Patent Number: 051184613
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The first embodiment of the present invention will be explained below with reference to FIGS. 3 to 7. FIG. 1 is a diagrammatic view showing a boiling-water reactor including a flow measuring apparatus according to the first embodiment of the present invention. The reactor includes a pressure vessel 1 with a reactor core 2 held therein. The core 2 is held within a shroud 6 and a steam separator 3 is provided over the shroud 6. The steam separator separates water or coolant from a steam generated at the core 2 and supplies dried steam to a turbine, not shown, and so on. A coolant separated from the steam flows down a passage, defined between the outer periphery of the shroud 6 and the inner wall of the pressure vessel 1, and is sent by a plurality of circulation pumps 10 to a location under the core 2. That coolant goes from below the core 2 up into the core 2 where it is bold. It is flowed out from above the core. In this way, the coolant circulates through the passage as set forth above. The circulation pumps 10, each, are driven, through a shaft 9, by a corresponding motor 11 which is mounted outside the pressure vessel. A coolant flow measuring means is provided in the reactor so as to accurately measure a flow rate of a coolant past the core and its flow distribution and monitor the state of the reactor. Openings 25A, 25B of pipes for a plurality of sets of core inlet differential pressure gauges 25 are provided at the core inlet 14 of the reaction core 2. These openings of the pipes are located at a core support plate of the reactor core 2 or at an entrance nozzle of a fuel assembly. Pressure signals corresponding to pressures at these openings are supplied to a differential pressure/flow converter 26 so that the flow rate of the coolant may be measured. Although in the arrangement shown in FIG. 3 the core inlet only, a plurality of systems are provided as the core inlet differential pressure gauge in a practical reactor. A plurality of additional pump section differential pressure gauges 23 are also provided to correct and back up the aforementioned core inlet differential pressure gauges 25 The pump section differential pressure gauge 23 is provided for each circulation pump. The present invention is applied to the systems for the pump section differential pressure meters 23. The openings 23A and 23B of the pipes for each pump section differential gauge meter are provided at the suction and discharge sides, respectively, of the respective circulation pump 10. A differential pressure signal is output from the pump section differential pressure gauge 23 and input to a pump section calculator 24. A speed transducer 22 measures the rotational speed of the motor 11 for driving the circulation pump 10. A speed signal is output from the speed transducer 22 and input to the pump section calculator 24. With the differential pressure between the suction and discharge sides and rotational speed of the pump 10 as parameters, a relation of these parameters and pumps' discharges are obtained in advance using a test stand for each circulation pump and also have been programmed in the pump section calculator 24. Thus the flow rate of the respective circulation pump 10 is measured by the pump section calculator 24. A flow signal for the respective circulation pump is output from the pump section calculator 24 and input to a calculator 27 so as to obtain a total flow rate of all the circulation pumps. A flow signal of the calculator 27 and that of the differential pressure/flow calculator 26 are input via a correction switch 28 to an operation monitor device 29 for the reactor. By the switching operation of the correction switch 28 it is possible to correct and back up the core plate differential pressure gauge 25 in the case of functional failure of this core plate differential pressure line. The speed transducer 22 for measuring the rotational speed of the motor 11 for driving the circulation pump 10 delivers a rotation speed signal to a pipe network model calculator 30. In the case where one or some of the circulation pumps 10 are stopped or driven at a lower rotational speed, the calculator 30 calculates a total of the flow rate of all the circulation pumps 10. A pipe network model equivalent to coolant flows in the pressure vessel 1, for example, flows from the respective circulation pumps 10 to a lower plenum is initially programmed in the calculator 30. A relation of pipe network model to the aforementioned flows will be explained below. FIG. 4 is a side view showing an area including the circulation pumps and FIG. 5 is a plan view diagrammatically showing that area. FIG. 4 is a side view as viewed from inside a zone below