JPS5987396A - Steam leakage suppression device of main steam isolation valve - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] When the main steam isolation valve of a boiling water nuclear power plant is closed,
The present invention relates to a steam leak suppression device for a main steam isolation valve that suppresses steam leakage from the main steam isolation valve.

[Technical background of the invention and its problems]

In a boiling water nuclear power plant, steam generated in a reactor pressure vessel is led directly to a turbine through a main steam pipe, and drives the turbine to generate electricity. Therefore, the sub-reactor coolant is directly converted to steam and guided to the turbine, and since the steam contains minute amounts of radioactive materials such as fission products and corrosion products, the main steam pipe is used to store the reactor. In order to prevent radioactivity from being released to the outside and to prevent reactor coolant from flowing out in the event of a rupture outside the vessel, the section where the main steam pipe penetrates the outer wall of the reactor containment vessel is Main steam isolation valves are provided on the inside and outside, respectively. Main steam isolation valves are installed in each of the four main steam pipes (2) in parallel, and are air or nitrogen gas operated. They are intended to be closed within a short period of time, and their functionality places particularly stringent demands on reliability of operation and low steam leakage rates upon closure.

Because the main steam isolation valve uses high-temperature, dry internal fluid as steam, the valve body and valve body are less likely to come into contact with each other than when the internal fluid is a relatively high-density, high-viscosity liquid such as water. The sealing performance of the sheet surface is 1. It is technically difficult to ensure 00%, and steam leakage can easily occur even from extremely small gaps on the sheet surface.Furthermore, minute dust may adhere to the sheet surface, causing the seal to deteriorate. If the layering properties are impaired, there is a risk that steam leakage beyond the permissible limit will occur.

Historically, the steam led to the main steam isolation valve contains radioactive materials, and if the steam leaks when the main steam isolation valve is closed, there is a risk of radioactive contamination. For steam isolation valves, there has been a strong demand for measures to prevent steam leakage from the main steam isolation valve when it is closed in an emergency.

[Purpose of the invention]

This invention was made in view of the above-mentioned circumstances, and the sealing performance of the seat surface where the valve body and the valve body come into contact with each other in the main steam isolation valve of a boiling water nuclear power plant is 100%.
To provide a steam leak suppression device for a main steam isolation valve that attempts to suppress leakage from its seat surface as much as possible by increasing the density and viscosity of internal high-temperature steam, even if it is not certain. [Summary of the Invention] When an isolation valve, such as the main steam isolation valve of a boiling water nuclear power plant, is closed, the internal fluid has low density and low viscosity, such as dry high-temperature steam. In the case of water, which is much denser and more viscous than steam, leakage is less likely to occur even if the sealing performance of the valve is the same. The steam leak suppression device for a main steam isolation valve according to the invention directly cools the steam on the upstream side of the main steam isolation valve with cooling water to strain the state of the water, and then The feature is that the leakage is suppressed as much as possible by guiding it to the steam isolation valve.

In the steam leak suppression device for the main steam isolation valve according to this invention,
In a boiling water nuclear power plant, main steam isolation valves are installed on the inside and outside of the part where the four main steam pipes penetrate the outer wall of the reactor containment vessel, respectively. In order to cool the steam in the main steam pipe upstream of the isolation valve and turn it into water, the main steam isolation valve is closed, and at the same time a pump sucks up cooling water from a pressure suppression pool, etc., and transfers it to the cooling pipe. through the main steam isolation valve to a spray nozzle provided in communication with the cooling pipe on the inner wall surface of the main steam pipe to which the cooling pipe is connected on the upstream side of the main steam isolation valve. The spray is applied directly to the steam in the main steam pipe.

[Embodiments of the invention]

An embodiment of the steam leak suppression device for a main steam isolation valve in a boiling water nuclear power plant according to the present invention will be described with reference to FIGS. 1 and 2.

(5) Figure 1 is a pipe system diagram of the steam leak suppression device for the main steam isolation valve according to the present invention. In a boiling water nuclear power plant, the steam generated in the reactor pressure vessel 1 is normally connected in four lines in parallel. The main steam pipes 2 are directly led to the turbine (not shown in the drawing) through the provided main steam pipes 2, but the main steam is isolated on the inside and outside of the part where the main steam pipes 2 penetrate the outer wall of the reactor containment vessel 3. Valves 4A and 4B are provided. Further, a pressure suppression pool 5 is attached to the reactor containment vessel 3, and a large amount of water is always stored therein.

