JPH07239262A - Water gauge - Google Patents

Abstract

PURPOSE:To provide a water gauge exhibiting high measurement accuracy even in case of low pressure boiling by inserting a limit orifice, having a hole above the center thereof, into the horizontal part of a reference head pipe and discharging gas well from the inside thereof thereby limiting conduction of liquid and filling the reference head pipe with water easily. CONSTITUTION:The water gauge comprises an upper piping 7 led out from a part above the water level in a reactor pressure vessel 4, a reference water level 8 coupled on the side thereof with the vertical part of a reference head pipe being led out from the lower part thereof, a lower piping 12 led out from a part lower than the water level in the vessel 4, and a differential pressure detector 6 coupled with the reference head pipe 8, wherein a limit orifice 20 having a semicircular hole 21a above the center thereof is inserted into the horizontal reference head pipe 10b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a water level gauge used in boiling water type and pressurized water type reactors.

[0002]

2. Description of the Related Art Reactor water level gauges use accurate output signals even in the event of a reactor accident, etc., in order to use their output elements in reactor water level control, reactor protection systems, and feedwater control systems. Need to supply. As shown in the system configuration diagram of FIG. 4, the principle of the conventional water level gauge of a nuclear reactor is that a reference water head 3 provided in a dry well 2 in a reactor containment vessel 1 partially shown and a side wall surface partially The water level in the reactor pressure vessel 4 is obtained by measuring the difference between the hydrostatic head and the hydrohead at the measurement point 5 in the reactor pressure vessel 4, which is shown by the differential pressure transducer 6.

The upper pipe 7 led out of the reactor pressure vessel 4 is connected to a reference water level gauge 8, and this reference water level gauge 8 is used.
The reference water surface 9 therein communicates with the vertical reference water head pipe 10a of the vertical portion forming the reference water head 3 and the horizontal reference water head pipe 10b of the horizontal portion connected thereto, and is connected to the differential pressure converter 6 via the stop valve 11. Connected.

On the other hand, the lower pipe 12 led out from the lower portion of the reactor pressure vessel 4 is connected to the differential pressure converter 6 via a stop valve 13. Each of the vertical reference water head pipe 10a and the horizontal reference water head pipe 10b has a restriction orifice for restricting the water in the reference water head pipe from flowing into the reactor pressure vessel 4.
14 are inserted.

Further, in the above water level gauge, the water level h is obtained from the differential pressure signal ΔP from the differential pressure converter 6 as follows. Here, the density of steam corresponding to the pressure in the reactor is ρg, the density of water is ρl, and the reactor water level at that time is h. Further, if the height of the reference head 3 is H and the density of the water is ρo, the differential pressure ΔP is expressed by the following equation (1).

ΔP = H · ρo {hρl + (H−h) ρg} (1)

Therefore, the reactor water level h is changed from the above equation (1) to the following equation (2). h = H (ρo−ρg) −ΔP / (ρl−ρg) (2)

Since the steam in the reactor pressure vessel 4 condenses on the inner wall of the reference water level device 8 and flows down into the reference water level device 8, in the vicinity of the connection part 15 between the reference water level device 8 and the vertical reference water head pipe 10a. The water temperature of is almost equal to the water temperature in the reactor pressure vessel 4. However, in the case of a reactor accident in which a main steam pipe breaks in a conventional water level gauge, it is expected that the atmospheric temperature of the water level gauge will reach a considerably high temperature in about 1 second after the pipe breakage.

Under such a circumstance, when a sudden pressure reduction occurs in the reactor pressure vessel 4 due to the break of the main steam pipe, the vertical reference water head pipe 10a which is the reference water level device 8 and the reference water head 3a.
And, when the water in the horizontal reference water head tube 10b boils under reduced pressure and flows into the reactor pressure vessel 4, as a result, the above equation (2)
Since the height H of the reference water head 3 changes at the time, and the accurate height H of the reference water head 3 at that time and after the accident is not known, the measurement result of the reactor water level h becomes inaccurate.

