JPH0434708B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a temperature monitoring device for a suppression pool installed in a containment vessel of a boiling water nuclear reactor.

[Technical background of the invention and its problems]

A suppression pool installed inside the reactor containment vessel is installed to ultimately secure coolant for the reactor during abnormal transients. In order to ensure the effective NPSH of the residual heat removal system pump, which injects coolant in the suppression pool into the reactor during abnormal transients and ensures the integrity of the reactor fuel,
Suppression pool water temperature must be monitored.

In conventional plants, the temperature of the suppression pool water is monitored using temperature measuring devices scattered within the suppression pool, but the temperature is only measured in the area where the temperature measuring devices are installed, and there is a time delay due to heat conduction. As a result, there is a time difference in the measured values of each temperature measuring device, making it impossible to grasp the heat capacity of the entire suppression pool, and it cannot be said that the temperature of the suppression pool water is being monitored correctly. Furthermore, it is difficult to grasp the temperature rise rate of the suppression pool water. Furthermore, in conventional plants, when the measured temperature of the suppression pool water reaches a certain set value, an alarm is displayed and the operator activates the suppression pool cooling mode. The temperature of the suppression pool water rises, and as a result, the effective NPSH of the residual heat removal system pump cannot be ensured, resulting in a situation where the coolant in the suppression pool cannot be injected into the reactor. In particular, in order to prevent human error due to the radiation leak accident at a nuclear power plant that recently occurred in the United States, we developed a temperature monitoring device that accurately grasps the conditions inside the suppression pool and provides accurate information to operators. The need for this has been pointed out.

[Purpose of the invention]

The purpose of the present invention is to grasp the temperature and temperature rise rate of the suppression pool water during abnormal transients in order to accurately ensure the effective NPSH of the residual heat removal system pump used during abnormal transients, and to To provide a temperature monitoring device that predicts the temperature in a suppression pool of a person and activates a suppression pool cooling mode when the predicted temperature reaches a suppression pool cooling mode setting value.

[Summary of the invention]

In other words, the feature of the present invention is that the heat capacity in the suppression pool during normal operation is determined by a calculation device from the values measured by the temperature measuring device and the water level measuring device installed in the suppression pool, and the heat capacity in the suppression pool during abnormal operation is calculated using a calculation device. The temperature and temperature rise in the suppression pool are calculated from the temperature of the flow rate flowing into the suppression pool, which is measured at the same time, and the heat capacity of the flow rate flowing into the suppression pool, which is calculated by a calculation device from the inflow flow rate. By calculating this, it is possible to alert the operator with a cathode ray tube display and an alarm display before the residual heat removal system becomes obstructed in ensuring effective NPSH, and to automatically start the suppression pool cooling mode.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below with reference to the drawings. In FIG. 1, a suppression pool 1 is installed within a primary containment vessel 3 that houses a reactor pressure vessel 2. As shown in FIG. During normal operation, steam generated within the reactor pressure vessel 2 is sent through the main steam pipe 4 to a turbine (not shown). The temperature in the suppression pool 1 is measured by temperature measuring devices 5 scattered within the suppression pool 1, and the water level in the suppression pool 1 is measured by a water level measuring device 6.

During abnormal transients, the reactor is isolated by closing the main steam isolation valve 7, so the reactor pressure increases, and in this state, water supply to the reactor is stopped and the reactor water level falls. Note that the reactor water supply system is not shown. In order to prevent the cooling of the reactor core from being interrupted due to a drop in the reactor water level, the reactor isolation cooling system (hereinafter referred to as RCIC) 8, which is one of the emergency cooling systems, opens the RCIC turbine stop valve 24. to start. The suppression pool 1 is driven by main steam from the main steam pipe 4.
The exhaust gas of the RCIC turbine 9 flows in. The flow rate and temperature of the exhaust gas from the RCIC turbine 9 are measured by a flow rate sensor 10 and a temperature sensor 11 provided in the exhaust pipe.

In addition, in order to prevent damage to the reactor pressure vessel 2 due to an increase in reactor pressure, the safety relief valve 12 is opened to exhaust steam to the suppression pool 1 and reduce the reactor pressure. The flow rate and temperature of the exhaust gas from the relief safety valve 12 can be obtained by a flow rate sensor 13 and a temperature sensor 14 provided on the exhaust pipe side. When the temperature of the suppression pool water rises, the effective NPSH of the residual heat removal system pump 15 is ensured in the low-pressure water injection mode that is activated when the reactor water level drops further, making it possible to inject coolant into the reactor. In order to do this, the residual heat removal system pump 15 is started, the suppression pool water is sent to the heat exchanger 16, the suppression pool water is cooled by heat exchange with the cooling water 17, and the suppression pool water is returned to the suppression pool 1. A suppression pool cooling mode is started in which the suppression pool 1 is cooled by the inflow.
At this time, the flow rate and temperature of the coolant used to cool the suppression pool are as follows:
The temperature is measured by a flow rate sensor 18 and a temperature sensor 19 provided on the inflow pipe side.

