RU2523436C1 - Apparatus for cleaning radioactive steam-gas mixture during accidental discharge of pressurised water reactor - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: apparatus for cleaning a radioactive steam-gas mixture during accidental discharge of a pressurised water reactor has a protective casing having safety valves, connected by a conduit pipe to series-arranged louvre separator and steam-jet ejector, located outside the protective casing. The separator is connected to an accumulator tank in the top part and to a container for collecting separated liquid in the lower part. The ejector is placed in a pond having perforated pipes around its periphery. The accumulator tank and the perforated pipes are connected by receivers. The pond is equipped with an air cooler and an exhaust hood over it. The exhaust hood is connected to a gas holding pipe which is fitted with aerosol filters. The gas holding pipe is connected by gas-relief lines to the separator and the conduit pipe. The accumulator tank and the pond are filled with an alkaline solution.

EFFECT: ensuring radiation safety and explosion safety during emergency triggering of safety valves of a pressurised water reactor owing to removal of the steam-gas mixture from the primary containment of the reactor.

4 cl, 2 dwg

Description

The invention relates to nuclear engineering, to means of ensuring explosion safety and radiation safety and can be used in the design of new generation water-cooled reactors, as well as for the modernization of existing nuclear power plants.

To ensure radiation safety at water-cooled reactors of nuclear power plants of various types (PWR, VVER, BWR, CANDU), in the event of an emergency increase in pressure in the reactor vessel and the operation of safety valves, protective hermetic shells are provided to localize the volume of radioactive vapor and gases and prevent them from entering the environment Wednesday In existing nuclear power plants with water-cooled reactors, the most widely used design scheme with two pressurized shells of prestressed concrete with a design pressure of 0.4-0.6 MPa. (Design of reactor containment systems for nuclear power plants. IAEA Safety Standards Series.

URL: http://www-pub.iaea.org/MTCD/publications/PDF/Pub1189_web.pdf pp. 89-107, No. NS-G-1.10. Vein. 2008.). The shells form the internal and external volumes of radiation protection of the reactor. In this case, the internal "primary protective shell" (PZO) localizes the gas-vapor mixture after the safety valves of the reactor, located in the internal volume of the PZO. The outer shell protects the reactor vessel from external influences and serves as a localizing volume for the discharge of the gas mixture when the safety valves PZO. From the volume between the shell housings, the gas-vapor mixture is discharged into the purification system - the system for ejecting filtered air from the annular space.

However, this design of the protective shells and the safety systems located in them does not allow for reliable prevention of the formation of explosive concentrations of hydrogen, which can lead to an explosion and, as a result, to the destruction of the shells and the release of radionuclides into the environment. This is explained by the peculiarities of the processes of purification of a gas-vapor mixture from radionuclides and hydrogen utilization, which are implemented in well-known steam localization systems after safety valves (SLPPK) at nuclear power plants.

Also known are devices for purifying a gas-vapor mixture from radioactivity with several stages of purification, where the main mass of isotopes is removed in the first stage, and the subsequent stages are the final “fine” purification. For example, in the process flow diagram of a boiling-water reactor (BWR), the discharge of radioactive vapor after the safety valves is carried out into the core pool of the core, which is the first stage of purification. In the basin located inside the PZO, with intense vapor condensation, the radioactive corrosion products are localized, and non-condensed radioactive gases (Xe, Kr) are released into the PZO atmosphere. Radioactive gases are then localized in the next stage of purification - in special filters.

As a rule, carbon-containing sorbents are used as filters that localize radioactive gases: isotopes of iodine, cesium, krypton. Other materials are also used.

A device is known in which “Thermoxide” is used as the second stage of purification of steam-gas mixture streams generated when excess pressure is released from under the protective shells of the reactor pressure vessel — inorganic spherical granular materials based on hydrated zirconium, titanium and tin oxides [RF patent No. 2197762, IPC G21F 9/02, G21C 9/004, published January 27, 2003]. "Thermoxide", localizing iodine isotopes, is not effective in purification from radioactive gases (Xe and Kr).

