PROTECTION DEVICE FOR PASSIVE FILLING PIPES OF THE MELT TRAP SHAFT

Abstract

A pipe protection device relates to emergency protection systems for nuclear power plants, and more particularly to devices for protecting pipes for passively filling the shaft of a core catcher, and can be used in the event of severe accidents that result in damage to the reactor vessel, as well as in other technical fields in which filter elements are used.

Description

[0001] Pipe protection device

[0002] Field of technology

[0003] The technical solution relates to emergency protection systems of nuclear power plants, in particular, to devices for protecting passive filling pipes of the core catcher shaft and can be used in severe accidents leading to the destruction of the reactor vessel.

[0004] Prior art

[0005] One of the technical means of managing a severe accident is the melt localization device (MLD), which ensures the reception, placement and cooling of the core melt. In this case, the MLD is cooled by a coolant that passively enters the trap shaft during the coolant leak from the primary circuit. This coolant (water) can carry solid foreign particles from the destruction of the thermal and other structures of the reactor. The presence of such particles in the trap shaft and their deposition on the melt catcher body reduces the efficiency of its cooling.

[0006] Pipe protection devices (PPD) for passive filling of the ULR shaft must ensure a reduction in the concentration of foreign particles in the coolant entering the ULR for cooling to acceptable values. PPDs must have high structural strength, since they are located in the zone of possible direct impact of large-sized flying objects that form during an emergency situation. To protect PPDs, they are placed inside concrete structures, while leaving a minimum opening at the top for the coolant to enter.

[0007] The filter elements themselves are located vertically in the UZT body and are filter pipes, the side surface of which has slits. The problem with using UZT is the danger of a large number of foreign particles entering, which can lead to clogging of the filter elements and a sharp drop in the efficiency of the filter elements, which reduces the efficiency of cooling the melt catcher body.

[0008] There are various known solutions that can be used as a device for protecting passive filling pipes of a trap shaft.

[0009] A filter module of a sump protection device in an emergency cooling system of a water-cooled nuclear reactor is known (RU Patent for Invention No. 2686684, published on 30.04.2019), characterized by the fact that it has filter elements located inside, which are a set of filter pipes.

[0010] The closest to the claimed invention is a pipe protection device (RU Patent for Utility Model No. 211181, published on 05 / 24 / 2022), containing a housing and vertical tubular filter elements installed on its support panel, equipped with intermediate solid support elements that fasten groups of filter elements and are arranged in a checkerboard pattern.

[0011] Such pipe protection devices have increased efficiency, but are susceptible to clogging when large volumes of coolant with debris flow through.

[0012] The objective of the present invention is to develop a pipe protection device that ensures the filtration of the heat carrier when a solution with a large amount of foreign impurities flows through it.

[0013] The technical result of the claimed invention consists in increasing the safety of using a pipe protection device by ensuring the filtration of the heat carrier when a solution with a large amount of foreign impurities flows through.

[0014] The technical result is achieved in that in the known pipe protection device, comprising a housing with a drain hole and vertical tubular filter elements installed on its lower support panel in several rows, secured with their upper ends in the upper support panel, an overflow chamber is located above the filter elements, connected to them, below the filter elements - a collection chamber, also connected to the filter elements and a discharge pipeline located below it, wherein the cross-section of the opening in the upper panel is made smaller than the total cross-section of the internal openings of the filter elements.

[0015] It is preferable to provide that the upper part of the housing is equipped with a filter grid.

[0016] It is advisable to equip the pipe protection device with a pipeline installed on the top panel and designed with the ability to remove the air lock.

[0017] It is recommended to implement a pipe protection device with a ratio of the cross-sections of the opening in the top panel and the total cross-section of the internal openings of the filter elements of at least five.

[0018] Brief description of drawing figures

[0019] Fig. 1 shows the operating principle of the pipe protection device at the initial stage of liquid inflow.

[0020] Fig. 2 shows the operating principle of the pipe protection device at the intermediate stage of liquid inflow.

[0021] Fig. 3 shows the operating principle of the pipe protection device at the final stage of liquid inflow.

[0022] The pipe protection device consists of a housing 1, filter elements 2, a lower support panel 3, an upper panel 5 with an opening 6. Below the upper panel 5, with a gap, an intermediate panel 7 is installed, in which the filter elements 2 are fixed. These two panels form an upper overflow chamber 12, which is connected to the internal cavity of the filter elements 2 through openings 8.

[0023] The bottom of the housing 1 and the lower support panel 3, in which the filter elements 2 are fixed, form a collection chamber 13, which is connected to the internal cavity of the filter elements 2 through openings 4. In addition, the collection chamber 13 is connected to the branch pipe 9, through which the purified coolant enters the shaft of the ULR1

[0024] To protect the device from flying objects formed during a rupture of the first circuit pipelines and to stop foreign objects of significant size, a fence 10 is provided, consisting of posts and a roof.

