KR820002393B1 - Automatic steam generator feedwater realignment system - Google Patents

Abstract

Particularly in a nuclear plant, a steam generator secondary piping system is automatically aligned in the event of a pipe break to a given one of multiple generators(28) by monitoring generator steam exit line press., comparing with setpoint, identifying any line falling below this value and closing the respective exit lines of the generators. Monitored outputs are compared with a 2nd setpoint after the lines are closed and the feedwater line(66) to a generator exhibiting a drop in press. is closed while the exit lines of generators not exhibiting a press. drop are opened.

Description

Automatic rearrangement of feed water piping of steam generator

1 is a schematic diagram of a nuclear power plant.

2 is a schematic of a typical multi-array steam generator.

3 is a schematic diagram of an auxiliary feed water system for the steam generator of FIG.

4 is a schematic circuit diagram of an apparatus for automatically rearranging the feed water system shown in FIG. 3 in the case of secondary line breaks in accordance with the present invention.

FIELD OF THE INVENTION The present invention relates generally to steam generator secondary piping systems, and more particularly to a method of automatic realignment of such piping systems for multiple steam generators.

Reactor steam generation systems typically use multiple steam generators that deliver steam to a common header and feed from a common condensate reservoir to drive one turbine. Currently, in many power plants, secondary line breaks are detected by monitoring each steam outlet pressure and feed water flow rate of the various steam generators in the system.

If a feedwater line breakdown occurs at the inlet to any steam generator, the pressure in the remaining steam generator will decrease the flow rate into the steam generators of the various steam generators in the common header, while increasing the flow through the broken line. do. Although pressure is detected in these devices, line breakage is detected by flow rate.

In such cases, corrective action is required to be carried out automatically, or the use of a flow restrictor in the feed water line. Flow limiters are undesirable because they increase the pump capacity required for normal operation. The automation of current methods used to correct breakage in feed water lines has been to use the capacitance signal as a means to manually carry out already established calibration operations. However, automated systems in response to flow signals are subject to large unnecessary reactor trips since the setpoints of flow rates have to be flexibly adjusted to adapt to changes in starting, stopping and regular power generation operations.

It is therefore an object of the present invention to provide a novel feed water rearrangement method which does not cause a trip and takes corrective action in case of secondary line breakage.

In short, the present invention provides a method for automatically rearranging a steam generator secondary piping system in the event of secondary line breakage to a steam generator in a system with multiple steam generators partially comprising a common piping system. to provide.

The method of the present invention senses the steam outlet pressure of several steam generators and compares the detected values with a predetermined first fixed point. The system operates in response to an indication that the pressure in any one steam generator has dropped below the first anchor point to close the main steam line disconnect valve of each steam generator. The steam outlet pressure is then detected again to indicate a steam generator that drops below the predetermined second fixed point to indicate secondary line breakage. The system operates in response to an indication that the second anchor point has been reached to the point of closing the feed water disconnect valve to the broken feed water line. The remaining intact steam generator can then be supplied with feed water and returned to the system.

The present invention will be described in more detail with reference to the accompanying drawings.

1 is a schematic of a typical pressurized water reactor to which the concept of the present invention is applicable. The reactor of FIG. 1 includes a vessel 10 which forms a pressurized vessel when sealed by the head assembly 12. The container has coolant introduction means 16 and coolant discharge means 14 formed therethrough and integrally formed thereon.

As is known in the art, the vessel 10 houses an atomic core configured as a plurality of nuclear fuel elements that generate a large amount of heat depending on the position of the control rod 58. The heat generated by the atomic core is transported from the core by the coolant flow which enters through the introduction means 16 and is discharged through the discharge means 14. In general, the flow discharged through the discharge means 14 is transferred to the heat exchange steam generator system 28 through the discharge conduit 26, in which the heated coolant stream is disposed in a heat exchange relationship with water. Which is roughly indicated by reference numeral 18) to generate steam.

The steam generated by the steam generator 28 is commonly used to drive the turbine 20 for power generation. The flow of coolant in the primary reactor system is conveyed by the pump 22 from the steam generator 28 to the introduction means 16 via the conduit 30. A closed refrigerant recirculation loop, i.e., a refrigerant pipe connecting the steam generator 10 and the steam generator 28, is included. Although the vessel shown in FIG. 1 is shown as having one such closed fluid flow system or loop, many such loops may be installed.

