JPS6025753B2 - Nuclear reactor core flow rate measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a nuclear reactor having a forced circulation loop (recirculation loop) consisting of a jet pump and a pump (recirculation pump) that supplies driving water for the jet pump. The present invention relates to a nuclear reactor core flow rate measurement device that corrects the core flow rate at the same time.

As shown in FIGS. 1 and 2, a boiling water reactor (BWR) includes a reactor core 2 loaded with nuclear fuel in a reactor pressure vessel 1, and a plurality of jet pumps 3 surrounding this core 2. is set at the lower part of the core bulkhead 2a, and this jet pump 3 guides the lubricating water to the lower part of the reactor core 2 through the water supply inlet nozzle 4 at the upper part of the reactor pressure vessel 1, and this flows into the core cooling water F from the lower part of the core to the upper part. By flowing as water, the fission energy from the nuclear fission reaction of the nuclear fuel is absorbed, and as a result, the cooling water is boiled and steam is generated.
The steam is dried by a steam separator 5 and a steam dryer 6 provided in the upper part of the core 2, and is sent as main steam G to the turbine through a main steam outlet nozzle 7.

By the way, the core cooling water F' flowing through the reactor core 2 is obtained as follows. That is, if water A is supplied into the reactor pressure vessel 1 by the feed water pump, the recirculation water connected to the jet pump 3 through the recirculation water inlet nozzle 8 and outlet nozzle 9 at the lower part of the reactor pressure vessel 1 The recirculated water circulated by the circulation pump 101 passes from the recirculated water inlet nozzle 8 to the inlet rising pipe of the jet pump 3, becomes jet pump driving water B, and is ejected from the nozzle of the jet pump 3 at high speed. The jet pump driving water B creates a suction flow C as shown in FIG. 3 (driving water B+suction flow C), which becomes the jet pump flow E and flows into the lower plenum region 11 at the lower part of the reactor. The sum of this jet pump flow E is from the lower plenum region 11 to the core 2.
, and becomes core cooling water F. In core 2,
The cooling water, which has become a two-phase flow of steam and water, flows into the upper plenum Toucheng 1.
2 and separated into steam and water by a steam separator 5. After the steam is further dried by a steam dryer 6,
It is sent to the turbine as main steam G. In addition, the water separated by the steam separator 5 is cooled by the feed water A and flows to the lower part of the outer circumference of the core bulkhead 2a. The recirculating water flows further downward through the external part of the recirculating water and exits the recirculating water nozzle 9.In such a boiling water reactor, the recirculating loop consists of a and b as shown in Figure 2. There are two systems, and they are designed to prevent the flow rate of core cooling water F from dropping suddenly due to stopping of the recirculation pump 10, etc.

When either system a or b of the recirculation pump 10 is stopped, the flow of cooling water within the reactor becomes as shown in FIG. 4. FIG. 4 shows a case where, for example, the recirculation pump 10 on the recirculation loop a side stops, but here the flow in the recirculation loop a is completely eliminated, so the flow of the jet pump flow E on the recirculation loop b side A part of this becomes a flow J that flows backward inside the jet pump 3 on the a side. Therefore, the flow rate of core cooling water F becomes F=E-J.

That is, when one of the two recirculation pumps 10 stops, cooling water flows back to the jet pump on the stopped side, and the core flow rate decreases by the amount of this backflow. However, in conventional reactor core flow measurement, the nozzle manometer detects the lid pressure and converts it into an electrical signal using a differential pressure transmitter, so even if there is a reverse flow, the differential pressure will be positive. Therefore, it is impossible to know whether the pump is started or stopped unless it is determined.

On the other hand, the differential pressure itself does not suddenly become zero even after the pump is stopped due to the inertia of the flow, but gradually changes until it reaches a minimum and shifts to the reverse flow side. The same thing also happens after startup. Therefore, if the backflow is started or stopped immediately after the pump is stopped or started, an error will occur in the backflow correction. FIG. 5 shows the pump start and stop signals and a backflow calculation circuit.

