JPH0139078B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of controlling a nuclear reactor recirculation pump, and more particularly to a method of controlling a jet pump to prevent cavitation.

In a boiling water reactor, a portion of the reactor water is taken out of the pressure vessel, raised in pressure by a recirculation pump, and returned to the pressure vessel as drive water for the jet pump. Driving water for the jet pump is ejected from the nozzle of the jet pump, and at the same time sucks in surrounding water from the jet pump throat, resulting in about three times as much reactor water as the driving water flowing out from the jet pump outlet.

The reactor water inside the reactor is subcooled from the saturated water in the upper plenum of the pressure vessel by the reactor feed water returned from the turbine system, but the amount of subcooling is not that large, so the jet pump is operated in a state where cavitation is likely to occur. ing. The effective suction head of a jet pump is determined by the pressure of the reactor water near the suction port and the saturated steam pressure, and the saturated steam pressure is determined by the enthalpy of the reactor water. Since the reactor is controlled to maintain a constant pressure, the enthalpy of the reactor water is determined by calculating the amount of subcooling of the reactor water from the coolant coming out from the reactor via the steam-water separator and the flow rate of the reactor feed water. You can monitor your head.

On the other hand, the required suction head of the jet pump is calculated from the flow rate of the jet pump. The cavitation generation area of a jet pump is the area where the effective suction head and the required suction head are equal. Therefore, the presence or absence of cavitation is determined by the process quantities necessary to evaluate the effective suction head, that is, the feed water flow rate or equivalent reactor output, the process quantities necessary to evaluate the necessary suction head, That is, it is determined by the jet flow rate and the equivalent core flow rate or recirculation pump speed.

Cavitation of the jet pump occurs in the reactor heat output range below cavitation line 1 shown in Figure 1, but conventionally, to prevent operation in this range 3, reactor steam temperature and reactor water temperature were measured. ,
An interlock line 2' was provided to run the recirculation pump back to the lowest speed when this temperature difference fell below a certain value. Such a conventional recirculation pump control method unnecessarily narrows the operating range of the nuclear reactor, and there is a risk that an unexpected recirculation pump runback may occur due to normal fluctuations in the reactor steam temperature.

The present invention has been made in consideration of the above-mentioned circumstances.The recirculation pump back interlock is designed to be as close to the actual jet pump cavitation line as possible, and the operating range of the nuclear reactor is expanded compared to the conventional one. The purpose is to select highly accurate signals for use in interlock to prevent unexpected runbacks due to measurement errors and fluctuations during normal operation.

A runback interlock according to the method of controlling a recirculation pump according to the present invention is shown in FIG. In addition,
In Figure 1, the vertical axis shows the reactor thermal output, which is expressed as a relative value of the reactor power or the reactor feed water flow rate.
The horizontal axis shows the core flow rate representing the relative value of the core flow rate or recirculation pump speed.

In FIG. 1, an interlock line 2 is provided for a jet pump cavitation line 1. The interlock line 2 is a straight line connecting the intersection point 6 with the cavitation line 1 on the recirculation pump maximum speed line 4 and the intersection point 5 between the reactor feed water flow rate 20% rated line 7 and the cavitation line 1. Let's call it line 7. When the reactor operating point enters the reactor thermal power region 3 below the interlock line 2, the recirculation pump automatically ramps back to minimum speed to prevent cavitation of the jet pump.

Curve 8 is the recirculation pump minimum speed line, curve 9
indicates the flow control curve. The actual interlock measures reactor thermal power or reactor feed water flow and core flow or recirculation pump speed and generates a runback signal in the sequence shown in FIG. In the following, the first signal will be explained using the core flow rate, which is the recirculation pump speed and the reactor core flow rate, and the second signal will be explained using the reactor output, which is the reactor feed water flow rate and the reactor output. This will be explained using a heat output signal.

