JPS63187194A - Nuclear reactor pressure controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a reactor pressure control device for a boiling water nuclear reactor (hereinafter referred to as BWR), and particularly relates to a reactor pressure control system for subcooling reactor water. The present invention relates to a nuclear reactor pressure control system that can prevent saturation boiling (hereinafter referred to as flushing) of reactor water or cavitation of a coolant recirculation pump or jet pump when the pressure decreases.

(Prior Art) In a BWR, the reactor pressure is controlled to a constant level by a pressure control device, and the reactor water level within the reactor is controlled to be constant by a water supply control system.

Therefore, under normal operating conditions, near the recirculation pump and near the jet pump, the temperature of the reactor water is sufficiently lower than the saturation temperature for the reactor pressure, that is, the subcooling is sufficiently large, and the design is such that flashing or pump cavitation does not occur. It has become.

Here, conditions for occurrence of flashing or cavitation and conditions for preventing these will be explained.

In general, the required NPSH (NPSH-NetPosit
ive 5uction Head) is given by the pump speed (n) and the pump flow In (q).
, q). On the other hand, the effective NPSH is expressed by how high the pump inlet pressure (P i n ) is relative to the saturation pressure (Psat) for the temperature of the inlet fluid. That is, the required NPSH and effective NPSH are shown as follows.

Required NPSH-F (n, q) - (1) Effective NPS
H=P i n - Ps a t (2) Generally, cavitation occurs when the required NPSH becomes larger than the available NPSH. In order to prevent this, the required NPSH may be made sufficiently small, or the effective NPSH may be made sufficiently large. Reducing the required NPSH requires changing the structure and characteristics of the pump itself.
It is difficult to change the pumps that are already installed.

Therefore, this is assumed to be unchanged, and any changes to it will not be considered. On the other hand, increasing the effective NPSH means
This is possible without changing the pump. That is, from the first and second equations described above, it can be seen that the pump inlet pressure (P in ) may be increased or the saturation pressure (Psat) of the pump inlet fluid may be reduced.

This means that cooler coolant is allowed to flow through the pump.

Flashing occurs when the effective NPSI becomes less than 0, i.e., when Pin becomes less than Psat,
The pump artificial fluid has already become two-phase and has bubbles. This phenomenon is not unique to pumps, but is similar to general reduced pressure boiling. In order to prevent flushing, the pump artificial pressure (P in ) can be made sufficiently high or Psat can be lowered, that is, the pump artificial fluid can be cooled. In normal BWR reactor operation, such preventive conditions are incorporated into the design, and cavitation or flashing does not occur.

Next is the conventional BWR1! Briefly explain what defense measures nuclear reactors have against cavitation or flashing. Generally, logic is provided to measure the temperature of the pump fluid and the reactor saturation pressure and run back the recirculation pump if subcooling becomes too small due to the difference between the pump fluid temperature and the reactor saturation pressure being below a certain value.

Logic is also provided to cause the recirculation pump to run back when the water supply flow rate falls below a certain value.

(Inventiveness! The problem you are trying to solve) This preventive measure against cavitation or flashing is to reduce the necessary NP by reducing the pump speed or flow rate.
The purpose is to reduce SH and prevent cavitation. However, it is not effective when the subcooling is significantly reduced, that is, when the effective NFS)1 is significantly reduced.

Under normal operating conditions, water that has been sufficiently cooled by the water supply system is injected into the reactor water, so the fluid to the cooling shrine recirculation pump has a sufficient degree of subcooling, and the saturation pressure (Psat) is also low enough. However, when the water supply to the reactor decreases due to a transient change such as a failure of the water supply control system, the subcooling degree of the fluid to the coolant recirculation pump decreases, and the corresponding saturation pressure (Psat) increases.

Therefore, the effective NPSH decreases, and cavitation or flashing may occur.

Logic is provided to close the main steam isolation valve at the reactor main steam pressure, but this does not work well in the case of transient events such as cavitation or flashing.

