JPS6129679B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a relief vent pipe, and more particularly to a relief vent pipe for a pressure suppression containment vessel of a boiling water nuclear reactor.

Figure 1 schematically shows the containment vessel of a conventional boiling water reactor, which includes a dry well 2 that houses a reactor pressure vessel 1, a donut-shaped torus-shaped pressure suppression chamber (hereinafter referred to as torus) 3, and a dry well 2 that houses a reactor pressure vessel 1. , and a vent system connecting these, and the torus 3 is filled with pool water 4, which is cooling water.

As shown in FIG. 2, the vent system consists of a vent pipe 5 and a relief vent pipe 6, and the lower portions of the vent pipe 5 and the relief vent pipe 6 are immersed in the pool water 4. The vent pipe 5 is installed in order to discharge the air in the dry well 2 and the reactor cooling released from the reactor into the dry well 2 into the pool water and condense it in the event of a coolant loss accident hypothetically rupturing a reactor pipe. ing. On the other hand, the relief vent pipe 6 is installed to directly release the steam released through the relief valve into the pool water 4 and condense the steam when the pressure inside the reactor pressure vessel is reduced.

When the relief valve is opened, the bubbles expand and compress repeatedly until the high-temperature, high-pressure steam released from the reactor pressure vessel escapes into the pool water, causing a large transient load (bubble pressure pulsations). Furthermore, during the period when steam is discharged from the relief vent pipe into the pool water, repeated loads act on the relief vent pipe and the structure in the pool water due to steam condensation vibrations that occur over a long period of time at the outlet of the relief vent pipe.

When the relief valve is closed, the steam released from the reactor pressure vessel to the relief vent pipe 6 stops.
The pool water 4 rises inside the pipe while water flows backward from the discharge port and condenses the water vapor inside the pipe. At this time, since the inside of the relief vent pipe 6 becomes negative pressure, the vacuum breaker 7 installed upstream of the relief vent pipe 6 operates, and air flows into the pipe. As a result, the water level that has risen within the relief vent pipe 6 also falls to a normal position.

An object of the present invention is to prevent damage to the reactor containment vessel.

The present invention is a relief vent pipe for condensing steam, and the point is that steam can be completely condensed by placing the relief vent pipe near the water surface without extending it into the water. This invention relates to a relief tube that is characterized by the following features.

By placing the outlet above the water surface as in the present invention, (1) The bubble pulsating load when air is released is eliminated.

(2) Repetitive fatigue stress directly applied to the vent pipe during steam condensation is eliminated.

(3) When the relief valve is closed, there is no backflow of water and there is no need for a vacuum breaker.

FIG. 3 shows an embodiment of the present invention.

The relief vent pipe 6 is cut at a position where it just touches the surface of the pool water 4.

When the relief valve is opened and high-temperature, high-pressure steam within the reactor pressure vessel flows into the relief vent pipe 6, the air within the relief vent pipe 6 is immediately pushed out by the steam. At this time, the relief vent pipe 6 is not immersed in water, so the air inside the relief vent pipe 6 is not compressed and is discharged to the extent that it slightly dents the surface of the pool water 4 directly below the discharge port.

Therefore, repeated loads due to bubble pulsations in the pool water 4 do not occur as in the prior art.

Subsequently, high-temperature, high-pressure steam from the reactor pressure vessel 1 is vigorously discharged from the discharge port. The relief valve operates when the pressure inside the reactor pressure vessel 1 is extremely high (approximately 80 kg/cm ² a), so the released steam collides with water at a very high speed and is completely destroyed. condensed into. This was confirmed by experiment. At this time, the vibration load accompanying steam condensation does not act on the relief vent pipe 6 either.

Even when the relief valve is closed, the pool water 4 does not flow back into the relief vent pipe 6, and as the relief vent pipe 6 is cooled by the atmosphere, atmospheric air slowly flows in from the outlet. I will do it.

Therefore, in the case of the present invention, the vacuum breaker 7
is no longer necessary, and at the same time, there is no sudden backflow of water and no load is applied to the relief vent pipe 6.

FIG. 4 shows a system in which the tip of the relief vent pipe 6 is formed into a nozzle 8 system, which allows the steam to be released even faster and is effective even when the flow rate of steam is relatively small.

FIG. 5 shows an umbrella 1 with holes 9 in the embodiment of FIG. 4.
0, and all holes 10 are submerged in water. However, the hole 9 is installed to a position close to the surface of a considerable amount of pool water 4.

As a result, the air released from the relief vent pipe 6 suddenly spreads widely in the pool water 4,
It goes out through hole 9 installed in umbrella 10, which is closer to the water surface. However, even in this case, since the hole 9 is shallowly immersed in water, the pressure of the bubbles hardly increases.

When steam is released, water whose temperature has increased due to condensation is released over a wide area along the cap 10, and surrounding water flows in through the holes 9. According to this embodiment, since the discharged steam always passes through water, the steam is completely condensed even at a small steam flow rate.