The steam leak suppression device for the main steam isolation valve according to the present invention, which is newly provided for the main steam system of the conventional boiling water nuclear power plant described above, includes a pump 6 that sucks up water in the pressure suppression pool 5; The outlet side of the pump 6 is connected to each main steam pipe 2 on the upstream side of the main steam isolation valve 4A provided inside the reactor containment vessel 3 via a cooling system valve 7 and a reversal valve 8. A cooling pipe line 9 is added.

Furthermore, as shown in the partially exploded side view of the connecting portion between the cooling pipe line 9 and the main steam pipe 2 in FIG. A through hole 10 is provided in the pipe wall, and a spray nozzle 11 is attached to the location where the through hole 10 opens to the inner wall surface of the main steam pipe 2 so as to communicate with the cooling pipe line 9, and the spray nozzle 11 is installed to communicate with the cooling pipe line 9. The cooled water is sprayed directly into the main steam pipe 2.

The main steam isolation valve steam leak suppression device according to the present invention, which has been newly added to the main steam system of a boiling water nuclear power plant, is designed to stop the pump 6 and prevent cooling when the power plant is operating normally. The system valve 7 and the check valve 8 are closed,
Cooling water from the pressure suppression pool 5 does not flow into the main steam pipe 2, and the steam generated in the reactor pressure vessel 1 is not affected by the newly added steam leak suppression device of the present invention. Main steam isolation valve 4A without receiving
, 4B to a turbine (not shown in the drawing).

When an emergency situation such as a rupture of the main steam pipe 2 occurs, the main steam isolation valves 4A and 4B are closed in a short period of time, and at the same time, the pump 6 is started and the cooling system valve 7 is opened, causing the inside of the pressure suppression pool 5 to be closed. The cooling water of It is sprayed into the steam inside the tube 2. When the cooling water is sprayed into the high temperature steam in the main steam pipe 2, the steam is cooled into water and guided to the already closed main steam isolation valve 4A. Water has physical properties that are much denser and more viscous than steam, so the seat surface where the valve body of the main steam isolation valve 4A is in contact with the valve body is covered with steam, which has a low density and low viscosity. Even if the seal is in such a state that leakage may occur, leakage is sufficiently suppressed when water is introduced into the main steam isolation valve 4A.

The sealing performance of 4B is improved.

In addition, in the embodiment shown in FIG.
1 shows the case of one, but if a plurality of these are provided or if they are provided all around the inner surface of the main steam pipe 2, the cooling effect on the steam will be further improved.

In addition, in FIG. 1, the cooling water is transferred to the pressure suppression pool 5.
However, this can also be drawn from other systems, such as a condensate storage tank.

〔Effect of the invention〕

As described in detail in the previous section regarding the embodiment of the steam leakage suppressing device for a main steam isolation valve according to the present invention, when the target main steam isolation valve is closed, the inner wall surface of the main steam pipe on the upstream side of the isolation valve is Cooling water is guided from a pressure suppression pool etc. to a spray nozzle installed in the main steam pipe, and is sprayed directly onto the steam in the main steam pipe in the vicinity to cool the water, which is much denser and more viscous than steam. When the main steam isolation valve is closed, the main steam isolation valve
Leakage from the isolation valve is suppressed and the sealing performance is improved, preventing steam containing radioactive materials from leaking outside and causing radioactive contamination in the event of an emergency when the main steam isolation valve is closed. This has the effect of improving the safety and reliability of the entire boiling water nuclear power plant.

(9)

[Brief explanation of the drawing]

Fig. 1 is a pipe line system diagram of a steam leak suppression device for a main steam isolation valve in an embodiment of the present invention, and Fig. 2 is a connection between the main steam pipe (2) and the cooling pipe line (9) in Fig. 1. FIG. 2... Main steam pipe, 4A, 4B... Main steam isolation valve, 5
... Pressure suppression pool, 6... Pump, 7... Cooling system valve, 8... Check valve, 9... Cooling pipe line, 11...
·spray nozzle. (7317) Agent Patent attorney Kensuke Norichika (and 1 other person) (10)

Claims (2)

[Claims] (1) In the main steam system of a boiling water nuclear power plant where main steam isolation valves are installed on the inside and outside of the part where the main steam pipe penetrates the outer wall of the reactor containment vessel, inside the reactor containment vessel. A cooling pipe line connected to the main steam pipe on the upstream side of the main steam isolation valve located at cooling water is supplied to the cooling pipe line via a cooling system valve, and the steam in the main steam pipe on the upstream side of the main steam isolation valve inside the reactor containment vessel is supplied from the spray nozzle to the cooling pipe line via a cooling system valve. A steam leak suppression device for a main steam isolation valve consisting of a pump that sprays cooling water directly into the main steam isolation valve. (2) A steam leakage control device for a main steam isolation valve according to claim 1, wherein the cooling water supplied by the pump is guided from a pressure suppression pool.