In FIG. 5, jet pump 3 on the side of recirculation loop a
The flow rate A flowing through the differential pressure transmitter 2 is an electric signal FTa.
, and the flow rate B flowing through the jet pump 3 on the side of the recirculation loop b is transmitted to a differential pressure transmitter. 21, it is converted into an electrical signal FTb. The differential pressure signals FTa and FTb are each output by a square root calculator 22.
, 23 and converted into flow rate signals Qa, Qb.
The flow rate signals Qa and Qb are calculated and their signs are determined by logic circuits 24 and 25 using relay contacts obtained from the operation/stop signals of the recirculation pumps 10 on the sides of the recirculation loops a and b. The calculation formula for the sign is determined as follows, where "1" indicates that the recirculation pumps 101 on the sides of recirculation loops a and b are stuck and running, and "0" indicates that they are stopped.

Each of the flow rate signals Qa and Qb is multiplied by these codes and inputted to an adder 26 to obtain a total flow rate signal F as a result. Therefore, if the jet pump backflow calculation is performed using the recirculation pump operation/stop signal using the backflow calculation circuit configured as described above, even if one of the recirculation pumps in the two recirculation loops a and b is stopped and backflow occurs, the core The flow rate of cooling water F can be determined accurately.

By the way, the flow rate characteristics of the jet pump when the recirculation pump is stopped are as shown in FIG. That is, when the recirculation pump 10 stops, the flow does not suddenly turn back due to the inertia of the flow, but the flow rate gradually decreases as shown from a to b in Figure 6a, and the flow rate reaches 0 seconds after the pump stops. (point C), and then the backflow amount gradually increases and changes from c to d. At this time, the change in the differential pressure of the manometer for measuring the flow rate of the jet pump becomes as shown in FIG. 6b. After the pump stops, the differential pressure decreases from e to f, and after a few seconds, the differential pressure becomes 0.
(point g), and then the differential pressure increases again from g to h. With respect to such flow rate characteristics, the above-mentioned method for adjusting the core flow rate assumes that the reverse flow starts immediately upon stopping the recirculation pump.

The result of adjusting the flow rate by such means is shown in FIG. 6e. As is clear from FIG. 6c, the above-mentioned shark correction means has the following drawbacks in processing the flow rate Qb.

That is, in processing the flow rate Qb, although the flow rate Qb actually changes as shown by the dashed line in the figure as Qb, → Qb2 → Q wide, according to the above-mentioned same correction method, Qb, → It is calculated as Qb5→Qb6→Qb3. Therefore, since the total flow rate is F=Qa+Qb, F is calculated as F,→F5→F6→F3.

The purpose of the present invention is to accurately determine the flow rate of core cooling water even if backflow occurs when a recirculation pump is started or stopped, by correlating the backflow calculation with the start or stop of the pump and correcting the core flow rate. The objective is to obtain a reactor zero flow rate measuring device for a nuclear reactor.

An embodiment of the present invention will be described below with reference to the drawings. 7th
The figure shows the time from when the recirculation pump stops until the backflow starts (to(
This figure shows the configuration of a device that corrects the core flow rate by performing reverse flow switching after TO.

As shown in FIG. 7, the high pressure side piping 2 is connected to the throat 3a of the jet pump 3 placed inside the reactor pressure vessel 1.
7 is connected to the high pressure side of the diaphragm of the differential pressure transmitter 20, while the low pressure side pipe 28 connected to the diffuser section 3b of the jet pump 3 is similarly connected to the low pressure side of the diaphragm of the differential pressure transmitter 20. This lid pressure transmitter 20 captures the mechanical pressure difference (differential pressure) between the pipes 27 and 28 as a deformation of the diaphragm, etc., and converts this mechanical pressure difference into an electrical signal. The electrical signal converted from the differential pressure transmitter 20' is applied to the process input device 31' of the electronic computer 30 via the signal line 29. Process input device 3
1 is applied to an arithmetic and control unit 32, and the output of this arithmetic and control unit 32 is applied to a storage device 33. Therefore, the output signal from the differential pressure transmitter 20 is read into the arithmetic and control unit 32 via the process input device 31,
It is also stored in the storage device 33. Also jet pump 3
A drive pump 34 and a pump drive motor 35 for driving the
The drive signal for the drive pump 34 or the opening/closing signal for the output valve 36 of the drive pump 34 is also sent to the process input device 3 via the signal line 29.
1 and stored in the arithmetic and control unit 32. In such a configuration, a timing chart for measuring the core flow rate is shown in FIG. 8. In the example described here, there are two recirculation loops for driving the jet pump 3, as shown in FIG. These two loops are designated as a and b, and a signal indicating that driving water is flowing to any one of the recirculation loops, such as the pump 34, the pump drive motor 35, or the outlet valve 36, is Da for the a and b loops. b. As shown in Figure 8,
When both signals Loa and Lob are off (pump stopped), a,
b It is assumed that the jet pumps in both loops are forward flow. Even when the a and b loops are turned on at the same time, it is assumed that the a and b loops are both in forward flow (case ■). In this case, when loops a and b turn off from the on state, loop b does not immediately become a reverse flow, but becomes a reverse flow after to. When loop b is turned on while loop a is on and b is off, the forward flow of loop b occurs after t. Similarly, for the status signals oa and b of the pumps in the a and b loops, the flow rate is calculated from the signals la and lb to la+lb or la, taking into consideration the times to, t, etc.
The correct core flow rate is measured by calculating 1 lb or 1 la+lb. Furthermore, for this to, t, there are cases where a predetermined time is used and cases where the electronic computer 30
The arithmetic and control unit 32 calculates the rate of change values of the signals la and lb, and uses other signals, constants, etc. as necessary. By using this instead of a predetermined value, the core flow rate can be measured more accurately. Although the above description has been made regarding the case where the arithmetic processing is performed by the electronic computer 30, it is of course possible to perform the processing by a logic circuit that performs the same arithmetic processing without necessarily using the electronic computer.