As a countermeasure against this, in order to limit the flow of water in the vertical reference water head tube 10a and the horizontal reference water head tube 10b, which have been conventionally boiled under reduced pressure, into the reactor pressure vessel 4, a cross-sectional view is shown in FIG. Such a restriction orifice 14 is attached to each of the vertical reference water head tube 10a and the horizontal reference water head tube 10b.

As shown in the sectional view of FIG. 5 (a) and the sectional view of FIG. 5 (b) taken along the line AA in FIG. 5 (a), the restriction orifice 14 is provided in the reference water head tubes 10a, 10b. Is concentric with a round hole 16a in the center. As described above, the reference water head pipe includes the vertical reference water head pipe 10a and the horizontal reference water head pipe 10b as shown in FIG. 4, and the restriction orifices 14 of the same shape shown in FIG. Was attached.

[0012]

When the vertical reference water head pipe 10a and the horizontal reference water head pipe 10b, which are the reference water head 3 of the water level gauge system, are filled with water, the vertical portion of the reference water head pipe is as shown in FIG. 6 (a). As shown in the cross-sectional view, the air 17 in the vertical reference water head tube 10a and the restriction orifice 14 provided in the middle thereof with a circular hole 16a shown in FIG. In addition, the vertical reference head 10a is used even when boiling under reduced pressure.
Then, the steam 18 flows in the central part and
Since 19 flows, the steam 18 easily escapes together with the restriction orifice 14, and the water 19 hardly escapes.

On the other hand, in the horizontal portion of the reference water head tube, when water is filled, as shown in the sectional view of FIG.
Since the buoyancy (gravity) moves the upper part of the reference water head tube, the air 17 in the horizontal reference water head tube 10b and the restriction orifice 14 is hard to escape. Further, as shown in Fig. 6 (b), when boiling under reduced pressure, the upper part of the reference water head tube is steamed as in the case of water filling.
Flows, and the water 19 flows in the lower part, so that the water 19 easily escapes but the steam 18 does not easily escape.

Therefore, there is a problem that the water level measurement value of the water level gauge in the normal state is affected by the air and steam remaining in the horizontal reference water head tube 10b. In addition, even when decompression boiling occurs due to a nuclear reactor accident, water 19
Due to the generated steam 18, there is a problem that the restriction of the flow into the reactor pressure vessel 4 is not sufficiently performed.

The object of the present invention is to make a hole above the center of a restriction orifice that is inserted in the horizontal portion of the reference water head tube so that gas can flow out well in the reference water head tube and the flow of liquid is restricted. Therefore, it is an object of the present invention to provide a water level gauge that can easily fill the reference water head tube with water and has high measurement accuracy when boiling under reduced pressure.

[0016]

In order to achieve the above object, a water level gauge according to the invention of claim 1 is connected to an upper pipe derived from an upper portion of a water surface of a container at a side portion and a reference water head pipe is led to a lower portion. In the water level gauge consisting of the reference water level gauge, a lower pipe derived from the lower part of the water surface of the container, and a differential pressure detector connected to the reference water head pipe, a hole above the center in the horizontal part of the reference water head pipe. It is characterized in that a restricted orifice having an opening is inserted.

The water level gauge according to the second aspect of the present invention is characterized in that the hole formed above the center of the restricting orifice inserted in the horizontal portion of the reference water head tube is one semicircle.
The water level gauge according to the invention of claim 3 is characterized in that the hole formed above the center of the restricted orifice inserted in the horizontal portion of the reference water head tube is a plurality of round holes. A water level gauge according to a fourth aspect of the present invention is characterized in that both sides of a hole formed above the center of the restriction orifice are inclined.

[0018]

According to the first aspect of the present invention, when water is filled in the water level gauge, the air in the horizontal portion of the reference water head tube and the restriction orifice inserted in this horizontal portion can be easily discharged from the hole formed above the center. Exit to. Further, upon boiling under reduced pressure, the steam generated from water flows in the upper part of the reference water head tube due to its buoyancy, and easily escapes from a hole formed above the center of the restriction orifice. However, the water flowing in the reference water head tube flows in the lower part by its weight, and the restriction orifice restricts the inflow to the reactor pressure vessel.

