RU20402U1 - DEVICE FOR CLEANING STREAMS OF STEAM-GAS MIXTURES FORMED BY RELIEF OF PRESSURE PRESSURE FROM UNDER PROTECTIVE SHELLS OF NUCLEAR POWER PLANTS - Google Patents

Abstract

1. A device for cleaning streams of steam-gas mixtures formed during the release of excess pressure from under the protective shells of nuclear power plants, containing a high-pressure reservoir with a cleaning solution, located inside the high-pressure reservoir in the volume of the cleaning solution, jet-type mixing devices and above them devices for distributing steam and gas mixtures along the cross section of the tank, drop separators located in the tank above the level of the washing solution, and the inlet and outlet fittings of the cleaned steam-gas mixture streams, characterized in that the jet-type mixing devices are made in the form of ejectors, and the filtering elements of the droplet separator installed in front of the outlet of the cleaned steam-gas flows mixtures made of fiberglass. 2. The device according to claim 1, characterized in that check valves are installed in the inlet openings of the ejector nozzles. The device according to claims 1 and 2, characterized in that the outlet openings of the ejector nozzles are equipped with locking devices.

Description

A device for cleaning flows of gas-vapor mixtures formed during the discharge of excess pressure from under the protective shells of nuclear power plants.

The utility model relates to devices for processing materials with radioactive contamination in order to eliminate this contamination, and can be used mainly for localizing the consequences of accidents at a nuclear power plant.

One of the measures to manage the accident, to prevent damage to the protective shell of a nuclear reactor is to relieve pressure from the protective shell by filtering the resulting radioactive media. During filtration, the vapor-gas mixture is cleaned of radioactive aerosols and volatile forms of radioactive molecular iodine and radioactive organic iodine to prevent the release of radioactive substances into the environment.

Currently, in connection with the large-scale commissioning of nuclear power plants, Russian specialists have been tasked with developing a highly efficient fission product capture system (FFP).

The analysis of scientific, technical and patent documentation, the results of studies of Russian models of UPD systems, joint Russian and foreign systems in Germany and the USA showed that the devices that are equipped with several stages of cleaning are the most effective, satisfying the requirements for cleaning gas-vapor mixtures from radioactive substances.

Typically, a device is a tank filled with a washing solution, under the level of which there are installed jet-type mixing devices (Venturi pipes, nozzles) and distributors placed above them, used to crush gas bubbles and equalize the vapor-gas mixture flow over the tank section. Drop separators (dehumidifiers) with filter elements made of metal fiber or metal mesh are placed above the level of the washing solution.

Let us consider in more detail the solutions known from the world level of technology, the technical essence of which is based on the structural elements described above.

IPC G21F 9/02, G21C 9/00

A device for cleaning flows of vapor-gas mixtures formed during the discharge of excess pressure from under the protective shells of nuclear power plants (see USSR patent No. 1718740, class O21R 9 / 02,14.04.89, applicant company Siemens Germany), including a pressure vessel with washing solution, Venturi washing devices located inside the pressure vessel in the volume of the washing solution, droplet separators and fiber filters, while the vents of the Venturi washing devices are located above the level of the washing solution in the zone of the greatest mountains isontal section of the pressure vessel, and overhead vents of the venturi washing devices are fitted with drop plates for droplet separation, and metal fiber filters are located above the surface of the washing solution, each of which consists of three layers, and the thickness of the fibers in the outer layers of each filter is from 8 up to 20 microns, in the inner layer from 8 to 7 microns, and the thickness of each layer of filters is 10-20 mm.

In accordance with the dependent claims of the invention under consideration, it can be improved, namely:

- in the high-pressure tank with the washing solution there are placed two differently inclined pipes relative to the horizontal, on which Venturi washing devices are located at right angles, having different lengths and ending in the same horizontal plane;

- Venturi washing devices in the volume of the washing solution may have two inlet zones located at a distance from one another in the direction of the gas-vapor mixture, and the distance between the zones is not less than twice the neck width of the Venturi washing device;

