JPS6048714B2 - nuclear fuel assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear fuel assembly equipped with a coolant flow distribution mechanism.

A fast breeder reactor that generally uses liquid metal as a coolant has a configuration as shown in FIG. 1, for example.

That is, a plurality of nuclear fuel assemblies containing nuclear fuel rods such as uranium are implanted in a reactor vessel 1 to form a reactor core 2, and a blanket fuel assembly region 3 is formed around the reactor core 2, and each nuclear fuel assembly is A coolant 4 represented by liquid sodium is circulated inside the body via a heat exchanger 5 and a pump system to extract the heat generated during nuclear fission to the outside, and at the same time transfer the heat generated during nuclear fission to the uranium 238 in the neutron blanket fuel region 3 generated in the reactor core 2. This uranium-238 is absorbed and converted into the artificial fissile material plutonium-239.
As shown in Fig. 2, the nuclear fuel assembly 15 is made up of a large number of nuclear fuel rods d arranged in a tube c that is connected to a hunt link a at the top and an entrance nozzle b at the bottom. The fluid enters the entrance nozzle through the hole 18 and exits from the handling head a in the direction of the arrow.

Incidentally, in this type of nuclear reactor, the central portion of the core 2 generates the largest amount of heat.

Therefore, from the standpoint of thermal efficiency and mechanical strength of the core fuel structure, it is necessary to keep the outlet temperature of each nuclear fuel assembly constant.
It is necessary to flow a coolant flow rate to each nuclear fuel assembly in proportion to the calorific value. Furthermore, since this type of nuclear reactor has a large calorific value per unit fuel element, the absolute value of the required flow rate of coolant is also large.

When coolant passes through a nuclear fuel assembly, a pressure loss occurs in proportion to approximately the square of its flow rate. This pressure loss acts as a force to levitate the nuclear fuel assembly. Therefore, in order to prevent the nuclear fuel assembly from floating due to this buoyant force and to support the nuclear fuel assembly while flowing an appropriate amount of coolant without any thermal effect in the reactor core where the temperature is several 100 degrees Celsius, for example, as shown in Fig. 1 is used. The internal structure of the furnace is adopted. That is, the furnace vessel j
1 is divided vertically into two by an upper partition wall 7 to form an upper low-pressure coolant chamber 8 above, and an intermediate partition wall 9 is provided below. A high-pressure coolant chamber 10 is formed between them. In addition, the intermediate partition wall 9
A bottom wall 11 is provided below, and a lower low-pressure coolant chamber 12 is formed between the bottom wall 11 and the intermediate partition wall 9. Furthermore, the upper partition wall 7 and the intermediate partition wall 9 are connected by a connecting pipe 1 as shown in FIG. In this connecting pipe 13, the one located in the reactor core 2 is provided with a horizontal hole 14, and the one in which the core nuclear fuel assembly 15 is located in the blanket fuel assembly region 3 is not provided with a horizontal hole. 16 is inserted and installed from the upper low pressure coolant chamber 8 side. A bottomed entrance nozzle 17 provided at the tip of the core nuclear fuel assembly 15 is inserted into the connecting pipe 13 from the upper low-pressure coolant chamber 8 side, and a plurality of nozzle holes 18 are provided on its side. A plurality of horizontal holes for introducing the coolant 4 from the high-pressure coolant chamber 10 into the entrance nozzle through the nozzle hole 18 are also provided on the side wall of the connecting pipe 13 facing the hole 18 . On the other hand, an entrance nozzle is also provided at the tip of the blanket nuclear fuel assembly 16 and inserted into a connecting pipe located in the blanket area. The connecting pipe in this area has no holes in the side wall, and the coolant 4 is introduced into the blanket nuclear fuel assembly 16 from the lower low-pressure coolant chamber 12 through the inflow hole provided in the bottom wall of the entrance nozzle. . The coolant 4 of the nuclear reactor configured as described above flows as follows. The coolant introduced into the high-pressure coolant chamber 10 is connected to the connecting pipe 13
horizontal hole 14 and nozzle hole 1 of entrance nozzle 17
8 into the core nuclear fuel assembly 15. At this time, the bottom wall of the entrance nozzle 17 is connected to the lower low pressure coolant chamber 1.
; Since it forms part of the wall of 2, the reactor core nuclear fuel assembly 1
A downward force acts on the nuclear fuel assembly 5 in FIG. 2, and this force and its own weight exceed the buoyancy force caused by the pressure loss of the nuclear fuel assembly upward, thereby preventing it from floating. In addition, coolant 4 is supplied into the blanket nuclear fuel assembly 16 from the lower low pressure coolant chamber 12 through a hole provided in the bottom wall of the entrance nozzle.
will be introduced. Since the amount of coolant 4 flowing into the blanket nuclear fuel assembly 16 is small compared to the pumping of the reactor core, the upward force is less than its own weight and does not cause the nuclear fuel assembly to float 3. The flow rate of the coolant passing through each nuclear fuel assembly 15 and 16 is adjusted by changing the size and number of the horizontal hole 14 of the connecting pipe 13 and the nozzle hole 18 of the entrance nozzle 17. However, as mentioned above, in order to improve the thermal efficiency and safety of the nuclear 4t sub-reactor, the flow rate of the coolant passing through each nuclear fuel assembly 15 and 16 must be finely adjusted in accordance with the position within the reactor. , it is necessary to make the outlet temperature of each nuclear fuel assembly uniform throughout the reactor. In addition, the conditions of the corners of the horizontal hole 14 of the connecting pipe 13 and the inlet and outlet corners of the nozzle hole 18 of the entrance nozzle 17 have a large effect on the flow condition of the coolant, but machining and inspection are difficult and errors in coolant distribution may occur. It is also the cause.