The present invention was developed in view of these points, and even in situations where the reactor pressure decreases or the water supply control system malfunctions, the equipment in the reactor can be maintained by preventing cavitation or flashing. It is an object of the present invention to provide a reactor pressure control device that can prevent exposure to two-phase flow and ensure good flow characteristics of reactor coolant.

[Structure of the invention]

(Means for Solving the Problems) The present invention provides a main steam isolation valve and a steam control valve installed in the main steam piping, and controls the reactor pressure to a predetermined set value by adjusting the steam control valve. the first pressure control device, the water supply flowmeter installed in the water supply piping that leads the water supply from the condenser to the reactor pressure vessel, the reactor water level gauge installed in the reactor pressure vessel, and the reactor water level gauge. When the reactor water level signal and the feed water flow rate signal from the feed water flow meter reach a predetermined set value at the same time, the second pressure controller changes the pressure set value of the first pressure control device and outputs a signal to close the main steam isolation valve. It is characterized by being equipped with a pressure control device.

(Function) According to the present invention, when a malfunction occurs in the water supply control system and the supply of water decreases, when the reactor water level and the water supply flow rate reach certain set values as determined by the reactor water level meter and the water supply flow meter. , detects and predicts a drop in reactor coolant subcooling, increases the reactor pressure by increasing the reactor pressure set point and closing the main steam isolation valve, and increases reactor coolant subcooling. to prevent cavitation or flashing.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a system schematic diagram showing an embodiment of the present invention.

In FIG. 1, a reactor water level gauge 16 is installed in the reactor pressure vessel 1 to detect the reactor water level within the reactor pressure vessel 1. As shown in FIG. Further, the reactor pressure vessel 11 is connected to the main steam pipe 2, and the downstream side thereof is connected to the turbine 5. A main steam isolation valve 3 and a steam control valve 4 are installed in the main steam pipe 2.

This steam control valve 4 is configured to be adjusted by a first pressure control device 9 that controls the reactor pressure at a constant level. A generator 6 is installed adjacent to the turbine 5, and a condenser 7 is installed below it. A water supply pipe 15 is connected to the condenser 7, and a water supply pump 8 is connected to the water supply plumber 5.
and a water supply flow meter 17 are installed.

The reactor water level signal 12 from the reactor water level gauge 16 and the water supply flow rate signal 11 from the water supply flow meter 17 are transmitted to the second pressure control device 10.
has been entered. When the reactor water level signal 12 reaches a certain set value and the feed water flow rate signal 11 reaches a certain set value, the main steam isolation valve closing signal 13J and the pressure control set value are changed from the second pressure control device 10. It is configured to output a pressure set point change signal 14.

The operation of this embodiment having such a configuration will be explained. Steam generated in the reactor pressure vessel 1 is guided by a main steam pipe 2, passes through a main steam isolation valve 3 and a steam control valve 4, and reaches a turbine 5, which rotates the turbine 5 and generates electricity by a generator 6. The steam that has rotated the turbine 5 is cooled and condensed in a condenser 7, and is again supplied to the reactor pressure vessel 1 via a water supply pipe 15 by a water supply pump 8. At this time, the opening degree of the steam control valve 4 is adjusted by the first pressure control device 9,
The reactor pressure and main steam pressure are controlled to certain values. Further, the reactor water level is constantly measured by the reactor water level gauge 16, and the flow rate of the feed water is constantly measured by the feed water flow meter 17.