The multi-stage steam localization scheme after the safety valves is also used for another type of pressurized water-water reactor: a pressurized water reactor. When the pressure in the primary circuit rises, a safety valve is activated, which dumps the coolant from the steam pressure compensator into the bubbler. In the bubbler, the localization of radioactive corrosion products occurs. If the pressure in the bubbler, in turn, exceeds the permissible, then the primary circuit medium is discharged into the PZO room. The pressure reduction inside the PZO at the outlet of the coolant is carried out by spraying cooling water in a steam-air medium. Along with the function of reducing pressure, the sprinkler system provides the removal of radioactive products from the atmosphere of the PZO. To remove radioactive products from the atmosphere of the PZO, chemicals are added to the sprayed water. For example, to bind iodine in WWER reactors, a special solution with potassium borate is added. The final cleaning of gases filling the internal volume of the PZO of the reactor vessel and the annular space between the shells is carried out using aerosol filters and a filtered gas discharge system into the ventilation pipe.

A known method of suppressing the radioactivity of steam after the safety valves of a pressurized water reactor, which is implemented using a device located inside the PZO and combining several stages of localization: condensation of steam and purification of the gas mixture. In this device for cleaning the flows of gas-vapor mixtures resulting from the overpressure discharge, the high-pressure tank with a washing solution is used as the first stage of cleaning [RF patent No. 2300151, IPC G21C 9/00, G21C 15/16, G21C 15/18, published May 27, 2007]. Inside the tank are jet-type mixing devices, devices for distributing the vapor-liquid mixture over the tank section, and also fiberglass droplets.

The known designs provide for the prevention of the formation of explosive concentrations of hydrogen, which, together with radioactive gases, enter the PZO atmosphere after the safety valve of the reactor is activated [RF patent No. 179191, IPC G21C 9/04, published July 27, 1996]. Passive catalytic hydrogen recombiners based on platinum, rhodium, osmium, iridium, ruthenium, or palladium, located at the upper points of the PZO, are intended for burning hydrogen in this SLPPK design.

The disadvantage of this design, which provides for the discharge of steam after the safety valves into the volume under the protective sheath, is the high humidity of the vapor-gas mixture, which is a consequence of the actions of pressure reduction systems inside the PZO and has a significant effect on reducing the performance of catalytic recombiners and aerosol filters with carbon-containing sorbents. For example, the adsorption properties of activated carbon SKT (peat sulfate), widely used in atomic energy, almost completely disappear when it is moistened. Therefore, in order to reduce the relative humidity of the vapor – gas mixture in the activity suppression units, coal-water heat exchangers, zeolite dehumidifiers, and thermoelectric refrigerators have to be installed in front of coal adsorbers [RF patent No. 2168778, IPC G21F 9/02, G21C 9/00, published June 10, 2001]. Passive catalytic hydrogen recombiners also lose their effectiveness when wetted: saturated steam condenses in the pores of the catalyst, preventing the penetration of hydrogen to the active surface of the equipment. Therefore, to reduce the relative humidity of the gas mixture in the catalytic combustion of hydrogen before entering the contact apparatus, the gas mixture is overheated by 50 ° C or more or a low temperature catalyst is used [RF patent No. 2360734, IPC B01J 21/06, B01J 21/04, G21C 9 / 06, B82B 1/00, published July 10, 2009]. Thus, the humidity of the vapor-gas mixture significantly complicates the construction of the SLPPK, increases the likelihood of an “explosive” mixture in the upper part under the protective shell and the probability of explosive destruction of the protective shells.

The objective of the invention is to provide a device for cleaning a radioactive vapor-gas mixture during an accidental release of a water-water nuclear reactor, which takes into account to the maximum extent the disadvantages of the catalytic method of hydrogen utilization, as well as the behavior of radioactive isotopes in various media and the peculiarities of phase (water-vapor) radioactivity transfer .

The problem is achieved by using the present invention, the technical result of which is to ensure radiation safety and explosion safety in the event of emergency operation of the safety valves of the pressurized water reactor by diverting the vapor-gas mixture outside the reactor PZO.

