JPH0422479B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a nuclear reactor feed water control device that controls a nuclear reactor feed water pump and maintains a constant water level in the reactor.

[Technical Background of the Invention] In general, for boiling water reactors, a reactor standard water level that is necessary for stable operation of the reactor is determined, and this reactor standard water level is determined in any operating state of the reactor. The deviation of the reactor water level from the water level must be within the permissible range. In the event that the reactor water level deviates from this allowable range, the reactor output must be reduced or the reactor must be shut down, and it is extremely difficult to maintain the reactor water level at the standard value in boiling water reactors. It's important. On the other hand, the reactor water level is subject to constant fluctuations due to the change in the flow rate of steam flowing out from the reactor to the turbine depending on the reactor output. Must be controlled. A reactor feed water control device is provided for this purpose, and usually, by changing the rotational speed of the reactor feed water pump or the opening degree of the flow rate adjustment valve provided at the outlet of the reactor feed water pump, Controls the flow rate of water supplied to the reactor.

Figure 3 shows an example. 1 is a nuclear reactor, 2 is a water supply pump for sending water into the reactor, and 3 is a flow rate adjustment device installed at the outlet of the water supply pump 2 to adjust the water supply flow rate. 4 is a water level setter that provides a water level reference signal; 5 is a water level detector that detects the reactor water level; 6 is a water level reference signal _L1 from the water level setter 4 and a water level signal _L2 from the water level detector 5; 7 is a water level controller that inputs the water level difference signal L ₃ and calculates the flow rate command signal _{L 4 ;} 8 is a flow rate that detects the flow rate of the water supply pump; Detector, 9 is a contact that turns on/off the pump flow rate signal L ₅ from the flow rate detector 8, which opens when the pump flow rate is low; 10 is a contact that passes the flow rate command signal L ₄ from the water level controller 7 and contact 9. a second calculator that inputs the pump flow rate signal _L5 ' and calculates the flow rate deviation signal _L6 ;
11 is a flow rate controller that inputs the flow rate deviation signal L ₆ and calculates an opening command signal L ₇ for the flow rate adjustment valve 3;
Reference numeral 12 denotes a contact that turns on/off the opening command signal L ₇ and remains closed until _the pump flow rate is low.

FIG. 4 is a block diagram showing the operation of the above configuration, where G ₁ S is a transfer function representing the water level controller 7;
G ₂ S is a transfer function representing the flow rate controller 11, G ₃ S is a transfer function representing the flow rate regulating valve 3, and G ₄ S is a transfer function representing the nuclear reactor 1. At this time, if the reference pump flow rate is not low (that is, contact 9 is closed and contact 12 is open), the transfer characteristic from the water level reference signal L ₁ S to the flow rate control deviation signal L ₆ S is expressed by the following equation.

L ₆ (S)=G ₁ (S)/1+G ₂ G ₃ (S)+G ₁ G ₂ G ₃ G ₄ (S) L ₁ (
S) ...(1) Normally, the water level controller 7 is expressed as a proportional gain, the flow rate adjustment valve 3 is 0 type (i.e. lim S→OG ₃ (S) = finite), and the reactor 1 is expressed as an integral characteristic, and the flow rate control Since the container 11 includes an integral element, G ₁ (S)=K lim S→OG ₂ (S)=∞ lim S→OG ₂ (S)=finite G ₄ (S)=1/+ _RS (T _R : reactor time constant) ...(2), and for step-like changes in L ₁ (S), by using the final value theorem of Laplace transform, the steady value of L ₆ is L ₆ = 0 ... …(3) becomes. Therefore, the flow rate command signal L ₄ and the pump flow rate signal L ₅ match, and the flow rate of the water supply pump 1 is controlled by the water level controller 7. However, when the water supply pump 2 is stopped, the flow rate signal L ₅ is always 0 regardless of the opening degree of the flow rate adjustment valve 3, and it does not match the flow rate command signal L ₄ and L ₆ ≠ 0... (4) Become. That is, since the flow rate controller 11 includes an integrator, the flow rate controller 11 is saturated according to the above equation (4), and the opening degree of the flow rate regulating valve 3 is always in a fully open state.

On the other hand, in a general nuclear power plant, a plurality of water supply pumps are installed, and normal water supply control is performed using some of these pumps (for example, two out of four pumps). The remaining water supply pumps are for backup purposes and are normally stopped, but if there is a possibility that the reactor water level deviates from the permissible range and drops suddenly, such as in the event of a failure of the normal system water supply pump, they will be started automatically. It is designed to supply water. However, as mentioned above, if the flow rate controller 11 is saturated when the pump is stopped, the flow rate of the automatically started water supply pump will remain at 100% or close to it for a certain period of time until the saturation of the flow rate controller 11 is resolved. The water would flow in an uncontrolled manner, conversely becoming supercharged water, causing the reactor water level to rise rapidly and deviate from the permissible range.

Therefore, even when the water supply pump 2 is stopped,
Contacts 9 and 12 are provided to prevent the flow rate controller 11 from becoming saturated. When the pump flow rate is low, contact 9 is open and contact 12 is closed, so the transfer characteristic from the flow rate command signal L ₄ to the opening command signal L ₇ is L ₇ (S) = G ₂ (S) / 1+G ₂ (S) L ₃ (S) ...(4). Therefore, the final value theorem of Laplace transform and (2)
From the formula, during steady state, L ₇ = L ₄ ...(5), so even when the water supply pump is stopped, the flow rate controller 11 will not be saturated, and the opening command signal
_L7 will be maintained at the same value as the flow rate command signal _L4 .

