JPH03215793A - Reactor container - Google Patents

Abstract

PURPOSE:To enhance the efficiency of removing fission products by scrapping by adding a surfactant to the pool water of a suppression chamber, thereby decreasing the region where the pool water attains an overheat state at the time of the vent operation of the container. CONSTITUTION:The surfactant is added to the pool water 3 of the suppression chamber 4 of the reactor container in a hermetic state which houses the reactor pressure vessel and a suppression chamber 4 filled with the pool water 3 in the internal bottom thereof. Surfactants of an animal and vegetable system, such as general-purpose higher alcohols and fatty acids and surfactants of a petroleum system, such as alkyl benzene, are used as the surfactant. Since the surface tension of the pool water is decreased in this way, the pool water is liable to boil eve if the degree of the overheating is small. The quantity of the heat to be removed of the pool water by the boiling is thus increased and the overheating region of the pool water is decreased. As a result, the possibility that the effect of removing the fission products degrades is lessened and the ratio at which radioactive materials are released to the outside of the reactor containing is lowered.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention relates to a reactor containment vessel of a nuclear power plant, etc., and in particular, the present invention relates to a nuclear reactor containment vessel of a nuclear power plant, etc. This invention relates to a nuclear reactor containment vessel that rarely releases substances outside the system.

(Prior art) In general, reactor containment vessels (R C
V) is the reactor pressure vessel (RPV) as shown in Figure 3.
) 1 airtightly housed in an upper conical dry well 2;
It consists of a wet well 5 in which a cylindrical suppression chamber (SP) 4 filled with pool water 3 is arranged. The suppression chamber 4 is a cylindrical container formed integrally with the dry well 2. Its bottom is fixed to the reactor building foundation 6 with anchor bolts, and the bottom is made of steel to prevent pool water 3 from leaking. A lining material 7 is pasted. The dry well 2 and the suppression chamber 4 are separated by a diaphragm floor 8, and a large number of vent pipes 9 are provided to communicate the dry well 2 and the suppression chamber 4. The upper end of each vent pipe 9 is fixed so as to open above the diaphragm floor 8, while the lower end is fixed so as to open into the pool water 3 within the suppression chamber 4. It also branches off from the main steam pipe 10 of the reactor pressure vessel 1, and is connected to a pressure relief valve (SR valve).
11 and a steam release pipe 12 for releasing steam into the pool.
will also be included. Further, a vent pipe 14 is provided in the upper space of the suppression chamber 4 via a pressure balance valve 13 .

Then, due to some unforeseen situation, reactor pressure vessel 1
If the boundary piping ruptures, fission products (
Reactor water and steam containing a large amount of F P) suddenly flow out from the fracture into the dry well 2 of the reactor containment vessel. The leaked high-temperature, high-pressure reactor water evaporates in the dry well 2 and becomes steam. This steam is introduced into the pool water 3 of the suppression chamber 4 via the vent pipe 9. The introduced steam is cooled and condensed by the pool water 3, and the fission products contained in the steam are scrubbed and removed. That is, while the steam containing the fission products becomes bubbles and rises in the pool water 3, the fission products are separated by gravity, moved into the pool water 3 by diffusion, or separated by inertial force. Or, due to steam condensation or the like, it adheres to the surface of the bubbles, that is, the pool water 3, and is removed.

The steam containing fission products that has thus leaked into the reactor containment vessel is condensed in the pool water and at the same time is washed away. As a result, an increase in the internal pressure of the dry well 2 and the suppression chamber 4 of the reactor containment vessel is suppressed, and radioactive substances are prevented from diffusing to the outside.

By the way, in the event of an accident, if the heat removal inside the reactor containment vessel is insufficient and a pressure difference of more than a predetermined value occurs between the internal pressure of the dry well 2 and the internal pressure of the suppression chamber 4 of the reactor containment vessel, the containment vessel A vent operation is performed. That is, the pressure balance valve 13 disposed in the upper space of the suppression chamber 4 opens, and a portion of the high-pressure steam is discharged to the outside of the system via the vent pipe 14. As a result, the dry well 2 and wet well 5 The pressure with is maintained in equilibrium.

