RU2761441C1 - Coolant flow filtration system of the sump tank of the emergency core cooling system - Google Patents

Abstract

FIELD: nuclear energy.

SUBSTANCE: invention relates to the field of nuclear energy, namely, to ensuring the safety of the operation of a nuclear power plant (NPP) in an accident due to the uninterrupted supply of coolant inside the protective shell of the NPP. The coolant flow filtration system of the tank-pit of the emergency core cooling system contains a tank-pit equipped with vertical separation barriers, round holes for coolant supply are made in the lid of the tank-pit. Guiding devices are vertically located under them, the inlet of which is located under the hole in the lid of the tank-pit, and the outlet is at the floor level of the tank-pit. Holes are made in the bottom of the tank-pit to drain the purified coolant. Separation barriers are located in the tank-pit room in such a way that they form the maximum path of the coolant from the guide devices to the holes for the discharge of the purified coolant. The separation barriers are made in the form of filter screens, made with the possibility of entrapping large pieces of debris.

EFFECT: coolant flow filtration system of the tank-pit of the core cooling system makes it possible to increase the safety of nuclear power plants in emergency conditions and can be used at nuclear power plants of various types.

3 cl, 2 dwg, 1 ex

Description

Technology area

The invention relates to the field of nuclear energy, namely to ensure the safety of a nuclear power plant (NPP) in an accident due to the uninterrupted supply of coolant inside the containment shell of the nuclear power plant.

Prior art

In the issue of ensuring the safety of nuclear power plants in emergency modes, an important role is played by the systems for emergency-planned cooling of the core and the removal of residual energy release. These systems are adapted both for the planned cooling down of a nuclear power plant during refueling and for emergency cooling in the event of a coolant leak in a serious accident by supplying a backup coolant to the reactor core. Such systems include feed pumps for boric acid solution (RBK), supplying it through pipelines to the core, borated water sump tanks, emergency boron injection systems, a sprinkler system, and emergency cooling heat exchangers. One of the key components are sump tanks, which are specially located inside the containment shell of the reactor in such a way that, in the event of a serious accident, all the liquid entering the containment due to leaks (water from circuit breaks, water from a sprinkler system, condensed steam, etc.) ) was collected in sump tanks located at the bottom of the containment, and water was withdrawn to the pumps of the emergency core cooling system (ECCS) and the sprinkler system directly from them. Another positive effect of the placement of sump tanks under the containment is the possibility of organizing the supply of water to the melt localization device for at least 72 hours without external sources of power supply. During normal operation, the sump tanks contain a stock of boric acid solution, which, in the event of an accident with a loss of coolant, is supplied by the emergency injection systems to the reactor core; after this stock is used up, it becomes critical to ensure the possibility of cleaning the liquid entering the sump tanks from fragments of destroyed in the event of a system failure (the so-called debris) for its subsequent supply to the core for cooling.

Under these conditions, the ability of the filter elements of the sump tanks to retain debris and other impurities in such a way as not to reduce the flow of the coolant supplied by pumps from the sump tanks to the core is of great importance for the safety of nuclear power plants in emergency modes. In this case, the initial flow of the coolant in the event of a rupture of large-diameter pipelines can be very large and carry a large amount of debris, which can lead to rapid clogging of the filter elements. To solve this problem, it is required to develop a filtering system for recirculating the coolant flow, which provides filtration of a large coolant flow in a passive mode.

To solve a similar problem, several different technical solutions were used.

A known method of purifying a liquid from impurities by passing a liquid flow through layers of filtering coalescent material formed into a block-modular coalescent filter (RF patent for invention No. 2541544, publ. 20.02.2015), in which a block-modular coalescent filter divides the flow into two different the volume of the separation zone, the first coarse cleaning zone and the second finishing zone; in the first, larger zone of primary separation, the speed of the liquid flow is reduced due to the expansion of the flow and it is directed for further extinguishing of energy into collectors of variable cross-section with slotted gaps of different sections, equipped with internal deflectors of different sizes and bending radii, after which the flow is divided by gravity into phases that are withdrawn from the primary separation zone; coarsely purified liquid with oil product residues is directed through a block-modular coalescent filter to the secondary separation zone of final treatment, where the flow is also separated by gravity into phases that are taken from the secondary separation zone; with an increase in the pressure drop across the block-modular coalescent filter, the liquid flow is automatically diverted to the secondary separation zone bypassing the filter through protective devices.

The disadvantage of this method is the impossibility of filtering a large flow of coolant in emergency mode.