First, the heat capacity in the suppression pool 1 during normal operation is determined as follows. During normal operation, no amount of heat flows into or out of the suppression pool 1, and the temperature of the suppression pool water is almost uniform. Therefore, from the measured value by the temperature measuring device 5, the heat capacity per unit volume of the suppression pool water is
Q ₀ can be found from the following formula.

Q ₀ =K ₀ Ct ₀ (1) where K ₀ is a conversion constant, C is specific heat, and t ₀ is a temperature measurement value. Further, the volume W ₀ of the suppression pool water is obtained based on the measurement value of the water level measuring device 6 of the suppression pool 1 and data on the shape of the suppression pool 1. As described above, by inputting the temperature and water level in the suppression pool 1, the calculation device calculates the heat capacity Q 0 and volume W 0 per unit volume of the suppression pool water, and further calculates the heat capacity Q ₀ and volume W ₀ per unit volume of the suppression pool water.
The heat capacity Q ₀ W ₀ can be found.

The fluid flowing into the suppression pool 1 during an abnormal transient is the exhaust gas of the RCI turbine 9 and the relief safety valve 12.
It is exhaust from.

The flow rate F ₁ of the exhaust gas of the RCIC turbine 9 is obtained from the measurement value of the flow rate sensor 10 . The temperature of the exhaust gas is obtained from the temperature sensor 11, and from this, the heat capacity Q ₁ per unit volume of the exhaust gas of the RCIC turbine 9 is determined.
The flow rate _F2 of the exhaust gas from the relief safety valve 12 is obtained from the flow rate sensor 13, and the temperature of the exhaust gas and the heat capacity _Q2 per unit volume of the exhaust gas from the relief safety valve 12 can be calculated from the temperature sensor 14. Therefore, the rate of increase ΔQ in the heat capacity per unit volume of the suppression pool water due to the inflow of the exhaust gas from the RCIC turbine 9 and the exhaust gas from the relief safety valve 12 is determined by the following equation.

△Q=Q ₁ F ₁ +Q ₂ F ₂ /W ₀ +W ₁ +W ₂ ...(2) Here, W ₁ and W ₂ are the exhaust gas of the RCIC turbine 9 flowing into the suppression pool 1 and the relief safety valve 12
is the volume of exhaust gas from the , and is determined by integrating F ₁ and F ₂ respectively.

Further, the heat capacity Q per unit volume of the suppression pool water at this time is Q=Q ₀ W ₀ +Q ₁ W ₁ +Q ₂ W ₂ /W ₀ +W ₁ +W ₂ (3). From the heat capacity Q per unit volume of the suppression pool water and its rate of increase △Q, use the following formula to calculate the temperature T of the suppression pool water and the rate of increase △T.
can be calculated.

T=Q/KC, △T=Q/KC...(4) However, K is a conversion constant and C is a specific heat.

The heat capacity when the suppression pool cooling mode is activated during an abnormal transient is determined as follows. If the heat exchange coefficient of the heat exchanger 16 is α _T , then the heat exchanger 1
The relationship between the amount of heat P ₁ flowing into 6 and the amount of heat P ₂ flowing out is shown by the following equation.

P ₂ =α _T P ₁ (0<α _T <1) ...(5) The flow rate of the suppression pool water sent to the heat exchanger 16 by the residual heat removal system pump 15 and the temperature after heat exchange are determined by the flow rate Sensor 18 and temperature sensor 1
9, and from this, the flow rate F ₃ of the coolant flowing into the suppression pool 1 in the suppression pool cooling mode and the heat capacity Q ₃ per unit volume are determined. Therefore, the rate of increase ΔQ' in the heat capacity per unit volume of the suppression pool water when the suppression pool cooling mode is activated is expressed by the following equation by modifying equation (2).

△Q′≡Q ₁ F ₁ +Q ₂ F ₂ −1/α _T (1−α _T )Q ₃ F ₃ /W
₀ +W ₁ +W ₂
...(6) Also, in this case, the heat capacity Q' per unit volume of the suppression pool water can be calculated by modifying equation (3) as Q'≡
Q ₀ W ₀ +Q ₁ +W ₁ +Q ₂ W ₂ -1/α _T (1-α _T )Q ₃ W ₃ /W ₀ +W ₁
+W ₂
...(7) becomes. From the heat capacity Q' per unit volume of the suppression pool water and its rate of increase △Q', the temperature T' of the suppression pool water when the suppression pool cooling mode is activated in the same way as equation (4) is calculated. The temperature increase rate △T′ can be calculated.

