Patent GB-1003410-A (GB)
Title: Improvements in and relating to nuclear reactor plant
IPC: G21D3/10
Filed: 1964-04-23
Abstract: 1,003,410. Nuclear power plant. SULZER BROS. Ltd. April 23, 1964 [May 17, 1963], No. 16892/64. Heading G6C. In a method of controlling a nuclear power plant, the temperature of the coolant at its exit from the reactor is maintained substantially constant and the rate of flow of load medium through the heat exchanger is controlled in dependence upon the temperature of the coolant leaving the heat exchanger and is, upon a change in reactor output, additionally adjusted by a signal dependent upon the changed reactor output, preferably a signal proportional to the reactor output. As shown in Fig. 2, a reactor 1 and a heat exchanger 2 are connected by ducts 3, 4 for the reactor coolant, the heat exchanger 2 being supplied with a load medium from a starting tank 5 via a pump 6 and a feed valve 7. The load medium is preheated, evaporated and superheated in the heat exchanger 2 from which it flows to a turbine 10 through a duct 8 and a valve 9 adjusted by a turbine speed governor 14. After leaving the turbine 10, the load medium is condensed in a condenser 11 and returned by a condensate pump 12 through a preheater 13 to the tank 5. The control of the plant proceeds as follows: an element 20 measuring the pressure of the live steam produced from the load medium acts by way of a signal generator 21 with a P.I. (i.e. a proportional-integral) characteristic to determine the desired value for the reactor output and this acts upon a flux controlling unit 22 which has a P.I. characteristic. The unit 22 also receives a measured value from a neutron flux detector 23 and delivers its output signal to a control rod mechanism 24. Gaseous coolant is circulated through the reactor by a pump 25 controlled by a Pi-controller 27 by the temperature at the reactor exit as measured by a temperature detector 26. The pump 25 also receives the output signal of the neutron flux detector 23 via a differentiating element 28 which can have a PD (i.e. a proportional differential) characteristic. This extra control of the pump 25 in accordance with neutron flux has the purpose of adapting the rate of coolant flow to changes in neutron flux very rapidly before the slowacting but finally predominant PI-eontroller 27 operates in dependence upon the coolant exit temperature. The rate of flow of load medium through the heat exchanger 2 is controlled by a temperature detector 30 acting through a slowacting Pi-controller 31 controlling the feed valve 7; the position of the valve being determined by an element 32 which acts by way of a P-controller 33 (i.e. a controller with proportional action) upon the pump 6. A change in reactor output as measured by the neutron flux detector 23 causes a change in the speed of the pump 25 and this is measured by a speedometer 35 and a signal is passed via a P-controller 36 to the feed valve 7 for regulating the rate of load medium flow through the heat exchanger 2. By this means, the rate of load medium flow is adapted to the changed reactor output before such a change takes effect via the sluggish temperature control system provided by the control loop 30, 31, 7. Control based on coolant temperature alone would give rise to considerable fluctuations in the temperature of the coolant leaving the heat exchanger when a change in load occurs, which temperature changes might even be sufficient to produce thermal shocks in the reactor. The additional control described above has the effect of reducing these temperature changes without the introduction of substantial control instability. Control instability, e.g. of the vapour temperature and pressure of the load medium or of the coolant temperature downstream of the heat exchanger can be reduced considerably if the rate of flow of load medium through the heat exchanger is further adjusted by a signal formed in dependence upon the shift of the point in the heat exchanger at which evaporation of the load medium terminates so as to oppose any instability associated with such shift. This may be effected as shown in Fig. 2 by providing trend thermocouples 51, i.e. thermocouples measuring the rate of temperature change with time, at three stations 50 along the coolant flow path, at least one station 50 being in the zone of relatively considerable variation of coolant temperature in order to detect the rate of shift of the point in the heat exchanger 2 at which evaporation terminates. The measured values are summed and applied via a P-controller 52 to the feed valve 7. Instead, the maximum value can be selected by means of a conventional maximum selector. In an alternative embodiment (Fig. 3, not shown), the desired value for the reactor output is supplied by a programmer to the Pi-controlling unit 22. Also the temperature of the coolant at its exit from the reactor is applied to a quick-acting control loop comprising a flow measuring element, a P-controller and the pump 25. The P-controller receives, as well as the signal from the Pi-controller 27, the measured value of the neutron flux from the neutron flux detector 23 via another P- controller. Also, the reactor output measured value which acts via the P-controller 36 upon the feed valve 7 is not sensed by a speedometer 35 but is determined by the neutron flux detector 23 and/or by the above-mentioned flow measuring element. Temperature detectors replace the trend thermocouples 51 and the temperatures measured by them are summed and applied via a differentiator to the feed valve 7. A P-controller can replace the differentiator in this embodiment, so that the position of the point of termination of evaporation as well as the speed of its shift can be measured and used of control purposes.