RU2408096C1 - Cleaning device of emergency discharge of radioactive steam-gas mixture from nps protective cover - Google Patents

Abstract

FIELD: power industry. ^ SUBSTANCE: invention can be used in depressurization systems from protective cover at accident beyond the design basis with full loss of power at NPS to prevent radioactive contamination of the environment. Cleaning device of emergency discharge of radioactive steam-gas mixture of NPS protective cover includes ejector, heat exchangers, sorption module and ventilation duct. Ejector is installed between electric fan and ventilation duct. At that, ejecting gas nozzle is connected to gas holder or other capacity with compressed gas or air, and outlet nozzle is connected to ventilation duct. Ejecting gas nozzle is connected to the outlet of electric fan the inlet of which is connected to branching: one branch is connected to active filtration system of radioactive steam-gas mixture from NPS protective cover, and the other one - to sorption module. ^ EFFECT: invention is aimed at maintaining the negative pressure in protective cover even at full loss of power at NPS irrespective of parametres of evacuated radioactive steam-gas medium, and technical characteristics of the cleaning system. ^ 1 cl, 1 dwg

Description

The invention relates to the field of nuclear energy, namely to localizing safety systems, and can be used in pressure relief systems from the protective shell of nuclear power plants during a beyond design basis accident with a complete loss of power supply to nuclear power plants of the first and second generations to prevent radioactive contamination of the environment as a result of leakages of combined cycle gas mixtures through leaks in the containment.

The problem of reliable environmental protection at nuclear power plants is one of the important factors restraining the development of nuclear energy. In the existing energy blocks of the first and second generation NPPs, devices are widely used to prevent environmental pollution and the localization of radioactive products, consisting of a protective shell over the power unit and an active ventilation system of the subshell space [Margulova T.Kh. Nuclear power plants. M .: Higher school, 1978. p.324] [1].

The protective shell is a localizing barrier for the bulk of the radioactive substances entering the gas phase during normal operation of the first and second generation nuclear power plants, while together with the active ventilation system and filters it ensures the limitation of the spread of radioactive substances with leaks (leaks), i.e. with some of the substances leaked from the containment into the environment. With the help of powerful electric fans in the protective shell, a vacuum is created in relation to the pressure in the atmosphere. In this case, the evacuated radioactive gas-vapor mixture is sent to the environment through the combined filter units [Komyshny V.N., Yagodkin I.V., Martynov P.N. et al. Abstracts of reports. Int. scientific and practical conf. "Aerosols and safety", October 24-28, 2005. Obninsk, Russia. P.218-219] [2] or special filters containing aerosol and sorption modules [Design of Off-Gas and Air Cleaning Systems at NPP. IAEA Technical Reports Series N 274 / Vienna: IAEA, 1987] [3]. The vacuum prevents leakage through leaks in the containment into the environment. In all the systems described above, sorbents based on impregnated activated carbon are used to localize the volatile compounds of radioactive iodine [Ustinov OA, Sukhanov L.P., Yakunin S.A., Rastunov L.N. Ross chemical Journal. 2005. V. 49, No. 4. S.54-60] [4]. The main disadvantage of these devices is that they require a constant supply of electricity. In the event of a failure of the ventilation system, for example, in an accident with the loss of all power sources at first and second generation nuclear power plants, reliable localization and cleaning of leaks is not provided, because overpressure occurs in the containment, and leaks through leaks enter the environment. In addition, the filters used have high aerodynamic drag and, in the absence of electricity, the radioactive vapor-gas mixture from the containment is not capable of passive operation, i.e. without application of external influence, pass through these filters.

In a beyond design basis accident involving partial or complete destruction of the reactor core, as a result of the formation of a large number of gaseous products, a sharp increase in pressure under the containment occurs. At the same time, there is a threat not only of the destruction of the sealed containment, but also the contamination of the territories adjacent to the nuclear power plant due to leaks of the radioactive vapor-gas mixture due to leakage of the containment.

To manage beyond design basis accidents at first-generation Russian nuclear power plants, a pressure relief is provided from under the containment due to the operation of the jet vortex condenser or special relief valves. In this case, the radioactive vapor-gas mixture formed as a result of the evaporation of the primary coolant enters the environment without purification in a passive mode. Subsequently, using powerful electric fans in the containment, a vacuum is created in relation to the pressure in the atmosphere, while the evacuated radioactive vapor-gas mixture is sent to special emergency filters [Kulyukhin S.A., Mikheev N.B., Falkovskii L.N. et al. Proc. Intern. Conf. "Jahrestagung Kerntechnik′09", May 12-14, 2009, Dresden, Germany. CD-ROM] [5]. The main disadvantage of this system is that its operation requires a constant supply of electricity. In conditions of loss of power supply, this system will not be able to work.

