JPS6055796B2 - pressure tube reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure tube nuclear reactor, and particularly to a pressure tube nuclear reactor that can improve the flow distribution of heavy water.

As shown in FIG. 1, a pressure tube type nuclear reactor consists of a large number of control rod guide tubes 5 containing control rods 7, a large number of pressure pipes 3 containing fuel assemblies 4, and internal pipes 3 and 5. The main components include a core tank 2, a calandria tank 1 that covers the outside of the core tank 2, and a seismic isolation plate 23 for supporting a large number of pipes 3 and 5 inside the core tank 2. ing.

As shown in FIG. 2, this seismic isolation plate 23 has a circular plate shape with protrusions around the periphery, and has a number of holes bored into it into which the pressure pipe 3 and the control rod guide pipe 7 are inserted. Each tube is supported by being inserted into this hole. Also, this seismic board 2
3, as shown in Figure 1, the core tank 2
It is generally installed near the middle of the height direction.
Therefore, since the seismic plate 23 partitions the core tank 2 into upper and lower chambers, the heavy water channels 26 and 27 through which the heavy water as a moderator supplied to the core tank 2 flows are the holes into which the pipes 3 and 5 are inserted. It is formed between and around the outer periphery as shown by the horizontal line in FIG. Core tank 2 is Countria tank 1
is supported by a support plate 30 at the upper part, and this support plate 3
A heavy water overflow reservoir A is formed with part of the core tank 2 and the calandria tank 1 with the bottom at 0.

The lower end of the core tank 2 is opened, and a packet 25 is provided in the calandria tank 1 so as to cover this opening. That is, the outer peripheral surface of the core tank 2 and the packet 2
During normal operation of the reactor, a free liquid level of heavy water is formed between the inner surface of the support plate 30 and the outer peripheral surface of the core tank 2 and the inner surface of the calandria tank 1. By applying helium (He) gas pressure to the heavy water dump space 8 that is formed, heavy water is prevented from overflowing from the packet 25.This dump space 8 is constructed by removing the He pressure when the reactor is shut down, thereby preventing the heavy water from flowing into the core tank 2. The packet 25 is provided to discharge the heavy water inside the packet 25. Therefore, when stopping the reactor in a hurry, it is necessary to discharge the heavy water quickly, so the heavy water on the upper side of the seismic insulation plate 23 is moved to the lower side. A large flow path is required for rapid movement, and this is the main role of the flow path 27.Heavy water is supplied to the core tank 2 as a neutron moderator through the control rod guide tube 5.From the core tank 2 The overflowing heavy water enters the overflow reservoir A, further passes through the heavy water circulation loop 10, enters the heat exchanger 11, and is cooled by heat exchange with cooling water in the cooling water loop 12.
It passes through a valve 22, removes impurities in a purification tower 15, and enters a dump tank 17. In other words, during normal operation, valves 20 and 21
is closed. The cooled heavy water in the dump tank 17 is sent to the control rod guide pipe 5 by the circulation pump 18 and circulated through the above flow path. A liquid poison (for example, boron-10) is dissolved in the heavy water to absorb neutrons and reduce the output.

That is, the output can be increased or decreased by changing the amount of liquid poison dissolved in heavy water. For example, when increasing the output, the valve 22 is closed and the valve 21 is opened. As a result, the heavy water in the loop 10 enters the poison removal tower 14 to remove poison, reducing the amount of poison dissolved in the heavy water and increasing the output. In the case of a decrease in output, the valves 21 and 22 are closed and the valve 20 is opened to introduce heavy water into the poison dissolving tank, increase the amount of dissolved poison, and reduce the output. 6 is a drive device for the control rods 7, 13 is a cooling water circulation pump for the heat exchanger 11, and 19 is a cooling water circulation pump in the core tank 2. This is a dump valve that is opened when heavy water is discharged to the dump tank 17.

In the pressure tube type nuclear reactor as described above, the overflow from the upper part of the core tank 2 is used as a heavy water circulation path from the core tank 2 due to the necessity of dumping as described above.