Although not shown in the loop shown in FIG. 1, one loop of each power plant operates in response to changes in the pressure of the primary system due to variations in temperature and changes in operating conditions to maintain a constant primary pressure. It includes a pressurizer.

The secondary side of the steam generator is disconnected from the primary coolant by the heat exchange tube 18. In the steam generator, the secondary fluid 34 is disposed in a heat exchange relationship with the primary coolant, so that the secondary fluid is heated to change into steam. The steam flow through the steam conduit 38, indicated by arrow 36, is for example sent to a turbine which is connected via a shaft 24 to the generator. The amount of steam discharged to the turbine is controlled by the throttle valve 20. After passing through the turbine 40, steam condenses in the condenser 20.

The condensate or condensate thus formed is passed through the conduit 50, the condensate pump 44, the feed water heater 46 and the feed water pump 48 as indicated by arrow 52, That is, return to the fuselage. The recycle secondary power generation system thus comprises a secondary fluid piping connecting the steam generator 28 to the turbine.

As mentioned previously, Figure 1 shows a simplified schematic diagram, in which two, three or four separate primary loops are connected between the reactor and the corresponding number of steam generators. For example, FIG. 2 shows a system using three loops and three corresponding steam generators. Similar parts are designated by the same numerals in other drawings. As referenced above, the primary coolant is introduced into the hot portion of each steam generator through conduit 26 and circulated through a plurality of heat exchange tubes 18. The plurality of heat exchange tubes transfer coolant to the cold portion of each steam generator 30 to be recycled through the reactor.

The water in the cylinder of the steam generator is converted into steam by heat transferred by the primary coolant circulating through the heat exchange tube 18. The steam generated by the various steam generators is transferred to the turbine for the main steam line 68 via the disconnect valve 32, the steam header 64, and the common steam line 38. On the return side of the turbine, a main feedwater source is provided to each feedwater line 66 of several steam generators via a common header and through disconnect valves 61 and chuck valves 56. Is provided. In addition, an auxiliary feed water line 60 is provided to satisfy low flow conditions such as those occurring at start up or shutdown of the power plant. The auxiliary feed water is injected into the feed water introduction line downstream of the main feed water line check valve 56.

In the preferred embodiment shown in FIGS. 3 and 4, the invention is applied to the auxiliary feed water line of the steam generation system of FIG. Two dissimilar feed water pump systems 70 and 72 are commonly used for safety.

Auxiliary feed water from each system 70 and 72 passes through a parallel flow control valve 74, which is adjusted to regulate the feed water level in each steam generator. The feed water exiting the flow control valve 74 is transferred to the feed water introduction line of the corresponding steam generator via the check valve 76 and two extra motor operated shut-off valves 78.

Referring to FIG. 2, it can be seen that the pressure in each main steam line of each steam generator is detected by the pressure sensor 54. In fact, each pressure tap 54 supplies three separate signals through the extra channels normally required for safety. The pressure signal associated with each channel is transmitted in parallel to two separate fixed point bistables, which are connected to the logic circuit shown in FIG. S ₁ and S ₂ indicate the bistable output for each loop.

According to the invention, the breakdown of the secondary line associated with any steam generator is first detected from the sensed steam outlet line pressure of each steam generator by comparing a predetermined first fixed point (ie 600 psia) with demagnetized parameters. .

Fixed point bistable is used for this purpose. If the pressure in any steam generator drops below the first fixed point, the corresponding fixed point bistable provides a suitable output S ₁ , which outputs each main steam disconnect valve 32 and each main feed water valve 61. ) (Shown in FIG. 2) to its closed position.

The sensed pressure is then compared to the second predetermined fixed point (ie 400 psia) by the fixed point bistable of the second set. If the detected pressure falls below the second fixed point indicative of failure, the steam generator corresponding to the detected pressure is detected by its corresponding fixed point bistable output S ₂ , and this fixed point bistable output is supplied to the corresponding auxiliary supply. Activate a suitable valve to disconnect the male line. At the same time, the steam outlet line to the rest of the steam generator can be opened for continued system operation at reduced power levels.