In a second-generation nuclear power plant with one containment during a beyond design basis accident, pressure release from under the containment occurs due to the operation of special emergency membranes or valves, while the passive or active radioactive gas mixture is cleaned in a special filtering device system ["Particulate Filtration in Nuclear Facilities. " IAEA Technical Reports Series N 325. Vienna: IAEA, 1991. P. 41-73] [6]. In most devices, Venturi scrubbers or multiscrubbers containing Venturi nozzles are used as the first stage to clean the vapor-gas stream from radioactive aerosols and inorganic forms of radioactive iodine. The effectiveness of their work is directly dependent on the speed of the stream passing through them. The higher the gas flow rate, the higher the efficiency of cleaning the gas mixture from radioactive aerosols. To remove volatile compounds of radioactive iodine, various sorption modules based on granular sorbents are used as the second stage. These filters have a high aerodynamic drag and are able to work only at high gas flow pressures. With a decrease in the pressure of the gas stream exiting in a passive mode from under the protective shell, firstly, the efficiency of the scrubbers decreases, and secondly, the passage of the vapor-gas mixture through the sorption modules practically stops. All this leads to the appearance of unorganized leaks of the radioactive vapor-gas mixture from under the protective envelope into the environment.

Closest to the claimed technical solution is a device for cleaning the emergency discharge of a radioactive gas mixture containing a prefilter, a regenerative heat exchanger, an ejector connected to the protective shell and other closed areas of the nuclear power plant, a ventilation pipe, a condensation module with a droplet separator and a sorption module based on a modified sorbent from molecular sieves [Antonov BV, Berkovich MV, Kamenskaya AN, Kornienko AG et al. "Passive device for cleaning the emergency discharge of a radioactive vapor-gas mixture in a beyond design basis accident at a nuclear power plant reactor." Utility Model Certificate No. 9658. Priority from 07.17.1998. Registered on April 16, 1999] [7].

This device operates as follows. In a beyond design basis accident involving rupture of a large diameter pipeline of the primary circuit or destruction of the reactor vessel, the pressure inside the containment increases to 0.5-0.7 MPa. In this case, the emergency valves of the pressure relief system automatically operate. A radioactive vapor-gas mixture with a temperature of 150-180 ° C and a humidity of 100% under a pressure of 0.5-0.7 MPa, having passed the pre-filter, enters the heating circuit of the sorption module. After it, the gas-vapor mixture is sent through the regenerative heat exchanger to the ejector, where it is mixed with the gas phase, which is sucked in by the ejector from various closed zones of the nuclear power plant. As a result of this, the temperature and pressure of the vapor-gas mixture decrease with the partial release of droplet moisture. After the ejector, the radioactive vapor-gas mixture enters the condensation module, where the condensation of the steam takes place with the simultaneous separation of droplet moisture on the separator. At this stage, not only the condensation of the bulk of the vapor occurs, but also the purification of the vapor-gas mixture from radioactive aerosols and inorganic forms of radioactive iodine. After the condensation module, the radioactive vapor-gas mixture is sent through the regenerative heat exchanger to the sorption module, where the vapor-gas mixture is purified from the organic forms of radioactive iodine, primarily methyl iodide.

The disadvantage of this device is that when the pressure of the gas stream exiting in the passive mode from under the protective shell decreases, firstly, the efficiency of the ejector decreases, and secondly, the passage of the vapor-gas mixture through the sorption module practically stops.

The aim of the invention is to increase the reliability of active and passive devices for cleaning the radioactive gas mixture from the containment in a beyond design basis accident with a complete loss of power supply at first and second generation NPPs by creating conditions under which the filtering process of the radioactive vapor and gas medium from the containment does not depend on parameters of the evacuated vapor-gas medium, as well as the technical characteristics of the cleaning system.

This goal is achieved by the fact that the ejector is installed between the ventilation pipe and the electric fan, while the ejection gas nozzle is connected to a gas holder or other container with compressed gas or air, the outlet nozzle is connected to the ventilation pipe, the ejected gas nozzle is connected to the outlet of the electric fan, the input of which is connected branching: one branch is associated with an active system for filtering a radioactive vapor-gas mixture from the containment at nuclear power plants, and the other with a sorption module.