-filters made of metal fibers are combined with each other in pairs. In an accident involving melting of a nuclear reactor zone, in

the protective shell rises pressure to a dangerous value, and the device for cleaning the vapor-gas mixture emerging from the protective shell is automatically connected to the shell and the ventilation pipe. The vapor-gas mixture flows through its inlet into the tank and, under the influence of the pressure difference at the inlet (pressure in the containment) and the outlet (atmospheric pressure) from the device, passes through the Venturi washing devices. In them there is an effective capture of aerosols and volatile fission products by dispersed washing liquid, which is sucked through nozzles into washing devices. The resulting vapor-liquid mixture leaves their Venturi washing devices and passes through the washing liquid in the high-pressure tank, where it is also cleaned

from aerosols and volatile fission products. Then, when the vapor-gas mixture passes through metal-fiber filters, aerosols that are not trapped in the washing liquid of the high-pressure tank, as well as aerosols generated by the bursting of air bubbles on the surface of the liquid, and droplets of liquid trapped in the gas-vapor mixture when leaving the washing liquid in the tank are captured.

This device, operating in the sliding pressure mode, showed good results in capturing aerosols and iodine.

However, it should be noted that some structural disadvantages of the known device do not allow the most efficient implementation of the cleaning process coming from the protective shell of the vapor-gas mixture.

Thus, the openings made in the side wall of the Venturi washing devices limit the flow rate of the injected washing solution from the tank, and therefore limit the ratio of the combined gas mixture of the washing solution to the decreasing solution. This does not contribute to a more intensive transfer of aerosols and volatile forms of iodine from a gaseous medium to a liquid one.

The proof of the existence of such a problem is that in the device according to the USSR patent No. 1718740 it was necessary to increase the number of holes - the Venturi washing devices have two inlet zones located at a distance from the other in the direction of the vapor-gas mixture (meaning holes in the side wall of the Venturi washing device).

The operation of making holes is laborious and expensive.

In addition, filters made of metal fibers having a micron lateral size located above the washing solution are subjected to corrosion damage by the fumes of the washing solution during the entire period of operation (30-50 years) in a trouble-free mode.

Therefore, in the event of an accident, a known filter cannot, due to the above-mentioned shortcomings, provide the necessary degree of purification of the gas-vapor mixture before being discharged into the environment, and it is necessary to provide for additional purification.

The closest to the claimed and adopted as a prototype is a device for the capture of fission products developed by Sulzer, Switzerland, used for ventilation of containment (see the collection of reports Improvement of the system for capturing products in accidents at WWER NPPs, Project: R 2.08 / 95. Results Projects Edition: Siemens Power Generation sponsored by

EUROPEAN COMISSION, namely task 2. Assessment of the state of affairs with the development of capture systems for fission products in the West, p. 14, 15, FIG. eleven).

The device, or the filter according to the text of the report, includes a high-pressure tank (vessel - in the Report) with washing solution, jet-type mixing devices (a set of Venturi nozzles - in the Report) located inside the high-pressure tank in the volume of the washing solution and above them gas and gas distribution devices mixtures (Sulzer mixing elements located in two layers in the middle of the tank along its section - in the Report), droplet separators (other layers of mixing elements located in the upper part of the body separate water droplets from yhodyaschego gas-vapor stream - the Report) located above the level of the cleaning solution, and inlet and outlet fittings to be cleaned gas-vapor mixture. The nozzles are surrounded by diffusion plates located above the nozzle exits to destroy the water jet and convert the flow into a rapidly moving foam. At the same time, aerosols from the vapor-gas mixture are captured by the washing solution.

The vapor-gas mixture, having converted into nozzles into the vapor-liquid mixture, moves upward and enters the Sulzer mixing elements immersed in the washing solution. Sulzer's mixing elements with open, self-intersecting flow channels scatter gases that carry aerosols in the liquid. The separating forces arising in the mixing elements break the gas stream into small bubbles, as a result of which the phase boundary is continuously renewed by the combination of bubbles and the formation of new bubbles. And since energy dispersion also takes place in the stream jet in the mixing element, the stream of bubbles and the mass transfer surface are preserved. Increased fluid turbulence increases mass transfer.

The advantage of the constructive implementation of the considered means of production is that it is equipped with a larger than the analogue described above, the number of steps for cleaning gas-vapor and vapor-liquid mixtures from radioactive substances, which ensures high efficiency of the device. But at the same time, the constructive implementation of the steps leads to shortcomings in the operation of the device as a whole. The implementation in the side wall of each Venturi nozzle of the inlet channels for the suction of the washing solution inside the nozzle limit the flow rate of the injected washing solution, thereby limiting the ratio of the gas-vapor mixture and the washing solution interacting to the side

lowering the latter. This, in turn, reduces the intensity of the transfer of aerosols and volatile forms of iodine from a gaseous medium to a liquid one.

