JP2616973B2 - Pressure reduction structure inside the containment vessel - Google Patents

Description

The present invention relates to a pressure reduction structure in a containment vessel,
More specifically, the present invention relates to a pressure reduction structure in a containment vessel that is suitable for condensing steam released at the time of a pipe break accident and suppressing an increase in internal pressure.

[Conventional technology]

In the containment vessel of a boiling water reactor, when a pipe breaks, the steam that has been jetted into the containment vessel is led to the substraction pool in the pressure suppression chamber, where it is condensed in water to suppress the rise in pressure inside the containment vessel. ing.

In other words, at the time of blow-down immediately after a pipe breakage accident, a large amount of steam energy stored in the reactor pressure vessel is released into the containment vessel, and the steam is condensed in the suppression pool.

Then, the heat transmitted to the suppression pool is released to the outside of the containment vessel using the residual heat removal system, and as long as the residual heat removal system functions properly, long-term cooling after the accident Sometimes the pressure in the containment is not a problem.

By the way, the pressure in the containment vessel during the long-term cooling process after a pipe breakage accident can be expressed as the sum of the steam partial pressure, the non-condensable gas partial pressure, and the hydrostatic pressure of the vent pipe for pushing steam from the dry well into the suppression pool. it can.

In the event of a pipe break, the inert gas that fills the containment vessel during normal operation moves along with the flow of steam from the dry well to the suppression pool and accumulates in the wet well without condensing in the pool. The partial pressure of the non-condensable gas increases in the wet well.

Here, consider dividing the dry well into a plurality.

FIG. 1 is an explanatory view of the internal structure of a reactor containment vessel in which a dry well is divided into two parts.

In FIG. 1, the reactor containment vessel is filled with an inert gas (nitrogen or the like) during normal operation, but the steam released to the dry well (I) 1 at the time of a pipe break accident is:
The inert gas flows into the suppression pool 3 together with the inert gas, and the vapor condenses in the water.

The non-condensable gas is accumulated in the vapor-phase wet well 2 above the suppression pool 3, and the wet well 2 passes through the check valve 5 to the dry well (I
I) Since it is connected to 1 ', if the internal pressure of the wet well 2 rises and exceeds the operating pressure of the check valve 5, the non-condensable gas flows into the dry well (II) 1' and II) Dispersed and accumulated in both 1 'and wet well 2.

FIG. 2 shows an evaluation of the effect when the dry well is divided into two parts. The horizontal axis indicates the dry well division ratio, and the vertical axis indicates the partial pressure of the non-condensable gas in the wet well. This example shows that when the dry well is divided into two parts, the partial pressure of the non-condensable gas can be reduced by about 30% as compared with the case where the division is not performed.

FIG. 3 is an explanatory view of the internal structure of the containment vessel different from FIG. 1 in which the dry well is divided into two parts.

That is, FIG. 3 shows the divided dry wells 1,1 '.
An example in which one of the dry wells 1 ′ includes a space portion of the reactor pressure vessel and the pressure suppression chamber and a space portion (cavity) below the reactor pressure vessel is shown.

In this example, the wet well 2 and the cavity are connected by the siphon 11 and the vent pipe 4 '. In the event of an accident, the water rises in the siphon 11 due to the increase in the pressure of the wet well 2, and the siphon 11 When the top of the is reached, fill the cavity with suppression pool water.

At this time, the water level in the vent pipe 4 'also rises due to the increase in the pressure of the wet well 2, but the vent pipe 4'
Is located above the siphon 11 and the cavity-side outlet of the vent pipe 4 'is above the normal suppression pool water level, so that water is continuously supplied from the vent pipe 4' to the cavity side. It does not flow.

When the pressure in the cavity rises due to the suppression pool water flowing into the cavity, the non-condensable gas in the cavity moves to the wet well 2 via the vent pipe 4 '. In the example, the injection of the suppression pool water into the cavity also has the advantage that the reactor core can be cooled from the outer wall of the containment vessel.

The conventional example of the residual heat removal system and the improved example of the residual heat removal system by dividing the dry well into a plurality of parts are as described above. Here, the residual heat removal system is simplified, or Consider a natural heat radiation system in which a water pool is provided on the outer periphery of the containment vessel so that heat can be removed from the containment vessel even when the heat removal system does not operate.

In this case, first, a large amount of retained water in the containment vessel absorbs heat and the temperature of the pool water rises, and heat is transmitted to the outer peripheral pool by a temperature difference between the inside and outside of the containment vessel wall. When the temperature of the outer pool reaches the saturation temperature, the outer pool water starts to evaporate, and the decay heat is removed in the form of latent heat of evaporation of the pool water.

