Patent GB-1520069-A (GB)
Title: Control system for a nuclear power producing unit
IPC: G21D3/08
Filed: 1976-04-12
Abstract: 1520069 Nuclear power plant control BABCOCK & WILCOX CO 12 April 1976 [25 Sept 1975] 14874/76 Heading G6C In a nuclear power plant comprising a pressurized coolant reactor 1, one or more once through steam generators 3, 4, a turbine generator 13, 14, 15 supplied with steam from the generators and means for maintaining coolant flow through the reactor and steam generators, a control system comprises a means 33 (Fig. 2) for generating a feed forward control signal representative of the desired power output of the plant, means 102 for adjusting the reactor heat release, means 75, 76 for adjusting the rate of flow of feed water to the steam generators and, optionally, means 19 for adjusting the rate of flow of steam from the steam generator to the turbine, said means 102, 75, 76 and 19 being solely responsive to and operated in parallel from the feed forward control signal whereby the reactor heat release, rate of feedwater flow and rate of steam flow are each maintained in a discrete functional relationship to the feed forward control signal. As shown in Fig. 2 the inputs transmitted by signal conductor 34 to the three separate control loops are first fed to function generators 61A, 62A and 63A so as to modify the control signal so that under normal conditions there is established the reactor heat release required to satisfy the then existing power demand and the rate of feedwater flow and steam flow required to maintain critical system parameters at set point. The signals in the various loops are further modified by error signals from four sub-loops (Fig. 3, not shown) in which the feed forward control signal, conditioned so that the output from a function generator in each of the sub-loops is representative of the correct or set point value of a critical system parameter, is compared with a signal representative of the actual value to generate the error signal. These signals are throttle pressure error (actual value signal generated by throttle pressure transmitter 41), average feedwater temperature error (actual value signal generated in temperature transmitters 46, 47), reactor coolant temperature error (actual value signal generated by summing unit 51 which averages signals from further summing units 52, 53 averaging input and output temperature signals from transmitters 54, 55 and 56, 57 respectively), and megawatt error (actual value signal generated by megawatt transmitter 42). These error signals, referred to in Fig. 2 by their initial letters, are applied as shown to respective summing units 64, 65 and 66 in the control loops to apply bias corrections to the feed forward control signal proportional to transient changes in the error signals. Moreover the prime integrals of particular ones of the various error signals are also applied as shown through integrating units 58, 59 and 60 to make steady state corrections to the control signals. In the case of the reactor output control loop, the modified control signal from summing unit is compared with a signal, corresponding to actual neutron power, generated in neutron power transmitter 48, and the output signal from difference unit 103 is applied through proportional plus integral unit 104 to operate control rod drives 102 so as to maintain the power output as the value established by summing unit 66. The steam flow control loop is analogous, except that to prevent improper steady state corrections to steam flow, a signal corresponding to megawatt error is subtracted from throttle pressure error in difference unit 70. As regards the feedwater flow control, the modified signal from summing unit 65 operates in parallel valves 75 and 76 and the total feed water flow to steam generators 3 and 4 is maintained equal to demand by a feed-back loop comprising flow signal transmitter 77, difference unit 78 and proportional plus integral unit 79. The output from unit 79 is transmitted through conductors 80, 81 to summing units 82, 83 to adjust the feedwater flows and consequently steam outputs equally, through respective local feed-back loops 84, 85, 86 and 87, 88, 89. The equality of feedwater flow is continuously modified to maintain the average coolant temperatures in loops A and B equal. A signal representative of the difference in average temperatures is generated in difference unit 90 and inputs to unit 93 receiving the control signal, and accordingly the feedwater flow to steam generator 3 is modified in accordance with said differences. An output from unit 93 applied to difference unit 95 causes an equal but opposite change in feedwater supply to steam generator 4. As so far described the flow control is slow in response, and to take into account rapid changes in average coolant temperature, coolant flow rate signals generated by 97, 99 are compared in difference unit 100 and the output transmitted to summing unit 92 so as to effect appropriate increase or decrease of feedwater flow to the steam generators. Moreover differences in average coolant loop temperatures resulting from changes in relative feedwater temperatures may be anticipated, e.g. in that if the temperature of the coolant entering reactor 1 from steam generator 3 should fall, bias control action from difference unit 101 acting on unit 92 to summing unit 93 decreases the flow to generator 4 and increases the flow to generator 3.