In this case, the steam etc. that leaked into the dry well 2 first passes through the pool water 3, and the sufficiently scrubbed steam is discharged through the vent pipe 14, so the rate at which radioactive substances are released outside the system is reduced. Very few.

(Problems to be Solved by the Invention) However, according to the conventional reactor containment vessel, when the containment vessel is vented, the internal pressure of the reactor containment vessel decreases.
Pool water in the suppression chamber may become overheated.

For example, the pressure is 0.4 MPa (about 4 atm), the saturation temperature T
The temperature distribution of the pool water 3 in the suppression chamber 4, which is in equilibrium with the vent steam whose temperature is 143° C., is as shown in FIG. In other words, the overall water temperature T of the pool water 3 is approximately 14% due to the convection that occurs in the height direction.
The temperature remains constant at 6℃. However, in the surface layer of the pool water 3, the degree of superheating ΔT is 3° C. compared to the saturation temperature T of 43° C.

Further, the saturation temperature T becomes higher toward the bottom of the pool where the head pressure of the pool water 3 increases, and the overheated region indicated by diagonal lines is formed up to the bottom of the suppression chamber 4. The opening of the vent pipe 9 etc. is usually approximately 3 m from the level of the pool water 3.
The escape steam is blown into the superheated region.

When steam containing a large amount of fission products is ejected into superheated pool water, the pool water rapidly evaporates toward the inside of the bubble, and the intense flow of steam can cause fission products to adhere to the bubble surface. It becomes difficult. As a result, the scrubbing efficiency of fission products by pool water decreases,
There is a possibility that the removal efficiency will decrease.

The present invention has been made to solve the above problems, and reduces the area where pool water in the suppression chamber becomes overheated during containment venting operations, thereby increasing the removal efficiency of fission products by scrubbing. The purpose is to provide a reactor containment vessel that can be maintained at a high altitude.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a hermetic reactor containment vessel that stores a reactor pressure vessel and is equipped with a suppression chamber whose inner bottom is filled with pool water. It is characterized by the addition of a surfactant to the pool water in the chamber.

(Function) According to the reactor containment vessel having the above configuration, since a surfactant is added to the pool water in the suppression chamber, the surface tension of the pool water is reduced. Therefore, even if the degree of superheating is small, the pool water easily boils, the amount of heat removed from the pool water by boiling increases, and the overheating region of the pool water becomes smaller. As a result, there is less risk that the removal effect of nuclear reaction products by scrubbing will be reduced, and the rate of radioactive materials released outside the reactor containment vessel can be significantly reduced.

(Example) Next, an example of the present invention will be described with reference to the accompanying drawings and compared with a conventional example. FIG. 1 is a sectional view of a main part of an embodiment of a nuclear reactor containment vessel according to the present invention, and is also a diagram showing the temperature distribution of pool water. The present invention is characterized in that a surfactant is added to the pool water, and the other components are the same as the conventional example shown in Figure 3, so the same elements are given the same reference numerals and duplicated. The explanation will be omitted.

That is, the containment vessel according to this embodiment is a reactor pressure vessel 1
The reactor containment vessel is a sealed nuclear reactor containment vessel including a suppression chamber 4 in which a pool water 3 is stretched at the inner bottom thereof, and a surfactant is added to the pool water 3 in the suppression chamber 4.

As the surfactant, a general-purpose higher alcohol, an animal or vegetable oil-based material such as fatty acid, or a petroleum-based material such as alkylbenzene is used. The surfactant may be added to the pool water 3 in advance, or may be added immediately before the containment vessel is vented.

By the way, the reason why when the pressure of the pool water is reduced as in the case of venting the containment vessel, the pool water does not boil even if it reaches the saturation temperature TS and is maintained in a superheated state will be explained below.

In general, the surface tension of the liquid acts on air bubbles generated and mixed in the liquid, so the liquid must be in a superheated state in order for bubbles consisting only of vapor to exist in thermodynamic equilibrium with the liquid. be. The equilibrium bubble radius γ in that case. The relationship between the degree of superheating ΔT and the degree of superheating ΔT is approximately expressed by the following equation (1) based on the Clasius-Clapeyron relation.