As mentioned above, suppression pool 1
By inputting the measured values of the inflow flow rate and temperature into the arithmetic unit 20 shown in FIG.
The temperature T and temperature rise rate △T of the suppression pool water after the inflow of the RCIC turbine exhaust and the relief safety valve exhaust are calculated and displayed on the cathode ray tube display 22 of the central control room control panel 21 to provide accurate information to operators. It can inform you of the temperature of the suppression pool water and the rate of temperature rise. In addition, when the temperature of the suppression pool water increases, calculate the temperature increase rate △T' assuming activation of the suppression pool cooling mode, and compare the current temperature increase rate △T with the following formula. .

τT+ΔT−ΔT′...(8) Here, τ is the set temperature for starting the suppression pool cooling mode. If it is determined from this comparison that the temperature rises to a preset temperature τ at which it is difficult to ensure the effective NPSH of the residual heat removal system pump 15, that is, if the inequality of equation (8) is established, the suppression pool cooling mode start automatically.

Furthermore, if the temperature continues to rise even after starting the suppression pool cooling mode, an alarm will be displayed on the alarm display device 23 of the central control room control panel 21 to alert operators to the temperature change in the suppression pool. At the same time, it can notify other suppression pools of the need to take measures to cool the water. The temperature T' of the suppression pool water after starting the suppression pool cooling mode is also calculated by the arithmetic unit and displayed on the cathode ray tube display 2 of the control panel 21.
Display on 2. This type of display allows operators to obtain extremely effective information for ensuring the health of the reactor, and by automatically starting the suppression pool cooling mode, it is possible to detect abnormalities during reactor transients by automatically starting the suppression pool cooling mode. Under certain conditions, even if an operator overlooks the system, the residual heat removal system pump remains effective.
NPSH can be secured and the integrity of the reactor fuel can be ensured when the reactor water level drops abnormally.

〔Effect of the invention〕

As described above, according to the present invention, the temperature of suppression pool water can be determined using a principle completely different from that of existing temperature measuring devices, and even if the existing temperature measuring device does not work for some reason, the temperature of the suppression pool water can be determined. The rate can be calculated and displayed, allowing operators to accurately grasp the condition of the suppression pool water.

As a result, operators can immediately take effective measures against the rise in temperature of the suppression pool water during plant transitions, and even in the event of an operator's oversight or erroneous operation, the suppression pool water temperature can be maintained. Since the reactor is healthy and the final source of cooling water is secured, operators can concentrate on other emergency operations, which has an extremely significant effect on improving the safety of nuclear power plants.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of piping and instrumentation of a nuclear power system to which the present invention is applied, and FIG. 2 is a block diagram illustrating an embodiment of the present invention. 1... Suppression pool, 2... Reactor pressure vessel, 3... Primary containment vessel, 4... Main steam pipe,
5... Temperature measuring device, 6... Water level measuring device, 7... Main steam pipe, 8... RCIC, 9... RCIC turbine, 1
0...RCIC turbine exhaust flow sensor, 11...
RCIC turbine exhaust temperature sensor, 12... Relief safety valve, 13... Relief safety valve exhaust flow rate sensor, 14
... Relief safety valve exhaust temperature sensor, 15 ... Residual heat removal system pump, 16 ... Heat exchanger, 17 ... Cooling water, 18 ... Suppression pool cooling mode flow rate sensor, 19 ... Suppression pool cooling Mode temperature sensor, 20... Calculation sensor, 21...
Central control room control panel, 22... CRT display,
23... Alarm display device, 24... RCIC turbine stop valve.

Claims (1)

[Scope of Claims] 1. Temperature measuring instruments scattered within a suppression pool installed in a reactor containment vessel, and a water level measuring instrument for measuring the water level of the suppression pool;
a first measuring device for measuring the flow rate and flow temperature of steam flowing into the suppression pool from the reactor during abnormal operation; and a first measuring device for measuring the flow rate and flow temperature of steam flowing into the suppression pool from the reactor isolation cooling system during abnormal operation. a second measuring device that measures the flow rate temperature; a third measuring device that measures the flow rate and flow rate temperature flowing into the suppression pool after activation of the suppression pool cooling mode during abnormal operation; and a suppression pool cooling mode. Before startup, the temperature and temperature increase rate in the suppression pool are determined from the heat capacity and change in heat capacity in the suppression pool by inputting the measured values from the first and second measuring devices. , calculates the predicted temperature in the suppression pool after a certain period of time based on this temperature and temperature increase rate, and when the calculated predicted temperature reaches the suppression pool cooling mode activation temperature, the suppression pool starts cooling. 1. A suppression pool temperature monitoring device comprising: a calculation device for activating a mode; and a display device for displaying calculation results obtained by the calculation device. 2. In the suppression pool temperature monitoring device according to claim 1, after starting the suppression mode, the measurement values measured by the first, second, and third measuring devices are inputted to suppress the suppression pool. It is characterized by comprising a calculation device that calculates the temperature and temperature increase rate in the suppression pool by determining the heat capacity and the change in heat capacity in the suppression pool, and a display device that displays the calculation results obtained by the calculation device. Temperature monitoring device for suppression pools.