the shroud 6 and at shroud support leg 12. Below a passage defined between the outer periphery of the lower portion of the shroud 6 and the inner wall of the pressure vessel 1 a ring-like pump deck 15 is located in a manner to close that passage. A plurality of circulation pumps 10 are arranged in a circumferential direction at equal intervals with each penetrating the pump deck 15. A nozzle 9a is provided at lower end of each circulation pump 10 and a coolant is sucked from a suction inlet at the upper end of the circulation pump 10 and discharged from the nozzle 9a. The lower end of the shroud 6 is supported by a cylindrical shroud support leg 12. Leg openings 13a are provided at the shroud support leg 12 with each provided at a location opposite to the front of circulation pump 10 and leg openings 13b are provided at a middle position between the adjacent circulation pumps 10. FIGS. 4 and 5 show the state of flows of a coolant discharged form the circulation pumps 10. A coolant flow f.sub.1 discharged from the nozzle 9a of the circulation pump 10 is divided into a circumferential flow f.sub.2 and a radial flow f.sub.3. The coolant flow f.sub.3 is into the lower plenum past the leg opening 13a. The flow f.sub.2 and a flow f.sub.2 coming from the adjacent circulation pump meet at a point g to provide a radial flow f.sub.3. The radial flow f.sub.3 is into the lower plenum past the leg clearance 13b. FIG. 6 shows a coolant flow pattern as a pipe network model. In the model thus prepared, the pipes corresponding to the flows in FIGS. 4 and 5 and branch points are represented by identical signs and the flow resistances of the respective pipes (flows) are denoted by .alpha..sub.1, .alpha..sub.2, .alpha..sub.3 and .alpha..sub.4 in FIG. 6. The model thus prepared is initially programmed into the pipe network model calculator 30. On the model, the respective flows are analytically calculated based on the rotational speed signals of the pumps entered into the model calculator 30 from the speed transducer 22 and the result of calculation (flow rate signal) is input to the correction switch 28. The correction switch 28 selectively switches the flow rate signal of the calculator 27 or that of the calculator 30, as required, to the operation monitor device 29. The correction of the signal of the calculator 27 and system back-up of the calculator 27 are performed by the signal of the model calculator 30. The analytical calculation as set out above will be explained below in more detail with reference to FIG. 7. In FIG. 7, Pi-1, and Pi and Pi+1 correspond to the respective circulation pumps 10 and represent the Q-H characteristics (including back-flow characteristics) of the respective circulation pumps. Here Q and H represent the flow rate of the pump and pressure loss (loss head), respectively. The symbols .alpha..sub.1, .alpha..sub.2, .alpha..sub.3 and .alpha..sub.4 represent pipe resistances, .alpha..sub.1 showing the discharge loss of the respective pumps (a loss involved upon the collide of the coolant discharged down from the pumps against the bottom of the pressure vessel 1), .alpha..sub.2 a loss between the respective pumps, .alpha..sub.3 a loss at the shroud support leg 12 and .alpha..sub.4 a pressure loss in the reactor (various losses suffered by the coolant returned back to the pumps 10 past the core 2, though there may be a change with time). X, Y, Z in FIG. 7 represent the flows of the respective locations. Analytically solving a multi-dimensional simultaneous nonlinear equation formulated, under the condition (1) of constant flows rate at the respective nodes (branch points) as well as under the condition (2) under which a given relation is obtained for the respective pipe pressure, using the model as shown in FIGS. 6 and 7 yields the respective flows X, Y and Z. That is, based on the condition. (1) Under which the flow rate of the coolant into the respective node (branch point) is equal to that discharged from that node, ##EQU1## provided that qi shows a suction flow rate or a discharge of the respective pipes 1,2,...m connected to the respective nodes and (2) under which the algebraic sum of the pressure losses (loss heads) is equal to zero in which if, with the pressure loss of the respective pipe represented by hi, hi&gt;0 when the flow is in a clockwise direction and hi&lt;0 when the flow is in a counterclockwise direction, then ##EQU2## provided that m denotes the number of unit pipes for one element pipe, the nonlinear simultaneous equation for the respective nodes is prepared and the respective flows are found by analytically solving that simultaneous equation. That is, in the various operation states of the respective circulation pumps (including a back-flow with some pump not