JPH04289493A - Primary system depressurization equipment - Google Patents

Abstract

PURPOSE:To provide a depressurization equipment to depressurize the primary system effectively during a small break LOCA in which the primary system pressure in a reactor facility and the like gradually decreases. CONSTITUTION:An automatic pressure relief valve V7 is provided in the main steam line so that it automatically activates to open when the primary system pressure decreases to 50kg/cm<2> during a LOCA to remove heat by the vaporization of the holding water in SG2 for a short period. After that, the secondary side of SG2 is depressurized down to near atmospheric pressure and gravity injection from a condensation tank 6 is started. Besides, a gas vent valve V6 is provided in a water chamber 7 in the SG2 so that the gas vent valve V6 is opened by the signal generated from the pressure gauge and the like of a pressurizer 3 during a LOCA to exhaust non-condensible gas mixed in the primary system to outside and to prevent the disturbance of cooling in SG2 due to the circulation and accumulation of gas.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is particularly applicable to small-rupture LOCA (Loss
The present invention relates to the configuration of a primary system decompression facility for effectively depressurizing the primary system in the event of a cooling accident.

0002

[Prior Art] In a PWR plant, in a major rupture LOCA where the primary system piping ruptures instantly, the pressure in the primary system becomes similar to the pressure in the containment vessel in several tens of seconds, but the pressure in the gas phase of the pressurizer When a small rupture occurs in a pipe or the like, the pressure in the primary system is gradually reduced as shown in FIG. therefore,
Conventional plants are designed with systems that inject cooling water under pressure using pumps, so that cooling water can be injected even when the pressure in the primary system remains high.

[0003] The present invention can also deal with small breaks in LOCA (for example, small breaks in piping in the gas phase section of a pressurizer) without relying on dynamic equipment such as pumps that require an external power supply, and can be placed in high places. This provides a means to enable the design of a passive safety system such as gravity injection from a tank. When designing a passive safety system, it is important to note that, for example, when injecting by gravity, the injection head is at most 1~1.
2Kg/cm2, so in the case of a small rupture accident where the pressure in the primary system gradually decreases as shown in Figure 4, the pressure in the primary system is forcibly reduced and the pressure in the primary system is replaced by injection from the gravity injection tank. Design measures are required to reduce the pressure to a point where it can start.

0004

[Problem to be Solved by the Invention] As a conventional example of such a primary system forced decompression equipment, as shown in FIG.
) A design in which the primary coolant is directly discharged into the containment vessel from the hot leg pressure reducing valve installed in the hot leg piping of the primary system, (b
) Designs have already been proposed in which water is discharged into water, such as a gravity injection tank, via a primary system automatic pressure reducing valve.

Of these, in design (a), if the primary system automatic pressure reducing valve is accidentally opened due to malfunction or erroneous operation, a large amount of primary cooling water will be released into the containment vessel, which will prevent decontamination, etc. inside the containment vessel. Therefore, long-term plant shutdown is required.

In the case of design (b), even if the valves open accidentally for a short time due to incorrect operation or malfunction, the accident can be resolved without contaminating the inside of the containment vessel, but these valves alone can prevent the primary damage. In order to sufficiently depressurize the system, the pressure drop in the decompression line from the pressurizer to the gravity injection tank is limited, so it is necessary to route very large-diameter piping.

The present invention has been made to solve these problems, and does not rely solely on releasing pressure from a pressure reducing valve installed in the primary cooling system, but also uses other means to reduce the pressure in the primary cooling system. The purpose of the present invention is to provide primary system pressure reducing equipment in which the capacity of the primary system automatic pressure reducing valve is optimized.

[0008]

[Means for Solving the Problems] The present invention provides a small fracture LOC
In order to accelerate the pressure reduction in the primary system even when the pressure in the primary system is gradually reduced, such as during time A, a cooling and pressure reduction system for the primary system using a steam generator is adopted, enabling cooling and pressure reduction by the steam generator. For this purpose, we adopted the following configuration.

(a) A secondary system pressure reducing valve is installed in the main steam piping. The function of the secondary system automatic pressure reducing valve is to automatically open when the primary system pressure drops to approximately 50 kg/cm2 during LOCA, etc., and for a short period of time, heat is removed by evaporation of the water retained in the SG. After that, the pressure on the secondary side of the SG is reduced to near atmospheric pressure and gravity injection from the condensate tank is started. As described above, cooling water is supplied to the secondary side of the steam generator, thereby making it possible to cool the primary system.