According to the second aspect of the invention, the fluid passing through the restricted orifice passes through one semicircular hole at the upper portion of the flow passage cross section, so that the resistance is small and at the lower portion is large.
In the invention according to claim 3, the fluid passing through the restricted orifice has a small resistance at the upper portion of the flow passage cross section and a large resistance at the lower portion. In the invention according to claim 4, the flow path resistance on both sides of the hole of the restricted orifice is small, and further, there is no accumulation of gas on both sides of the hole.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. It should be noted that the same components as those of the above-described conventional technique are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in the system configuration diagram of FIG. 1, the water level gauge includes a reference water level gauge 8 provided in the dry well 2 in the reactor containment vessel 1 and a reactor pressure vessel 4
The upper pipe 7 derived from the upper part of is connected.

Further, in the vertical reference water head pipe 10a which is a vertical portion of the reference water head 3 derived from the lower part of the reference water level device 8, the stop valve 11 and the water in the reference water head pipe are prevented from flowing into the reactor pressure vessel 4. A horizontal reference water head tube 10b, which is a horizontal portion of the reference water head 3 in which a limiting orifice 14 for limiting is inserted and another limiting orifice 20 is further inserted, is connected to the differential pressure converter 6. On the other hand, the lower pipe 12 led out from the lower portion of the reactor pressure vessel 4 is configured to be connected to the differential pressure converter 6 via a stop valve 13.

The limiting orifice 20 inserted in the horizontal reference water head tube 10b is a sectional view of FIG. 2 (a) and FIG.
As shown in the sectional view taken along the line BB in FIG. 2A in FIG. 2B, the semicircular hole 21a is located above the center in the horizontal reference water head tube 10b.
Is open. Also, the semi-circular hole 21 of this restricted orifice 20
Inclinations 21b and 21c are formed on both sides of a.

Next, the operation of the above-described structure will be described. In the case where the water level gauge is filled with water, in the vertical reference water head tube 10a, the air 17 in the vertical reference water head tube 10a is the same as the conventional one.
6 rises in the central portion of the pipe as shown in FIG. 6 (a), so that it easily passes through the central hole 16a of the restriction orifice 14.

The air 17 in the horizontal reference water head tube 10b is also
As shown in FIG. 6 (b), the air 17 moves in the upper part of the horizontal reference water head tube 10 b due to buoyancy (gravity), so that the semicircular hole 21 a opened above the center of the restricted orifice 20 can be easily formed. Since water passes through and no air remains inside, water filling in the reference water head pipe in the water level gauge is easily performed. In addition, the semicircular hole 21
Since the slopes 21b and 21c are provided before and after a, the flow resistance of the air is small and the air hardly remains.

When the water in the reference water head tube is boiled under reduced pressure due to a nuclear reactor accident or the like, steam is generated from the water, and FIG.
As shown in the vertical pipe portion of (a) and the horizontal pipe portion of FIG. 6 (b), in the vertical reference head pipe 10a, steam 18 is provided in the central portion of the pipe.
Flows, and the water 19 flows in the vicinity of the inside of the pipe. In the horizontal reference water head tube 10b, steam 18 flows in the upper part of the pipe and water 19 flows in the lower part of the pipe.

Therefore, in the vertical reference water head tube 10a, the steam 18 easily passes through the central hole 16a of the restriction orifice 14,
The flow of water 19 is restricted. Further, in the horizontal reference water head tube 10b, the steam 18 moves in the upper part of the pipe due to buoyancy (gravity), but since the semicircular hole 21a of the restricting orifice 20 is above the center, the steam 18 easily passes. To do. However,
The lower part of the semicircular hole 21a obstructs the flow of the water 19 and its passage is restricted.

As a result, the steam 18 generated in the water level gauge system during boiling under reduced pressure easily escapes in the vertical reference water head tube 10a and the horizontal reference water head tube 10b, and the inclination around the semi-circular hole 21a of the restriction orifice 20 is increased. The flow resistance is small due to 21b and 21c, and the steam 18 does not remain. Further, since the restriction orifice 20 effectively restricts the water 19 in the pipe from flowing into the reactor pressure vessel 4 along with the steam 18,
The water level can be measured with high accuracy during and after boiling under reduced pressure.