The specified technical result is achieved by the fact that the device for cleaning the radioactive vapor-gas mixture during an emergency ejection of a water-water nuclear reactor includes a protective shell with safety valves placed in it, connected by a pipeline to a series-mounted louvre separator and a steam-jet ejector located outside the protective shell, the separator being the upper part is connected to a hydraulic reservoir equipped with receivers, and in the lower part is connected to a reservoir for collecting the separated liquid, the ejector is located in the pool, along the perimeter of which there are perforated pipes connected to the receivers, the pool is equipped with an air heat exchanger and an exhaust hood mounted above it, connected to the gas holding pipe, in which aerosol filters are placed, while the gas holding pipe is connected by blow-off lines with a separator and a pipeline, and the hydraulic tank and the pool are filled with an alkaline solution.

In a particular embodiment of the device, the hydraulic capacity is filled with a 1% alkaline solution.

In a particular embodiment of the device, the pool is filled with an alkaline solution of pH> 8.

In a particular embodiment of the device, aerosol filters are made of carbon-containing fabric.

The invention is illustrated by graphic illustrations.

Figure 1 shows a device for cleaning a radioactive vapor-gas mixture during an accidental release of a water-cooled nuclear reactor.

Figure 2 shows the connection of a device for cleaning a radioactive vapor-gas mixture during an emergency release of a water-cooled nuclear reactor to pipelines after safety valves to an existing water-cooled power reactor.

In figure 1, 2 positions indicated:

1 - reactor;

2 - protective shells;

3 - safety valves;

4 - pipeline;

5 - hydraulic capacity;

6 - receivers;

7 - separator;

8 - sealed container;

9 - steam jet ejector;

10 - pool;

11 - perforated pipes;

12 - exhaust hood;

13 - holding pipe;

14 - aerosol filters;

15 - air heat exchanger;

16 - purge lines;

17 - bubbler;

18 - sprinkler system;

19 is a system for ejecting filtered air from an annular space;

20 - heat removal system;

21 - a tank of water;

22 - a system of catalytic combustion of hydrogen at the upper points of the PZO.

A device for cleaning a radioactive vapor-gas mixture during an emergency release of a water-water nuclear reactor works as follows.

The vapor-gas mixture through the safety valves 3 of the reactor 1 is fed through a pipe 4 located outside the protective shells 2, first to the louver type separator 7. In the pipeline 4, through which the vapor-gas mixture is supplied to the separator 7, a water supply is arranged for humidifying the steam (not shown in FIG.), Since the vapor-gas mixture after the safety valve 3 becomes overheated. The need to install the louvre separator 7 is due to the presence of wave-like plates, the gas-vapor mixture sharply rotates several times, as a result of which droplets of moisture under the action of inertial forces fall on the walls and flow down, so the gas-vapor mixture is separated from the water.

In the separator 7, the radioactive corrosion products are localized in water. These radioactive substances are mainly found in suspended particles, which are carried out only with drip moisture. Isotopes ²⁴ Na, ¹⁸ F, and tritium are also retained in the condensate.

Next, the steam is humidified to absorb the radioactive ¹³¹ I. For this, 1% alkaline solution (NaOH or KOH) is squeezed out of the hydroelectric capacity 5 with compressed air supplied from the receivers 6. The alkaline solution is fed into the spray device of the inlet of the separator 7.

The separated liquid from the separator 7 is discharged into an airtight container 8. Pre-humidification of the steam and removal of the separated liquid can reduce the activity of steam.

Purified from radioactive corrosion products and partially from ¹³¹ I, ¹³⁷ Cs, the gas-vapor mixture from the separator 7 through the pipeline 4 enters the second stage of purification. This stage is the pool 10, which plays the role of a passive condenser of the vapor-gas mixture and the final cleaning of radioactive corrosion products. In pool 10, an alkaline environment (water) with a pH≥8 is maintained. Due to this, ¹³¹ I is not carried out through the evaporation mirror of pool 10 and only gaseous fission products (Xe, Kr) and hydrogen that are not dissolved in water can escape. Inside the pool 10 is a steam jet ejector 9 for condensation of the supplied vapor-gas mixture, connected to the pipeline 4.

The passive type system provides complete condensation of the vapor-gas mixture due to the use of the steam jet ejector 9 and excludes its emission through the evaporation mirror of the pool 10.

To localize radioactive gases and remove hydrogen above the pool 10, an exhaust hood 12 is installed. The exhaust hood 12 is connected to a vertical flow pipe for holding gases - a holding pipe 13.

