Patent Number: 
Section: claims

1. A reactor shutdown system that stops nuclear reaction in a reactor in an event of a malfunction in a nuclear facility includinga reactor that accommodates therein a control rod pulled out from or inserted into a fuel assembly,a control-rod drive unit that drives the control rod in pulling and inserting directions,a power source that supplies power to the control-rod drive unit, anda power converter that is provided between the control-rod drive unit and the power source and that converts power supplied from the power source to supply the power to the control-rod drive unit, whereinwhen power supply is cut off, the control-rod drive unit inserts the control rod into the fuel assembly to stop the nuclear reaction in the reactor,comprising:a breaker that is interposed between the power converter and the control-rod drive unit and that is configured to shut the power supplied from the power converter to the control-rod drive unit;a main stop-control device that is configured to control the breaker to cut off the power supply to the control-rod drive unit in the event of a malfunction in the nuclear facility, the main stop-control device being a digital device including a storage unit and an arithmetic unit configured to execute various programs stored in the storage unit for safety protection of the nuclear facility;an auxiliary stop-control device that is configured to control the power converter to cut off the power supply to the control-rod drive unit in the event of a malfunction in the nuclear facility, the auxiliary stop-control device being an analog device and being configured by using electric circuit parts such as a switch and a relay and connecting respective contact points with an electric wire; anda detection sensor connected to the main stop-control device and configured to detect an operating condition of the nuclear facility, whereinthe main stop-control device is configured to receive the detection signal issued from the detection sensor and configured to transmit the received detection signal to the auxiliary stop-control device,when having determined to stop the nuclear reaction in the reactor based on the received detection signal, the main stop-control device is configured to transmit a first reactor-shutdown signal to the breaker,when having determined to stop the nuclear reaction in the reactor based on the received detection signal, the auxiliary stop-control device is configured to transmit a second reactor-shutdown signal to the power converter,upon reception of the first reactor-shutdown signal, the breaker is configured to cut off the power supply to the control-rod drive unit and configured to transmit a block signal to the auxiliary stop-control device, andthe auxiliary stop-control device includes a block circuit that is configured to block the second reactor-shutdown signal transmitted to the power converter, based on the received block signal, wherein the block circuit is configured to block the second reactor-shutdown signal from the auxiliary stop-control device when the main stop-control device is operated normally, and the auxiliary stop-control device is configured to operate only when the main stop-control device is not functioning normally due to a failure. 2. The reactor shutdown system according to claim 1, wherein the auxiliary stop-control device includes a delay circuit that delays time for transmitting the second reactor-shutdown signal to the power converter by an amount of delay time since reception of the detection signal by the main stop-control device until transmission of the block signal from the breaker to the auxiliary stop-control device.