The temperature of the suppression pool water in the containment reaches its maximum value when the decay heat is balanced with the amount of heat released from the containment vessel, and thereafter decreases as the decay heat decreases.

When comparing the natural heat radiation method using the above outer pool with the heat radiation method using the residual heat removal system, in the natural heat radiation method, heat is transferred using the temperature difference as the driving force,
The pool water temperature in the containment vessel is higher and the saturated vapor pressure is higher than in the method of radiating heat using the residual heat removal system.

Therefore, measures for maintaining the pressure in the containment vessel at a reasonable design value or less are more important than the method of radiating heat using the residual heat removal system.

 Here, consider the vapor pressure in the containment vessel.

In a quasi-steady state where the change is gentle, as in a long-term cooling process, the vapor pressure in the wet well is a saturated vapor pressure corresponding to the vapor temperature, and the vapor temperature of the wet well is the surface temperature of the suppression pool water. Is considered equal to

Therefore, in order to keep the vapor pressure in the containment vessel low, the surface temperature of the suppression pool water may be kept low.

However, in practice, the temperature stratification develops in the lower part of the pool, so that the water temperature in the lower part of the pool becomes low even in the outer peripheral pool.

The fourth is an example in which the temperature distribution in the suppression pool and the outer peripheral pool is analyzed, and it can be seen that a region having a low water temperature is also formed below the outer peripheral pool.

By the way, in the outer peripheral pool, an upward flow is generated along the wall surface due to heat radiation from the storage container, and this flow forms a large circulation in the pulley.

However, as shown in FIG. 4, when there is a sufficiently large pool width with respect to the boundary layer, the downward flow velocity becomes extremely gentle, and the mixing of the liquids by circulation is poor.

According to a simple evaluation, about 90% of the heat released from the containment vessel is transmitted from the suppression pool to the peripheral pool, and among them, the temperature located at the top of the temperature stratification shown in Fig. 4 It is known that the region where is uniform greatly contributes to the heat transfer.

Therefore, if the temperature on the outer peripheral pool side corresponding to the region that greatly contributes to the heat transfer can be reduced, the temperature of the suppression pool water in the storage container, that is, the saturated vapor pressure in the suppression pool can be reduced.

On the other hand, the present applicant has previously proposed a technique of providing a pool water circulation control plate in the outer pool water of the containment vessel (Japanese Patent Laid-Open No. 63-75594).

[Problems to be solved by the invention]

The pool water circulation control plate is erected vertically in the center of the outer peripheral pool of the containment vessel, and the circulation of pool water due to heat radiation from the containment vessel flows upward and downward from the pool water circulation control plate. In this case, the mixing ratio of the liquid in the outer peripheral pool is increased to lower the temperature thereof, and the temperature of the suppression pool water in the containment vessel, that is, the saturated vapor pressure in the suppression pool is reduced.

The present invention simplifies the residual heat removal system, or provides a water pool around the containment vessel so that heat can be removed from the containment vessel even if the residual heat removal system does not operate. The purpose of the heat dissipation method is to increase the mixing ratio of liquid per unit time in the outer peripheral pool in the cooling process after the pipe breakage accident, and thus increase the temperature of the suppression pool water in the containment vessel. That is, it is an object of the present invention to provide a highly safe pressure reduction structure in a reactor containment vessel that can lower the saturation vapor pressure in a suppression pool earlier than before.

[Means for solving the problem]

The object is to provide a dry well containing a nuclear reactor, a suppression chamber having a coolant therein, a suppression pool in the suppression chamber, a wet well that is a vapor phase of the suppression pool, the dry well and the dry well. In the atomic path containment vessel provided with a vent pipe connecting the suppression pool and further having a pool storing water on the outer periphery of the containment vessel and having a pool water circulation control board in the outer periphery pool water, as the pool water circulation control board, In order to accelerate the downward flow of natural convection in the pool induced by the upward flow along the wall surface of the containment vessel, this is achieved by providing a pool water circulation control plate in which the distance from the wall surface of the containment vessel increases toward the lower part of the pool.

[Action]

If a pool water circulation control plate is arranged in the outer pool water so that the flow path becomes narrower toward the lower part of the flow path of the descending flow, the descending flow is accelerated, and if there is no pool water circulation control plate, or the pool water circulation The control plate reaches the bottom of the pool with a larger flow velocity than in the case where the control plate is erected vertically, and temperature stratification at the bottom of the pool is quickly avoided.

