JPH03590B2 - - Google Patents

Description

[Detailed description of the invention] During an emergency shutdown of the reactor reaction in a fast breeder reactor, the temperature of liquid sodium inside the reactor drops rapidly, and the flow rate of liquid sodium flowing into the reactor decreases from 100% of the rated value. This decreases to 9.5%. The liquid sodium flowing into the furnace is much lower in temperature than the liquid sodium remaining in the furnace, and as the flow rate decreases, the jet no longer has the ability to penetrate the liquid sodium inside the furnace.
The inflow low temperature liquid sodium is not sufficiently mixed with the remaining high temperature liquid sodium, and the high temperature liquid sodium and the low temperature liquid sodium form separate layers. Since high-temperature liquid sodium has a lower specific gravity than low-temperature liquid sodium, a stratification phenomenon occurs in which a layer of high-temperature liquid sodium floats on a layer of low-temperature liquid sodium. At this time, since there is a layer of high-temperature liquid sodium in the upper part and low-temperature liquid sodium in the lower part, a large temperature difference occurs in the axial direction of the reactor pressure vessel, and a large temperature gradient occurs in the reactor body material. This temperature gradient occurs at structural discontinuities and places where stress concentration is likely to occur.
For example, if it occurs in the nozzle, it will cause problems in terms of the structure of the reactor vessel.

Figure 1 shows an overview of the structure of the reactor vessel.
A liquid sodium inlet nozzle 2 and a liquid sodium outlet nozzle 3 are attached to the body, and an inner cylinder 4 is disposed within the body to guide the liquid sodium upward. The inner cylinder 4 has a height near the center of the outlet nozzle 3 for the purpose of securing a coolant flow path necessary for the decay heat removal operation that is performed after stopping the normal output operation after the liquid sodium pipe breaks. A large number of small-diameter flow holes 5 are bored on the circumference, and when the stratification phenomenon occurs, low-temperature liquid sodium flows from these flow holes 5 to the outlet nozzle 3, and inside the outlet nozzle 3. The low-temperature liquid sodium and the high-temperature liquid sodium separate to form a layer, creating a severe circumferential temperature distribution at the exit nozzle, which poses problems in the structure of the reactor vessel.

Figure 2 shows this state, with a relatively thin intermediate layer M at intermediate temperature sandwiched between the high-temperature liquid sodium H layer and the low-temperature liquid sodium L layer, which are mixed by diffusion. When the liquid level rises and exceeds the height of the flow hole 5 of the inner cylinder 4, the low temperature liquid sodium L flows out from the flow hole 5, and the low temperature liquid sodium L and the high temperature are sandwiched between the thin intermediate layer M at the outlet nozzle 3. A layer of liquid sodium H forms, creating a large temperature gradient in the container.

The present invention has been proposed in order to eliminate such problems, and includes arranging a group of flow holes in an inner cylinder installed in the shell of a reactor vessel at the level of the outlet nozzle in the shell. , a row of upper flow holes is arranged above the flow holes, and the low temperature liquid sodium flowing out from each flow hole mixes with the high temperature liquid sodium and then reaches the outlet nozzle part. The present invention relates to a reactor vessel for a fast breeder reactor characterized by:

In the present invention, as described above, a group of flow holes is arranged in a row at the outlet nozzle level in the inner cylinder installed in the shell of the reactor vessel.
When the liquid level in the furnace drops from the upper end of the inner cylinder due to a pipe breakage accident, etc., liquid sodium quickly flows out from the flow hole group, and the liquid level in the annular part formed between the shell and the inner cylinder drops too much. This prevents the outlet nozzle from becoming exposed.

In addition, the low-temperature liquid sodium flowing out from the flow hole group and the flow hole group above it,
After being mixed with high-temperature liquid sodium and reaching an intermediate temperature, it enters the outlet nozzle section, so the temperature difference in the liquid sodium layer is reduced, and severe temperature distribution in the nozzle section where stress concentration is likely to occur is avoided.
Furthermore, when the stratification phenomenon of the high-temperature and low-temperature liquid sodium occurs, one row of upper flow holes is provided above the flow holes, so that the liquid sodium flows from the flow holes in the upper part of the inner cylinder. The outflow amount is suppressed to a minimum, and the interface between the low-temperature and high-temperature liquid sodium in the inner cylinder can quickly reach the upper end of the inner cylinder, and only one row of flow holes is provided above the outlet nozzle. As has been confirmed through experiments, by keeping the reactor in place, the axial temperature gradient of the outlet nozzle can be sufficiently alleviated, and the structural safety of the reactor vessel can be ensured. be.