operated), respective constants (an equivalent pipe resistance and pump's back-flow characteristic) of the pipe network model are initially found using the pump section differential pressure meter 23 and stored in the model calculator 30. If the respective flows rate are analytically found using these constant values and the flow rate through the core is corrected using the core inlet differential pressure gauge, then the accuracy with which the coolant is circulated through the core can remarkably be enhanced irrespective of whether or not the circulation pumps 10 are rotated at equal rotational speed. Even if any hindrance occurs for some reason or other upon the measuring of the flow rate by the core inlet differential pressure gauge 25, it is possible to maintain a requisite measuring accuracy even upon the measuring of the flow rate by the model calculator 30 only. By optimizing (recorrecting) the value of the respective constant of the model either periodically or at a proper time at the aforementioned steps, an adequate preparation can adjustably be made against a variation in the pressure loss in the core with time, for example, at the end of a fuel cycle, thus maintaining the measurement of the flow with high accuracy. Since the requisite accuracy is obtained upon the measurement of the flow rate by the model calculator 30, a system thus obtained can be simplified at low cost. It is only necessary to send the rotational speed data of the respective pump from the corresponding speed transducer 22 mounted on the corresponding drive motor 11 of corresponding circulation pump 10 to the model calculator 30 and then find the respective flows rate from the rotational speed of the pumps (some somewhat varying at its rate) and both the Q-H characteristic inherent in the respective pump and respective constant of the pipe network model which has initially been found and stored as already set out above. The flow rate thus found is displayed on the operation monitor device 29. It may be possible to use both the measurement of the flow rate by the model calculator 30 and the measurement of the flow rate by either the differential pressure at the core inlet section or the differential pressure in the inlet and outlet of the circulation pump 10. Since the flow rate measuring apparatus of the present invention is applied to the flow rate measuring apparatus for measuring a coolant flow rate in the boiling-water reactor, it is possible to readily and accurately control the operation of the reactor and to achieve high reliability with which the reactor is controlled. FIG. 8 shows an apparatus according to a second embodiment of the present invention. The second embodiment includes a control unit 31 with a pipe network calculator 30 incorporated therein. A speed transducer 22 detects the rotational speed of the respective circulation pump and sends it to the control unit 31. In FIG. 8, the speed transducer 22, though being shown as being two in number, is provided for each motor of the respective circulation pump. The control unit 31 calculates the flow rate of a coolant as in the aforementioned embodiment and sends a control signal to the corresponding motor 11 of the respective circulation pump, thus controlling the operation of the circulation pump 10 and hence a circulation coolant flow. It is to be noted that the control unit 31 delivers a position control signal of a control rod and other signals so that it is possible to control the core output and the operation of a whole reactor. Although in the aforementioned embodiment the present invention has been explained as being applied to the apparatus for measuring a flow rate of a circulation coolant in the pressure vessel for the boiling water reactor, it is not restricted to the aforementioned embodiment. In a heat exchanger, a boiler, an agitating apparatus in a chemical plant, a dialyzing apparatus, a gas reactor, a solid/fluid separator and so on, a complex flow/circulation passage is formed in a container or vessel through which a fluid flows. Even in the apparatuses, it has been difficult to accurately measure the state of the flow of a fluid in the container when these apparatuses are operated under an off-normal condition. There is a growing demand for an apparatus for precisely measuring a flow rate of a fluid in the container (vessel) in a complicated flow pattern as in the case of the flow rate measuring apparatus of the present invention. If the flow rate measuring apparatus of the present invention is applied to the various apparatuses, the flow rate of the fluid in proper location or locations in the container can readily and accurately be measured, and the aforementioned apparatuses can be managed or controlled exactly and very reliably