JPH0427896A - Emergency condenser - Google Patents

Abstract

PURPOSE:To maintain nuclear reactor pressure within an appropriate range and to facilitate lessening operators' work load, prevention of miss operation and improvement of nuclear reactor safety by providing a low regulating valve on a condensate return pipe and controlling opening degree of the value in relation to the nuclear reactor pressure. CONSTITUTION:A flow regulation valve 8 is provided and the value is controlled by a control device 10 of valve opening degree when pressure signal 9 of a nuclear reactor is fed for controlling. The control device 10 of valve opening degree generates control signal of valve opening degree 0%, under a condition of nuclear reactor pressure less than lower controlling limit value A, and generates the control signal of valve opening degree 100%, under a condition of nuclear reactor pressure higher than upper controlling limit value B. The device 10 generates the control signal demanding proportional opening degree to difference between the nuclear reactor pressure and the aforementioned lower controlling limit value A, under a condition of the reactor pressure staying between the lower controlling limit value A and the upper controlling limit value B. The control device 10 of valve opening degree controls the flow regulating valve 8 and there is no possibility that pressure in a nuclear reactor pressure vessel 1 excessively drops down even though letting steam and condensate circulate under natural convection basis.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention is designed to prevent the collapse of a nuclear reactor when reactor isolation occurs in a nuclear power plant and a normal condenser becomes unusable. It relates to an emergency condenser used to remove heat, and in particular, to an emergency condenser that can remove decay heat without excessively lowering the reactor pressure.

(Prior art) An emergency condenser is used to transfer reactor decay heat outside the containment vessel when reactor isolation occurs, such as a main steam isolation valve closure event, and the main condenser becomes unusable. It has the function of removing heat.

FIG. 4 is a schematic diagram of a conventional emergency condenser.

In this figure, a reactor core 2 is housed in a reactor pressure vessel 1-, and a gas phase region inside the reactor pressure vessel 1 is connected to a steam supply pipe 3.
It is connected to the heat exchanger tube bundle 5 in the cooling water storage tank 4 by. The heat transfer tube bundle 5 is communicated with the liquid phase region of the reactor pressure vessel 1 by a condensate return pipe 6 . Note that the condensate return pipe 6 is provided with an isolation valve 7.

The operation of the emergency condenser with the above configuration is as follows. When a reactor isolation event occurs, the reactor is scrammed. However, the generation of steam due to decay heat continues and the reactor pressure increases. When the reactor pressure reaches a certain limit, a high pressure signal is generated, which causes the isolation valve 7 to open.

The steam in the reactor pressure vessel 1 is led from the steam supply pipe 3 to the heat transfer tube bundle 5 in the cooling water storage tank 4, where it is heat removed and condensed.
The water is condensed. This condensate is returned into the reactor pressure vessel 1 via a condensate return pipe 6 and an isolation valve 7. By continuing the above series of processes, the temperature of the cooling water in the cooling water storage tank 4 is raised by the heat transferred from the heat transfer tube bundle 5, and eventually boils, and the steam generated thereby is released into the atmosphere. Vented inside.

Therefore, the installation position of the emergency condenser including the cooling water storage tank 4 is above the reactor, and the steam in the steam supply pipe 3 and the condensate return pipe 6 are connected to each other without depending on any external power. Due to the difference in density between the steam and condensate, natural circulation based on gravity generates circulation of steam and condensate, allowing decay heat to be removed.

(Problems to be Solved by the Invention) As described above, conventional emergency condensers remove decay heat through natural circulation due to gravity. Also,
Anticipating that heat removal performance would deteriorate due to contamination of heat exchanger tubes, etc., the design was designed to provide heat removal performance that exceeds the required value. Therefore, if the heat exchanger tubes are clean, excessive heat will be removed, resulting in an excessive drop in reactor pressure. Such an excessive decrease in reactor pressure is undesirable in terms of maintaining the integrity of the reactor pressure vessel.

Therefore, if there is an excessive drop in the reactor pressure vessel as described above, the operator manually closes the isolation valve 7 to reduce the amount of heat removal and prevent the excessive pressure drop. I was doing it. As described above, conventional emergency condensers sometimes require manual operation by an operator.

The present invention has been made based on the above circumstances, and is capable of coping with aging changes in heat transfer performance due to contamination of heat transfer tube bundles, etc., and without causing an excessive drop in pressure within the reactor pressure vessel. The purpose is to provide an emergency condenser that does not require manual operation.

