RU2247434C1 - Reactor flooding passive system water tank - Google Patents

Abstract

FIELD: nuclear power engineering; reactor flooding in emergency leakage situations involving failure of ac power supplies.

SUBSTANCE: proposed water tank is made in the form of leak-proof tank disposed above reactor to provide for coolant drain therefrom to reactor due to hydrostatic head. Top part of tank mounts perforated plate and steam atomizer. Perforated plate and steam atomizer confine space of cold water coming in contact with steam and regulate coolant flow from water tank to reactor. Drain manifold that shapes coolant jet flow from tank is made in the form of different-height tubes which facilitates adjustment of rate of coolant drain to reactor.

EFFECT: enhanced safety of reactor units equipped with proposed water tanks.

1 cl, 4 dwg

Description

The invention relates to nuclear energy and can be used at nuclear power plants (NPPs) with pressurized water reactor plants as a system of emergency gulf and cooling of the reactor core.

In order to ensure the filling of the active zone of water-cooled reactor installations (RU) in case of emergency leaks in the reactor plants, along with pumping systems for emergency cooling of the zone, hydraulic capacity systems (CU) with a coolant reserve, for example, an aqueous solution of boric acid, are provided at nuclear power plants. In the event of large accidental leaks from the reactor installations, a large flow rate of the coolant is required for the quick re-filling of the reactor zone, for which purpose hydroelectric tanks with compressed gas are provided at nuclear power plants. Gas pressures in hydraulic tanks are lower than the working pressure of the medium in the reactor plants. The volume of hydraulic reservoirs does not exceed the volume of the coolant in the reactor installation and is designed for short-term supply of coolant to the reactor installation.

For long-term supply of coolant to the reactor zone with large leaks occurring with the imposition of loss of alternating current sources at nuclear power plants, hydraulic reservoir systems with a large supply of coolant having a relatively low working pressure of the medium are provided. The supply of coolant from them occurs due to the hydrostatic column. The inclusion of these hydraulic systems in the work occurs in a passive manner, but at a pressure lower than the connection of hydraulic tanks with a gas cushion. Such a system of hydraulic reservoirs is described in the invention under the name “Power plant” and is protected by a patent (IPC 7 G 21 C 15/18, RU 2108630 C1, publ. 04/10/1998).

The hydraulic reservoir system proposed in this patent is adopted for the present invention as a prototype.

According to the description of the prototype, the storage tank of this system communicates with the reactor with two pipes. Namely, through the lower drain pipe, designed to supply coolant to the reactor, and through the upper inlet pipe, which is connected by a pipe to the main circulation pipe of the reactor at the exit of the steam generator.

On the pipelines connecting the hydraulic reservoir to the reactor, check valves are installed.

A non-return valve installed on the pipeline connecting the upper nozzle of the hydraulic reservoir with the reactor installation is a type of valve that cannot be opened. It opens when the pressure in the reactor installation decreases below the value set for the system. The hydraulic capacity is protected from repeated pressure by installing safety valves on the pipelines.

To change the flow rate of the coolant from the hydraulic tank as it is emptying, a collector is installed inside the hydraulic tank, profiling the flow.

From the point of view of ensuring the safety of the reactor installation, the most important design characteristics of the hydraulic capacity are the maximum flow rate of the hydraulic capacity and the time to reach the maximum flow rate after opening the non-permanently opening valve. These design values are determined from the conditions for ensuring the safety of the reactor installation at the maximum design leak from the reactor installation with the imposition of the loss of alternating current sources at nuclear power plants.

The hydraulic capacity proposed in the prototype has a significant drawback, unacceptable for the safety of the reactor installation. Namely, the gulf system, being made of hydraulic reservoirs with the design specified in the prototype, will have a time to reach the design flow rate, significantly exceeding the allowable design time, and a long period of unstable operation.

The main reason for non-project work is thermally nonequilibrium processes that inevitably occur in hydraulic reservoirs when steam entering the tank interacts with a large mass of cold coolant (water) contained in the hydraulic reservoir.

In the prototype, the drain manifold is a height-perforated cylinder located inside the tank. This design of the collector creates difficulties in setting up or changing the flow characteristics of the hydraulic capacity.

The objective of the invention is the use of constructive solutions that maximally reduce thermally nonequilibrium processes in order to ensure the design supply of the coolant from the hydraulic tank to the reactor.

The solution to this problem is achieved by the fact that in the known hydraulic capacity for a passive emergency water system with reactor water containing, the upper one has an inlet pipe for steam and the lower one has a drain pipe for water, the new one is that the hydraulic tank inside is equipped with a perforated plate and a vapor diffuser, while the perforated plate is installed in the upper part and horizontally mounted on the side wall of the hydraulic reservoir, and the diffuser is mounted above the perforated plate and communicated with the inlet of the hydraulic reservoir.

In addition, the hydraulic capacity can be additionally provided inside with lower drain pipes of different heights, performing the function of a drain collector profiling coolant flow.

The supply of hydraulic capacity with a perforated plate and a steam diffuser limits the interaction of the volume of cold water with steam, which accelerates the process of pressure growth in the hydraulic capacity to the pressure in the reactor installation.