In FIG. 6, a duct 11 as shown in the figure is installed near the outlet of the relief vent pipe 6 of the embodiment shown in FIG. Many holes 9 are made in the underwater part of the duct 11 which is immersed in the pool water 4, and the upper and lower parts of the duct 11 are penetrated.

When the air in the relief vent pipe 6 is released, the water level in the duct 11 is pushed down a little, but all the air is released from the through hole 12 in the upper part of the duct 11.

When releasing a large amount of steam, the hole 9 on the side of the duct 11
Cold water flows in from the duct, condenses the released steam, and flows out from the bottom of the duct 11.

Further, when small steam is released, the water temperature inside the duct 11 rises and flows out from the hole 9 around the duct 11 as shown by the arrow in the figure. Also, water flows in from below the duct 11, but when the steam flow is smaller, the steam condensation rate is greater than the steam outflow rate, so the water level inside the duct 11 rises, and even in this case, the steam condenses more completely. can be expected.

FIG. 7 is similar to the embodiment shown in FIG. 6, except that the lower side of the duct 13 is covered with a plate with holes 14 in the same manner as the side surfaces. However, what is characteristic here is that the hole 15 on the side is an "opening outward" hole, whereas the hole 14 on the lower side is an "opening inward" hole.

Depending on the way the holes are formed, the side holes 15 have a large resistance to the flow flowing in from the outside, and a small resistance to the flow flowing out from the inside.

On the other hand, for the bottom hole, the opposite is true.

Therefore, as shown by the arrows in the figure, water flows easily into the duct 13 through the lower hole 14 and out through the side hole 15.

This works to further promote the flow when the steam flow rate is small as described in the embodiment of FIG.

This embodiment is particularly effective in the case of a relief vent pipe with a relatively small steam flow rate.

FIG. 8 shows another embodiment of the present invention.

The relief vent pipe 6 extends into the pool water 4, and a number of holes 16 are installed in the water-immersed part of the relief vent pipe 6. The total flow area of these holes 16 is set to be larger than the flow path area of the relief vent pipe 6, and the diameter of the holes 16 is preferably about 1 cm. Moreover, this hole 16 is drilled to a position just below the surface of the pool water 4, which is a distinctive feature.

Furthermore, a duct 17 as shown in the figure is installed around the outlet of the relief vent pipe 6.
This duct 17 is a little deeper than the tip of the relief vent pipe 6, and a hole 9 is installed in the side surface of the duct 17 in the depth of the water, as in the embodiment shown in FIG.

According to this embodiment, slightly compressed air bubbles are released from the hole 16 when air is released, but the air bubbles are broken up and released, and the discharge water depth is shallow, and the duct 1
Since the bubbles are immediately released from the top of the tank 7 onto the water surface, no bubble pulsation occurs. Furthermore, the same effect as in the case of FIG. 6 is obtained when steam is released.

Other embodiments of the present invention are shown in FIGS. 9 and 10.

Similar to the embodiment described above, the relief vent pipe 6
There is an outlet just below the surface of the pool water. On the outside of the relief vent pipe 6 slightly above this discharge port,
There is a sliding duct 18. This duct 18
is normally held at the position shown in FIG. 9 by a magnetic stopper 19 installed above it. Further, from this duct 18, an arm 20
A piston 21 with a gap 22 is installed inside the outlet of the relief vent pipe 6 through the opening.

When the relief valve operates and the air in the relief vent pipe 6 is released, the air in the pipe is released through the gap 22, but as the flow rate increases, it begins to push down the piston 21.

When the air has almost finished being discharged and steam is coming out, the piston 21 is completely pushed down to the stopper 23 of the discharge port, and the duct 18 is also completely lowered into the pool water 4 as shown in FIG. ing.

As a result of the above, it is possible to directly release air into the air, and to release steam reliably into water, so that there is no bubble pulsation and reliable steam condensation can be expected. Here the arrows indicate the flow of steam.

Furthermore, when the relief valve is closed and no more steam is released, the steam in the relief vent pipe 6 condenses and becomes negative pressure, causing the pool water 4 to rapidly flow back into the relief vent pipe 6. The water flow at this time returns the piston 21 into the pipe, and the duct 18 is also returned to its original position above the outlet.

According to the present invention, the load when the relief valve is activated can be greatly reduced, and a vacuum breaker is not required, so it is possible to provide an economical and highly safe reactor containment vessel.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of the reactor containment vessel of a boiling water reactor, Figure 2 is a vertical sectional view of the pressure suppression chamber in Figure 1,
FIG. 3 is a structural diagram of a relief vent pipe according to a preferred embodiment of the present invention, and FIGS. 4 to 10 are structural diagrams of other embodiments of the present invention. 1...Reactor pressure vessel, 2...Dry well,
3...Pressure suppression chamber, 4...Pool water, 6...Relief vent pipe.

Claims (1)

[Claims] 1. In the relief vent pipe that guides the steam in the reactor vessel into the coolant in the pressure suppression chamber and condenses it,
A relief vent pipe characterized in that a discharge port at a tip of the relief vent pipe is disposed above the liquid surface of the coolant near the liquid surface, and is open toward the liquid surface.