Three bistables are provided per fixed point and per loop to meet safety requirements. As described earlier, three pressure signals from the main steam line of each steam generator are transmitted in parallel to the corresponding bistable S ₁ and S ₂ . To avoid unnecessary trips, the output from the three bistable S ₁ of each loop is gated by two of the three logic elements 80.

Outputs from multiple logic devices 80 are connected to each unit of common OR gate 82.

When two of the three bistables in a loop indicate that the pressure in the loop drops below the first fixed point, the output of the OR gate 82 is the main feed water valve and the main steam line disconnect valve of each steam generator. Send signal 84 to close the mode. If the detected pressure at the steam outlet line of any one steam generator indicates that the pressure of the steam generator continues to fall below the second fixed point, the corresponding bistable provides a suitable output S2. If two of the three bistable S ₂ in any given loop indicate that the second peak is exceeded after a preselected time after the command is issued to close the main midline valve, two of the three logic elements 94 are suitable. An output is provided to the AND gate 86, the output of which closes the corresponding motor actuated valve 78 in each logical train (installed for spare) coupled with the steam generator at a pressure below the second fixed point. And via an AND gate 88 and an OR gate 92 to a suitable auxiliary feed water valve control unit. The AND gate 86 also receives an input signal from the output signal of the OR gate 82 which assures that the steam line disconnect valve is closed to prevent false auxiliary feed water valve commands.

The output of each AND gate 86 is converted to an input corresponding to an AND gate 88 coupled with another loop to prevent closure of the auxiliary feed water valve in more than one loop at a time. The OR gates 92 are each provided to alternately drop the manual adjustment of the auxiliary feed water disconnect valve in the loop, and the manual reset 96 resets the system in case of a spurious signal.

The output of the logic element 94 is connected to the AND gate 86 after a predetermined time after the main steam line valve closing command is issued to prevent the system from malfunctioning in response to a transient caused by the main steam line valve closing. It is blocked by the switch module 85 to prevent delivery.

Thus, according to the present invention, if two of the three pressure signals from a steam generator fall below the first predetermined fixed point, all main steam line disconnect valve mill feed water valves are closed. This action prevents vapor in the intact secondary loop from escaping out of the broken line.

Steam generators with broken secondary lines continue to discharge until equilibrium pressure is obtained. When this pressure falls below the second predetermined fixed point, an auxiliary feed water disconnect signal is generated to isolate the broken pipe from the common portion of the feed water system.

The system logic is to prevent the auxiliary feed water motor actuating valve from closing in the remaining intact loop.

At any time, the operator may ignore the automatic disconnection signal by the manual reset 96 and the manual adjustment unit 98. In this way the system of the present invention rearranges the feed water system in the event of secondary line breakdown in a portion of the system that is not commonly arranged among several generators to provide the continuous operation capability of the remaining undamaged steam generators. Indicating that the pressure of one or more steam generators falls below a second predetermined fixed point indicates that a pipe break has occurred in a common header for several steam generators and appropriate action is taken.

Moreover, although the previous embodiment applies the present invention to detecting feed water line breakage, it may similarly indicate the steam line breakage corresponding to the present invention.

Claims (1)

Means 54 for sensing the pressure in the steam outlet line of each steam generator and providing an electrical output indicating the sensed pressure to automatically rearrange the steam generator's secondary piping system in case of pipe breakage of the steam generator. A method for causing said method to perform the steps of: comparing a sensed output with a first predetermined fixed point and providing a second output (S ₁ ) when said sensed value falls below a first fixed point; In response to closing the steam outlet line 68 to each steam generator 28, comparing the second predetermined fixed point with the sensed output after closing the steam outlet line, from the comparison of the second fixed point, Indicating the detected value dropped below the second fixed point and the corresponding steam generator as a third electrical output (S ₂ ), and the supply water line to the steam generator whose pressure dropped below the second fixed point in response to the third electrical output ( Closing 66) Feedwater pipe automatically reordering method of the steam generator, characterized in that the steps a.

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