JPH077091B2 - Boiling water reactor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a boiling water nuclear reactor, and particularly to a boiling water nuclear reactor having a simple structure and sufficient steam separation performance.

[Conventional technology]

The steam-water separator at the upper part of the reactor core of a conventional boiling water reactor comprises a steam-water separator and a steam dryer above it.

The air / water separator is a vertical axial flow centrifugal type, and a plurality (about 200) of water / water separation units are arranged in parallel above the shell head. The structure of the steam separator is shown in FIG. The steam-water mixed liquid leaving the core enters the lower end of the steam-water separator from the plenum at the upper part of the core through the stand pipe 3 and is given a rotational motion by the inlet vane 12 where it is swirled upward in the tube 13 by free swirling motion. As it travels, water and steam are separated due to the centrifugal effects that accompany it. At the top of the tube 14, water gathers and falls. On the other hand, the steam component goes axially upward and enters the steam dryer.

The steam dryer is a collection of parallel corrugated plates. The structure is shown in FIG. The steam changes its traveling direction many times while passing between corrugated plates, and the water in the steam is guided to the main steam pipe after the moisture in the steam hits the corrugated plate-shaped surface to remove the moisture. The separated drain is guided to the outside through the steam dryer drain pipe 16.

In large reactors, the two types of moisture separators described above can be used to reduce the outlet mixture.
Although it has a sufficient performance of 1 wt% or less, the pressure loss of steam due to these devices cannot be ignored, and it is necessary to take these devices out of the furnace at the time of refueling, but the weight is heavy and they are not transferred. There are drawbacks in that it takes time and labor is required for the inspection due to its complicated structure, and the inspector during that period is exposed to some extent.

As another gas-liquid separator, there is a bleeder moisture separator, which is a corrugated plate type or a micropore type moisture separator.

[Problems to be solved by the invention]

The above-mentioned conventional technique is adopted for a large-scale nuclear reactor having high power and high power density. Large reactors have a high power density, so the steam that enters the steam-water separator has a large proportion of water, and the high-performance steam-water separator and steam dryer as in the conventional example remove sufficient moisture. I needed to do it. However, since the power density is low in small and medium-sized furnaces, a large-scale air / water separator unlike the conventional example is not required, and a light-water / water separator having good maintainability is desired.

An object of the present invention is to provide a steam / water separator for a small-to-medium-sized nuclear reactor, which is lightweight, has good maintainability, and has a small pressure loss.

[Means for solving problems]

 The means for achieving the above object will be described below.

In large reactors with high power density, the amount of voids generated per unit volume of the core is large, and the rate of vapor rise increases accordingly. Therefore, the water accompanying it is also lifted up, and the so-called slag flow region (a state in which a large water soul is contained in the steam) continues up to the upper core. That is, as shown in FIG. 4, the moisture content in the core portion gradually decreases with elevation, and a considerable amount of moisture is present in the core upper portion and the stand pipe portion. Therefore, in a large reactor, it was necessary to remove a large amount of moisture with a centrifugal steam separator.

On the other hand, in small and medium-sized nuclear reactors with low power density, the amount of steam generated per volume in the core is small, so the amount of water entrained is small,
It will be in a relatively gentle boiling state. That is, as shown in FIG. 4, the moisture content in the core portion drops sharply in the upper portion of the core, and the moisture content in the stand pipe portion is low. Therefore, the conventional high-performance steam separator is not required.

Based on this point of view, as a gas-liquid separation means, aiming to provide a gravity drop type water-water separation area, specifically, in the middle of the steam flow path between the stand pipe in the reactor and the main steam pipe inlet. The diameter from the equipment that provides the cavity area and discharges the height of the cavity area from below to above the cavity area.
The boiling water reactor is characterized in that it is higher than the maximum arrival height of water droplets of 3 cm or more and the steam flow passage cross-sectional area of the cavity region is wider than the flow passage cross-sectional area of the stand pipe.

[Action]

A mixture of air and water is injected into the hollow region from below, and water drops are removed by gravity falling in the hollow region to obtain the action of drawing out steam with less water content.