There is also known a method for purifying a process fluid from contaminating mechanical impurities and a floating liquid medium (RF patent for invention No. 2626833, publ. 02.08.2017), in which the process fluid to be purified is sent to a flow sump, the process fluid is purified from mechanical impurities and a floating liquid medium by gravitational sedimentation of mechanical impurities and the ascent of a floating liquid medium from a thin flat layer formed by a moving mixture of the process liquid to be purified and a part of the purified process liquid, while both components of the mixture are preliminarily fed into the mixer (homogenizer), in which the jets of the purified and part of the pure process liquid are directed towards each other with an equal cross-section at the point of collision of the jets, and then the resulting mixture is fed into a flow-through settler through a horizontal slotted diffuser with a width equal to the inner width of the settler and with a height that ensures a laminar flow regime thin flat layer.

Closest to the claimed invention is a device for producing purified water (RF patent for utility model No. 157474, publ. of which at least one chamber is a working chamber, and the other is a sludge compactor, and the working chamber is equipped with an ejection system located in its lower part, and submersible membranes are installed in the upper part of the chambers above the bypass openings connected to the purified water drainage pipeline.

The disadvantage of this technical solution, as well as those listed above, is the impossibility of filtering a large flow of coolant in an emergency mode.

Disclosure of invention

The objective of the present invention is to develop a system for filtering the coolant flow of the sump tank of the emergency core cooling system (ECCS), which provides filtration of a large coolant flow in a passive mode.

The technical result of the present invention is to improve the safety of nuclear power plants in emergency modes by increasing the filtration efficiency of a large flow of coolant in a passive mode.

The technical result is achieved by the fact that in the well-known system for filtering the coolant flow of the sump tank of the emergency core cooling system containing the sump tank equipped with vertical dividing barriers, round holes are made in the sump tank cover for supplying the coolant, guiding devices are vertically located under them, the inlet of which is located under the hole in the cover of the sump tank, and the outlet is at the floor level, holes are made in the bottom of the sump to drain the purified coolant, the separating barriers are located in the room of the sump in such a way that they form the maximum path of the coolant from the guides devices to the holes for the outlet of the purified heat carrier.

The technical result is also achieved by the fact that the separating barriers are made in the form of filter grids, made with the possibility of retaining large pieces of debris.

The technical result is also achieved by the fact that the guiding devices form a channel for the coolant outlet, while some sections of the separation barriers are made impermeable to the coolant.

Brief Description of the Figures of the Drawings

FIG. 1 shows a general view of the NPP coolant recirculation filtering system.

FIG. 2 shows the results of a preliminary hydraulic calculation of the flow in one of the sections of the system body.

The filtration system for the coolant flow of the ECCS system sump consists of a sump tank 1, with vertical dividing barriers 2, round holes are made in the tank lid for supplying the coolant, guiding devices 3 are vertically located under them, the inlet of which is located under the hole in the tank cover - sump 1, and the outlet is at the level of the floor of the sump tank 1, holes are made in the bottom of the sump tank 1 to drain the purified heat carrier, dividing barriers 2 are located in the room of the sump tank 1 in such a way that they form the maximum path of the heat carrier from the guiding devices 3 to the holes for the outlet of the purified heat carrier.

Implementation of the invention

The filtration system of the coolant flow of the tank-sump of the ECCS system works as follows. In the event of a severe accident with a rupture of pipelines, a large flow of coolant with a high content of debris enters the lid of the sump tank 1, from where it enters the sump tank 1 through the inlet holes of the guiding devices 3 and through the outlets of the guiding devices 3 located at the floor level of the sump tank 1 falls on the floor of the tank-sump 1. Since the separation barriers 2 are located in the room of the tank-sump 1 in such a way that they form the maximum path of the coolant from the holes in the lid of the tank-sump 1 to the holes 4 for removing the purified coolant, the flow of the coolant on the way to the holes 4 manages to spread debris over a large area of the floor of the tank-sump 1, which eliminates clogging of the holes 4 for removing the cleaned coolant with debris, thereby collecting the cleaned coolant for subsequent use when cooling the containment shell. Holes 4 for draining the cleaned heat carrier can be additionally equipped with filters that provide filtration of the heat carrier flow, however, the important role of the present invention is that the bulk of the debris, including its largest pieces, remain on the floor of the sump tank 1 and do not clog the filters placed in the holes 4 for the removal of the purified heat carrier.

The dividing barriers 2 in a preferred embodiment of the invention are made in the form of filter grids made with the possibility of retaining large pieces of debris. This makes it possible to reduce the amount of debris remaining on the floor of the sump tank 1 in the middle between the separation barriers 2 and thereby additionally protect the filters in the openings 4 for removing the cleaned heat carrier from debris. In addition, individual sections of the dividing barriers 2 can be made impermeable to the coolant in order to organize debris accumulation zones, which also makes it possible to additionally protect the holes 4 from debris for removing the cleaned coolant. Such areas can be selected on the basis of numerical modeling of the coolant flows, depending on the configuration of the guiding devices 3 and separation barriers 2. The purified coolant, thus, enters the “clean” zone of the sump tank 1 and is supplied by the shortest route to openings 4 for removing the purified coolant ... The coolant with an increased concentration of debris is directed to the peripheral zones with the organization of debris sedimentation zones. Ultimately, the coolant from the peripheral zones also enters the filters of the openings 4 for removing the cleaned coolant, however, the amount of debris that has reached them is significantly reduced.