As a result, the mixing ratio of the liquid per unit time in the outer peripheral pool is higher than before, and the pool water temperature in the area that greatly contributes to the heat transfer of the outer peripheral pool is increased when there is no pool water circulation control plate or when the pool water circulation It becomes lower earlier than when the control plate is erected vertically.

〔Example〕

 Hereinafter, the present invention will be described with reference to the drawings.

 FIG. 5 shows an embodiment of the present invention.

That is, in FIG. 5, the pool water circulation control plate 9 is installed in the outer peripheral pool 8 so that the flow path area on the side of the containment wall 10 below the pool 8 is widened. When the flow rising along the containment wall surface 10 tries to form a circulation in the pool 8 and descend, the pool water circulation control plate 9 reduces the flow path area.
This accelerates the downward flow, and the accelerated downward flow is generated by the pool 8 at a larger flow rate than when the pool water circulation control plate 9 is not provided or when the pool water circulation control plate 9 is set up vertically. To quickly avoid temperature stratification at the bottom of the pool 8.

As a result, the mixing ratio of the liquid per unit time in the outer peripheral pool 8 is higher than in the past, and the pool water temperature of the region that greatly contributes to the heat transfer of the outer peripheral pool 8 becomes higher when the pool water circulation control plate 9 is not provided. Alternatively, the temperature may be lowered earlier than when the pool water circulation control plate 9 is erected vertically, and the temperature of the suppression pool water in the containment vessel, that is, the saturated vapor pressure in the suppression pool may be lowered earlier than before. Can be.

That is, the present invention is intended to utilize a physical phenomenon of an increase in momentum due to an increase in flow velocity.

FIG. 6 shows a second embodiment of the present invention. In the embodiment of FIG. 6, a plurality of outer peripheral pool water circulation control plates 9 are provided. In addition to the same effects as in the embodiment shown in FIG. 5, the holes 12 provided in the plurality of outer peripheral pool water circulation control plates 9 at different positions have the effect of further promoting the mixing of the liquid in the outer peripheral pool 8. is there.

〔The invention's effect〕

As described above, the present invention simplifies the residual heat removal system, or
According to the present invention, a natural heat radiation method in which a water pool is provided around the containment vessel so that heat can be removed from the containment vessel even when the residual heat removal system does not operate, In the cooling process after the accident, the mixing ratio of the liquid per unit time in the outer peripheral pool is increased from the conventional level, and the temperature of the suppression pool water in the containment vessel, that is, the saturated vapor pressure in the suppression pool, is reduced earlier than before. Thus, it is possible to obtain a pressure reduction structure in the reactor containment, which can be reduced to a minimum and has excellent safety.

[Brief description of the drawings]

FIG. 1 is an explanatory view of the internal structure of a reactor containment vessel in which a dry well is divided into two parts, FIG. 2 is a characteristic diagram of non-condensable gas pressure showing an effect when the dry well is divided into two parts, and FIG. FIG. 4 is an explanatory view of the internal structure of the reactor containment vessel which is divided into two parts and is different from FIG. 1, FIG.
The drawings are explanatory views of the internal structure of the containment vessel showing the first and second embodiments of the present invention, respectively. 1 ... dry well (I), 1 '... dry well (I
I) 2, wet well, 3 ... suppression pool, 4 and 4 '... vent pipe, 5 ... check valve, 6 ...
... dry well bulkhead, 7 ... core, 8 ... outer peripheral pool,
9 ... pool water circulation control board, 10 ... wall of containment vessel, 11 ...
... siphon, 12 ... hole.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-61995 (JP, A) JP-A-58-2691 (JP, A) JP-A-63-75594 (JP, A) 27499 (JP, U)

Claims (2)

(57) [Claims] 1. A dry well containing a nuclear reactor, a suppression chamber having a coolant therein, a suppression pool in the suppression chamber, a wet well that is a vapor phase of the suppression pool, and the dry well. The atomic path containment vessel provided with a vent pipe connecting the suppression pool and further having a pool in which water is stored on the outer periphery of the containment vessel, and a pool water circulation control board provided in the outer periphery pool water. In order to accelerate the downward flow of natural convection in the pool induced by the upward flow along the containment wall surface, a pool water circulation control plate is provided, in which the distance from the containment wall surface increases toward the lower part of the pool. Pressure reduction structure inside the containment vessel. 2. A plurality of outer peripheral pool water circulation control plates according to claim 1, wherein a plurality of outer peripheral pool water circulation control plates whose distance from the wall surface of the containment vessel increases toward the lower part of the pool are shifted. Pressure reduction structure inside the PCV with holes.