JPH0763869A - Channel flow rate regulation type fuel assembly - Google Patents

Abstract

PURPOSE:To flatten coolant temperature distribution of a fuel assembly by providing at least one cylindrical flow rate regulation element in a wrapper tube, and a plurality of flow rate control rods in the inside of the inwall of the wrapper tube. CONSTITUTION:A fuel assembly incorporates fast reactor fuel elements 3, flow rate regulation elements 4 and flow rate control rods 1 whose end caps are welded and sealed into wrapper tubes 2. The rods 1 are made of stainless steel and disposed in a space formed of the neighboring fuel elements 3 of the inwall and the inside of the wrapper tubes 2 respectively. The flow rate regulation elements 4 are circular tubes made of stainless steel, have an inlet hole in the lower side and an outlet hole in the upper side, the inlet hole is disposed in the neighborhood of a reactor core and the outlet hole is arranged in the lower side than the upper end of the reactor core. Two or more flow rate regulation elements 4 can be disposed on the circumference in consideration of fuel assembly heat production distribution of each fuel assembly. Thereby the fuel elements can be cooled effectively, the maximum temperature of coated tubes can be lowered or the outlet temperature of the fuel assemblies of coolant can be increased, fuel life can be lengthened and damage is difficult to occur.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a channel fuel flow control type fuel assembly used for a core fuel assembly of a fast breeder reactor and a blanket fuel assembly arranged in and around the core.

[0002]

2. Description of the Related Art A core fuel assembly and a blanket fuel assembly of a conventional fast breeder reactor (both together are referred to as "fuel assembly").
Say ) Has a structure in which the fuel elements, in which the spacer wires are spirally wound around the outer periphery, are arranged in a lattice in the trumpet tube.

Further, in the above structure, since the cross-sectional area between the inside of the trumpet tube and the fuel element is large and the flow rate distribution inside the assembly is different, as disclosed in JP-B-51-6318, A structure has been invented in which the shape and the cross-sectional area of the spacer wire wound around the element are changed, and in addition to this, the shape of the inner wall of the trumpet tube is changed and ribs are arranged on the inner wall.

[0004]

However, the fuel assembly using the spacer wire has the following drawbacks. If the wire winding pitch is increased, the effect of mixing the coolant is not sufficient. When the wire winding pitch is shortened, the pressure loss of the assembly increases.

Further, the fuel assembly disclosed in Japanese Patent Publication No. 51-6318 has a drawback in that the peripheral flow rate suppressing mechanism cannot change the flow rate distribution inside the assembly.

The present invention has been made in view of the above circumstances, and by disposing at least one cylindrical flow rate adjusting element in the trumpet tube and a plurality of flow rate suppressing rods inside the inner wall of the trumpet tube, The purpose is to flatten the temperature distribution of the coolant in the fuel assembly.

[0007]

To achieve the above object, the present invention provides a trumpet tube having a hexagonal cross section, a plurality of fuel elements arranged in a regular lattice in the trumpet tube, and at least one fuel element. And a plurality of flow suppressing rods respectively disposed in the space formed by the inner wall of the trumpet tube and the adjacent fuel elements inside thereof, wherein the flow adjusting element has a cylindrical shape, A coolant inlet hole is provided near the lower end of the core, and a coolant outlet hole is provided near the upper end of the core. The trumpet tube has an entrance nozzle at the lower part and a handling head having an outlet hole at the upper end. It is characterized by that.

[0008]

The flow rate adjusting element is a circular pipe made of stainless steel and has an inlet hole and an outlet hole. Coolant enters through the inlet hole and exits through the outlet hole. The inlet hole is arranged near the lower end of the core, and the outlet hole is arranged below the upper end of the core. In the case of an ordinary core fuel assembly near the center of the core, the coolant temperature at the center of the assembly is higher than that at the periphery, and the maximum cladding temperature is likely to occur. By providing a new flow path in the assembly, the flow rate adjusting element can calculate the coolant flow rate in the assembly from the distribution shown by the chain line in FIG.
Change as shown in the actual battle. On the other hand, since the power density per channel is as shown by the broken line, the coolant temperature distribution in the assembly is flattened and the maximum coating temperature is reduced. In the case of a core fuel assembly or blanket fuel assembly around the core, the maximum cladding temperature is likely to occur at a position away from the center of the assembly. To reduce. In the figure, the chain line shows the case without the conventional flow rate adjusting element, the solid line shows the case with the flow rate adjusting element of the present invention, and the broken line shows the output intensity per channel.

The flow restraining rod is placed between the trumpet tube and the fuel element of a conventional fuel assembly, and the channels (coolant flow path between the fuel element and the fuel element, the fuel element and the trumpet tube). The flow rate of the coolant flow path between) is suppressed. Figure 5
As shown in Fig. 2, in the case of a normal fuel assembly, the channel between the fuel element and the trumpet tube has a large flow passage cross-sectional area of the channel. Double the flow rate. On the other hand, the power density per channel is almost the same as the broken line. Therefore, the temperature of the coolant around the assembly is lower than that in the center, and the temperature of the coolant at the outlet of the assembly is low. The flow rate suppressing rod changes the flow rate distribution of the coolant from the distribution shown by the chain line in FIG. 5 to the distribution shown by the solid line in FIG. 5 by suppressing this useless flow rate, and lowers the maximum temperature of the cladding tube. Alternatively, the coolant outlet temperature is increased. In the figure, the chain line represents the conventional wire spacer, the solid line represents the flow rate adjusting rod of the present invention, and the broken line represents the power density per channel.