...(+) However, J is the work equivalent of heat, σ is the surface tension of the liquid, 0,
ρ and L are v at the saturation temperature T, respectively
r
s vapor density, liquid density, and heat of vaporization. FIG. 4 illustrates this relationship using pressure P as a parameter. As is clear from the above equation (1) and the relationship shown in FIG. 4, a considerable degree of superheating ΔH is required to generate fine bubbles.

In other words, the degree of superheating ΔH of the liquid increases, and the equilibrium bubble radius γ0 calculated from equation (1) above decreases. Boiling will occur when the radius becomes comparable to the radius of a certain bubble nucleus.

However, since the conventional pool water 3 shown in FIG. 2 has a high surface tension, it is difficult to form the fine bubbles necessary for boiling to start. Therefore, there is a drawback that the heat removal effect due to boiling is small, and the overheated region tends to be formed over a wide range as shown by the hatched area. Since the pool water is already saturated or superheated at the outlet of the vent pipe 9, the efficiency of removing nuclear reaction products by scrubbing is reduced.

Therefore, in this embodiment, by adding a surfactant to the pool water 3, the surface tension σ of the pool water 3 is reduced, and when the bubble radius γ0 is kept constant according to the above equation (1), ΔT becomes small. , boiling is more likely to occur. Therefore, as shown in Figure 1, the reduced pressure boiling area is expanded compared to the conventional example shown in Figure 2, and the heat removal effect by boiling is increased, so the overheating area of pool water during reduced pressure boiling is reduced. can do. In Fig. 1, the pressure P is 0.4 MPa (approximately 4 atm), similar to the conventional example shown in Fig. 2.
, is a cross-sectional view showing the boiling state of pool water 3 in the suppression chamber 4 in equilibrium with vent steam S 2 whose saturation temperature T 1 is 143°C. In the case of this example,
The saturation temperature T, at the surface of the pool water 3 is 143°C, but since the heat removal effect by boiling is large, the pool water temperature T is 145°C, and the superheat degree ΔT at the surface is 1 degree lower than before. It is about degree. The overheated region partially appears in more than half of the total depth of the pool water as shown by diagonal lines, while the region less than half of the total depth is filled with pool water at saturated temperature or subcooled water.

Therefore, since the opening position of the vent pipe 9 where the escape steam is spouted out during the venting operation of the containment vessel is filled with subcooled water, there is little rapid evaporation of pool water into the bubbles that are spouted and formed. The contained fission products are effectively attached to the inner surface of the bubbles and separated and removed into the pool water 3.

In other words, even when the containment vessel is vented, a large amount of radioactive materials contained in the leaked reactor water and steam are effectively scrubbed by the pool water 3, so that fission products, etc. are discharged outside the reactor containment vessel. This eliminates the risk of being damaged, and the safety of the nuclear power plant can be further improved.

〔Effect of the invention〕

As explained above, according to the reactor containment vessel according to the present invention, since a surfactant is added to the pool water in the suppression chamber, the surface tension of the pool water is reduced. Therefore, even if the degree of superheating is small, pool water tends to boil.
The amount of heat removed from the pool water by boiling increases, reducing the overheating area of the pool water. As a result, there is less risk that the removal effect of nuclear reaction products by scrubbing will be reduced, and the rate of radioactive materials released outside the reactor containment vessel can be significantly reduced.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part of an embodiment of the reactor containment vessel according to the present invention, and also shows the temperature distribution of pool water, and FIG. 2 shows a suppression chamber of a conventional reactor containment vessel. FIG. 3 is a cross-sectional view showing an example of the configuration of a conventional reactor containment vessel, and FIG. 4 shows the relationship between the degree of superheating of water and the equilibrium bubble radius. This is a graph showing. 1...Reactor pressure vessel (RPV), 2...Dry well, 3...Pool water, 4...Supplement/Solution chamber, 5...Wet well, 6...Reactor building Foundation, 7... Lining material, 8... Diaphragm floor, 9... Bent pipe, 10... Main steam pipe, 11.
...Pressure relief valve (SR valve), 12...Steam relief pipe, 1
3...Pressure balance valve, 14...Vent piping.

Claims (1)

[Claims] A nuclear reactor which is a sealed nuclear reactor containment vessel that stores a reactor pressure vessel and is equipped with a suppression chamber whose inner bottom is filled with pool water, wherein a surfactant is added to the pool water of the suppression chamber. Containment vessel.