 2 b ・・・ ・・・ ・・・
... (5) Sa = 2 (a + b) (a +
2b )−(π)/(2)a2・・・・・・・・・(6
) Sr=r (a + b) 2 - (π)/(2) a' (7) Equal flow rate (Qr = Qa) in the peripheral flow path β and the central flow path γ When flowing, A=Ar from equation (3)
=A-・・・・・・・・・・・・・・・・・・
(8) Also, when considering a liquid metal cooled nuclear reactor, the following equation is approximately satisfied as the relationship between a and b.

b/a+0.2・・・・・・・・・・・・・・・・・・
(9) From the above relational expression, it can be seen that the pressure loss is greater in the central flow path γ than in the peripheral flow path β, as shown below.

迅ΔPr -ΔP-Φ 0.47AAr'75/S3r> 0-(10) This relationship shows that the actual pressure difference before and after the fuel eastern part 2 is equal (ΔP
This is contrary to the fact that r=ΔPa).

This is because equation (10) was derived based on the assumption (8) that the flow rates in the central flow path γ and the peripheral flow path β are equal; in reality, a larger flow rate flows in the peripheral flow path β corresponding to equation (10). It turns out. The amount of heat transferred to the peripheral flow path β and the central flow path γ is equal because the amount of surface area of the fuel bottle facing these flow paths is equal.

This means that the average coolant temperature in the peripheral flow path β is higher than that in the central flow path γ. In order to increase the thermal efficiency of the fuel assembly, it is necessary to reduce this temperature difference.

As an example, the coolant temperature distribution at the upper end position of the core portion of the fuel bundle portion 2 in FIG. 6 shows a distribution as shown in FIG. 9 when shown corresponding to cross section A in FIG. 7.

Since the temperature of the coolant in the outermost peripheral flow path β in contact with the trumpet tube 7 is lower than that in the central flow path γ, the temperature of the trumpet tube 7 is lower than that of the fuel pin 5 and the wire 4.

As a result, a difference in thermal expansion occurs in the radial direction between the trumpet tube and the fuel portion consisting of the fuel pin 5 and wire 4 inside the trumpet tube. This thermal expansion difference that occurs in the initial stage of the fuel is between 0.1 and 0.
．． This is about 2 baskets, and can be absorbed by the net clearance between fuel bins at the time of manufacture.

On the other hand, as the combustion progresses, the amount of swelling of the fuel pins 5 increases because the amount of neutron irradiation is larger and the temperature is higher, resulting in a difference in radial expansion between the fuel pin bundle and the trumpet tube 7.

10 and 11 show the relationship between an increase in the amount of fast neutron irradiation and changes in the fuel pin bundle and the amount of radial expansion of the wrapper tube 7 in a typical fuel assembly.

When the fast neutron irradiation amount reaches 2.0×1023 n/c+#, the radial dimension LP of the fuel pin bundle becomes about 3.5 degrees larger than the dimension W of the trumpet tube 7. If this amount becomes larger than the sum of the clearances between the fuel pin bundle and the trumpet tube 7 during manufacturing, the fuel bottle will be damaged, such as the wire 4 biting into the fuel pin 5 or the fuel pin 5 being deformed and cracking occurring. As combustion progresses, the fuel pin bundle and trumpet tube 7
In order to prevent the clearance between the fuel bottles from becoming zero, the clearance between the fuel bins must be 0°2 mm or more.

However, in this case, since the fuel pin bundle is loose in the early stage of combustion, there is a concern that fretting wear damage due to fluid vibration of the fuel pins 5 may occur.

[Object of the invention] The present invention has been made to solve the above problems,
It has a structure that controls the flow rate of each flow path in the fuel assembly during reactor operation, and is capable of eliminating or reducing the interaction between the fuel pin bundle and the wrapper tube due to the difference in radial expansion. An object of the present invention is to provide a fuel assembly for a breeder reactor.