Droplet separators made of corrugated sheet steel (mixing elements located above the level of the washing solution in the middle of the tank and in the upper part of it) are subject to destruction under conditions of constant evaporation of the washing solution. Therefore, in the event of an accident, the known filter will not be able to provide the necessary degree of purification of gas-vapor and vapor-liquid mixtures before being discharged into the environment.

The authors of this application have created such a device that eliminates the disadvantages of the objects of the same purpose known from the prior art and described above.

The inventive utility model is a device for cleaning flows of gas-vapor mixtures formed during the discharge of excess pressure from under the protective shells of nuclear power plants, as well as the prototype, contains a high pressure tank with a washing solution, jet devices are located inside the high pressure tank in the volume of the washing solution and above them are devices for distributing the vapor-liquid mixture, droplet separators placed in the tank above the level of the washing solution, and fittings for the input and output of the cleaned streams gas-vapor mixtures.

The inventive device differs from the prototype in that the jet-type mixing devices are made in the form of ejectors, and the filter elements of the droplet separator installed in front of the outlet fitting of the cleaned flows of vapor-gas mixtures are made of fiberglass.

In accordance with dependent clause 2 of the utility model formula, the device also differs in that check valves are installed in the inlet openings of the ejector nozzles, and dependent clause 3 of the utility model formula provides for supplying the outlet openings of the ejector nozzles with locking devices.

Improving the design of the device in accordance with the formula of the utility model, and especially with the features of the distinctive part of the formula, implies the achievement of the following advantages over the prototype:

1. The use of ejectors, not Venturi nozzles, will significantly change the ratio of the detergent and steam-gas mixture entering into the interaction towards an increase in the detergent solution. This will lead to a more intensive transfer of the mass (aerosols, iodine) from the vapor-gas mixture to the washing solution;

2. The implementation of the filter elements of the droplet separator from fiberglass eliminates their corrosion, while the likelihood of corrosion destruction of metal fibers is high. This probability

due to the micron size of the fiber across. However, on the other hand, such a minimum size of metal fiber is necessary to achieve a given degree of purification of the vapor-gas mixture from the smallest particles of aerosols and drops of washing solution.

The experimental tests of the claimed utility model carried out by the authors revealed that iodine sorption occurs on the fiberglass filter elements, which increases the purification coefficient of gas-vapor mixtures.

It should be noted that metal fiber is much more expensive compared to fiberglass; moreover, metal fiber is not produced in Russia.

3. Installing check valves in the inlet openings of the nozzles of the ejectors and supplying the outlet openings of the nozzles with shut-off devices prevent filling in the standby mode of the bottom cavity of the high pressure tank and the inlet of the vapor-gas mixture. Due to this, hydraulic shocks that occur during the initial period of operation of the cleaning device are excluded, when, in the absence of check valves and shut-off devices, the cold washing solution located in the inlet of the gas-vapor mixture and in the bottom cavity of the tank contacts the gas-vapor mixture having the maximum flow rate, temperature and pressure.

Hydraulic shocks can also occur with significant fluctuations, either in the direction of decreasing or increasing the consumption of the vapor-gas mixture supplied during the emergency release from the containment. Check valves, adjusting the flow rate of a gas-vapor mixture, eliminate this negative phenomenon.

The absence of vibrations of the cleaning device accompanying hydraulic shocks ensures stable operation, its strength and stability.

The inventive utility model meets all criteria of patentability.

She is new because at the moment, the applicant has not identified any known solutions from the prior art characterized by the same set of features.

The utility model is industrially applicable since it is characterized by specific design features, each of which is reproducible and does not contradict the use of the claimed device in an industrial environment. Moreover, the entire set of features and each feature individually are aimed at achieving the expected technical result - highly efficient cleaning of gas-vapor mixtures formed in the protective shells of nuclear reactors in an accident at nuclear power plants from radioactive aerosols and volatile forms

radioactive iodine while ensuring reliable operation of the device design and its component parts.

To confirm the above, we present a description of the design of the device and its operation.

The utility model is illustrated by drawings. In FIG. 1 shows a General view of the device for cleaning in section; in FIG. 2 and 3 - the design of the ejector nozzle in p. 2 and 3 formulas of a utility model.