As another embodiment, a logic circuit in which the above-mentioned time-limiting relay is used is shown in FIG. That is, in FIG. 9, Xa to Xd are relays, Ti to m are time-limited relays, and these relays Xa to Xh, Ti to n and their output contacts are combined and logically configured as shown in FIG. 9a. The output stage relays Xe, Xf, Xg, and Xh are connected to the 9th arithmetic circuit.
If it is installed as shown in FIG. b, the same arithmetic processing as using an electronic computer can be performed, and the core flow rate can be measured accurately. Furthermore, although the above-mentioned example has been described as an example in which there are two recirculation loops, it goes without saying that the same idea can be applied to any number of loops.

In addition, the present invention can be implemented with various modifications without changing the gist thereof. As described above, according to the present invention, even if backflow occurs when starting and stopping the recirculation pump, the backflow calculation is related to the start and stop of the pump and the zero flow rate of the furnace is corrected. , it is possible to provide a nuclear reactor that can accurately determine the flow rate of core cooling water.

[Brief explanation of the drawing]

Figure 1 is a partially cutaway perspective view of the configuration of a boiling water reactor, Figure 2 is a configuration diagram to explain the flow of fluid in the reactor, and Figure 3 is an inflow and outflow to the jet pump. Figure 4 is a diagram to explain the flow of fluid when the recirculation pump stops, Figure 5 is a diagram to explain the flow of fluid when the recirculation pump is stopped.
The figure is a backflow calculation circuit diagram showing an example of a reactor core flow rate measuring device, Figures 6 a to c are diagrams showing flow characteristics of a jet pump, and Figure 7 is a configuration explanatory diagram showing an embodiment of the present invention. 8th
The figure is a forward flow/reverse flow determination timing diagram in the same embodiment, and FIGS. 9a and 9b are diagrams showing another embodiment with different logic circuits and arithmetic circuits used in the present invention. 20, 21... Differential pressure transmitter, 22, 23...
...square root calculator, 24, 25... logic circuit,
26...adder, 30...electronic computer. Fig. 1 Fig. 3 Fig. N Ship Fig. 4 Fig. 5 Fig. 6 Towball diagram Vertical Fig. 9

Claims (1)

[Claims] 1. A plurality of jet pumps that circulate cooling water in the core of a nuclear reactor, at least two recirculation pumps that supply driving water to the jet pumps, and a cooling water that is provided in each of the jet pumps and that flows into each of the jet pumps. A differential pressure detector that detects a flow rate and a device that determines the polarity of a detected value obtained by the differential pressure detector are provided, and the sum of the polarized flow values detected by each of the differential pressure detectors is provided. is measured as the core flow rate, and if another recirculation pump is in operation when the recirculation pump starts or stops, the recirculation pump that started or stopped will be driven by the recirculation pump that started or stopped. 1. A nuclear reactor core flow rate measuring device, characterized in that the polarity of the detected value obtained from the differential pressure detector of the jet pump is reversed.