〔Example〕

 An embodiment of the present invention will be described below with reference to FIG.

A plurality of (about 200) stand pipes 3 are provided from the shell head 2 above the core portion 1, and steam generated in the core and accompanying moisture are guided to the steam separator 4 through the stand pipe 3. The diameter of the stand pipe 3 is about 11 cm, which is thicker than that of a large-scale furnace in order to suppress the rising speed of water. Also, the length of the stand pipe 3 is
The length of the upper plenum water 5 shall be about 30 cm from the top of the shroud head so that the upper end of the stand pipe is exposed from the water surface. The water / water separator 4 has a height of about 5 m and a diameter of about 6 m, which is equal to the inner diameter of the pressure vessel, so that water drops having a diameter of about 3 cm or more can be removed by gravity fall. The water separated by gravity falls on the upper plenum water 5 and is recirculated to the lower part of the core.

The water is separated and the steam moves upward, enters the steam dryer 6 above the steam separator, further removes mist-like water droplets, and then is conveyed to the turbine through the main steam pipe 7.

According to this embodiment, compared with the conventional example, the centrifugal steam separator was eliminated, a large cavity was created, and the length of the stand pipe was shortened to about 50 cm. The pressure loss in the kg / cm ² atmosphere is virtually zero. Further, the pressure loss of the steam dryer portion is negligible as compared with the steam separator portion. The improvement in thermal efficiency due to the decrease in pressure loss corresponds to 0.15% in terms of heat output.

Further, by significantly reducing the weight of the steam separator (shroud head) that needs to be transferred when refueling, the reactor opening and closing operations can be performed quickly.

Further, since the centrifugal type water-water separator having a complicated shape is eliminated, it is not necessary to inspect the welded portion or the like during its use period, which contributes to the effect of reducing the radiation exposure of the worker.

Water droplets discharged from the stand pipe in association with steam are gravity-dropped and removed by two kinds of mechanisms depending on the size of the water droplets.

(1) When a large water drop is sucked out of the stand pipe at a certain initial velocity v _0, it draws an emission line trajectory according to the initial velocity and falls due to gravity. Therefore, the height of the steam separator is
It should be higher than the maximum reaching height of these water drops.

(2) For small water drops, the final drop velocity is defined when the drop velocity balances the air resistance. Therefore, when the vapor rising speed in the space is higher than the maximum falling speed, the water droplets cannot fall and are pushed upward together with the steam. Therefore, a sufficient space cross-sectional area is required to reduce the steam flow velocity so that sufficiently small water droplets can fall.

Hereinafter, the specifications of the steam separation device required by the above mechanism will be quantitatively evaluated.

(1) Spatial height The maximum arrival height of a particle with an initial velocity v ₀ can be expressed by the following formula.

x = v ₀ ² / 2g (1) Now, the initial velocity of water droplets in small and medium-sized reactors is 6m / s, which is half that in large reactors.
Since it is a degree, x becomes very large at 18 m. In order to reduce this, the diameter of the stand pipe may be increased, the speed may be reduced or the direction of the stand pipe may be licked so that the discharged water droplets hit the lateral wall. In order to set the space height to about 5 m, the diameter of the stand pipe may be increased from about 8 cm to about 11 cm.

(2) Spatial cross-section area The final velocity due to particle drop resistance is c: Resistance coefficient (1 for spherical shape) ρ: Atmosphere density (36kg / m ³ ) f: Cross sectional area

Vapor velocity in the plenum of small and medium-sized reactors is half that of large reactors
Since it is about 1 m / s, the diameter is 3 cm in this space from equation (2).
The above water drops can be dropped and removed.

The second embodiment of the present invention is as follows.