Therefore, in order to give flow to the heavy water in the core tank 2,
Since it is necessary to supply heavy water to the lower side of the core tank 2 as shown in the first diagram, the heavy water outflow holes 24 bored in the control rod guide pipes 5 through which the heavy water flows out into the core tank 2 are installed in the seismic insulation plate. It is located in the lower part of the reactor core tank 2, and has heavy water passages 26 and 27 of the seismic insulation plate 23 shown in FIG. It is configured to form. That is, if heavy water flows out above the seismic isolation plate 23, the heavy water flow will be formed only above the earthquake isolation plate 23 because the heavy water outlet is at the upper end of the core tank 2. Therefore, although the outflow hole 24 is provided as shown in the figure, even in such a configuration, there are portions in the core tank 2 where the flow of heavy water is not formed. In view of the above, an object of the present invention is to increase the flow rate of moderator in the upper part of the reactor core. A feature of the present invention is that the moderator supply device disposed in the central part of the power landlier tank has moderator spouting ports in each area above and below the seismic plate in the power landlier tank. The moderator supply device disposed around the landria tank has a moderator outlet in a region below the seismic plate. The present invention was made by studying in detail the flow distribution of heavy water in the core tank 2 of the pressure tube nuclear reactor shown in FIG. The results of this study are described below. The heavy water that has flowed to the bottom of the seismic board 23 is transferred to the top of the seismic board 23.
It moves through channels 26 and 27 formed in the seismic plate 23, but inevitably a large amount of water flows from the part with less resistance.In other words, the flow area is much larger than that of the channel 26. The flow rate flowing through the flow path 27 is overwhelmingly large, and heavy water forms a main flow near the outer periphery of the seismic plate 23 and near the inner wall surface of the core tank 2, and almost no flow is formed near the center of the core tank 2. This state is shown in FIGS. 3 and 4.

As shown in Fig. 3, move the seismic plate 23 in the radial direction. When the flow rate distribution in the height direction of the core tank 2 in each region was investigated, the results shown in FIG. 4 were obtained.

In FIG. 4, the flow rate distributions in regions C and 2 are omitted.
As can be seen from Fig. 4, the flow rate of heavy water passing through the seismic plate 23 is approximately 0.25 k9 /
S, and about 1.6k in the outermost area
It can be seen that at 9/S, the flow rate to the region is about 6.4 times that of the region A.

(The diagram in FIG. 4 shows the flow rate distribution when the seismic isolation plate 23 is provided near the center of the core tank 2 in the height direction, as shown in FIG. 1. In cases where there is a significant difference in the flow rate of heavy water, if liquid poison is injected into or removed from the heavy water moderator, most of the heavy water will escape to the channel 27 outside the core below the seismic isolation plate 23, as described above. Therefore, during a transient period, the liquid poison concentration (dissolved amount) only below the seismic plate 23 increases or decreases.

Therefore, the power distribution in the core height direction is greatly affected by the liquid poison operation, which not only adversely affects the integrity of the fuel but also induces senone vibration in the core height direction, which poses a problem in reactor control. Furthermore, the heavy water circulating in the reactor receives heat from neutrons and gamma heat generation in the reactor core, and its temperature increases.
Therefore, as described above, the heavy water temperature is cooled by cooling water in the heat exchanger 11 and flows into the core. However, as mentioned above, most of the heavy water in the core tank 2 escapes to the flow path 27 outside the core below the seismic isolation plate 23, so the heavy water temperature distribution in the core tank 2 is as shown in Figure 5. The temperature is very high in the central region, and there is little margin for the boiling point.
Therefore, when the output increases slightly or the temperature of the cooling water inside the pressure tube 3 increases, the heavy water may boil and radioactive tritium may be released outside the reactor. Furthermore, it is known that this type of nuclear reactor has the highest output in the center of the core, and the output decreases toward the outside.

Therefore, in order to make the power distribution in the radial direction of the furnace uniform,
It is desirable to increase the poison concentration in the central portion, that is, to increase the flow rate of heavy water in the central portion, but in the conventional configuration described above, the flow rate of heavy water is completely opposite, and this also poses a problem in output control. These drawbacks are caused by the fact that the flow rate of heavy water in the core tank 2 is low near the center and high near the outer periphery, as described above, so if the flow rate of heavy water is optimized, the above drawbacks can be eliminated. will be resolved.

Therefore, for example, one way to eliminate this cause is to enlarge the heavy water flow holes 26, but in this case, the pitch of the pressure pipes 3 must be widened from the viewpoint of the strength of the seismic plate 23.