Due to the delay of gases occur:

- decay of gamma-active short-lived isotopes, including ¹⁶ N;

- the formation of long-lived non-gaseous fission products from gaseous precursors.

The resulting isotopes in the form of coarse aerosols can be in the air for a short time and settle on the holding tube 13.

The dimensions (cross section and height) of the holding pipe 13 are chosen so that the gas holding time is at least 20 minutes - the time of almost complete decay of the longest-lived gas ¹³⁷ Xe and its transformation into a daughter isotope of the biologically dangerous ¹³⁷ Cs.

At the end of the exposure tube 13, aerosol filters 14 made of carbon-containing fabric are installed to ensure the exclusion of radioactive substances into the atmosphere. In the pool 10 there is a complete condensation of the vapor-gas mixture, both due to the volume of water and due to the operation of the passive cooling system by the air heat exchanger 15. Therefore, the aerosol filters 14 are operational even when the safety valve 3 is open for a long time.

Hydrogen leaving the surface of the pool 10 is diluted with air to prevent the formation of explosive concentrations in the holding pipe 13. For this, perforated pipes 11 are located above the water surface of the pool 10, to which air receivers 6 are connected. To eliminate the accumulation of hydrogen in the device after closing the safety valves 3 of the reactor 1 from the upper ("dead end") points of the separator 7 and pipe 4, blow-off lines 16 are provided in the holding pipe 13.

This device can be used to upgrade existing nuclear power plants with pressurized water reactors of various types (figure 2). After the safety valves 3, which discharge the vapor-gas mixture into the internal “air” volume of the PZO (in BWR reactors — into the core pool), the pipeline 4 is connected to the pipeline, which is laid through penetrations in protective (localizing) shells and connected to the cleaning device a radioactive vapor-gas mixture in the event of an emergency release of a pressurized-water nuclear reactor. In this technological scheme, a two-stage purification from radioactive corrosion products will be performed: in the pool 10 and in the separator 7.

Thus, when the safety valves 3 of the primary circuit are activated, they are excluded from work:

- sprinkler system 18 connected to a system for removing heat 20 from the PZO and to the tank with water 21;

- a system for the catalytic combustion of hydrogen 22 at the upper points of the PZO;

- a system for ejecting filtered air from the annular space 19, located between the casings of the protective shells 2.

These systems remain part of the nuclear installation and are used in normal operation and in an accident with the release of coolant into the internal volume of the PZO.

The security of this technical solution is achieved by:

- effective cleaning and use in passive systems of the properties of the phase transfer of radioactivity: corrosion products, gaseous products, aerosols, including ¹³¹ I;

- continuous removal of hydrogen into the atmosphere and exclusions from the steam localization scheme of the hydrogen burning unit.

Ensuring radiation safety and explosion safety with the help of this device is that:

- purification of the radioactive vapor-gas mixture is carried out within the reactor installation on a passive system of multi-stage localization, taking into account the features of the phase transfer of isotopes,

- the removal of the vapor-gas mixture purified from radioactivity is carried out into the atmosphere,

- hydrogen utilization is carried out by discharging it into the atmosphere without installing hydrogen burning inside the PZO.

Claims (4)

1. A device for cleaning a radioactive vapor-gas mixture during an emergency ejection of a water-water nuclear reactor, comprising a protective sheath with safety valves placed in it, connected by a pipe to sequentially installed louvre separator and a steam-jet ejector located outside the protective sheath, the separator in the upper part is connected to the hydraulic reservoir equipped with receivers, and in the lower part connected to a container for collecting the separated liquid, the ejector is located in the pool, along the perimeter of which The perforated pipes are installed, connected to the receivers, the pool is equipped with an air heat exchanger and an exhaust hood mounted above it, connected to the gas holding pipe, in which aerosol filters are placed, while the gas holding pipe is connected by blow-off lines to the separator and the pipeline, and the hydraulic tank and the pool are filled alkaline solution. 2. The device according to claim 1, characterized in that the hydraulic reservoir is filled with a 1% alkaline solution. 3. The device according to claim 1, characterized in that the pool is filled with an alkaline solution of pH> 8. 4. The device according to claim 1, characterized in that the aerosol filters are made of carbon-containing fabric.

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