[Summary of the Invention] That is, the present invention arranges a plurality of fuel pins each having a wire spirally wound around the outer circumferential surface thereof in a trumpet tube, and connects a handling head to the top of the trumpet tube and an entrance nozzle to the bottom. In the fuel assembly, a flow passage blocker is provided on the inner circumferential surface of the trumpet tube, wireless fuel bottles with no wire wrapped around the flow passage blocker are arranged, and fuel pins arranged in the center are connected to each other. are adjacent to 3
This fuel assembly is characterized in that only one of the fuel pins is a wireless fuel bottle, and the other fuel pins are fuel pins wrapped with wire.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Note that parts in FIG. 1 that are the same as those in FIG. 6 are indicated by the same reference numerals, and explanations of overlapping parts will be omitted.

The difference between the fuel assembly of the present invention and the conventional wire-wound fuel assembly shown in FIG. wireless bin 9).
A peripheral flow path closing body 10 is provided between the trumpet tube 7 and the trumpet tube 7, and a detent 11 is formed on the surface of the closing body 10 to support the wireless bottle 9.

That is, in FIG. 1, the fuel pin 5 adjacent to the trumpet tube 7 is a wireless bin, and as shown partially enlarged in FIG.
A peripheral flow path blocker is interposed between the two.

This peripheral flow path closing body 10 includes a corrugated portion 10a formed by forming a thin plate into a corrugated shape, and a frame portion 10b that supports and fixes the corrugated portion 10a.
It consists of Further, the corrugated portion 10a has dimples 1
1, a projection 12 is formed on the frame portion 10b by press working or the like. Note that the closure body 10 does not need to span the entire length of the wireless bin 9, and may be just a portion of it, such as a grid spacer or the like. In this case, the fixing method may be a grid spacer fixing method that does not use tie rods, or a fixing method using tie rods using several of the wireless bins 9 (for example, corner bins). Although the dimples 11 are not shown in the peripheral flow path closing body 10 of FIG. 7, they are attached by welding or the like.

FIG. 2 shows an example in which the peripheral channel closing body 10 is made of a thin plate, and the dimples 11 can be formed by, for example, a press. In the shape of the closure body 9 as shown in FIG. 2, if the surface area in contact with the flow is large, the flow resistance becomes large and the effect of blocking the peripheral flow path becomes large.

In the fuel assembly configured in this way, the peripheral flow path β
When the peripheral flow path blocker 10 is present, the flow resistance increases, the coolant flow rate decreases, and it becomes possible to bring the average coolant temperature in the peripheral flow path β closer to that in the central flow path γ. This is effective in reducing the amount of radial expansion difference that occurs between the fuel pin bundle and the wrapper tube, and improving the thermal efficiency of the fuel assembly.

In addition, since the C wireless bin exists adjacent to the wrapper tube 7, the difference in radial expansion between the fuel pin bundle and the wrapper tube can be tolerated by the diameter of the wire, unlike a conventional fuel assembly. This makes it possible to eliminate or reduce the interaction between the two.

3 to 5 are cross-sectional views showing only the upper half of another embodiment of the present invention.

3 and 4 show the fuel pin 5 adjacent to the trumpet tube 7.
This is an example in which not only is the wireless bin 9, but there are also wireless bins 9 inside it. 3 shows an example in which the central fuel pin 5 is a wireless bin 9, and FIG. 4 shows an example in which the fuel pins 5 immediately outside the central fuel pin 5 are wireless bins 9. In the embodiments shown in FIGS. 3 and 4, the tolerance for the difference in radial expansion between the fuel bottle bundle and the wrapper tube is larger than in the example shown in FIG. 1, eliminating the interaction between the two. Or there is a greater possibility of reducing it.

In Fig. 1, the fuel pin 5 adjacent to the trumpet tube 7 is used as a wireless bin 9, and the wire winding start points of the fuel pins 5 located inside the trumpet pipe 7 are shifted by 120 degrees between the adjacent ones, and the bin pitch is P, and the fuel pin When the diameter of the wire 4 is 2a1 and the diameter of the wire 4 is 2b, the radius of the wire 4 is set so as to satisfy the following relationship.