The present invention has been made in view of the above points and eliminates the above causes, and allows a predetermined flow rate of coolant to be distributed to each nuclear fuel assembly, thereby contributing to improving the thermal efficiency and safety of the nuclear reactor. It provides nuclear fuel assemblies. That is, as shown in FIG. 2, the present invention provides a nuclear fuel assembly in which a large number of nuclear fuel rods d are arranged in a wrapper tube c to which a handling head a is connected to the upper part and an entrance nozzle b (or 17) is connected to the lower part. For example, as shown in FIGS. 3 to 5, the entrance nozzle 17 has a long diameter hole 19 in the longitudinal direction of the side surface, and the inner surface corner 20 is curved or tapered so as to close the long diameter hole 19. The nuclear fuel assembly is characterized in that a flow regulating plate 22 having a plurality of coolant inflow holes 21 is detachably provided.

Hereinafter, one embodiment of the nuclear fuel assembly according to the present invention will be described with reference to FIGS. 3 to 5.

FIG. 3 shows only the main part of the entrance nozzle 17 of the nuclear fuel assembly, FIG. 4 is a sectional view taken along line AA in FIG. 3, and FIG. 5 is a sectional view taken along line BB in FIG. 4. It is. In each figure, elongated long-diameter holes 19 are formed at 90° intervals on the side surface of the entrance nozzle 17, and a flow rate adjusting plate 22 having the same shape as the hole is fitted into the hole 19. The flow rate regulating plate 22 has four rounded coolant inlet holes 21 formed by cutting the inner corner 20 into a curved surface. A flow rate adjusting plate is removably fitted and fixed in the long diameter hole 19, and the diameter of the coolant inflow hole 21 is arbitrarily selected, and the corners of the inlet and outlet of the hole 21 are rounded by cutting curved surfaces. It exhibits low resistance when the coolant flows.
The coolant flows in from the inflow hole 21 of the entrance nozzle 17 of the nuclear fuel assembly, removes the reaction heat from the nuclear fuel, and emits light from the handling head. In order to be able to be inserted and removed freely, the inner surface of the inflow hole 21, that is, the corner on the outlet side of the coolant, is machined to form a curved surface in advance, so that the coolant flows smoothly and the flow rate can be easily adjusted. This also has the effect of minimizing distribution errors caused by damage caused by the coolant.

