Interlocks, reactor protection system

Operability requirements should be stated for the reactor protection system and for instrumentation and logic for other safety systems, together with limits on response times, instrument drift and accuracy, where appropriate. Interlocks teqnired by the safety analysis report should be identified and relevant operability reqnire-ments should be stated. 

Modifications in the reactor protection system to enable defeating interlocks or overriding protective trips... 

The possibUity of bypassing interlocks and trips of the reactor protection system shall be carefully evaluated and appropriate means of protecting interlocks and trips that are important to safety from being inadvertently bypassed shall be incorporated into the reactor protection system. 

The reactor protection system (RPS) is a safety-related system that is designed to monitor key operating plant variables and to cause alarms, control rod insertions, or scram, as the occasion may require when off-normal conditions occur. The reactor trip system (RTS) is part of the RPS and includes those power sources, sensors, initiation circuits, logic matrices, bypasses, interlocks, racks, panels, control boards, actuation devices, and actuated devices, that are required to initiate reactor shutdown. The RTS automatically initiates control rod insertion when required to assure that acceptable fuel design limits are not exceeded. It is designed to fail safe for most internal component failures. The RTS can also be actuated manually by operator action. 

Safety systems require certain conditions to be satisfied to remain available. Protection interlocks are specified and irrqrlemented to prevent erroneous changes in these operational conditions or configurations. These safety interlocks are implemented in the protective logic units of the reactor protection system. 

The reactor protection system evaluates the interlock conditions in the same way as the trip conditions described above. Therefore, the protective interlocks are generated by the protective logic units. 

Rack 1 (first from the left standing in front of the console) is the Safety Display and Command Rack, which belongs to the reactor protection system. In all its engineering aspects, it is equivalent to rack three in the main console hardwired, functionally and electrically independent, its indicator panel implements the Safety Parameter Display Unit, its command panel includes the manual triggering, interlock and reset pushbutton of the protection and active-safety systems. This rack in the secondary console includes all the equipment that is required to shutdown the reactor and to keep the reactor in a safe shutdown condition... 

The protection system was designed to avoid any unsafe condition. It was subdivided into two subsystems, the nuclear detection subsystem and the interlock subsystem. The nuclear detection subsystem is used to monitor neutron flux level and period. It is composed of 8 nuclear channels to monitor the neutron flux from start up to 100% of full power (100 watts), including comparators and isolation ampliBers. Three channels are used in the start-up region, and the others in the intermediate and power regions. In each region we have three measurements of the neutron flux (power) and three measurements of the period. The nuclear channels are complemented by two linear channels, used (alternatively) to control the reactor in automatic mode. Figure 5 shows the relative location of the detectors, and the operational interval of them. 

Dust control includes both external and internal methods. Source ventilation, hood ventilation, and room ventilation are typical external methods. Interned methods include reactor ventilation and the use of a closed charging system, which provides a suction transfer of powder into an evacuated reactor. Dust control equipment should be interlocked with production machinery to assure simultaneous operation and protection. 

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