However, if the pitch of the pressure tubes 3 (generally 24c!n) is increased, the core reactivity decreases, as shown in FIG. 6, and the neutron economy worsens. There are also cases where the reactor does not become critical unless the enrichment of the fuel is increased. Another method of improving the heavy water flow rate distribution is to provide a dump channel near the center of the seismic isolation plate 23, but this is extremely difficult to realize in the current configuration due to space constraints. . The present invention has been conceived in view of the above matters, and one embodiment of the present invention will be described below with reference to FIGS. 7 and 8.

FIG. 7 is a sectional view of a power landlier tank and a reactor core tank, and the same parts are given the same reference numerals as above.

The difference from the configuration shown in FIG. 1 is that heavy water outflow holes 31 are also provided on the upper side of the seismic insulation plate 23.

This heavy water outflow hole 31 is placed at a position to ensure the flow rate near the center of the core from the seismic isolation plate 23 to the upper part of the core as shown in FIG. The size of the holes 31 or the number of holes to be drilled are determined so that the overall flow rate distribution is large near the center of the core and small on the outside, taking into account the flow rate of heavy water flowing upward from the flow path 26. ing. In this embodiment, in order to increase the flow rate of heavy water near the center of the reactor core, heavy water outflow holes are provided in the control rod guide tube 5 located near the center of the reactor core, one on the upper side of the seismic plate 23, and one on the lower side of the seismic plate 23. In the other control rod guide tubes 5, one is provided only at the lower side of the seismic isolation plate 23.

The heavy water flow rate situation with this configuration is shown in Figure 8.
Similar to the examples shown in FIGS. 3 and 4, FIG. 8 shows that the core tank 2 is divided in the radial direction into regions A to I in order from the center.
The flow rate changes in the core height direction are shown for each region. From this figure, at the position of the seismic plate 23, in the area A, the weight is about 3.7k9/in the area S1, it is about 1.2kg/
It can be seen that the flow rate in the central part of the core is approximately three times that in the outer part.

The optimal flow rate ratio between the central and outer parts of the core varies depending on various specifications, such as the number of fuel assemblies and their dispersion rate within the core. good.

In this example, a large number of heavy water outflow holes are provided in the control rod guide tube near the center of the reactor core, and they are also provided above the seismic plate to increase the flow rate near the center of the reactor core, thereby stabilizing the power distribution of the reactor core. This also makes it easier to control the reactor output.

That is, uniform output control is possible only by adjusting the poison concentration. According to the present invention, the flow rate of moderator above the seismic plate in the center of the core can be increased, and the power distribution of the core can be flattened.

This facilitates power control of the reactor.

[Brief explanation of the drawing]

Figure 1 is a schematic explanatory diagram of a pressure tube nuclear reactor, Figures 2 and 3 are plan views of seismic plates, Figure 4 is a diagram showing the heavy water flow rate distribution in the reactor shown in Figure 1, Figure 5 is a schematic diagram of the core showing the temperature situation in the height direction of the core tank, Figure 6 is a diagram showing the relationship between the arrangement pitch of fuel assemblies and reactivity, and Figure 7 is a diagram of one of the heavy water outflow devices of the present invention. A side sectional view of a core tank showing an example,
FIG. 8 is a diagram showing the heavy water flow rate distribution of the embodiment shown in FIG. 7. 1... Force land rear tank, 2... Core tank, 3... Pressure pipe, 5... Control rod guide tube, 9...・Heavy water, 23... Seismic plate, 24, 31... Heavy water outflow hole, 26, 27.
...Heavy water flow path.

Claims (1)

[Claims] 1. A calandria tank filled with a moderator containing liquid poison, a plurality of pressure pipes penetrating the calandria tank and into which fuel assemblies are loaded, and a plurality of pressure pipes installed inside the calandria tank to control the pressure. In a pressure tube nuclear reactor comprising a seismic plate through which a pipe passes and has a flow path for the moderator, and a device for supplying the moderator into the calandria tank, disposed in the center of the calandria tank. The moderator supply device has moderator spout ports in each area above and below the seismic plate in the calandria tank, and the moderator supply device is arranged in a peripheral area of the calandria tank. The device is a pressure tube nuclear reactor, characterized in that the device has a moderator spout in a region below the seismic plate.