Thus, dividing barriers 2 separate the "clean" and "dirty" zones of the sump tank 1 and provide preliminary separation of the flow into "clean" and "dirty".

Separating barriers 2 can be made in the form of a self-cleaning filter made of a slotted grid. Cleaning of such a filter is carried out with a directed stream of water coming from the guiding devices 3.

The guiding devices 3 can be made in the form of a cylinder with impermeable side walls or walls made of filter gratings.

In addition, in a preferred embodiment of the present invention, the guiding devices 3 can be connected in pairs by dividing barriers 2, while the dividing barriers 2 form a channel for the coolant out of the guiding device 3, and the sections of the dividing barriers 2 adjacent to each guiding device 3 are made impermeable to the heat carrier. This solution allows, on the one hand, to provide a long path of the coolant to the holes 4 of the purified coolant outlet, and on the other hand, the formation of a coolant channel at the outlet from the guide device 3 in such a way (Fig. 1) to ensure that the coolant is twisted in the guide devices 3 around the axis guiding device 3, which ensures the maximum flow rate of the coolant at the outlet of the guiding device 3, which, in turn, allows this flow to remove debris to the maximum distance from the guiding devices 3 so that the debris does not block the outlet openings of the guiding devices 3.

The effectiveness of the separation barriers 2 is determined by the ratio of the amount of water coming from the "dirty" zone to the clean one, to the amount of water entering the sump tank.

As an example of a specific implementation of the present invention, an accident can be considered, for example, with a loss of coolant in a steam generator box.

A rupture of a large-diameter pipeline leads to a salvo discharge of the coolant from the primary circuit of the nuclear power plant.

Water flows from the steam generator box through the gap between the overlap and the protective shell to the cover of the sump tank 1.

In this case, the maximum water consumption takes place for no more than 1 min. After an accident, the flow rate decreases and stabilizes approximately at the level of the safety systems flow rate (passive and active parts of the ECCS, sprinkler system).

In this case, water through the guiding devices 3 with a diameter of up to 2 m begins to flow into the sump tank 1. The total volume of water in this case can be up to 240 m ³ .

Then the water level in the "clean" and "dirty" area of the sump tank 1 is leveled due to the flow of clean water through the separation barriers 2 and contaminated water through the guiding devices 3 without filter barriers. At the same time, when the first portion of water enters the tank-sump 1, the debris with a high degree of probability will not fall into the "clean" zone.

After the start of the ECCS system and the sprinkler system, circulation is established with a maximum flow rate in each sump tank 1 0.81 m ³ / s

The results of a preliminary hydraulic calculation of the flow in one section of the sump tank corresponding to the lower part of FIG. 1, with a similar development of the situation are presented in FIG. 2. The diagrams of velocities at different levels (0.5; 1.0; 1.5 and 1.95 m from the floor level) in the sump tank with a total coolant flow rate of 2000 kg / s (which is typical for the initial stage of an accident with a loss of coolant; the maximum flow rate during the operation of ECCS systems is about 800 kg / s). In the above calculation, the contamination of the mesh of the separation barriers 2 was not taken into account, however, the estimated calculations with partially contaminated surfaces showed a similar flow pattern. A preliminary calculation shows the general movement of the coolant (shown in Fig. 2 by arrows) along the maximum path from the guiding elements 3 to the holes 4 for removing the coolant.

Industrial applicability

The system for filtering the coolant flow of the ECCS system sump allows increasing the safety of nuclear power plants in emergency modes and can be used at nuclear power plants of various types.

Claims (3)

1. A filtration system for the coolant flow of the sump tank of the emergency core cooling system, containing a sump tank equipped with vertical dividing barriers, characterized in that round holes for coolant supply are made in the sump tank cover, guiding devices are vertically located under them, an inlet which is located under the hole in the lid of the sump tank, and the outlet is at the level of the floor of the sump tank, holes are made in the bottom of the sump tank for draining the purified coolant, dividing barriers are located in the tank-sump room in such a way that they form the maximum path of the coolant from guiding devices to the holes for the outlet of the purified heat carrier. 2. The filtration system according to claim 1, characterized in that the separating barriers are made in the form of filter grids made with the possibility of retaining large pieces of debris. 3. The filtration system according to claim 1, characterized in that the guiding devices form a channel for the coolant outlet, while some sections of the separation barriers are made impermeable to the coolant.

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