(b) A gas vent valve is installed in the water chamber of the steam generator. The function of the gas vent valve is to automatically open when the pressure in the primary system drops to about 50 kg/cm2, such as during LOCA, to discharge non-condensable gas mixed in the primary system to the outside of the system, and to prevent gas circulation and accumulation. This is to prevent steam generator cooling from being inhibited by

[0011]

[Function] Figure 3 shows an example of examining the primary system pressure reduction characteristics due to the action of the small capacity primary system automatic pressure reducing valve installed in the gas phase section of the pressurizer and the cooling of the steam generator.

This analysis example is based on the primary system automatic pressure reducing valve V5 in FIG.
This is based on the assumption that one of them opens accidentally and a small LOCA occurs, but once the pressure in the primary system reaches 80K,
Although it settles at about g/cm2, primary system pressure reduction is started by automatically opening the other primary system automatic pressure reducing valves. When the primary system pressure is reduced to approximately 50Kg/cm2, S
The G secondary system automatic pressure reducing valve opens automatically, the steam generator starts cooling, and the pressure reduction in the primary system is rapidly accelerated. Eventually, the pressure in the primary system was reduced to almost the same pressure as the pressure inside the containment vessel, indicating that gravity injection from the gravity injection tank started smoothly.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a layout diagram of a primary system depressurizing equipment according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram of the system of FIG. 1.

In FIGS. 1 and 2, 1 is a reactor containment vessel, 2 is a steam generator (SG), 3 is a pressurizer, 4 is a high-performance pressure accumulator tank, 5 is a gravity injection tank, and 6 is a condensate tank. be. In addition, V1 and V2 are isolation valves that are open during normal operation;
V3 and V4 are check valves, V5 is primary system automatic pressure reducing valve,
V6 is a normally closed gas vent valve, and V7 is a secondary automatic pressure reducing valve.

In FIGS. 1 and 2, the primary system decompression equipment is as follows:
It is composed of a primary system automatic pressure reducing valve V5, a steam generator 2, a secondary system automatic pressure reducing valve V7, a condensate tank 6, etc. The passive safety injection equipment is composed of these primary system decompression equipment, a high-performance pressure accumulator tank 4 for supplying core cooling water, a gravity tank 5, and the like. Primary system automatic pressure reducing valve V5, pressurizer 3
Opens by low pressure (approx. 90Kg/cm2) signal,
Secondary system automatic pressure reducing valve V7 is pressurizer pressure low (approximately 50Kg/c
m2) Opens by signal. Further, in FIG. 2, a vent valve V6 is installed in the water chamber 7 of the steam generator, and is opened by a low pressure signal (approximately 50 kg/cm2) from the pressurizer 3 to discharge the water into the gravity injection tank 5.

[0016]

[Effects of the Invention] As explained above, the effects of the present invention are as follows.

(a) By removing the hot leg pressure reducing valve (see Figure 5) that directly releases the primary coolant into the containment vessel as in the past, there is no possibility that the primary coolant will be released into the containment vessel due to incorrect operation or malfunction. Such risks could be reduced.

(b) The capacity of the primary system pressure reducing valve that discharges from the gas phase part of the pressurizer to the gravity injection tank is very small (for example,
Valve diameter 4 inches x 1 + 8 inches x 2) was completed.

[Brief explanation of the drawing]

FIG. 1 is a layout diagram of a primary system decompression equipment that is an embodiment of the present invention.

FIG. 2 is an explanatory diagram of the system in FIG. 1.

FIG. 3 is a diagram showing the pressure reduction performance of the primary system pressure reduction equipment of the present invention.

FIG. 4 is a diagram showing changes in primary system pressure during small fracture LOCA.

FIG. 5 is a diagram showing a conventional example of forced decompression equipment for the primary system.

[Explanation of symbols]

1 Reactor containment vessel 2 Steam generator (SG) 3 Pressurizer 4 High-performance pressure accumulator tank 5 Gravity injection tank 6 Condensate tank 7 SG water chamber

Claims (1)

[Claims] 1. In a primary system depressurization equipment for a pressurized water reactor, a circulation system consisting of a reactor vessel and a steam generator is provided with a secondary system automatic depressurization valve in the main steam piping line of the steam generator, A means for cooling the steam generator in an emergency is provided, and a gas vent valve is provided in the water chamber of the steam generator.
Primary system decompression equipment characterized by preventing the accumulation of non-condensable gas in a steam generator.