RU2152088C1 - System for evacuating gas from under water- moderated reactor cover - Google Patents

Abstract

FIELD: water-moderated nuclear reactors. SUBSTANCE: bypass pipeline installed in reactor unit at shutoff valve of injection piping has throttle and steam-gas mixture indicator. Injection piping and bypass pipeline sections between cover and steam space are rising up without water seals; entrance in bypass pipeline from injection piping is organized in vertical section of injection piping and exit from bypass pipeline, directly downstream of shutoff valve. EFFECT: improved safety of nuclear power station. 1 dwg

Description

 The invention relates to nuclear installations of the water-water type, and more particularly to gas removal systems from under the reactor cover.

 Removing the vapor-gas mixture from the upper volumes of the equipment of the reactor plants became an urgent task after the accident at Three Mile Alend NPP in 1979, which led to the revision of the program for the construction of nuclear power plants in the United States and other industrialized countries.

 A technical solution / 1 / is known, in which the reactor lid is connected to the steam cavity of the pressure compensator by a pipeline with two reinforcement units mounted on it in series.

 If necessary, the valves are opened to remove the vapor-gas mixture from under the reactor lid.

 The disadvantage of this technical solution is its complexity / the need to control six units of reinforcement / and the uncertainty of control of the valves, which entails a decrease in reliability.

It is necessary to have a sensor under the reactor cover that provides reliable information on the presence of a gas-vapor mixture under the cover. The sensor should operate at a temperature of 300 - 320 ^o C, a pressure of 12 - 16 MPa, close to the core.

 The closest analogue is / 2 /.

 The device has an injection pipe connecting the internal cavity of the reactor above the discharge pipes with the steam cavity of the pressure compensator. Shut-off valves are installed on the injection pipeline, for example a non-return valve, which opens under the influence of a differential pressure or forcibly.

 The disadvantage of this technical solution is that the check valves "stick", and to open them requires a significant pressure drop on them / 0.2 - 1 MPa /.

 Forced opening requires a reliable signal about the presence of a gas-vapor mixture in the reactor.

 The complexity of the sensor to obtain such a signal is indicated in the analysis / 1 /.

 The technical result of the invention is to increase the safety of nuclear power plants.

 The technical result is achieved by the fact that a bypass pipe is installed on the injection pipeline at the shut-off valve with a throttle device and an indicator of the gas-vapor mixture installed in the bypass pipe, while the injection pipe and the bypass pipe from the cover to the vapor cavity are lifted, without the formation of hydraulic locks, the input into the bypass pipeline from the injection pipeline is made on a vertical section of the injection pipeline, and the exit from the bypass pipeline is made directly behind hydrochloric armature.

 The gas removal system from under the cover of the reactor of the water-type reactor installation includes a reactor 1 with a housing 2, a cover 3 and an active zone 4. A pressure compensator 5 with a steam cavity 6 and a water cavity 7. The vapor cavity 6 is connected to the cover 3 with an injection pipe 8, on which shutoff valves 9 are installed, inlet pipes 10 and outlet pipes 11 connected to the steam generators 12 are connected to the housing 2. Circulating pumps 13 are installed on the supply pipes 10. The vapor cavity 6 of the compensator is pressurized I 5 is connected with a bubbler, a condenser 14, discharge line 15, on which the armature 16. In the injection duct 8 from the shutoff valve 9 is installed with a bypass pipe 17 mounted thereon throttling device 18 with the indicator gas mixture 19 in the bypass conduit 17.

 The breathing pipe 20 connects the water cavity 7 of the pressure compensator 5 with the discharge pipe 11.

 The system operates as follows.

 In the nominal operating modes, the thermal energy of the core 4 is removed by the coolant pumped by the circulation pumps 13 through the supply pipelines 10, the discharge pipelines 11. The generated heat energy is transmitted to the steam generators 12.

 Part of the coolant will flow from under the cover 3 through the injection pipe 8 and the bypass pipe 17 into the vapor space 6 of the pressure compensator 5.

 Shut-off valve 9 is closed.

