The reactor I&C (the control and safety system) controls the nuclear reactor operation and guarantees its nuclear safety. A reactor protection system is the most important one according to the nuclear safety. The protection system consists of 4 operational power measuring (OPM) and 4 independent power protection (IPP) channels. Only the 3 OPM and IPP channels are active and evaluated in the logic ‘two out of three’, the fourth ones operate in the stand by mode and can substitute a fault of one active channel.
The OPM channels receive signals from wide range fission chambers RJ1300. The channels evaluate the chamber signal according to the reactor power in the pulse or current/Campbell range. They calculate the reactor power and the power rate in the full reactor power range, they compare the calculated values with the safety limits, and, if the safety limits are exceeded, they initiate the safety circuits. Apart from it, they send the operational data to the control system and to adjacent individual displays on the operator’s desk of the human machine interface (HMI) in the control room.
Control desk of reactor
The IPP channels are equipped with boron chambers SNM 12. The signals from the boron chambers are evaluated in the pulse range, and the IPP channels measure the power only in the two last decades of the reactor power range. They also evaluate the power and the power rate, send data to the control system and to their displays, and initiate a safety action if safety limits are exceeded.
The safety circuits of the reactor I&C is formed by a relay system with utilization of high quality relays with forced contacts to guarantee high reliability of operation. A vote logic receives the safety signals. The vote logic evaluates the inputs from the OPM channels in the logic ‘2 out of 3’, from the IPP channels independently ‘2 out of 3’, and the safety signal from the control system is evaluated in the logic 1 out of 1. If the conditions for the safety action request are met in at least one group (OPM, IPP or Control System), the power supply (48V DC) to the control rods is broken by the safety circuits, the rods fall down and stop the chain reaction (reactor scram). A safety (scram) button can also be used to scram the reactor.
The control system receives data from the OPM and IPP channels, it checks received values with each other and against the safety limits. The control system calculates the average values of the reactor power and the power rate; then, it evaluates the deviation between the real power and the demanded power value set by the operator. The control system sends data to the HMI and receives commands from it. If the commands are permitted, it carries them out. The control system also serves as an automatic power regulator system and controls the movement of the control rods to achieve the required reactor power. The HMI enables the communication between the reactor I&C and the operator. It consists of a computer with CRT displays and indicators to show the operational status of the reactor, as well as a keyboard, buttons to control the reactor and a printer. The HMI also stores data about the history of the reactor operation.
The power supply system is situated in a switchgear room in the reactor hall. The I&C systems important to nuclear safety use a standby supply to guarantee their operation for necessary time in the event of an electricity network failure.
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