The drawing shows a diagram of the proposed device for cleaning the emergency discharge of the radioactive vapor-gas mixture from the protective shell of nuclear power plants, where 1 is the protective shell, 2 is the reactor, 3 is the steam generator, 4 is the ejector, 5 is the nozzle of the ejection gas, 6 is the supply of ejected gas, 7 is ejector mixing chamber, 8 - ejector outlet nozzle, 9 - gas holder or container with compressed gas or air, 12-17 - solenoid valves on springs, 18 - active filter system filter unit, 19 - electric fan, 20 - sorption module, 21 - pipeline for supplying steam from those of the heat exchanger into the heat transfer channels of the filter of the passive filtration system, 22 - the pipeline for returning condensate to the steam generator, 23 - heat transfer channels, 24 - the pre-filter, 25 - the aerosol filter, 26 - the sorption filter, 27 - the ventilation pipe. The sorption module includes a prefilter, heat exchange channels connected to the pipelines of the heat circuit, aerosol and sorption filters.

An active filtration system implies all the standard systems for cleaning the radioactive vapor-gas mixture from the containment at first and second generation nuclear power plants, which require a constant supply of electricity to operate.

A device for cleaning the emergency discharge of a radioactive vapor-gas mixture from the protective shell of a nuclear power plant works as follows.

In normal operation of the reactor installation, the electromagnetic valves 12-14 are in the closed position, and the valves 15-17 are in the open. The heat exchange channels 23 in the sorption module 20 are in a heated state due to the steam entering them in a small amount from the steam generator 3. The heated state of the tube mass of the heat exchange channels ensures that the sorption module is in constant readiness for work after opening the electromagnetic valves 12-14 and closing the valves 15 and 16.

In the design modes of operation of the power unit, the electromagnetic valves 15-17 are open and the vacuum in the protective shell 1 is created due to the operation of the electric fan 19, and the evacuated radioactive vapor-gas mixture is cleaned on the filter block of the active filtration system 18.

During design emergency leaks of their thermal circuits of the power unit, the pressure increases in the volume of the containment shell 1, however, the active filtration system maintains a vacuum during operation due to the operation of the electric fan 19. In this case, the evacuated radioactive gas-vapor mixture is sent to the filter block of the active filtration system 18. After removing excess pressure under the containment, i.e. in the absence of the threat of excessive pressure under the containment, valves 15-17 are closed.

If during beyond design basis emergency situations associated with rupture of large diameter pipelines of the primary circuit or destruction of the reactor vessel, the active ventilation system fails due to a complete lack of power supply or because of a power outage to the electric fan 19, solenoid valves 12-14 open (automatically when completely de-energized or with the help of the operator in case of loss of power on the electric fan 19), and valves 15 and 16 are closed. The gas medium from the gas holder (or containers with compressed gas or air) 9 is sent to the ejector 4, where it is mixed with the gas phase sucked by the ejector from the protective shell through the sorption module. Because the mass of the tube of the heat transfer channels 23 of the sorption module 20 is kept in a constant heated state by connecting the heat transfer channels to the heat carrier path, the radioactive vapor-gas mixture is heated with the drip moisture contained in the mixture drained, and the entire gas mixture is overheated. Next, the evacuated radioactive vapor-gas mixture is cleaned on the sorption module 20. As a result of the ejector 4 in the protective shell 1, a constant vacuum is created with respect to atmospheric pressure. After the ejector 4, the vapor-gas mixture purified from radioactivity enters the ventilation pipe 27. By creating a vacuum in the protective shell 1, an unorganized release of the radioactive vapor-gas mixture through leaks in the protective shell 1 into the environment without purification is eliminated, i.e. pollution is prevented. After removal of excess pressure under the containment, the supply of electricity and the absence of the threat of excessive pressure under the containment, valves 12-14 and 17 are closed.

The proposed device in relation to the previously known devices of active and passive filtration systems has a new positive feature, namely, that it maintains a vacuum in the protective shell even when the nuclear power plants of the first and second generations are completely de-energized with one protective shell, regardless of the parameters of the evacuated vapor-gas medium, as well as the technical characteristics of the cleaning system.

The technical and economic effect is to increase the safety of nuclear power plants due to the prevention of accidental releases of radioactive gas and steam mixture during beyond design basis accidents at nuclear power plants of the first and second generations with one protective shell and ensuring the retention of radioactive substances in the size of the sanitary protection zone of the nuclear power plant.

Claims (1)

A device for cleaning the emergency discharge of a radioactive vapor-gas mixture from the protective shell of a nuclear power plant, containing an ejector, heat exchangers, a sorption module and a ventilation pipe, characterized in that the ejector is installed between the ventilation pipe and the electric fan, while the nozzle of the ejection gas is connected to a gas tank or other container with compressed gas or by air, the outlet nozzle is connected to the ventilation pipe, the ejected gas nozzle is connected to the outlet of the electric fan, the input of which is connected to the outlet leniyu: one branch is associated with an active filtration system radioactive gas mixture from the containment to the other NPP - a sorption module.