Patent GB-942319-A (GB)
Title: Improvements in or relating to control systems for nuclear reactors
Inventor: FAWCETT SYDNEY
IPC: G21D3/04
Filed: 1960-07-06
Abstract: 942,319. Controlling nuclear reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. June 22, 1961 [July 6, 1960], No. 23618/60. Heading G6C. A nuclear reactor has a reactor shut down system, means sensitive to predetermined abnormal variations in reactor performance and operable through an electrical circuit to bring the shut down system into operation, shortcircuiting means for routine testing of the electrical circuit and further means sensitive to said predetermined abnormal variations in reactor performance for overriding the effect of the short-circuiting means so as to allow shut down of the reactor when the short-circuiting means is in operation and said variations occur. The reactor shown in Fig. 1 has a control system of the type disclosed in Specification 887, 392 and comprising "fine" control rods 15 supported by cables 16 attached to a winch 17. The movement of the winch 17 is controlled by a controller 37 connected to the output of an amplifier 32 having three inputs. To one input is fed a voltage Vr from a potentiometer 34 representing a pre-set temperature, to a second input is fed a voltage Vt from one of the thermocouples 18 at the outflow end of each fuel channel 12 as selected by the switch 21, while to a third input is fed the differential with respect to time derived by a circuit 29 of the difference between, or ratio of, the voltage Vf from a neutron flux measuring ion chamber 28 and the voltage Vc from a flow meter 30 in the coolant dust 25. In addition, "coarse" control rods 38 are provided movable irreversibly into channels 39 by a winch 40 controlled by a controller 41 to provide a "restrained" shut down system which can be manually restored, a clutch 42 is provided in association with the rods 38 and controlled by a primary emergency controller 43 to allow emergency shut down by release of the rods, and alarm signal generators 44, 45, 46 and 47 are provided to emit signals in the event of "restrained" or emergency shut down conditions arising. Generator 44 receives the output of circuit 29, generator 45 the voltage Vt, generator 46 coolant pressure along a pipe 54, and generator 47 the output from a fuel element thermocouple 58. A secondary emergency shut down system is also provided, e.g. a device having balls of magnetic neutronabsorbing material restrained from entering the reactor by a magnetic field which is caused to collapse in the event of emergency conditions occurring at a level higher than those reached by transients consequent upon operation of the primary emergency shut down system. In Fig. 2 is shown a typical "two out of three" protection circuit having three pairs of contacts C1, C2 and C3 each associated with one of an appropriate group of three alarm signal generators and connected in a circuit to a relay A. This has a series of contacts A1, A2, A3... connected to respective clutches 42 associated with control rods 38. In order that the clutches 42 should not be released during routine testing of the relay A, a temporary by-pass connection BP is applied across the contacts A1, A2, A3... so that they can be opened during the test. However, this has the effect of removing primary emergency facilities from the reactor during the test and since an emergency may arise at this time, the contact BP has in series with it a shut down contact CSD1. An abnormal condition now arising will cause a signal to pass to the "restrained" shut down controller 41 and it is arranged that this signal operates on relay CSD in the controller 43 to open contact CSD1. Whilst this will cause an emergency shut down under conditions only justifying a "restrained" shut down, this is preferable to the alternative of risking failure to shut down on the occurrence of emergency conditions.