JPH0469358B2 - - Google Patents

Description

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view schematically showing a conventional water level gauge in a pressure vessel, FIG. 2 is a partially schematic cross-sectional view showing an embodiment of the water level meter according to the present invention, and FIGS. 3 and 4 are respectively FIG. 3 is a schematic side view showing another example of the reference water head shown in FIG. 2; 1...Reactor pressure vessel, 2...Upper impulse pipe, 3
... Reference water level device, 4 ... Reference water level, 5 ... Reference water head, 6 ... Differential pressure converter, 7 ... Measurement point in pressure vessel, 8 ... Reference water head pipe, 9 ... Lower impulse pipe, 10
...Containment vessel, 11...Dry well, 12...
Heat insulation panel, 13... Upper horizontal piping, 14... Cooling fin, 15... Cooling jacket, 16... Cooling water.

Claims (1)

[Scope of Claims] 1. A reactor pressure vessel, an upper impulse pipe provided to penetrate the upper side wall of the reactor pressure vessel, and an upper impulse pipe provided to penetrate the upper impulse pipe and the lower side wall of the reactor pressure vessel. A lower impulse pipe provided, a reference water head pipe provided with the upper impulse pipe and the upper part communicating with the upper impulse pipe, and a lower end of the reference water head pipe and the lower impulse pipe are connected in communication with each other. In the water level gauge, an upper horizontal pipe is provided which communicates with the upper impulse pipe and the reference water head pipe and has an inner diameter smaller than that of the upper impulse pipe, and the upper horizontal pipe is connected to the upper guide pipe. A water level gauge for a nuclear reactor, characterized in that the pressure pipe has a predetermined downward slope from the pressure pipe to the reference water head pipe, and a cooling means for cooling the upper horizontal pipe is provided in a portion of the upper horizontal pipe adjacent to the upper impulse pipe. 2. The atom according to claim 1, wherein the downward slope from the upper impulse pipe of the upper horizontal pipe to the reference water head pipe is between 20/1000 and 60/1000. Furnace water level gauge. * Theory [Technical Field of the Invention] The present invention relates to a water level gauge for a light water reactor suitable for a boiling water reactor or a pressurized water reactor. [Technical Background of the Invention] Since the output of a nuclear reactor water level gauge is used for reactor water level control, reactor protection system, and water supply control system, it provides an accurate water level signal even in the event of a reactor accident. There is a need. As shown in Fig. 1, the reactor water level gauge is constructed by connecting an upper impulse pipe 2 to the upper side wall surface of the reactor pressure vessel 1, which is partially shown in cross section only from the side, and connecting the upper impulse pipe 2 to the other end of the upper impulse pipe 2. A reference water level device 3 is installed at a higher position than the impulse pipe 2.
A lower impulse pipe 9 is also connected to the lower side of the pressure vessel 1, and a differential pressure converter 6 is connected between the reference water level device 3 and the lower impulse pipe 9 via a valve V to obtain a reference water head. It has a structure in which it communicates with a pipe 8. In the figure, reference numeral 4 indicates the reference water level in the reference water level device 3, 5 indicates the reference water head in the reference water head pipe 8, 7 indicates the measurement point in the pressure vessel, 10 indicates the partial containment vessel, and 11 indicates the dry well. It shows. By the way, the principle of the water level gauge is to determine the water level by measuring the difference between the reference water head 5 provided in the dry well 11 and the static water head at a measurement point in the reactor pressure vessel 1 using a differential pressure converter 6. . [Problems with Background Art] However, the water level gauge having the above configuration has the following drawbacks. That is, during normal operation of the reactor, the steam in the reactor pressure vessel 1 flows into the reference water level gauge 3 from the upper impulse pipe 2 and condenses to maintain the reference water level 4. Therefore, the reference water head in the reference water level gauge 3 The water in No. 5 is at a high temperature. In such a situation, if a sudden depressurization occurs in the reactor pressure vessel 1 due to a rupture in the main steam, etc., the water in the reference water level gauge 3 will cause a decompression boiling phenomenon, causing the measuring device that detects the differential pressure to malfunction. Output shows abnormal value. In addition, when the reactor isolation cooling system is operating, cold water sprayed from the head spray (not shown) at the upper part of the reactor pressure vessel 1 enters into the upper impulse pipe 2 and blocks this upper impulse pipe 2. Therefore, the inside of the upper impulse pipe 2 and the inside of the reference water level vessel 3 become in a negative pressure state due to rapid cooling. At this time, there was a problem in that the output of the differential pressure converter 6 showed an abnormal value, and erroneous signals were provided to each control device. [Object of the Invention] The present invention has been made to eliminate