FIG. 3 shows another embodiment of the restricting orifice inserted in the horizontal reference water head tube 10b.
As shown in the cross-sectional view of FIG. 3A and the cross-sectional view of FIG. 3B taken along the line CC in FIG.
A plurality of round holes 23a are formed above the center in b, and slopes 23b and 23c are provided on both sides of each round hole 23a.
Also in this restricted orifice 22, the same operation and effect as in the above-described embodiment can be obtained.

Although the number and shape of the holes formed in the restricted orifices 20 and 22 are the semicircular holes 21a or the plurality of round holes 23a in the above embodiment, the shape, size, and quantity are the same as those in the above embodiment. It is not limited to the example and may be selected as appropriate. The slopes 21b, 21c, 23b, and 23c formed on both sides of the hole are the flow directions of the water 19, the air 17, and the steam 18 passing through the hole, and the flow of the air 17 and the steam 18 which are intended to pass therethrough. It suffices to set the road resistance to be small and to prevent residual, and to set the angle and direction of the water 19 to which an appropriate resistance is applied.

[0030]

As described above, according to the present invention, in the system piping of the water level gauge, it is possible to suppress the outflow of the reference head water when the pressure is suddenly decreased, and the change in the height of the reference head during and after the pressure decrease is small. , It becomes possible to measure the water level in the reactor with high accuracy. Further, when the reference water head pipe is filled with water, it is possible to improve the accuracy and reliability of the water level gauge by improving the air release in the pipe.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of a water level gauge according to an embodiment of the present invention.

2A and 2B are cross-sectional views of a restriction orifice according to an embodiment of the present invention, in which FIG. 2A is a cross-sectional view and FIG. 2B is a cross-sectional view taken along the line BB of FIG.

3A and 3B are cross-sectional views of a restriction orifice of another embodiment according to the present invention, in which FIG. 3A is a sectional view and FIG. 3B is a sectional view taken along the line CC of FIG.

FIG. 4 is a system configuration diagram of a conventional water level gauge.

5A and 5B are sectional views of a conventional restricted orifice, in which FIG. 5A is a sectional view and FIG. 5B is a sectional view taken along the line AA of FIG.

FIG. 6 is a schematic diagram of a fluid in a pipe, (a) is a vertical portion,
(B) shows a horizontal part.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Reactor containment vessel, 2 ... Dry well, 3 ... Standard water head, 4 ... Reactor pressure vessel, 5 ... Measuring point in reactor pressure vessel, 6 ... Differential pressure transducer, 7 ... Upper piping, 8 ... Standard Water level,
9 ... Standard water surface, 10a ... Vertical reference water head tube, 10b ... Horizontal reference water head tube, 11, 13 ... Stop valve, 12 ... Lower piping, 14, 20, 22 ...
Restriction orifice, 15 ... Joining part, 16a, 23a ... Round hole, 17 ...
Air, 18 ... Steam, 19 ... Water, 21a ... Semi-circular hole, 21b, 21c,
23b, 23c ... Inclination.

Claims (4)

[Claims] 1. A reference water level gauge connected to an upper pipe derived from above the water surface of a container at a side portion and a reference water head pipe derived to a lower part, a lower pipe derived from below the water surface of the container, and the reference water head pipe. A water level gauge comprising a differential pressure detector connected to the water level gauge, wherein a limiting orifice having a hole above the center is inserted in the horizontal portion of the reference water head tube. 2. The water level gauge according to claim 1, wherein the hole formed above the center of the restriction orifice inserted in the horizontal portion of the reference water head tube is one semicircle. 3. The water level gauge according to claim 1, wherein the holes formed above the center of the restricted orifice inserted in the horizontal portion of the reference water head tube are a plurality of round holes. 4. The water level gauge according to claim 1, wherein both sides of a hole formed above the center of the restricted orifice are inclined.