 The throttle device 18 is selected in such a way that the coolant leakage from under the cover 3 in the pressure compensator 5 maintains the concentration of boric acid in the water cavity 7 of the pressure compensator 5, which is equal to the concentration of boric acid in the reactor 1, inlet 10 and outlet 11 pipelines. The decrease in pressure in the reactor installation and the associated flow of water from the pressure compensator 5 through the breathing pipe 20 will not affect the operation of the active zone 4.

 In case of violation of the nominal operating conditions in the coolant, a gas-vapor mixture may occur (for example, due to boiling of the coolant in the core 4, the occurrence of a steam-zirconium reaction, etc.).

 The vapor-gas mixture will accumulate under cover 3. This, in turn, will aggravate the malfunction of the reactor installation. In this situation, the gas-vapor mixture will go naturally but bypass pipeline 17. The gas indicator 19 will generate a signal about the presence of the gas-vapor mixture in the bypass pipeline 17. By this signal, shut-off valve 9 is opened and the gas-vapor mixture will leave from under cover 3 into the vapor cavity 6 of the pressure compensator 5.

 Unconditioned oxygen and hydrogen gases may be present in the gas-vapor mixture, therefore they are removed from the vapor cavity 6 together with the steam into a bubbler condenser 14. Oxygen and hydrogen are removed to the afterburning system (not shown in the diagram).

 When the vapor-gas mixture is removed under the cover 3, it disappears naturally and the signal about its presence in the indicator of the gas-vapor mixture 19 and the shutoff valve 9 are closed.

 When the circulation pumps 13 are stopped, the shutoff valves 9 are opened and the reactor 1, the pressure compensator 5, in conjunction with the discharge pipe 11, the breathing pipe 20, and the injection pipe 8 form communicating vessels and the overall coolant level will be set in them, which will be located in their common upper parts i.e. in the pressure compensator.

 The absence of hydraulic locks on the injection pipe 8 and the bypass pipe 17 provides the formation of communicating vessels from the reactor 1, the pressure compensator 5 when the circulation pumps 13 are stopped and the shut-off valve 9 is open.

 The entrance to the bypass pipe 17 on the vertical section of the injection pipe 8 and the exit from the bypass pipe 17 immediately behind the shut-off valve 9 ensures the heating of the injection pipe and shut-off valve 9 during operation of the reactor installation, since dead-end "blind" sections will not form on the injection pipeline 8. In the vertical section at the inlet of the injection bypass pipe 17 to the shut-off valve 9 there will be natural circulation.

 In emergency stop conditions, this is especially important.

 As the Three Mile Island accident showed, a gas-vapor bubble formed in the upper part of the reactor, which reached the upper part of the core and naturally began to collapse, and water “hung” in the pressure compensator. The staff did not know about this situation and periodically turned off the coolant recharge, i.e. the level gauge in it showed a coolant overflow in the reactor installation.

 Various level gauges are currently being developed to determine the presence of vapor-gas bubbles in the upper part of the reactor.

 The proposed invention solves this problem more simply and more reliably with a level gauge in a pressure compensator.

 It is not possible to evaluate the economic effect of the invention, because The invention is aimed at improving the safety of nuclear power plants.

Sources of information:
1. Damn. 320.000.00.00.000 G3. Reactor installation V-320, Hydraulic circuit diagram. OKB Gidropress 1992

 2. SU 1072644 A, 12.30.84 g.

Claims (1)

 The gas removal system from under the cover of the reactor of a nuclear power plant of a water-water type, including a reactor with a body, a cover and an active zone, a pressure compensator with steam and water cavities, the steam cavity of which is connected to the reactor cover with an injection pipe with shutoff valves installed on it , inlet and outlet pipelines, steam generators, circulation pumps, bubbler condenser, outlet pipe with fittings connecting the vapor cavity of the pressure compensator with bubbler condenser ohm, the breathing pipe connecting the water cavity of the pressure compensator with the discharge pipe, characterized in that the bypass pipe is installed on the injection pipe at the shut-off valve with a throttle device and an indicator of the gas mixture in the bypass pipe, while the injection pipe and the bypass pipe from the cover to the vapor cavity are made with a rise with the possibility of forming communicating vessels, the entrance to the bypass pipe from the injection pipe is made vertically th injection pipe section and the output of the bypass line is formed immediately after the shut-off valve.