Fig. 5 shows a diagram in which the effect of separating moisture by gravity is applied to a steam dryer. A cylinder 9 serving as a flow diverter is provided above the steam separator 8 so that the steam containing water released from the steam separator 8 rises in the cylinder. Here, large water drops are removed by gravity fall. The steam once reaches near the top head 10, then descends to the outside of the cylinder 9 and advances from the main steam pipe 7 to the turbine. Water drops that have fallen off due to gravity falling in the cylinder 9 collide with the top head 10 by inertia and are removed. The removed water drops are drained by connecting the wall of the pressure vessel and the wall of the cylinder 9 and recirculated to the lower side of the core.

The third embodiment of the present invention shown in FIG. 6 can also obtain the same effect by providing an elbow pipe or an L-shaped tunnel 11 as a flow diverting means at the main steam pipe inlet. In this case, since the cross-sectional area for ascending the steam can be made larger than the case where the cylinder 9 is provided, the ascending speed of the steam becomes slower, and the effect of separating water and water by gravity falling becomes greater.

The fourth and fifth embodiments of the present invention are as follows.

FIGS. 7 and 8 are diagrams in which the present invention is applied to a small-to-medium-sized boiling water type natural circulation furnace.

FIG. 7, which is the fourth embodiment, is an example in which the moisture separation effect by gravity fall is applied to a steam separator, and FIG. 8, which is the fifth embodiment, is an example in which the same effect is applied to a steam dryer. is there.

In the case of a boiling water type natural circulation reactor, since the power density of the core part 1 is low and the generated steam has a low flow velocity, the effect of separating moisture by gravity drop of water droplets is high.

〔The invention's effect〕

According to the present invention, since the centrifugal steam-water separator or the parallel wave plate type steam dryer is not required, the thermal efficiency is improved by reducing the pressure loss, the cost is reduced by simplifying the internal structure of the reactor, and the reactor is closed and closed. This has the effect of simplifying the work and reducing inspection lines due to the reduction of the welding lines of the in-core structure and the accompanying reduction in the worker's exposure dose.

[Brief description of drawings]

FIG. 1 is a sectional view of a nuclear reactor according to a first embodiment of the present invention, and FIG.
Figure is a vertical cross section of a centrifugal steam-water separator in a conventional nuclear reactor, Figure 3 is a perspective view of the main parts of a corrugated plate steam dryer in a conventional nuclear reactor, and Figure 4 is a high power density core and low A graph showing the water content for each elevation of the power density core,
FIG. 5 is a sectional view of a reactor according to a second embodiment of the present invention,
FIG. 7 is a cross-sectional view of a reactor according to a third embodiment of the present invention, and FIG. 7 is a fourth embodiment of the present invention, which is a cross-sectional view of a reactor when applied to a small-to-medium-sized boiling water reactor, The figure is also a sectional view of a nuclear reactor according to the fourth embodiment. 1 ... Core part, 2 ... Shroud head, 3 ... Stand pipe, 4 ... Steam-water separator, 5 ... Upper plenum water, 6 ... Steam dryer, 7 ... Main steam pipe, 8 ... Steam Water separator, 9 ... Cylinder, 10 ... Top head, 11 ... Elbow piping, 12 ... Inlet vane, 13 ... Chew, 14 ... Chube top, 15 ... Corrugated plate, 16 ... Drain pipe.

Claims (3)

[Claims] 1. A device for providing a hollow region in the middle of a steam flow path between a stand pipe in a nuclear reactor and an inlet of a main steam pipe, and discharging steam from the lower part to the upper part of the height of the hollow region to the hollow region. The boiling water reactor is characterized in that it is higher than the maximum arrival height of water droplets having a diameter of 3 cm or more from, and the steam channel cross-sectional area of the cavity region is wider than the channel cross-sectional area of the stand pipe. 2. The hollow region is provided between a stand pipe and a steam dryer in a nuclear reactor, and a device for discharging steam from the lower part to the upper part of the hollow region is the stand pipe. The boiling water nuclear reactor according to claim 1. 3. The hollow region is arranged between a steam-water separator in a nuclear reactor and an inlet of a main steam pipe via a vertical flow diverting means for steam arranged in front of the main steam inlet. The boiling water nuclear reactor according to claim 1.