If a problem occurs in the water supply control system, the water supply flow rate will decrease, and the reactor water level will also decrease. This water supply flow rate signal 11
and the reactor water level signal 12 are manually input to the second pressure control device 10. The reactor water level reaches the “reactor water level low” set value,
When the water supply flow rate reaches the set value of the "water supply flow rate sheet", the second pressure control device 10 outputs a pressure set point change signal 14 that increases the set value of the first pressure control device 9. Furthermore, when the reactor water level decreases and reaches the set value of "Reactor water level low" and the feed water flow rate reaches the set value of "Feed water flow rate", the second pressure control device 10 sends the main steam isolation valve 3 A main steam isolation valve closing signal 13 is output to close the main steam isolation valve. The setting value for "Reactor water level low" is "Level 3" which has been used in conventional BWR type reactors, and "Reactor water level low paper" is "Level 2".
” can be used. The setting value of the “feed water flow rate paper” can be determined individually, as the response to loss of feed water flow rate differs depending on each reactor, or it can be set to 20% or less of the rated feed water flow rate. Good too.

FIG. 2 is a diagram showing the response change in reactor pressure when the feed water flow rate is completely lost. In the figure, the solid line represents the reactor pressure response change in the conventional nuclear reactor, and the dotted line represents the reactor pressure response change according to this embodiment. According to this, when the feed water flow rate decreases due to a malfunction in the feed water control system, in contrast to conventional reactors where the reactor pressure decreases at the same time, according to this embodiment, the reactor pressure set value is increased. In addition, the main steam isolation valve is closed, so
Reactor pressure is rising.

FIG. 3 is a diagram showing the response change of the effective NFSH when the water supply flow rate is completely lost. In the figure, the solid line represents the response change of effective NFSH in the conventional nuclear reactor, and the dotted line represents the response change of effective NFSH according to this embodiment.

In the figure, the effective NPSH drops considerably in the conventional reactor, but in this example, it is maintained sufficiently high because the reactor pressure set value is increased and the main steam isolation valve is closed. . Therefore, even if the subcooling degree decreases due to a malfunction in the water supply control system, flashing and cavitation will not occur.

Although an example has been shown in which the two means of increasing the pressure set point and the main steam isolation valve are used simultaneously, these means may be operated individually. Similar effects can be obtained in this case as well.

〔Effect of the invention〕

As described above, according to the present invention, even in a transient event where the feed water flow rate decreases and the subcooling degree decreases due to a malfunction in the feed water control system, a decrease in reactor pressure is prevented and the N
P S H' can be maintained high. Therefore, even in such a situation, flashing and cavitation can be prevented from occurring, so the integrity of the reactor equipment is ensured and the circulation of coolant to the reactor core is not inhibited.

[Brief explanation of the drawing]

Fig. 1 is a system schematic diagram showing an embodiment of the present invention, Fig. 2 is a diagram comparing response changes in reactor pressure according to an embodiment of the present invention with conventional technology, and Fig. 3 is a diagram according to an embodiment of the present invention. Effective NP
It is a diagram comparing response changes of SI with conventional technology. 1... Reactor pressure vessel, 2... Main steam piping, 3...
- Main steam isolation valve, 4... Steam control valve, 5... Turbine, 9... First pressure control device, 10... Second pressure control device, 11... Water supply? IXtm signal, 12... Reactor water level detection signal, 13... Main steam isolation valve closing signal,
14...Pressure set point change signal, 15...Water supply piping,
16... Reactor water level gauge, 17... Water supply flow meter. Applicant's agent Mr. Sato (Assistant figure 2) Figure 3

Claims (1)

[Claims] A main steam isolation valve and a steam control valve installed in the main steam piping, a first pressure control device that adjusts the steam control valve to control the pressure of the reactor to a predetermined set value, and a first pressure control device that controls the reactor pressure to a predetermined set value, and supplies water from the condenser. A water supply flow meter installed in the water supply piping leading to the reactor pressure vessel, a reactor water level gauge attached to the reactor pressure vessel, a reactor water level signal from the reactor water level meter, and detection of the water supply flow rate by the water supply flow meter. changing the pressure setting value of the first pressure control device when the signal reaches a predetermined setting value at the same time;
A nuclear reactor pressure control device comprising: a second pressure control device that outputs a signal to close the main steam isolation valve.