In FIG. 2, a reactor heat output signal 11 and a core flow rate signal 12 are input to a calculator 13. Although normal process values may be used here, it is easier to express logic by standardizing them, so
In this calculator 13, the furnace heat output Q _Ta is inputted as the furnace heat output signal 11 and the core flow rate signal 12.
The core flow rate W _Ta is normalized and converted into a reactor thermal output ratio Q _T1 and a core flow rate ratio W _T1 , which indicate the ratio with the respective rated values. And the reference device 15 is the first
Coefficients A and b when the interlock line 2 passing through the intersections 5 and 6 shown in the figure is expressed by the first equation, which is a linear function of the reactor thermal output Q _T and the core flow rate W _T , and the core shown in FIG. Based on the flow rate signal 12, the calculator 13
For example, using the core flow rate W _T1 corresponding to the core flow rate W' _T1 in Fig. 1, which is found from Equation 2, calculate the reactor heat output ratio Q _T2 corresponding to the reactor heat output Q' _T2 in Fig. 1, for example.
Calculate.

Q _T = aW _T + b ... (1) Q _T2 = aW _T1 + b ... (2) The adder 14 calculates the furnace heat output ratio Q _T1 obtained from the calculator 13 based on the furnace heat output signal 11 and the reference device 15
Compare the furnace heat output ratio _{Q T2 determined by} The lineback signal generator 16
send to A runback signal generator 16 generates a runback signal to the recirculation pump (not shown) when ΔQ _T is negative, ie, when the actual detected furnace thermal power is below interlock line 2.

Furthermore, if the reactor thermal output falls below the reactor feed water flow rate 20% rated line 7, cavitation will occur or the reactor water level will drop, so the reactor water level will be raised by running back the recirculation pump. This can prevent unnecessary control rod scram and cavitation.

The interlock line 2 according to the present invention is closer to the actual cavitation line 1 than the conventional interlock line 2', and can expand the operating range of the reactor accordingly. In contrast, reliability could be improved by using more accurately measured reactor thermal power, reactor feed water flow rate, core flow rate, or recirculation pump speed. It can be measured. In addition, because the main steam pipes are kept warm during the cold shutdown process of the reactor, the main steam temperature measured remains high even when the reactor water becomes low temperature, so the apparent difference with the reactor water temperature is large. The problem of the circulation pump not running back can also be eliminated.
Furthermore, even when the reactor thermal output drops below the 20% rated reactor feed water flow rate line, unnecessary control rod scrams can be prevented by running back the recirculation pump.

In a system in which the recirculation pump is operated at a constant speed and the flow rate is controlled by a valve, cavitation of the jet pump can be prevented by reducing the valve opening to the minimum using the runback interlock line signal according to the present invention.

In this example, the explanation was made using the values of the reactor power, which is the reactor thermal output, and the reactor flow rate, but in Fig. 1, the relative amount of the reactor feed water flow rate is used instead of the reactor power, and Even if the relative value of the recirculation pump speed is used instead of the core flow rate, a diagram similar to that of FIG. 1 will be obtained, and the same operation and effect as in the embodiment described above can be obtained.

[Brief explanation of drawings]

FIG. 1 is a curve diagram for explaining a runback interlock related to a recirculation pump control method, and FIG. 2 is a block diagram showing an embodiment of the present invention. 11... Reactor heat output signal, 12... Core flow rate signal, 13... Arithmetic unit, 14... Adder, 16...
Runback signal generator.

Claims (1)

[Claims] 1 Using one of the recirculation pump speed and the reactor core flow rate as the first set value, using one of the reactor feed water flow rate and the reactor power as the second set value, and using the first set value as the second set value. Using the set value and the second set value, find the recirculation pump maximum speed line indicating the speed range of the recirculation pump, the cavitation line indicating the cavitation generation area of the jet pump, and the reactor feed water flow rate 20% rated line, The intersection of the recirculation pump maximum speed line and the cavitation line is the first set point, and the intersection of the reactor feed water flow rate 20% rated line and the cavitation line is the second set point.
A linear function equation is obtained from the first set point and the second set point, and the detected values of the reactor corresponding to the first set value and the second set value are set to the linear function equation or A method for controlling a recirculation pump, comprising transmitting a runback signal to the recirculation pump when the reactor feed water flow rate falls below first and second set values determined by a 20% rated line.