As a result, when the flow rate adjusting element and the flow rate suppressing rod are used together, the power density per channel and the flow rate become substantially proportional as shown by the solid line in FIG. 6, and the cladding tube temperature is further reduced. In the figure, the chain line indicates the normal fuel assembly, the solid line indicates the combined use of the flow rate adjusting element and the flow rate adjusting rod, and the broken line indicates the power density per channel.

[0011]

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a channel flow rate control type fuel assembly showing one embodiment of the present invention, and FIG. 2 is a vertical cross-sectional view showing the concept of a channel flow rate control type fuel assembly showing one embodiment of the present invention. 3 (a) and 3 (b) are cross-sectional views showing an arrangement example of the flow rate adjusting element. The structure of the channel flow rate control type fuel assembly shown in FIG. 1 and FIG. 2 is a conventional one in which a cladding is loaded with fuel pellets containing uranium (U) and plutonium (Pu), blanket pellets containing depleted uranium, and a shield. A fuel element 3, a flow rate adjusting element 4, and a flow rate suppressing rod 1 for a fast reactor, in which upper and lower end plugs are welded and hermetically sealed, are incorporated in a trumpet tube 2. On the lower side,
The entrance nozzle has a handling head on the upper side. The flow rate suppressing rods 1 are stainless steel rods and are arranged in the space formed by the inner wall of the trumpet tube 2 and the adjacent fuel element inside thereof. The arrows in FIG. 2 indicate the flow of the coolant.

The flow rate adjusting element 4 is a circular pipe made of stainless steel and has an inlet hole 5 on the lower side and an outlet hole 6 on the upper side. The inlet hole 5 is arranged near the lower end of the core, and the outlet hole 6 is arranged below the upper end of the core. The positions and the number of the flow rate adjusting elements 4 are determined in consideration of the heat generation distribution in each fuel assembly,
Two or more can be arranged. For example, when a channel flow rate control type fuel assembly is used for the blanket fuel assembly, heat is generated about 2 to 3 times the average on the core center side, so the design is as shown in FIG.

The lower entrance nozzle supports the channel flow rate control type fuel assembly by taking in a coolant and mounting it on the core support plate, as in the case of a normal fuel assembly. The trumpet tube is designed to separate the other coolant flow passages from other core components and maintain structural strength, similar to a normal fuel assembly. The handling head at the upper end serves as an outlet for the coolant and also serves as a grip allowance of the refueling machine.

[0014]

According to the present invention described in detail above, the following effects are exhibited. The channel flow rate is efficiently cooled by using the flow rate adjusting element and the flow rate suppressing rod. As a result, the maximum cladding temperature can be lowered, or the outlet temperature of the coolant assembly can be increased, which prolongs the fuel life and lowers the maximum cladding temperature in the event of an abnormality such as an accident. The effect of increasing the thermal efficiency of the turbine is to make the fuel less likely to be damaged or to raise the operating temperature.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a channel flow rate control type fuel assembly showing an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view showing the concept of a channel flow rate control type fuel assembly showing an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing an arrangement example of a flow rate adjusting element showing an embodiment of the present invention.

FIG. 4 is a graph showing a change in flow rate and a power density per channel according to the presence / absence of a flow rate adjusting element according to the embodiment of the present invention.

FIG. 5 is a graph showing a change in flow rate and a power density per channel in the case of the conventional wire spacer and the case of the flow rate adjusting rod of the present invention, showing an embodiment of the present invention.

FIG. 6 shows an embodiment of the present invention, showing changes in the flow rate in the case of a normal fuel assembly and in the case of using the flow rate adjusting element and the flow rate adjusting rod of the present invention together, and the output per channel. Indicates the density.

[Explanation of symbols]

 1 Flow rate suppression rod 2 Trumpet pipe 3 Fuel element 4 Flow rate adjustment element 5 Inlet hole 6 Outlet hole

Claims (1)

[Claims] 1. A trumpet tube having a hexagonal cross section, a plurality of fuel elements and at least one flow rate adjusting element arranged in a regular lattice in the trumpet tube, an inner wall of the trumpet tube and an inner side thereof. And a plurality of flow rate restraining rods respectively disposed in the spaces formed by the adjacent fuel elements, wherein the flow rate adjusting element is cylindrical and has a coolant inlet hole near the lower end of the core and near the upper end of the core. A channel flow rate controllable fuel assembly characterized in that an outlet hole for a coolant is provided in each of the fuel cells, an entrance nozzle is formed in the lower portion of the trumpet tube, and a handling head having an outlet hole in the upper end is formed.