The present invention will be described below with reference to the illustrated embodiments.

In FIG. 3, a liquid sodium inlet nozzle 12 and a liquid sodium outlet nozzle 13 are arranged in the shell 11, and an inner cylinder 14 installed in the shell 11 has a large number of them arranged on the circumference at the height of the center of the outlet nozzle 13. A small-diameter flow hole 15 is formed, and a small-diameter flow hole 16 is further formed above the flow hole 15 in the circumferential direction.

The low temperature liquid sodium enters the body 11 from the inlet nozzle 12, but when a stratification phenomenon occurs, the low temperature liquid sodium and the high temperature liquid sodium remaining in the vessel form a layer, and the liquid level of the low temperature liquid sodium increases. rises, and the flow hole 15 of the inner cylinder 14
The low temperature liquid sodium exceeding the height flows out from the flow hole 15, and at the outlet nozzle 13, the low temperature liquid sodium and the high temperature liquid sodium flow out of the vessel while forming a layer. When the liquid level of the low-temperature liquid sodium rises further and exceeds the height of the flow hole 16, the low-temperature liquid sodium flowing out from the flow hole 16 becomes a high-temperature liquid flowing down the annular portion between the shell 1 and the inner cylinder 4. It mixes with sodium, reaches an intermediate temperature, enters the outlet nozzle 13, and quickly replaces the layer of high temperature liquid sodium with a layer of intermediate temperature liquid sodium on top of the layer of low temperature liquid sodium. Temperature gradients that occur in equipment can be alleviated.

Figure 4 shows this state, where a layer of low-temperature liquid sodium L and a layer of high-temperature liquid sodium H are sandwiched between them by a relatively thin layer of intermediate temperature mixed by diffusion. When the surface rises and the liquid level exceeds the height of the flow hole 15, the low temperature liquid sodium L flows out from the flow hole 15, and the outlet nozzle 13 is temporarily filled with a layer of low temperature liquid sodium L and high temperature liquid sodium H. However, when the liquid level of the low-temperature liquid sodium L rises further and exceeds the height of the flow hole 16, the flow hole 16
Low-temperature liquid sodium L leaked out, and cylinder 11
It mixes with high temperature liquid sodium H in the annular part 17 between the inner cylinder 14 and the inner cylinder 14, reaches an intermediate temperature, and passes through the outlet nozzle 1.
3 parts of low-temperature liquid sodium L is filled above the layer, thereby making it possible to reduce the temperature difference between the layers and the thermal stress based thereon. The position of the flow hole 16 is set at such a height that the low temperature liquid sodium flowing out from the flow hole 16 can be mixed with the high temperature liquid sodium before reaching the outlet nozzle 13.

Figures 5 and 6 show the results of a simulation experiment using water, respectively, and Figures 7 and 8 show the results of the conventional structure and the structure of the present invention at the upper and lower measurement points A and B of the outlet nozzle section, respectively. The change in temperature of liquid sodium over time is shown, and the results demonstrate that the present invention is highly effective.

Although the present invention has been described above with reference to embodiments, the present invention is, of course, not limited to these embodiments, and can be modified in various ways without departing from the spirit of the invention. .

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of the reactor vessel of a conventional fast breeder reactor, FIG. 2 is a longitudinal sectional view showing the state at the time of emergency shutdown of the reactor reaction, and FIG. 3 is a longitudinal sectional view of the reactor vessel of a conventional fast breeder reactor. FIG. 4 is a vertical cross-sectional view showing an embodiment of the reactor vessel, FIG. 4 is a longitudinal cross-sectional view showing the state at the time of emergency shutdown of the reaction in the reactor, and FIGS. 5 and 6 are the reactor vessels of the conventional reactor vessel and the present invention, respectively. 3 is a chart showing experimental results of temperature changes of liquid sodium at the outlet nozzle portion of the device. 11... Trunk, 11'... Y piece part, 12...
Inlet nozzle, 13... Outlet nozzle, 14... Inner cylinder, 16... Flow hole.

Claims (1)

[Claims] 1. In an inner cylinder installed in the reactor vessel shell, one row of flow holes is arranged at the level of the outlet nozzle in the shell, and one row of upper flow holes is arranged above the same flow hole group. A nuclear reactor vessel for a fast breeder reactor, characterized in that the low temperature liquid sodium flowing out from each of the flow holes is configured to mix with the high temperature liquid sodium and then reach the outlet nozzle section.