The drain manifold must provide the rate of reduction of the coolant flow rate from the hydraulic reservoirs to the reactor as specified by the design of the reactor installation. One of the significant positive features of this invention is that the collector is proposed to perform in the form of a set of drain pipes of different heights. With this design of the collector, profiling of the flow and its adjustment at the facility can be carried out using throttle washers placed on the outer lower ends of the drain pipes.

The invention is illustrated by drawings.

Figure 1 gives a sketch of the hydraulic capacity.

Figure 2 shows the relationship of hydraulic capacity with the reactor installation.

Figure 3 shows the flow characteristic of the hydraulic capacity without a perforated plate and a steam diffuser.

Figure 4 shows the flow characteristic of the hydraulic capacity, equipped with a perforated plate and a steam diffuser.

The hydraulic reservoir for the passive system of the emergency reactor bay (Fig. 1) is a sealed vessel 1. The dimensions of the vessel (D and H) and their number are selected based on the required coolant supply. The hydraulic reservoir has an upper inlet pipe 2 and inside the housing devices: steam diffuser 3; perforated plate 4 (hole sheet) and a drain manifold, consisting of lower drain pipes 5 of different heights, the smallest of which is the lower drain pipe. The perforated plate 4 is installed inside the hydraulic reservoir in the upper part and horizontally mounted on the side wall, blocking the entire cross section of the hydraulic reservoir, and is made with evenly distributed holes. Steam diffuser 3 is located above the perforated plate 4, its outlet openings create a steam outlet up.

Depending on the design of the drain manifold, the hydraulic reservoir may have one or more drain pipes 5 whose lower outer ends 6 are interconnected. For example, a four-stage drain collector of hydraulic capacity used in the tests corresponds to a set of four drain pipes 5 (Fig. 1).

The hydraulic reservoir for the passive system of the emergency gulf of the reactor works as follows. When leaks occur in the reactor installation (Fig. 2), consisting of a reactor 7, a hot thread of the main circulation circuit 8, a steam generator 9 and a cold thread of the main circulation circuit 10, the pressure drops in the reactor installation. When the pressure drops to a certain design value, the non-return-opening check valve 11 opens on the pipe 12 connecting the top of the hydraulic reservoir with the main circulation pipe of the reactor installation. When steam is formed in the reactor installation in the region 13 of the connection of the pipe 12 with the cold thread of the main circulation circuit 10, steam (or a mixture of steam with gas) begins to flow into the upper part of the hydraulic tank. In the hydraulic reservoir, steam is distributed using a diffuser 3 and, condensing, heats the water in the upper part of the hydraulic reservoir. The perforated plate 4 limits the volume of cold water interacting with the steam, which reduces the time of pressure increase in the hydraulic capacity to the pressure in the reactor installation and leads to the opening of the check valve 14 on the drain pipe 15 connecting the hydraulic tank to the reactor installation. The drain pipe 15 is connected to the internal volume of the hydraulic reservoir using the lower outer ends 6 of the drain pipes 5.

In figure 2, the collector, for example, is schematically represented in the form of three pipes 5. At the beginning of the operation of the hydraulic reservoir, the coolant flows through all three pipes, and this ensures the maximum flow rate. As the coolant level in the hydraulic tank decreases, the number of pipes through which the coolant flows out decreases stepwise, which creates a stepwise decreasing coolant flow from the hydraulic tank to the reactor 7. Depending on the amount of the initial coolant flow rate into the reactor, the height of the hydraulic tanks above the reactor 7 is selected.

Figure 3 shows the flow characteristic of the hydraulic capacity, when tested without a perforated plate and diffuser, and figure 4 shows the flow characteristic of the hydraulic capacity, which is equipped with a perforated plate and a diffuser when tested, and its comparison with the design flow characteristic is given. The test results show that the design solutions proposed in this invention provide a given flow characteristic.

The design of the hydraulic reservoir proposed in this invention has a new positive property, it provides a given design flow rate from the hydraulic reservoir both in terms of growth rate and in magnitude, and thereby ensures the design level of fuel temperature in the reactor installation during an emergency leak from the reactor installation. The design of the drain reservoir of the hydraulic reservoir provides the adjustment of the design flow rate using throttles placed outside the hydraulic reservoir.

The technical and economic effect of the invention consists in increasing the safety level of reactor facilities equipped with hydraulic tanks of the proposed design, in beyond design basis accidents with leakage from the reactor installation with the loss of all alternating current sources at the nuclear power plant.

Claims (2)

1. The hydraulic reservoir for the passive system of the emergency gulf of the reactor, having an upper inlet pipe for steam and a lower drain pipe for water, characterized in that the hydraulic reservoir is provided with a perforated plate and a vapor diffuser, while the perforated plate is installed in the upper part and horizontally mounted on the side wall hydraulic capacity, and the diffuser is mounted above the perforated plate and connected to the inlet pipe of the hydraulic capacity. 2. The hydraulic reservoir according to claim 1, characterized in that it is additionally equipped with lower drain pipes of different heights.

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