Pf cho a + (r cho +2) b ・−・・・−(1
1) The condition for the wire 4 to pass through the minimum gap between the fuel pins 5 is P≧2 (a + b)...
......(12). From formulas (11) and (12), a ≦<2f+3)b ・・・・・・・・・・・・・・・
...(13) If the ratio of fuel bottle pitch P and diameter 2a is L, then L= (P)/(2a)...
......(14) (11>, (13), (14) formula, L≧27r-ton......
・・・・・・・・・(15)(11),(13),(15
) If a and blP are determined to satisfy the equation, wire 4
The diameter 2b can be made smaller than the minimum gap between the fuel pins 5, and the gap between the trumpet tube 7 and the adjacent fuel pin 5 can be narrowed compared to conventional fuel assemblies. In addition, the flow area of the peripheral flow path β can be reduced and the flow resistance can be increased, which reduces the coolant flow rate and brings the average coolant i degree of the peripheral flow path β closer to that of the central flow path γ. becomes possible.

This increases the thermal efficiency of the fuel assembly and at the same time
It is possible to eliminate or reduce the interaction between the fuel bottle bundle and the wrapper tube due to the difference in radial expansion that occurs between the two. This is the example shown in Figure 7! When applied to , the number of wires 4 entering and exiting the channel inside the wireless bin 9 adjacent to the wrapper tube 7 is even smaller than the channel inside.

Therefore, by reducing the bottle pitch' to compensate for the small flow resistance, the flow resistance can be increased, and the temperature can be made uniform in the flow path between the fuel bin bundle and the trumpet tube. It is possible to eliminate or reduce this interaction.

[Effects of the Invention] As detailed above, according to the present invention, a flow path blocker is provided in the peripheral flow path on the inner wall surface of the trumpet tube, and the fuel pin adjacent to the flow path blocker is made wireless. By using fuel pins, the flow rate of the coolant in the peripheral channels is reduced, thereby bringing the temperature to the same as that of the coolant in the inner channels, increasing the thermal efficiency of the fuel assembly, and at the same time reducing the flow rate of the coolant in the peripheral channels, thereby increasing the thermal efficiency of the fuel assembly. It becomes possible to eliminate or reduce the interaction between the two due to the difference in radial expansion that occurs between them.

[Brief explanation of the drawing]

1 and 2 are for explaining one embodiment of the fuel assembly according to the present invention, FIG. 1 is a cross-sectional view thereof, and FIG. 2 is an enlarged view of the main part of FIG. 1. 3 to 5 are cross sectional views showing each other embodiment according to the present invention only halfway from the center, and FIGS. 6 to 11 illustrate a conventional fuel assembly. Fig. 6 is a schematic longitudinal sectional view of the fuel assembly, and Fig. 7 is A of Fig. 6.
- A cross-sectional view cut and enlarged in the direction of arrow A, FIG. 8 is a partial view of FIG. 7, and FIG. 9 is a curve diagram showing the relationship between the radial direction of the fuel assembly and the coolant temperature; FIG. 10 is a schematic plan view showing the length of the inner surface of the trumpet tube and the fuel pin, and FIG. 11 is a curve diagram showing the relationship between the fast neutron irradiation amount and the radial expansion φ. 1... Entrance nozzle part 2.
・・・・・・・・・・・・Fuel eastern part 3・・・・・・・・・・・・Handling head part 4・
......Wire 5...Fuel pin 6...Support plate 7... ...Trumpet pipe 8...Entrance nozzle hole 9.
・・・・・・・・・・・・Wireless Bin 10・・・・・・
...... Peripheral flow path blocker 11 ......
・・・Demple 12・・・・・・・・・Patent attorney who represents Tsubo Suyama Sa − ? Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure υ

Claims (2)

[Claims] (1) In a fuel assembly in which a plurality of fuel pins each having a wire wound spirally around the outer circumferential surface are arranged in a line in a trumpet tube, a handling head is connected to the upper part of the trumpet tube, and an entrance nozzle is connected to the lower part of the trumpet tube. A flow path blocker is provided on the inner circumferential surface of the pipe, and wireless fuel pins with no wire wrapped around the flow path blocker are arranged, and the fuel pins are arranged in the center and three fuel pins are adjacent to each other. A fuel assembly characterized in that only one of the fuel pins is a wireless fuel pin and the other fuel pins are wire-wound fuel pins. (2) The fuel assembly according to claim 1, wherein the flow passage blocker has a corrugated plate attached to the frame plate, and dimples are formed on the inner surface of the corrugated plate to be in contact with the fuel pins. .