[Problems with Background Art] However, this is only a characteristic during steady state, and a bump will occur when the contacts 9 and 12 are switched unless the opening command signal L ₇ and the pump flow rate signal L ₅ match. This is contact 9 and contact 12
This is because the opening command signal L ₇ and pump flow rate signal L ₅ are switched by , and if there is a deviation between the two, that deviation is output through the flow controller 11 and a bump is created in the opening command signal L ₇ . Occur.

On the other hand, the opening command signal L ₇ and the pump flow rate signal L ₅ are
Since the characteristics between the opening degree and the flow rate of the flow rate regulating valve 3 are nonlinear, they usually do not match. For this reason, in the conventional configuration, bumps always occur when switching contacts 9 and 12, and the flow rate of water supplied to the reactor fluctuates.
As a result, the reactor water level fluctuated, and there was a risk that the deviation from the reactor standard water level would deviate from the permissible range. Furthermore, since the pump flow rate signal _L5 , which is a feedback signal, is directly turned on/off, failure of the contact directly reduces the reliability of the flow rate control system, which is not desirable in terms of reliability.

[Object of the Invention] An object of the present invention is to provide a stable nuclear reactor control device by eliminating fluctuations in reactor water that occur when switching between a pump flow rate signal and an opening command signal when the pump flow rate is low.

[Summary of the Invention] Therefore, the present invention inputs the deviation between the command flow rate and the output of the flow controller when the pump flow rate is low into the integral element of the flow rate controller, and inputs the deviation between the command flow rate and the actual flow rate when the pump flow rate is not low. It is characterized by inputting the deviation of .

[Embodiment of the Invention] The present invention will be described below based on an embodiment shown in FIGS. 1 and 2. FIG. 1 is a block diagram of a nuclear reactor feed water control system showing one embodiment of the present invention. In the figure, the same symbols or the same or equivalent parts as in FIG _. 3 are shown, and the points that are different from those in FIG. A new contact 13 and arithmetic unit 14 are provided, which close when _the input point and pump flow _rate are low. This is the point where the signal L ₆ is input to the third arithmetic unit 14 and the output of the third arithmetic unit 14 is input to the integrator 15 of the flow rate controller 11 .

FIG. 2 is a block diagram showing the operation of the above structure. In the figure, the same symbols as in FIG. 4 indicate the same or equivalent parts, and the transfer function G ₂ (S) of the flow rate controller 11 is expressed as G ₂ (S)=G ₂ '(S) + 1/TS...(6) It is divided into integrator and other parts. Contact 12
Since the contact point 13 is open when the pump flow rate is not low, the operation when the pump flow rate is not low is exactly the same as in FIG. 4.

On the other hand, if the pump flow rate is low, the flow command signal
The transfer characteristic from L ₄ to the opening command signal L ₇ is L ₇ (S) = {G'(S)・TS+1}L ₄ (S)
-G'(S)・TS・L ₅ (S)/1+TS...(7) Therefore, the final value theorem of Laplace transform and (2)
From the equation, it becomes stationary that L ₇ =L ₄ ...(8), which is the same as equation (5). Therefore, the steady operation when the pump flow rate is low is also similar to the conventional configuration.

However, in this embodiment, contact 1
Pump flow signal turned on/off at 3 and 12
_L5 ' and opening command signal _L7 ' are input only to the integrator 15 of the flow rate controller 11. Therefore, when switching contacts 12 and 13, the pump flow rate signal
Even if there is a deviation between L ₅ and the opening command signal L ₇ , no bump will occur in the opening command signal L ₇ , and the opening command signal L 7 will be returned to the opening command signal L ₇ at a gentle speed determined by the integration time constant T of the integrator. changes.

[Effects of the Invention] As described above, according to the present invention, when the pump flow rate is low, the deviation between the command flow rate and the flow rate controller output is input into the integral element of the flow rate controller, and when the pump flow rate is not low, the command flow rate is inputted into the integral element of the flow rate controller. Since the deviation between the pump flow rate and the actual flow rate is input, when the pump flow rate is switched from low to low, no bumps occur, there is no fluctuation in the reactor feed water flow rate, and the reactor water level is stably controlled. Furthermore, since the feedback signal circuit is configured to have no contact at all times, highly reliable flow rate control is possible.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a reactor feed water control system according to an embodiment of the present invention, Fig. 2 is a control block diagram of Fig. 1, and Fig. 3 is a block diagram of a conventional reactor feed water control system. FIG. 4 is a control block diagram of FIG. 3. 1... Nuclear reactor, 2... Water supply pump, 3... Flow rate adjustment valve, 4... Water level setter, 5... Water level detector,
6...First computing unit, 7...Water level controller, 8...
Flow rate detector, 10... Second computing unit, 11... Flow rate controller, 12... Contact that closes when the pump flow rate is low, 13... Contact that closes when the pump flow rate is low, 14
. . . third arithmetic unit, 15 . . . integrator of the flow rate controller 11.

Claims (1)

[Claims] 1. A water level controller that calculates a command flow rate signal for a reactor feed water pump according to a deviation water level signal between a reference water level signal and an actual water level signal of the reactor, and a water level controller that calculates a command flow signal for a reactor feed water pump according to a water level signal that differs between a reference water level signal and an actual water level signal of the reactor, and A reactor feed water control device comprising a flow rate controller including an integral element that controls the flow rate of a reactor feed water pump according to a deviation flow rate signal, wherein the calculation element other than the integral element of the flow rate controller receives the deviation flow rate signal. while inputting the deviation flow signal to the integral element when the reactor feedwater pump flow rate is not low;
A nuclear reactor feed water control device characterized in that a deviation signal between the command flow signal and the flow controller output signal is input when the command flow signal is low.