The present invention also makes it easier to process the inlet and outlet corners of the coolant inflow hole 21 into any desired shape compared to the conventional example, and the shape of the hole can be accurately inspected. As a result, errors in flow rate distribution during machining of the inflow hole 21 can be minimized.

FIG. 6 shows another embodiment of the nozzle portion of the nuclear fuel assembly of the present invention, with the right half being a longitudinal sectional view and the left half being a side view.

In this embodiment, a long diameter hole, that is, a large diameter hole 23 is formed in each part where the inflow hole 21 in FIG.
4 is removably fitted into the flow rate adjusting plate 25. Further, the corners of the inner and outer surfaces of the inflow hole 24 are machined to be tapered so that the flow of the coolant can be smoothly adjusted. When the flow regulating plate of this embodiment is used, the strength of the entrance nozzle 17 is superior to that of the conventional example, and the flow rate distribution error can be minimized.

Note that the shape of the large diameter hole 23 is arbitrarily selected depending on the processing accuracy. FIG. 7 shows the inlet hole 2 of the flow rate adjusting plate 22 in FIG. 3.
The shape of 1 is not perpendicular to the entrance nozzle 17, but is approximately 4
This shows an example in which the inflow hole 26 has an angle of 5 degrees and a streamlined shape.

This embodiment has the effect of preventing the occurrence of cavitation due to an increase in local flow velocity due to the sudden change in direction of the coolant flow at the inlet hole 26, and also facilitating the formation of a flow distribution mechanism. Note that the hole 26 can be formed by any method such as electrolytic machining, electrical discharge machining, or machining. As explained above, according to the present invention, the flow rate of the coolant flowing in the nuclear fuel assembly can be set with high precision, and the coolant distribution for the reactor can be improved to improve the thermal efficiency and safety of the reactor. A nuclear fuel assembly having a mechanism can be provided.

[Brief explanation of the drawing]

Fig. 1 is a sectional view schematically showing a nuclear reactor to explain the operation of a conventional nuclear fuel assembly, Fig. 2 is a vertical sectional view showing a conventional nuclear fuel assembly, and Figs. 3 to 5 are in accordance with the present invention. 3 shows only the entrance nozzle part of one embodiment of the nuclear fuel assembly according to the invention, FIG. 3 is a side view, and FIG.
A' sectional view, Figure 5 is a BB' sectional view in Figure 4,
FIG. 6 and FIG. 7 are longitudinal sectional front and side views respectively showing the entrance nozzle portion of another embodiment of the nuclear fuel assembly according to the present invention. 1...Reactor vessel, 2...Reactor core, 3
...Blanket area, 4 ... Coolant, 5 ... Heat exchanger, 6 ... Pump system, 7 ... Upper partition wall , 8... Upper low pressure coolant chamber, 9... Intermediate partition wall, 10...
... High pressure coolant chamber 5, 11 ... Bottom wall, 12
...Lower low pressure coolant chamber, 13...Connecting pipe, 14...Horizontal hole, 15...Core nuclear fuel assembly, 16...・Blanket nuclear fuel assembly, 1? ...Entrance nozzle, 18...
... Nozzle hole, 19 ... Long diameter hole, 20 ...
... Inner corner, 21θ ... Coolant inflow hole, 2
2...Flow rate adjustment plate.

Claims (1)

[Claims] 1. In a nuclear fuel assembly formed by arranging a large number of nuclear fuel rods in a wrapper tube with a handling head connected to the upper part and an entrance nozzle connected to the lower part, the entrance nozzle has a long diameter hole in the longitudinal direction of the side surface, and the long diameter hole is 1. A nuclear fuel assembly comprising a removably installed flow control plate having a plurality of coolant inlet holes whose inner corners are curved or tapered so as to be closed.