the above-mentioned drawbacks, and is aimed at preventing the boiling of the reference head water of the water level gauge due to the depressurization of the reactor pressure vessel that occurs during a nuclear reactor accident, and preventing the boiling of the reference water head during the head spray operation. It is an object of the present invention to provide a reactor water level gauge that can prevent negative pressure phenomena in a pressure impulse pipe and a reference water level gauge, and can reduce costs. [Summary of the Invention] That is, the present invention provides a nuclear reactor pressure vessel, an upper impulse pipe provided to penetrate an upper side wall of the reactor pressure vessel, and an upper impulse pipe and a lower side wall of the reactor pressure vessel. A lower impulse pipe provided through the upper impulse pipe, a reference water head pipe provided with the upper part communicating with the upper impulse pipe, and a lower end of the reference water head pipe and the lower impulse pipe communicate with each other. In the water level gauge equipped with a differential pressure transducer connected to A water level for a nuclear reactor, characterized in that the water level has a predetermined downward slope from the upper impulse pipe to the reference water head pipe, and a cooling means for cooling the upper horizontal pipe is provided in a portion of the upper horizontal pipe adjacent to the upper impulse pipe. It is a total. [Embodiments of the Invention] Hereinafter, an embodiment of a nuclear reactor water level gauge according to the present invention will be described with reference to FIG. 2, in which the same parts as in FIG. 1 are denoted by the same reference numerals. The water level gauge for a nuclear reactor according to the present invention is located at the outer side of the heat insulation panel 12 surrounding the reactor pressure vessel 1 of the upper impulse pipe 2 taken out from the reactor pressure vessel 1. A slope of 20 to 60/1000 is provided to connect the upper horizontal pipe 13, which has an inner diameter smaller than that of the upper impulse pipe 2 and has a narrow pipe diameter. Further, cooling fins are provided in a part of the upper horizontal pipe 13 close to the upper impulse pipe 2 for cooling, and a reference water surface 4 is formed at this part. The other end of the upper horizontal pipe 13 is connected to the upper end of the reference water head pipe 8, and the lower end of the reference water head pipe is connected to the differential pressure converter 6. The other end of the differential pressure converter 6 is connected to a measurement point 7 in the pressure vessel of the reactor pressure vessel 1 through a lower impulse pipe 9.
It is connected to the. According to such a configuration, during normal operation of the reactor, steam in the reactor pressure vessel 1 flows through the upper impulse pipe 2.
The steam flows through the upper impulse pipe 2 and the horizontal pipe 13 into the connection part, and is condensed in the upper horizontal pipe 13 in the area of the cooling fins 14 . The upper horizontal pipe 13 is provided with a downward gradient of 20/1000 to 60/1000 so that the upper impulse pipe 2 side is higher than the upper end of the reference water head pipe, so condensed water is continuously replenished. The slope of this upper horizontal piping was determined through experiments so that droplets generated by condensation can easily flow toward the reference water head pipe due to the downward slope, and the difference in height of the upper horizontal piping is minimized. It is a value. Therefore, a reference water level 4 of a constant liquid level is formed in the upper horizontal pipe by the inflow of condensed water. Since the temperature of this reference water head 5 is almost the ambient temperature,
Boiling of the reference water head 5 due to the depressurization of the reactor pressure vessel 1 that occurs during a nuclear reactor accident can be prevented. In addition, in the upper impulse tube 2 of the present invention, the upper horizontal tube 13 portion is shorter than that of the conventional one, and the upper impulse tube 2
Since there is no rising part of the water to the reference water surface 4, there is no fear that the cold water will block the upper impulse pipe 2 during head spray operation, and the reference water head 5 side will not become negative pressure. In addition, in FIG. 2, the cooling fins 14 are installed in a part of the horizontal pipe 13 closer to the upper impulse pipe 2, but the present invention is not limited to this, and as shown in FIG. The cooling fins 14 may be installed up to the falling part. Also, instead of the cooling fins 14 in FIG. 3, a cooling jacket 15 is installed as shown in FIG. 4, and cooling water 16 is provided at both ends of the cooling jacket 15.
A similar effect can be obtained by flowing . [Effects of the Invention] As explained above, according to the present invention, it is possible to prevent the boiling phenomenon of the reference water head accompanying the depressurization of the reactor pressure vessel, and also to prevent the phenomenon of blockage of the upper impulse pipe during head spray operation. The water level gauge is working stably.
A reliable water level signal can be provided. Additionally, because the conventional condensation tank has been removed and the inner diameter of the pressure piping has been made smaller and thinner, there is also the secondary effect of significantly reducing costs.