[Structure of the Invention] (Means for Solving the Problems) The emergency condenser of the present invention includes a cooling water storage tank, a heat transfer tube bundle in the cooling water storage tank, and a reactor pressure applied to the heat transfer tube bundle. A device comprising a steam supply pipe that supplies steam in the vessel, and a condensate return pipe that returns condensate generated by condensation of steam in the heat transfer tube bundle to the reactor pressure vessel, wherein the condensate The return pipe is provided with a flow rate adjustment valve, and the opening degree of the flow rate adjustment valve is controlled by a valve opening degree control device that receives a reactor pressure signal as a control input.

(Function) In the emergency condenser of the present invention having the above configuration, the valve opening degree control device issues a control signal of the valve opening degree 0% when the reactor pressure is below the control lower limit value, and opens the valve when it is above the control upper limit value. Emit a control signal with 100% accuracy. Further, when the value is between the control lower limit value A and the control upper limit value, a control signal is issued that requests an opening proportional to the difference between the reactor pressure and the control lower limit value.

Since the opening degree of the flow rate regulating valve is controlled as described above, there is no fear that the reactor pressure will drop excessively even if the steam and condensate are circulated by natural circulation.

(Embodiment) FIG. 1, in which the same parts as in FIG. 4 are given the same reference numerals, is a schematic diagram of an embodiment of the present invention, and FIG. FIG. 3 is a diagram showing the pressure change inside the reactor pressure vessel during the operation of the above-mentioned embodiment in comparison with a case where the isolation valve is not operated by a worker in a conventional emergency condenser.

In FIG. 1, a flow rate adjustment valve 8 is provided in place of the isolation valve 7 of the previous embodiment, and this flow rate adjustment valve is controlled by a valve opening degree control device 10 which receives a reactor pressure signal 9 as a control input.

FIG. 2 shows the control characteristics of the valve opening control device 10. That is, the valve opening control device 1o issues a control signal with a valve opening of 0% when the reactor pressure is below the control lower limit value A, and issues a control signal with a valve opening of 100% when it is above the control upper limit B. Further, when the control value is between the control lower limit value A and the control upper limit value B, a control signal is issued that requests an opening proportional to the difference between the reactor pressure and the control lower limit value A.

Since the valve opening control device f10 controls the flow rate regulating valve 8 as described above, even if the steam and condensate are circulated by natural circulation, the pressure in the reactor pressure vessel 1 will not decrease excessively. That's not it. That is, according to the emergency condenser of the present invention, as shown by the solid curve C1 in FIG. held constant. On the other hand, in the conventional emergency condenser shown in FIG. 4, if the isolation valve 7 is not operated, the dashed line curve C in FIG.
As shown in 2, the reactor pressure gradually and continuously decreases after the isolation valve 7 is opened, and eventually shows an excessive decrease that is inconvenient for maintaining the integrity of the reactor pressure vessel.

C. Effects of the Invention As is clear from the above, in the emergency condenser of the present invention, a flow rate adjustment valve is provided in the condensate return pipe, and the opening degree of this valve is controlled in relation to the reactor pressure. That's what I do. Therefore, unlike conventional emergency condensers, operators do not have to manually operate isolation valves, and the M reactor pressure can be maintained within an appropriate range, reducing the burden on operators and causing errors in operation. It is possible to prevent this and improve the safety of nuclear reactors.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of one embodiment of the present invention, Fig. 2 is a diagram showing the control characteristics of the isolation valve controller in the embodiment, and Fig. 3 is the pressure inside the reactor pressure vessel during operation of the embodiment. FIG. 4 is a diagram showing changes in a conventional emergency condenser in comparison with a case where the isolation valve is not operated by a worker in a conventional emergency condenser. FIG. 4 is a schematic diagram of the conventional emergency condenser. 1...Reactor pressure vessel 2...Reactor core
3...Steam supply pipe 4...Cooling water storage tank
5 ・Heat transfer tube bundle 6... Condensate return pipe 7...
... Isolation valve 8 ... Flow rate adjustment valve 9 ... Reactor pressure signal 10 ... Valve opening control device A ...
... Control lower limit value B... Control upper limit value C, C2.
·····curve

Claims (1)

[Claims] A cooling water storage tank, a heat transfer tube bundle in the cooling water storage tank, a steam supply pipe that supplies steam in the reactor pressure vessel to the heat transfer tube bundle, and steam condensed and generated in the heat transfer tube bundle. and a condensate return pipe for returning condensate to the reactor pressure vessel, the condensate return pipe is provided with a flow rate adjustment valve, and the opening degree of the flow rate adjustment valve is controlled and inputted using a reactor pressure signal. An emergency condenser characterized by being controlled by a valve opening control device.