The device comprises a high pressure tank 1 with a washing solution 2 filling the tank 1 to level A. Inside the high pressure tank 1 in the volume of the washing solution 2 there are jet-type mixing devices 3. Above the devices 3 also in the volume of the washing solution 2 are devices 4 for distributing the gas-vapor mixture over the cross section of the tank 1, made of corrugated stainless steel mesh. Above level A of the washing solution 2, droplet separators 5 and 6 are placed in the pressure vessel 1.

At the bottom 7 and cover 8, respectively, a fitting 9 of the input of the gas-vapor mixture and a fitting 10 of the exit of the gas-vapor mixture are installed.

The mixing devices 3 of the jet type are made in the form of ejectors, in each of which between the nozzle 11 and the mixing chamber 12 there is an annular gap 13 for injecting the washing solution 2 from the tank 1 into the mixing chamber 12.

The droplet separator 5 is made of corrugated mesh, and the filter elements 14 of the droplet separator 6 installed in front of the fitting Ш are made of fiberglass.

A check valve 15 made in the form of a ball or piston can be installed in the inlet of the nozzle 11 of each ejector, and the outlet of the nozzle 11 of each ejector can be equipped with a shut-off device 16, for example, in the form of a membrane.

The purification of steam-gas mixture flows when excess pressure is released from protective shells in the event of an accident at a nuclear power plant will occur as follows.

Notes of gas-vapor mixtures enter the device for cleaning from the protective shell through the nozzle 9 with the same thermodynamic parameters as the conditions in the protective shell.

The vapor-gas mixture enters the nozzles 11 of the ejectors 3, where the reduced pressure arising due to the accelerated movement of the vapor-gas mixture inside the nozzles 11 is used to suction the washing solution 3 into the high-speed medium inside the ejector 3 through the annular gap 13.

1 / ss // /:, 7

The suction solution 2 forms a droplet mist that traps aerosols and volatile iodine.

Gas and drops of solution 2, leaving the ejectors 3, fall into the washing solution 2 in the tank 1. When passing through the layers of solution 2 upwards, most of these drops are captured by it, therefore, small aerosols remain in solution 2, however, a certain amount of drops are released from the solution at bursting gas bubbles on its surface. The size of the droplets is very small, so the capture of submicron aerosols and volatile iodine trapped in the droplets is carried out at two stages of cleaning located above the level of the washing solution: first on a droplet eliminator 5 from a corrugated mesh, and then on a droplet eliminator 6 with filtering elements 14 made of ultrafine fiberglass, which able to capture not only aerosols, but also volatile iodine.

After passing through the drip trap 6, the vapor-gas mixture purified by 99.99% from radioactive aerosols and by 99.9% from all forms of iodine is released into the atmosphere.

When installing check valves 15 in the inlets of the nozzles 11 of the ejectors and supplying shut-off devices 16 to the outlets of the nozzles 11, the initial period of operation of the cleaning device can be characterized as follows.

The flows of the gas-vapor mixture, coming through the nozzle 9 into the ejector 3, raise the check valves 15, then break the membrane 16 and enter the washing solution 2 in the tank 1. And then the process is carried out as described above.

As soon as the consumption of gas-vapor mixtures is significantly reduced, the check valves 15 are lowered, closing the inlet openings of the nozzles 11, preventing the failure of the washing solution 2 from the tank 1 into the bottom cavity of the tank 1, and therefore, hydraulic shocks and vibrations. The cleaning device is in stable mode.

Claims (3)

1. A device for cleaning flows of vapor-gas mixtures generated during the discharge of excess pressure from under the protective shells of nuclear power plants, containing a pressure tank with a washing solution, jet-type mixing devices located inside the pressure tank in the volume of the washing solution and devices for distributing the gas-vapor mixture above them mixtures over the cross section of the tank, droplet separators placed in the tank above the level of the washing solution, and fittings for the inlet and outlet of the cleaned flows of gas-vapor mixtures, tlichayuscheesya in that the jet-type mixing devices are in the form of ejectors, and the filter elements droplet separator installed before fitting erasable output streams of steam and gas mixes are made of fiberglass.  2. The device according to claim 1, characterized in that check valves are installed in the inlets of the nozzles of the ejectors. 3. The device according to claims 1 and 2, characterized in that the outlet openings of the nozzles of the ejectors are equipped with locking devices.