[0025] The air cushion formed inside the device is removed through pipeline 11, installed on the top panel 5.

[0026] The total cross-section of all internal openings of filter elements 4 is not less than five times larger than the cross-section of opening 6 in the preferred embodiment.

[0027] The pipe protection device works as follows.

[0028] A severe accident, the initial event of which is a rupture of the primary circuit pipeline and failure of the pumps of the emergency cooling system of the reactor plant, is characterized by a release of the primary circuit coolant, while the flow rate into the leak may exceed 20 m 3 / s. The volume of coolant entering the containment is limited by the volume of coolant in the reactor installation (about 380 m 3 ).

[0029] This coolant (water) can carry solid foreign particles from the destruction of thermal insulation, nearby pipes or other reactor structures. The presence of such particles in the trap shaft and their deposition on the trap body reduces the efficiency of its cooling.

[0030] The time of intensive coolant flow and complete drying of the reactor installation is tens of seconds. During this time, there is intensive movement of the coolant in the rooms of the protective shell, which ensures the transportation of foreign particles present in the coolant over a significant distance, including their entry into the UZT. During this period of operation of the UZT, the coolant must be cleaned by filtration, while foreign impurities accumulate on the filter surfaces.

[0031] After the reactor unit is drained, the flow from the primary circuit stops. The speed of the coolant in the containment vessel drops to almost zero, and the impurities contained in it settle on the floor of the containment vessel under the force of gravity. The flow of foreign impurities into the UZT drops significantly, and the coolant can be fed into the ULR shaft via other routes, bypassing the filter surfaces.

[0032] The trap shaft must be filled by the time the reactor melt enters the melt trap. The time required to melt the internal elements and the reactor vessel is calculated to be at least one hour.

[0033] The proposed design of the UZT allows solving the problem of limiting the flow of debris into the melt trap shaft.

[0034] At the initial stage of the UZT operation (Fig. 1), the coolant with foreign impurities in a limited design volume enters the UZT through opening 6 in the upper panel 5 and flows down to the lower panel 3. Then the coolant is cleaned on the filter elements 2 and enters the cavity 13 and the branch pipe 9. The filter surfaces of the elements 2 become clogged with foreign impurities.

[0035] The operation of the UZT at the intermediate stage is shown in Fig. 2.

[0036] At this stage, a layer of foreign impurities 14 is formed on the filter surfaces 2. The level of the coolant in the UZT increases. Due to the increase in the level of the coolant inside the UZT, the flow rate at the outlet remains constant. The air that was inside the housing and brought in with the coolant stream is removed from the housing through the pipeline 11.

[0037] The nature of the UZT operation does not change until all filter surfaces are clogged with a sufficient layer of accumulated foreign impurities and the coolant level rises to the level of the intermediate panel 7.

[0038] The operation of the UZT at the final stage is shown in Fig. 3.

[0039] By this time the reactor unit is drained, the coolant movement decreases, foreign impurities settle on the floor of the protective shell. The filter surfaces of the UZT are clogged with foreign impurities and the coolant level rises to the intermediate panel 7 and accordingly to the upper open ends of the filter elements 8, the clean coolant overflows into the filter elements 2 and then enters the collection chamber 10 and the branch pipe 11.

[0040] Thus, the proposed design of the UZT ensures a reduction in the amount of foreign impurities entering the melt catcher shaft and an increase in the efficiency of its cooling.

[0041] Industrial applicability

[0042] The pipe protection device can be used in emergency protection systems of nuclear power plants, in particular, in devices for protecting passive filling pipes of the core catcher shaft, as well as in other areas of technology using filter elements.

Claims

1. A pipe protection device comprising a housing (1) with a drain hole (9) and vertical tubular filter elements (2) mounted in several rows on its lower support panel (3), secured with their upper ends in an upper support panel (5), characterized in that an overflow chamber (12) is located above the filter elements (2) and connected to them, a collection chamber (13) is located below the filter elements (2), also connected to the filter elements (2) and a discharge pipeline (9) located below it, in that part of the upper support panel (5) under which the filter elements (2) are not secured, an opening (6) is made, wherein the cross-section of the opening (6) is made smaller than the total cross-section of the internal openings (8) of the filter elements (2).

2. A pipe protection device according to claim 1, characterized in that the upper part of the housing (1) is equipped with a filter grid.

3. A pipe protection device according to claim 1, characterized in that it is additionally provided with a pipeline (11) installed on the top panel (6) and designed with the possibility of removing an air lock.

4. A pipe protection device according to paragraph 1, characterized in that the ratio of the cross-sections of the opening (6) in the top panel and the total cross-section of the internal openings (8) of the filter elements is at least five.

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